PCCP and PhysChemComm

Readers will be aware that the RSC currently publishes three journals in the physical chemistry area, Physical Chemistry Chemical Physics (PCCP), Faraday Discussions and PhysChemComm. You are of course reading one of them – PCCP!

Faraday Discussions documents the long-established series of Faraday Discussion meetings. The papers presented at the meeting are published in the journal together with a record of the discussion contributions made, providing an important record of current international knowledge and views in the field concerned. See www.rsc.org/faraday_d for more information on the series.

PhysChemComm is an electronic only journal launched in 1998 to provide authors with a medium for rapid publication and to encourage the use of colour, movies and animated graphics. The journal can be accessed from www.rsc.org/physcc. When PhysChemComm was launched the advantages of the e-only journal as a medium for very fast publication and electronically enhanced articles were clear. Since then, major reductions in times to publication for the RSC print journals have been achieved and PCCP can now publish its Communications as quickly as PhysChemComm publishes. The number of articles in PhysChemComm requiring electronic enhancements has been fewer than predicted and most of these requirements can now be accommodated by the electronic supplementary information service (www.rsc.org/esi) that accompanies the printed version of PCCP. It has become clear that there is now no real advantage to an e-only journal in the physical chemistry field and the decision has been taken to cease publication of PhysChemComm at the end of 2003.

Following this Editorial we list all of the PhysChemComm articles that have been published since the journal's launch, together with the abstracts. Alongside each abstract you will find the URL to the original article. All past PhysChemComm content will be free to access from January 2004 from the RSC website and will be available indefinitely. This Editorial is also available online on the PCCP pages – www.rsc.org/pccp – and readers can click directly from the links in the online Editorial directly to the PhysChemComm articles.

With the closure of PhysChemComm we wish to develop PCCP such that PCCP Communications receive higher visibility. Naturally we also wish to keep the strengths of PhysChemComm, the major one of which was undoubtedly the support of members of the editorial board. With this in mind, we are delighted to welcome the former PhysChemComm editorial board members Professor Graham Fleming (Berkeley), Professor Aart Kleyn (Leiden), and Professor Berend Smit (Amsterdam) to the PCCP editorial board from January 2004. They will have special responsibilities for promoting and encouraging Communications within PCCP.

The current criterion for acceptance of a PCCP Communication is that the article contains original and highly significant work whose interest to the PCCP readership and impact on the subject warrants rapid publication. The “urgency” criterion will remain paramount and Communications in PCCP will continue to be published rapidly, typically in less than 50 days from receipt to print publication. We will seek to reduce this time even further as Communications will be treated as a “premium” service by our editors.

To ensure high visibility each Communication will feature a graphical abstract for the article in the contents list, so that it really stands out from the crowd! Published Communications will by definition fulfil the prime novelty criterion. They will thus be highlighted on the PCCP homepage as a “Hot Article”, and hence be free to access for all.

It just remains to us to say thank you to all editorial board members, authors and referees who supported PhysChemComm. All readers of this editorial, and former authors of PhysChemComm articles, are strongly encouraged to continue publishing their work as PCCP Communications!

We look forward to receiving your Communications (and longer articles!) for PCCP next year. Meanwhile, please enjoy reading the PhysChemComm abstracts; many seminal works were published in PhysChemComm during the five years of its existence. Don't forget the full articles can be freely accessed via www.rsc.org/physcc.

With best wishes,
Susan Appleyard	Mike Ashfold
Managing Editor	Chairman, Editorial Board

PhysChemComm abstracts 1998–2003

1998

Grain boundary migration at finite temperature: an ab initio molecular dynamics study

S. C. Watson and P. A. Madden, PhysChemComm, 1998, 1, 1 [http://dx.doi.org/10.1039/a806053c].

The process of migration of two types of symmetric grain boundaries at high temperatures in crystalline sodium has been studied with an efficient ab initio molecular dynamics method, which allowed the use of ca. 6700 atoms. Rapid migration of one boundary is achieved by a small amplitude collective shuffling of the atomic positions. The other boundary appears immobile on the simulation timescale, and reasons for this are discussed.

A scanning tunneling microscopy study of rabbit metallothionein

Jason J. Davis, H. Allen O. Hill, Arnd Kurz, Claus Jacob, Wolfgang Maret and Bert L. Vallee, PhysChemComm, 1998, 1, 12 [http://dx.doi.org/10.1039/a806057f].

The application of scanning probe methods to the high-resolution imaging of biological structure has been developing rapidly during the past few years. In contrast to diffraction and electron microscopy methods, imaging is direct and can be carried out under fluid. Scanning Tunneling Microscopy (STM) allows a resolution of electronic as well as topographic structure, and we are accordingly interested in its application to the high resolution imaging of metalloproteins. Metallothionein has been imaged under buffered solution by in situ STM. The dumbbell morphology has been resolved and the metal centers appear to give rise to enhanced tunneling current.

Conformational landscapes in flexible organic molecules: 3-phenylpropanol

John M. F. Elks, Romano T. Kroemer, June McCombie, Evan G. Robertson, John P. Simons and Melinda Walker, PhysChemComm, 1998, 1, 23 [http://dx.doi.org/10.1039/a806580b].

3-phenylpropanol has been studied in a jet-cooled environment, using laser induced fluorescence and mass selected R2PI excitation spectroscopy of the S₁ ← S₀ electronic transitions. Several conformer origins are observed for both the isolated molecule and its hydrated clusters. Partially resolved rotational band contours of the two strongest monomer features have been analysed with the aid of a new program, developed to fit experimental band contours using correlation analysis. Comparison with ab initio molecular orbital calculations, conducted at the MP2/6-31G* level for the ground state and CIS/6-31G* for the first electronically excited singlet state, allows assignment to two folded conformers with GG and AG conformations about their Cα–Cβ and Cβ–Cγ bonds. The stability of these conformers is discussed with reference to van der Waals interactions and compared to other related molecules – 2-phenylethanol, n-propyl and n-butylbenzene and 1-propanol.

Interactive Raman spectra of adamantane, diamantane and diamond, and their relevance to diamond film deposition

P. W. May, S. H. Ashworth, C. D. O. Pickard, M. N. R. Ashfold, T. Peakman and J. W. Steeds, PhysChemComm, 1998, 1, 35 [http://dx.doi.org/10.1039/a808830f].

Laser Raman spectra have been obtained for crystalline adamantane, diamantane, and natural type II diamond, as well as for a diamond film grown by chemical vapour deposition (CVD). The spectra are presented in JCAMP format to allow on-line interaction with the data by the reader, and 3D structure animations are presented showing the most probable vibrational mode causing each peak in the various spectra. The spectra are compared to those often seen from CVD diamond films, and which contain peaks that have previously been assigned to 'nanophase' diamond. Although there is a superficial correlation between the peak positions for the polymantanes and those seen in CVD diamond, the conclusion is that the nanophase diamond peaks are not an intrinsic vibrational mode of a polymantane, but instead must be a result of some other aspect of the nanophase scale of the films, such as surface modes.

1999

A sufficient condition for the angle parameter of the complex dilatation transformation

Meishan Zhao and Stuart A. Rice, PhysChemComm, 1999, 2, 1 [http://dx.doi.org/10.1039/a900479c].

We discuss a sufficient condition for the determination of the angle parameter of the complex dilatation transformation that is often used for the location of dynamical resonances. We show, as one example, that the proposed condition yields the exact value of this angle parameter for the case of a harmonic potential. The formulation of the sufficient condition permits it to be used for general potentials. We illustrate the utility of the proposed method by calculating the location of the resonance supported by a potential introduced in a model study by Moiseyev, Certain and Weinhold. The results obtained are very close to, but more accurate than, those previously reported, and they are obtained with less computational effort.

Time-dependent wavepacket study of the vibrational predissociation of He₂Br₂

Paul J. Krause and David C. Clary, PhysChemComm, 1999, 2, 5 [http://dx.doi.org/10.1039/a900605b].

A time-dependent quantum mechanical approach is used to study the vibrational predissociation of He₂Br₂. This system is particularly challenging to study because two intermolecular bonds are broken in the predissociation process and therefore three-degrees of freedom need to be treated explicitly. The vibrational predissociation lifetimes and an estimate of the vibrational product distributions are obtained. Studying colour plots of the evolving wavepacket provides a picture of the dissociation process. It is found that He₂Br₂ is very similar to He₂Cl₂ and dissociates via a sequential mechanism.

Environmentally benign decomposition of potassium nitrate on zeolites

Bin Shen, Yuan Chun, Jian Hua Zhu, Ying Wang, Zhen Wu, Jia Rong Xia and Qin Hua Xu, PhysChemComm, 1999, 2, 9 [http://dx.doi.org/10.1039/a902666e/].

Due to the interaction with the support, KNO₃ loaded on zeolite NaY began to decompose near 513 K, much lower than when unsupported. Through a special redox process, moreover, KNO₃ can be mainly decomposed at 673 K while the release of NO_x is suppressed by more than 90%.

Proton transfer mechanism in the ionic methanol dimer

S. Martrenchard, G. Grégoire, C. Dedonder-Lardeux, C. Jouvet and D. Solgadi, PhysChemComm, 1999, 2, 15 [http://dx.doi.org/10.1039/a903329g].

The intracluster proton transfer reaction in the methanol ionic dimer has been re-investigated using VUV ionization with synchrotron radiation. The energetic thresholds of the proton transfer issued from the methyl group or the hydroxy group have been obtained. These results are discussed in view of previous calculations and experiments.

Properties of the double well potential and relaxation processes in a model glass

F. Demichelis, G. Viliani and G. Ruocco, PhysChemComm, 1999, 2, 20 [http://dx.doi.org/10.1039/a901889a].

We use computer simulation to investigate the topology of the potential energy V({R}) and to search for double well potentials (DWPs) in a model glass. By a sequence of newtonian and dissipative dynamics we find different minima of V({R}) and the energy profile along the least action paths joining them. At variance with previous suggestions, we find that the parameters describing the DWPs are correlated. Moreover, the trajectory of the system in the 3N-d configurational phase space follows a quasi-1-d manifold. The motion parallel to the path is characterized by jumps between minima, and is nearly uncorrelated from the orthogonal, harmonic dynamics.

Ab initio study of the π*←n electronic transition in formic acid–(water)n (n = 1, 2) hydrogen bonded complexes

Gustavo Velardez, Jean Louis Heully, J. Alberto Beswick and Jean Pierre Daudey, PhysChemComm, 1999, 2, 24 [http://dx.doi.org/10.1039/a904105b].

Hydrogen bonded complexes of formic acid with one or two molecules of water have been studied using multiconfigurational SCF and second-order perturbation theory (CASSCF/CASPT2). Equilibrium geometries in the ground electronic state, S₀, and vertical S₁←S₀ transition energies have been calculated for the three 1 ∶ 1 complexes, and four 1 ∶ 2 conformers found. The most stable conformers are the six-membered ring structures for the 1 ∶ 1 and 1 ∶ 2 complexes in agreement with previous calculations. All vertical transitions are blue-shifted with respect to the corresponding monomer transition.

Sedimentation equilibria of colloidal hard rod dispersions

Rosalind Allen, David Goulding and Jean-Pierre Hansen, PhysChemComm, 1999, 2, 30 [http://dx.doi.org/10.1039/a905089b].

The concentration profiles of suspensions of cylindrical rods in a gravitational field are calculated within Onsager theory and its Parsons–Lee extension. The calculated profiles are very sensitive to the aspect ratio, for a given volume of the rods.

Carotenoid mediated B800–B850 coupling in LH2

Brent P. Krueger, Gregory D. Scholes, Ian R. Gould and Graham R. Fleming, PhysChemComm, 1999, 2, 34 [http://dx.doi.org/10.1039/a903172c].

Ab initio calculations of the excited state properties of a portion of the LH2 complex consisting of a supermolecule of two B850 bacteriochlorophyll (BChl), one B800 BChl, and one rhodopin glucoside carotenoid show significant mixing between the BChl and carotenoid states. Calculation of the B800–B850 coulombic coupling, through the transition density cube method, both with and without the carotenoid reveal that the carotenoid affects an increase in the B800–B850 coupling via an indirect (superexchange) mechanism. This carotenoid-mediated coupling explains a portion of the difference between the B800–B850 energy transfer rate determined experimentally and through traditional (Förster) calculations.

The formation of enantiospecific phases on a Cu{110} surface

Q. Chen, C. W. Lee, D. J. Frankel and N. V. Richardson, PhysChemComm, 1999, 2, 41 [http://dx.doi.org/10.1039/a905986e].

Both R- and S-phenylglycine and a quantitatively well defined mixture of the two enantiomers have been studied on Cu{110} surfaces. At saturation coverage, the molecules form well ordered, chiral structures with a chiral unit cell which ensures that the low energy electron diffraction (LEED) patterns of the two enantiomers are readily differentiated. Comparison is made with analogous structures observed for the non-chiral species glycine and R-, S-alanine adsorbed on Cu{110}.

Simulating the self-assembly of model membranes

Maddalena Venturoli and Berend Smit, PhysChemComm, 1999, 2, 45 [http://dx.doi.org/10.1039/a906472i].

Dissipative particle dynamics simulations are presented of the self assembly of surfactant bilayers. The effect of changes in the chain length and stiffness of the surfactants on the properties of the model membranes are studied. We observe that changes of the stiffness have significant effects if these changes are made close to the head group of the surfactant. If, on the other hand, changes are made at the end of the tail of the surfactant, the properties of the bilayer are similar to the properties of a bilayer consisting of flexible chains.

Surface dilational behaviour of spread dipalmitoyl phosphatidyl glycerol monolayers

R. Wüstneck, P. Enders, N. Wüstneck, U. Pison, R. Miller and D. Vollhardt, PhysChemComm, 1999, 2, 50 [http://dx.doi.org/10.1039/a906516d].

The stress relaxation process in spread dipalmitoyl phosphatidyl glycerol (DPPG) monolayers was investigated by using the pendant drop technique as a microfilm balance in combination with the axisymmetric drop shape analysis. The stress relaxation caused by a transient drop volume change was analysed by a new model, which takes into account material inhomogeneity by means of a distribution of relaxation times. The surface pressure decay in the DPPG monolayers at 35 and 40 °C is governed by 2 main relaxation times. One is of the order of 20 s, the other one is in the range of 200–600 s. The π/A isotherms, the surface dilational modulus, and the higher relaxation times are influenced by temperature and by the presence of electrolyte in the subphase; 0.15 mol dm⁻³ NaCl yields a smaller area demand per molecule in the monolayer. Harmonic oscillation experiments were carried out and the dilational elasticities and viscosities were determined for different frequencies in the range between the two main relaxation times. Both the elasticities and the viscosities, depend on frequency. The surface rheological behaviour is structurally viscous, i.e. high viscosities at small frequencies, which decrease at faster deformations. The results are related to the surface dilational rheological behaviour of dipalmitoyl phosphatidyl choline (DPPC) monolayers.

The gas phase acidity of HBF₄ (HF–BF₃)

A. H. Otto, PhysChemComm, 1999, 2, 62 [http://dx.doi.org/10.1039/a907705g].

The gas phase acidity of the complex superacid HBF₄ and the interaction of BF3 with HF as well as the F⁻ detachment from BF₄⁻ have been calculated ab initio using high accuracy energy models [CBS-4, CBS-Q, CBS-QB3, G1, G2(MP2) and G2] as well as the density functional B3LYP formalism. All methods but CBS-4 and G1 provide practically equal acidity data for the gas phase and one may recommend 288–289 kcal mol⁻¹ for the Gibbs free energy and 291–292 kcal mol⁻¹ for the corresponding enthalpy at 298 K. The complex HF–BF₃ is unstable in vacuo as the Gibbs free energy of decomposition into HF and BF₃ is predicted to be between −3.6 and −4.6 kcal mol⁻¹ depending on the method used. The conjugated base BF₄⁻ is stable with respect to fluoride ion detachment. We recommend 81–82 kcal mol⁻¹ and 72–73 kcal mol⁻¹ for the enthalpy and the Gibbs free energy, respectively.

Observation of a laser-induced transmittance modification in Ni²⁺ doped CsCdCl₃

Ueli Oetliker and Christian Reber, PhysChemComm, 1999, 2, 67 [http://dx.doi.org/10.1039/a907907f].

The absorbance of the narrow ³A₂ → ¹A₁ (O point group symmetry approximation) crystal-field transition in CsCdCl₃ doped with Ni²⁺ ions can be influenced by a laser tuned to a strong inter-excited state transition reported earlier for this material. The intensity of the band maximum at 525.2 nm decreases to nearly zero for the duration of a laser pulse in resonance with the intense ¹A₁ ↔ ³T₂ inter-excited state transition at 701.7 nm which couples the ¹A₁ and ³T₂ states. Detuning the coupling laser wavelength reduces the effect considerably and thus confirms the importance of this particular inter-excited state transition for the control of a conventional transition from the electronic ground state.

Improved coefficients for the scaling all correlation and multi-coefficient correlation methods

Christine M. Tratz, Patton L. Fast and Donald G. Truhlar, PhysChemComm, 1999, 2, 70 [http://dx.doi.org/10.1039/a908207g].

We have re-optimized the coefficients for ten scaling all correlation (SAC) methods, five empirical infinite basis (EIB) methods, and 18 multi-coefficient (MC) correlation methods, including the special cases of multi-coefficient SAC and multi-coefficient Gaussian-2 and Gaussian-3. The new parameterization is based on a training set of 82 atomization energies except for multi-coefficient Gaussian-2, which is restricted to H and the first period (nuclear charge ≤ 9) and is based on a training set of 52 atomization energies. Each method may be employed with or without including core-correlation effects, which are based on a new set of parameters optimized on a 123-molecule training set. The mean unsigned error in the atomization energies of the 82-molecule set is reduced on average by 20% when the new parameters used here are adopted.

Ion sputtering as a probe of liquid surfaces

M. A. Gleeson, T. T. Nuver, J. Lourenço, A. M. C. Moutinho, J. Los and A. W. Kleyn, PhysChemComm, 1999, 2, 80 [http://dx.doi.org/10.1039/a907932g].

We have measured the energy and angular distribution of the ions emitted from a perfluoropolyether liquid polymer surface due to an incident 320 eV Ar⁺ beam. The anion distributions are comprised almost exclusively of F⁻. Substantial amounts of high-energy F⁻ recoils are produced, which can be attributed to multiple-collision processes. The production of these high-energy recoils indicates a very open surface structure, which allows hard (small impact parameter) collisions between Ar⁺ and individual functional groups of the polymer. Scattered Ar⁺ is only observed for small total scattering angles.

2000

Bonding energies of rare gases with aromatic molecules: rotational spectrum and dynamics of pyridazine⋯neon

Walther Caminati, Sonia Melandri, Adele Dell'Erba and Paolo G. Favero, PhysChemComm, 2000, 3, 1 [http://dx.doi.org/10.1039/a909649c].

The rotational spectrum of the pyridazine⋯Ne complex, a species observable in supersonic expansions, has been measured by free jet absorption millimeter wave spectroscopy. The equilibrium configuration, dynamics and dissociation energy have been deduced from the spectroscopic constants. The equilibrium distance of Ne with respect to the center of mass of the molecule is 3.26 Å, with the Ne atom tilted by 5.8° from the perpendicular to the center of mass of the ring towards the mid-point of the two nitrogen atoms. The dissociation energy is estimated, from the centrifugal distortion constant D_J, to be ca. 0.8 kJ mol⁻¹.

Quantum representation of dynamical systems: new bending modes of acetylene

J.-M. Champion, M. Abbouti Temsamani and S. Oss, PhysChemComm, 2000, 3, 5 [http://dx.doi.org/10.1039/b001934h].

Through well-established methods of group theory, we suggest how to construct new basis sets in the four-dimensional system of bending modes in acetylene. A novel, comprehensive family of vibrational modes is found allowing one to improve the partial analyses available for this molecule in terms of local/normal quantum numbers. We provide the general features of our technique for future extensions to other, more complex systems of current interest.

The re-oxidation of the substoichiometric TiO₂(110) surface in the presence of crystallographic shear planes

R. A. Bennett, PhysChemComm, 2000, 3, 9 [http://dx.doi.org/10.1039/b001938k].

Re-oxidation of reduced oxide surfaces is a fundamental step in catalysis and related fields. This paper reports the first study of the re-oxidation, at elevated temperature, of crystallographic shear planes (CSPs) occurring on the non-stoichiometric rutile TiO₂(110) surface by scanning tunnelling microscopy (STM). The re-oxidation occurs by the reaction of interstitial Tiⁿ⁺ ions dissolved in the crystal bulk with oxygen at the surface to re-grow new TiO₂ layers on the surface. The CSPs act as nucleation centres for the re-growth and are, in general, preserved during the early stages of the re-oxidation. CSPs appear in pairs on the surface and sandwich a layer of rutile that is displaced by one half an atomic step height from the original terrace. Each step edge of the pair shows markedly different structure and growth rate. The growth of the surface also takes place on the displaced region between CSP pairs.

Size discrimination of colloidal nanoparticles by thiol-functionalized MCM-41 mesoporous molecular sieves

Priyabrata Mukherjee, Murali Sastry and Rajiv Kumar, PhysChemComm, 2000, 3, 15 [http://dx.doi.org/10.1039/b002419h].

Thiol-functionalized MCM-41 mesoporous materials with a well-defined pore size of 40 Å may be used to discriminate between colloidal gold and silver particles in a mixture. More specifically, the thiol-functionalized MCM-41 material selectively entraps colloidal gold particles (size 35 Å) in the pores from a mixture of the gold and silver particles of size 70 Å. The gold particles are held in the matrix via thiolate linkages and this process has been studied using UV-vis spectroscopy and thermogravimetry/differential thermal analysis. This approach is promising for application in bioseparation methodologies as well as in the generation of one-dimensional superstructure assemblies.

External heavy-atom effect on fluorescence kinetics

Mário N. Berberan-Santos, PhysChemComm, 2000, 3, 18 [http://dx.doi.org/10.1039/b002307h].

Fluorescence quenching in fluid solution by the external heavy-atom effect usually follows simple Stern–Volmer kinetics, and the quenching effect is gauged by the magnitude of the bimolecular quenching rate constant. However, it is the increased unimolecular S₁→T_n intersystem crossing rate constant of the perturbed fluorophore in the perturber–fluorophore complex that can be directly compared with that of the unperturbed fluorophore. From a simple model for external heavy atom quenching in fluid solution, the decay law is predicted to be singly exponential for all quencher concentrations, and a new expression for the unimolecular S₁→T_n intersystem crossing rate constant of the perturbed fluorophore is obtained. The same problem, but in rigid solution, is also discussed for the first time. The model now predicts a nonexponential fluorescence decay law, from which the unimolecular S₁→T_n intersystem crossing rate constant of the perturbed fluorophore can be directly determined.

The effect of deposition of negatively charged particles on the electrokinetic behaviour of oppositely charged surfaces

Andrew P. Michelmore and Robert A. Hayes, PhysChemComm, 2000, 3, 24 [http://dx.doi.org/10.1039/b001277g].

Two models have recently been proposed to explain the electrokinetic properties of surfaces with electrostatically deposited particles (R. A. Hayes, Colloids Surf., A, 1999, 146, 89, and M. Zembala and Z. Adamczyk, Langmuir, 2000, 16, 1593). However, supporting experimental data is sparse. In this study, the effects of particle size, particle coverage and ionic strength on the electrokinetic behaviour of positively charged surfaces with negatively charged particles deposited were investigated by streaming current measurements. Results confirm that deposition of oppositely charged particles decrease the magnitude of the zeta potential of the underlying surface. Reversal of the zeta potential was observed at all particle sizes with larger particles reversing the potential at lower coverages. The results presented are fitted to the respective models, and the relative merits of each are discussed.

Mixed quantum classical steps: a DVR hopping method

Adolfo Bastida, José Zúñiga, Alberto Requena, Nadine Halberstadt and J. Alberto Beswick, PhysChemComm, 2000, 3, 29 [http://dx.doi.org/10.1039/b002769n].

A new method that allows to mix a quantum and a classical description in a system where the quantum dynamics involves both bound and continuum states is presented. The description of the quantum degrees of freedom is based on a discrete variable representation (DVR), and the coupling with the classical degrees of freedom follows the surface hopping method using the fewest switches algorithm developed by Tully¹⁰ (J. C. Tully, J. Chem. Phys., 1990, 93, 1061). The method is applied to the simple model of a quantum particle (wave packet) colliding with a “classical” particle adsorbed on a solid surface, which has been studied by other methods.

Geometry-based simulation of the hydration of small molecules

Timothy H. Plumridge, Gerald Steel and Roger D. Waigh, PhysChemComm, 2000, 3, 36 [http://dx.doi.org/10.1039/b003723k].

The behaviour of water structure-makers and breakers is of practical importance in protein folding in aqueous solution (G. Nemethy, Angew. Chem., Intl. Ed. Engl., 1967, 6, 195), but the mechanism for this process is not fully understood (K. A. T. Silverstein, A. D. J. Haymet and K. A. Dill, J. Am. Chem. Soc., 1998, 120, 3166). A computer simulation has been developed, of water structure around solutes, using only hydrogen bond geometry data rather than traditional forcefield methods. The simulation builds networks of hydrogen bonded water around structure-makers such as sulfate and phosphate, but not around structure-breakers such as urea and guanidinium. We have tested the software with a preliminary set of 17 varying solutes and our results are generally consistent with existing practical data.

Spectroscopic investigation of complexation between various tetracyclines and Mg²⁺ or Ca²⁺

Matthias O. Schmitt and Siegfried Schneider, PhysChemComm, 2000, 3, 42 [http://dx.doi.org/10.1039/b005722n].

The complexation of various “normal” tetracyclines and anhydrotetracycline with Mg²⁺ and Ca²⁺ was investigated under physiological conditions (aqueous Tris buffer at pH 7.0 and 8.5) by spectrometric titration. The generated sets of UV-Vis absorption and fluorescence spectra were analysed by two techniques, namely (i) classical evaluation which relies on the occurrence of isosbestic points and (ii) multivariate fitting employing the program Specfit. The latter yields not only the conditional binding constants, but also, for each tested kinetic scheme, the absorption or emission spectra of the individual metal–tetracycline complexes. It was found that absolute values of binding constants and deduced spectra are in all cases in favour of a consecutive metal ion complexation yielding 1 ∶ 1 and 2 ∶ 1 metal–tetracycline ion complexes.

Predissociation lifetimes of the B-state of I⁷⁹Br

E. A. Volkers, A. E. Wiskerke, R. Mooyman, M. J. J. Vrakking and S. Stolte, PhysChemComm, 2000, 3, 56 [http://dx.doi.org/10.1039/b006982p].

The predissociation of the B (³Π₀₊) state of I⁷⁹Br is studied by measuring its one photon absorption spectrum in a cold molecular beam by REMPI detection of the atomic photo fragments. In this work, we present the absolute frequencies as well as the line shapes of the transitions to the vibrational levels v' = 22 to v' = 34 of the B (³Π₀₊) state. These results provide the lacking information needed to fully interpret the outcome of the femtosecond experiments. They also provide important spectroscopic data required to acquire a more accurate theoretical description of the intersecting ³Π₀₊ surfaces. The predissociative lifetimes of the short lived levels (τ < 2 ps) have been determined from the observed linewidth. It is found that the linewidths, and thus the predissociative lifetime, oscillate as a function of the vibrational quantum number. All observed spectral transitions obey a Fano-profile lineshape from which the Fano-parameters have been extracted.

Anomalous size dependence of the non-linear mobility of DNA

Leonid L. Frumin, Sergey E. Peltek, Shmuel Bukshpan, Victor V. Chasovskikh and Gleb V. Zilberstein, PhysChemComm, 2000, 3, 61 [http://dx.doi.org/10.1039/b007756i].

A strong drift velocity non-linearity of the (doublestranded) DNA molecules vs.≕ the electric field was discovered in gel electrophoresis. The non-linear drift velocity of the longer molecules is higher than that of the short ones, depending on the molecular size in a complex fashion. This behavior contrasts with that of the ordinary, linear, drift velocity where short molecules move faster than the long ones. The molecular size dependence of the non-linear velocity or the non-linear mobility has a non-monotonous wave-like character. The non-linear mobility offers possibilities of manipulating the drift velocity at will—the DNA fragments of different size can be made to move in opposite directions in pulsed field gel electrophoresis.

Vibronic structure in the luminescence spectra of tetragonal d2 and d8 complexes analyzed by wavepacket dynamics on two-dimensional potential surfaces

Myriam Triest, Steve Masson, John K. Grey and Christian Reber, PhysChemComm, 2000, 3, 64 [http://dx.doi.org/10.1039/b008386k].

The luminescence spectra of the tetragonal trans-ReO₂(vinylimidazole)₄⁺ complex and the square planar Pd(SCN)₄²⁻ and Pt(SCN)₄²⁻ complexes all show vibronic progressions in two predominant vibrational modes. In the first complex, the vibronic progressions involve high-frequency and low-frequency metal–ligand modes. In the square planar complexes, the two vibrational modes have similar frequencies. At the intermediate resolution, often observed experimentally, these compounds provide an example of the missing mode (or MIME) effect. Wavepacket dynamics on two-dimensional surfaces explain in a visual and intuitively appealing way the spectroscopic features. The distinct effects are caused by the different frequency ratios between the two modes of the two-dimensional models describing each complex. The emitting state structure determined from the spectra reveals similar changes along a bending normal coordinate for Pd(SCN)₄²⁻ and Pt(SCN)₄²⁻.

Ab initio MO/statistical theory prediction of the OH + HONO reaction rate: evidence for the negative temperature dependence

W. S. Xia and M. C. Lin, PhysChemComm, 2000, 3, 71 [http://dx.doi.org/10.1039/b007803o].

The reaction of OH radical with cis- and trans-HONO has been investigated by ab initio molecular orbital and variational transition-state theory calculations. The overall mechanism has been elucidated and found to be quite complex. The bimolecular rate constants for the major reaction paths have been calculated and compared with existing, conflicting kinetic data. The total rate constant for the production of H₂O and NO₂ was concluded to have noticeable negative temperature dependence below 1000 K. The following two expressions are recommended for atmosphere and combustion modeling applications: k₁ = 4.12 × 10¹² (T/300)^−0.8 cm³ mol⁻¹ s⁻¹, 200–500 K; k₁ = 1.77 × 10⁷T^1.5 exp [+1260/T] cm³ mol⁻¹ s⁻¹, 500–2000 K. The predicted rate constant for the low-temperature regime agrees quantitatively with the result of Burkholder et al. (Int. J. Chem. Kinet., 1992, 24, 711) measured at 298 < T < 373 K.

Onset temperature of slow dynamics in glass forming liquids

Srikanth Sastry, PhysChemComm, 2000, 3, 79 [http://dx.doi.org/10.1039/b008749l].

The behaviour of a model glass forming liquid is analyzed for a range of densities, with a focus on the temperature interval where the liquid begins to display non-Arrhenius temperature dependence on relaxation times. Through analyzing the dynamics along with the properties of local potential energy minima sampled by the liquid, a crossover or onset temperature Ts is identified, below which the liquid manifests slow dynamics, and a change in the character of typical local potential energy minima.

2001

An experimental and computational investigation of the structure and vibrations of dimethylethylenediamine, a model for poly(ethylenimine)

Scott E. Boesch, Shawna S. York, Roger Frech and Ralph A. Wheeler, PhysChemComm, 2001, 4, 1 [http://dx.doi.org/10.1039/b009250i].

A combination of hybrid Hartree–Fock/density functional calculations and Raman and IR spectroscopy has been used to perform a vibrational analysis of N,N′-dimethylethylenediamine (DMEDA) and provide band assignments for the experimental spectroscopic data. The structures and vibrational frequencies of several low energy conformations of DMEDA were calculated. The lowest energy structure was found to be TGT with a single intramolecular hydrogen bond. The effect of intramolecular hydrogen bonding on the structures and vibrational frequencies was investigated. Liquid DMEDA is found to be predominantly a mixture of two conformations: TGT with one intramolecular hydrogen bond and TGT with no intramolecular hydrogen bonds.

On the efficient sampling of pathways in the transition path ensemble

Thijs J. H. Vlugt and Berend Smit, PhysChemComm, 2001, 4, 11 [http://dx.doi.org/10.1039/b009865p].

Transition path sampling is a numerical technique to compute transition rates between two stable states without having to assume a priori information about a dividing surface. However, when there are many different pathways to go from one stable state to another, for example, when there are many saddle points in the free energy surface, it can be difficult to sample all possible pathways within the timescale of a single simulation. In this work, we demonstrate the use of parallel tempering to overcome this problem.

Simple suppressing method of thermal runaway in microwave heating of zeolite and its application

Ohgushi Tatsuo and Wakana Akiko, PhysChemComm, 2001, 4, 18 [http://dx.doi.org/10.1039/b009067k].

4A, 13X and Na-mordenite (Na-M) reached higher temperatures by the microwave radiation of 5–10 min in the 500 W radiation power and were completely damaged. When 5A was added to 4A, 13X or Na-M with a suitable ratio, the heating temperature of the mixture was suppressed to a desirable range and the mixture reached the dehydration degree of >85% in 15–20 min. The mixtures irradiated in desirable conditions only slightly decreased their absorption ability for water (by <5% per radiation treatment). The proposed method could quickly and simply reactivate the zeolites up to a high level with a domestic type microwave oven.

Dissociative hydrogen transfer in indole–(NH₃)_n clusters

C. Dedonder-Lardeux, D. Grosswasser, C. Jouvet and S. Martrenchard, PhysChemComm, 2001, 4, 21 [http://dx.doi.org/10.1039/b100573l].

The dynamics of excited state indole–(NH₃)_n clusters has been investigated with two-color two-photon ionization. Mass spectra recorded with delayed ionization indicate that a hydrogen transfer reaction indole(S₁)–(NH₃)_n → C₈H₆N˙ + NH₄(NH₃)_n−1 occurs for n = 3, 4, 5.

Entrapment and catalytic activity of gold nanoparticles in amine-functionalized MCM-41 matrices synthesized by spontaneous reduction of aqueous chloroaurate ions

Priyabrata Mukherjee, Chitta Ranjan Patra, Rajiv Kumar and Murali Sastry, PhysChemComm, 2001, 4, 24 [http://dx.doi.org/10.1039/b101056p].

There is tremendous current interest in the generation of nano-hybrid materials using silicate mesoporous materials. We describe herein a new process for the synthesis of gold nanoparticle–amine functionalized MCM-41 hybrid materials by the spontaneous reduction of chloroaurate ions within the silicate matrix. The gold nanoparticles thus formed are bound to the pores of the MCM-41 framework by amine functional groups and show excellent catalytic activity in hydrogenation reactions.

Time-lapse potentiometric imaging of active filiform corrosion using a scanning Kelvin probe technique

G. Williams, H. N. McMurray, D. Hayman and P. C. Morgan, PhysChemComm, 2001, 4, 26 [http://dx.doi.org/10.1039/b100835h].

The kinetics and mechanism of filiform corrosion occurring on polymer coated AA2024-T3 aluminium alloy are investigated using a scanning Kelvin probe technique (SKPT). Repeated scanning by SKPT is used to generate a time-lapse animation showing the dynamic evolution of localised free corrosion potential (E_corr) patterns. E_corr values in the head region of propagating filaments are up to 150 mV lower that the intact polymer coated surface, indicating local depassivation. However, E_corr values in the filament tail are ca. 100 mV higher than background, indicating superpassivation. Spatial analysis of instantaneous E_corr distributions indicates that anodic metal dissolution is concentrated at the leading edge, and cathodic oxygen reduction at the trailing edge, of active filament heads. Temporal analysis of time-dependent E_corr distributions shows that filaments propagate at a constant speed and do not intersect.

Hydrogen bond analysis of Type 1 antifreeze protein in water and the ice/water interface

Pranav Dalal, Jared Knickelbein, A. D. J. Haymet, Frank D. Sönnichsen and Jeffry D. Madura, PhysChemComm, 2001, 4, 32 [http://dx.doi.org/10.1039/b101331i].

Antifreeze proteins (AFPs) are a group of structurally very diverse proteins with the unique capability of inhibiting ice crystal growth. Although significant progress has been made in the identification of different families of these proteins, the molecular mechanism of their action is unclear. The previously postulated mechanism of hydrogen bonding between the threonine residues of AFP and the water molecules in the ice surface has been disproved by mutation studies with non-polar residues. Currently, the mechanism of antifreeze activity cannot be fully understood from experimental or computational studies. Computational modeling studies have examined protein–ice interactions, mostly in vacuo. These studies have neglected the effects of the water phase. It has been shown that the vacuum is a very poor approximation for the water properties. Thus, to gain an insight into the molecular mechanism of these proteins we have computationally modeled a more realistic system comprising of AFP Type I from winter flounder (HPLC6), water and ice without any constraints. The results from this study show that the protein forms hydrogen bonds with the water molecules in the ice/water interfacial region. However, a comparison of the results with the protein in water simulations shows that there is no significant gain of hydrogen bonds for protein in the interfacial region compared to in the solvent. These results support the hypothesis that hydrogen bonding is not the primary reason for interaction of HPLC6 with the ice/water interfacial region.

Pressure-induced amorphization of hydrated Na-X zeolite

Hongjian Liu, Richard A. Secco and Yining Huang, PhysChemComm, 2001, 4, 37 [http://dx.doi.org/10.1039/b102080n].

X-ray diffraction patterns of hydrated Na-X zeolite at 1 atm and 22 °C, recovered from high pressure experiments at pressures up to 9 GPa, showed progressive amorphization with increasing pressure. The largest reduction in crystallinity is observed between pressures of 4 and 5 GPa followed by a gradual, continued decrease in ordering up to the maximum pressure. The last vestiges of crystal structure persist to 8 GPa but the sample is completely amorphous at 9 GPa. Heating to 873 K in a differential scanning calorimetry (DSC) apparatus after decompression showed a shift in the broad dehydration endotherm to lower temperatures and a decrease in the endotherm width with increasing pressure. Follow-up X-ray patterns at 1 atm and 295 K after heating showed significant changes in peak intensities and width of the amorphous background signature. These observations are consistent with the negative thermal expansion of Na-X zeolite which results in further compression of the remnant lattice on heating.

Thermodynamics of dilute solution of Gd in Bi

Jiawei Sheng, Hajimu Yamana and Hirotake Moriyama, PhysChemComm, 2001, 4, 40 [http://dx.doi.org/10.1039/b101001h].

The thermodynamics of dilute solution of Gd in Bi were determined by means of the electromotive force (EMF) measurement method using a cell consisting of molten chloride and liquid bismuth in temperature range from 775 to 1055 K, with the Gd molar fraction range from about 10⁻⁵ to 10⁻³. Gd concentration has less effect on the activity coefficient. A considerable increase of the activity coefficient on the temperature was observed. The heat of formation of liquid Gd–Bi alloys was deduced from the measured activity coefficient. There is a linear dependence of experimental ΔH^M_Gd–Bi on the Gd concentration. The experimental results of ΔH^M_Gd–Bi were compared with the values predicted by Miedema’s model.

On the dimers of the VIB group: a new NIR electronic state of Mo₂

D. Kraus, M. Lorenz and V. E. Bondybey, PhysChemComm, 2001, 4, 44 [http://dx.doi.org/10.1039/b104063b].

Laser vaporized Mo₂ is trapped in solid neon at 7 K and investigated by optical spectroscopy using a Fourier transform spectrometer. Besides the well known A ¹Σ⁺_u ← X ¹Σ⁺_g and a(³Λ) → X ¹Σ⁺_g transitions, a new NIR transition, denoted as ã ³Σ⁺_u → X ¹Σ⁺_g based on DFT calculations, is detected with the help of optical absorption and laser induced fluorescence spectroscopy. The visible A ¹Σ⁺_u ← X ¹Σ⁺_g transition of the mixed CrMo is observed for the first time in the gas phase using cavity ringdown absorption spectroscopy.

Perspective: Quantum computing and nuclear magnetic resonance

Jonathan A. Jones, PhysChemComm, 2001, 4, 49 [http://dx.doi.org/10.1039/b103231n].

Quantum information processing is the use of inherently quantum mechanical phenomena to perform information processing tasks that cannot be achieved using conventional classical information technologies. One famous example is quantum computing, which would permit calculations to be performed that are beyond the reach of any conceivable conventional computer. Initially it appeared that actually building a quantum computer would be extremely difficult, but in the last few years there has been an explosion of interest in the use of techniques adapted from conventional liquid state nuclear magnetic resonance (NMR) experiments to build small quantum computers. After a brief introduction to quantum computing I will review the current state of the art, describe some of the topics of current interest, and assess the long term contribution of NMR studies to the eventual implementation of practical quantum computers capable of solving real computational problems.

Application of generalized two-dimensional correlation theory to gel permeation chromatographic analysis

Kenichi Izawa, Toshiaki Ogasawara, Hideki Masuda, Hirofumi Okabayashi and Isao Noda, PhysChemComm, 2001, 4, 57 [http://dx.doi.org/10.1039/b103810a].

This report demonstrates the promising potential for the application of generalized two-dimensional correlation analysis to time dependent GPC elution profiles, in analysis of complex dynamic variations in the sol–gel polymerization process.

Theoretical study of [4 + 2] cycloadditions of some 6- and 5-member ring aromatic compounds on the Si(001)-2 × 1 surface: correlation between binding energy and resonance energy

Xin Lu, M. C. Lin, Xin Xu, Nanqin Wang and Qianer Zhang, PhysChemComm, 2001, 4, 60 [http://dx.doi.org/10.1039/b104187h].

By means of first-principles density functional cluster model calculations, we demonstrate that the binding energies of the [4 + 2] cycloaddition products of the 6- and 5-member ring aromatic compounds on the Si(001) surface depend strongly on their resonance energies.

The heat of formation of dilute solution of lanthanides in bismuth

Jiawei Sheng, Hajimu Yamana and Hirotake Moriyama, PhysChemComm, 2001, 4, 63 [http://dx.doi.org/10.1039/b104626h].

The heat of formation of dilute solution of lanthanide in bismuth was deduced from the activity coefficient of lanthanides in bismuth solution. The experimental values were compared with estimations of these values using Miedema’s model. There is a simplified linear relation of the heat of formation of liquid Ln–Bi alloys with the 2/3 power of the metallic volumes of lanthanides, which is a useful tool for predicting the current unknown values. By introducing a correction constant in the Miedema’s model, the predicted data agreed well with experimental data.

Rotational excitation from a molecular mirror: NO scattering from Ru(0001)-(1 × 1)H

Bart Berenbak, Bernd Riedmüller, Charles T. Rettner, Daniel J. Auerbach, Steven Stolte and Aart W. Kleyn, PhysChemComm, 2001, 4, 66 [http://dx.doi.org/10.1039/b104823f].

The rotational state distributions of NO molecules scattered off the (1 × 1)H-covered Ru(0001) surface have been investigated by resonance enhanced multi-photon ionisation (REMPI). Angular and energy distributions reported earlier for this scattering channel, show an angular spread of only ⋍8° (θ_i = 60°, E_i = 2.1 eV), combined with small translational energy loss in the collision (E_f/E_i = 0.91). These observations suggest scattering from a very weakly corrugated surface, a ‘molecular mirror’, and a high probability to yield cold rotational distributions. The present experiments, however, reveal substantial rotational excitation, accompanied by rotational rainbows for higher quantum numbers (J > 20). The rotational temperatures increase from <T_rot> = 450 K at an incidence energy E_i = 0.32 eV, to <T_rot> = 950 K at E_i = 1.50 eV. The kinetic to rotational energy transfer efficacy, appears to be slightly higher than for NO scattering of the fairly inert Ag(111) surface. This system has much wider angular spread and larger translational energy losses. Assuming parallel momentum conservation in the collision the observed rotational excitation would lead to an angular spread that is considerably smaller than that observed for an incoming angle of θ_i = 15°.

MIDIX basis set for the lithium atom: Accurate geometries and atomic partial charges for lithium compounds with minimal computational cost

Jason D. Thompson, Paul Winget and Donald G. Truhlar, PhysChemComm, 2001, 4, 72 [http://dx.doi.org/10.1039/b105076c].

We present a MIDIX basis set for Li that accurately predicts geometries, charge distributions, and partial atomic charges for a test set of compounds at a reasonable cost. MIDIX basis sets, which are also called MIDI!, are heteroatom-polarized split-valence basis sets in which the polarization functions are optimized in order to predict realistic molecular geometries and atomic partial charges. The MIDIX basis set uses the core, inner valence, and outer valence basis functions of the MIDI basis set plus an additional Gaussian basis function. We optimized the p exponent to obtain realistic predictions of geometry, density dipole moments, and Löwdin dipole moments at the Hartree–Fock and hybrid density functional levels of theory, using the mPW1PW91 hybrid density functional for the latter. The MIDIX basis set predicts Hartree–Fock geometries and Hartree–Fock and hybrid density functional Löwdin dipole moments more accurately than either the 3-21G(d) or 6-31G(d) basis set for most of the compounds in our training set. It also predicts more accurate Hartree–Fock and hybrid density functional density dipole moments than the 3-21G(d) basis set. The present results show that the basis set is expected to be very useful for calculating geometries and electrostatic properties of lithium compounds containing H, C, N, O, F, Si, P, S, Cl, Br, and I, especially organolithium and lithium–sulfur compounds.

Perspective: The visualisation of chemical processes for electronic publishing and presentations

P. W. May, PhysChemComm, 2001, 4, 78 [http://dx.doi.org/10.1039/b103982m].

Over the past ten years, there has been a huge increase in desktop computer power, leading to explosive growth of the internet and the now widespread use of electronic media for publication and presentation of scientific documents. These new innovations have provided a challenge, as well as great opportunity, for a visual subject such as chemistry to present itself in a much more appealing way than has previously been possible. This article attempts to demonstrate how easy it is to create visually impressive chemical images and animations, as well as interactive structures and spectra, for use in lectures, on-line courses, electronic journal articles, web pages, etc. This is intended to be an introductory article to show potential authors how easy it is to add valuable extra content to their scientific documents, and at the same time make them more visually attractive. Topics covered include: animated gif images, creating and displaying interactive 3D molecular structures, creating 3D structure animations, creating and displaying molecular orbitals, and interactive spectra.

Surface enhanced Raman scattering from bare cobalt electrode surfaces

D. Y. Wu, Y. Xie, B. Ren, J. W. Yan, B. W. Mao and Z. Q. Tian, PhysChemComm, 2001, 4, 89 [http://dx.doi.org/10.1039/b105667k].

Surface enhanced Raman spectra (SERS) of adsorbed species from a bare cobalt (Co) bulk electrode were observed for the first time with confocal Raman microscopy. A combined AFM, Raman and electrochemical study shows that a proper roughening procedure is vitally important for obtaining good-quality surface Raman spectra from the Co electrode. The surface enhancement factor ranges from 2 to 3 orders of magnitude, depending critically on the surface roughening procedure. The present study provides a bright prospect for the wide investigation of systems of practical application.

Glucose induced in-situ reduction of chloroaurate ions entrapped in a fatty amine film: formation of gold nanoparticle–lipid composites

Anand Gole, Ashavani Kumar, Sumant Phadtare, A. B. Mandale and Murali Sastry, PhysChemComm, 2001, 4, 92 [http://dx.doi.org/10.1039/b106564e].

The formation of gold nanoparticle–lipid composite films by glucose-induced reduction of chloroaurate ions entrapped in thermally evaporated fatty amine films is described. Simple immersion of films of the salt of octadecylamine and chloroaurate ions (formed by immersion of thermally evaporated fatty amine films in chloroauric acid solution) in glucose solution leads to the facile in-situ reduction of the metal ions to form gold nanoparticles in the fatty amine matrix. The formation of gold nanoparticles is readily detected by the appearance of a violet color in the film and thus forms the basis of a possible new, gold nanoparticle-based colorimetric sensor for glucose. The formation of the fatty amine salt of chloroauric acid and the subsequent reduction of the metal ions by glucose has been followed by quartz crystal microgravimetry, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy and transmission electron microscopy measurements.

A comparison of numerical and analytical approaches for reduction of rotational and vibration–rotational spectra of diatomic molecules to parameters of radial functions

John A. Coxon and Marcin Molski, PhysChemComm, 2001, 4, 96 [http://dx.doi.org/10.1039/b104631b].

The communication presents a numerical test of the three most popular methods used for direct inversion of the highly resolved IR and MW spectra of diatomic systems: (A) the numerical techniques such as those described by Coxon (J. A. Coxon and P. G. Hajigeorgiou, J. Mol. Spectrosc., 1991, 150, 1, ref. 1; J. A. Coxon, J. Mol. Spectrosc., 1992, 150, 274, ref. 2), Bernath (J. M. Campbell, M. Dulick, D. Klapstein, J. B. White and P. F. Bernath, J. Chem. Phys., 1993, 99, 8379, ref. 3; H. G. Hedderich, M. Dulick and P. F. Bernath, J. Chem. Phys., 1993, 99, 8363, ref. 4; M. Dulick, K. Q. Zhang, B. Guo and P. F. Bernath, J. Mol. Spectrosc., 1998, 188, 14, ref. 5), Le Roy (J. Y. Seto, R. J. Le Roy, J. Verges and C. Amiot, J. Chem. Phys., 2000, 113, 3067, ref. 6) and their co-workers; (B) the analytical approach developed by Ogilvie (J. F. Ogilvie, J. Phys. B, 1994, 27, 47, ref. 7); and (C) its improved version, called deformational self-consistent (DS-c) procedure, proposed by Molski (M. Molski, J. Phys. Chem., 1999, 103, 5269, ref. 8; M. Molski, Chem. Phys. Lett., 1999, 306, 88, ref. 9; M. Molski, Chem. Phys. Lett., 2001, 342, 293, ref. 10). The results obtained for the test molecule LiH X ¹Σ⁺ indicate that the energy levels and radial parameters generated by Ogilvie’s Radiatom program are not sufficiently accurate for use in external applications.

The preparation and characterization of ZnO–PANI (polyaniline) composite film on PATP (ρ-aminothiophenol)/Au

Z. X. Zheng, Y. Y. Xi, H. G. Huang, L. L. Wu and Z. H. Lin, PhysChemComm, 2001, 4, 100 [http://dx.doi.org/10.1039/b107714g].

A novel ZnO (zinc oxide)–PANI (polyaniline) composite film on PATP (ρ-aminothiophenol)/Au was prepared by electrochemical-assembly (ECA) and sol–gel technique, and this composite film shows excellent luminescent performance and high photoelectrochemical conversion efficiency, which can be industrially used for luminescent nanomaterials and treating wastewater containing methyl orange.

Extreme high rotational excitation of ClO

Robert Aures, Karl-Heinz Gericke, Masahiro Kawasaki, Christof Maul, Yukio Nakano, Gundula Trott-Kriegeskorte and Zhenya Wang, PhysChemComm, 2001, 4, 102 [http://dx.doi.org/10.1039/b108052k].

We observed the population of extremely high non-thermal rotational states of ClO (J_max = 130.5) upon photodissociation of Cl₂O. State-resolved and isotope-specific detection of nascent ClO is performed by observing single colour (2 + 1) resonance enhanced multiphoton ionisation (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm. The REMPI spectrum is assigned to the ClO(C²Σ⁻, v′ = 0 ← XΠ²_Ω, v = 0) transition. The non-thermal population of rotational states is highly inverted, peaking at J = 107.5. The photodissociation of Cl₂O is a classical example for the pure impulsive model, as a consequence of the Cl₂O mass distribution and a weak dependence of the upper potential energy surface on the bond angle. Cl₂O can thus be used as clean source for laboratory generation of highly excited ClO molecules with a defined non-thermal rotational population. In kinetic studies using ClO from Cl₂O as precursor the high rotational excitation needs to be considered carefully.

The self-reaction of hydroperoxyl radicals: ab initio characterization of dimer structures and reaction mechanisms

Rongshun Zhu and M. C. Lin, PhysChemComm, 2001, 4, 106 [http://dx.doi.org/10.1039/b107602g].

The global potential energy surfaces of singlet and triplet H₂O₄ systems have been searched at the B3LYP/6-311G(d, p) level of theory; their relative energies have been calculated at the G2M(CC5)// B3LYP/6-311G(d, p) level. The results show that the most stable intermediate out of the 11 open-chain and cyclic dimers of HO₂ is the singlet HO₄H chain-structure with C₁ symmetry which lies 19.1 kcal mol⁻¹ below the reactants. The transition states for the production of H₂O₂ + O₂ (singlet and triplet), H₂O + O₃ and H₂ + 2O₂ have been calculated at the same level of theory. The results show that the most favored product channel, producing H₂O₂ + ³O₂, occurs by the formation of a triplet six-member-ring intermediate through head-to-tail association with a dual hydrogen-bonding energy of 9.5 kcal mol⁻¹. The intermediate fragments to give H₂O2 + ³O₂via a transition state, which lies below the reactants by about 0.5 kcal mol⁻¹. There are four channels over the singlet surface which can produce ¹O₂; all the transition states associated with these channels lie above the reactants by 2.8–5.6 kcal mol⁻¹ at the G2M level. Similarly, the O₃ and H₂ formation channels also occur over the singlet surface with high energy barriers, 5.2 and 74.2 kcal mol⁻¹, respectively; their formation is kinetically unimportant.

Perspective: Molecules as products; the good, the bad and the eccentric

A. J. McCaffery and R. J. Marsh, PhysChemComm, 2001, 4, 112 [http://dx.doi.org/10.1039/b108077f].

Guided by experimental findings, we develop a nuclear dynamical theory of molecular collisions that accounts quantitatively for product distributions in a wide range of inelastic and reactive processes. Two simple equations are sufficient for this purpose. The first represents the principal mechanism by which linear momentum of relative motion is converted to angular momentum via a torque arm of molecular dimension. The second is a statement of energy conservation and this (together with the requirement that products be formed in well-defined quantum states) constitutes the boundary condition within which the mechanism must operate. Boundary conditions vary widely with system and with process and give great variety to the final rotational state distributions. Both equations may be represented in velocity–angular momentum diagrams from which the origins of the characteristic features of many processes, particularly their product rotational state distributions, may be identified. Quantitative calculations reproduce experimental data over a wide range of inelastic and reactive collisions and for molecules in low-lying or highly excited states. Input data in the calculations consists of little more than atomic mass, bond length and velocity distributions (and reaction enthalpy for reactive processes). Collisional behaviour in this model is characteristic of an individual molecule and we outline the beginnings of a classification scheme that categorises molecules as good (efficient) or bad (inefficient) in terms of their ability to convert linear-to-angular momentum within the constraints appropriate to system and process. Molecules such as the hydrides of heavier elements fall into a category we term eccentric as a result of unusual (but predictable) collisional properties.

Ab initio study of ammonium perchlorate combustion initiation processes: unimolecular decomposition of perchloric acid and the related OH + ClO₃ reaction

R. S. Zhu and M. C. Lin, PhysChemComm, 2001, 4, 127 [http://dx.doi.org/10.1039/b109523b].

The unimolecular decomposition of HClO₄ has been investigated at the G2M//B3LYP/6-311+G(3df, 2p) level of theory. Above 500 K, the decomposition process was found to depend strongly on pressure below 200 atm. The rate constants at the high- and low-pressure limits were predicted to be k₁^∞ = 1.5 × 10¹⁷ exp(−26500/T) s⁻¹ and k₁⁰ = 3.39 × 10³⁰T^−10.9 exp(–29430/T) cm³ molecule⁻¹ s⁻¹, respectively. Under the atmospheric-pressure condition, the predicted first-order rate coefficient for the temperature range 300–3000 K, k₁ = 5.0 × 10⁵¹T^−11.64 exp(−30700/T) s⁻¹, agrees reasonably with experimental data obtained at 550–750 K by different experimental groups. We have also calculated the rate constants for the bimolecular reaction of OH with ClO₃ producing HClO₄ by association/stabilization and HO₂ + ClO₂ by association/fragmentation. At the high-pressure limit, the rate constants can be given as: k₋₁ = 3.2 × 10⁻¹⁰T0.07 exp(–25/T) cm³ molecule⁻¹ s⁻¹ and k₂ = 2.1 × 10⁻¹⁰T^0.09 exp(−18/T) cm³ molecule⁻¹ s⁻¹, respectively, for the temperature range 300–3000 K. Under the atmospheric pressure condition, the OH + ClO₃ reaction produces predominately the HO₂ + ClO₂ products.

Non-photochemical spectral hole-burning in the ²E ← ⁴A₂ transition of crystalline NaMgAl(oxalate)₃·9H₂O:Cr(III)

Matthew L. Lewis and Hans Riesen, PhysChemComm, 2001, 4, 133 [http://dx.doi.org/10.1039/b110096c].

Non-photochemical spectral hole-burning in the ²E ← ⁴A₂ transition of crystalline NaMgAl(oxalate)₃·9H₂O:Cr(III and its temperature dependence is reported and a hole-burning mechanism is proposed. This is the first report of non-photochemical hole-burning in the ²E ← ⁴A₂ transition of chromium(III) in a crystal.

Structure and dynamics of the Mu adduct of diketene

Iain McKenzie, Brenda Addison-Jones, Jean-Claude Brodovitch, Khashayar Ghandi and Paul W. Percival, PhysChemComm, 2001, 4, 136 [http://dx.doi.org/10.1039/b110704f].

The radical formed by muonium addition to diketene has been studied by transverse field muon spin rotation (TF-µSR) and muon avoided level-crossing resonance (µALCR). The TF-µSR spectrum shows that muonium adds to only one site in diketene, and it is clear from the µALCR spectrum that the radical product contains two inequivalent sets of protons. The muon and proton hyperfine coupling constants (hfcs) were determined at several temperatures between 280 and 362 K. The muon hfc falls with increasing temperature, one proton hfc increases, and the other remains constant. The magnitude and temperature dependence of the hfcs support assignment of the 4-muonomethyl-oxetan-2-on-4-yl radical. Density functional calculations were performed to model the temperature dependence of the hfcs. The results are consistent with a preferred conformation of the muoniated methyl group in which the C–Mu bond eclipses the orbital containing the unpaired electron.

Assignment of the near-UV absorption spectrum of C₆₀

A. Sassara, G. Zerza and M. Chergui, PhysChemComm, 2001, 4, 139 [http://dx.doi.org/10.1039/b109221a].

The absorption spectrum of C₆₀ embedded in Ne matrices in the 410–360 nm region is revisited. A complete assignment of the absorption lines therein is proposed in terms of transitions to the ungerade states 1 ¹G_1u, 1 ¹T_1u and 2 ¹T_1u states, with progressions of Jahn–Teller h_g modes and of the totally symmetric a_g modes. We also identify a new progression at λ ≤ 375 nm, which we attribute to the transition to the 2 ¹T_2u state and its h_g and g_g Jahn–Teller modes. Its pure electronic origin is at ∼26700 cm⁻¹.

2002

Ionic to molecular transition in AlCl₃: an examination of the electronic structure

Leonardo Bernasconi, Paul A. Madden and Mark Wilson, PhysChemComm, 2002, 5, 1 [http://dx.doi.org/10.1039/b107715e].

AlCl₃ crystallizes as an ionic solid but melts to form a molecular liquid consisting of Al₂Cl₆ units. In order to see if this transition involves a major change in electronic structure, the dimer and crystal of AlCl₃ are examined with the aid of generalized gradient corrected density functional theory (GGC-DFT) calculations and the electronic wavefunctions examined with the aid of a Wannier localisation transformation of the Kohn–Sham eigenfunctions. The change from octahedral to tetrahedral coordination of Al which is observed on melting has been induced by simply rescaling the unit cell parameters, and the variations in the hybridization of the Wannier orbitals across the transition have been analysed thoroughly. The predominantly ionic character of the interactions across the ionic to molecular transition is confirmed, validating the use of ionic interaction potentials to represent AlCl₃ and relatedsystems. Dipole moments of the single ions have been estimated from the position of the Wannier function centres and they are found to reproduce with remarkable accuracy the values predicted by a polarizable ionic interaction potential. A similar analysis has been carried over to the AlBr₃–Al₂Br₆ system, which is known to consist of molecular units in both crystal and gas phase.

Two-dimensional correlation gel permeation chromatography (2D correlation GPC) study of the sol–gel polymerization of octyltriethoxysilane. HCl-concentration dependence

Kenichi Izawa, Toshiaki Ogasawara, Hideki Masuda, Hirofumi Okabayashi, Charmian J. O'Connor and Isao Noda, PhysChemComm, 2002, 5, 12 [http://dx.doi.org/10.1039/b107635c].

Two-dimensional correlation gel permeation chromatography (2D GPC) was used to elucidate intricate details of the initial ten minutes of the sol–gel transition of n-octyltriethoxysilane (OTES), catalysed by 0.5 and 2.0 M HCl·H₂O. The results demonstrate that the features of 2D GPC correlation spectra directly reflect the dynamic variation of reactions or interactions present during the polymerization process.

Perspective: Femtosecond two-dimensional infrared spectroscopy: IR-COSY and THIRSTY

Nien-Hui Ge and Robin M. Hochstrasser, PhysChemComm, 2002, 5, 17 [http://dx.doi.org/10.1039/b109935c].

The femtosecond two-dimensional infrared (2D IR) spectroscopy that was recently developed shows great promise for determining the dynamics of molecular structure at ultrafast time scales that are hard to access by NMR and X-ray diffraction methods. This Perspective focuses on the IR-COSY and THIRSTY methods that are based on heterodyned three pulse photon echoes. The relationships of 2D spectral properties coupling, structure, correlated fluctuations, energy transfer, and orientational motions to experimental results on small peptides and molecules are described. The status of this exciting new field is also discussed.

Perspective: Resonances in bimolecular reactions

Kopin Liu, Rex T. Skodje and David E. Manolopoulos, PhysChemComm, 2002, 5, 27 [http://dx.doi.org/10.1039/b110570a].

In this Perspective we briefly review our recent studies which prove unequivocally the existence of a quantum dynamical resonance in the F + HD → HF + D reaction. The signatures of the resonance in the integral and differential cross sections of this reaction are elucidated. The interplay between experiment and theory is crucial in establishing the existence of a resonance in a bimolecular reaction and in revealing its physical characteristics.

Self-organization of triple-stranded carbon nanoropes

C.-J. Su, D. W. Hwang, S.-H. Lin, B.-Y. Jin and L.-P. Hwang, PhysChemComm, 2002, 5, 34 [http://dx.doi.org/10.1039/b110151j].

Novel self-organized carbon nanoropes consisting of three helically coiled multi-wall nanotubes with a remarkable constant pitch over several microns were grown by the lanthanide oxide-catalyzed decomposition of gaseous acetylene on aluminophosphate (AlPO₄-5) support. Direct characterization by the stereo transmission electron microscope and scanning electron microscope has convincingly shown that these three strands entwine with each other helically, which are presumably kept together by both the spontaneous curvature and van der Waals (vdW) attraction.

Applicability of thermoacoustical parameters for the computation of available volume in liquid systems

J. D. Pandey, Ranjan Dey and Bishan Datt Bhatt, PhysChemComm, 2002, 5, 37 [http://dx.doi.org/10.1039/b109599d].

Available volumes in pure liquids and binary liquid mixture at varying temperature have been computed using thermoacoustical parameters and the values thus obtained are compared with the values obtained from a thermodynamic relation of the available volume. Fairly good agreement between the values from the two methods proves the applicability of thermoacoustical parameters for the computation of the available volume in pure liquids and liquid mixtures.

Perspective: Ultrafast vibrational spectroscopy in condensed phases

Minhaeng Cho, PhysChemComm, 2002, 5, 40 [http://dx.doi.org/10.1039/b110898k].

A variety of ultrafast vibrational excitation and probing methods are first discussed and it is shown that various vibrational spectroscopies can be devised by combining multiple excitation and probing methods. A few ultrafast vibrational spectroscopic methods in condensed phases, which have already been demonstrated and used to study vibrational relaxation phenomena and structural analysis of small polypeptides, are briefly summarized. Then, a number of novel ultrafast vibrational spectroscopies that have been theoretically investigated are discussed by emphasizing their differences from other existing methods. Perspectives on how these ultrafast vibrational spectroscopies in centrosymmetric and non-centrosymmetric condensed phases can be applied to the investigations of chemical reaction dynamics, solvation dynamics, time-dependent structural evolutions of polyatomic molecules such as proteins will be mentioned.

Energy transfer efficiency distributions in polymers in solution during folding and unfolding

Goundla Srinivas and Biman Bagchi, PhysChemComm, 2002, 5, 59 [http://dx.doi.org/10.1039/b200595f].

Distribution of fluorescence resonance energy transfer (FRET) efficiency between the two ends of a Lennard-Jones polymer chain both at equilibrium and during folding and unfolding has been calculated, for the first time, by Brownian dynamics simulations. The distribution of FRET efficiency becomes bimodal during folding of the extended state subsequent to a temperature quench, with the width of the distribution for the extended state broader than that for the folded state. The reverse process of unfolding subsequent to a upward temperature jump shows different characteristics. The distributions show significant viscosity dependence which can be tested against experiments.

The enhanced photoluminescence of zinc oxide and polyaniline coaxial nanowire arrays in anodic oxide aluminium membranes

Z. X. Zheng, Y. Y. Xi, P. Dong, H. G. Huang, J. Z. Zhou, L. L. Wu and Z. H. Lin, PhysChemComm, 2002, 5, 63 [http://dx.doi.org/10.1039/b201201d].

A novel nanomaterial, an array of zinc oxide (ZnO) and polyaniline (PANI) coaxial nanowires, was synthesized using an anodic aluminum oxide (AAO) membrane as the template. The morphology of these coaxial nanowires was observed with transmission electron microscope (TEM). The experiments on photoluminescence (PL) of coaxial nanowires and their array in AAO membrane show that the visible emission band of ZnO shifts from 530 to 400 nm for the coaxial nanowires array in AAO membrane, and to a lower wavelength (385 nm) for coaxial nanowires in NaOH solution. When compared with the PL spectrum of ZnO nanowires array in AAO membrane, an about 100 times PL enhancement was found in the PL spectrum of ZnO and PANI coaxial nanowires array in AAO membrane. The possible explanations for these two blue shifts of visible emission band of ZnO and the PL enhancement were presented.

Vibrational modes of CH bonds in n-paraffin molecular chains: an algebraic description

T. Marinković and S. Oss, PhysChemComm, 2002, 5, 66 [http://dx.doi.org/10.1039/b201553f].

We apply the one-dimensional vibron model to compute energies and infrared intensities of CH vibrational modes (stretching and bending states) of n-paraffin molecules. We consider the possible onset of interactions between different kinds of bending motions as well as that of anharmonic resonances between CH stretching modes and CH bending overtone/combination vibrations.

Perspective: Spectroscopy of reactive potential energy surfaces

Daniel M. Neumark, PhysChemComm, 2002, 5, 76 [http://dx.doi.org/10.1039/b202218d].

This perspective reviews experiments in which spectroscopy rather than scattering is used to probe reactive potential energy surfaces. The application of negative ion photodetachment to the transition state spectroscopy of benchmark reactions is described, followed by a brief description of recent transition state spectroscopy experiment starting from clustered precursor anions that probe the effects of solvation on transition state spectroscopy and dynamics. Experiments on the spectroscopy of open-shell pre-reactive complexes are also discussed.

Convergence from clusters to the bulk solid: an ab initio investigation of clusters Na_nCl_n (n = 2–40)

Jinfeng Lai, Xin Lu and Lansun Zheng, PhysChemComm, 2002, 5, 82 [http://dx.doi.org/10.1039/b202278h].

The electronic structures of a series of sodium chloride clusters (NaCl)_n (n = 2–40) cut out from the NaCl solid have been investigated by means of ab initio calculations. The calculation results demonstrated a good correlation of the topologic parameters N_d (the total amount of dangling bonds of a cut-out cluster) and β (the average dangling bonds on each in-cluster atom) with the stability of clusters as well as an evident convergence from clusters to the bulk solid. Particularly, we found that the effective charges on the Cl anions are more site dependent than size dependent.

Laser-induced breakdown spectroscopy at metal–water interfaces

Honoh Suzuki, Hisanobu Nishikawa and I-Yin Sandy Lee, PhysChemComm, 2002, 5, 88 [http://dx.doi.org/10.1039/b202597c].

Visible light emission from metal–water interfaces at laser-induced breakdown (LIB) has been observed for aluminium, titanium and platinum. The spectra are found to consist of broadband continuum without any discrete atomic lines, which may be useful as a pulsed light source for spectroscopy. A simple thermal diffusion model combined with blackbody radiation is described, the numerical result of which agrees fairly well with the observed spectra.

Molecular conformation in the gas phase and in solution

P. Butz, G. E. Tranter and J. P. Simons , PhysChemComm, 2002, 5, 91 [http://dx.doi.org/10.1039/b203810b].

The article explores the correlation between the ultra-violet circular dichroism of chirally substituted benzene molecules in solution, and their absolute configurations determined on the basis of infrared (or ultraviolet) spectroscopy, coupled with ab initio computation, in the gas phase. New results for isolated and solvated molecules in the ephedra class of drugs are presented. They lead to a revision of the current sector rules associated with excitation into the ¹L_b state of the benzene ring and suggest a new strategy for bridging the gap between isolated molecular and solvated cluster structures determined in the gas phase and the structures adopted in condensed media.

Are guanine tetrads stabilised by bifurcated hydrogen bonds? An AIM topological analysis of the electronic density

Guillaume Louit, Alexandre Hocquet, Mahmoud Ghomi, Michael Meyer and Jürgen Sühnel, PhysChemComm, 2002, 5, 94 [http://dx.doi.org/10.1039/b204736e].

Following a previous publication (M. Meyer, M. Brandl and J Sühnel, J. Phys. Chem. A, 2001, 105, 8223–8225) on quantum mechanical calculations of guanine tetrads where the issue of the difference between bifurcated and Hoogsteen conformations was addressed geometrically and energetically, we tackle the problem from the Atoms in Molecules (AIM) point of view of the topological analysis of the electronic density. We provide electronic argumentation to discuss the bifurcated or Hoogsteen issue, from the analysis of density and laplacian at the bond critical point criteria, and from the integration of atomic properties. The Hoogsteen hydrogen bonding network appears to be stronger than the bifurcated one, and benefits more from cooperativity.

The effect of lithium triflate and lithium bromide on the vibrational frequencies of DMEDA

Shawna S. York, Scott E. Boesch, Ralph A. Wheeler and Roger Frech, PhysChemComm, 2002, 5, 99 [http://dx.doi.org/10.1039/b204103k].

An experimental and computational investigation of the structures and vibrational frequencies of N,N′-dimethylethylenediamine–lithium triflate (DMEDA–LiTf; Tf⁻ = CF₃SO₃⁻) has been done using a combination of hybrid Hartree–Fock/density functional calculations and Raman and IR spectroscopy. Band assignments for DMEDA–LiBr were made by comparing the experimental Raman and IR spectra of a 5 ∶ 1 DMEDA–LiBr sample with the calculated vibrational frequencies of the DMEDA–Li⁺ and DMEDA–LiBr complexes. Band assignments for DMEDA–LiTf were made by comparing the experimental spectra of samples over a composition range of 20 ∶ 1 to 1.5 ∶ 1 with calculations done on the DMEDA–LiTf complexes. The effect of the lithium cation and lithium triflate on the geometries and vibrational frequencies of the DMEDA will be examined. The combined experimental data and computational results clearly show that the intramolecular hydrogen bonding in pure DMEDA is broken upon addition of lithium bromide or lithium triflate.

Distance tunnelling characteristics of solid/liquid interfaces: Au(111)/Cu²⁺/H₂SO₄

Gabor Nagy, Dirk Mayer and Thomas Wandlowski, PhysChemComm, 2002, 5, 112 [http://dx.doi.org/10.1039/b205720b].

This study examined the liquid part of solid/liquid interfaces at the atomic level. By measuring distance tunnelling characteristics the height of the potential barrier between the tip and the sample, i.e., the potential energy field the tunnelling electrons are exposed to, can be obtained, and this provides direct access to double layer properties. We found exponential IS-characteristics for the bare and the oxidised Au(111) surface, while non-exponential behaviour was obtained in the presence of ordered adlayers. The influence of the local environment just within the Helmholtz layer is strong enough to perturb the tunnelling process significantly. The electrolyte properties in the Gouy region do not change with electrode potential, the liquid in the tunnelling gap has only an average effect by lowering the barrier height.

More reliable partial atomic charges when using diffuse basis sets

Jason D. Thompson, James D. Xidos, Timothy M. Sonbuchner, Christopher J. Cramer and Donald G. Truhlar, PhysChemComm, 2002, 5, 117 [http://dx.doi.org/10.1039/b206369g].

We present a method that alleviates some of the sensitivity to the inclusion of diffuse basis functions when calculating partial atomic charges from a Löwdin population analysis. This new method locally redistributes that part of the Löwdin population that comes from diffuse basis functions so that the final charges closely resemble those calculated without diffuse functions. We call this method the redistributed Löwdin population analysis (RLPA). The method contains one parameter for each atomic number, and we optimized the parameter for the 6-31+G(d) basis set. The method has been tested on compounds that contain H, Li, C, N, O, F, Si, P, S, Cl, and Br. For a test set of 398 compounds with experimental and high-level theoretical dipole moments, the dipole moments derived from the charges obtained by standard Löwdin population analysis have errors 35% larger than those obtained by the corresponding RLPA using the same basis set. In judging the quality of the RLPA with respect to the test set of dipole moments, we have also found that dipole moments derived from Mulliken population analysis have errors 120% larger than those derived from RLPA for the same basis set. The new method is particularly successful for the 207 systems containing only first row atoms (H, C, N, O, F) for which the errors in the dipole moments computed from the partial atomic charges obtained by standard Löwdin and Mulliken analysis are respectively 115 and 419% larger than those obtained by RLPA.

Temperature-resolved, in-situ powder X-ray diffraction of silver iodide under microwave irradiation

G. R. Robb, A. Harrison and A. G. Whittaker, PhysChemComm, 2002, 5, 135 [http://dx.doi.org/10.1039/b207258k].

Some unexpected properties of the ionic conductor, silver iodide, when heated by 2.45 GHz microwave radiation are investigated using temperature-resolved, in-situ powder X-ray diffraction. The lowering of the phase transition temperature can be explained by multi-phonon interactions with the microwaves and low-lying transverse optic modes.

Mesoporous silicates as nanoreactors for synthesis of carbon nanotubes

Mónika Urbán, Zoltán Kónya, Dóra Méhn, Ji Zhu and Imre Kiricsi, PhysChemComm, 2002, 5, 138 [http://dx.doi.org/10.1039/b203767j].

Multi-wall carbon nanotubes (MWNT) were synthesized by a novel method using mesoporous MCM-41 and MCM-48 silicates as nanoreactors in the absence of any metal traces. Transmission electron microscopy (TEM) studies revealed that the quality of carbon nanotubes obtained was very promising, the diameter distribution is very narrow.

Perspective: Calculation of anharmonic vibrational spectroscopy of small biological molecules

R. B. Gerber, B. Brauer, S. K. Gregurick and G. M. Chaban, PhysChemComm, 2002, 5, 142 [http://dx.doi.org/10.1039/b208000a].

The role of anharmonic effects in the vibrational spectroscopy of small biological molecules and their 1 ∶ 1 complexes with water is discussed. The strengths and limitations of the vibrational self-consistent field (VSCF) method and its extensions as a computational tool for this purpose are examined. Anharmonic coupling between different vibrational modes is found to be very important for these systems, even for fundamental transitions, and incorporation of these effects seems essential for quantitative interpretation of experimental data. Both analytical, empirical force fields, and potential surfaces computed from electronic structure methods are used in VSCF calculations of several benchmark systems and compared with experimental spectroscopic data. Glycine in several conformers, the glycine–water complex, and N-methylacetamide are among the systems discussed. The main conclusions are: (1) Electronic structure methods such as MP2/DZP and density functional B97, give very good agreement with experimental data. Thus, MP2 and B97 clearly provide an accurate description of the anharmonic interactions. VSCF calculations, including all modes, with MP2, B97 and other successful methods are presently feasible for molecules with up to 15–20 atoms. (2) The electronic structure methods seem to give spectroscopic predictions in much better accord with experiment than standard empirical force fields such as AMBER or OPLS. The anharmonic couplings provided by these methods differ greatly, in the cases tested to date, from the ab initio ones. The implications of these results for future modeling of small biomolecules are discussed. Comments are provided on future directions in this subject, including extensions to large biomolecules.

Adsorption behaviour of DNA bases at the Au(111) electrode

A. P. M. Camargo, H. Baumgärtel and C. Donner, PhysChemComm, 2002, 5, 151 [http://dx.doi.org/10.1039/b208139c].

We report on the adsorption of adenine as well as on the coadsorption of adenine/thymine and uracil/thymine on Au(111). Adenine is chemisorbed in two different states. Mutual interaction between adenine and thymine could be detected only at negative potentials where both molecules are oriented with their plane parallel to the surface. This interaction depends on the concentration of thymine, the pH value, the temperature and the roughness of the surface. At positive potentials where thymine/adenine are oriented perpendicular to the electrode surface, from our experiments no hints to their interaction could be found. Thymine prevents the uracil adsorption and no cocondensation signal between the noncomplementary bases thymine/uracil was found.

Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques

Ellen L. Heeley, Ariana C. Morgovan, Wim Bras, Igor P. Dolbnya, Anthony J. Gleeson and Anthony J. Ryan, PhysChemComm, 2002, 5, 158 [http://dx.doi.org/10.1039/b206832j].

Shear induced crystallization of commercial grade polyethylenes (PE) have been investigated using simultaneous SAXS and WAXS, enabling real time studies of the kinetics and structure development to be performed.

Surface diffusion control of the photocatalytic oxidation in air/TiO₂ heterogeneous reactors

R. Tsekov, E. Evstatieva and P. G. Smirniotis, PhysChemComm, 2002, 5, 161 [http://dx.doi.org/10.1039/b207965h].

The diffusion of superoxide radical anions on the surface of TiO₂ catalysts is theoretically considered as an important step in the kinetics of photocatalytic oxidation of toxic pollutants. A detailed analysis is performed to discriminate the effects of rotation and adsorption bond vibrations on the diffusion coefficient. A resonant dependence of the diffusivity on the lattice parameters of the TiO₂ surface is discovered showing that the most rapid diffusion takes place when the lattice parameters are twice as large as the bond length of the superoxide radical anions. Whereas the rotation and vibrations normal to the catalyst surface are important, the anion bond vibrations do not affect the diffusivity due to their low amplitudes as compared to the lattice parameters.

Perspective: Dynamics of cluster anions: a detailed look at condensed-phase interactions

Andrei Sanov and W. Carl Lineberger, PhysChemComm, 2002, 5, 165 [http://dx.doi.org/10.1039/b209239e].

This Perspective reflects on several recent advances in the studies of structure and dynamics of cluster anions, bridging the gap between ‘cluster’ and condensed phases. Applications involving photofragment and photodetachment spectroscopy, as well as femtosecond time-resolved experiments, are described. Special emphasis is given to the effects of microscopic solvation on the electronic structure and reactivity of negative ions in heterogeneous and homogeneous cluster environments. Some recent breakthroughs in experimental methodology are also outlined, in particular the application of photofragment and photoelectron methods and the imaging technique to the studies of molecular cluster anions.

2003

Guanine tetrads interacting with metal ions. An AIM topological analysis of the electronic density

Guillaume Louit, Alexandre Hocquet, Mahmoud Ghomi, Michael Meyer and Jürgen Sühnel, PhysChemComm, 2003, 6, 1 [http://dx.doi.org/10.1039/b210911e].

The interaction of guanine tetrads with various alkaline, alkaline earth and transition metal ions has been studied by means of an AIM topological analysis of the electronic density based on density functional calculations. The interaction between metal ion and ligand has been characterized in terms of the Laplacian of the electronic density, the Hamiltonian kinetic energy density and the Lagrangian kinetic energy density. The influence of the metal ion–ligand interaction on tetrad hydrogen bonding is also discussed.

Solvent caging of internal motions in myoglobin at low temperatures

Alexander L. Tournier, Jiancong Xu and Jeremy C. Smith, PhysChemComm, 2003, 6, 6 [http://dx.doi.org/10.1039/b209839c].

Experimental and simulation studies have reported the presence of a transition in the internal dynamics of proteins at 220 K. This transition has been correlated with the onset of activity in several proteins. The role of the solvent in the dynamical transition has been the subject of increased attention. Here simulation techniques are used to distinguish dynamical features inherent to the protein energy landscape from those induced by the surrounding solvent. The present results indicate that the protein dynamical transition primarily affects the side-chains on the outer layers of the protein. Moreover, the results indicate that the solvent restrains protein motions at low temperatures.

Non-photochemical spectral hole-burning mediated by water molecules in interligand pockets of [Cr(terpy)₂]³⁺

Hans Riesen and Lynne Wallace, PhysChemComm, 2003, 6, 9 [http://dx.doi.org/10.1039/b209460f].

Low temperature fluorescence line-narrowing (FLN) and spectral hole-burning experiments (SHB) were performed in the ²E←⁴A₂ spin–flip transition of [Cr(2,2′:6′,2″-terpyridine)₂]³⁺ in frozen ethylene glycol/water (2 ∶ 1) and DMSO/water (2 ∶ 1) glasses. In the FLN experiments an average ²E splitting of 23 cm⁻¹ is observed. It is concluded that the interaction with water molecules in pockets provided by the ligands is most likely to be responsible for the relatively efficient non-photochemical hole-burning. Fast spectral diffusion and spontaneous hole-filling prevent the observation of holes above 20 K. The FLN and SHB experiments were performed by using a diode laser.

Perspective: Quantum dynamical characterization of unimolecular resonances

Hong Zhang and Sean C. Smith, PhysChemComm, 2003, 6, 12 [http://dx.doi.org/10.1039/b300284p].

We give a selective review of quantum mechanical methods for calculating and characterizing resonances in small molecular systems, with an emphasis on recent progress in Chebyshev and Lanczos iterative methods. Two archetypal molecular systems are discussed: isolated resonances in HCO, which exhibit regular mode and state specificity, and overlapping resonances in strongly bound HO₂, which exhibit irregular and chaotic behavior. Future directions in this field are also discussed.

Intermittent dynamics and hyper-aging in dense colloidal gels

Hugo Bissig, Sara Romer, Luca Cipelletti, Veronique Trappe and Peter Schurtenberger, PhysChemComm, 2003, 6, 21 [http://dx.doi.org/10.1039/b211806h].

We investigate the slow dynamics of strongly aggregated particle gels by diffusing wave spectroscopy (DWS) using a charge coupled device (CCD) camera as a multispeckle detector. The evolution of the slow dynamics after the gel-point is followed using two different techniques, the multispeckle method and a novel correlation scheme, time resolved correlation (TRC), which allows us to obtain time resolved information on the dynamics of the gel. We find that the intensity autocorrelation function measured by multispeckle DWS exhibits an ultraslow relaxation, whose characteristic time strongly depends on the age of the gel. An analysis of the TRC data reveals that the slow dynamics is intermittent. We propose that the intermittency is due to rare disruptions or formations of bonds affecting the elastic backbone of the network, which lead to sudden long range rearrangements of the particle position and thus to a sudden change of the speckle pattern.

Reactivity of α,β-unsaturated carbonyl compounds towards nucleophilic addition reaction: a local hard–soft acid–base approach

Paritosh Mondal, Kalyan Kr. Hazarika and Ramesh Ch. Deka, PhysChemComm, 2003, 6, 24 [http://dx.doi.org/10.1039/b301675g].

The Fukui function f_k⁺ and local softness s_k⁺ are assigned as reactivity parameters for nucleophilic addition reaction in acrolein, methylacrylate, methylmethacrylate, acryloylchloride, cinnamaldehyde and cinnamoylchloride. All calculations were performed at the HF level of theory using 6-31G, 6-31G** and TZV basis sets. The condensed local softness calculated using a Löwdin population is compared with the local softness calculated from a Mulliken population. The most probable sites for nucleophilic attack on the α,β-unsaturated carbonyl compounds are determined from local reactivity descriptors: they are quite reliable to predict the reactivity relative to atomic charges.

Origin of the sub-diffusive behavior and crossover from sub-diffusive to super-diffusive dynamics near a biological surface

Arnab Mukherjee and Biman Bagchi, PhysChemComm, 2003, 6, 28 [http://dx.doi.org/10.1039/b212786e].

Diffusion of a tagged particle near a constraining biological surface is examined numerically by modeling the surface-water interaction by an effective potential. The effective potential is assumed to be given by an asymmetric double well constrained by a repulsive surface towards r → 0 and unbound at large distances. The time and space dependent probability distribution P(r,t) of the underlying Smoluchowski equation is solved by using the Crank–Nicholson method. The mean square displacement shows a transition from sub-diffusive (exponent α ≈ 0.46) to a super-diffusive (exponent α ≈ 1.75) behavior with time and ultimately to diffusive dynamics. The decay of self intermediate scattering function (F_s(k,t)) is non-exponential in general and shows a power law behavior at the intermediate time. Such features have been observed in several recent computer simulation studies on the dynamics of water in proteins and micellar hydration shells. The present analysis provides a simple microscopic explanation for the transition from the sub-diffusivity and super-diffusivity. The super-diffusive behavior is due to escape from the well near the surface and the sub-diffusive behavior is due to the return of quasi-free molecules to form the bound state again, after the initial escape.

Generation of [M_m-phenyl]⁻ (M = Mn–Cu) complexes in the gas phase: Metal cluster anions inducement of a selective benzene C–H cleavage

Xiaopeng Xing , Hongtao Liu and Zichao Tang, PhysChemComm, 2003, 6, 32 [http://dx.doi.org/10.1039/b302761a].

This article reports on the generation of [M_m-phenyl]⁻ (M = Mn–Cu) complexes, which are very rare cases in chemistry. Experimental results showed that the typical cation products for the reactions of all 3d transition metal clusters (Sc–Cu) with benzene were different [M_m(C₆H₆)_n]⁺ (M = Sc–Cu) species, while the typical anion products for the late 3d transition metals were [M_m–C₆H₅]⁻ (M = Mn–Cu) complexes. Their formation mechanisms, which involve anion metal clusters inducing a selective benzene C–H cleavage in the gas phase, were proposed.

Synthesis of CdS nanoparticles within thermally evaporated aerosol OT thin films

S. Shiv Shankar, Sayandev Chatterjee and Murali Sastry, PhysChemComm, 2003, 6, 36 [http://dx.doi.org/10.1039/b303919f].

In this paper, we discuss the synthesis of cadmium sulfide (CdS) quantum dots within thermally evaporated sodium bis(2-ethylhexyl)sulfosuccinate (AOT) thin films. This procedure uses electrostatic interactions to entrap positively charged cadmium ions into thin films of the anionic surfactant AOT by a simple immersion of the film in electrolyte solution. Thereafter, the composite film is treated with H₂S gas/Na₂S solution resulting in the in-situ formation of CdS nanoparticles in the quantum size regime. It is believed that the ability of AOT molecules in the thermally evaporated thin films to form reverse micelles is responsible for the CdS nanoparticle size control observed. Investigation of the entrapment of cadmium ions in the AOT film and subsequent quantum dot synthesis was carried out by quartz crystal microgravimetry (QCM), UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) measurements.

“Wash and go”: sodium chloride as an easily removable catalyst support for the synthesis of carbon nanotubes

Andrea Szabó, Dóra Méhn, Zoltán Kónya, Antonio Fonseca and János B. Nagy, PhysChemComm, 2003, 6, 40 [http://dx.doi.org/10.1039/b305670h].

A sodium chloride supported cobalt catalyst was found to be active in the synthesis of carbon nanotubes by a CCVD method.

Algebraic description of n-alkane molecules: first overtone of CH stretching modes

Tijana Marinković and Stefano Oss, PhysChemComm, 2003, 6, 42 [http://dx.doi.org/10.1039/b304717b].

The one-dimensional algebraic model is applied to analyze infrared spectra of n-alkane molecules. We consider CH stretching vibrations in both fundamental (v = 1) and first overtone (v = 2) energy regions. We show that a relatively small set of well-defined parameters leads to a very good agreement with observed data. Both CH₂ and CH₃ vibrations are accounted for. In particular, we suggest that first overtone infrared spectra can be fairly well described without adding complex anharmonic (Fermi) interactions. Their inclusion is required however to obtain a closer agreement with the available experimental spectra.

Formation energies of lithium intercalations in AlSb, GaSb and InSb

Hou Zhu-feng , Zhu Zi-zhong , Huang Mei-chun and Yang Yong, PhysChemComm, 2003, 6, 47 [http://dx.doi.org/10.1039/b304985j].

By using the ab initio norm-conserving pseudopotential method, the lithium intercalations in AlSb, GaSb and InSb have been studied. The formation energies, changes of volumes, electronic structures and charge densities of the lithium interactions in zinc blende-type antimonides Li_xMSb (M = Al, Ga, In) are presented. Our calculations show that during lithium insertion in MSb the lithium intercalation formation energy per lithium atom are all around 2.0 eV. The volume expansions of AlSb, GaSb and InSb due to lithium insertions are relatively large, which might imply that the limit of Li intercalation in antimonides should be small.

H₂O-catalyzed formation of O₃ in the self-reaction of HO₂: a computational study on the effect of nH₂O (n = 1–3)

R. S. Zhu and M. C. Lin, PhysChemComm, 2003, 6, 51 [http://dx.doi.org/10.1039/b304383e].

The effect of nH₂O (n = 1–3) on the association energies of H₂O complexes and on the barriers for the formation of O₃ in the self-reaction of HO₂ reaction has been investigated by ab initio molecular orbital calculations at the modified Gaussian-2 (G2M) level of theory. The results show that H₂O can affect the complex and O₃ formation processes: the more H₂O molecules participating in the reaction, the higher stability of the association complexes and the greater the lowering of the O₃ elimination barrier becomes. For the isomers of the reactions, more hydrogen bonds being formed in the complexes enhances their stabilities. A preliminary kinetic calculation shows that below room temperature, H₂O may enhance the formation of O₃ noticeably.

Thermoacoustical approach to the intermolecular free-length of liquid mixtures

J. D. Pandey, Ranjan Dey and J. Chhabra, PhysChemComm, 2003, 6, 55 [http://dx.doi.org/10.1039/b307435h].

The intermolecular free-length is evaluated by making use of thermoacoustical parameters followed by a comparative study. To achieve this objective, thermoacoustical parameters of four ternary and two quaternary liquid mixtures have been computed. These parameters have been utilized to calculate the available volume (V_a), which in turn has been used to compute intermolecular free-length (L_f) for the systems under investigation. The computed values of L_f have then been compared with the values estimated from well-established thermodynamic and ultrasonic methods. To the best of our knowledge, this investigation is a pioneering attempt in evaluation of intermolecular free-length involving multicomponent liquid mixtures by making use of thermoacoustical parameters.

Theoretical studies on hyperpolarizabilities and UV-vis-IR spectra of a diamminecobalt(III) tetripeptide transition-metal complex

Chensheng Lin, Kechen Wu, Mingxin Zhang and Chaoyong Mang, PhysChemComm, 2003, 6, 59 [http://dx.doi.org/10.1039/b307832a].

The second-order polarizabilities and the UV-vis-IR spectra of a transition-metal complex Co(NH₃)₂(L-ala–gly–gly) have been studied by using the MP2 and TDHF methods. The complex has a maximum β component in the direction from the N(alanyl) group to the N(glycyl) groups. A transparent optical spectrum region from 0.55 to 5.5 µm was found, which offers potential applications as an optical material. The alkyl substitution of the glycyl group only slightly affected the β value and retained the IR transparent region but may cause the molecules to have a favorite packing fashion in the bulk crystal that leads to larger second-order nonlinear optical coefficients.

Theoretical studies of the electronic properties of confined aromatic molecules in support of electronic confinement effect

Lei Z. Zhang and Peng Cheng, PhysChemComm, 2003, 6, 62 [http://dx.doi.org/10.1039/b307440d].

Theoretical studies of the electronic properties of three confined aromatic molecules—benzene, naphthalene and anthracene—have been presented in support of the electronic confinement effect. The confined space of the cavities has been modeled using a mica sheet with the molecule–surface distance in the range of 1.5–4.0 Å. Evidence of the confinement has been revealed by semiempirical calculations, which are theoretically interpreted by means of the Hückel molecular orbital theory. It has been found that the HOMO has been predicted to be more sensitive to the confinement than the LUMO and the overall effect is a reduction on the band gap of the frontier molecular orbitals when the molecule–surface distance is less than ca. 2.5 Å. The variations of the frontier orbital energies and band gaps are correlated with the increase of both Coulomb integral, α, and resonance integral, β. The order of magnitude of the energy increment of Δα and Δβ values is evaluated from data of the above semiempirical calculations. It is also found that the confinement effect is associated with the conjugated system of the aromatic molecules. The theoretical evaluations here prove that confining organic molecules in the cavities is sufficient to alter their electronic properties as a consequence of changes in the molecular orbital energies and band gaps.

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