Themed collection Molecular Dynamics in the Gas Phase

This themed collection includes a collection of articles on molecular dynamics in the gas phase.

We review the progress in low-energy electron collisions with molecular systems relevant to developing new chemo-radiotherapies and provide an experimentalist's perspective of the field.

We discuss how one can initiate, image, and disentangle the ultrafast elementary steps of thermal-energy chemical dynamics, building on advances in controlling molecules, producing ultrashort mid-infrared pulses, and frontier imaging techniques.

We present a review of the capabilities of the density functional based Tight Binding (DFTB) scheme to address the electronic relaxation and dynamical evolution of molecules and molecular clusters following energy deposition via either collision or photoabsorption.

Atomic and molecular (A&M) databases that contain information about species, their identities and radiative/collisional processes are essential and helpful tools that are utilized in many fields of physics, chemistry, and chem/phys-informatics.

We explore time- and momentum-resolved photoelectron diffraction imaging (TMR-PED) to visualize hydrogen dynamics during methanol dication dissociation. Our approach allows real-time tracking of hydrogen migration and molecular fragmentation.

Bond-forming reactions induced in mixed clusters of coronene and C₆₀ by energetic impact of argon ions are modeled using molecular dynamics simulations. A wide range of reaction products and growth mechanisms are identified.

We present an investigation of the ultrafast dynamics of the polycyclic aromatic hydrocarbon fluorene initiated by an intense femtosecond near-infrared laser pulse (810 nm) and probed by a weak visible pulse (405 nm).

Time-dependent blue shift of action spectra in storage rings are used to determine the radiative cooling rate of naphthalene dimer cations, (C₁₀H₈)₂⁺. DFTB-EXCI and Monte-Carlo models are successful in reproducing infrared cooling temporal evolution.

Previous studies of dissociative recombination and vibrational excitation of BeH⁺ are extended to high collision energy, taking into account vibrational continua -dissociative excitation-and several Rydberg series of dissociative states of BeH⁺.

This work is an attempt to decipher if an aniline dication can isomerize to a picoline dication in a given astrochemical environment and if the dissociation of such dications could be a source of kinetically hot fragment ions.

Photofragmentation spectra of protonated vanillin were recorded in the 3000–3700 cm⁻¹ and 225–460 nm ranges, using room temperature infrared multiphoton dissociation and cryogenic ultraviolet photodissociation spectroscopies, respectively.

2D Resonant Auger maps showing the site-specific excitations in butadiene.

The gas-phase infrared spectra of neutral carbon clusters are measured in a wide spectral range.

Real-time dynamics of vibrationally and electronically excited I₂ molecules has been investigated experimentally using the pump–probe technique.

Equal energy sharing PEPECO measurements at 10 and 20 eV yielded photodouble ionization triple-differential cross sections for C₆H₆ and C₅H₅S, which were characterized by a new multi-Gaussian fit method based on He to allow a molecular comparison.

The rate coefficient for two deuterium substituted isotopologues of reaction CH₃ + HBr → CH₄ + Br has been determined using the quasiclassical trajectory (QCT) method.

Double ionization results in a number of prominent fragmentations producing two singly-ionized fragments with kinetic energies of up to a few eV.

5-Fluorouracil is now routinely used in chemo- and radiotherapy. When incorporated into DNA, 5FU is bound to the sugar backbone to form 5FUrd, enhancing damage in radiation therapy.

Combined experiment/theory study on ionized ferrocene molecules. We found that, due to the population of a specific long-lived excited state, charge screening effects from the iron atom and delayed fragmentations occur leading to unexpected dynamics.

In various astronomical environments, an interplay of bottom-up growth and top-down destruction processes takes place. To unravel this, ionic fragments of benzonitrile are used as reactants for low-temperature ion-molecule reactions with acetylene.

Electron attachment to Co(CO)₃NO clusters in argon, dissociative attachment via CO and/or NO ligand losses, neutral dissociations and NO ligand dissociation.

The quantum dynamics of vibrational polaritons arising from the interaction of a bistable molecule with the quantized mode of a microcavity is investigated using an asymmetric double-well potential as a simplified model of a reactive molecule.

A general flowchart for building up kernel-based machine-learning PES models.

The O(³P) + D₂ reaction takes place on two potential energy surfaces of symmetry ³A′ and ³A′′. Based on the shape of the PESs, the ³A′′ should always be more reactive. However, ³A′ is more reactive for energies around the classical barrier.

K-edge photoexcitation of n-butyltin-oxo cage photoresist cores leads to (multiple) ionization and butyl group loss.

Protonated mixed pyrene–water clusters, (Py)_m(H₂O)_n H⁺, where m = [1–3] and n = [1–10], are generated using a cryogenic molecular cluster source. Collision induced dissociation is employed to explore the proton localisation in these systems.

Bond-breaking in CCl₄via dissociative electron attachment (DEA) has been studied using a velocity map imaging (VMI) spectrometer.

Dissociative electron attachment shows functional group-dependent site selectivity in H⁻ ion channels in aliphatic thiols. It also results in energetic S⁻ ions by a sequential dissociation, a reaction applicable to thiol-containing atmospheres.

Bond breaking and making by fast and slow electrons in the trifluoroacetyl chloride molecule and its clusters is revealed.

We present the low temperature gas-phase vibrational spectrum of ionised 1-cyanonaphthalene (1-CNN⁺) in the mid-infrared region.

Acetonitrile (CH₃CN) is present in the interstellar medium (ISM) in a variety of environments.

The mulitphoton ionisation spectra of phenol from S₀ to D₀ and D₁via S₁ and S₂ are characterised by quantum dynamics simulations including the laser pulse explicitely showing direct and indirect photo-ionisation channels.

Formation of NaCl by radiative association is studied by non-adiabatic dynamics at background temperatures ranging up to 50 000 K.

Dense carbon dioxide phases, confined in the micropores of a pure siliceous zeolite Silicalite-1, are identified and characterised with the use of in situ Raman scattering, by monitoring the dynamics of the corresponding Fermi resonance.

The aim of the present paper is to bring clarity, through simplicity, to the important and long-standing problem: does resonance contribute to the forward-angle scattering of the F + H₂ reaction?

Molecules are flexible objects. Despite the rigidity of the phenyl ring, aminoacetophenones in the gas phase are prototype systems suitable for the study of several internal motions: acetyl torsion, methyl internal rotation and amine roto-inversion.

Argonaute (Ago) proteins mediate target recognition guiding miRNA to bind complementary mRNA primarily in the seed region.

The mutual neutralization reaction in collisions of Li⁺ with CN⁻ is a promising candidate for rigorous multi-dimensional ab initio studies of atom-molecule charge transfer processes.

The on-the-fly direct dynamics variational multi-configuration Gaussian (DD-vMCG) method is validated using the Ibele–Curchod model molecular systems: ethene, DMABN and fulvene.

Multioccupancy and stability of He@sII clathrate hydrates from first-principles computations.

The delayed photodecay of tin clusters Sn₂₂⁻ shows a single dissociation pathway by break-off of neutral Sn₇. The distribution of decay constants is translated into an energy distribution, deriving the ensemble temperature and dissociation energy.

Absolute differential cross section for elastic electron scattering from the isoflurane molecule, both experiment and theory, at an incident electron energy of 100 eV. A significant match between the two is evident.

The present study investigates the photofragmentation behavior of iodine-enhanced nitroimidazole-based radiosensitizer model compounds in their protonated form using near-edge X-ray absorption mass spectrometry and quantum mechanical calculations.

Quantum wavepackets are propagated on the excited states of coronene and circumcoronene in the UV-VIS range to study their time evolution. In the figure, the simulated absorption spectra of both systems over the cathedral of the city of Salamanca.

Photodissociation of permanganate near λ = 500 nm produces electronically excited MnO₂⁻, suggesting a ground state dissociation mechanism.

The intrinsic fluorescence lifetime and excited state barrier of the green fluorescent protein (GFP) model chromophore HBDI anion are found in the gas-phase by fs-pump pulse measurements.

Fluorescence-excitation spectra and dispersed fluorescence spectra of gaseous oxazines at 100 K. Combining vibrationally resolved spectra with TD-DFT calculations enable assignment of important vibrations that couple with the electronic transition.

Double photoionization of isoxazole molecules leads to hitherto unexplored photodissociation mechanisms and provides deeper insight into the photophysics of five-membered heterocyclic molecules containing two heteroatoms.

The unimolecular fragmentation channels of highly excited cationic carbon clusters have been measured with a time-of-flight mass spectrometer after photofragmentation.

Potential energy surface profiles for ground state and the first excited-state of 2,2-diphenyl-2H-chromene (DPC) including two conical intersections that govern the ring-opening and photoisomerization reaction dynamics of the DPC system.

We report quantum calculations involving the dynamics of rotational energy-transfer processes, by collision with He atoms in, of molecular species which share the presence of the CN backbone considered of importance in interstellar environments.

We introduce the theory of high-order harmonic generation by homonuclear diatomic cations. The elliptically polarised harmonics can be produced using the orthogonal two-colour field and the cations whose molecular orbital does not have nodal planes.

We show experimental evidence that ionizing radiation is able to cross-link two collagen mimetic peptide triple helices in the gas phase, challenging the previously proposed water-mediated collagen cross-linking mechanism.

The lowest six potential energy surfaces of LiH₂⁺ were obtained (ic-MRCI-F12 level), where four of them were studied for the first time. Using the quasiclassical trajectory method cross sections were obtained for all the reaction channels.

The increasing demand for natural gas as a clean energy source has emphasized the need for efficient gas separation technologies.

This study found that CO₂ and N₂O catalyze a fast production of H₃O⁺ and OH, the main atmospheric oxidant. Theoretical calculations showed that CO₂ and N₂O are reformed into excited vibrational levels, quenched by collisions in microseconds.

Near-edge X-ray absorption mass spectrometry (NEXAMS) around the N and O K-edges was employed ongas-phase peptides to probe the electronic transitions related totheir protonation sites, namely at basic side chains, the N-terminus and the amide oxygen.

We underscore a solid agreement between experimental and computational studies on solvation of pristine/protonated Cu_n⁺ (n = 1–2) in H₂. For instance, with n = 1, the initial shell comprises four covalently bound H₂; subsequent ones are non-covalent.

Simultaneous trapping of merged cation and anion beams in the HEIBT paves the way for controlled MN of molecular and cluster ions.

We experimentally and theoretically investigate interatomic Coulombic decay in small helium clusters. The electronic and nuclear dynamics for these systems are studied in detail using the energy distributions of the ionic fragments.

This work probes electron-driven ionization of TCA. New fragment ions are identified by mass spectrometry and experimental appearance energies show excellent agreement with calculated threshold energies for the most significant pathways.

An analytical derivation for achieving velocity map imaging (VMI) with no spherical aberations is described. Simulations show how this method can be used for operating the CSR-ReMi in a VMI mode with an extremely large source volume.

This work highlights the importance of the secondary processes at low energies in the radiation damage due to their very large cross sections, and it aims to provide benchmark data for the development of suitable models.

Radiation damage in a biological system is studied by secondary ionization of dopant clusters in helium nanodroplets following excitation or ionization of the droplet matrix.

The excited state dynamics of four derivatives of the green fluorescent protein chromophore are investigated in the gas phase using time-resolved photoelectron spectroscopy and in water femtosecond fluorescence upconversion.

The crossover point is precisely situated within the potential well of the first excited state of the CaH₂⁺ system, causing the majority of intermediates within the well to return back to the reactant channel.

Experiments with ice nanoparticles in molecular beams show that individual nitric acid molecules do not fully dissociate.

The gas-phase reaction between hydroxyl radicals with ketenimine, resulting in the formation of glycolonitrile, exhibits remarkable efficiency in the interstellar medium conditions.

The photophysics of biochromophore ions often depends on the isomeric or protomeric distribution, yet this distribution, and the individual isomer contributions to an action spectrum, can be difficult to quantify.