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Issue 38, 2007
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Selected ion flow tube cation–molecule reaction studies and threshold photoelectron photoion coincidence spectroscopy of cyclic-C5F8

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Abstract

The product ion branching ratios and rate coefficients have been measured using a selected ion flow tube (SIFT) at 298 K for the bimolecular reactions of cyclic-C5F8 with several atomic and molecular cations. The majority of reactions occur at the collisional rate calculated by the modified average dipole orientation theory, with the exception of H2O+ for which the reaction efficiency is only 55%. Apart from H2O+ and N+, the similarity of the product ion branching ratios determined from threshold photoelectron photoion coincidence (TPEPICO) and ion–molecule data suggests that long-range electron transfer is the dominant mechanism for reactions involving ions with recombination energies between 12 and 17 eV. For N+, the product ion branching ratios are very different to those produced by photoionisation; this result may be explained if some of the N-atom products are formed electronically excited. The onset of an ionisation signal of c-C5F8 measured by TPEPICO spectroscopy occurs at 12.25 ± 0.05 eV. This is much higher than the value of the first adiabatic ionisation energy determined from electron ionisation (11.24 ± 0.10 eV), He (I) photoionisation (11.30 ± 0.05 eV), and an independent high resolution threshold photoelectron spectrum (11.237 ± 0.002 eV). The ground electronic state of c-C5F8+ has very weak intensity under threshold electron conditions. The TPEPICO spectrum of c-C5F8 recorded from 12–23 eV shows detection of the parent ion and the daughter ions C4F6+ and C5F7+, with their appearance energies increasing in this order. Ion yield curves and branching ratios have been determined. Using Gaussian 03, the enthalpy of formation of c-C5F8 at 298 K has been determined to be −1495 kJ mol−1.

Graphical abstract: Selected ion flow tube cation–molecule reaction studies and threshold photoelectron photoion coincidence spectroscopy of cyclic-C5F8

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Publication details

The article was received on 30 Mar 2007, accepted on 09 Jul 2007 and first published on 02 Aug 2007


Article type: Paper
DOI: 10.1039/B704862A
Citation: Phys. Chem. Chem. Phys., 2007,9, 5222-5231
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    Selected ion flow tube cation–molecule reaction studies and threshold photoelectron photoion coincidence spectroscopy of cyclic-C5F8

    M. A. Parkes, S. Ali, R. P. Tuckett, V. A. Mikhailov and C. A. Mayhew, Phys. Chem. Chem. Phys., 2007, 9, 5222
    DOI: 10.1039/B704862A

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