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

Parkes, M. A. and Ali, S. and Tuckett, R. P. and Mikhailov, Victor A. and Mayhew, C. A. (2007) Selected ion flow tube cation–molecule reaction studies and threshold photoelectron photoion coincidence spectroscopy of cyclic-C5F8. Physical Chemistry Chemical Physics, 9 (38). pp. 5222-5231. ISSN 1463-9076

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URL of Published Version: http://dx.doi.org/10.1039/b704862a

Identification Number/DOI: doi:10.1039/b704862a

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-C$$_5$$F$$_8$$ 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 H$$_2$$O$$^+$$ for which the reaction efficiency is only 55 %. Apart from H$$_2$$O$$^+$$ 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 $$c$$-C$$_5$$F$$_8$$ 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 $$c$$-C$$_5$$F$$_8^+$$ has very weak intensity under threshold electron conditions. The TPEPICO spectrum of $$c$$-C$$_5$$F$$_8$$ recorded from 1223 eV shows detection of the parent ion and the daughter ions C$$_4$$F$$_6^+$$ and C$$_5$$F$$_7^+$$, 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 $$c$$-C$$_5$$F$$_8$$ at 298 K has been determined to be $$\sim$$1495 kJ mol$$^{-1}$$

Type of Work: Article 2007 (Publication) Schools (1998 to 2008) > School of Chemical Sciences School of Chemistry, School of Physics QD ChemistryQC Physics University of Birmingham The authors, Royal Society of Chemistry 727 YES

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