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Vibrational and electronic excitations in fluorinated ethene cations from the ground up

Tuckett, R. P. and Harvey, Jonelle and Hemberger, Patrick and Bodi, Andras (2013) Vibrational and electronic excitations in fluorinated ethene cations from the ground up. Journal of Chemical Physics. (In Press)

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Valence threshold photoelectron spectra of four fluorinated ethenes; C2H3F, 1,1-C2H2F2, C2HF3 and C2F4 were recorded at the Swiss Light Source with 0.002 eV resolution. The adiabatic ionization energies were found to be 10.364 ± 0.007, 10.303 ± 0.005, 10.138 ± 0.007 and 10.110 ± 0.009 eV, respectively. The electronic ground state of each cation shows well resolved multi-component vibrational progressions, the dominant transitions being in the C=C stretching mode. Density functional theory (DFT) based Franck–Condon simulations are used to model the vibrational structure and assign the spectra, sometimes revising previous assignments. An additional vibrational progression in the first photoelectron band of 1,1-C2H2F2 indicates that the ground electronic state of the molecular ion is no longer planar. It is shown that ab initio vibrational frequencies together with the observed vibrational spacings do not always suffice to assign the spectra. In addition to symmetry rules governing the transitions, it is often essential to consider the associated Franck–Condon factors explicitly. Ionization to higher lying excited valence electronic states were also recorded by threshold ionization up to 23 eV photon energy. EOM-IP-CCSD/cc-pVTZ calculations confirmed historic electronic state assignments, and untangled the ever more congested spectra with increasing F-substitution. Previous attempts at illuminating the intriguing dissociative photodissociation mechanism of fluorinated ethenes are reconsidered in view of new computational and experimental results. We show how non-statistical F-atom loss from C2H3F+ is decoupled from the ground state dissociation dynamics in the energy range of its state. Both the statistical and the non-statistical dissociation processes are mediated by a plethora of conical intersections.

Type of Work:Article
Date:March 2013 (Publication)
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemistry
Subjects:QD Chemistry
Institution:University of Birmingham
Copyright Holders:American Institute of Physics
ID Code:1314
Refereed:YES
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