Threshold photoelectron photoion coincidence spectroscopy and selected ion flow tube reactions of CHF3: comparison of product branching ratios§

Abstract

The threshold photoelectron and threshold photoelectron photoion coincidence spectra of CHF3 in the range 13.5–24.5 eV have been recorded. Ion yields and branching ratios have been determined for the three fragments , and CF+. The mean kinetic energy releases into fragment ions involving either C–H or C–F bond cleavage have been measured, and compared with statistical and impulsive models. behaves in a non-statistical manner characteristic of the small-molecule limit, with the ground electronic state and low-lying excited states of being largely repulsive along the C–H and C–F coordinates, respectively. The rate coefficients and product ion branching ratios have been measured at 298 K in a selected ion flow tube for the reactions of CHF3 with a large number of gas-phase cations whose recombination energies span the range 6.3 through 21.6 eV. A comparison between the branching ratios from the two experiments, together with an analysis of the threshold photoelectron spectrum of CHF3, shows that long-range charge transfer probably occurs for the Ar+ and F+ atomic ions whose recombination energies lie above ca. 15 eV. Below this energy, the mechanism involves a combination of short-range charge transfer and chemical reactions involving a transition state intermediate. §In honour of Professor John Simons’ 70th birthday Festschrift.