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 CHF 3 in the range 13.5-24.5 eV have been recorded. Ion yields and branching ratios have been determined for the three fragments CF þ 3 , CHF þ 2 and CF þ . 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. CHF þ 3 behaves in a non-statistical manner characteristic of the small-molecule limit, with the ground electronic state and low-lying excited states of CHF þ 3 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 CHF 3 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 CHF 3 , shows that long-range charge transfer probably occurs for the Ar þ and F þ 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.

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

“…For F + (RE = 17.42 eV), the agreement between the branching ratios is much better, within the 15% error we define as indicating agreement. 41 For Ne + (RE = 21.56 eV), however, there is poor agreement, and many more fragments are formed than from photoionisation at this energy. For this ion, therefore, it is likely that a compact collision complex is forming and reaction proceeds by a short range process.…”

The photoionization dynamics of the three structural isomers of dichloroethene

“…Comparison of <f> t to impulsive and statistical models can indicate which mechanism operates. The analysis and models have been discussed in detail in previous papers [18,19]. For a pure impulsive model, <f> t is determined solely by kinematics, being given by μ b / μ f where μ b is the reduced mass of the two atoms whose bond is broken and μ f is the reduced mass of the two product fragments [20].…”

Chapter 3: Trifluoromethyl Sulphur Pentafluoride, SF5CF3: Atmospheric Chemistry and Its Environmental Importance via the Greenhouse Effect

“…Agreement within ca. ±15 % is taken as evidence for possible long-range charge transfer [56]. We have made this comparison for the reactions of SF 5 CF 3 with those cations whose concentrations are the highest in the mesosphere, and might therefore be expected to contribute to the removal of SF 5 CF 3 from the earth's atmosphere.…”