Variation with temperature of the electron attachment to SO2F2

Abstract

The total electron attachment rate constant k_a(〈ε〉,T) for SO₂F₂ has been measured, in a buffer gas of N₂, as a function of the mean electron energy 〈ε〉 (0.046–0.911 eV) and temperature T (300–700 K) using an electron swarm technique. From the measured k_a(〈ε〉,T), the total electron attachment cross sections σ_a(ε,T) were determined. At 300 K the σ_a(ε,T) exhibits a maximum at ∼0.22 eV which is due to dissociative electron attachment and an increase below ∼0.1 eV which is due to the formation of parent negative ions SO₂F⁻₂ at near zero energy. At T=400 K, σ_a(ε,T) has only one main peak at ∼0.13 eV which is due only to dissociative electron attachment reflecting the depletion of the parent anions and the prevalence of the fragment negative ions as T increases. The main peak of σ_a(ε,T) shifts to lower electron energies with increasing T so that at 700 K the peak is located at ∼0.03 eV. The value, σ_da(ε_max), of the total electron attachment cross section at the peak energy ε_max increases by a factor of ∼32 as T increases from 300 to 700 K. The analysis of these results—and similar earlier work—leads to the conclusion that the increase in σ_da(ε,T) for the dissociative electron attachment processes in molecules, with increasing T results mainly from an increase with T of the internal energy (principally vibrational) of the molecule.