Comparison of calculated and experimental thermal attachment rate constants forSF6in the temperature range200–600K

Electron-attachment cross sections are calculated for the process $e^{\mathrm{-}}$+${\mathrm{SF}}_6$→${\mathrm{SF}}_6$ ${\mathrm{}}^{\mathrm{-}}$ in the energy range 1–200 meV. An electron scattering approximation is used in which diatomiclike potential energy curves near the equilibrium ${\mathrm{SF}}_6$ ground state are constructed from recent spectroscopic data. Excellent agreement is found over the entire energy range with experimental attachment cross sections at a temperature of 300 K for s-wave (l=0) scattering. The same calculation, with appropriate adjustment of the thermal populations, is used to calculate attachment rate constants k(ε¯) in the range 50–600 K for both s- and p-wave scattering. Comparisons are made with four independent sets of measured rate constants in the range 200–600 K, after adding an experimental estimate of the attachment rate for the process $e^{\mathrm{-}}$+${\mathrm{SF}}_6$→${\mathrm{SF}}_5$ ${\mathrm{}}^{\mathrm{-}}$+F. Good agreement is found with three sets of data, and poorer agreement with the fourth. The calculation shows that the true s-wave behavior of the rate constant, in which k(ε¯) is independent of ε¯, will be realized only at temperatures T less than 115 K, and that the observed constancy in the range 300–600 K is accidental. Theory predicts approximately a 9% increase in k(ε¯) as T is lowered from 300 to 200 K.