On the protonation and proton affinity of SF 6

Abstract

The kinetics of the protonation of SF6 were examined in a combined flowing afterglow/selected-ion flow tube study of the reactions of H + 3, CH + 5, N 2OH +, HCO +, C 2H + 7, C 2H +, and H 3O + with SF 6 in hydrogen carrier gas at pressures in the range 0.20–0.46 Torr and at a temperature of 298 ± 2 K. Production of SF 6H + was observed, but only as a minor (1%) channel in the reaction of HCO + with SF 6. Otherwise SF + 5 was observed as the dominant product ion. The proton affinity (PA) of SF 6 was derived from the observed reactivities and non-reactivities with SF 6 to be 138 ± 3 kcal mol −1. The low rate coefficient for the reaction of HCO + with SF 6, k = 5.5 × 10 −12 cm 3 molecule −1 s −1, was used to derive a value for PA(SF 6) of 137 ± 1 kcal mol −1 which is the value recommended for adoption.