On the protonation and proton affinity of SF6

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, N2OH+, HCO+, C2H+7, C2H+, and H3O+ with SF6 in hydrogen carrier gas at pressures in the range 0.20–0.46 Torr and at a temperature of 298 ± 2 K. Production of SF6H+ was observed, but only as a minor (1%) channel in the reaction of HCO+ with SF6. Otherwise SF+5 was observed as the dominant product ion. The proton affinity (PA) of SF6 was derived from the observed reactivities and non-reactivities with SF6 to be 138 ± 3 kcal mol−1. The low rate coefficient for the reaction of HCO+ with SF6, k = 5.5 × 10−12 cm3 molecule−1 s−1, was used to derive a value for PA(SF6) of 137 ± 1 kcal mol−1 which is the value recommended for adoption.