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 H3+, CH5+, N2OH+, HCO+, C2H7+, C2H7+, and H3O+ with SF6 in hydrogen carrier gas at pressures in the range 0.20-0.46 Torr and at a temperature of 298 +/- 2K. Production of SF6H+ was observed, but only as a minor (1%) channel in the reaction of HCO+ with SF6. Otherwise SF5+ 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 x 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.