Gas-Phase Reactions of Sulfur Hexafluoride with Transition Metal and Main Group Atomic Cations: Room-Temperature Kinetics and Periodicities in Reactivity

Abstract

Gas-phase reactions of SF(6) were investigated with 46 different atomic metal and main group cations at room temperature using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. The atomic ions were produced at about 5500 K in the ICP source and allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction downstream in a flow tube in helium buffer gas at 0.35 +/- 0.01 Torr and 295 +/- 2 K. Rate coefficients and product distributions were measured for the reactions of fourth-row atomic ions from K(+) to Se(+), of fifth-row atomic ions from Rb(+) to Te(+) (excluding Tc(+)), and of sixth-row atomic ions from Cs(+) to Bi(+). The early transition metal ions react with SF(6) very efficiently (k/k(c) = 0.56-0.96) to produce MF(m)(+) (m = 1-4) and SF(n)(+) (n = 1-4) ions, whereas the late transition metal ions react much less efficiently (k/k(c) < 0.2) to form M(+)(SF(6)) adduct ions. Reactions of SF(6) with Ca(+), Sr(+), Ba(+), Ge(+), and As(+) proceed efficiently (k/k(c) = 0.35-0.85) through various channels, while all other main group metal ions are inert toward sulfur hexafluoride. Primary and secondary adduct formation was observed to exhibit equilibrium kinetics, and the standard free energy change for SF(6) addition is found to correlate with the efficiency of addition according to log[k/k(c)] = -8.7 + 7.8 log[-DeltaG(o)/(kcal mol(-1))]. Several MF(m)(+) ions were observed to react further with SF(6) to produce MF(m+k)(+), SF(n)(+), and MF(m)(+)(SF(6)) as secondary products.