Methylsulfonyl and Methoxysulfinyl Radicals and Cations in the Gas Phase. A Variable-Time and Photoexcitation Neutralization−Reionization Mass Spectrometric and ab Initio/RRKM Study

Abstract

The title radicals were produced by femtosecond collisional electron transfer in the gas phase and studied by the methods of variable-time neutralization−reionization mass spectrometry combined with fast-beam laser photoexcitation and G2(MP2) ab initio/RRKM calculations. The methylsulfonyl radical (CH3SO2•, 1) was calculated to be bound by 59 kJ mol-1 against the lowest-energy dissociation to CH3• and SO2 at 0 K and to have a heat of formation ΔHf,298(1) = −211 ± 4 kJ mol-1. When formed by vertical electron transfer, radical 1 dissociated rapidly due to a large Franck−Condon energy, EFC = 141 kJ mol-1. The reverse addition of CH3• to the sulfur atom in SO2 had a potential energy barrier of 1.3 kJ mol-1 and Arrhenius parameters, log A = 12.19 and Ea = 5.4 kJ mol-1. The calculated addition rate constant, k295 = 1.7 × 1011 cm3 mol-1 s-1, was in excellent agreement with the previous measurement of Simons et al. The methoxysulfinyl radical (CH3OSO•, 2) was calculated to exist as an equilibrium mixture of syn (...