The methylsulfinyl radical CH3SO examined

Abstract

Methylsulfinyl radical, a key intermediate in marine atmospheric chemistry, plays a central role in the oxidation of dimethyl sulfide. CH₃SO has been extensively studied here with ab initio quantum mechanical methods, with methods as complete as CCSDT(Q) in conjunction with basis sets as large as cc-pV(5+d)Z. In this research, we report high-level computations for the ground and first excited electronic states of the methylsulfinyl radical. The structures of the ²A′′ and à ²A′ states are quite different with S–O distances of 1.499 and 1.652 Å, respectively. The to à adiabatic energy difference is predicted to be 45.1 kcal mol⁻¹, compared to 21.1 kcal mol⁻¹ for the analogous well-characterized methylperoxy radical CH₃OO. The CH₃SO barrier to internal rotation is 0.92 kcal mol⁻¹. The unknown ²A′′ torsional vibrational frequency τ is predicted to be 142 cm⁻¹ (harmonic) and 128 cm⁻¹ (anharmonic). Our predictions of the à ²A′ excited state vibrational frequencies are the first to be reported.