Density functional investigation of atmospheric sulfur chemistry II. The heat of formation of the XSO2 radicals X=H,CH3

The ΔfH0 (298 K) of HSO2 is estimated as −42.6±2 kcal/mol through calculations using Dunningʹs basis sets up to cc-pV6Z and Popleʹs 6-311+G(3df,2p). This estimation differs from previous G2 calculations and from our own G3 result of −37.1 kcal/mol. Similarly, the ΔfH0 (298 K) CH3SO2 is estimated as −56.3 kcal/mol, in good agreement with Bensonʹs prediction, −55.0 kcal/mol, and again in disagreement with the G2 value, −47.6 kcal/mol. Finally, we propose a revision of the enthalpy of formation of the CH3S radical. On the basis of the density functional theory (DFT) calculations, we propose a value of 28.8±1 kcal/mol, slightly lower than the presently accepted value of 29.78±0.44 kcal/mol.