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

The Delta H-f(0) (298 K) of HSO2 is estimated as -42.6 +/-2 kcal/mol through calculations using Dunning's basis sets up to cc-pV6Z and Pople's 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 Delta H-f(0) (298 K) CH3SO2 is estimated as -56.3 kcal/mol, in good agreement with Benson's 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. (C) 2001 Elsevier Science B.V. All rights reserved.