Ab initio investigations on the HOSO2+O-2 -> SO3+HO2 reaction

HOSO2 radical is the key intermediate for the oxidation SO2 to SO3 by OH ra dical in the atmosphere. The structural aspects and the energetics of the r eaction HOSO2+O-2--> SO3+HO2 have been studied using Moller-Plesset (MP2) a nd density functional (DFT) techniques with 6-31G** and triple-zeta, quadru ple-zeta, and quintuple-zeta quality basis sets including diffuse basis fun ctions. The detailed theoretical analyses have further revealed that this r eaction could proceed through the formation of intermediate complexes and a n intramolecular proton transfer like transition state. The energetics of t hese intermediate reactions has been studied in detail. The use of MP2 meth ods to study such radical mechanisms had some characteristic symmetry-break ing problem with larger basis sets. This unphysical situation with larger b asis set MP2 calculations in this hypervalent system has been explained thr ough the interpretation of the relevant energy surface. (C) 2000 American I nstitute of Physics. [S0021-9606(00)31402-7].