The reaction pathways of sulfur vapor (S-3) with sulfur dioxide ((SO2)-S-1) on the triplet and singlet potential energy surfaces have been investigated at the G3B3//B3LYP/6-311++G(3df,3pd) level. Two stable collision complexes, (3)IN1 and (1)IN1 have been considered on the triplet and singlet potential energy surfaces, respectively. Calculations reveal that there exists one intersystem crossing between triplet and singlet potential energy surfaces. Four kinds of products P-1((SO)-S-3 + (SO)-S-3), P-2(trans-(OSSO)-O-1), P-3(cis-(OSSO)-O-1) and P-4(S-3(2) + O-3(2)) are obtained through variety of transformations of (3)IN1 and (1)IN1. The results show that the S-3 + (SO2)-S-1 reaction proceeds only with triplet surfaces to produce P-1((SO)-S-3 + (SO)-S-3) at temperature range of 200 - 1000 K. (C) 2010 Elsevier B. V. All rights reserved.