The reaction mechanism Of C-2 + H2S has been investigated using ab initio method. On the basis of calculations using CCSD(T) in conjunction with 6-311++G(d, pd) basis set with the geometry optimized at MP2/6-311++G** level, the H-abstraction reaction on the triplet energy potential surface is an exothermic process with formation of a precomplex as an intermediate, which further dissociate to yield HS((2)Sigma(+)) + CCH((2)Sigma(+)) with an energy barrier of 4.9 kcal mol(-1). The addition of H2S((1)A(1)) to C-2((1)Sigma(g)(+)) on leads to a bound intermediate H2SCC((1)A') (3,3-dihydrodicarbonsulfide), which can further isomerize into HSCCH((1)A) (thiohydroxyacetylene) in a one-step hydrogen migration process. (C) 2002 Elsevier Science B.V. All rights reserved.