Crossed-beam reaction of carbon atoms with sulfur containing molecules.: I.: Chemical dynamics of thioformyl (HCS X2A′) formation from reaction of C(3Pj) with hydrogen sulfide, H2S(X1A1)

The reaction between ground state carbon atoms, C(P-3(j)), and hydrogen sulfide, H2S(X(1)A(1)), was studied at four average collision energies between 16.7 and 42.8 kJ mol(-1) using the crossed molecular beam technique. The reaction dynamics were deducted from time- of- flight spectra and from laboratory angular distributions combined with ab initio calculations. These data suggest that the reaction proceeds through an addition of C(P-3(j)) to the sulfur atom to form a triplet CSH2 van der Waals complex. Successive H atom migration on the triplet or singlet surface forms a thiohydroxycarbene intermediate, HCSH, which decomposes through a tight exit transition state to HCS (X(2)A') + H(S-2(1/2)). At lower collision energies, a weak L-L' coupling leads to isotropic center-of-mass angular distributions. As the collision energy rises, the angular distributions show increasing forward scattering thereby documenting that the reaction goes through an osculating HCSH complex. Identification of the HCS isomer under single collision conditions is a potential one- step pathway by which to form organo-sulfur molecules in interstellar environments during the collision of the comet Shoemaker-Levy 9 with Jupiter, and in combustion flames of sulfur containing fuels. (C) 1999 American Institute of Physics. [S0021-9606(99)01205-2].