The adiabatic and diabatic reactions of S(1D) atoms with OCS: Internal state distribution of the S2 products

OCS at low pressure was photodissociated at 248 nm. It was shown by two photon laser induced fluorescence (LIF) that the concentration of the S(1D) atoms produced decays with time due to collisions with undissociated OCS molecules. In contrast, the S(3P) atom concentration rises from zero or nearly zero to a maximum and then subsequently decays. The S(1D) atoms react with OCS molecules to give S2 (X 3Σg), S2(a 1Δg), and S(3P). The rotational and vibrational distribution of the diatomic products was studied by LIF. The diabatic product S2(X 3Σg) was entirely in the v=0 state and was rotationally cold. The adiabatic product S2(a 1Δ) was probed in the v=1 state and had a fairly narrow non-Boltzmann type rotational distribution peaking at J=65. We speculate that the reaction takes place through a C2v COS2 intermediate. The adiabatic and diabatic reactions are characterized by sequential and concerted C–S bond breaking, respectively.