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

Abstract

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 (X³Σ_g), S₂(a¹Δ_g), and S(³P). The rotational and vibrational distribution of the diatomic products was studied by LIF. The diabatic product S₂(X³Σ_g) was entirely in the v=0 state and was rotationally cold. The adiabatic product S₂(a¹Δ) 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 C_2v COS₂ intermediate. The adiabatic and diabatic reactions are characterized by sequential and concerted C-S bond breaking, respectively.