Abstract: Carbonyl sulfide (OCS) was excited and dissociated at ~230 nm, and the CO(XΣ+g,v=0,J=42~65) fragment was detected by using (2+1) resonance-enhanced multiphoton ionization at 229825~230000 nm. From the velocity map image of CO+, the kinetic energy and angular distributions of CO fragments were directly obtained. Besides the dominated channel of S(D)+CO(XΣ+g,v=0), S(3P) atom was also observed in photodissociation of OCS at 230 nm. The branching ratio of the S(3P) channel was about 05%, and slightly increased with the rotational excitation of CO fragment from J=56 to 65. With the aid of the recent high-level potential energy surfaces of the excited electronic states of OCS, the S(3P) formation mechanism was proposed. Once absorbing an ultraviolet photon at ~230 nm, the excited OCS in AA′ state is produced initially, and then dissociates to yield S(3P) atom via spin-orbital coupling to b3A″ state.

Key words: carbonyl sulfide (OCS), photodissociation, resonance enhanced multiphoton ionization, branching ratio, ion velocity imaging