Direct Detection of S( 3 P) and S( 1 D) Generated in the O( 1 D) + OCS Reaction: Mechanism of the Formation of S 2 (X 3 Σ g - and a 1 Δ g ).

Highly vibrationally excited disulfur S2 in the X3 Σg - and a1 Δg states has been detected in the gaseous mixture of O3 and OCS irradiated with light at 266 nm. Generation of CO2 in the reaction system has been reported; however, no direct detection of sulfur atoms (S(3 P) and S(1 D)) has been made. In the present study, we have employed the two-photon laser-induced fluorescence (2P-LIF) technique to detect S(3 P) and S(1 D) directly and recorded the time profiles of the atoms at varying pressures of OCS. Kinetic analyses of the profiles show that (i) S(1 D) is generated in the O(1 D) + OCS reaction and consumed by the S(1 D) + OCS reaction, and (ii) S(3 P) is mainly generated in the O(1 D) + OCS reaction instead of quenching of S(1 D) by collisions with OCS and ambient gases. The vibrational levels v = 19 and 10 of the respective electronic states X3 Σg - and a1 Δg of S2 were detected in the O3 /OCS/266 nm system. The two vibrational levels cannot be generated by the available energy of the S(3 P) + OCS reaction, giving evidence that S2 in the X3 Σg - and a1 Δg states are generated by the S(1 D) + OCS reaction.