Resonance-state selective photodissociation of OCS (2 1Σ+): Rotational and vibrational distributions of CO fragments

Abstract

The rotational and vibrational state distributions of the CO fragments produced through the photodissociation of OCS in the vacuum ultraviolet (VUV) region (150–155 nm), OCS (2 1Σ+)→CO (X 1Σ+)+S(1S), are derived for the three lowest quasi-bound vibrational resonances (v*=0−2) in the 2 1Σ+ state. The rotational state distributions of the CO fragments in the vCO=0 and 1 vibrational states are determined, respectively, by the analysis of the rotational structures in the laser-induced fluorescence (LIF) spectra of the A1Π–X 1Σ+(0,0) and (1,1) transitions of CO. The rotational temperatures of CO in the vCO=0 state are low (∼100 K) for all the three resonances, while those in the vCO=1 state are substantially higher, i.e., 2210, 940, and 810 K for v*=0, 1, and 2, respectively. The vibrational state distributions of CO are derived from the Doppler spectroscopy of the counterpart S(1S) fragments. From the analysis of the observed Doppler profiles, it is found for all the three lowest vibrational resonances of OCS that the vibrational distributions are represented well by the Boltzmann-type distribution with a vibrational temperature of around 7000 K. On the basis of these new findings, the energy partitioning in the photodissociation process through these three vibrational resonances in the 2 1Σ+ state is discussed.