Vacuum ultraviolet photodissociation dynamics of OCS via the F Rydberg state: The S(³P_{J = 2, 1, 0}) product channels^†

Vacuum ultraviolet (VUV) photodissociation dynamics of carbonyl sulfide was investigated experimentally by using a tunable photolysis light source and the time-sliced velocity map ion imaging technique. Ion images of S(³P_{J =2, 1, 0}) dissociation products were measured at five photolysis wavelengths from 133.26 nm to 139.96 nm, corresponding to the F Rydberg state of OCS. Two dissociation channels: S(³P_J)+CO(X¹Σ⁺) and S(³P_J)+CO(A³Π) were observed with the former being dominant. The vibrational states of CO co-products were partially resolved in the ion images. The product total kinetic energy releases, anisotropy parameters (β), and the branching ratios of high-lying CO vibrational states were determined for the S(³P_J )+CO(X¹Σ⁺) channel. We found that the anisotropy parameters suddenly changed from negative to positive when OCS was excited to the higher vibrational levels of the F state. Furthermore, the anisotropy parameters for S(³P_J) products of J = 2, 1, 0 were even different. These anomalous phenomena may result from the simultaneous existence of both parallel and perpendicular dissociation mechanisms, suggesting the involvement of other electronic states with different symmetry in the initially-excited energy region. This work provides a further understanding of the nonadiabatic couplings in the VUV photodissociation process of OCS.