Ultraviolet photodissociation of OCS: product energy and angular distributions

The ultraviolet photodissociation of carbonyl sulfide (OCS) was studied using three-dimensional potential energy surfaces and both quantum mechanical dynamics calculations and classical trajectory calculations including surface hopping. The transition dipole moment functions used in an earlier study [J. A. Schmidt, M. S. Johnson, G. C. McBane, and R. Schinke, J. Chem. Phys. 137, 054313 (2012)] were improved with more extensive treatment of excited electronic states. The new functions indicate a much larger contribution from the 1(1)A(") state ((1)Σ(-) in linear OCS) than was found in the previous work. The new transition dipole functions yield absorption spectra that agree with experimental data just as well as the earlier ones. The previously reported potential energy surfaces were also empirically modified in the region far from linearity. The resulting product state distributions Pv, j, angular anisotropy parameters β(j), and carbon monoxide rotational alignment parameters A0 ((2))(j) agree reasonably well with the experimental results, while those computed from the earlier transition dipole and potential energy functions do not. The higher-j peak in the bimodal rotational distribution is shown to arise from nonadiabatic transitions from state 2(1)A(') to the OCS ground state late in the dissociation.