Photodissociation of CS and SiO from Excited Rovibrational Levels

Photodissociation due to ultraviolet (UV) photons is a dominant molecular destruction process in a variety of UV-irradiated interstellar (IS) environments. While most astrochemical models adopt photodissociation rates computed from cross sections out of the molecule's ground rovibrational level ($v=0,J=0$), they also assume a standard local IS radiation field and opacity due to standard IS dust. However, none of these conditions are satisfied in a host of environments including photodissociation regions, protoplanetary disks, and outflows from AGB stars. To allow for the calculation of reliable photodissociation rates, we compute cross sections from all bound $v,J$ levels of the ground electronic state for two example molecules, CS and SiO. The cross sections are computed for a large number of excited electronic states using a two-state fully quantum perturbation approach. New ab initio potential energies and transition dipole moment functions, used in the photodissociation calculations, were obtained at the MRCI+Q level of theory using the quantum chemistry package MOLPRO. Applications of the $v,J$-state-resolved cross sections will be presented as well as LTE photodissociation cross sections which assume a Boltzmann distribution of initial $v,J$ levels.