UV photodissociation rates and cross sections of the NaS molecule including diabatization and spin–orbit coupling

Abstract

Based on previously reported high-accuracy electronic states of the ΛΣ presentation, we calculate the temperature-dependent photodissociation cross sections and rates of the NaS molecule in the ultraviolet region. The calculation includes transitions from the ground state X2Π to several excited electronic states, up to 12Δ. Particular attention is given to the nonadiabatic couplings between the 22Π-32Π and A2Σ+-22Σ+ states and their influence on the photodissociation dynamics. Spin–orbit coupling among the avoiding crossing electronic states and the ground state as well as the nonadiabatic couplings are incorporated through diabatic representation. Photodissociation cross sections obtained from the coupled channel calculations are compared with adiabatic results that include only spin–orbit coupling. The results show that nonadiabatic interactions significantly modify the cross sections near the avoided crossing regions and induce the pronounced Feshbach resonances. Using the local thermodynamic equilibrium cross sections, photodissociation rates of NaS are further evaluated under the standard interstellar radiation field and blackbody radiation fields. The rates show a relatively weak dependence on the molecular temperature. These results provide useful data for astrochemical modeling of NaS in ultraviolet radiation environments.