Theoretical study of the radiative properties of the triplet states of the NH radical: Transition dipole moments, radiative lifetimes, photodissociation cross sections

Abstract

Ab initio transition dipole moments between the X 3Σ− and the A 3Π states of NH and the 2 3Σ− and 2 3Π dissociative states have been computed. These transition dipole moments have been used to compute photodissociation cross sections and interstellar photodissociation rates for NH. Photodissociation rates for NH in the interstellar radiation field range from 1.9 to 4.7×10−10 s−1 depending on the field used. Direct dissociation via the 2 3Σ− and 2 3Π states is found to be the only important pathway for photodestruction of NH in diffuse interstellar clouds. A large photodissociation cross section is found for the A 3Π–2 3Σ− transition and a method for photolyzing NH in the laboratory is suggested. Einstein A coefficients and radiative lifetimes have also been computed for the A–X transition and are compared with recent theoretical and experimental work.