Temperature-dependent direct photodissociation cross sections and rates of AlCl

Abstract

ABSTRACT The photodissociation process of aluminium monochloride (AlCl) plays an important role in modelling the chemistry of the circumstellar envelope. In this work, direct photodissociation cross sections of AlCl have been computed for transitions from the ground X1Σ+ state to six low-lying excited electronic states by using ab initio potential energy curves and transition dipole moments, which are obtained by the internally contracted multireference configuration-interaction method with Davidson correction and the aug-cc-pV6Z basis set. State-resolved cross sections for transitions from 38 958 rovibrational levels (υ″ ≤ 100, J″ ≤ 400) of the ground X1Σ+ state have been obtained for photon wavelengths from 500 Å to the dissociation threshold. Photodissociation cross sections in local thermal equilibrium are evaluated for gas temperatures from 500 to 10 000 K. Using the computed cross sections, temperature-dependent photodissociation rates of AlCl in the interstellar and blackbody radiation fields are determined. The results can be applied to the investigation of the chemical evolution of Al in the envelope of carbon-rich and oxygen-rich stars.