The Photodissociation of Interstellar CH+

Abstract

Three new excited states of CH+ which can be reached by a dipole transition from the ground state with photon energies less than 13.6 eV have been obtained from accurate theoretical calculations. As these states are unbound with respect to nuclear motion, photon absorption into them results in dissociation of the molecule. Photodissociation cross sections have been calculated, and the CH+ photodissociation rates in the interstellar radiation field as a function of optical depth have been determined. The rates are approximately 500 times larger than previously assumed. We have compared these new photodissociation rates with the rates of other CH+ destruction mechanisms in three different models of the interstellar medium. Photodissociation appears to be a significant destruction mechanism in any model requiring large interstellar radiation fields.