Effect of non-adiabatic coupling on the isotopic dependence of the photodissociation cross section of CO

Abstract

Calculations of the photodissociation cross sections of CO from the ground X 1 Σ + state into the coupled Rydberg B 1 Σ + state and the valence dissociative D' 1 Σ + state have been carried out using the smooth exterior complex scaling (SECS) method. Results are presented for all of the 6 isotopomers involving the 12 C, 13 C, 16 O, 17 O and 18 O isotopes. The absorption profiles of the predissociating resonances induced by non-adiabatic coupling vary considerably from one isotopomer to another. It is confirmed that resonance widths obtained simply from a diagonalization of the complex Hamiltonian do not give a true indication of the absorption profile. A correct profile is only obtained when the sum over all resonant and non-resonant continuum states is performed. A brief discussion is given of the implications for isotopic fractionation in interstellar CO.