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

Calculations of the photodissociation cross sections of CO from the ground X state into the coupled Rydberg B state and the valence dissociative D state have been carried out using the smooth exterior complex scaling (SECS) method. Results are presented for all of the 6 isotopomers involving the 12C, 13C, 16O, 17O and 18O 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.