A study of vibronic coupling in excited neutral and ionic states of carbon dioxide

Dispersed fluorescence spectroscopy and photoelectron spectroscopy have been employed to study vibronic coupling in excited neutral and ionic states of carbon dioxide. The dispersed fluorescence excitation spectra of the CO2+B˜(001)2Σg+→X˜(001)2Πu and the B˜(002)2Σu+→X˜(002)2Πg transitions have revealed new structure. Some of this structure can be assigned to nsσg or nd Rydberg series converging onto the CO2+C˜(001)2Σu+ threshold or to an np Rydberg series converging onto the CO2+C˜(002)2Σg+ threshold. Autoionisation from Rydberg states belonging to these series results in the formation of ions with one or two quanta of the asymmetric stretching mode being excited. The HeI excited photoelectron spectra of the CO2+B˜2Σu+andC˜2Σg+ states reveal extensive and complex vibrational structure. Transitions involving the non-totally symmetric bending and asymmetric stretching modes have been observed. The occurrence of these normally forbidden transitions is attributed to vibronic interactions.