Vibrational branching ratios and asymmetry parameters in the photoionization of CO2 in the region between 650 angstrom and 840 angstrom

The vibrational branching ratios and asymmetry parameters for CO2 have been determined in the wavelength region of 650 Angstrom to near the ionization onset at about 840 Angstrom. The study was performed using synchrotron rad iation from the Daresbury storage ring that was dispersed with a 5 m gratin g monochomator that afforded resolution of 0.1 Angstrom to 0.2 Angstrom. Th is resolution allowed the study of the branching ratios and asymmetry param eters with enough detail to see the changes in the parameters within the pr onounced autoionization structure in CO2 in this wavelength region. While t he electron spectrometer resolution was not sufficient to resolve the spin orbit and Renner-Teller splitting in the photoelectron spectra, we are able to fit the data with a model that identifies the major structure in terms of the symmetric stretch and elements of the asymmetric stretch and bending modes. A calculation of the expected relative vibrational excitations base d upon the Franck-Condon principle clearly showed non-Franck-Condon behavio r in some of the vibrational-electronic transitions.