SHAPE-RESONANCE-ENHANCED CONTINUUM CONTINUUM COUPLING IN PHOTOIONIZATION OF CO2

We have measured photoionization branching ratios and photoelectron as ymmetry parameters for photoionization of CO2 leading to the first fou r electronic states of CO2+ over the photon energy range from 20 to 50 eV. The motivation for this work was the prediction by Lucchese [J. C hem. Phys. 92, 4203 (1990)] that the sigma(u) shape resonance in the ( 4sigma(g))-1 C2SIGMA(g)+ ionization channel would influence the photoi onization dynamics in the other valence-shell continua through continu um-continuum channel interaction, with the main effect occurring in th e (3sigma(u))-1 B2SIGMA(u)+ channel. Indeed, clear evidence for this p henomenon is observed in this channel, the most prominent indication b eing a broad, shallow minimum in the asymmetry parameter at approximat ely 40 eV. Comparisons of the present results with theory and other me asurements reflect good overall agreement and provide some guidance re garding the effectiveness of alternative approximations used in the th eoretical calculations.