Resonance effects in the 5. sigma. sup minus 1 photoionization channel of CO

Vibrational branching ratios and photoelectron angular distributions are reported for the 5{sigma}{sup {minus}1} photoionization channel of CO in the range 16 eV{lt}{ital h}{nu}{lt}45 eV. Striking non-Franck--Condon effects are observed in both the branching ratios and angular distributions as a result of various autoionizing states and a {sigma} shape resonance that lie in this spectral range. The goal of the present measurement was to observe definitive evidence for the {sigma} shape resonance via its non-Franck--Condon effects on the vibrational ionization channels. Guided by recent calculations (Smith, Lynch, and McKoy, J. Chem. Phys. {bold 85}, 6455 (1986)), we examined the broad structure in the vibrational branching ratios and angular distributions in the range 25 eV {lt}{ital h}{nu}{lt}40 eV. There, we found clear evidence for the {sigma} shape resonance in the quantities {beta}({ital v}{sup +}=0 and 1) and {sigma}({ital v}{sup +}=2)/{sigma}({ital v}{sup +}=0). Substantial differences between theory and experiment for the {sigma}({ital v}{sup +}=1)/{sigma}({ital v}{sup +}=0) branching ratio, however, serve to define the limitations of the current single-channel picture for this process.