THE EFFECT OF VIBRATIONAL AND ELECTRONIC AUTOIONIZATION ON THE CO-750ANGSTROM( A(2)PI VIBRATIONAL POPULATIONS IN THE WAVELENGTH RANGE 618)

Vibrationally resolved relative fluorescence cross sections have been measured for the CO+ A(2) Pi --> X(2) Sigma(+) transition using monoch romated synchrotron radiation between 618 and 750 Angstrom. In this wa velength region the photoionization spectrum is dominated by intense a utoionizing resonances belonging to the Rydberg series converging onto the various vibrational levels of the CO+ A(2) Pi or the B-2 Sigma(+) ionization thresholds. Autoionization from these Rydberg states into the CO+ A2 Pi State causes significant variations to occur in the A(2) Pi --> X(2) Sigma(+) fluorescence cross sections and the CO+ A(2) Pi vibrational branching ratios. The results indicate that, in most cases , vibrational autoionization favours the ionization channel representi ng the minimum change in the vibrational state of the ion core. Howeve r, in one wavelength region, the experimental data appear to disagree with the theoretical propensity rule for vibrational autoionization. T he effects of electronic autoionization from the Rydberg series conver ging onto the B-2 Sigma(+) threshold are compared with simple Franck-C ondon predictions and theoretical cross sections calculated using a tw o-step multichannel quantum defect approach.