THE EFFECT OF AUTOIONIZATION ON THE H2CO-2(2) VIBRATIONAL BRANCHING RATIOS IN THE WAVELENGTH RANGE 800-970 ANGSTROM(XB)

Vibrational branching ratios have been measured for the H2CO+ X B-2(2) state using photoelectron spectroscopy and monochromated synchrotron radiation. In the wavelength range encompassed by the present study th e photoionization cross section is dominated by intense autoionizing r esonances, most of which belong to Rydberg series converging onto the B 2A1 threshold. Autoionization from these Rydberg states causes consi derable variations to be observed in the vibrational branching ratios, The present data have been recorded over several Rydberg members, and the results indicate that autoionization tends to produce a vibration al distribution in the ion that is characteristic of the vibrational l evel in the neutral excited states.