PHOTOELECTRON ANGULAR-DISTRIBUTIONS AND VIBRATIONAL BRANCHING RATIOS OF CO (2-PHOTON IONIZATION VIA THE B 1-SIGMA+ STATE(1))

We present vibrational branching ratios and photoelectron angular dist ributions for resonantly enhanced (2 + 1)-photon ionization of CO. The excitation ladder involves the B 1SIGMA+ (v(i) = 0 or 1) Rydberg stat e. Contrary to expectations fostered by the Franck-Condon principle, i onization via v(i) = 0 branches into vibrational states v+ = 0-4. Such phenomena are also observed in the case of v(i) = 1, but only to a mi nor extent. The angular emission patterns of the photoelectrons ejecte d during the ionizing step are of distinct character in that they are highly anisotropic for DELTAv = v(i)-v+ = 0 processes, but show isotro py when due to DELTAv not-equal 0 transitions. The photoelectron angul ar distribution which accompanies the DELTAv = 0 ionization of B(v(i) = 1) shows p-wave character, and hence we may postulate a spherical po tential of the Rydberg ion core. The same approximation should hold fo r the v(i) = 0 state. The dissimilar appearance of the angular distrib utions when ionizing from this level invites the hypothesis of two ind ividually different ionization channels.