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

We present vibrational branching ratios and photoelectron angular distributions for resonantly enhanced (2 + 1)-photon ionization of CO. The excitation ladder involves the B 1SIGMA+ (v(i) = 0 or 1) Rydberg state. Contrary to expectations fostered by the Franck-Condon principle, ionization 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 minor extent. The angular emission patterns of the photoelectrons ejected during the ionizing step are of distinct character in that they are highly anisotropic for DELTAv = v(i)-v+ = 0 processes, but show isotropy when due to DELTAv not-equal 0 transitions. The photoelectron angular distribution which accompanies the DELTAv = 0 ionization of B(v(i) = 1) shows p-wave character, and hence we may postulate a spherical potential of the Rydberg ion core. The same approximation should hold for the v(i) = 0 state. The dissimilar appearance of the angular distributions when ionizing from this level invites the hypothesis of two individually different ionization channels.