G. Sha et al., PHOTOELECTRON ANGULAR-DISTRIBUTIONS AND VIBRATIONAL BRANCHING RATIOS OF CO (2-PHOTON IONIZATION VIA THE B 1-SIGMA+ STATE(1)), The Journal of chemical physics, 99(6), 1993, pp. 4334-4339
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.