G. Sha et al., PHOTOELECTRON ANGULAR-DISTRIBUTION AND ION VIBRATIONAL BRANCHING RATIO - THE (2-PHOTON IONIZATION OF E(1)PI-STATE-ALIGNED CO MOLECULES(1)), The Journal of chemical physics, 99(10), 1993, pp. 7687-7695
We report vibrational level channeling and photoelectron angular distr
ibutions which characterize the single-step photoionization of the E 1
PI Rydberg state of CO. Particular attention is paid to the influence
of the intermediate state's rotational preparation and its spatial ali
gnment. The two-photon excitation is tuned to populate the lowest poss
ible J values of E, which permits us to isolate a single magnetic subl
evel of this intermediate state. Vibrational branching is found to be
insensitive to the choice of the excitation line and does not match th
e predictions suggested by the Franck-Condon factors for a CO E 1PI(v1
) --> CO+ X2 SIGMA+ (v+) direct ionization. A competitive autoionizati
on from the three-photon-energy state S1 may be responsible for this a
nomalous behavior. The phenomenological pattern of photoelectron distr
ibutions can in all cases be rationalized on the basis of the intermed
iate state alignment. A separate chapter of the discussion is devoted
to P(2) pumping, since it provides a particularly simple situation whe
re all excited molecules are oriented with their axes parallel to the
light vector E, which makes this case tractable to a quantitative calc
ulation. Its results show qualitative agreement with the experimental,
observations. The remaining discrepancy can be attributed to the auto
ionization which has not been considered in the calculation.