PHOTOELECTRON ANGULAR-DISTRIBUTION AND ION VIBRATIONAL BRANCHING RATIO - THE (2-PHOTON IONIZATION OF E(1)PI-STATE-ALIGNED CO MOLECULES(1))

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.