ROTATIONALLY RESOLVED NEAR-THRESHOLD PHOTOIONIZATION OF THE 1B1 VALENCE ORBITAL OF H2O AND D2O

Results of theoretical studies of rotationally resolved ion distributions for near-threshold photoionization of the 1b, valence orbital of H2O and D2O are reported and compared with measured spectra. Agreement between the calculated and measured spectra is very encouraging. The calculated and measured spectra reveal both type a and type c transitions in contrast to type c transitions only expected in an atomiclike picture. Type a transitions arise from odd (mainly p wave) angular momentum components of the photoelectron matrix elements which are due to l mixing in the electronic continua. These type a transitions are quite molecular in origin and are similar to nonatomiclike transitions seen in resonance enhanced multiphoton ionization of excited states of diatomic molecules. Useful rotational selection rules are also obtained.