UNEXPECTED PRODUCT FINE-STRUCTURE DISTRIBUTIONS IN (3+1)-PHOTON IONIZATION OF XENON

Three-photon resonance enhanced four-photon ionization of xenon shows preferential formation of Xe+(2P1/2) when intermediate ns[3/2]1 Rydberg states are excited in the three-photon step. Here, the nl[K]J notation refers to jcl coupling, in which the angular momentum of the ion core, jc, is coupled to the orbital angular momentum of the Rydberg electron l to give K, which is then coupled to the Rydberg electron's spin to give J. The primes following l denote states belonging to the 2P1/2 core. Multichannel-quantum-defect theory identifies these intermediates as nearly pure Rydberg states belonging to the Xe+(2P3/2) core. An equivalent behavior is found for the 7s'[1/2]1 intermediate state which preferentially produces Xe+(2P3/2). On the other hand, for nd and nd' resonances we observe final-state distributions which closely mirror the core character of the intermediate state. The suppression of the parent core channel for s-type Rydberg states is shown to be due to a Cooper minimum in the ns→p transitio n amplitudes. As a consequence, minor components of the resonance state wave functions play a major role in the selection of the final ionization channel, in particular via the much larger amplitudes of nd'→f' transitions. © 1995 The American Physical Society.