STATE-TO-STATE PHOTOIONIZATION DYNAMICS PROBED BY ZERO KINETICS ENERGY (ZEKE) PHOTOELECTRON-SPECTROSCOPY

High-resolution ZEKE (zero kinetic energy photoelectron) spectroscopy is a tool to study molecular photionisation processes with rotational resolution. Rotationally resolved ZEKE spectra for several molecules (NO, H2S and benzene) are discussed in detail and a qualitative model for the investigation of the state-selective ionisation dynamics is employed. This compound-state model provides a simple approach for the qualitative understanding of rotationally resolved ionisation processes and the underlying symmetry selection rules. The description is extended to the interpretation of the ZEKE spectra of benzene and C2v asymmetric rotor molecules (H2O, H2S). From these considerations the rotational selection rules that govern the ZEKE spectra of these and similar molecules can be predicted. A comparison with recent experimental results on H2S and new measurements on benzene demonstrates the importance of electronic symmetry selection rules in ZEKE spectroscopy.