High-resolution photoelectron spectroscopy with angular selectivity - a tool to probe valence-Rydberg states and couplings in HCl(+).

Abstract

Due to strong electron correlation effects and electron coupling with nuclear motion, the molecular inner-valence photoionization is still a challenge in electron spectroscopy, resulting in several interesting phenomena such as drastic changes of angular dependencies, spin-orbit induced predissociation, and complex interplay between adiabatic and nonadiabatic transitions. We investigated the excited electronic states of HCl(+) in the binding energy range 27.5-30.5 eV using synchrotron radiation based high-resolution inner-valence photoelectron spectroscopy with angular resolution and interpreted the observations with the help of ab initio calculations. Overlapping electronic states in this region were disentangled through the analysis of photoelectron emission anisotropies. For instance, a puzzling transition, which does not seem to obey either an adiabatic or a nonadiabatic picture, has been identified at ∼28.6 eV binding energy. By this study, we show that ultrahigh-resolution photoelectron spectroscopy with angular selectivity represents a powerful tool to probe the highly excited ionic molecular electronic states and their intricate couplings.