Photoionization of pyrrole from the $$B_2$$ state: a computational study on the effects of Rydberg–valence mixing

Abstract

Does the optically bright $$B_2(\pi \rightarrow \pi ^*)$$ transition in pyrrole correspond to an inter-valence or to a mixed valence–Rydberg transition? State-of-the-art electronic structure methods provide inconclusive results and relegate the answer to future time-resolved photoelectron spectroscopy experiments. Here, benchmark calculations of photoionization cross sections, asymmetry parameters and molecular frame photoelectron angular distributions (MFPADs) have been performed with the aim of discerning between the two types of transitions. In particular, we show that MFPADs are very sensitive probes of the electronic wave function and that accurate experimental MFPADs could be used to identify the electronic character of the $$B_2$$ state.