Propensity rules in photoelectron circular dichroism in chiral molecules I: Chiral hydrogen

TL;DR

This paper investigates the physical mechanisms behind photoelectron circular dichroism in chiral molecules, revealing that it arises from propensity rules related to electron rotation and charge displacement, using hydrogen atom models.

Contribution

It introduces a theoretical framework based on bound chiral wave functions to explain the origin of asymmetry in photoelectron emission in chiral molecules.

Findings

Dichroism originates from sensitivity to electron rotation sense.

Asymmetry depends on charge displacement orthogonal to light polarization.

The model applies to aligned molecular ensembles and broader chiral systems.

Abstract

Photoelectron circular dichroism results from one-photon ionization of chiral molecules by circularly polarized light and manifests itself in forward-backward asymmetry of electron emission in the direction orthogonal to the light polarization plane. What is the physical mechanism underlying asymmetric electron ejection? How "which way" information builds up in a chiral molecule and maps into forward-backward asymmetry? We introduce instances of bound chiral wave functions resulting from stationary superpositions of states in a hydrogen atom and use them to show that the chiral response in one-photon ionization of aligned molecular ensembles originates from two propensity rules: (i) Sensitivity of ionization to the sense of electron rotation in the polarization plane. (ii) Sensitivity of ionization to the direction of charge displacement or stationary current orthogonal to the polarization plane. In the companion paper we show how the ideas presented here are part of a broader picture valid for all chiral molecules and arbitrary degrees of molecular alignment.