Generalized perspective on chiral measurements without magnetic interactions

TL;DR

This paper unifies various electric-dipole based chiral discrimination methods, revealing a common vectorial form of the chiral response that depends on molecular pseudoscalars and field configurations, enabling efficient detection without magnetic interactions.

Contribution

It provides a unified theoretical framework for multiple chiral measurement techniques, highlighting the fundamental vectorial nature of the chiral response and extending methods to arbitrary electric field polarizations.

Findings

Chiral response has a universal vector form involving molecular pseudoscalars and field pseudovectors.

The efficiency of chiral signals depends on the non-coplanarity of vectors forming a triple product.

The framework applies to both bound and continuum state phenomena and arbitrary electric field polarizations.

Abstract

We present a unified description of several methods of chiral discrimination based exclusively on electric-dipole interactions. It includes photoelectron circular dichroism (PECD), enantio-sensitive microwave spectroscopy (EMWS), photoexcitation circular dichroism (PXCD), and photoelectron-photoexcitation circular dichroism (PXECD). We show that, in spite of the fact that the physics underlying the appearance of a chiral response is very different in all these methods, the enantio-sensitive and dichroic observable in all cases has a unique form. It is a polar vector given by the product of (i) a molecular pseudoscalar and (ii) a field pseudovector specified by the configuration of the electric fields interacting with the isotropic ensemble of chiral molecules. The molecular pseudoscalar is a rotationally invariant property, which is composed from different molecule-specific vectors and in the simplest case is a triple product of such vectors. The key property that enables the chiral response is the non-coplanarity of the vectors forming such triple product. The key property that enables chiral detection without relying on the chirality of the electromagnetic fields is the vectorial nature of the enantio-sensitive observable. Our compact and general expression for this observable shows what ultimately determines the efficiency of the chiral signal and if, or when, it can reach 100%. We also discuss the differences between the two phenomena, which rely on the bound states, PXCD and EMWS, and the two phenomena using the continuum states, PECD and PXECD. Finally, we extend these methods to arbitrary polarizations of the electric fields used to induce and probe the chiral response.