A setup for studies of photoelectron circular dichroism from chiral molecules in aqueous solution

TL;DR

This paper introduces a novel experimental setup, EASI, for measuring photoelectron circular dichroism in aqueous solutions, revealing large asymmetries influenced by hydration and enabling studies of chiral molecules in liquid environments.

Contribution

The paper presents a new experimental design, EASI, that enables PECD measurements in aqueous solutions, expanding the scope of chiral analysis in liquids and hydration effects.

Findings

PECD asymmetries are significantly larger than in traditional methods.

Demonstrated PECD detection on gas-phase fenchone and liquid water.

First liquid-phase PECD data from fenchone and aqueous solutions.

Abstract

We present a unique experimental design that enables the measurement of photoelectron circular dichroism (PECD) from chiral molecules in aqueous solution. The effect is revealed from the intensity difference of photoelectron emission into a backward-scattering angle relative to the photon propagation direction when ionizing with circularly polarized light of different helicity. This leads to asymmetries (normalized intensity differences) that depend on the handedness of the chiral sample and exceed the ones in conventional dichroic mechanisms by orders of magnitude. The asymmetry is largest for photon energies within several electron volts above the ionization threshold. A primary aim is to explore the effect of hydration on PECD. The modular and flexible design of our experimental setup EASI (Electronic structure from Aqueous Solutions and Interfaces) also allows for detection of more common photoelectron angular distributions (PADs), requiring distinctively different detection geometries, and typically using linearly polarized light. A microjet is used for liquid-sample delivery. We describe EASI's technical features and present two selected experimental results, one based on synchrotron-light measurements and the other performed in the laboratory, using monochromatized He-II $\alpha$ radiation. The former demonstrates the principal effectiveness of PECD detection, illustrated for prototypic gas-phase fenchone. We also discuss the first data from liquid fenchone. In the second example we present valence photoelectron spectra from liquid water and NaI aqueous solution, here obtained from a planar-surface microjet (flatjet). This new development features a more favorable symmetry for angle-dependent photoelectron measurements.