# Low-Energy Photoelectron Spectroscopy and Scattering from Aqueous Solutions and the Role of Solute Surface Activity

## TL;DR

This study explores how low-energy electrons interact with aqueous solutions, revealing insights into electron scattering and its effects on measuring electron binding energies.

## Contribution

The paper introduces a method to quantify inelastic electron scattering in aqueous solutions using liquid-jet photoemission spectroscopy.

## Key findings

- A minimum of ≳17 eV electron kinetic energy is required for accurate aqueous-phase electron binding energy measurements.
- Photoelectrons from surface-active solutes experience less scattering at low kinetic energies compared to homogeneously distributed solvents.
- Liquid-jet photoemission spectroscopy can probe surface-active solute dynamics near ionization thresholds.

## Abstract

Experimental insights into low-kinetic-energy electron
scattering
in aqueous solutions are essential for an improved understanding of
electron-driven chemistry and radiobiology, and the development and
informed application of aqueous-phase electron-based spectroscopy
and dichroism methods. Generally, in aqueous environments and for
electron kinetic energies below 12–15 eV, significant and,
thus far, incompletely understood low-energy-transfer inelastic electron
scattering with solvent molecules preponderates. This leads to cascades
of tens-of-meV kinetic-energy losses that distort nascent photoelectron
spectra, prevent direct and accurate electron-binding-energy measurements,
and limit possibilities to determine electron-scattering cross sections
at especially low electron kinetic energies. Here, we quantify aqueous-phase
inelastic-scattering-based energy losses using 1–30 eV kinetic
energy photoelectrons and liquid-jet photoemission spectroscopy, specifically
by photoionizing an exemplary surface-active solute and comparing
the results with those from the homogeneously distributed aqueous
solvent. Thereby, we identify a general ≳17 eV electron-kinetic-energy
requirement for the direct and accurate measurement of aqueous-phase
electron binding energies, irrespective of interfacial concentration
profiles. Further, at electron kinetic energies from 10 eV down to
a few-eV above the ionization threshold, we observe and quantify lower
degrees of scattering for photoelectrons generated from surface-active
solutes, allowing moderately distorted surface-active-solute photoemission
peaks to be resolved down to just few-eV electron kinetic energies.
These results demonstrate that liquid-jet photoemission spectroscopy
can be used to probe interfacial surface-active-solute dynamics and
dichroism effects close to ionization thresholds, in stark contrast
to similar experiments on homogeneously distributed solution components.
Furthermore, they offer novel insights into low-electron-kinetic-energy
scattering in aqueous environments, thereby addressing the current
lack of reliable experimental data in this critical energy range.