Cs$^{+}$ Solvated in Hydrogen - Evidence for Several Distinct Solvation Shells

TL;DR

This study investigates cesium ions solvated in hydrogen, revealing distinct solvation shells and unusual ion abundance patterns, supported by experimental mass spectra and preliminary theoretical calculations.

Contribution

It provides evidence for multiple concentric, solid-like solvation shells around Cs$^+$ in hydrogen, with detailed spectral analysis and initial density functional theory insights.

Findings

Dominance of even-numbered hydrogen ions contrasts previous studies.

Identification of anomalies at specific cluster sizes indicating shell formation.

Preliminary DFT calculations support shell structure hypotheses.

Abstract

Helium nanodroplets are doped with cesium and molecular hydrogen and subsequently ionized by electrons. Mass spectra reveal H$_x$Cs$^{+}$ ions that contain as many as 130 hydrogen atoms. Two features in the spectra are striking: First, the abundance of ions with an odd number of hydrogen atoms is very low; the abundance of HCs$^+$ is only 1 % that of H$_2$Cs$^+$. The dominance of even-numbered species is in stark contrast to previous studies of pure or doped hydrogen cluster ions. Second, the abundance of (H$_2$)$_n$Cs$^+$ features anomalies at n = 8, 12, 32, 44, and 52. Guided by previous work on ions solvated in hydrogen and helium we assign the anomalies at n = 12, 32, 44 to the formation of three concentric, solid-like solvation shells of icosahedral symmetry around Cs$^+$. Preliminary density functional theory calculations for n $\le$ 14 are reported as well.