Fission of Multiply Charged Cesium and Potassium Clusters in Helium Droplets - Approaching the Rayleigh Limit

TL;DR

This study investigates multiply charged cesium and potassium clusters in helium droplets, revealing smaller cluster sizes than previously known and approaching the Rayleigh limit, with implications for cluster fission mechanisms.

Contribution

It provides new measurements of doubly and triply charged alkali clusters, showing they are smaller than previously reported and closer to the Rayleigh limit, enhancing understanding of cluster stability.

Findings

Doubly charged cesium and potassium clusters are smaller than previously reported.

Potassium dications approach the Rayleigh limit, indicating high fissility.

Triply charged cesium clusters as small as Cs19^{3+} are observed.

Abstract

Electron ionization of helium droplets doped with cesium or potassium results in doubly and, for cesium, triply charged cluster ions. The smallest observable doubly charged clusters are $Cs_{9}^{2+}$ and $K_{11}^{2+}$; they are a factor two smaller than reported previously. The size of potassium dications approaches the Rayleigh limit nRay for which the fission barrier is calculated to vanish, i.e. their fissilities are close to 1. Cesium dications are even smaller than nRay, implying that their fissilities have been significantly overestimated. Triply charged cesium clusters as small as $Cs_{19}^{3+}$ are observed; they are a factor 2.6 smaller than previously reported. Mechanisms that may be responsible for enhanced formation of clusters with high fissilities are discussed.