Evolution and ion kinetics of a XUV-induced nanoplasma in ammonia clusters

TL;DR

This study investigates the evolution and ion kinetics of a nanoplasma in ammonia clusters induced by XUV pulses, revealing rapid charge neutralization and the ejection of excited molecular ions through advanced measurement techniques.

Contribution

It provides a detailed analysis of nanoplasma evolution and ion kinetics in ammonia clusters using covariance mapping and time-resolved ion energy measurements, expanding previous research.

Findings

Charge neutralization occurs on a sub-picosecond timescale.

Correlated proton emission significantly influences plasma dynamics.

Ejection of ro-vibrationally excited H₂⁺* ions from clusters.

Abstract

High-intensity extreme ultraviolet (XUV) pulses from a free-electron laser can be used to create a nanoplasma in clusters. In Ref. [Michiels et al. PCCP, 2020; 22: 7828-7834] we investigated the formation of excited states in an XUV-induced nanoplasma in ammonia clusters. In the present article we expand our previous study with a detailed analysis of the nanoplasma evolution and ion kinetics. We use a time-delayed UV laser as probe to ionize excited states of H and H$_2^+$ in the XUV-induced plasma. Employing covariance mapping techniques, we show that the correlated emission of protons plays an important role in the plasma dynamics. The time-dependent kinetic energy of the ions created by the probe laser is measured, revealing the charge neutralization of the cluster happens on a sub-picosecond timescale. Furthermore, we observe ro-vibrationally excited molecular hydrogen ions H$_2^{+*}$ being ejected from the clusters. We rationalize our data through a qualitative model of a finite-size non-thermal plasma.