Exploration of dynamical regimes of irradiated small protonated water clusters

TL;DR

This study investigates how small protonated water clusters respond dynamically to various laser frequencies and intensities using advanced quantum-classical simulations, revealing size-dependent stability and vibrational behaviors.

Contribution

It provides a detailed theoretical analysis of the laser-induced dynamics of small water clusters across a range of frequencies and intensities, incorporating self-interaction corrections for accurate electron emission modeling.

Findings

IR coupling affects light H+ ions directly

UV and high intensities cause rapid ionization and Coulomb explosion

Larger clusters are more resistant to Coulomb pressure

Abstract

We explore from a theoretical perspective the dynamical response of small water clusters, (H$_2$O)$_n$H$_3$O$^+$ with $n=1,2,3$, to a short laser pulse for various frequencies, from infrared (IR) to ultra-violet (UV) and intensities (from $6\times10^{13}$ W/cm$^2$ to $5\times10^{14}$ W/cm$^2$). To that end, we use time-dependent local-density approximation for the electrons, coupled to molecular dynamics for the atomic cores (TDLDA-MD). The local-density approximation is augmented by a self-interaction correction (SIC) to allow for a correct description of electron emission. For IR frequencies, we see a direct coupling of the laser field to the very light H$^+$ ions in the clusters. Resonant coupling (in the UV) and/or higher intensities lead to fast ionization with subsequent Coulomb explosion. The stability against Coulomb pressure increases with system size. Excitation to lower ionization stages induced strong ionic vibrations. These maintain rather harmonic pattern in spite of the sizeable amplitudes (often 10% of the bond length).