Heteronuclear Limit of Strong-Field Ionization: Fragmentation of HeH$^+$ by Intense Ultrashort Laser Pulses

TL;DR

This study investigates the fragmentation dynamics of the polar molecule HeH$^+$ under intense ultrashort laser pulses, revealing that direct vibrational excitation, rather than electronic excitation, governs the process, with detailed pathway reconstruction.

Contribution

It provides the first detailed experimental and theoretical analysis of vibrational excitation and fragmentation pathways in HeH$^+$, contrasting with symmetric molecules and expanding understanding of strong-field molecular dynamics.

Findings

Vibrational excitation dominates fragmentation dynamics.

Reconstructed ionization pathways and bond length evolution.

Contrasts with symmetric molecules enhance general understanding.

Abstract

The laser-induced fragmentation dynamics of this most fundamental polar molecule HeH$^+$ are measured using an ion beam of helium hydride and an isotopologue at various wavelengths and intensities. In contrast to the prevailing interpretation of strong-field fragmentation, in which stretching of the molecule results primarily from laser-induced electronic excitation, experiment and theory for nonionizing dissociation, single ionization and double ionization both show that the direct vibrational excitation plays the decisive role here. We are able to reconstruct fragmentation pathways and determine the times at which each ionization step occurs as well as the bond length evolution before the electron removal. The dynamics of this extremely asymmetric molecule contrast the well-known symmetric systems leading to a more general picture of strong-field molecular dynamics and facilitating interpolation to systems between the two extreme cases.