Observation and dynamic control of a new pathway of H$_3^+$ formation

TL;DR

This paper demonstrates a novel method for producing H$_3^+$ ions through single photoionization of hydrogen dimers, combining experimental femtosecond laser techniques with theoretical simulations, which could explain interstellar H$_3^+$ abundance.

Contribution

It introduces a new pathway for H$_3^+$ formation from ultracold hydrogen gas, supported by experimental and ab-initio simulation data.

Findings

H$_3^+$ can be formed via photoionization of H$_4$

Dominant formation channel involves hydrogen atom ejection

Supports explanation for high interstellar H$_3^+$ abundance

Abstract

We propose and experimentally demonstrate that the trihydrogen cation (H$_3^+$) can be produced via single photoionization of the molecular hydrogen dimer (H$_4$). Using near-infrared, femtosecond laser pulses and coincidence momentum imaging, we find that the dominant channel after single ionization of the dimer is the ejection of a hydrogen atom within a few hundred femtoseconds, leaving an H3+ cation behind. The formation mechanism is supported and well reproduced by an ab-initio molecular dynamics simulation. This is a new pathway of H$_3^+$ formation from ultracold hydrogen gas that may help explain the unexpected high abundance of H$_3^+$ in the interstellar medium in the universe.