Room temperature detection of the (H2)2 dimer

TL;DR

This paper reports the first detection of the hydrogen dimer (H2)2 at room temperature using cavity ring down spectroscopy, providing new insights into its structure and serving as a benchmark for theoretical studies.

Contribution

The study demonstrates room temperature detection of (H2)2, previously thought unfeasible, using advanced spectroscopic techniques, and offers detailed analysis of its rotational structure.

Findings

First room temperature detection of (H2)2

Resolved rotational structures observed at 1.2 micron

Provides benchmark data for future theoretical models

Abstract

The hydrogen dimer, (H2)2, is among the most weakly bound van der Waals complexes and a prototype species for first principles ab initio studies. The detection of the (H2)2 infrared absorption spectrum was reported more than thirty years ago at a temperature of 20 K. Due to the sharp decrease of the (H2)2 abundance with temperature, a detection at room temperature was generally considered as hardly achievable. Here we report the first room temperature detection of partly resolved rotational structures of (H2)2 by cavity ring down spectroscopy at sub-atmospheric pressures, in the region of the first overtone band of H2 near 1.2 micron. The quantitative analysis of the absorption features observed around ten allowed or forbidden transition frequencies of the monomer provides insight on the structure of this elusive species and a benchmark for future theoretical studies.