Visible line intensities of the triatomic hydrogen ion from experiment and theory

TL;DR

This study combines high-sensitivity experimental spectroscopy and ab initio calculations to accurately measure and predict the visible line intensities and Einstein B coefficients of the H3+ ion, including chaotic states.

Contribution

It provides the first detailed experimental measurements of visible line intensities of H3+ and validates ab initio predictions with high precision, even for chaotic states.

Findings

Experimental line intensities measured up to high excitation energies.

Ab initio predictions agree well with experimental data.

Validated the use of a precise dipole moment surface for chaotic states.

Abstract

The visible spectrum of H3+ is studied using high-sensitivity action spectroscopy in a cryogenic radiofrequency multipole trap. Advances are made to measure the weak ro-vibrational transitions from the lowest rotational states of H3+ up to high excitation energies providing visible line intensities and, after normalisation to an infrared calibration line, the corresponding Einstein $B$ coefficients. {\it Ab initio} predictions for the Einstein $B$ coefficients are obtained from a highly precise dipole moment surface of H3+ and found to be in excellent agreement, even in the region where states have been classified as chaotic.