Hyperfine, rotational, and vibrational structure of the triplet ground state of Rb molecules

TL;DR

This study uses high-resolution spectroscopy to map the hyperfine, rotational, and vibrational structure of ultracold Rb molecules in the triplet ground state, revealing insights into singlet-triplet mixing and potential energy models.

Contribution

It provides detailed spectroscopic data and an improved coupled-channel model for Rb molecule states, enhancing understanding of their energy structure.

Findings

Hyperfine structure varies weakly with vibrational level

Energy shifts indicate singlet-triplet mixing at deep binding energies

Data helps refine potential energy models for Rb molecules

Abstract

We have performed high-resolution two-photon dark-state spectroscopy of an ultracold gas of Rb molecules in the triplet ground state at a magnetic field of about 1000 G. The vibrational ladder as well as the hyperfine and low-lying rotational structure is mapped out. Energy shifts in the spectrum are observed due to singlet-triplet mixing at binding energies as deep as a few hundred GHz x h. This information together with data from other sources is used to optimize the potentials of the triplet and singlet states in a coupled-channel model. We find that the hyperfine structure depends weakly on the vibrational level. This provides a possible explanation for inaccuracies in recent Feshbach resonance calculations.