Precision spectroscopy of the hydrogen molecular ions: present status of theory and experiment

TL;DR

This paper reviews recent experimental and theoretical advances in the precision spectroscopy of hydrogen molecular ions, focusing on HD$^+$, and discusses the current limitations in theoretical calculations related to spin structure.

Contribution

It provides a comprehensive overview of recent experimental results and analyzes the main theoretical challenges, especially in calculating the spin structure of HD$^+$.

Findings

Proton-deuteron mass ratio inferred from spectroscopy data

Current theoretical calculations are limited by spin structure complexities

Experimental techniques have achieved high precision in HD$^+$ measurements

Abstract

We review recent experiments on HD$^+$ spectroscopy. The reduced proton-deuteron mass to electron mass ratio, $\mu_{pd}/m_e$, is inferred from the comparison of theory and experiment. Theoretical issues related to the calculations of the spin structure, which are currently the main limiting factor of theoretical accuracy, are discussed.