The possible use of high-resolution rovibrational spectroscopy of the hydrogen molecular ions ${\mathrm{H}}_2{}^{+}$ and ${\mathrm{HD}}^{+}$ for an independent determination of several fundamental constants is analyzed. While these molecules had been proposed for the metrology of nuclear-to-electron mass ratios, we show that they are also sensitive to the radii of the proton and deuteron and to the Rydberg constant at the level of the current discrepancies colloquially known as the proton size puzzle. The required level of accuracy, in the ${10}^{-12}$ range, can be reached both by experiments, using Doppler-free two-photon spectroscopy schemes, and by theoretical predictions. It is shown how the measurement of several well-chosen rovibrational transitions may shed light on the proton-radius puzzle, provide an alternative accurate determination of the Rydberg constant, and yield significantly more precise values of the proton-to-electron and deuteron-to-proton mass ratios.

• Received 11 May 2016

DOI:https://doi.org/10.1103/PhysRevA.94.050501