Comb-calibrated Raman Spectroscopy of Molecular Hydrogen

Molecular hydrogen and its isotopologues are key systems to test quantum electrodynamics (QED) at molecular length scales, as their energy levels can be calculated with high accuracy[1]. Comparison of the theoretical values with highly accurate experimental determinations of transition frequencies allows one to test QED and theories beyond the standard model of particle physics[2]. Recent accurate measurements of rovibrational frequencies of HD and D2, covering mostly the second overtone band, have shown a systematic deviation between measured and calculated transition frequencies. Yet, available measurements on H2 are characterized by uncertainties one order of magnitude larger than theory.