Complete g–u symmetry breaking in highly excited valence states of the HD molecule

We performed a study of rovibrational energy levels of the H̄ 1Σ+g and B̄ 1Σ+u states in HD in a three-photon experiment involving extreme ultraviolet (XUV), visible, and ultraviolet laser radiation. An analysis of level shifts with respect to adiabatic energies, deduced from level energies in H2 and D2, shows strong non-adiabatic interaction between these two states, implying complete g–u symmetry breaking over a wide range of v and J quantum numbers.