The B 1Σ+u, B′ 1Σ+u,C 1Πu, and D 1Πu states of hydrogen. A b i n i t i o calculation of rovibronic coupling in H2, HD, and D2

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Abstract
The nonadiabatic rovibronic structures of the B, B’, C, and D states of H2, HD, and D2 have been calculated up to the common dissociation limit of the first three of these electronic states using the ab initio adiabatic potential curves and nonadiabatic coupling functions published recently by Wolniewicz and one of us. The homogeneous (Σ+–Σ+ and Π–Π) and heterogeneous (Σ+–Π+) interactions are treated simultaneously by numerical solution of the coupled vibrational equations for each J value from J=0 to J=6. The calculated nonadiabatic energy shifts, which show strong v‐ and J‐dependent variations within each electronic state and which spread over approximately ±50 cm−1 for J=6 in H2, yield rovibronic structures in very good agreement with spectroscopic term values. A number of published spectroscopic assignments, including states close to the dissociation limit, must be reevaluated in the light of this calculation. The remaining energy errors are nuclear‐mass dependent and are attributed to the neglected nonadiabatic interactions with the higher members of the 1Σ+u and 1Πu Rydberg series. The convergence errors of the Born–Oppenheimer energies of all four electronic states treated here appear to be at most 2 cm−1 for the highest bound vibrational states and less than 1 cm−1 for the lowest ones.