The B 1Σ+u, B′ 1Σ+u, C 1Πu, and D 1Πu states of the H2 molecule. Matrix elements of angular and radial nonadiabatic coupling and improved a b i n i t i o potential energy curves

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Abstract
The B, B’, C, and D states of H2 are represented over wide ranges of the internuclear distance R by considerably more flexible electronic wave functions than the ones previously employed by Kolos, Rychlewski, and one of us (L.W.). These are used to compute the nonadiabatic coupling matrix elements for the homogeneous B’–B and D–C and the heterogeneous C–B, C–B’, D–B, and D–B’ interactions over a wide range of R values. The adiabatic potential curves obtained from the new electronic wave functions yield vibrational term values which, for the v=0 levels, lie within 0.6 to 2.2 cm−1 of the experimental ones in these four electronic states of H2. After subtracting the nuclear‐mass‐dependent contributions to these ab initio errors, which can be estimated by comparing H2 with D2, the remaining electronic errors near the equilibrium internuclear distances of these electronic states are approximately 0.3 cm−1 (C and D state) and 1 cm−1 (B and B’ state). In the C, D, and B’ states this represents improvements by 0.7, 6, and 8 cm−1, respectively, over the previous ab initio values.