Lowest order relativistic corrections to the energies of the B 1Σu state of H2

The lowest order relativistic corrections to the electronic energies have been computed for the B 1Σu state of H2 in the interval 1.0 ≤ R ≤ 30 a0. The total correction at the equilibrium separation, R = 2.43 a0 amounts to −2.126 cm−1. The absolute shifts of the vibrational levels of H2 change monotonically with v for v ≤ 27 from −2.090 to −1.538 cm−1 as compared with the −1.918 cm−1 shift of the dissociation limit. The computed shifts are used to place the v = 0 levels of H2 and D2 on a absolute energy scale and a comparison with experiment is performed.