Non-adiabatic corrections to the energies of the pure vibrational states of

Nonrelativistic energies of all fifteen pure vibrational states of the H 2 molecule have been recalculated with much higher accuracy than before. In the calculations we employed explicitly correlated Gaussian functions and an approach where the Born–Oppenheimer (BO) approximation is not assumed. The wave function of each state was expanded in terms of 10 000 Gaussians whose nonlinear parameters were optimized using a procedure involving the analytical energy gradient. The obtained non-BO energies combined with the recent BO adiabatic energies of Pachucki and Komasa [K. Pachucki, J. Komasa, J. Chem. Phys. 129 (2008) 034102] allowed us to determine new improved values of the non-adiabatic corrections for the considered states.