THE A(3)SIGMA(+)(G) STATE OF THE HYDROGEN MOLECULE

The Born-Oppenheimer potential energy curve and the adiabatic corrections for the a(3) Sigma(g)(+) state of the hydrogen molecule have been recalculated for a wide range of internuclear distance using explicitly correlated wavefunctions in elliptic coordinates. The calculated potential energy curve is lower than the previous one by more than I cm(-1). The energies of the vibrational levels and rotational constants for this state have been also computed. In addition, the nonadiabatic corrections have been estimated on the basis of an approximate Van Vleck formula. The estimated nonadiabatic shift for the lowest level of H-2 has been independently confirmed by comparing the nonadiabatic energy calculated by Bishop and Cheung with the adiabatic energy presented in this work. It is shown that by taking into account estimated nonadiabatic corrections as well as relativistic and radiative effects, excellent agreement with experiment is achieved. (C) 1995 Academic Press, Inc.