Experimental Born-Oppenheimer potential for the X-1 Sigma(+) ground state of HeH+: Comparison with the ab initio potential

All literature on vibration-rotational and pure rotational transition energ ies for the X(1)Sigma(+) state.of (HeH+)-He-4, (HeH+)-He-3, (HeD+)-He-4 and (HeD+)-He-3 have been employed in a direct least-squares fit of the radial ly dependent Hamiltonian. The Born-Oppenheimer potential is represented by a modified Lennard-Jones function that provides for correct behavior in the near dissociation long-range region. Only 19 adjustable parameters were re quired to represent the 166 measured transition energies, which are reprodu ced almost to within the measurement accuracies. The fitted potential and B orn-Oppenheimer breakdown functions are shown to be in good agreement with the results of nb initio calculations. The results are used to obtain high- order centrifugal distortion constants as well as level widths for quasi-bo und levels. (C) 1999 Academic Press.