Construction of theoretical hybrid potential energy curves for LiH(X (1)Sigma(+)).

Various all-electron and valence-electron potential energy curves for LiH(X (1)Sigma(+)) are compared and assessed. Hybrid potential energy curves are constructed from all-electron potentials at short range and a valence-electron calculation otherwise. This approach provides for the X state of LiH an overall potential curve, which is ionic at equilibrium, and presents an avoided crossing with the excited A state, leading to neutral dissociation products. The classical turning points predicted by these purely theoretical hybrid potentials are compared with those of the experimentally based inverted-perturbation approach (IPA) potentials for both (7)LiH and (7)LiD. Predicted vibrational energy-level spacings show reasonable (less than or approximately 1 cm(-1)) agreement with the corresponding IPA values. Rotation and vibration-rotation transition energies arising from the most accurate hybrid potential are shown to compare very favorably with recent high-resolution spectroscopic data on (7)LiH and (7)LiD.