Construction of theoretical hybrid potential energy curves for LiH(XΣ+1)

Various all-electron and valence-electron potential energy curves for LiH(XΣ+1) 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 Li7H and Li7D. Predicted vibrational energy-level spacings show reasonable (≲1cm−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 Li7H and Li7D.