Valence bond description for the ground state and several low-lying excited states of LiH

TLDR: In this article, a detailed and successful valence bond explanation for the variation curve of the dipole moment with respect to the distance R for the first excited state is also presented.

Abstract: Of these three bonded tableaux, the first two consist of the covalent bond between the atomic orbital Hls and the hybrid atomic orbitals of Li 2s and Li 2p,, while the last one corresponds to the ionic structure Li+H-. Further analyses showed that, compared with the covalent structures, the ionic structure Li+H- contributes less to the binding energy and the dipole moment of the ground state of LiH. This result differs from that based on MO theory. Our results clearly indicate that an electron will transfer from lithium to hydrogen in the range 5.0-7.0 a.u., which explains the so-called “harpoon” mechanism in the molecular-beam dynamics. A detailed and successful valence bond explanation for the variation curve of the dipole moment ~1 with respect to the distance R for the first excited state is also presented. There are two opposite effects, namely the contribution from the ionic structure Li+H- and the non-equivalent sp hybridization of the atomic orbitals on lithium, which make the dipole moment of the first excited state vary with R and lead the direction of ~1 to reverse at approximately 6.0a.u. A brief discussion of the other three excited states is given.