Abstract
We built a full-dimensional analytical potential energy surface of the ground electronic state of Li2H from ca. 20,000 ab initio multi-reference configuration interaction calculations, including core–valence correlation effects. The surface is flexible enough to accurately describe the three dissociation channels: Li (2s 2S) + LiH (1Σ+), Li2 (1Σg+) + H (1s 2S) and 2Li (2s 2S) + H (1s 2S). Using a local fit of this surface, we calculated pure (J = 0) vibrational states of Li2H up to the barrier to linearity (ca. 3400 cm−1 above the global minimum) using a vibrational self-consistent field/virtual state configuration interaction method. We found 18 vibrational states below this barrier, with a maximum of 6 quanta in the bending mode, which indicates that Li2H could be spectroscopically observable. Moreover, we show that some of these vibrational states are highly correlated already ca. 1000 cm−1 below the height of the barrier. We hope these calculations can help the assignment of experimental spectra. In addition, the first low-lying excited states of each B1, B2 and A2 symmetry of Li2H were characterized.
Highlights
It is well known that the most characteristic property of the metal atom in a molecular complex is its facility of spontaneously yielding electrons to the surrounding ligands or the surrounding solvent molecules
The same trend is observed for the diatomic species LiH and Li2: the equilibrium distances, dissociation energies and vertical ionization energies of both diatomics are in reasonably good agreement with experimental values and the recent aug-cc-pVTZ/multi-reference configuration interaction (MRCI)-F12 calculations of Yuan et al [14]
MRCI data points randomly scattered in a wide range of the valence coordinates enabled us to fit the potential energy surface with good accuracy, in the neighborhood of the global minimum energy point, and for the long-range region approaching to the atomization limit 2Li + H and LiH + Li and Li2 + H dissociation limits
Summary
It is well known that the most characteristic property of the metal atom in a molecular complex is its facility of spontaneously yielding electrons to the surrounding ligands or the surrounding solvent molecules. For the electronic ground state of Li2 H using double many-body expansion fitting based on 3726 ab initio energies calculated at the multi-reference configuration interaction (MRCI) level. Developed a PES fitting in a many-body expansion manner from 30,000 ab initio energies calculated at the MRCI-F12 level These PESs have been used in recent time-dependent quantum dynamical studies on the H + Li2 (X1 Σ+ g ) reaction [14,15,16,17,18]. Our first aim in this work is to calculate the vibrational energy levels of Li2 H from a new global analytical PES of the ground electronic state. We wanted to characterize the first low-lying excited electronic states of Li2 H and the ground state of Li2 H+
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