Trends in low-lying electronic states of XH 2 (X = Li, Na, K)

Abstract

Relativistically-corrected CCSD(T), IC-MRCI and IC-MRCI+ Q have been employed in an investigation of low-lying states of LiH 2, NaH 2 and KH 2. The lowest 2A 1 and 2Σ − states were found to be purely repulsive, in agreement with previous predictions. Equilibrium structures of the 2B 2, 2B 1 and 2 Σ g + states have been calculated and are in good agreement with available theoretical data. For the C 2 v species the main factor determining the structure and stability was the relative orientations and occupations of the valence p atomic orbital of the metal and the H 2 1σ g orbital. The presence of occupied p orbitals in the metal ligand increased the stability of the D ∞ h species. Spectroscopic parameters of the 2B 2, 2B 1 and 2 Σ g + states of KH 2 are reported here for the first time.