Trends in low-lying electronic states of XH2 (X = Li, Na, K)

Relativistically-corrected CCSD(T), IGNIRCI and IC-MRCI+ Q have been employed in an investigation of low-lying states of LiH2, NaH2 and KH,. The lowest (2)A(1) and (2)Sigma(-) states were found to be purely repulsive, in agreement with previous predictions. Equilibrium structures of the B-2(2), B-2(1) and 2 Sigma(+)(g) states have been calculated and are in good agreement with available theoretical data. For tile C-2 nu species the main factor determining the structure and stability was the relative orientations and occupations of the valence p atomic orbital of tile metal and the H2 1 sigma(g) orbital. The presence of occupied p orbitals in the metal ligand increased the stability of the D-infinity/l species. Spectroscopic parameters of the B-2(2), B-2(1) and 2 Sigma(+)(g) states of KH2 are reported here for the first time. (c) 2007 Elsevier B.V. All rights reserved.