An Ab Initio Electronic Structure Investigation of the Ground and Excited States of ScH(+), YH(+), and LaH().

Multireference configuration interaction (MRCI), Davidson-corrected MRCI (MRCI+Q), coupled-cluster singles, doubles, and perturbative triples [CCSD(T)], and frozen-core full configuration interaction (fcFCI) calculations were carried out using large, correlation-consistent basis sets to investigate the excited states of the Sc atom and the spin-free and spin-orbit coupled potential energy profiles, energetics, spectroscopic constants, and electron populations of low-lying states of MH(+) (M = Sc, Y, La). The core electron correlation effects, complete basis set effects, and spin-orbit coupling effects were also evaluated. The first four electronic states of all MH(+) are 1(2)Δ, 1(2)Σ(+), 1(2)Π, and 2(2)Σ(+) with 1σ(2)1δ(1), 1σ(2)2σ(1), 1σ(2)1π(1), and 1σ(2)3σ(1) single-reference electron configurations, respectively. These states of MH(+) can be represented by the M(2+)H(-) ionic structure. The ground states of ScH(+), YH(+), and LaH(+) are 1(2)Δ(3/2), 1(2)Σ(+)(1/2), and 1(2)Δ(3/2) with 55.45, 60.54, and 62.34 kcal/mol bond energies, respectively. The core electron correlation was found to be vital for gaining accurate predictions on the ground and excited state properties of MH(+). The spin-orbit coupling effects are minor for ScH(+) but become substantial moving to YH(+) and LaH(+). Overall, the results of this work are in good agreement with the limited set of experimental findings of MH(+) available in the literature and will be of use for future investigations. Furthermore, the theoretical approaches, findings, and trends reported here are expected to aid studies of similar species.