Chromium dihydride (CrH2): theoretical evidence for a bent5B2ground state

Abstract

Ab initio molecular electronic structure theory has been used to study two likely candidates for the quintet ground state of CrH2 at the self-consistent field, the single and double excitation configuration interaction (CISD), the single and double excitation coupled cluster (CCSD), and the single, double, and perturbative triple excitation coupled cluster (CCSD(T)) levels of theory. The largest basis sets utilized for geometry optimizations, designated two-f TZ2P, have a contraction scheme of Cr(14s11p6d2f/10s8p3d2f), H(5s2p/3s2p). At the CCSD(T) level of theory using this two-f TZ2P basis, a bent (C2v symmetry) 5B2 state is predicted to lie a mere 4·2 kcal mol-1 (4·5 kcal mol-1 including zero-point vibrational energy correction) lower in energy than linear (D∞h symmetry) 5Σg + HCrH. Theoretical predictions for the equilibrium geometry, harmonic vibrational frequencies, and isotopic frequency shifts of the 5B2 state compare favourably with the results of recent matrix isolation FT-IR work by Xiao, Hauge,...