Ab Initio Study of Molecular and Electronic Structures of Early Transition Metal Trihydrides MH₃ (M = Sc, Ti, V, Fe)

Ab initio calculations with accounting for electronic correlation were carried out for ScH 3, VH 3, TiH 3, and FeH 3 . Relative energies of excited states of the molecules were evaluated by the equation-of-motion coupled cluster method in the single and double approximation (EOM-CCSD) and ground-state properties were calculated at coupled cluster singles doubles level augmented by pertrubative correction for connected triple excitation (CCSD(T)). The ground electronic states of the molecules were found to have high-spin and planar ( D 3 h ) equilibrium geometries. The molecules TiH 3 and VH 3 possess low-lying degenerate electronic states. However, the Jahn−Teller distortion of these states was investigated and found to be small. Correlation corrections to equilibrium internuclear distances, harmonic vibrational frequencies, and infrared intensities are shown to be significant. A comparison of theoretical and available experimental data on the molecules was performed.