Spin-Orbit Coupling Effects in Di-Hydrides of Third-Row Transition Elements

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Spin‐orbit coupling (SOC) effects were investigated for low‐lying electronic states in the di‐hydrides of third‐row transition elements by using MCSCF+MRMP2, +FOCI, and +SOCI methods with the SBKJC basis sets augmented by a set of f functions for transition elements and a set of p functions for hydrogen atoms, where MCSCF, MRMP2, FOCI, and SOCI are abbreviations of multi‐configuration self‐consistent field, multi‐reference second‐order Mo/ller‐Plesset, first‐order configuration interaction, and second‐order configuration interaction, respectively. Before the inclusion of SOC effects, six di‐hydrides (LaH2, HfH2, TaH2, WH2, OsH2, and IrH2) are lower in energy than the corresponding dissociation limits (transition element and a hydrogen molecule). All of these di‐hydrides have bent structures at their energy minima, and the ground states are 2A1, 1A1, 4B1, 5B2, 3B2, and 2A1, respectively. After the inclusion of SOC effects, the ground states are assigned to E1/2, A1, E1/2, A1, A1, and E1/2 in the double‐group representation of C2v symmetry. It can be concluded that SOC effects are not so important in LaH2, HfH2, and TaH2, while they become important in describing bending potential energy curves of low‐lying electronic states in WH2, OsH2, and IrH2.