Potential energy surfaces for the insertion of Ta and Ta+ into H2

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Abstract
We compute the bending potential energy surfaces of 12 electronic states of TaH2 and TaH+2 using the complete active space multiconfiguration self-consistent field (CAS-MCSCF) followed by multireference singles+doubles configuration interaction (MRSDCI) calculations. Spin–orbit effects are also included using the relativistic configuration interaction (RCI) approach. We find that the 4F ground state of Ta atom requires a barrier of ∼24 kcal/mol for insertion into H2 while the 5F ground state of Ta+ does not insert into H2. The low-spin excited states of Ta and Ta+ are considerably more reactive with H2. We find three nearly-degenerate bent electronic states of 4B1, 4A2, and 4B2 symmetries as the candidates for the ground state of TaH2. Likewise 3B1 and 3A1 electronic states of TaH+2 are nearly-degenerate candidates for the ground state. The spin–orbit coupling strongly mixes some of these states leading to bond angle changes of up to 10°.