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

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°.