Theoretical study of spin–orbit coupling and kinetics in spin-forbidden reaction between Ta(NH 2 ) 3 and N 2 O

The activation mechanism of the nitrous oxide (N 2 O) with the Ta(NH 2 ) 3 complex on the singlet and triplet potential energy surfaces has been investigated using the hybrid exchange correlation functional B3LYP. The minimum energy crossing point (MECP) is located by using the methods of Harvey et al. The rate-determining step of the N–O activation reaction is the intersystem crossing from 1 2 to 3 2 . The reacting system will change its spin multiplicities from the singlet state to the triplet state near MECP-1, which takes place with a spin crossing barrier of 32.5 kcal mol −1 , and then move on the triplet potential energy surface as the reaction proceeds. Analysis of spin–orbit coupling (SOC) using localized orbitals shows that MECP-1 will produce the significant SOC matrix element, the value of SOC is 272.46 cm −1 , due to the electron shift between two perpendicular π orbitals with the same rotation direction and the contribution from heavy atom Ta. The rate coefficients are calculated using Non-adiabatic Rice-Ramsperger-Kassel-Marcus (RRKM). Results indicate that the coefficients, k ( E ), are exceedingly high, k ( E ) > 10 12 s −1 , for energies above the intersystem crossing barrier (32.5 kcal mol −1 ); however, in the lower temperature range of 200–600 K, the intersystem crossing is very slow, k ( T ) < 10 −6 s −1 .