DFT study of the spin-forbidden reaction between Ti+ and N2O

The mechanism of the spin-forbidden reaction Ti+(4F) + N2O(X1Σ) → TiO+(2Δ) + N2(X1Σg+) on both doublet and quartet potential energy surfaces has been investigated at the B3LYP level of theory. Crossing seam between the potential energy surfaces and possible spin inversion process are discussed by means of the intrinsic reaction coordinate (IRC) approach. To emphasize the importance of charge transfer, the Ti+ ionic and O atomic charges with orbital NBO populations along the quartet IRC path are calculated. The calculated results indicated there is one crossing seam between the doublet and quartet potential energy surfaces, and spin inversion should occur in the exit channel. But it occurs only near the transition state 4Ti+-TS. The activation energy from Ti+(4F) to TiO+(2Δ) via 4Ti+-TS is calculated to be 1.43 kcal/mol. And due to the charge transfer N2O molecule becomes bent, which is a favorable process for the title reaction. Therefore, the reaction efficiency is most likely to be determined by the activation energy from Ti+(4F) to TiO+(2Δ) via 4Ti+-TS. These results are in good agreement with experimental observations.