Ab Initio Calculations on Sequential Reactions of Nitric Oxide with Titanium Ions in the Gas Phase.

Potential energy surfaces of sequential reactions of NO with Ti ion in the gas phase were investigated for various spin multiplicities using the coupled-cluster and the multireference configuration interaction methods. The mechanisms of Ti reactions with up to four NO molecules were fully determined, with all transition-state structures being found by relaxed surface scans and confirmed by the intrinsic reaction coordinate (IRC) calculations. The reaction mechanisms are consistent with the products observed in mass spectrometric experiments. In the first reaction, the nitrogen atom and TiO ion are produced with intersystem crossings for singlet and triplet states. The OTi(NO) complex is formed in the second reaction, and the third reaction involves N-N bond formation, yielding the NO molecule and TiO ion. The fourth NO molecule reacts with the TiO ion in an electron-transfer reaction to produce final products TiO and NO. The coupled-cluster relative energies were used as a reference to evaluate the overall performance of common density functionals for this particular reaction.