STEREODYNAMIC CONTROL OF COLLISION-INDUCED NONADIABATIC DYNAMICS OF NO (A2Σ+) WITH H2, N2, CO, AND H2O: INTERMOLECULAR INTERACTIONS DRIVE COLLISION OUTCOMES

Nitric oxide (NO) is a radical derived from combustion and atmospheric chemistry with a role in the formation of secondary pollutants. NO concentrations are often determined using laser-induced fluorescence (LIF) on the A2Σ+ ← X2Π transition band. However, the electronic quenching of NO (A2Σ+) resulting from the collision with other molecular species gives rise to competing nonradiative pathways to the electronic ground state of NO. Cross sections and rate constants of NO (A2Σ+) electronic quenching have been experimentally determined for various common molecular collision partners, to correct LIF measurements. Unfortunately, the underlying photochemical mechanisms responsible for the electronic quenching are unclear. In this thesis, we describe the development of high-quality PESs that reveal new physical insights into the intermolecular interactions and conical intersections that facilitate the branching between the nonreactive electronic quenching, reactive electronic quenching, and scattering of NO (A2Σ+) with H2, N2, CO, and H2O. The PESs are calculated at the EOM-EA-CCSD/d-aug-cc-pVTZ//EOM-EA-CCSD/aug-cc-pVDZ and EOM-EA-CCSD/d-aug-cc-pVTZ//EOM-EA-CCSD/aug-cc-pVTZ levels of theory, to secure a balanced treatment of the valence and Rydberg electronic states and an accurate description of the open-shell character of NO. Our PESs show that H2 is incapable of electronically quenching NO (A2Σ+) at low collision energies; instead, the two molecules will likely undergo scattering. The PESs of NO (A2Σ+) with N2 and CO are highly anisotropic while the PESs of NO (A2Σ+) with H2O are highly isotropic. Additionally, the PESs of NO (A2Σ+) with N2, CO, and H2O show evidence of electron transfer from NO (A2Σ+) into the lowest unoccupied molecular orbital of the collision partner, that is, the harpoon mechanism. Finally, our computational results stand in good agreement with the experimental cross sections