Stereodynamic Control of Collision-Induced Nonadiabatic Dynamics of NO (A 2Σ+) with H2, N2, and CO: Intermolecular Interactions Drive Collision Outcomes

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 125; no. 40; pp. 8803 - 8815
• Main Authors: Guardado, José L, Hood, David J, Luong, Kate, Kidwell, Nathanael M, Petit, Andrew S
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.10.2021
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.1c05653

Intermolecular interactions, stereodynamics, and coupled potential energy surfaces (PESs) all play a significant role in determining the outcomes of molecular collisions. A detailed knowledge of such processes is often essential for a proper interpretation of spectroscopic observations. For example, nitric oxide (NO), an important radical in combustion and atmospheric chemistry, is commonly quantified using laser-induced fluorescence on the A 2Σ+ ← X 2Π transition band. However, the electronic quenching of NO (A 2Σ+) with other molecular species provides alternative nonradiative pathways that compete with fluorescence. While the cross sections and rate constants of NO (A 2Σ+) electronic quenching have been experimentally measured for a number of important molecular collision partners, the underlying photochemical mechanisms responsible for the electronic quenching are not well understood. In this paper, we describe the development of high-quality PESs that provide new physical insights into the intermolecular interactions and conical intersections that facilitate the branching between the electronic quenching and scattering of NO (A 2Σ+) with H2, N2, and CO. The PESs are calculated at the EOM-EA-CCSD/d-aug-cc-pVTZ//EOM-EA-CCSD/aug-cc-pVDZ level of theory, an approach that ensures 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 (A 2Σ+) at low collision energies; instead, the two molecules will likely undergo scattering. The PESs of NO (A 2Σ+) with N2 and CO are highly anisotropic and demonstrate evidence of electron transfer from NO (A 2Σ+) into the lowest unoccupied molecular orbital of the collision partner, that is, the harpoon mechanism. In the case of ON + CO, the PES becomes strongly attractive at longer intermolecular distances and funnels population to a conical intersection between NO (A 2Σ+) + CO and NO (X 2Π) + CO. In contrast, for ON + N2, the conical intersection is preceded by an ∼0.40 eV barrier. Overall, our work shines new light into the impact of coupled PESs on the nonadiabatic dynamics of open-shell systems.