Theoretical Study of the Photochemical Mechanisms of the Electronic Quenching of NO(A 2Σ+) with CH4, CH3OH, and CO2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2023-08, Vol.127 (34), p.7228-7240
• Main Authors: Bridgers, Aerial N., Urquilla, Justin A., Im, Julia, Petit, Andrew S.
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.3c03981

The electronic quenching of NO­(A 2Σ+) with molecular partners occurs through complex non-adiabatic dynamics that occurs on multiple coupled potential energy surfaces. Moreover, the propensity for NO­(A 2Σ+) electronic quenching depends heavily on the strength and nature of the intermolecular interactions between NO­(A 2Σ+) and the molecular partner. In this paper, we explore the electronic quenching mechanisms of three systems: NO­(A 2Σ+) + CH4, NO­(A 2Σ+) + CH3OH, and NO­(A 2Σ+) + CO2. Using EOM-EA-CCSD calculations, we rationalize the very low electronic quenching cross-section of NO­(A 2Σ+) + CH4 as well as the outcomes observed in previous NO + CH4 photodissociation studies. Our analysis of NO­(A 2Σ+) + CH3OH suggests that it will undergo facile electronic quenching mediated by reducing the intermolecular distance and significantly stretching the O–H bond of CH3OH. For NO­(A 2Σ+) + CO2, intermolecular attractions lead to a series of low-energy ON–OCO conformations in which the CO2 is significantly bent. For both the NO­(A 2Σ+) + CH3OH and NO­(A 2Σ+) + CO2 systems, we see evidence of the harpoon mechanism and low-energy conical intersections between NO­(A 2Σ+) + M and NO­(X 2Π) + M. Overall, this work provides the first detailed theoretical study on the NO­(A 2Σ+) + M potential energy surface of each of these systems and will inform future velocity map imaging experiments.