Theoretical Study of the Photochemical Mechanisms of the Electronic Quenching of NO(A²Σ⁺) with CH₄, CH₃OH, and CO₂.

ABSTRACT: The electronic quenching of NO(A²Σ⁺) with molecular partners occurs through complex non-adiabatic dynamics that occurs on multiple coupled potential energy surfaces. Moreover, the propensity for NO(A²Σ⁺) electronic quenching depends heavily on the strength and nature of the intermolecular interactions between NO(A²Σ⁺) and the molecular partner. In this paper, we explore the electronic quenching mechanisms of three systems: NO(A²Σ⁺) + CH₄, NO(A²Σ⁺) + CH₃OH, and NO(A²Σ⁺) + CO₂. Using EOM-EA-CCSD calculations, we rationalize the very low electronic quenching cross-section of NO(A²Σ⁺) + CH₄ as well as the outcomes observed in previous NO + CH₄ photodissociation studies. Our analysis of NO(A²Σ⁺) + 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(A²Σ⁺) + CO₂, intermolecular attractions lead to a series of low-energy ON-OCO conformations in which the CO₂ is significantly bent. For both the NO(A²Σ⁺) + CH₃OH and NO(A²Σ⁺) + CO₂ systems, we see evidence of the harpoon mechanism and low-energy conical intersections between NO(A²Σ⁺) + M and NO(X²Π) + M. Overall, this work provides the first detailed theoretical study on the NO(A²Σ⁺) + M potential energy surface of each of these systems and will inform future velocity map imaging experiments.

SUBMITTER: Bridgers AN 

PROVIDER: S-EPMC10476188 | biostudies-literature | 2023 Aug

REPOSITORIES: biostudies-literature