Theoretical Study of the Photochemical Mechanisms of the Electronic Quenching of NO( A 2 Σ + ) with CH 4 , CH 3 OH, and CO 2 .

The electronic quenching of NO( A 2 Σ + ) with molecular partners occurs through complex non-adiabatic dynamics that occurs on multiple coupled potential energy surfaces. Moreover, the propensity for NO( A 2 Σ + ) electronic quenching depends heavily on the strength and nature of the intermolecular interactions between NO( A 2 Σ + ) and the molecular partner. In this paper, we explore the electronic quenching mechanisms of three systems: NO( A 2 Σ + ) + CH 4 , NO( A 2 Σ + ) + CH 3 OH, and NO( A 2 Σ + ) + CO 2 . Using EOM-EA-CCSD calculations, we rationalize the very low electronic quenching cross-section of NO( A 2 Σ + ) + CH 4 as well as the outcomes observed in previous NO + CH 4 photodissociation studies. Our analysis of NO( A 2 Σ + ) + CH 3 OH suggests that it will undergo facile electronic quenching mediated by reducing the intermolecular distance and significantly stretching the O-H bond of CH 3 OH. For NO( A 2 Σ + ) + CO 2 , intermolecular attractions lead to a series of low-energy ON-OCO conformations in which the CO 2 is significantly bent. For both the NO( A 2 Σ + ) + CH 3 OH and NO( A 2 Σ + ) + CO 2 systems, we see evidence of the harpoon mechanism and low-energy conical intersections between NO( A 2 Σ + ) + M and NO( X 2 Π) + M. Overall, this work provides the first detailed theoretical study on the NO( A 2 Σ + ) + M potential energy surface of each of these systems and will inform future velocity map imaging experiments.