Nitric oxide (NO) radicals are reactive intermediates monitored in combustion and in the atmosphere by laser-induced fluorescence with the X2Π→A2Σ+ transition. Accurate measurements of NO concentrations rely upon precise fluorescence quantum yields, which are hindered by nonradiative collisional quenching of NO (A2Σ+) with ambient molecular species such as molecular oxygen (O2). Utilizing velocity map imaging and 1+1 resonance-enhanced multiphoton ionization (REMPI), we previously obtained the relative translational energy and product state distribution of NO (X2Π, v′′=0) from nonreactive quenching of NO (A2Σ+) with O2 (X3Σg-). Our work provided evidence that the NO3 collision complex is generated prior to dissociated products, O2 (c1Σu-) is generated in coincidence with NO (X2Π), and that NO is produced with a propensity to rotate perpendicular to the pπ* molecular orbital. We extend our studies to encompass a more complete picture of the NO (A2Σ+) + O2 (X3Σg-) nonreactive quenching dynamics by reporting the NO (X2Π, v′′=1, 2) product state distributions for comparison with our earlier results. Complementary high-level theoretical calculations will also be presented to explore regions of strong coupling between potential energy surfaces known as conical intersections. Indeed, the quenching of NO (A2Σ+) with O2 proceeds through conical intersections that significantly influence the dynamical signatures imprinted on the collision products.

Nonreactive collisional quenching of NO (A2Σ+) radicals with O2 (X3Σg-): Product state distribution of the NO (X2Π) products

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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