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Title:The Photochemical Pathways For The Nonreactive Electronic Quenching Of No (a2Σ+) By Co And H2o
Author(s):Guardado Sandoval, Jose
Contributor(s):Petit, Andrew S.; Kidwell, Nathanael M.
Subject(s):Photodissociation and photochemistry
Abstract:Nitric oxide (NO) is an important pollutant produced in combustion. Laser-induced fluorescence (LIF) on the \textit{A}$^2\Sigma^+\to$ \textit{X}$^2\Pi$ band is a common approach for quantifying the amount of NO and determining the physical conditions inside operating combustion engines. However, NO (\textit{A}$^2\Sigma^+$) is known to undergo reactive and nonreactive electronic quenching with molecular species, providing alternative photochemical pathways that compete with fluorescence. For example, the nonreactive electronic quenching cross sections of NO (\textit{A}$^2\Sigma^+$) with CO and H$_2$O at 300 K are 6 \AA$^2$ and 120 \AA$^2$, respectively. The underlying photochemical mechanisms responsible for this electronic quenching are not well-understood. In this talk we describe our efforts to develop high-quality potential energy surfaces (PESs) that provide insights into the long-range interactions and conical intersections that facilitate nonreactive electronic quenching of NO (\textit{A}$^2\Sigma^+$) by CO and H$_2$O. In order to ensure a balanced treatment of the valence and Rydberg electronic states as well as an accurate description of the open-shell character of NO we use the electron-attachment equation of motion coupled cluster with singles and doubles method (EOM-EA-CCSD). Our results demonstrate significant differences between the NO (\textit{A}$^2\Sigma^+$)+CO and NO (\textit{A}$^2\Sigma^+$)+H$_2$O systems in terms of the strength of the long-range attractive interactions, the impact of neighboring Rydberg states, and the shape of the PESs in the vicinity of the conical intersections responsible for the electronic quenching. In particular, we rationalize the large electronic quenching cross section of NO (\textit{A}$^2\Sigma^+$) with H$_2$O by the presence of relatively strong long-range attractions that steer the NO (\textit{A}$^2\Sigma^+$)+H$_2$O system into an excited-state collision complex that is bound by over 4500 cm$^{-1}$. Overall, this work sheds new light on the mechanisms for nonreactive electronic quenching of NO (\textit{A} $^2\Sigma^+$) with molecular partners.
Issue Date:2021-06-25
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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