Revealing Atom-Radical Reactivity at Low Temperature Through the N + OH Reaction

Abstract

More than 100 reactions between stable molecules and free radicals have been shown to remain rapid at low temperatures. In contrast, reactions between two unstable radicals have received much less attention due to the added complexity of producing and measuring excess radical concentrations. We performed kinetic experiments on the barrierless N((4)S) + OH((2)Π) → H((2)S) + NO((2)Π) reaction in a supersonic flow (Laval nozzle) reactor. We used a microwave-discharge method to generate atomic nitrogen and a relative-rate method to follow the reaction kinetics. The measured rates agreed well with the results of exact and approximate quantum mechanical calculations. These results also provide insight into the gas-phase formation mechanisms of molecular nitrogen in interstellar clouds.

THE C(3P) + NH3REACTION IN INTERSTELLAR CHEMISTRY. II. LOW TEMPERATURE RATE CONSTANTS AND MODELING OF NH, NH2, AND NH3ABUNDANCES IN DENSE INTERSTELLAR CLOUDS

“…N 2 itself is produced by atomic nitrogen reactions with small neutral radicals (Daranlot et al 2012;Le Gal et al 2014) which experimental and theoretical studies have shown to be less efficient than previously assumed (Daranlot et al 2012;Daranlot et al 2013;Daranlot et al 2011;Jorfi & Honvault 2009;Loison et al 2014a;Ma et al 2012 (Vigren et al 2012) which is nonetheless sufficient to make this process the major source of NH radicals in current gas-phase astrochemical models (Le Gal et al 2014). Reaction (R1) is problematic due to the endothermicity of the N + + para-H 2 (p-H 2 ) reaction (Zymak et al 2013).…”

Detection of circumstellar nitric oxide

“…which are barrierless (Daranlot et al 2011;Bergeat et al 2009) and therefore rapid at the low temperatures of interstellar clouds. NO is formed from nitrogen atoms and hydroxyl radicals through reaction (1) and becomes a major intermediate in the synthesis of N 2 through reaction (2).…”

An accurate study of the dynamics of the C+OH reaction on the second excited 14A″ potential energy surface

“…The astrophysical interest of reactions between free radicals has motivated an ample list of recent studies of collisions between open-shell atoms such as C( 3 P), [1][2][3][4][5][6][7] N( 4 S), [8][9][10] F( 2 P), [11][12][13][14] O( 3 P), [15][16][17][18] or S( 3 P) (Refs. 19 and 20) with the hydroxyl radical OH( 2 ).…”

“…Recent examples of the possibilities of such approaches have been reported for the N+OH reaction. 9,10 In those works, quasi-classical trajectory (QCT) and quantum mechanical (QM) calculations were performed to obtain reaction probabilities, cross sections, and rate constants. A comparison with measured rate constants was also presented in Ref.…”