Spectroscopic identification and stability of the intermediate in the OH + HONO ₂ reaction

Abstract

The reaction of nitric acid with the hydroxyl radical influences the residence time of HONO2 in the lower atmosphere. Prior studies [Brown SS, Burkholder JB, Talukdar RK, Ravishankara AR (2001) J Phys Chem A 105:1605-1614] have revealed unusual kinetic behavior for this reaction, including a negative temperature dependence, a complex pressure dependence, and an overall reaction rate strongly affected by isotopic substitution. This behavior suggested that the reaction occurs through an intermediate, theoretically predicted to be a hydrogen-bonded OH-HONO2 complex in a six-membered ring-like configuration. In this study, the intermediate is generated directly by the association of photolytically generated OH radicals with HONO2 and stabilized in a pulsed supersonic expansion. Infrared action spectroscopy is used to identify the intermediate by the OH radical stretch ( 1) and OH stretch of nitric acid ( 2) in the OH-HONO2 complex. Two vibrational features are attributed to OH-HONO2: a rotationally structured 1 band at 3516.8 cm ؊1 and an extensively broadened 2 feature at 3260 cm ؊1 , both shifted from their respective monomers. These same transitions are identified for OD-DONO 2. Assignments of the features are based on their vibrational frequencies, analysis of rotational band structure, and comparison with complementary high level ab initio calculations. In addition, the OH (v ‫؍‬ 0) product state distributions resulting from 1 and 2 excitation are used to determine the binding energy of OH-HONO2, D0 < 5.3 kcal⅐mol ؊1 , which is in good accord with ab initio predictions.atmospheric chemistry ͉ hydroxyl radical ͉ nitric acid ͉ reaction intermediate N itric acid is a chemically inactive and photochemically stable reservoir for reactive HO x and NO x species in the atmosphere. In the troposphere, HONO 2 is usually removed by dry deposition or rainout faster than it is photochemically converted back to NO x , making it a permanent sink for NO x (1, 2). In the upper troposphere and stratosphere, where there is no rain, HONO 2 can be removed by solar photolysis and reaction with OH (3, 4),This reaction results in the conversion of HONO 2 into reactive NO x species, because the unstable nitrate radical rapidly decomposes into NO or NO 2 .Kinetic studies have shown that the OH ϩ HONO 2 reaction is unusual in several respects (3, 5-11), particularly under the temperature and pressure conditions found in the lower atmosphere. Under these conditions, this reaction exhibits a negative temperature dependence, a pressure dependence, and a strong kinetic isotope effect. The indirect mechanism inferred from these studies consists of initial OH radical addition forming an energized OH-HONO 2 * intermediate, followed by redissociation or reaction to form products. The energized intermediate can also be temporarily stabilized by collisions with bath gas M, and then redissociate to reactants or decompose to products as shown in the following scheme:The unusual kinetic behavior arises because of enhanced formation and collisional st...

Temperature-(208–318 K) and pressure-(18–696 Torr) dependent rate coefficients for the reaction between OH and HNO&lt;sub&gt;3&lt;/sub&gt;

“…Most of the experimental studies were carried out in the mid-70s to mid-80s (Margitan et al, 1975;Smith and Zellner, 1975;Wine et al, 1981;Jourdain et al, 1982;Kurylo et al, 1982;Margitan and Watson, 1982;Marinelli and Johnston, 1982;Ravishankara et al, 1982;Devolder et al, 1984;Smith et al, 1984;Connell and Howard, 1985;Jolly et al, 1985;Stachnik et al, 1986) with only the most recent and comprehensive studies of the reaction (Brown et al, 1999(Brown et al, , 2001) extending the temperature range to those found at the tropopause. Experimental (Carl et al, 2001;McCabe et al, 2003;O'Donnell et al, 2008b) and theoretical (Xia and Lin, 2001;Gonzalez and Anglada, 2010) work examining the details of the reaction mechanism highlight continuing interest in this complex reaction, which proceeds via formation of a pre-reaction complex, HO-HNO 3 (Aloisio and Francisco, 1999;Brown et al, 1999Brown et al, , 2001Xia and Lin, 2001;O'Donnell et al, 2008a). HO-HNO 3 can (a) dissociate into reactants, (b) rearrange to form products via a transition state which lies somewhat higher in energy than the reactants or (c) experience collisional deactivation by bath gas molecules.…”

Temperature (208–318 K) and pressure (18–696 Torr) dependent rate coefficients for the reaction between OH and HNO&lt;sub&gt;3&lt;/sub&gt;

“…Most of the experimental studies were carried out in the mid-70s to mid-80s (Margitan et al, 1975;Smith and Zellner, 1975;Wine et al, 1981;Jourdain et al, 1982;Kurylo et al, 1982;Margitan and Watson, 1982;Marinelli and Johnston, 1982;Ravishankara et al, 1982;Devolder et al, 1984;Smith et al, 1984;Connell and Howard, 1985;Jolly et al, 1985;Stachnik et al, 1986) with only the most recent and comprehensive studies of the reaction (Brown et al, 1999(Brown et al, , 2001 extending the temperature range to those found at the tropopause. Experimental (Carl et al, 2001;McCabe et al, 2003;O'Donnell et al, 2008b) and theoretical (Xia and Lin, 2001;Gonzalez and Anglada, 2010) work examining the details of the reaction mechanism highlight continuing interest in this complex reaction, which proceeds via formation of a pre-reaction complex, HO-HNO 3 (Aloisio and Francisco, 1999;Brown et al, 1999Brown et al, , 2001Xia and Lin, 2001;O'Donnell et al, 2008a). HO-HNO 3 can (a) dissociate into reactants, (b) rearrange to form products via a transition state which lies somewhat higher in energy than the reactants or (c) experience collisional deactivation by bath gas molecules.…”

Do We Still Need a Laboratory to Study Advanced Oxidation Processes? A Review of the Modelling of Radical Reactions used for Water Treatment

“…Another often-investigated ion influencing AOP and SR-AOP reactions is nitrate. The reaction with a hydroxyl radical of its conjugate acid (nitric acid) was investigated theoretically, and a hydrogen-bonded OH-HONO 2 intermediate was confirmed with an estimated lifetime of ∼40 ps [98]. A similar investigation was the subject of another work [73].…”