ONIOM QM/MM investigation of iodide oxidation by ozone on an aqueous particle
Authors: Roose Antoine , Toubin Céline , Réal Florent , Finkenzeller Henning , Volkamer Rainer , Ammann Markus , Vallet Valérie 
Published: March 2022

&lt;p&gt;Recently, Koenig et al. [1] measured both gas phase iodine species and particulate iodine (iodate and iodide) in the lower stratosphere indicating that tropospheric multiphase redox reactions prevent poorly soluble gaseous iodine species from removal by wet deposition leading to injections of inorganic iodine into the lower stratosphere. This may influence stratospheric ozone depletion both indirectly through activation of iodide to molecular halogens and directly through the aqueous phase reaction of ozone (O&lt;sub&gt;3&lt;/sub&gt;) with iodide [2]. The product of this reaction, IO&lt;sup&gt;-&lt;/sup&gt;, is reacting with I&lt;sup&gt;-&lt;/sup&gt; to I&lt;sub&gt;2&lt;/sub&gt;(g) under most circumstances. Sakamoto et al. [3] have suggested that in addition IO(g) may be formed. The primary reaction of iodide with O&lt;sub&gt;3&lt;/sub&gt; depends on pH. Solute strength effects and the extent of a surface reaction have not been sufficiently established [3,4].&lt;/p&gt;&lt;p&gt;An hybrid ONIOM QM/MM method [5] has been used to investigate the reactivity of ozone on a iodide-containing slab of water. The reaction pathway has been determined both at the interface and in the bulk aqueous phase. Both singlet and triplet state surfaces are investigated as the triplet state can be reached through photoexcitation of ozone or by spin state change along the reaction coordinate. These theoretical calculations provide insight into the uptake process at the molecular scale. Comparisons with experimental measurements performed using a trough reactor [6] coupled to Cavity Enhanced &amp;#8211; Differential Optical Absorption Spectroscopy (CE-DOAS) [7,8] are also discussed.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;br&gt;[1]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; T. K. Koenig &lt;em&gt;et al.&lt;/em&gt;, PNAS, &lt;strong&gt;117&lt;/strong&gt;, 4 (2020). &lt;br&gt;[2]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; L. J. Carpenter &lt;em&gt;et al.&lt;/em&gt;, Nat. Geosci., &lt;strong&gt;6&lt;/strong&gt; (2013).&lt;br&gt;[3]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; Y. Sakamoto &lt;em&gt;et al.&lt;/em&gt;, J. Phys. Chem. A, &lt;strong&gt;113&lt;/strong&gt;, 27 (2009).&lt;br&gt;[4]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; C. Moreno &lt;em&gt;et al.&lt;/em&gt;, Phys. Chem. Chem. Phys., &lt;strong&gt;22 &lt;/strong&gt;(2020)&lt;br&gt;[5]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; L. W. Chung &lt;em&gt;et al.&lt;/em&gt;, Chem. Rev., &lt;strong&gt;115&lt;/strong&gt;, 12 (2015)&lt;br&gt;[6]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; L. Artiglia &lt;em&gt;et al.&lt;/em&gt;, Nat. Commun., &lt;strong&gt;8&lt;/strong&gt; (2017)&lt;br&gt;[7]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; M. Wang &lt;em&gt;et al.&lt;/em&gt;, Atmos. Meas. Tech., &lt;strong&gt;14&lt;/strong&gt;, (2021).&lt;br&gt;[8]&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; R. Thalman and R. Volkamer, Atmos. Meas. Tech., &lt;strong&gt;3&lt;/strong&gt;, (2010).&lt;/p&gt;