Nitrate radical

{{for|the compound {{chem|N|2|O|3}}|dinitrogen trioxide}} {{Chembox | ImageFile = Nitrate radical overview.png | ImageFileL1 = Nitrate-3D-vdW.png | ImageFileR1 = Nitrate-3D-balls.png | OtherNames = Nitrooxy radical | IUPACName = Nitrate radical | SystematicName = Trioxidonitrogen(•) | Section1 = {{Chembox Identifiers | CASNo = 12033-49-7 | PubChem = 5360456 | ChEBI = 29329 | ChemSpiderID = 13268797 | Gmelin = 1573 | StdInChI=1S/NO3/c2-1(3)4 | StdInChIKey = YPJKMVATUPSWOH-UHFFFAOYSA-N | SMILES = [N+](=O)([O-])[O] }} | Section2 = {{Chembox Properties | N=1|O=3 }} }}

'''Nitrogen trioxide''' or '''nitrate radical''' is an oxide of nitrogen with formula {{chem|NO|3}}, consisting of three oxygen atoms covalently bound to a nitrogen atom. This highly unstable blue compound has not been isolated in pure form, but can be generated and observed as a short-lived component of gas, liquid, or solid systems.<ref name=wayne1991/>

Like nitrogen dioxide {{chem|NO|2}}, it is a radical (a molecule with an unpaired valence electron), which makes it paramagnetic. It is the uncharged counterpart of the nitrate anion {{chem|NO|3|−}} and an isomer of the peroxynitrite radical {{chem|OONO}}.<ref name=wayne1991/>

Nitrogen trioxide is an important intermediate in reactions between atmospheric components, including the destruction of ozone.<ref name="wayne1991">R. P. Wayne, I. Barnes, P. Biggs, J. P. Burrows, C. E. Canosa-Mas, J. Hjorth, G. Le Bras. G. K. Moortgat, D. Perner, G. Poulet, G. Restelli, and H. Sidebottom (1991): "The nitrate radical: Physics, chemistry, and the atmosphere". ''Atmospheric Environment. Part A. General Topics''. volume 25, issue 1, pages 1-203. {{doi|10.1016/0960-1686(91)90192-A}}</ref><ref name=grah1978>Richard A. Graham and Harold S. Johnston (1978): "The photochemistry of the nitrate radical and the kinetics of the nitrogen pentoxide-ozone system". ''Journal of Physical Chemistry'', volume 82, issue 3, pages 254-268. {{doi|10.1021/j100492a002}}</ref>

==History== The existence of the {{chem|NO|3}} radical was postulated in 1881-1882 by Hautefeuille and Chappuis to explain the absorption spectrum of air subjected to a silent electrical discharge.<ref name=wayne1991/>

==Structure and properties== The {{chem|NO|3}} radical does not react with water.<ref name=wayne1991/>

The absorption spectrum of {{chem|NO|3}} has a broad band for light with wavelengths from about 500 to 680&nbsp;nm, with three maxima in the visible at 590, 662, and 623&nbsp;nm. Absorption in the range 640–680&nbsp;nm does not lead to dissociation but to fluorescence: specifically, from about 605 to 800 nm following excitation at 604.4&nbsp;nm, and from about 662 to 800&nbsp;nm following excitation at 661.8&nbsp;nm.<ref name=wayne1991/> In water solution, another absorption band appears at about 330&nbsp;nm (ultraviolet). An excited state {{chem|NO|3|*}} can be achieved by photons of wavelength less than 595&nbsp;nm.<ref name=wayne1991/>

==Preparation== Nitrogen trioxide can be prepared in the gas phase by mixing nitrogen dioxide and ozone:<ref name=wayne1991/> : {{chem|NO|2}} + {{chem|O|3}} → {{chem|NO|3}} + {{chem|O|2}} This reaction can be performed also in the solid phase or water solutions, by irradiating frozen gas mixtures, flash photolysis and radiolysis of nitrate salts and nitric acid, and several other methods.<ref name=wayne1991/>

Nitrogen trioxide is a product of the photolysis of dinitrogen pentoxide {{chem|N|2|O|5}}, chlorine nitrate {{chem|ClONO|2}}, and peroxynitric acid {{chem|HO|2|NO|2}} and its salts.<ref name=wayne1991/>

:N₂O₅ → NO₂ + '''NO₃'''

:2 ClONO₂ → Cl₂ + 2 '''NO₃'''

== Atmospheric occurrence ==

=== Formation at night === In the atmosphere, the formation of nitrate radical also occurs from the reaction:<ref name="wayne1991" /><ref name=":1">{{Cite journal |last1=Brown |first1=Steven S. |last2=Stutz |first2=Jochen |date=2012 |title=Nighttime radical observations and chemistry |url=https://xlink.rsc.org/?DOI=c2cs35181a |journal=Chemical Society Reviews |language=en |volume=41 |issue=19 |pages=6405–6447 |doi=10.1039/c2cs35181a |pmid=22907130 |bibcode=2012CSRev..41.6405B |issn=0306-0012|url-access=subscription }}</ref><chem display="block">NO2 + O3 -> NO3 + O2</chem>NO<small>₃</small> concentrations maximize during the night due to the absence of photolysis.<ref name=":1" /> In its nightly abundance, the nitrate radical can oxidize volatile organic compounds (VOCs).<ref name=":1" /><ref name=":2">{{Cite journal |last1=Ng |first1=Nga Lee |last2=Brown |first2=Steven S. |last3=Archibald |first3=Alexander T. |last4=Atlas |first4=Elliot |last5=Cohen |first5=Ronald C. |last6=Crowley |first6=John N. |last7=Day |first7=Douglas A. |last8=Donahue |first8=Neil M. |last9=Fry |first9=Juliane L. |last10=Fuchs |first10=Hendrik |last11=Griffin |first11=Robert J. |last12=Guzman |first12=Marcelo I. |last13=Herrmann |first13=Hartmut |author13-link=Hartmut Herrmann|last14=Hodzic |first14=Alma |last15=Iinuma |first15=Yoshiteru |date=2017-02-13 |title=Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol |journal=Atmospheric Chemistry and Physics |language=English |volume=17 |issue=3 |pages=2103–2162 |doi=10.5194/acp-17-2103-2017 |doi-access=free |issn=1680-7316 |pmc=6104845 |pmid=30147712 |bibcode=2017ACP....17.2103N }}</ref>

When NO<small>₃</small> is formed, its subsequent reaction with nitrogen dioxide NO<small>2</small> produces dinitrogen pentoxide N₂O₅, which serves as a reservoir for NO<small>₃</small>:<ref name="wayne1991" /> <chem display="block">NO2 + NO3 + M -> N2O5 + M</chem>

=== Reaction with VOCs === As a dominant nighttime oxidizing agent, NO₃ reacts with a variety of VOCs, in which the mechanism and the rate of the reaction will depend on the species. As an example, oxygenates such as aldehydes are oxidized by abstracting an H-atom, resulting in nitric acid HNO₃ as one of the products.<ref name=":1" /> The lifetime of NO₃ in the presence of these compounds typically ranges from minutes to days.<ref name=":1" />

Conversely, unsaturated hydrocarbons (e.g. alkenes) are commonly oxidized by adding the nitrate radical to a carbon double bond.<ref name=":1" /> The reaction rates with these species are higher compared to those of oxygenates, notably affecting the abundance of the unsaturated hydrocarbons.<ref name=":1" /><ref name=":3">{{Cite journal |last1=Wang |first1=Jie |last2=Wang |first2=Haichao |last3=Tham |first3=Yee Jun |last4=Ming |first4=Lili |last5=Zheng |first5=Zelong |last6=Fang |first6=Guizhen |last7=Sun |first7=Cuizhi |last8=Ling |first8=Zhenhao |last9=Zhao |first9=Jun |last10=Fan |first10=Shaojia |date=2024-01-23 |title=Measurement report: Atmospheric nitrate radical chemistry in the South China Sea influenced by the urban outflow of the Pearl River Delta |url=https://acp.copernicus.org/articles/24/977/2024/ |journal=Atmospheric Chemistry and Physics |language=English |volume=24 |issue=2 |pages=977–992 |doi=10.5194/acp-24-977-2024 |bibcode=2024ACP....24..977W |doi-access=free |issn=1680-7316}}</ref> In forested areas, for instance, NO₃ can rapidly oxidize biogenic volatile organic compounds (BVOCs), such as terpenes and isoprene, which have been studied to contribute as a source of secondary organic aerosols (SOAs).<ref name=":1" /><ref name=":2" /><ref name=":3" />

=== Rapid daytime photolysis === The reaction that efficiently removes the nitrate radical from the troposphere during the day is its photolysis:<chem display="block">NO3 + hv -> NO2 + O</chem><chem display="block">NO3 + hv -> NO + O2</chem>in which the pathway followed will depend on the wavelength.<ref name="wayne1991" /><ref name=":1" /> When the sun is overhead, the photodissociation reaches maximum rates ranging from J = 0.02 to 0.2 s⁻¹.<ref name="wayne1991" /> Therefore, the daytime lifetime of NO₃ is usually less than 5 seconds.<ref name="wayne1991" /><ref name=":3" />

==References== <references> </references>

{{Nitrogen compounds}}

Category:Nitrogen oxides Category:Free radicals