Reactions initiated by radicals (HOx, NOx)

Main Research line: Atmospheric Chemistry
Main Researcher: Josep M. Anglada

Radicals are among the most reactive species in the atmosphere. The key chemical compounds are HOx (OH and HO2) and NOx (NO, NO2, and NO3) and these species are involved in catalytic cycles where they react and reform continuously.
Hydroxyl radical is the most important oxidizing species in the atmosphere. It reacts with almost all atmospheric trace gases so it is responsible for keeping the troposphere clean. This is why it is known as the “detergent of the atmosphere”.

Nitrogen oxides NO and NO2 play an important role in the formation and loss of tropospheric ozone, whereas NO3 is the most important atmospheric oxidant at night time. Nitrogen oxides react also with water vapor producing nitric acid (HNO3), which contributes to the acid rain and removes nitrogen oxides from the atmosphere.

What we do
We are interested in knowing the reactivity of radicals with different atmospheric trace gases. In most cases the oxidation reactions by these radicals takes place according to the well-known hydrogen abstraction mechanism, in which the radical abstracts one hydrogen atom from the species to be oxidized. However we have found that in other important processes the oxidation occurs by a proton coupled electron transfer mechanism, in which a proton is transferred from the trace gas to the radical and, simultaneously, one electron is transferred from a different side of the trace gas to the radical. In many of these cases the reactivity is enhanced.

The Figure shows the reaction mechanism for the oxidation of HNO3 by NH2 and the oxidation of NH3 by OH. The first one takes place through a proton coupled electron transfer mechanism and the second one involves a conventional hydrogen atom transfer mechanism. Both reactions can form a new atmospheric catalytic cycle. (J. Am. Chem. Soc., 2014, 136, 6834)

The Figure shows the reaction mechanism for the oxidation of HNO3 by NH2 and the oxidation of NH3 by OH. The first one takes place through a proton coupled electron transfer mechanism and the second one involves a conventional hydrogen atom transfer mechanism. Both reactions can form a new atmospheric catalytic cycle. (J. Am. Chem. Soc., 2014, 136, 6834)

Related publications

Santiago Olivella, Josep M. Anglada, Albert Solé,.Josep M. Bofill, Mechanisms of the Gas Phase Hydrogen Transfer from OH Group to Oxygen-Centered Radicals: Proton Transfer Coupled Electron Transfer versus Radical Hydrogen Abstraction, Chem.-Eur.J, 2004, 10, 3404

Josep M. Anglada, Complex Mechanism of the Gas Phase Reaction between formic Acid and Hydroxyl Radical. Proton Coupled Electron Transfer versus Radical Hydrogen Abstraction Mechnisms, J. Am. Chem. Soc, 2004, 126, 9809

Javier Gonzalez and Josep M. Anglada, Effect of a single water molecule in the gas phase oxidation of nitric acid by hydroxyl radical. A theoretical investigation, J. Phys. Chem. A, 2010, 114, 9151–9162

Josep M Anglada, Santiago Olivella, Albert Solé, Unexpected Reactivity of Amidogen Radical in the Gas Phase Degradation of Nitric Acid, J. Am. Chem. Soc, 2014, 136, 6834

J. Gonzalez ,J. M. Anglada, R. J. Buszek and J. S. Francisco, The Impact of Water on the OH + HOCl Reaction, J. Am. Chem. Soc, 2011, 133, 3345-3353

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