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Issue 16, 2018

Kinetics of the reaction of CO3˙(H2O)n, n = 0, 1, 2, with nitric acid, a key reaction in tropospheric negative ion chemistry

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Abstract

A significant fraction of nitrate in the troposphere is formed in the reactions of HNO3 with the carbonate radical anion CO3˙ and the mono- and dihydrated species CO3˙(H2O)1,2. A reaction mechanism was proposed in earlier flow reactor studies, which is investigated here in more detail by quantum chemical calculations and experimental reactivity studies of mass selected ions under ultra-high vacuum conditions. Bare CO3˙ forms NO3(OH˙) as well as NO3, with a total rate coefficient of 1.0 × 10−10 cm3 s−1. CO3˙(H2O) in addition affords stabilization of the NO3(HCO3˙) collision complex, and thermalized CO3˙(H2O) reacts with a total rate coefficient of 6.3 × 10−10 cm3 s−1. A second solvent molecule quenches the reaction, and only black-body radiation induced dissociation is observed for CO3˙(H2O)2, with an upper limit of 6.0 × 10−11 cm3 s−1 for any potential bimolecular reaction channel. The rate coefficients obtained under ultra-high vacuum conditions are smaller than in the earlier flow reactor studies, due to the absence of stabilizing collisions, which also has a strong effect on the product branching ratio. Quantum chemical calculations corroborate the mechanism proposed by Möhler and Arnold. The reaction proceeds through a proton-transferred NO3(HCO3˙) collision complex, which can rearrange to NO3(OH˙)(CO2). The weakly bound CO2 easily evaporates, followed by evaporation of the more strongly attached OH˙, if sufficient energy is available.

Graphical abstract: Kinetics of the reaction of CO3˙−(H2O)n, n = 0, 1, 2, with nitric acid, a key reaction in tropospheric negative ion chemistry

Supplementary files

Article information


Submitted
17 Nov 2017
Accepted
19 Feb 2018
First published
20 Feb 2018

This article is Open Access

Phys. Chem. Chem. Phys., 2018,20, 10838-10845
Article type
Paper

Kinetics of the reaction of CO3˙(H2O)n, n = 0, 1, 2, with nitric acid, a key reaction in tropospheric negative ion chemistry

C. van der Linde, W. K. Tang, C. Siu and M. K. Beyer, Phys. Chem. Chem. Phys., 2018, 20, 10838 DOI: 10.1039/C7CP07773D

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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