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

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

Article type
Paper
Submitted
17 11 2017
Accepted
19 2 2018
First published
20 2 2018
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2018,20, 10838-10845

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

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