Ion reactions in atmospherically-relevant clusters: mechanisms, dynamics and spectroscopic signatures

Abstract

Reactions of nitrogen oxides with seawater are of major atmospheric importance, but microscopic understanding of these processes is still largely unavailable. In this paper we explore models of reactions of N₂O₄ with ions in water in order to provide molecular-level understanding of the processes. Presented here are studies of N₂O₄ interacting with two ions, SO₄²⁻ and Cl⁻, in small water clusters. Reactions of the asymmetric conformer of N₂O₄ with SO₄²⁻ ions in water clusters are studied via ab initio molecular dynamics (AIMD) simulations in order to unravel the microscopic mechanism of the processes and predict the timescales of different steps. Spectroscopic signatures of the reaction are proposed. The mechanisms of chloride substitution and hydrolysis of symmetric and asymmetric N₂O₄ are explored via intrinsic reaction coordinate (IRC) calculations. Spectroscopic calculations for relevant species suggest possible experimental signatures for the processes. The results of these model ion-N₂O₄ reactions in water throw light on the molecular-level mechanisms of the reactions of nitrogen oxides with seawater.