Catalytic Role for Water in the Atmospheric Production of ClNO

Abstract

High level ab initio calculations of clusters comprised of water, HCl, and ON-ONO2 are used to study nitrosyl chloride (ClNO) formation in gas phase water clusters, which are also mimics for thin water films present at environmental interfaces. Two pathways are considered, direct formation from the reaction of gaseous HCl with ON-ONO2 and an indirect pathway involving the hydrolysis of ON-ONO2 to form HONO, followed by the reaction of HONO with HCl to form ClNO. Surprisingly, direct formation of ClNO is found to be the dominant channel in the presence of water despite the possibility of a competing hydrolysis of ON-ONO2 to form HONO. A single water molecule effectively catalyzes the ON-ONO2 + HCl reaction, and in the presence of two or more water molecules the reaction to form ClNO becomes spontaneous. Direct formation of ClNO is fast at room and ice temperatures, indicating the possible significance of this pathway for chlorine activation chemistry in both the polar and midlatitude troposphere, in volcanic plumes and indoors. The reaction enthalpies, activation energies, and rate constants for all studied reactions are reported. The results are discussed in light of recent experiments. Disciplines Chemistry CommentsReprinted (adapted) Jerusalem, 91904, Israel ReceiVed: December 24, 2009; ReVised Manuscript ReceiVed: February 21, 2010 High level ab initio calculations of clusters comprised of water, HCl, and ON-ONO 2 are used to study nitrosyl chloride (ClNO) formation in gas phase water clusters, which are also mimics for thin water films present at environmental interfaces. Two pathways are considered, direct formation from the reaction of gaseous HCl with ON-ONO 2 and an indirect pathway involving the hydrolysis of ON-ONO 2 to form HONO, followed by the reaction of HONO with HCl to form ClNO. Surprisingly, direct formation of ClNO is found to be the dominant channel in the presence of water despite the possibility of a competing hydrolysis of ON-ONO 2 to form HONO. A single water molecule effectively catalyzes the ON-ONO 2 + HCl reaction, and in the presence of two or more water molecules the reaction to form ClNO becomes spontaneous. Direct formation of ClNO is fast at room and ice temperatures, indicating the possible significance of this pathway for chlorine activation chemistry in both the polar and midlatitude troposphere, in volcanic plumes and indoors. The reaction enthalpies, activation energies, and rate constants for all studied reactions are reported. The results are discussed in light of recent experiments.

Computational Studies of Atmospherically-Relevant Chemical Reactions in Water Clusters and on Liquid Water and Ice Surfaces

“…18,19 ONONO 2 and N 2 O 5 are postulated to disproportionate on an aqueous surface, and theory supports incipient ionization. 11,13,18,19 Due to the level of quantum theory involved, these theoretical approaches model the aqueous layer by small water clusters. 18,19 More recent AIMD simulations of this system in a water slab geometry were performed, which employ a more realistic model of an extended aqueous surface.…”

“…11,13,18,19 Due to the level of quantum theory involved, these theoretical approaches model the aqueous layer by small water clusters. 18,19 More recent AIMD simulations of this system in a water slab geometry were performed, which employ a more realistic model of an extended aqueous surface. 17 Both cluster and bulk studies indicate that water has a profound influence on the oxide's geometry and promotes charge separation between fragments: (NO δ+ ,NO 3 δ− ) for ONONO 2 and (NO 2 δ+ ,NO 3 δ− ) for N 2 O 5 , forming a species more amenable to reaction.…”

Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol

“…[4][5][6][7][8] Such hydrated cluster environments may play a key role in interpreting chemical reactions that occur in the atmosphere where these species exist. [9][10][11][12][13][14][15][16][17][18][19][20][21] As a practical matter, theoretical simulations of the reaction dynamics can be greatly simplified in a cluster environment compared to solution since only a few water molecules need to be represented. While the detailed connection between cluster phase and solution phase chemistry has been the subject of great interest, it is not clear when a cluster is sufficiently large to model the solution.…”

Femtosecond timescale deactivation of electronically excited peroxides at ice surfaces

“…They serve as tropospheric 'minireactors'. Surface reactions of adsorbed molecules are believed to play a key role in atmospheric chemistry [11][12][13][14][15]. Much less is known concerning the role of ice particles in reactions and this is largely an open issue.…”