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Resolving the HONO formation mechanism in the ionosphere via ab initio molecular dynamic simulations.

ABSTRACT: Solar emission produces copious nitrosonium ions (NO(+)) in the D layer of the ionosphere, 60 to 90 km above the Earth's surface. NO(+) is believed to transfer its charge to water clusters in that region, leading to the formation of gaseous nitrous acid (HONO) and protonated water cluster. The dynamics of this reaction at the ionospheric temperature (200-220 K) and the associated mechanistic details are largely unknown. Using ab initio molecular dynamics (AIMD) simulations and transition-state search, key structures of the water hydrates-tetrahydrate NO(+)(H2O)4 and pentahydrate NO(+)(H2O)5-are identified and shown to be responsible for HONO formation in the ionosphere. The critical tetrahydrate NO(+)(H2O)4 exhibits a chain-like structure through which all of the lowest-energy isomers must go. However, most lowest-energy isomers of pentahydrate NO(+)(H2O)5 can be converted to the HONO-containing product, encountering very low barriers, via a chain-like or a three-armed, star-like structure. Although these structures are not the global minima, at 220 K, most lowest-energy NO(+)(H2O)4 and NO(+)(H2O)5 isomers tend to channel through these highly populated isomers toward HONO formation.

SUBMITTER: He R

PROVIDER: S-EPMC4855577 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Resolving the HONO formation mechanism in the ionosphere via ab initio molecular dynamic simulations.

He Rongxing R Li Lei L Zhong Jie J Zhu Chongqin C Francisco Joseph S JS Zeng Xiao Cheng XC

Proceedings of the National Academy of Sciences of the United States of America 20160411 17

Solar emission produces copious nitrosonium ions (NO(+)) in the D layer of the ionosphere, 60 to 90 km above the Earth's surface. NO(+) is believed to transfer its charge to water clusters in that region, leading to the formation of gaseous nitrous acid (HONO) and protonated water cluster. The dynamics of this reaction at the ionospheric temperature (200-220 K) and the associated mechanistic details are largely unknown. Using ab initio molecular dynamics (AIMD) simulations and transition-state s ...[more]

PMID: 27071120

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Resolving the HONO formation mechanism in the ionosphere via ab initio molecular dynamic simulations.

Publications

Resolving the HONO formation mechanism in the ionosphere via ab initio molecular dynamic simulations.

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