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Metastable Nitric Acid Trihydrate in Ice Clouds.

ABSTRACT: The composition of high-altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long-predicted phase, alpha-nitric acid trihydrate (alpha-NAT), is presented. This phase was characterized by a combination of X-ray and neutron diffraction experiments, allowing a convincing structure solution. Furthermore, vibrational spectra (infrared and inelastic neutron scattering) were recorded and compared with theoretical calculations. A strong interaction between water ice and alpha-NAT was found, which explains the experimental spectra and the phase-transition kinetics. On the basis of these results, we propose a new three-step mechanism for NAT formation in high-altitude ice clouds.

SUBMITTER: Weiss F

PROVIDER: S-EPMC4819521 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Metastable Nitric Acid Trihydrate in Ice Clouds.

Weiss Fabian F Kubel Frank F Gálvez Óscar Ó Hoelzel Markus M Parker Stewart F SF Baloh Philipp P Iannarelli Riccardo R Rossi Michel J MJ Grothe Hinrich H

Angewandte Chemie (International ed. in English) 20160216 10

The composition of high-altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long-predicted phase, alpha-nitric acid trihydrate (alpha-NAT), is presented. This phase was characterized by a combination of X-ray and neutron diffraction experiments, allowing a convincing structure solution. Furthermor ...[more]

PMID: 26879259

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