Related Experiment Video
Updated: Mar 25, 2026

A Microfluidic Approach for the Study of Ice and Clathrate Hydrate Crystallization
Published on: August 18, 2022
Metastable Nitric Acid Trihydrate in Ice Clouds
Fabian Weiss1, Frank Kubel2, Óscar Gálvez3
1Institut für Materialchemie, Technische Universität Wien, Getreidemarkt 9/BC/01, 1060, Wien, Austria.
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.
Related Concept Videos
Reactions of Acid Anhydrides
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Overview
The nitrous acid is unstable. Hence, it is formed in situ from a solution of sodium nitrite and cold aqueous acids such as hydrochloric or sulfuric acid. In an acidic solution, the –OH group of nitrous acid undergoes protonation to give oxonium ion, followed by...
Preparation of Acid Anhydrides
The carboxylate ion acts as a nucleophile that attacks the carbonyl carbon of the acid chloride to form a tetrahedral intermediate. Subsequently, the re-formation of the carbonyl group with the loss of the chloride ion as a leaving group leads to the formation of an acid...
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism
The Equilibrium Constant
Phase Transitions: Sublimation and Deposition

