Metastable nitric acid hydrates - Possible constituents of polar stratospheric clouds?

Abstract

Crystallization kinetics of the metastable modifications of Nitric Acid Dihydrate (NAD) was investigated by time-dependent X-Ray Diffraction (XRD) measurements. Kinetic conversion curves were evaluated adopting the Avrami model. The growth and morphology of the respective crystallites and particles were monitored in situ on the cryo-stage of an Environmental Scanning Electron Microscope (ESEM) under a partial pressure of nitrogen gas (0.5 Torr, 67 Pa). The morphologies were used to adapt the InfraRed (IR) extinction spectra by T-matrix calculation using respective optical indices of NAD. The results show a significant dependence of the band shapes on different morphologies. © The Royal Society of Chemistry.