ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-3-1779-2003 FTIR spectroscopic studies of the simultaneous condensation of HCl and H2O at 190 K – Atmospheric applications Xueref I. 1 2 Dominé F. 1 Laboratoire de Glaciologie et de Géophysique de l’Environnement, CNRS, 54 rue Molière, B.P.96, 38402 Saint Martin d’Hères CEDEX, France Now at: Department of Earth and Planetary Sciences & Division of Engineering and Applied Sciences, Harvard University, 20 Oxford Street, Cambridge MA 02138, USA 27 10 2003 3 5 1779 1789 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/3/1779/2003/acp-3-1779-2003.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/3/1779/2003/acp-3-1779-2003.pdf

Type II polar stratospheric cloud particles are made up of ice that forms by water vapor condensation in the presence of numerous trace gases, including HCl. These gaseous species can co-condense with water molecules and perturb ice structure and reactivity. In order to investigate the effect of co-condensing dopants on the structure of ice, we have designed an experimental system where ice films can be stabilized at 190 K, a temperature relevant to the polar stratosphere. We have co-condensed different HCl:H<sub>2</sub>O gaseous mixtures, with ratios 5:1, 1:10, 1:50 and 1:200 and studied the solids formed by infrared spectroscopy. The IR spectra obtained show that: (1) HCl is likely undergoing ionic dissociation when it is incorporated by co-condensation into the ice at 190 K; (2) this dissociation is done by several water molecules per HCl molecule; and (3) significant differences between our spectra and those of crystalline solids were always detected, and indicated that in all cases the structure of our solids retained some disorganized character. Considering the major impact of HCl on ice structure observed here, and the well known impact of the structure of solids on their reactivity, we conclude that the actual reactivity of stratospheric ice particles, that catalyze reactions involved in ozone depletion, may be different from what has been measured in laboratory experiments that used pure ice.