Carbon dioxide segregation in 1:4 and 1:9 CO.sub.2:H.sub.2O ices

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.10.005 Byline: Robert Hodyss, Paul V. Johnson, Grazyna E. Orzechowska, Jay D. Goguen, Isik Kanik Keywords: Ices; Ices; IR spectroscopy; Satellites; surfaces; Photochemistry Abstract: The mid-infrared spectra of mixed vapor deposited ices of CO.sub.2 and H.sub.2O were studied as a function of both deposition temperature and warming from 15 to 100 K. The spectra of ices deposited at 15 K show marked changes on warming beginning at 60 K. These changes are consistent with CO.sub.2 segregating within the ice matrix into pure CO.sub.2 domains. Ices deposited at 60 and 70 K show a greater degree of segregation, as high as 90% for 1:4 CO.sub.2:H.sub.2O ice mixtures deposited at 70 K. As the ice is warmed above 80 K, preferential sublimation of the segregated CO.sub.2 is observed. The kinetics of the segregation process is also examined. The segregation of the CO.sub.2 as the ice is warmed corresponds to temperatures at which the structure of the water ice matrix changes from the high density amorphous phase to the low density amorphous phase. We show how these microstructural changes in the ice have a profound effect on the photochemistry induced by ultraviolet irradiation. These experimental results provide a framework in which observations of CO.sub.2 on the icy bodies of the outer Solar System can be considered. Author Affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA Article History: Received 25 June 2007; Revised 11 October 2007