Physisorption of CO.sub.2 on non-ice materials relevant to icy satellites

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.04.012 Byline: C.A. Hibbitts (a), J. Szanyi (b) Keywords: Spectroscopy; Satellites; composition; Jupiter; satellites; Saturn; satellites Abstract: CO.sub.2 is known to adsorb onto clay and other minerals when a significant atmospheric pressure is present. We have found that CO.sub.2 can also adsorb onto some clays when the CO.sub.2 partial pressure is effectively zero under ultra-high vacuum (UHV) if cooled to the surface temperatures of the icy satellites of Jupiter and Saturn. The strength of adsorption and the spectral characteristics of the adsorbed CO.sub.2 infrared (IR) [nu].sub.3 absorption band near 4.25 [mu]m depend on the composition and temperature of the adsorbent. CO.sub.2 remains adsorbed onto the clay mineral montmorillonite for 10 s of min when exposed to a vacuum of [approximately equal to]1x10.sup.-8 Torr at [approximately equal to]125 K. CO.sub.2 does not adsorb onto serpentine, goethite, or palagonite under these conditions. A small amount may adsorb onto kaolinite. When heated above 150 K under vacuum, the CO.sub.2 desorbs from the montmorillonite within a few minutes. The [nu].sub.3 absorption band of CO.sub.2 adsorbed onto montmorillonite at 125 K is similar to that of the CO.sub.2 detected on the saturnian and Galilean satellites and is markedly different from CO.sub.2 adsorbed onto montmorillonite at room temperature. We infer the adsorption process is physisorption and postulate that this mechanism may explain the presence and spectral characteristics of the CO.sub.2 detected in the surfaces of these outer satellites. Author Affiliation: (a) Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA (b) Pacific Northwest National Laboratories, EMSL, Richland, WA 99352, USA Article History: Received 31 December 2005; Revised 14 March 2007