Ion irradiation of crystalline H.sub.2O-ice: Effect on the 1.65-[mu]m band

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.02.006 Byline: Rachel M.E. Mastrapa (a), Robert H. Brown (b) Keywords: Ices; Infrared observations; Kuiper belt objects; Radiation chemistry; Spectroscopy Abstract: We have found that 0.8 MeV proton irradiation of crystalline H.sub.2O-ice results in temperature dependent amorphization. The H.sub.2O-ice's phase was determined using the near infrared spectrum from 1.0 [mu]m (10,000 cm.sup.-1) to 2.5 [mu]m (4000 cm.sup.-1). In crystalline H.sub.2O-ice, the 1.65-[mu]m (6061 cm.sup.-1) band is strong while it is nearly absent in the amorphous spectrum [Schmitt, B., Quirico, E., Trotta, F., Grundy, W.M., 1998. In: Schmitt, B., de Bergh, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Norwell, MA, 1998, pp. 199-240]. In this experiment, at low temperatures (9, 25, and 40 K), irradiation of crystalline H.sub.2O-ice produced the amorphous H.sub.2O-ice's spectrum. However, at 50 K, some crystalline absorptions persisted after irradiation and at 70 and 100 K the crystalline spectrum showed only slight changes after irradiation. Our results agree with previous H.sub.2O-ice irradiation studies examining the crystalline peaks near 44 and 62 [mu]m by Moore and Hudson [Moore, M.H., Hudson, R.L., 1992. Astrophys. J. 401, 353-360] and near 3.07 [mu]m by Strazzulla et al. [Strazzulla, G., Baratta, G.A., Leto, G., Foti, G., 1992. Europhys. Lett. 18, 517-522] and by Leto and Baratta [Leto, G., Baratta, G.A., 2003. Astron. Astrophys. 397, 7-13]. We present a method of measuring band areas to quantify the phase and radiation dose of icy Solar System surfaces. Author Affiliation: (a) Astrophysics Branch, NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035-1000, USA (b) Department of Planetary Sciences, The University of Arizona, Tucson, AZ 85721, USA Article History: Received 6 December 2005; Revised 14 February 2006