Ion irradiation of crystalline H2O–ice: Effect on the 1.65-μm band

We have found that 0.8 MeV proton irradiation of crystalline H2O–ice results in temperature dependent amorphization. The H2O–iceʹs phase was determined using the near infrared spectrum from 1.0 μm (10,000 cm−1) to 2.5 μm (4000 cm−1). In crystalline H2O–ice, the 1.65-μm (6061 cm−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 H2O–ice produced the amorphous H2O–iceʹs 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 H2O–ice irradiation studies examining the crystalline peaks near 44 and 62 μm by Moore and Hudson [Moore, M.H., Hudson, R.L., 1992. Astrophys. J. 401, 353–360] and near 3.07 μm 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.