Vacuum-Ultraviolet Optical Properties of Cryogenic Water Ices

The optical properties of cryogenic water ices in the vacuum-ultraviolet spectral range are studied.

The optical properties of crystalline and amorphous water ices in the temperature range from 20 K to 160 K in the vacuum-ultraviolet spectral range are relevant for all solar system icy bodies.  The change in the optical properties during the phase transition from amorphous to crystalline water ice is of great importance to the data-analysis during many NASA solar system missions, as for example  CASSINI. Preliminary results collected using the Synchrotron Ultraviolet Radiation Facility SURF III show greatly improved accuracy in the derived optical constants between 120 and 200 nm wavelength in comparison to previous measurements. The experimental set up consists of a 2.2 m normal-incidence monochromator and a custom-build chamber that allows the study of cyogenically grown ices. In a next step we plan to measure the effects of trace impurities of CO₂, CH₄, O₂, H₂O₂, polycyclic aromatic hydrocarbons, and NH₃ at 0.1%, 1%, and 10% concentration. Most ices in solar system bodies also contain organic contaminants and this work will improve our understanding of solar system planets and their moons.