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P. A. Gerakines, M. H. Moore (NASA/GSFC), R. L. Hudson (Eckerd College \& NASA/GSFC)
The two most important energetic processes thought to drive interstellar and Solar-System ice chemistry (apart from purely thermal effects) are ultraviolet (UV) photolysis and exposure to cosmic rays. In the vast majority of the literature it has been assumed that both photolysis and cosmic-ray bombardment drive similar chemical reactions in icy materials, but no quantitative comparisons of UV- and ion-driven chemistries have ever been published. The cosmic-ice laboratory at NASA/GSFC is now capable of performing both UV photolysis and proton bombardment in the same experimental set-up, with samples created under the same conditions. Here we present direct quantitative comparisons of these effects on various mixtures of H2O, CO2, and CO (important molecules in both Solar-System and interstellar ices) at T=15-100 K. Equivalent energy doses have been applied in the form of UV photons (approx. 6 eV photon-1) or 0.8 MeV protons. Product formation rates are compared and differences discussed in terms of the radiation/ice interaction in each case. Ramifications are discussed for ices near protostars, on the surfaces of the Jovian satellites, and in comets.
P.A.G. holds a National Research Council-NASA/GSFC Research Associateship.