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P. A. Gerakines (NRC/NAS & Code 691, NASA's Goddard Space Flight Center), M. H. Moore (Code 691, NASA's Goddard Space Flight Center), R. L. Hudson (Eckerd College)
It has recently been shown that CO2 is abundant in many lines of sight with a molecular cloud component, and comparisons with laboratory spectra suggest that some fraction of CO2 is intimately mixed with H2O and CH3OH (Gerakines et al. 1999). The two most important energetic processes thought to drive interstellar and Solar-System ice chemistries (apart from purely thermal effects) are ultraviolet (UV) photolysis and exposure to cosmic rays, but few quantitative comparisons of UV- and ion-driven chemistries have ever been published. The cosmic-ice laboratory at NASA's GSFC is 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, CH3OH and CO2 at T ~ 18\,K. Equivalent energy doses have been applied in the form of UV photons (approx. 10\,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 in the dense interstellar medium and in comets.
P.A.G. holds a National Research Council-NASA/GSFC Research Associateship.
Gerakines, P.A., Whittet, D.C.B., Ehrenfreund, P., et al., 1999, ApJ, 522, 357.