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[128.06] Energetic Processing of H₂O:CH₃OH:CO₂ Interstellar Ice Analogs: UV Photolysis vs. Ion Bombardment

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.

Reference:

Gerakines, P.A., Whittet, D.C.B., Ehrenfreund, P., et al., 1999, ApJ, 522, 357.