In the interstellar medium, UV photolysis of ice mantles encasing dust grains is thought to be the mechanism that drives the synthesis of “complex” molecules. The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, high-energy cosmic rays penetrate and ionize the molecular clouds, generating secondary electrons. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. The UV light emitted by these electronically excited hydrogen molecules is generally thought to photoprocess interstellar ice mantles to generate “complex” molecules. In addition to producing UV light, the large numbers of low-energy (&lt; 20 eV) secondary electrons, produced by cosmic rays, can also directly initiate radiolysis reactions in the condensed phase. We hypothesize that cosmic-ray induced low-energy electron processing of interstellar ices may occur via three mechanisms:(1) the interaction of cosmic rays with gaseous molecular hydrogen producing low-energy electrons that can interact with the surface (top few molecular layers) of cosmic ices, (2) the interaction of cosmic rays with molecules within cosmic ices generating a cascade of low-energy electrons that can interact with the surface and the bulk of the ice mantles, (3) the interactions of the cosmic rays with the dust grain beneath the ice mantle engendering low-energy electrons that can interact with the bottom ice layers in contact with the dust grain. The goal of our studies is to understand the low-energy, electron-induced processes that occur when high-energy cosmic rays interact with interstellar ices. Using post-irradiation temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS), we have investigated the radiolysis initiated by low-energy (5 – 20 eV) electrons in condensed methanol, ammonia, and water at ~ 90 K under ultrahigh vacuum (1×10<sup>−9</sup> Torr) conditions. Our experimental results suggest that low-energy, electron-induced condensed phase reactions may contribute to the interstellar synthesis of “complex” molecules previously thought to form exclusively via UV photons.

Role of low-energy (<20 eV) electrons in astrochemistry

253rd National Meeting (2017)

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