While gas-phase reactions and surface reactions on bare carbonaceous or silicaceous dust grains contribute to cosmic chemistry, energetic processing via photochemistry and radiation chemistry of cosmic ices is thought to be the dominant mechanism for the cosmic synthesis of prebiotic molecules. Radiation chemistry is defined as the “study of the chemical changes produced by the absorption of radiation of sufficiently high energy to produce ionization.” Ionizing radiation in cosmic chemistry includes high-energy particles (e.g., cosmic rays consisting mostly of protons) and high-energy photons (e.g., extreme-UV (12.4 –124 eV), X-rays, and γ-rays). In contrast, photochemistry is defined as photon-induced electronic excitation not involving ionization. In addition to photochemistry, vacuum-UV (6.2 –12.4 eV) light may initiate radiation chemistry because the threshold for producing low-energy electrons in condensed matter is lower than the gas phase ionization energy for a given molecule. For example, photoelectric emission threshold of condensed water is ~10.2 eV, which is smaller than the gas phase ionization energy of 12.6 eV for gaseous water. Because most previous astrochemical studies have used light sources that produce &gt; 10 eV photons, discerning the role of photochemistry vs. radiation chemistry in astrochemistry is challenging. We will compare and contrast previous radiolysis and photolysis studies of three important cosmic ice constituents: water, methanol, and ammonia.

Photochemistry and radiation chemistry of cosmic ice analogs

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.