Proton and Electron Irradiations of CH4:H2O Mixed Ices

Abstract

The organic chemistry occurring in interstellar environments may lead to the production of complex molecules that are relevant to the emergence of life. Therefore, in order to understand the origins of life itself, it is necessary to probe the chemistry of carbon-bearing molecules under conditions that simulate interstellar space. Several of these regions, such as dense molecular cores, are exposed to ionizing radiation in the form of galactic cosmic rays, which may act as an important driver of molecular destruction and synthesis. In this paper, we report the results of a comparative and systematic study of the irradiation of CH4:H2O ice mixtures by 1 MeV protons and 2 keV electrons at 20 K. We demonstrate that our irradiations result in the formation of a number of new products, including both simple and complex daughter molecules such as C2H6, C3H8, C2H2, CH3OH, CO, CO2, and probably also H2CO. A comparison of the different irradiation regimes has also revealed that proton irradiation resulted in a greater abundance of radiolytic daughter molecules compared to electron irradiation, despite a lower radiation dose having been administered. These results are important in the context of the radiation astrochemistry occurring within the molecular cores of dense interstellar clouds, as well as on outer Solar System objects.

Infrared Spectral Signatures of Nucleobases in Interstellar Ices I: Purines

“…However, the detection of purines (as well as other complex organic molecules) via infrared absorption spectroscopy presents several challenges, many of which were discussed in the works of Rosa et al [21,22]. One of the more noteworthy challenges is the fact that the infrared absorption spectrum of an astronomical target is densely populated by absorption bands: many of these bands are attributable to simple, volatile molecules that condense on interstellar dust grains in dense clouds to form an icy mantle, such as H 2 O, NH 3 , CH 4 , CO, and CH 3 OH [3,23,24], although some of these bands are also likely attributable to complex organic molecules that are synthesised as a result of the processing of these simple molecular ices by galactic cosmic rays and Lyman-α photons [1,[24][25][26][27][28][29][30].…”