Effects of 150–1000 eV Electron Impacts on Pure Carbon Monoxide Ices Using the Interstellar Energetic-Process System (IEPS)

Abstract

Pure CO ice has been irradiated with electrons of energy in the range 150 − 1000 eV with the Interstellar Energetic-Process System (IEPS). The main products of irradiation are carbon chains C n (n = 3, 5, 6, 8, 9, 10, 11, 12), suboxides, C n O (n = 2, 3, 4, 5, 6, 7), and C n O 2 (n = 1, 3, 4, 5, 7) species. CO 2 is by far the most abundant reaction product in all the experiments. The destruction cross-section of CO peaks at about 250 eV, decreases with the energy of the electrons and is more than one order of magnitude higher than for gas-phase CO ionization. The production cross-section of carbon dioxide has been also derived and is characterized by the competition between chemistry and desorption.Desorption of CO and of new species during the radiolysis follows the electron distribution in the ice. Low energy electrons having short penetration depths induce significant desorption. Finally, as the ice thickness approaches the electron penetration depth the abundance of the products starts to saturate. Implications on the atmospheric photochemistry of cold planets hosting surface CO ices are also discussed.

Electron-stimulated desorption from molecular ices in the sub-keV regime

“…Contrary to N 2 ice, a lot of chemistry can already happen during the irradiation of CO ice, as many carbon chain species can be formed. Refs 21,32 are examples of studies of the irradiation-induced chemistry in CO ice, which includes formation of many C n , C n O and C n O 2 species. Although we cannot probe the chemistry happening in the ice here, we can observe one of the main products desorbing in the gas phase, CO 2 .…”

“…The electron energy dependence in the sub-keV regime has been comparatively little explored. Two studies to our knowledge report desorption yield curves as a function of electron energies in this range 10,21 . Ref.…”

“…In ref. 21, the energy deposition profile of electrons in the ice is described and used to explain the observed electron energy dependence of electron-induced chemistry in CO ice. The results on electron-stimulated desorption are however not discussed.…”

Understanding the Molecular Kinetics and Chemical Equilibrium Phase of Frozen CO during Bombardment by Cosmic Rays by Employing the PROCODA Code

“…Carbon monoxide (CO) is one of the most abundant molecules throughout the universe, and, according to Huang et al (2020), serves as the dominant carbon reservoir in molecular gas. CO is not only ubiquitous in the gas phase of several regions of the interstellar medium (ISM; e.g., Lacy et al 1984;Ehrenfreund & Cami 2010, and references therein), but its detection in astrophysical ices in cold interstellar and circumstellar regions has also become routine (e.g., Herbst & van Dishoeck 2009;Boogert et al 2015, and references therein).…”

Density and Refractive Index of Carbon Monoxide Ice at Different Temperatures

“…In other scenarios, like in the ISM, the harsh irradiation conditions on CO act as a source for the formation of new species or changes in their structure. In the laboratory, these conditions have been reproduced to evaluate the formation of other species depending on whether pure CO is irradiated (van Dishoeck & Black 1988;Loeffler et al 2005;Jamieson et al 2006;Seperuelo-Duarte et al 2010;Ciaravella et al 2012;Huang et al 2020; or the irradiation involves a mixture of CO along with other species: N 2 , O 2 , H 2 O, CO 2 , NH 3 , CH 4 , or CH 3 F (Brucato et al 1997;Hudson & Moore 1999;Satorre et al 2000;Takano et al 2003;Bennett et al , 2010Bennett et al , 2011Kaiser et al 2014;Maity et al 2014;Lin et al 2019;Schmidt et al 2019;Turner et al 2021). Irradiation experiments have also been used to study the photodesorption of carbon monoxide (Muñoz Caro et al 2016).…”