Cosmic-Ray-Driven Chemistry in the CH₃CH₂OH/NH₃ Interstellar Ice Analog

Ethyl alcohol (CH3CH2OH) and ammonia (NH3) are prominent molecules in interstellar medium (ISM). Studying their astrochemically relevant reactions is crucial to advancing our understanding of astrochemical processes. To model astrochemically relevant ices on interstellar grain surfaces, pure CH3CH2OH, pure NH3, and CH3CH2OH/NH3 ices were deposited onto a cold substrate. The effects of cosmic ray irradiation, an important driver of ISM chemistry, were simulated by using 5 keV electron bombardment. Subsequently, the desorption of reaction products from the icy mantles into the gas phase was modeled through temperature-programed desorption (TPD). The compositional changes in the ice were continuously monitored during the TPD experiments. In separate experiments, desorbed molecules were captured and isolated in an Ar matrix for identification. Chemical changes were monitored by using Fourier transform infrared (FTIR) spectroscopy. Electron irradiation induced the formation of various species on the ices. For pure CH3CH2OH ice, the reaction products included CH4, CH3CH3, CH2CH2, CH3CH2CH3, CH2CHOH, CH2O, CH3CHO, CH2CO, CH3C(O)CH3, CH3COOH, CO, CO2, HĊO, H2ĊOH, CH3OH, CH2CHCHO, and HCOOH. For pure NH3 ice, the experimental results were consistent with previous studies. In the case of CH3CH2OH/NH3 ice mixtures, in addition to the products detected in single-component experiments, the formation of N- and O-containing organic molecules such as acetamide (CH3C(O)NH2), formamide (NH2CHO), and isocyanic acid (HNCO) was observed. These findings contribute to our understanding of the chemical evolution of prebiotic molecules in the ice phase of the ISM.