Abstract During the star and planet formation, ultraviolet (UV) irradiation of ices on dust grain surfaces at low temperatures (∼10 −20 K) is considered an efficient pathway for interstellar complex organic molecules (iCOMs) in the inter- and circum-stellar medium (ISM/CSM). In this work, a series of laboratory experiments was performed to investigate the UV photo-processing of binary ice mixtures (CH4:O2) under the simulated astrophysical environments. A variety of newly formed products, e.g. CH2O, CH3OH, O3, CO, CO2, H2O, H2O2, HCOOH, CH3CH2OH, and CH3CHO, are observed and identified after UV irradiation. In addition, the photo-production rates of new species and the photo-destruction cross-sections of CH4/CD4 are also obtained. These experimental results provide key information for understanding the photo-chemical processing of CH4- and O2-containing ices under astronomically relevant conditions. Furthermore, the observation of some organic compounds (e.g. CH2O and CH3OH) and non-organic compounds (e.g. O3 and H2O) demonstrates that the ices of CH4 and O2 may play an essential role in the production of complex organic compounds and the evolution of circulated oxygen in space. Importantly, the formation reaction scheme of new species obtained here provides insight into the possible reaction pathways towards complex molecules observed from the ISM/CSM.
Ge et al. (Wed,) studied this question.