Solid-state production of complex organic molecules: H-atom addition versus UV irradiation

摘要

Complex organic molecules (COMs) have been observed in comets, hot cores andcold dense regions of the interstellar medium. It is generally accepted thatthese COMs form on icy dust grain through the recombination reaction ofradicals triggered by either energetic UV- photon or non-energetic H-atomaddition processing. In this work, we present for the first time laboratorystudies that allow for quantitative comparison of hydrogenation and UV-inducedreactions as well as their cumulative effect in astronomically relevantCO:CH3OH=4:1 ice analogues. The formation of glycolaldehyde (GA) and ethyleneglycol (EG) is confirmed in pure hydrogenation experiments at 14 K, exceptmethyl formate (MF), which is only clearly observed in photolysis. Thefractions for MF:GA:EG are 0 : (0.2-0.4) : (0.8-0.6) for pure hydrogenation,and 0.2 : 0.3 : 0.5 for UV involving experiments and can offer a diagnostictool to derive the chemical origin of these species. The GA/EG ratios in thelaboratory (0.3-1.5) compare well with observations toward different objects.