CARBON DIOXIDE INFLUENCE ON THE THERMAL FORMATION OF COMPLEXORGANIC MOLECULES IN INTERSTELLAR ICE ANALOGS

International audienceInterstellar ices are submitted to energetic processes (thermal, UV, and cosmic-ray radiations) producing complexorganic molecules. Laboratory experiments aim to reproduce the evolution of interstellar ices to better understandthe chemical changes leading to the reaction, formation, and desorption of molecules. In this context, the thermalevolution of an interstellar ice analogue composed of water, carbon dioxide, ammonia, and formaldehyde isinvestigated. The ice evolution during the warming has been monitored by IR spectroscopy. The formation ofhexamethylenetetramine (HMT) and polymethylenimine (PMI) are observed in the organic refractory residue leftafter ice sublimation. A better understanding of this result is realized with the study of another ice mixturecontaining methylenimine (a precursor of HMT) with carbon dioxide and ammonia. It appears that carbamic acid, areaction product of carbon dioxide and ammonia, plays the role of catalyst, allowing the reactions toward HMTand PMI formation. This is the first time that such complex organic molecules (HMT, PMI) are produced from thewarming (without VUV photolysis or irradiation with energetic particles) of abundant molecules observed ininterstellar ices (H2O, NH3, CO2, H2CO). This result strengthens the importance of thermal reactions in the ices’evolution. HMT and PMI, likely components of interstellar ices, should be searched for in the pristine objects ofour solar system, such as comets and carbonaceous chondrites