The chemical stability of CH3OH on cold interstellar grains: heat-induced dehydrogenation processes of methanol

International audienceIn interstellar media, stable hydrogen-containing molecules, like CH3OH, may be easily dissociated following irradiation by energetic cosmic rays, to form either stable or unstable chemical species. Laboratory experiments have already proved that when ices containing CH3OH are irradiated with high-energy photons or energetic particles, many chemical primary fragments are formed, due to the dissociation of C-H or O-H bonds. Are these hydrogen-containing molecules chemically stable in dark dust clouds? What is the behaviour of molecules like CH3OH in non-energy-induced processes? An understanding of the thermal reactions between methanol and radical species in their ground states at cryogenic temperatures is of primary importance in the astrochemical context. We experimentally show that the reaction between ground-state nitrogen atoms and CH3OH leads to dehydrogenation processes of methanol to form CH3O, H2CO and HCO chemical fragments via thermal chemistry initiated at temperatures below 10 K. These results underline the problem of the low chemical stability of some species formed and destroyed in interstellar media without any contribution of cosmic ray particles or high-energy photons