ContextMethods. Infrared and mass spectroscopy are used to monitor NH 3 :CO 2 ice mixture evolution during both warming and VUV photon irradiation.Results. Carbamic acid and ammonium carbamate can be produced thermally in a 1:1 ratio from NH 3 and CO 2 above 80 K. They can be also formed in a 28:1 ratio by less efficient processes such as energetic photons. Our study and its results provide fresh insight into carbamic acid formation in interstellar ices. Conclusions. We demonstrate that care is required to separate irradiation-induced reactivity from purely thermal reactivity in ices in which ammonia and carbon dioxide are both present. From an interstellar chemistry point of view, carbamic acid and ammonium carbamate are readily produced from the ice mantle of a typical interstellar grain and should therefore be a detectable species in molecular clouds.

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Aminomethanol (NH 2 CH 2 OH) is formed at low temperature from the purely thermal reaction of NH 3 and H 2 CO in laboratory interstellar ice analogs. We report for the first time its infrared and mass spectra. We study its reaction and desorption kinetics using Fourier transform infrared spectroscopy and mass spectrometry. Its reaction rate is estimated to be k(T ) = 0.05 × exp(−4.5(kJ mol −1 )/RT ) and its desorption energy to be E des = 58 ± 2 kJ mol −1 . NH 2 CH 2 OH can also contribute to the 5-8 μm region of thermally processed ices encountered in many young stellar objects. Gas phase NH 2 CH 2 OH may be present in hot core regions, when the frozen material is desorbed.

We study low temperature reactivity of methylamine (CH3NH2) and carbon dioxide (CO2) mixed within different ratios, using FTIR spectroscopy and mass spectrometry. We report experimental evidence that the methylammonium methylcarbamate [CH3NH3(+)][C3NHCO2(-)] and methylcarbamic acid (CH3NHCOOH) are formed when the initial mixture CH3NH2:CO2 is warmed up to temperatures above 40 K. An excess of CH3NH2 favors the carbamate formation while an excess of CO2 leads to a mixture of both methylammonium methylcarbamate and methylcarbamic acid. Quantum calculations show that methylcarbamic acid molecules are associated into centrosymmetric dimers. Above 230 K, the carbamate breaks down into CH3NH2 and CH3NHCOOH, then this latter dissociates into CH3NH2 and CO2. After 260 K, it remains on the substrate a solid residue made of a well-organized structure coming from the association between the remaining methylcarbamic acid dimers. This study shows that amines can react at low temperature in interstellar ices rich in carbon dioxide which are a privileged place of complex molecules formation, before being later released into "hot core" regions.