Context. Studing chemical reactivity in astrophysical environments is an important means for improving our understanding of the origin of the organic matter in molecular clouds, in protoplanetary disks, and possibly, as a final destination, in our solar system. Laboratory simulations of the reactivity of ice analogs provide important insight into the reactivity in these environments. Here, we use these experimental simulations to investigate the Strecker synthesis leading to the formation of aminoacetonitrile in astrophysicallike conditions. The aminoacetonitrile is an interesting compound because it was detected in SgrB2, hence could be a precursor of the smallest amino acid molecule, glycine, in astrophysical environments. Aims. We present the first experimental investigation of the formation of aminoacetonitrile NH 2 CH 2 CN from the thermal processing of ices including methanimine (CH 2 NH), ammonia (NH 3 ), and hydrogen cyanide (HCN) in interstellar-like conditions without VUV photons or particules. Methods. We use Fourier Transform InfraRed (FTIR) spectroscopy to monitor the ice evolution during its warming. Infrared spectroscopy and mass spectroscopy are then used to identify the aminoacetonitrile formation. Results. We demonstrate that methanimine can react with − CN during the warming of ice analogs containing at 20 K methanimine, ammonia, and [NH + 4− CN] salt. During the ice warming, this reaction leads to the formation of poly(methylene-imine) polymers. The polymer length depend on the initial ratio of mass contained in methanimine to that in the [NH + 4− CN] salt. In a methanimine excess, long polymers are formed. As the methanimine is progressively diluted in the [NH + 4− CN] salt, the polymer length decreases until the aminoacetonitrile formation at 135 K. Therefore, these results demonstrate that aminoacetonitrile can be formed through the second step of the Strecker synthesis in astrophysical-like conditions.

HCN is a molecule central to interstellar chemistry, since it is the simplest molecule containing a carbon-nitrogen bond and its solid state chemistry is rich. The aim of this work was to study the NH 3 + HCN → NH + 4 CN − thermal reaction in interstellar ice analogues. Laboratory experiments based on Fourier transform infrared spectroscopy and mass spectrometry were performed to characterise the NH + 4 CN − reaction product and its formation kinetics. This reaction is purely thermal and can occur at low temperatures in interstellar ices without requiring non-thermal processing by photons, electrons or cosmic rays. The reaction rate constant has a temperature dependence of k(T ) = 0.016 +0.010 −0.006 s −1 exp( −2.7±0.4 kJ mol −1 RT ) when NH 3 is much more abundant than HCN. When both reactants are diluted in water ice, the reaction is slowed down. We have estimated the CN − ion band strength to be A CN − = 1.8±1.5×10 −17 cm molec −1 at both 20 K and 140 K. NH + 4 CN − exhibits zeroth-order multilayer desorption kinetics with a rate of k des (T ) = 10 28 molecules cm −2 s −1 exp( −38.0±1.4 kJ mol −1 RT ). The NH 3 + HCN → NH + 4 CN − thermal reaction is of primary importance because (i) it decreases the amount of HCN available to be hydrogenated into CH 2 NH, (ii) the NH + 4 and CN − ions react with species such as H 2 CO, or CH 2 NH to form complex molecules, and (iii) NH + 4 CN − is a reservoir of NH 3 and HCN, which can be made available to a high temperature chemistry.

Context. Aminoacetonitrile (AAN) has been detected in 2008 in the hot core SgrB2. This molecule is of particular interest because it is a central molecule in the Strecker synthesis of amino acids. This molecule can be formed from methanimine (CH 2 NH), ammonia (NH 3 ) and hydrogen cyanide (HCN) in astrophysical icy conditions. Nevertheless, few studies exist about its infrared (IR) identification or its astrophysical characterization. Aims. We present in this study a characterization of the pure solid AAN and when it is diluted in water to study the influence of H 2 O on the main IR features of AAN. The reactivity with CO 2 and its photoreactivity are also studied and the main products were characterized. Methods. Fourier transformed infrared (FTIR) spectroscopy of AAN molecular ice was performed in the 10-300 K temperature range. We used temperature-programmed desorption coupled with mass spectrometry detection techniques to evaluate the desorption energy value. The influence of water was studied by quantitative FTIR spectroscopy and the main reaction and photochemical products were identified by FTIR spectroscopy. Results. We determined that in our experimental conditions, the IR limit of AAN detection in the water ice is about 1 × 10 16 molecule cm −2 , which means that the AAN detection is almost impossible within the icy mantle of interstellar grains. The desorption energy of pure solid AAN is of 63.7 kJ mol −1 with ν 0 to 10 28 molecule cm −2 s −1 , which implies that the presence of this molecule in the gas phase is only possible in hot cores. The glycine (Gly) formation from the AAN through the last step of the Strecker synthesis seems to be impossible in astrophysical-like conditions. Furthermore, AAN is photoresistant to vacuum ultra-violet radiation, which emphasizes the fact that AAN can be considered as a Gly reservoir molecule.