Experimental investigation of aminoacetonitrile formation through the Strecker synthesis in astrophysical-like conditions: reactivity of methanimine (CH₂NH), ammonia (NH₃), and hydrogen cyanide (HCN)

¹ Université de Provence, Laboratoire de Physique des Interactions Ioniques et Moléculaires, Centre de St-Jérôme, Avenue Escadrille Normandie-Niemen, 13397 Marseille, France
e-mail: gregoire.danger@univ-provence.fr
² École Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France
³ Université Paris-Sud, Astrochimie et Origines, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France
⁴ CNRS, 91405 Orsay, France

Received: 30 June 2011
Accepted: 25 August 2011

Abstract

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 astrophysical-like 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 NH₂CH₂CN from the thermal processing of ices including methanimine (CH₂NH), ammonia (NH₃), 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 [NH₄^{+ −}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 [NH₄^{+ −}CN] salt. In a methanimine excess, long polymers are formed. As the methanimine is progressively diluted in the [NH₄^{+ −}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.