Aminoacetonitrile characterization in astrophysical-like conditions

Aix-Marseille Université et CNRS, Laboratoire de Physique des Interactions Ioniques et Moléculaires, UMR 7345, Centre de St-Jérôme, case 252, Avenue Escadrille Normandie-Niémen, 13397 Marseille Cedex 20, France
e-mail: Fabien.Borget@univ-amu.fr

Received: 2 February 2012
Accepted: 23 March 2012

Abstract

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 (CH₂NH), ammonia (NH₃) 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 H₂O on the main IR features of AAN. The reactivity with CO₂ 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  ×  10¹⁶ 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 ν₀ to 10²⁸ 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.