Formaldehyde and methylamine reactivity in interstellar ice analogues as a source of molecular complexity at low temperature

Université d’Aix-Marseille, Laboratoire de Physique des Interactions Ioniques et Moléculaires, UMR CNRS 7345, Centre de St-Jérôme, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France
e-mail: fabrice.duvernay@univ-amu.fr

Received: 9 July 2012
Accepted: 24 October 2012

Abstract

Context. Laboratory simulations on interstellar or cometary ice analogues are crucial to understand the formation of complex organic molecules that are detected in the interstellar medium (ISM). Results from this work give hints on physical and chemical processes occurring in space and can serve as a benchmark for dedicated space missions.

Aims. The aim of this work is to consolidate the knowledge of ice evolution during the star formation process by investigating the influence of thermal reactions as a source of molecular complexity in the ISM. In this study, we are interested in the thermal reactivity between two interstellar molecules, formaldehyde (H₂CO) and methylamine (CH₃NH₂) in water ice analogues.

Methods. We used Fourier transform infrared spectroscopy, mass spectrometry, and B3LYP calculations to investigate the thermal reaction between formaldehyde and methylamine (¹⁴N and ¹⁵N) at low temperature in water ice analogues.

Results. We demonstrate that methylamine and formaldehyde quickly react in water ice analogues for astronomically relevant temperatures and form N-methylaminomethanol CH₃NHCH₂OH. The measured activation energy of this reaction, 1.1 ± 0.05 kJ mol^-1 (1.8 ± 0.08 kJ mol^-1 with methylamine ¹⁵N), allows the reaction to proceed in interstellar ices, when the ices are gently warmed, as it occurs in young stellar objects, in photo-dissociation regions, or in comets. Therefore, CH₃NHCH₂OH is likely to be found in these objects. This hypothesis is confirmed by numerical simulations that clearly show that the formation of N-methylaminomethanol is likely at low temperature. Isotopic experiments as well as photochemical studies have also been performed to better characterise the ice evolution induced by heat and ultraviolet radiation during star formation.