Dust as interstellar catalyst
I. Quantifying the chemical desorption process
1 LERMA, Université de Cergy Pontoise, Observatoire de Paris, PSL Research University, Sorbonne Universités, UPMC Univ. Paris 06, CNRS UMR 8112, 5 mail Gay Lussac, 95000 Cergy Pontoise Cedex, France
2 Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
3 Max Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, 85741 Garching, Germany
4 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
Received: 27 February 2015
Accepted: 9 October 2015
Context. The presence of dust in the interstellar medium has profound consequences on the chemical composition of regions where stars are forming. Recent observations show that many species formed onto dust are populating the gas phase, especially in cold environments where UV- and cosmic-ray-induced photons do not account for such processes.
Aims. The aim of this paper is to understand and quantify the process that releases solid species into the gas phase, the so-called chemical desorption process, so that an explicit formula can be derived that can be included in astrochemical models.
Methods. We present a collection of experimental results of more than ten reactive systems. For each reaction, different substrates such as oxidized graphite and compact amorphous water ice were used. We derived a formula for reproducing the efficiencies of the chemical desorption process that considers the equipartition of the energy of newly formed products, followed by classical bounce on the surface. In part II of this study we extend these results to astrophysical conditions.
Results. The equipartition of energy correctly describes the chemical desorption process on bare surfaces. On icy surfaces, the chemical desorption process is much less efficient, and a better description of the interaction with the surface is still needed.
Conclusions. We show that the mechanism that directly transforms solid species into gas phase species is efficient for many reactions.
Key words: astrochemistry / solid state: refractory / solid state: volatile / ISM: abundances / ISM: molecules / molecular processes
© ESO, 2015