Dust as interstellar catalyst I. Quantifying the chemical desorption
  process
  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 CR 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 into astrochemical models. Methods. We present a
collection of experimental results of more than 10 reactive systems. For each
reaction, different substrates such as oxidized graphite and compact amorphous
water ice are used. We derive a formula to reproduce the efficiencies of the
chemical desorption process, which considers the equipartition of the energy of
newly formed products, followed by classical bounce on the surface. In part II
we extend these results to astrophysical conditions. Results. The equipartition
of energy describes correctly 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
to gas phase species is efficient for many reactions.
