Dust as interstellar catalyst - II. How chemical desorption impacts the
  gas
  Context. Interstellar dust particles, which represent 1% of the total mass,
are recognized to be very powerful interstellar catalysts in star-forming
regions. The presence of dust can have a strong impact on the chemical
composition of molecular clouds. While observations show that many species that
formed onto dust grains populate the gas phase, the process that transforms
solid state into gas phase remains unclear. Aims. The aim of this paper is to
consider the chemical desorption process, i.e. the process that releases solid
species into the gas phase, in astrochemical models. These models allow
determining the chemical composition of star-forming environments with an
accurate treatment of the solid-phase chemistry. Methods. In paper I we derived
a formula based on experimental studies with which we quantified the
efficiencies of the chemical desorption process. Here we extend these results
to astrophysical conditions. Results. The simulations of astrophysical
environments show that the abundances of gas-phase methanol and H2O2 increase
by four orders of magnitude, whereas gas-phase H2CO and HO2 increase by one
order of magnitude when the chemical desorption process is taken into account.
The composition of the ices strongly varies when the chemical desorption is
considered or neglected. Conclusions. We show that the chemical desorption
process, which directly transforms solid species into gas-phase species, is
very efficient for many reactions. Applied to astrophysical environments such
as Rho Oph A, we show that the chemical desorption efficiencies derived in this
study reproduce the abundances of observed gas-phase methanol, HO2, and H2O2,
and that the presence of these molecules in the gas shows the last signs of the
evolution of a cloud before the frost.
