A Revised Description of the Cosmic Ray-Induced Desorption of
  Interstellar Ices
  Non-thermal desorption of ices on interstellar grains is required to explain
observations of molecules that are not synthesized efficiently in the gas phase
in cold dense clouds. Perhaps the most important non-thermal desorption
mechanism is one induced by cosmic rays (CRs), which, when passing through a
grain, heat it transiently to a high temperature - the grain cools back to its
original equilibrium temperature via the (partial) sublimation of the ice.
Current cosmic-ray-induced desorption (CRD) models assume a fixed grain cooling
time. In this work we present a revised description of CRD in which the
desorption efficiency depends dynamically on the ice content. We apply the
revised desorption scheme to two-phase and three-phase chemical models in
physical conditions corresponding to starless and prestellar cores, and to
molecular cloud envelopes. We find that inside starless and prestellar cores,
introducing dynamic CRD can decrease gas-phase abundances by up to an order of
magnitude in two-phase chemical models. In three-phase chemical models our
model produces very similar results to the static cooling scheme - when only
one monolayer of ice is considered active. Ice abundances are generally
insensitive to variations in the grain cooling time. Further improved CRD
models need to take into account additional effects in the transient heating of
the grains, introduced for example by the adoption of a spectrum of CR
energies.
