Thermal desorption of astrophysically relevant molecules from
  forsterite(010)
  We present temperature programmed desorption (TPD) measurements of CO,
CH$_4$, O$_2$ and CO$_2$ from the forsterite(010) surface in the sub-monolayer
and multilayer coverage regimes. In the case of CO, CH$_4$ and O$_2$,
multilayer growth begins prior to saturation of the monolayer peak, resulting
in two clearly distinguishable desorption peaks. On the other hand a single
peak for CO$_2$ is observed which shifts from high temperature at low coverage
to low temperature at high coverages, sharpening upon multilayer formation. The
leading edges are aligned for all the molecules in the multilayer coverage
regime indicating zero order desorption. We have extracted multilayer
desorption energies for these molecules using an Arrhenius analysis. For
sub-monolayer coverages, we observe an extended desorption tail to higher
temperature. Inversion analysis has been used to extract the coverage dependent
desorption energies in the sub-monolayer coverage regime, from which we obtain
the desorption energy distribution. We found that owing to the presence of
multiple adsorption energy sites on the crystalline surface the typical
desorption energies of these small molecules are significantly larger than
obtained in previous measurements for several other substrates. Therefore
molecules bound to crystalline silicate surfaces may remain locked in the solid
state for a longer period of time before desorption into the gas phase.
