How chemistry influences cloud structure, star formation, and the IMF
  In the earliest phases of star-forming clouds, stable molecular species, such
as CO, are important coolants in the gas phase. Depletion of these molecules on
dust surfaces affects the thermal balance of molecular clouds and with that
their whole evolution. For the first time, we study the effect of grain surface
chemistry (GSC) on star formation and its impact on the initial mass function
(IMF). We follow a contracting translucent cloud in which we treat the
gas-grain chemical interplay in detail, including the process of freeze-out. We
perform 3d hydrodynamical simulations under three different conditions, a pure
gas-phase model, a freeze-out model, and a complete chemistry model. The models
display different thermal evolution during cloud collapse. The equation of
state (EOS) of the gas becomes softer with CO freeze-out and the results show
that at the onset of star formation, the cloud retains its evolution history
such that the number of formed stars differ (by 7%) between the three models.
While the stellar mass distribution results in a different IMF when we consider
pure freeze-out, with the complete treatment of the GSC, the divergence from a
pure gas-phase model is minimal. We find that the impact of freeze-out is
balanced by the non-thermal processes; chemical and photodesorption. We also
find an average filament width of 0.12 pc ($\pm$0.03 pc), and speculate that
this may be a result from the changes in the EOS caused by the gas-dust thermal
coupling. We conclude that GSC plays a big role in the chemical composition of
molecular clouds and that surface processes are needed to accurately interpret
observations, however, that GSC does not have a significant impact as far as
star formation and the IMF is concerned.
