Carbon Cations and Silicon Atoms in the ISM: modeling their charge
  exchange reaction
  The time-dependent rate coefficients for the charge exchange reaction C+ + Si
-> C + Si+ for doublet and quartet states have been determined with ab initio
quantum calculations coupled with a non-adiabatic transition model based on a
simple Landau-Zener picture. This reaction plays a key role in determining the
abundances of C, Si, and their ions, in the ISM since these abundances affect
the fine structure cooling and hence the star formation rates. We also provide
additional calculations to evaluate the differences between the gas evolution
as obtained by using the empirical rate estimates found in the current
literature and the calculations presented in this work which are based on our
more realistic evaluation of such rates from ab initio transition probabilities
. We shall thus show here that the new rates yield important differences for
metal-rich environments where $T<10^4$ K and the UV flux is almost negligible,
while becoming less important at higher T values and higher photon fluxes.
