\begin{table}%t1
\caption{Overview of the processes included in the ISM~model used. For~H and He~ionization equilibrium is explicitly calculated, for other elements collisional ionization equilibrium~(CIE) is assumed. Both the heating and cooling strongly depend on the ionization fraction~$x_{\rm e}$. Exact expressions adopted for the various processes can be found in: 
1) Wolfire et~al. (\citeyear{WHMTB95}); 2) Raga et~al. (\citeyear{RML97}); 
3) Verner \& Ferland (\citeyear{VF96}); 4) Silva \& Viegas (\citeyear{SV01}).} \label{ism_tbl}
%\centering
\par
\begin{tabular}{lcl}
\hline  \hline
 Process &             Comment &             Ref.    \\
 \hline
 \emph{Heating} & & \\
 ~~Cosmic Ray & ionization rate $\rm \zeta_{CR}=1.8$~$\times$ $10^{-17}~{\rm s}^{-1}$   & 1  \\
 ~~Photo Electric & FUV field from stars & 1  \\
\hline
 \emph{Cooling} & & \\
 ~~$e$,H$_0$ impact   & H, He, C, N, O, Si, Ne, Fe & 2, 4 \\
\hline
 \emph{Ionization} & & \\
 \emph{~\& recombination} & & \\
 ~~UV & ionization assumed for & \\
      & species with $E_i< 13.6 \rm{eV}$ &  \\
 ~~Cosmic Ray & H, He only; primary & 1 \\
            & \& secondary ionizations & \\
 ~~Collisional & H, He only & 3 \\
 ~~Radiative recombination & H, He only & 3 \\	    
 ~~CIE & assumed for metals & \\ 
\hline	     	 	 
\end{tabular} 
\end{table}