\begin{table}%t4
  \caption{\label{tab:abu-cool}The different run models.}
 %\centerline
{ \begin{tabular}{cccccc}
    \hline
    Model & \textit{X}(CO)            & \textit{X}(O)             & \textit{X}(H$_2$O)$_{\rm out}$& \textit{X}(H$_2$O)$_{\rm in}$ & $G_0$\\ \hline\noalign{\smallskip}
    1$^a$ & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-8}$ & $1\times10^{-5}$ & 1\\
    2     & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-8}$ & $1\times10^{-6}$ & 1\\
    3     & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-8}$ & $1\times10^{-4}$ & 1\\
    4     & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-9}$ & $1\times10^{-5}$ & 1\\
    5     & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-7}$ & $1\times10^{-5}$ & 1\\
    6     & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-7}$ & $1\times10^{-4}$ & 1\\
    7     & $1\times10^{-4}$ & $5\times10^{-4}$ & $1\times10^{-8}$ & $1\times10^{-5}$ & 1000\\ \hline
  \end{tabular}}
 \smallskip   
 Columns 2 to 5 report 
    the adopted abundances of the main gas coolants: \textit{X}(CO), \textit{X}(O) and the 
    H$_2$O abundance in the $T \geq 100$~K region \textit{X}(H$_2$O)$_{\rm in}$ and outer 
    region \textit{X}(H$_2$O)$_{\rm out}$. Column~5 reports the FUV illuminating 
    field $G_0$. Note: $^a$~Model 1 is the reference for the studies of
    the water line spectrum presented in Sect.~\ref{sec:predicted-water-line}. 
  \end{table}