\begin{table}%t2
\par
\caption {\label{environments}Physical parameters for the typical interstellar phases \mbox{considered}.}
%\centerline
 {
\begin{tabular}{cccccc}
\hline
\hline
  & MC$^a$  & CNM$^b$ & WNM$^c$  & WIM$^d$  & Orion Bar \\
\hline
$G_{0}$                   & $0.01$    & $1$                  & $1$                & $1$        & $14~000$          \\
$n_{\rm H} \; (\rm{cm}^{-3})$ & $300$     & $30$                 & $0.4$              & 0.1        & $10^{4}$           \\
$T \; (\rm{K})$     & $20$      & $100$                & $6000$             & 8000       & $400$              \\
$n_{\rm e} \; (\rm{cm}^{-3})$ & $0.03$    & $0.045$              & $0.04$             & 0.1        & $3$                \\
$n_{\rm H^{+}}/n_{\rm H}$         & $0$       & $1.2 \times 10^{-3}$ & $0.1$              & 0.99        & $10^{-4}$          \\
$n_{\rm C^{+}}/n_{\rm H}$         & $10^{-4}$ & $1.3 \times 10^{-4}$   & $1.3 \times 10^{-4}$ & 10$^{-3}$  & $2 \times 10^{-4}$ \\
\hline
\end{tabular}}
\par
\smallskip
$n_{\rm H}$ the hydrogen density, $T$ the gas 
temperature, $n_{\rm e}$ the electrons density, $n_{\rm H^{+}}$ the proton density, and~$n_{\rm C^{+}}$ the density of atomic carbon ions.\\
$^a$ Molecular cloud.
$^b$ {Cold neutral medium.}
$^c$~{Warm neutral medium.}
$^d$~{Warm ionized medium.}
\end{table}