\begin{table}%t5
%\centering
\par
\caption{\label{tab:pdr}Physical conditions relevant to a dense PDR.}
\small \begin{tabular}{cc}
\hline\hline
Physical quantity    &  Value \\
\hline
\noalign{\smallskip}
$n_{\rm H}$  &  10$^4$ \ccm\\
$A_{\rm v}^{\rm tot}$ &  10   \\
size &   0.61~pc \\
 $\chi_{\rm left} $ &  100  \\
 $\chi_{\rm right}$ &  1  \\
 $T_{\rm gas}$   &   30~K  \\
 $T_{\rm dust}$   &  $A_{\rm v}$ dependent  \\
 size distribution of grains &  same as in Table~\ref{tab:model} \\
\noalign{\smallskip}
\hline
\end{tabular}
\end{table}