\begin{table}%t4
\caption{
\small Results of PDR model calculations for ensembles of clumps having
same mass and density. $\phi_{\rm A}$ is the area filling factor of the
clumps.
\label{tab_ens}}
\begin{tabular}{lllllll}
\hline
\hline
($n_{\rm cl}$,~ $\chi$) & $N$(H$_2$)$_{\rm ens}$ & $M_{\rm ens}$ & $M_{\rm cl}$ & $N_{\rm ens}$ &
\cbyco$_{\rm ens}$ & $\Phi_{\rm A}$\\
(\cmcub, $\ast$)  & cm$^{-2}$ & \msun\ & \msun\ &  &  & \\
\hline\noalign{\smallskip}
                &  $4.0\times10^{21}$  &	2.9 &    0.001 & 2859  &    0.43  &   3.3\\
                &  $7.0\times0^{21}$  &	5.0 &    0.01 &  500  &    0.22  &   2.7\\
(10$^5$, 10$^2$) &  $1.2\times10^{22}$  &	8.6 &    0.1 &   86  &    0.11  &   2.2\\
                &  $2.3~\times10^{22}$  &    16.4 &    1.0 &   16  &    0.06  &   1.9\\
                &  $4.0\times10^{22}$  &    28.6 &     10 &    3  &    0.03  &   1.6\\
\hline
\par
                & $2.0\times10^{21}$  &     1.4 &    0.001 & 1429 &  1.14  &   1.7\\
                & $6.0\times10^{21}$  &     4.3 &    0.01 &  429 &  0.22  &   2.3\\
(10$^5$, 10$^3$) & $1.1\times10^{22}$  &     7.9 &    0.1 &   79 &  0.13  &   2.0\\
                & $1.9\times10^{22}$  &    13.6 &    1.0 &   14 &  0.07  &   1.6\\
                & $3.7\times10^{22}$  &    26.4 &     10  &    3&   0.04  &   1.6\\
\hline
\par
                &  $3.0\times10^{21}$  &	2.1 &    0.1 &   21 & 0.9  & 2.4\\
(10$^4$, 10$^3$) &  $6.0\times10^{21}$  &	4.3 &    1.0 &    4 & 0.4  & 2.2\\
                &  $9.0\times10^{21}$  &	6.4 &   10 &    1 & 0.3  & 2.5\\
\hline
\end{tabular}
\par
$\ast$ In Draine units.
\end{table}