\begin{table}%t10
\caption{H$_2$ volume densities and \H\ and \D\ column densities, derived
in the LVG approximation.}
\label{tab_lvg}
%\centerline
{\small
\begin{tabular}{cccccc}
\hline \hline
    &  \multicolumn{2}{c}{\H\ } & & \multicolumn{2}{c}{\D\ } \\
%\cline{2-3} \cline{5-6}
 Source   &  $n_{\rm H_2}$ & $N({\rm N_2H^+})$ & &  $n_{\rm H_2}$ &  $N({\rm N_2D^+})$ \\
          & ($\times 10^{6}$ \cmc ) & ($\times 10^{13}$ \cmq ) & & ($\times 10^{6}$ \cmc ) & ($\times 10^{11}$ \cmq ) \\
\hline
05345+3157 &  2.4  &  3.2 & & 8.0  &   8.6 \\
05373+2349  &  2.8  &  5.0 & & 9.0 &  6.7 \\
18144+3157 &  1.6  &  11 & & -- & --  \\
18511+0146 &  1.0  &  3.9 & & -- & --  \\
18517+0437 &  1.7  &  3.5 & & -- & -- \\
19092+0841 &   1.3  &  7.2 & & -- & -- \\
20126+4104 &   2.6  &  8.6 & &  6.4 &  8.0 \\
20216+4107 &  1.5  &  1.1 & & 1.0 &  6.0 \\
20343+4129$^{a}$ &  0.4 & 4.0 &  &  3.0 &  2.9  \\
20343+4129$^{b}$ &  1.0 &  9.6  & & 6.0 & 30 \\
22172+5549 &   4.0  &    1.4 & & -- & -- \\
\hline
\end{tabular}
}
$^{a}$  Peak at ($-$8\arcsec , 4\arcsec ).
$^{b}$  Peak at (13\arcsec , 0\arcsec ).
\end{table}