\begin{table}%t8
%\centering
\par
\caption {\label{ratios}$J=3\rightarrow 2/1\rightarrow 0$ integrated intensity ratios. Data were taken 
from JS06 and this paper.}
\begin{tabular}{lcccccc}
\hline \hline
\noalign{\smallskip}
&  \multicolumn{2}{c} {(0,~20)}&   \multicolumn{2}{c} {(20,~0)}& \multicolumn{2}{c} {(--20,~0)} \\ \cline{2-3} \cline{4-5} \cline{6-7}
  Molecule   &  Ambient   &   Precursor &   Ambient  &    Precursor  &    Ambient     &  Precursor\\       
\hline
  H$^{13}$CO$^+$ &      0.2  & 0.5 & $\la $0.2 & 0.4  &  $\la $0.2 &   0.09 \\
HN$^{13}$C &    $\la $0.1 &  $\la $0.3 &$\la $0.1& $\la $0.1&   $\la $0.1 & $\la $0.3\\  
\par
\hline \hline
&  \multicolumn{2}{c} {(0,~0)}&   \multicolumn{2}{c} {(0, --10)}& \multicolumn{2}{c} {(0, --20)} \\ \cline{2-3} \cline{4-5} \cline{6-7}
 Molecule   &  Ambient   &   Precursor &   Ambient  &    Precursor  &    Ambient     &  Precursor\\       
\hline
  H$^{13}$CO$^+$ &  0.5 & 1.6 & $\la$0.1 & 0.6  & $\la$0.5  & 0.2   \\
HN$^{13}$C & 0.4  & $\la$0.2  & $\la$0.2 &$\la$0.1  & $\la$0.2 &$\la$0.3 \\ \hline
\end{tabular}
\end{table}