\begin{table}%t2
%\centering
\par
\caption{\label{tab2}Molecular column densities\tablefootmark{*}.}
\begin{tabular}{llcl}
\hline \hline \noalign{\smallskip}
\multicolumn{1}{l}{Mol} & \multicolumn{1}{c}{$T_{\rm rot}$} & 
\multicolumn{1}{l}{Observed} & \multicolumn{1}{c}{PDR Model}  \\ 
\multicolumn{1}{l}{} & \multicolumn{1}{c}{(K)} & 
\multicolumn{1}{c}{(cm$^{-2}$)} & \multicolumn{1}{c}{(cm$^{-2}$)}  \\ 
\hline\noalign{\smallskip}
$^{13}$CO  & 27   & $4.7 \times 10^{16}$ &   $3.5 \times 10^{16}$\tablefootmark{b}\\
C$^{18}$O  & 34   & $6.9 \times 10^{15}$ &   $3.5 \times 10^{15}$\tablefootmark{b}    \\
H$^{13}$CO$^+$  & 20\tablefootmark{c}   & $1.7 \times 10^{12}$\tablefootmark{c}    &  $9.3 \times 10^{11}$\tablefootmark{b} \\
CS & 25   & $6.3 \times 10^{13}$   &  $6.7 \times 10^{13}$     \\
o$-$H$_2^{18}$O     & 8.5\tablefootmark{a}   & $2.7 \times 10^{12}$    &  $2.9  \times 10^{12}$\tablefootmark{b,d}      \\
CH  & 19\tablefootmark{a} & $5.6 \times 10^{13}$    &  $3.3 \times 10^{14}$ \\
NH  & 10--20\tablefootmark{a}  & 1--$5 \times  10^{13}$   &  $5.1\times 10^{11}$ \\
\hline
\end{tabular}
\tablefoot{\tablefoottext{*}{The rotational diagrams used the 30~m and HIFI lines;}
\tablefoottext{a}{assumed rotational temperature;}
\tablefoottext{b}{assuming $^{12}$C/$^{13}$C~=~50 and $^{16}$O/$^{18}$O~=~500;}
\tablefoottext{c}{from Rizzo et~al. (2005);}
\tablefoottext{d}{assuming an ortho-to-para ratio of 3.}}
\end{table}