\begin{table}%t1
\caption{Column densities and $^{16}$OH/$^{18}$OH ratios for the best fit carried out to the $^{16}$OH and $^{18}$OH ground state lines. Columns~1 and~2 show the Gaussian fit parameters from the \ion{H}{i} observations of \citet{garwood}.\label{tab_col}}
%\centerline
{\begin{tabular}{cccc}
\hline 
\hline 
Velocity       & {\it FWHM}         & $N({\rm ^{16}OH})$ & $^{16}$OH/$^{18}$OH \\
(km~s$^{-1}$)  & (km~s$^{-1}$)& ($10^{15}$~cm$^{-2}$) &  \\
\hline 
$-108\pm2$                    & $7\pm4$            & $0.56\pm0.39$    & $\rm 460^{+90}_{-50}$\\   
$-82\pm4$                     & $28\pm12$          & $9.0\pm3.9$      & $\rm 460^{+90}_{-50}$\\ 
$-44.0\pm0.6/(-52\pm6)^a$     & $8\pm2$ ($17\pm5$) & $3.5\pm1.8$      & $\rm 450^{+100}_{-60}$\\ 
$-24.4\pm0.8$                 & $14\pm2$           & $5.4\pm1.8$      & $\rm 370^{+110}_{-50}$\\ 
$+1.1\pm0.4$                  & $19\pm1$           & $7.6\pm3.4$      & $\rm 430^{+80}_{-40}$\\
$+15.7\pm0.3$                 & $7\pm1$            & $3.6\pm2.3$      & $\rm 360^{+80}_{-50}$\\
$+31\pm4$                     & $21\pm14$          & $5.4\pm3.8$      & $\rm 540^{+100}_{-50}$\\
$+66.7\pm0.5/(+52.8\pm0.9)^b$ & $16\pm1$ ($11\pm2$)& $\rm 32^{+6}_{-4}$   & $\rm 320^{+70}_{-30}$\\ 
\hline
Total       &         & 67.0                  &       \\
\hline 
\end{tabular}}
\par
\smallskip
$^a$ These two components are too close to separate in our model and the best fit line shape
requires only the $-44.0$~km~s$^{-1}$ component.\\
$^b$ The \ion{H}{i} data resolve 2 components in \object{Sgr~B2}. However, our fit requires
only one of these (at 66.7~km~s$^{-1}$) to reproduce the ISO spectrum.
\end{table}