\begin{table}%t7
\caption{\label{Table: max absorption}Estimated  largest possible absorption intensity~$T_{\rm b}$ at different observing frequencies for {\it optically thick  absorption  lines}  assuming that the background temperature is the~CMB.}
%\centering
\par
\begin{tabular}{c	c   c  c }
\hline \hline  \noalign{\smallskip}
Obs. Freq.  &  \multicolumn{3}{c}{Max intensity   $\mid T_{\rm b}\mid$}  \\
&$ T_{\rm ex}$ = 0  & $ T_{\rm ex}$ = $0.90$ $\times$ $T_{\rm CMB}$  & $ T_{\rm ex}$ = $0.98$ $\times$ $T_{\rm CMB}$  \\ 
 $[$GHz$]$ &	  [mK] &	  [mK] &	  [mK]\\
\hline
   1	& 2700	&	270  & 54  \\
50	& 1700	 &	250 		&	51 \\
100	& 1000	&	210		& 	42\\
200	& 290	&	97		&	21\\
300	& 73	&	33		&	7.5\\
400	& 17	&	9.1		&	2.2\\
500	& 3.6	&	2.2		&	0.6\\
600	& 0.74	&	0.5		&	0.1\\
\hline
\end{tabular}
\tablefoot {We have calculated this using  Eq.~(\ref{solution})  and  $T_{\rm ex}$~=~0, $ T_{\rm ex}$~= $0.90$~$\times$ $T_{\rm CMB}$  and $ T_{\rm ex}$~= $0.98$~$\times$ $T_{\rm CMB}$. Note that these values are {\it redshift \mbox{independent}}.}
\end{table}