\begin{table}%t
%\centering
\par
\caption{\label{tab1}Principal line identifications in the Mars FTS spectrum.}
\begin{tabular}{llll}
\hline\hline\noalign{\smallskip}
Line Number & Species   & Transition & Frequency (GHz)   \\
\hline 
1 & Ortho H$_2$O  & 1$_{10}$--1$_{01}$ & 556.94    \\
2 & CO            & $J=6$--5 & 691.491            \\
3 & Para H$_2$O   & 2$_{11}$--2$_{02}$ & 752.03    \\
4 & CO            & $J=7$--6 & 806.65            \\
5 & CO            & $J=8$--7 & 921.8             \\
6 & Para H$_2$O   & 2$_{02}$--1$_{11}$ & 987.93   \\
7 & CO            & $J=9$--8 & 1036.91            \\
8 & Ortho H$_2$O  & 3$_{12}$--3$_{03}$ & 1097.37    \\
9 & Para H$_2$O   & 1$_{11}$--0$_{00}$ & 1113.34    \\
10 & CO            & $J=10$--9 & 1152.01$^{*}$             \\
11 & Ortho H$_2$O  & 3$_{12}$--2$_{21}$ & 1153.13    \\
12 & Ortho H$_2$O  & 3$_{21}$--3$_{12}$ & 1162.91   \\
13 & Para H$_2$O   & 4$_{22}$--4$_{13}$ & 1207.64    \\
14 & Para H$_2$O   & 2$_{20}$--2$_{11}$ & 1228.79    \\
15 & CO            & $J=11$--10 & 1267.01            \\
16 & H$_2$O   & 6$_{25}$-5$_{32}$ & 1322.06                   \\
17 & CO            & $J=12$--11 & 1382.0            \\
18 & H$_2$O   & 5$_{23}$-5$_{14}$ & 1410.6                   \\
\hline
\end{tabular}
\tablefoot{The line to continuum ratios for  H$_2$O lines 11 and 12 are shown in Fig.~\ref{close} and for CO line 15 in Fig.~\ref{CO}. $^{*}$This line is blended with 11.}\vspace*{2.5mm}
\end{table}