\begin{table}%f3
\newcommand{\T}{\rule{0pt}{2.6ex}}
\newcommand{\B}{\rule[-1.2ex]{0pt}{0pt}}
\caption{Observed, beam averaged column densities of vinyl cyanide
(C$_2$H$_3$~CN) and vinyl acetylene (C$_2$H$_3$~CCH).}
\label{vinylcols}
%\centerline
{\begin{tabular}{lccccc}
\hline \hline
 & \multicolumn{2}{c}{\underline{C$_2$H$_3$~CN}$^{a}$} & &
 \multicolumn{2}{c}{\underline{C$_2$H$_3$~CCH}$^{a}$} \\
\T Source & $T_{\rm ex}$ & $N$ & & $T_{\rm ex}$ & $N$ \\
 & (K) & (cm$^{-2}$) & & (K) & (cm$^{-2}$) \\
\hline
\T Orion KL & 140 & $1.9 \times 10^{14}$ & & [150] & $<$$4.5 \times 10^{14}$  \\
W51 e1/e2 & [150] & $1.6 \times 10^{14}$ & & [150] & $<$$6.8 \times 10^{14}$ \\
S140 & [150] & $<$$1.0 \times 10^{13}$ & & [150] & $<$$2.4 \times 10^{14}$ \\
\B W3(OH) & [150] & $<$$1.3 \times 10^{13}$ & ~~~ & [150] & $<$$2.1 \times 10^{14}$ \\
\hline
\end{tabular}}
\medskip
\par
$^{a}$ Upper limits are taken at 3$\sigma$ noise-level
over 10 \kms, assuming the $T_{\rm ex}$ given in square brackets. 
\end{table}