\begin{table}%t1
\caption{\label{con2exps}Summary of CO and N$_2$ experiments.} 
%\centerline
{\small  
\begin{tabular}{l l c c c} 
\hline\hline  \noalign{\smallskip}
Experiment & Composition & Temperature~(K) & Thickness (ML)&Lamp flux ($10^{13}$~photons~cm$^{-2}$~s$^{-1}$)\\ 
\hline  \noalign{\smallskip}
1&$^{13}$CO&15&4&4.7\\ 
2&$^{13}$CO&22&3.5&4.7\\ 
3&$^{13}$CO&27&3.5&4.7\\ 
4&$^{13}$CO$^{a \rm}$&16&3&4.7\\ 
5&$^{15}$N$_2$&16&4&4.7\\ 
6&$^{13}$CO:$^{15}$N$_2$ mixed&16&4:4&4.7\\%&0.18/0.08/0.04$^a$&\\
7&$^{15}$N$_2$/$^{13}$CO layered&16&1/4&4.7\\
\hline                                   
\end{tabular}}
\smallskip
$^{a}$ Annealed ice (i.e. deposited at 27~K and then cooled down to 16~K).
\par
\end{table}