\begin{table}%t1
\caption {\label{tab:ph_exps}Experimental parameters for UV-irradiation experiments.}            
%\centerline
 {\begin{tabular}{l c c c c}       
\hline\hline                
Exp. &Species &Temp.$^{a}$  & Thick. &UV flux\\
 & &(K) & (ML) &(10$^{13}$ cm$^{-2}$ s$^{-1}$)\\
\hline                % inserts double horizontal lines
1 &CH$_3$OH &20 &21 &1.1\\%done
2 &CH$_3$OH &30 &19 &1.1\\%done
3 &CH$_3$OH &50 &20 &1.1\\%done
4 &CH$_3$OH &70 &22 &1.1\\%done
5 &CH$_3$OH &20 &19 &4.3\\%done
6 &CH$_3$OH &50 &15 &4.3\\%done
7&CH$_3$OH:CO &20 &12:17 &1.1\\%done
8&CH$_3$OH:CO &30 &12:11 &1.1\\%done
9&CH$_3$OH:CO &50 &16:7 &1.1\\%done
10&CH$_3$OH:CH$_4$ &30 &11:27 &1.1\\%done
11&CH$_3$OH:CH$_4$ &50 &11:6 &1.1\\%done
12&CH$_3$OH:CO &20 &6:60 &1.1\\%done
13 &CH$_3$OH &20 &6 &1.1\\%
14 &CH$_3$OH &50 &6 &1.1\\%done
15 &CH$_3$OH &20 &4 &4.3\\%done
16 &CH$_3$OH &50 &8 &4.3\\%done
17$^{b}$  &CH$_3$OH &20 &18 &1.1\\%done
18$^{c}$ &CH$_3$OH &20 &20 &1.1\\%done
19 &CH$_3$OD &20 &$\sim$20 &1.1\\%done
20 &CH$_3$OD &50 &$\sim$20 &1.1\\%done
21 &CD$_3$OH &20 &$\sim$20 &1.1\\%9
22 &CD$_3$OH &50 &$\sim$20 &1.1\\
\hline
\end{tabular}}
\par
\smallskip
$^{ a}$ The ice-deposition and -irradiation temperature.\\
$^{ b}$ Following irradiation the ice is quickly heated to 50~K for 
2~h.\\
$^{c}$ Following irradiation the ice is quickly heated to 70~K for 
2~h.
\end{table}