\begin{table}%t2
%%\centering

\par
\caption{\label{Mobile surface species}Mobile surface species.}
\begin{tabular}{llrl} 
\hline\hline\noalign{\smallskip}
     & Species    &    Adsorption         & Ref. \\
     &            &    Energy $E_D/k$ (K) &      \\
\hline
 1   &  $*$H      &    350.0   & 1 \\                  
 2   &  $*$H$_2$  &    450.0   & 1 \\                  
 3   &  $*$He     &    100.0   & 2 \\                 
 4   &  $*$C      &    800.0   & 1 \\                  
 5   &  $*$N      &    800.0   & 1 \\                  
 6   &  $*$O      &    800.0   & 1 \\                  
 7   &  $*$S      &   1100.0   & 1 \\                  
 8   &  $*$CH     &    645.0   & 3 \\                  
 9   &  $*$NH     &    604.0   & 3 \\                  
 10  &  $*$OH     &   1259.0   & 3 \\
 11  &  $*$CH$_2$ &    956.0   & 3 \\         
 12  &  $*$NH$_2$ &    856.0   & 3 \\        
 13  &  $*$CH$_3$ &   1158.0   & 3 \\         
 14  &  $*$NH$_3$ &   1107.0   & 3 \\         
\hline
\end{tabular}
\tablebib{(1) Tielens \& Allamandola (\cite{Tielens87});
(2) Tielens \& Hagen (\cite{Tielens82}); (3) Allen   \& Robinson    (\cite{Allen}).}
\end{table}