\begin{table}%t3
\caption{\label{sim_val}Defined binding, hopping and swapping energies of H$_2$O and~CO$_2$.}
%\centerline
{\begin{tabular}{c c}
\hline\hline 
Barrier type$^{a}$   &   Energy / K \\  
\hline
$\varepsilon_{\rm b}^{\rm H_2O-H_2O}$	  & 1000\\
$\varepsilon_{\rm b}^{\rm CO_2-CO_2}$	& 500 \\
$\varepsilon_{\rm b}^{\rm H_2O - CO_2}$ & 400\\
 $\varepsilon_{\rm h}^{\rm H_2O}$     & 2400 \\
$\varepsilon_{\rm h}^{\rm CO_2}$& 1200 \\
    $\varepsilon_{\rm s}^{\rm H_2O-CO_2}$ & 3600 \\
 $\varepsilon_{\rm s}^{\rm CO_2-H_2O}$     & 3600 \\
\hline
\end{tabular}}
\par
\medskip
$^{a}$ b  = binding, h = hopping, s = swapping.
\end{table}