\begin{table}%t6
%\centering
\par
\caption{Reflection coefficient, $R$, as a function of the Mach number 
and $\chi$, the ratio of the temperature
of the CDL to the pre-shock temperature.
\label{tab:r_coeff}}
\begin{tabular}{l|llll}
\hline\hline
$M$ & \multicolumn{4}{c}{$\chi$} \\
    & 1.0 & 0.5 & 0.1 & 0.01 \\   
\hline
 1.40 & 0.075 & 0.239 & 0.567 & 0.839 \\
 2.00 & 0.115 & 0.261 & 0.575 & 0.842 \\
 3.00 & 0.199 & 0.342 & 0.632 & 0.866 \\
 5.00 & 0.356 & 0.490 & 0.731 & 0.906 \\
10.0  & 0.588 & 0.688 & 0.847 & 0.949 \\
20.0  & 0.765 & 0.828 & 0.919 & 0.974 \\
40.0  & 0.875 & 0.910 & 0.959 & 0.987 \\
100   & 0.948 & 0.963 & 0.983 & 0.995 \\ 
\hline
\end{tabular}
\end{table}