\begin{table}%t2
%\centering
\par
\caption{\label{table:2}Fit with five parameters.} 
\small \begin{tabular}{c c c c c c} 
\hline\hline  
Data set & $A_1$ & $B_1$ &$A_2$ & $B_2$ &$D$  \\  
& $\sigma_{A1}$ & $\sigma_{B1}$ &$\sigma_{A2}$ & $\sigma_{B2}$ &$\sigma_D$\\ 
& $\left({{{\rm ppm}^2}\over{\mu{\rm Hz}}}\right)$ & (s) & $\left({{{\rm ppm}^2}\over{\mu{\rm Hz}}}\right)$ & (s) & $\left({{{\rm ppm}^2}\over{\mu{\rm Hz}}}\right)$\\  
\hline  \noalign{\smallskip}
   SPMb & 1.52 & 1292 &0.55 & 433 & \phantom{0}4 $\times  10^{-3}$   \\ 
        & 0.02 &   18 &0.02 & 12 & \phantom{0}3 $\times  10^{-3}$    \\ 
   SPMg & 0.74 & 1302 &0.25 & 419 & \phantom{0}1 $\times  10^{-3}$ \\
        & 0.02 & 37   &0.02 & 27 & \phantom{0}3 $\times  10^{-3}$ \\
   SPMr & 0.26 & 1321 &0.07& 403 & \phantom{0}1 $\times  10^{-3}$  \\
        & 0.02 &  105 &0.01& 89 & \phantom{0}3 $\times  10^{-3}$  \\
   PMO6 & 0.50 & 1349& 0.14& 439 & 20 $\times  10^{-3}$ \\
        & 0.02 & 55  & 0.02& 42 & \phantom{0}3 $\times  10^{-3}$  \\
\hline  
\end{tabular}
\end{table}