\begin{table}%t2
\caption{\label{C2-energy-rates}Rate coefficients for C$_2$ in the Red Rectangle at a distance of 6$''$ to the central star. }            
 %\centerline
{\small                         
\begin{tabular}{l l l l l l l l l}        
\hline\hline\noalign{\smallskip}
Number & Spontaneous & Rate\tablefootmark{a} & Number & Pumping & Rate\tablefootmark{a} & Number & Intercombination & Rate\tablefootmark{a}\\
& emission    & $k$ [s$^{-1}$] &  & transition & $k$ [s$^{-1}$] & & transition & $k$ [s$^{-1}$]\\
\hline\noalign{\smallskip}                        % inserts single horizontal line
1 & $A^1 \Pi_u$ $\rightarrow$ $X^1 \Sigma^+_g$ & 5.1(4) & 7 & $X^1\Sigma^+_g$ $\rightarrow$ $A^1 \Pi_u$	& 4.0($-4$) & 13 &  $a^3$ $\Pi_u$ 	$\rightarrow$ 	$X^1 \Sigma^+_g$ & 	3.8($-4$)\\
2 &   $A^1 \Pi_u$ $\rightarrow$ 	$X^1 \Sigma^+_g (v^*)$	&	2.0(4) & 8 & $X^1 \Sigma^+_g (v^*)$ $\rightarrow$ $A^1 \Pi_u$	& 1.9($-4$) & 14 & $a^3 \Pi_u (v^*)$$\rightarrow$  	$X^1 \Sigma^+_g (v^*)$	&	1.3($-2$)\\
3  &  $d^3 \Pi_g$ $\rightarrow$ 	$a^3 \Pi_u$			&	7.0(6) & 9 & $a^3$$\Pi_u$  $\rightarrow$ $d^3 \Pi_g$		& 1.7($-3$)&  15 & $X^1 \Sigma^+_g (v^*)$ $\rightarrow$ $a^3$$\Pi_u$ 	&	7.0($-2$)\\
4 &  $d^3 \Pi_g$ $\rightarrow$ 	$a^3 \Pi_u (v^*)$		&	2.3(6) & 10 & $a^3$$\Pi_u (v^*)$ $\rightarrow$ $d^3$$ \Pi$$_g$ & 7.1($-4$) & 16 &  $X^1 \Sigma^+_g (v^*)$ $\rightarrow$ $a^3 \Pi_u (v^*)$ 	&	5.5($-3$)\\
5 &  $d^3 \Pi_g (v^*)$	$\rightarrow$	$a^3$$ \Pi_u$		&	2.8(6) & 11 & $a^3$$\Pi_u$  $\rightarrow$ $d^3 \Pi_g (v^*)$		& 5.4($-4$) & 17 & $a^3 \Pi_u (v^*)$ $\rightarrow$ 	$X^1 \Sigma^+_g$	& 	1.0($-1$)\\
6 &  $d^3 \Pi_g (v^*)$	$\rightarrow$	$a^3 \Pi_u (v^*)$		&	7.8(6) & 12 & $a^3$$\Pi_u (v^*)$ $\rightarrow$ $d^3 \Pi_g (v^*)$	& 1.3($-3$)\\
\hline                                    %inserts single line
\end{tabular}}
\tablefoot{\tablefoottext{a}{Values in brackets give exponents to base 10.}}
\end{table}