\begin{table}%t4
\caption{\label{prodiontot}Column ionization rates for electron precipitation  with Maxwellian spectra of different characteristic energies.}
\small%\centering
\par
\begin{tabular}[h]{lllc}
\hline\hline 
Species 			& \multicolumn{2}{c}{This work} 					& \citet{Perry99}			\\
 			& \multicolumn{1}{c}{1~keV}				& \multicolumn{1}{c}{50~keV}	&  \multicolumn{1}{c}{50~keV}				\\
\hline\noalign{\smallskip}
e$^-$				& $2.00 \times 10^{11}$	& $1.86 \times 10^{11}$		& $1.83 \times 10^{11}$	\\
H$^+$ from H		& $8.57 \times 10^8$	& $1.03 \times 10^7$		&  $2.38 \times 10^7$ 	\\
H$_2^+$ 			& $1.92 \times 10^{11}$	& $1.78 \times 10^{11}$	 	& $1.70 \times 10^{11}$ 	\\
H$^+$ from H$_2$	& $7.59 \times 10^9$	& $2.49 \times 10^9$		& $6.74 \times 10^9$ 	\\
He$^+$			& $1.89 \times 10^8$	& $5.08 \times 10^9$		& $6.12 \times 10^9$	\\
He$^{++}$		& $1.28 \times 10^7$	& $1.57 \times 10^8$		& 					\\
CH$_4^+$		& $5.57 \times 10^3$	& $1.80 \times 10^8$		& $6.12 \times 10^7$	\\
CH$_3^+$		& $4.28 \times 10^3$	& $1.38 \times 10^8$		& $5.84 \times 10^7$	\\
CH$_2^+$		& $7.21 \times 10^2$	& $2.05 \times 10^7$		& $8.28 \times 10^6$	\\
H (neutral dissociation of H$_2$)				& $1.18 \times 10^{11}$	& $1.12 \times 10^{11}$		&  					\\
\hline
\end{tabular} 
\end{table}