\begin{table}%t9
\caption{\label{table:ion}Parameters derived in Sect.~4.4.}
%\centerline
 {
\begin{tabular}{c c c c c c c c}
\hline\hline\\[-3.2mm]
Source & $x({\rm H_2D^+})$ & $x({\rm H_3^+})$ & $x({\rm e})_l$$^{a}$ & $x({\rm e})_u$ & $\langle x({\rm e}) \rangle$$^{b}$ & $\zeta_{\rm H_2}$$^c$ & $C_i$\\[0.5mm]
 & [$10^{-9}$] & [$10^{-8}$] & [$10^{-8}$] & [$10^{-7}$] & [$10^{-7}$] & [$10^{-16}$ s$^{-1}$] & [$10^3$~cm$^{-3/2}$ s$^{1/2}$]\\
\hline
Ori~B9~E & 2.0 & 1.8 & 2.0/3.0 & 6.4 & 3.4 & 2.0/1.0 & 2.6\\
Ori~B9~N & 1.0 & 0.9 & 1.0/2.0 & 6.3 & 3.3 & 2.5/1.3 & 4.1\\
\hline
\end{tabular}}
\medskip
\par
$^{a}$ The first value is calculated from Eq.~(\ref{eq:low_x(e)}), whereas the second value is calculated from Eq.~(\ref{eq:lowxe2}).
$^{b}$ This is the mean value between the lower and upper limit, where $x({\rm e})_l$ is calculated from Eq.~(\ref{eq:lowxe2}).
$^{c}$ The second value is derived by including HCO$^+$ in the analysis (see text).
\end{table}