\begin{table}%t2
\caption{\label{tabparam}Parameters used for the computation of production rates.}
%\centerline
{\small
\begin{tabular}{lcccc}
\hline\hline\noalign{\smallskip}
UT date  & $\langle r_{{\rm h}}\rangle$ & $v_{\rm exp}$  & Temp. & $\beta_{0\rm H_2O}^*$ \\[0cm]
[mm/dd.d] & [AU] &    [\kms]  & [K] & [s$^{-1}$]        \\
\hline\noalign{\smallskip}
03/06.60    & 1.518 & 0.70 & 45 & $1.42\times10^{-5}$ \\
03/15.64    & 1.413 & 0.70 & 45 & $1.43\times10^{-5}$ \\
03/24.59    & 1.311 & 0.78 & 50 & $1.47\times10^{-5}$ \\
04/02.63    & 1.216 & 0.80 & 55 & $1.43\times10^{-5}$ \\
04/13.62    & 1.113 & 0.80 & 65 & $1.39\times10^{-5}$ \\
04/26.9     & 1.018 & 0.85 & 70 & $1.38\times10^{-5}$ \\
04/30.2     & 1.000 & 0.85 & 70 & $1.36\times10^{-5}$ \\
05/02.0     & 0.993 & 0.85 & 70 & $1.38\times10^{-5}$ \\
05/02.6     & 0.990 & 0.85 & 70 & $1.38\times10^{-5}$ \\
05/16.0     & 0.962 & 0.85 & 70 & $1.46\times10^{-5}$ \\
\hline\noalign{\smallskip}
\multicolumn{5}{l}{H$_2$O--H$_2$O total cross section = $5\times10^{-14}$ cm$^2$} \\
\multicolumn{5}{l}{Electron density scaling factor $x_{\rm ne} = 0.2$} \\
\hline
\end{tabular}}
\par
\medskip
$^*$ Photo-dissociation rate at 1 AU from the Sun.
\end{table}