\begin{table}%t1
\caption{\label{tab1}W49N absorption line components.}
%\centerline
{\small
\begin{tabular}{c c c c c c c  }
\hline\hline
$v_{\rm LSR}$ & $\Delta v$ & $N({\rm OH^+})$ & $N({\rm H_2O^+})$ & $\rm OH^+/ H_2O^+$ & $f({\rm H_2})$\tablefootmark{a} \\
$\rm km~s^{-1}$ & $\rm km~s^{-1}$ & $10^{13}\rm cm^{-2}$ & $10^{13}\rm cm^{-2}$ \\
\hline
6.6   &  5.1   &  2.9 & 0.42 &  6.8 & 0.034 \\
13.4  &  4.6   &  2.2 & 0.69 &  3.2 & 0.082 \\
21.2  &  7.0   &  8.2 & 0.56 &  14.6 & 0.015 \\
34.7  &  9.0   &  26.1 & 2.68 &  9.7 & 0.023 \\
43.5  &  8.4   &  7.5 & 0.72 &  10.5 & 0.021 \\
62.5  &  13.3  &  18.9 & 1.67 &  11.3 & 0.019 \\
\hline
\end{tabular}}
\tablefoot{\tablefoottext{a}{Using Eq.~(1) for an assumed temperature of 100~K and an assumed electron abundance 
of $1.4 \times 10^{-4}$.  The required molecular fraction, $f({\rm H}_2)$, scales as $T^{-0.5}~x_{\rm e}$.}}
\end{table}