\begin{table}%ta1
%\centering
\par
\caption{\label{lab-data}Quantum numbers of rotational transitions of H$_2$O$^+$  described in the present work, calculated frequencies~(MHz) with   uncertainties in parentheses$^a$; lower state energies $E_{\rm lo}$~(K) and Einstein $A$-values (10$^{-3}$~s${^-1}$)}
\begin{tabular}[t]{ccr@{}lrr}
\hline \hline \noalign{\smallskip}
\multicolumn{4}{l}{$N'_{K_a'K_c'} - N''_{K_a''K_c''}$}   & & \\[2pt]
\hline\noalign{\smallskip}
$J' - J''$ & $F' - F''$ & \multicolumn{2}{c}{frequency} & 
\multicolumn{1}{c}{$E_{\rm lo}$} & \multicolumn{1}{c}{$A$} \\
\hline
\multicolumn{4}{l}{$1_{10}{-}1_{01}$, {\it para}}  &  & \\
\hline
$1.5{-}0.5$ &     $b$     &  604678&.6~(25) & 0.005 &  1.3 \\
$1.5{-}1.5$ &     $b$     &  607227&.3~(19) & 0.000 &  6.2 \\
$0.5{-}0.5$ &     $b$     &  631724&.1~(37) & 0.005 &  5.6 \\
$0.5{-}1.5$ &     $b$     &  634272&.9~(24) & 0.000 &  2.8 \\
\hline
\multicolumn{4}{l}{$1_{11}{-}0_{00}$, {\it ortho}}\\
\hline
$1.5{-}0.5$ & $1.5{-}0.5$ & 1115150&.75~(85) & 0.122 & 17.1 \\
$1.5{-}0.5$ & $0.5{-}0.5$ & 1115186&.18~(81) & 0.122 & 27.5 \\
$1.5{-}0.5$ & $2.5{-}1.5$ & 1115204&.15~(82) & 0.000 & 31.0 \\
$1.5{-}0.5$ & $1.5{-}1.5$ & 1115262&.90~(82) & 0.000 & 13.9 \\
$1.5{-}0.5$ & $0.5{-}1.5$ & 1115298&.33~(87) & 0.000 &  3.5 \\
$0.5{-}0.5$ & $0.5{-}0.5$ & 1139541&.54~(103)& 0.122 &  3.7 \\
$0.5{-}0.5$ & $1.5{-}0.5$ & 1139560&.58~(94) & 0.122 & 14.8 \\
$0.5{-}0.5$ & $0.5{-}1.5$ & 1139653&.69~(94) & 0.000 & 29.4 \\
$0.5{-}0.5$ & $1.5{-}1.5$ & 1139672&.73~(103)& 0.000 & 18.3 \\
\hline
\end{tabular}
\tablefoot{\tablefoottext{a}{Numbers in parentheses are 1$\sigma$ uncertainties in units of the 
least significant figures. These values should be viewed with some caution, 
in particular for the {\it para} transition, see text.}
\tablefoottext{b}{$F$ is redundant for {\it para} transitions; $F = J$ may be assumed. The lowest {\it para} state is 30.01~K above the lowest {\it ortho} state.}}
\end{table}