\begin{table}%t1
 \caption{\label{freq}$J' \leftarrow J''$ (with $J''=0-7$) rotational
transitions (MHz) and, for measured frequencies, corresponding
observed-calculated (o--c) differences (kHz) for CF$^+$ and
$^{13}$CF$^+$ together with the determined spectroscopic parameters.
The latter are compared with the theoretical values as well as
previous literature data.}  
\par
%\centerline
$$
\begin{tabular}{llr@{.}lr@{.}lcccllr@{.}lr@{.}l}
\hline\hline
\multicolumn{2}{c}{Transition}& \multicolumn{4}{c}{CF$^+$}       &&&& \multicolumn{2}{c}{Transition}& \multicolumn{4}{c}{$^{13}$CF$^+$} 
\\
$J'$ & $J''$ & \multicolumn{2}{c}{Freq.}& \multicolumn{2}{c}{o--c}&&&& $J'$ & $J''$ & \multicolumn{2}{c}{Freq.}& \multicolumn{2}{c}{o--c} 
\\
\hline
1 & 0 & 102587&535(18)$^a$ &\multicolumn{2}{c}{--}&&&& 1 & 0 &  97749&417(17)$^a$ &\multicolumn{2}{c}{--}\\
2 & 1 & 205170&520(50)     &   8&91               &&&& 2 & 1 & 195494&701(50)     &   4&35 \\
3 & 2 & 307744&351(50)     & --18&36               &&&& 3 & 2 & 293231&703(36)$^a$ &\multicolumn{2}{c}{--}\\
4 & 3 & 410304&565(50)     &  14&09               &&&& 4 & 3 & 390956&310(50)     &  12&31 \\
5 & 4 & 512846&493(50)     & --3&82               &&&& 5 & 4 & 488664&322(50)     & --22&98 \\
6 & 5 & 615365&648(109)$^a$&\multicolumn{2}{c}{--}&&&& 6 & 5 & 586351&717(50)     &   9&49 \\
7 & 6 & 717857&446(210)$^a$&\multicolumn{2}{c}{--}&&&& 7 & 6 & 684014&248(99)$^a$ \\
8 & 7 & 820317&332(351)$^a$&\multicolumn{2}{c}{--}&&&& 8 & 7 & 781647&831(181)$^a$
\\
\hline
\multicolumn{2}{c}{Parameter} & \multicolumn{4}{c}{CF$^+$} &&&&&& \multicolumn{4}{c}{$^{13}$CF$^+$} \\
\hline
\multicolumn{2}{c}{This work - exp} \\
$B_0$ & (MHz) & 51294&1474(32)   &\multicolumn{2}{c}{}&&&&&& 48875&0531(33)   \\
$D_0$ & (MHz) &     0&189955(83) &\multicolumn{2}{c}{}&&&&&&     0&172373(59) \\
\multicolumn{2}{c}{This work - theo$^b$} \\
$B_0$ & (MHz) & 51307&7          &\multicolumn{2}{c}{}&&&&&& 48887&9        \\
$D_e$ & (MHz) &     0&189        &\multicolumn{2}{c}{}&&&&&&     0&171        \\
$H_e$ &  (Hz) & 8&$05\times10^{-2}$&\multicolumn{2}{c}{}&&&&&& 6&$96\times10^{-2}$ \\
\multicolumn{2}{c}{Plummer et~al. \cite{PAHD86}}   \\
$B_0$ & (MHz) & 51294&1143(26)   \\
$D_0$ & (MHz) &     0&18803(10)  \\
\multicolumn{2}{c}{Kawaguchi \& Hirota \cite{KH85}}\\
$B_0$ & (MHz) & 51293&6(19)   \\
$D_0$ & (MHz) &     0&18567(42)  \\
\multicolumn{2}{c}{Gruebele et~al. \cite{GPS86}}   \\
$B_0$ & (MHz) & 51296&45(23)$^c$     \\
$D_0$ & (MHz) &     0&189930(14)$^c$ \\
$H_e$ &  (Hz) &     7&$000(27)\times10^{-2}$\\
\hline
\end{tabular}
$$
\medskip
\par
$^a$  Calculated values on the basis of the spectroscopic
parameters obtained from the fit (see second part of the table). In
parentheses the estimated accuracy is given. The errors on the
spectroscopic parameters employed are not the standard uncertainties
reported in table, but those directly from SPFIT/SPCAT program:
$B_0 = 51294.1474(92)$~MHz and $D_0 = 0.189955(236)$~MHz.
\\
$^b$  For computational details, see text. $\Delta B_{\rm vib}$
(CF$^+$) = 278.4~MHz, $\Delta B_{\rm vib}$($^{13}$CF$^+$) = 258.9 MHz,
$\Delta B_{\rm el}$ (CF$^+$) = --5.5 MHz, $\Delta B_{\rm el}$($^{13}$CF$^+$)
= --5.0 MHz.
\\
 $^c$  Derived from the Dunham coefficients reported in Table~2 of Gruebele et~al. \cite{GPS86}.
 \end{table}