\begin{table}%T2
   \caption{\label{tab:1514h}Rotational transition frequencies and spectroscopic constants of $^{15}$NNH$^+$.}
  \small%\centerline
{
  \begin{tabular}{ccccc}
    \hline\hline \noalign{\smallskip}
    $J'$ & $J$ & {Observed} & {Obs.-calc.} & {Uncert.$^{{a}}$} \\
         &     & {(MHz)}    & {(kHz)}      & {(kHz)}               \\
    \hline \noalign{\smallskip}
    1  &  0  &   90~263.8330$^{{b}}$ & --2.3 & 10. \\
    3  &  2  &  270~783.5870           &  8.1 & 20. \\
    4  &  3  &  361~035.5242           &  0.7 &  5. \\
    5  &  4  &  451~279.5385           & --2.4 &  5. \\
    6  &  5  &  541~513.6509           &  1.5 &  5. \\
    7  &  6  &  631~735.8673           &  0.2 &  5. \\
    8  &  7  &  721~944.2091           & --3.1 & 15. \\\noalign{\smallskip}
    \mcl{5}{l}{rms$_{\rm res}$$^{{c}} = 3.6$~kHz}\\
    \mcl{5}{l}{$\sigma^{d} = 0.350$} \\ 
    \hline 
    \mcl{2}{l}{Constant$^{{e}}$} & &
    \mcl{2}{r}{Correlation matrix} \\
    \hline
    \mcl{2}{l}{$B_0$ / MHz} &  45~132.08283(23) & 1.000 \\
    \mcl{2}{l}{$D_J$ / kHz} &       82.5747(28)  & --0.943 & 1.000 \\
    \hline
  \end{tabular}}
  \smallskip
    $^{{a}}$  Uncertainties estimated as explained in the text.\\
    $^{{b}}$  From \citet{Gudeman-PhDTh82}.\\
    $^{{c}}$  Rms error of residuals: $\sqrt{\frac{\sum {\rm residual}^2}{{N\;{\rm observations}}}}$.\\
    $^{{d}}$ Fit standard deviation: $\sqrt{\frac{\sum {\rm (residual/uncert.)}^2}{{\rm degrees\;of\;freedom}}}$.\\
    $^{{e}}$ Standard errors are reported in parentheses in units of the last quoted digits.
 \end{table}