\begin{table}%T4
  \caption{\label{tab:1514d}Rotational transition frequencies and spectroscopic constants of $^{15}$NND$^+$.}
  \small%\centerline
{
  \begin{tabular}{ccccc}
    \hline\hline \noalign{\smallskip}
    $J'$ & $J$ & {Observed} & {Obs.-calc.} & {Uncert.$^{{a}}$} \\
         &     & {(MHz)}    & {(kHz)}      & {(kHz)}               \\
    \hline  
     4  &  3  &  299~029.7997 &   4.9 &  5. \\
     5  &  4  &  373~776.8770 &   2.4 &  5. \\
     6  &  5  &  448~517.0446 &   2.7 &  5. \\
     7  &  6  &  523~248.9086 &  --5.5 &  5. \\
     8  &  7  &  597~971.1055 &  --3.2 &  5. \\
     9  &  8  &  672~682.2388 &  --4.4 &  5. \\
    10  &  9  &  747~380.9405 &   5.5 &  5. \\\noalign{\smallskip}
    \mcl{5}{l}{rms$_{\rm res}$ $^{{b}} = 4.2$~kHz}\\
    \mcl{5}{l}{$\sigma^{c} = 1.006$} \\\noalign{\smallskip}
    \hline  \noalign{\smallskip}
    \mcl{2}{l}{Constant$^{{d}}$} & &
    \mcl{2}{r}{Correlation matrix} \\
    \hline  
    \mcl{2}{l}{$B_0$ / MHz} &  37~380.56770(36) & 1.000 \\
    \mcl{2}{l}{$D_J$ / kHz} &       57.6047(25)  & --0.932 & 1.000 \\
    \hline
  \end{tabular}}
  \smallskip
     $^{{a}}$  Uncertainties estimated as explained in the text.\\
     $^{{b}}$  Rms error of residuals: $\sqrt{\frac{\sum {\rm residual}^2}{{N\;{\rm observations}}}}$.\\
     $^{{c}}$ Fit standard deviation: $\sqrt{\frac{\sum {\rm (residual/uncert.)}^2}{{\rm degrees\;of\;freedom}}}$.\\
    $^{{d}}$ Standard errors are reported in parentheses in units of the last quoted digits.
\end{table}