\begin{table}%T3
    \caption{\label{tab:1415d}Rotational transition frequencies and spectroscopic constants of N$^{15}$ND$^+$.}
  \small%\centerline
{
  \begin{tabular}{ccccc}
    \hline\hline \noalign{\smallskip}
    $J'$ & $J$ & {Observed} & {Obs.-calc.} & {Uncert.$^{{a}}$} \\
         &     & {(MHz)}    & {(kHz)}      & {(kHz)}               \\
    \hline 
     4  &  3  &  304~058.9449  & --0.8 &  5. \\
     5  &  4  &  380~062.9822  &  0.3 &  5. \\
     6  &  5  &  456~059.8857  &  1.1 &  5. \\
     7  &  6  &  532~048.2255  & --1.7 &  5. \\
     8  &  7  &  608~026.5845  &  1.6 &  5. \\
     9  &  8  &  683~993.5241  & --0.9 &  5. \\
    10  &  9  &  759~947.6328  &  5.9 & 30. \\\noalign{\smallskip}
    \mcl{5}{l}{rms$_{\rm res}$$^{{b}} = 2.5$~kHz}\\
    \mcl{5}{l}{$\sigma^{c} = 0.270$} \\ 
    \hline  \noalign{\smallskip}
    \mcl{2}{l}{Constant$^{{d}}$} & &
    \mcl{2}{r}{Correlation matrix} \\
    \hline 
    \mcl{2}{l}{$B_0$ / MHz} &  38~009.27047(12) & 1.000 \\
    \mcl{2}{l}{$D_J$ / kHz} &       59.44560(95)  & --0.935 & 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}