\begin{table}%t1
\caption{Spectroscopic parameters$^a$ (MHz) of amino acetonitrile.}
\label{t:spectro_param}
\small%\centerline
$$
\begin{tabular}{lr@{}l}
\hline\hline
Parameter                        &\multicolumn{2}{c}{Value} \\
\hline
$A$                       & 30~246&.456~1~(71)   \\
$B$                       &  4~761&.061~02~(84)  \\
$C$                       &  4~310&.751~23~(76)  \\
$D_K \times 10^3$        &     676&.62~(99)       \\
$D_{JK} \times 10^3$     &   $-$55&.298~6~(69)   \\
$D_J \times 10^3$        &       3&.068~53~(68)  \\
$d_1 \times 10^6$        &  $-$671&.60~(40)       \\
$d_2 \times 10^6$        &   $-$28&.893~(106)     \\
$H_K \times 10^6$        &      30&.$^b$           \\
$H_{KJ} \times 10^6$     &    $-$2&.686~1~(268)  \\
$H_{JK} \times 10^9$     &  $-$120&.1~(72)        \\
$H_J \times 10^9$        &       9&.593~(276)     \\
$h_1 \times 10^9$        &       2&.989~(225)     \\
\hline
\end{tabular}$$
\medskip
$(a)$ Watson's $S$-reduction was employed in the representation~$I^r$.
The dimensionless weighted rms of the fit is 0.51, therefore, the numbers in
parentheses may be considered as two standard deviations in units
of the least significant figures. \\
$(b)$ Assumed value (see Sect.~\ref{ss:aanfreq}).
\end{table}