\begin{table}%t8
\caption{\label{PrCN_parameters}Spectroscopic parameters$^a$ (MHz) of \textit{n}-propyl cyanide.}
\small%\centerline
 $${
\begin{tabular}{lr@{}lr@{}l}
\hline \hline
Parameter & \multicolumn{2}{c}{\textit{anti}} & \multicolumn{2}{c}{\textit{gauche}}  \\
\hline
$A$                        & 23~668&.319~31~(143)  &  10~060&.416~49~(108)  \\
$B$                        &  2268&.146~892~(147) &   3267&.662~408~(301) \\
$C$                        &  2152&.963~946~(168) &   2705&.459~572~(290) \\
$D_K \times 10^3$          &     240&.653~(29)       &       60&.235~(6)        \\
$D_{JK} \times 10^3$       &   $-$10&.826~31~(92)   &    $-$18&.264~70~(117)  \\
$D_J \times 10^6$          &     398&.674~(69)       &   3195&.064~(207)      \\
$d_1 \times 10^6$          &   $-$46&.637~(42)       &$-$1037&.470~(55)       \\
$d_2 \times 10^6$          &    $-$0&.590~1~(59)    &    $-$77&.186~4~(183)   \\
$H_K \times 10^6$          &       2&.5               &        1&.806~(18)       \\
$H_{KJ} \times 10^9$       &     372&.4~(24)         &   $-$517&.3~(35)         \\
$H_{JK} \times 10^9$       &   $-$20&.67~(20)        &        9&.92~(68)        \\
$H_J \times 10^9$          &       0&.353~(11)       &        4&.486~(56)       \\
$h_1 \times 10^9$          &       0&.117~(14)       &        2&.505~(29)       \\
$h_2 \times 10^{12}$       &        &$-$              &      524&.6~(135)        \\
$h_3 \times 10^{12}$       &        &$-$              &      111&.3~(31)         \\
$L_{KKJ} \times 10^{12}$   &        &$-$              &       30&.6~(31)         \\
$L_{JK} \times 10^{12}$    &        &$-$              &     $-$4&.11~(78)        \\
\hline
\end{tabular}}$$
\medskip
$^a$ Watson's $S$-reduction was used in the representation~$I^r$. Numbers in parentheses are one standard deviation in units of the least significant figures. Parameter values with no uncertainties given were estimated. A~long dash indicates parameters that are determinable in theory, but could
not be determined with significance here.
\end{table}