\begin{table}%t2
%\centering
\par
\caption{\label{der-parameter}Derived spectroscopic parameters$^a$ (cm$^{-1}$, MHz, unitless) 
of methylidynium, $^{12}$CH$^+$ in its $X\ ^1\Sigma ^+$ and $A\ ^1\Pi$ 
electronic states from a global fit involving four isotopologs.}

\begin{tabular}[t]{lc}
\hline \hline
Parameter & \multicolumn{1}{c}{Value} \\
\hline\noalign{\smallskip}
\multicolumn{2}{c}{$X\ ^1\Sigma ^+$} \\
\hline
$Y_{10}$                                                      &     2~857.569~2~(92)   \\
${\it \Delta} ^{\rm C} _{10}$                                 &       $-$1.120~(137)	 \\
${\it \Delta} ^{\rm H} _{10}$                                 &       $-$1.715~9~(86)	\\
$Y_{20}$                                                      &      $-$59.318~7~(60)	\\
${\it \Delta} ^{\rm H} _{20}$                                 &       $-$1.578~(188)	 \\
$Y_{01}$                                                      &   425~058.66~(248)      \\
${\it \Delta} ^{\rm C} _{01}$                                 &       $-$7.974~9~(105)  \\
${\it \Delta} ^{\rm H} _{01}$                                 &       $-$9.226~3~(76)	\\
$Y_{11}$                                                      &  $-$14~859.0~(67)	 \\
${\it \Delta} ^{\rm H} _{11}$                                 &       $-$7.222~(33)	 \\
$Y_{02}$                                                      &      $-$41.905~(20)	 \\
${\it \Delta} ^{\rm H} _{02}$                                 &      $-$24.36~(86)	 \\
\hline\noalign{\smallskip}
\multicolumn{2}{c}{$A\ ^1\Pi$} \\
\hline 
$T$(H)\tablefootmark{b}                                                    &    23~619.707~(5)       \\
$T$(D)\tablefootmark{b}                                                      &    23~760.102~(5)       \\
$Y_{10}$(H)                                                   &     1~864.485~(8)       \\
${\it \Delta} ^{\rm C} _{10}$(H)                              &          1.244~(145)     \\
$Y_{10}$(D)                                                   &     1~367.294~(8)       \\
${\it \Delta} ^{\rm C} _{10}$(D)                              &       $-$2.876~(306)     \\
$Y_{01}$                                                      &   356~391.8~(29)        \\
${\it \Delta} ^{\rm C} _{01}$                                 &       $-$0.56~(33)       \\
${\it \Delta} ^{\rm H} _{01}$                                 &       $-$1.630~(12)      \\
$Y_{11}$                                                      & $-$27~538.7~(71)        \\
${\it \Delta} ^{\rm H} _{11}$                                 &       $-$1.604~(98)      \\
\hline
\end{tabular}
\tablefoot{\tablefoottext{a}{The electronic term values $T$, and the vibrational parameters 
$Y_{i0}$ are given in cm$^{-1}$; all other $Y_{ij}$ are given in MHz; the ${\it \Delta} ^{\rm X} _{ij}$ are unitless. Numbers in parentheses are one standard deviation in units of the least significant figures.}
\tablefoottext{b}{Determined with respect to the lowest allowed energy levels of each electronic state.}}
\end{table}