\title{OBSERVATION AND ANALYSIS OF ION-PAIR TRANSITIONS OF
I$_2$ COOLED IN A SUPERSONIC
FREE-JET EXPANSION}
\author{J.~TELLINGHUISEN}
\address{Department of Chemistry, Vanderbilt University, Nashville,
TN~37235}
\author{\underline{X.~ZHENG}, F.~FEI, and M.~C.~HEAVEN}
\address{Department of Chemistry, Emory University, Atlanta,
GA~30322}
\begin{document}
\maketitle
The $A^{\prime }$ state of I$_2$ was observed for the first time in a free-jet expansion, where it was prepared by ArF laser excitation of I$_2$/Ar mixtures close to the nozzle \footnote{J.~Tellinghuisen, S.~Fei, X.~Zheng, and M.~C.~Heaven, Chem.~Phys.~Lett. 176, 373 (1991).}. Twenty-seven bands in the v$^{\prime \prime }=0$ progression of the $D^{\prime }-A^{\prime }$ transition were studied by laser excitation spectroscopy, leading to the following improved constants (cm$^{-1}$) for the $A^{\prime }$ and $D^{\prime }$ states:
\vspace{1em}
\begin{tabular}{r@{ = }l@{ }r@{ = }l@{ }r@{ = }l}
$B_0^{\prime \prime }$ & $0.028054$, &
$B_e^{\prime }$ & $0.020526$, &
$\alpha_e^{\prime }$ & $5.3\times 10^{-5}$, \\
$\omega _e^{\prime }$ & $103.953$, &
$\omega _ex_e^{\prime }$ & $0.2097$, &
$\omega_ey_e^{\prime }$ & $2.687x10^{-4}$.
\end{tabular}
\vspace{1em}
Many bands of the $\beta -A$ transition have also been observed. These
originate from $A$, $v^{\prime \prime }=0$, and terminate on levels with $%
25\leq v^{\prime }\leq 68$ of the $\beta $ state. Full analyses of both band
systems will be presented.
\end{document}