\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}