**\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}**