THE $B \rightarrow X$ TRANSITION IN XeI
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Date
1996
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Ohio State University
Abstract
The $B (1/2 ^{2}P_{3/2}) \rightarrow X (1/2 ^{2}\Sigma^{+}$) transition in XeI (2385-2490\AA) has been recorded at high resolution for the single isotopomer $^{136}Xe_{127}I$, using a Tesla discharge source and a CCD array detector. The high signal-to-noise capabilities of the detector make it possible to measure the discrete vibrational structure in this system for the first time. The assignments consist of 86 $v^{\prime}-v^{\prime\prime}$ bands spanning 15 upper-state levels (assigned as $v^{\prime} = 3-17$) and 17 lower-state levels (tentatively assigned as $v^{\prime} =0-16$). A vibrational analysis yields the following spectroscopic constants ($cm^{-1}$): $\Delta T_{e} = 40 047.8, \omega_{e}^{\prime} = 110.6, \omega_{e}x_{e}^{\prime} =0.217, \omega_{e}^{\prime\prime} = 24.0, \omega_{e}x_{e}^{\prime\prime} =0.66$. A fit of the data to a near-dissociation expansion indicates that the $X$ state has a dissociation energy ($\cal{D}_{e}$) of 267$\pm$$3 cm^{-1}$ and support 28 bound vibrational levels. However, there are signs that our lowest observed $v^{\prime\prime}$ level may not be $v^{\prime\prime}$ =0, so these values should be considered lower limits. Trial-and-error Franck-Condon calculations are used to locate the $B$- and $X$-state potential curves relative to each other, fixing the X-state $R_{e}$ at a value 0.7-0.8 \AA larger than that for the $B$ state. When the spectra of the rare-gas halides were first investigated over 20 years ago, it appeared that only in XeF and XeCl could discrete bands be discerned in the dominant $B \rightarrow X$ and $D \rightarrow X$ systems. The emission spectra of all other RgX species were modeled as bound-free. Now it appears that faint violet-degraded band structure in the short-wavelength wings of these systems, of the sort measured and analyzed here, may be more the rule than the exception. With the completion of the present work, all four of the XeX species have now been vibrationally characterized, similar work having been completed recently for $XeBr^{a}$.
Description
$^{a}$ J. O. Clevenger and J. Tellinghuisen, J. Chem. Phys., 103, 9611-9620 (1995).
Author Institution: Department of Chemistry, Vanderbilt University
Author Institution: Department of Chemistry, Vanderbilt University