RADIATIVE LIFETIMES OF THE $0^{-}_{u}$ SUBLEVELS OF THE RARE GAS EXCIMERS$^{\ast}$
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Date
1986
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Ohio State University
Abstract
Some years $ago^{1}$ we studied the structure of the low lying excited states of the rare gas excimers using a simple model hamiltonian based on parameterized quantities called the $\Sigma-\Pi$, spin-orbit, and singlet-triplet splittings. We were also able to estimate radiative lifetimes of the $1_{u}$ sublevel of the $^{3}\Sigma^{+}_{u}$ state, which where used to select among the available experimental data, yielding values of 5, 3, 0.3, and $0.1 \mu \sec$ for $Ne_{2}{^{\ast}}, Ar_{2}{^{\ast}}, Kr_{2}{^{\ast}}$, and $Xe_{2}{^{\ast}}$ respectively. In subsequent kinetic studies the third component of the $^{3}\Sigma^{+}_{u}$ state, designated $O^{-}_{u}$, has been supposed either to be entirely metastable, or has been otherwise ignored. In the present investigation we expand our pervious model hamiltonian to include rotational coupling among the $^{1,3}\Sigma^{+}_{u}$ and $^{1,3}\Pi_{u}$ states. We find that for all four $Rg_{2}^{\ast}$ species the thermally averaged radiative lifetime of the $O^{-}_{u}$ sublevel should be between 2 and $10 \mu \sec$. In the case of $Ne_{2}^{\ast}$, which is well described by Hund's case (b) the lifetime is nearly independent to J (the $F_{1}$ and $F_{3}$ components have lifetimes about twice that of $F_{2}$). While for $Xe_{2}{^{\ast}}$, which is essentially case (c), the lifetime varies inversely with $J(J+1) (\tau_{1} \gg \tau_{3} = \tau_{2})$. In high-pressure gas experiments, collisional mixing of the three triplet components would probably prevent their separate observation. In a beam experiment, the low-J levels of $Xe_{2}^{\ast} O_{u}^{-}$ would be quite long lived, and the total population would decay non-exponentially.
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$^{1}$ D. C. Lorents, D. J. Eckstrom, D. L. Huestis, SRI International Report No. MP 73-2 (1973). * Supported by the Office of Naval Research Address of Author: Chemical Physics Laboratory, SRI International, Menlo Park, CA 94025
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