ON THE ORIGIN OF THE ROTATIONAL STATE DEPENDENCE OF THE DECAY OF $^{1}B_{3u}$ PYRAZINE. ANGULAR MOMENTUM SELECTION RULES IN INTERSYSTEM $CROSSING^{1}$ $^{1}B_{3u}$
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Date
1983
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Ohio State University
Abstract
Pyrazine, as noted above, exhibits a fluorescence decay which is biexponential in character. Studies of this decay under collision-free conditions reveal a strong rotational state dependence of the $A^{+}/A^{-}$ ratio, as first reported two years ago at this conference. We now describe further experiments which show that, under nanosecond excitation conditions, $A^{+}/A^{-}$ scales as $2J^{\prime} + 1$but $\tau^{+}$ and $\tau^{-}$ are $J^{\prime}$ independent. By considering the spin-orbit properties of triplet pyrazine in the condensed phase, and transforming the problem into the gas phase, we then demonstrate that this behavior is to be expected whenever J (the total angular momentum quantum number), but not P (the projection of J on the top axis), is conserved in the intersystem crossing process. Some possible origins of the breakdown in the $\Delta P = 0$ selection rule will be discussed. $^{1}$Work supported by the National Science Foundation. $^{2}$G. ter Horst, J. Kommandeur, and D. W. Pratt, 36th Symposium on Molecular Spectroscopy, June, 1981, Paper FB10.
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Author Institution: Department of Chemistry, University of Pittsburgh