ESR SPECTRA OF MATRIX ISOLATED $LiO_{2}$
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Date
1984
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Ohio State University
Abstract
ESR spectra have been obtained for $LiO_{2}$ trapped in krypton and nitrogen matrices, and are consistent with an ionic model, $Li^{+}O_{2}^{{-}}$, of $C_{2V}$ symmetry. Each spectrum has a triplet structure arising from the three principle values of the g-tensor. In Kr, the values are $g_{zz}=2.0570, g_{xx}=2.0095$ and $g_{yy}=2.0024$. For the $N_{2}$ matrix, $g_{zz}=2.0667$ and $g_{xx}=2.0080 (g_{yy}$ was not determined because of overlap with intense N atom transistions centered at $g=2.0014$). The $g_{zz}$ transistion in $N_{2}$ has a well resolved hyperfine quartet structure arising from $^{7}Li (I=3/2)$, with $a_{zz}=2.33G$, and the $g_{yy}$ transistion in Kr has $a _{yy}=2.65G$. Hyperfine structure was not resolved for $g_{xx}$ in either matrix. An apparent but poorly resolved quadrupole interaction is observed for $g_{zz} (N_{2})$ and $g_{yy} (Kr)$. The alkali cation lifts the degeneracy of the $O_{2}{^{-}}$ HOMO and splits it into an in plane orbital, $\Pi^{\ast}_{X}(b_{1})$, and an out of plane orbital, $\Pi^{\ast}_{y}(a_{2})$. The splitting parameter between the two orbital, $|\delta|$, decreases down the series $NaO_{2}, KO_{2}, RbO_{2}$, then increases for $CsO_{2}(1)$. $|\delta|$ is inversely proportional to $\triangle g_{zz}$, the shift from the free electron g value. The $g_{zz}$ values for $LiO_{2}$ support the ``inversion model'' for $CsO_{2}$ where the ground state configuration changes from $^{2}A_{2}$ to $^{2}B_{1}$.
Description
(1) D.M. Lindsay, D.R. Herschbach, and A.L. Kwiram, Chem. Phys. Let. 25, 175 (1974).
Author Institution: Department of chemistry, City University of New York, The City College
Author Institution: Department of chemistry, City University of New York, The City College