MAGNETIC CIRCULAR DICHROISM OF THE RYDBERG TRANSITIONS IN BENZENE USING SYNCHROTRON RADIATION
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Date
1981
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Ohio State University
Abstract
This study reports magnetic circular dichroism (MCD) measurements on benzene vapor using the synchrotron radiation source (Tantalus 1) at the University of Wisconsin-Madison. The apparatus used will be described. The spectrum was scanned from 190-136 nm with attention focussed on the Rydberg transitions starting with line 3R (Wilkinson $nomenclature^{1}$) at 152.2 nm. The $3R^{\prime}$ origin shows a prominent MCD A term whereas the R series origins show no significant MCD. This shown that if both the R and $R^{\prime}$ series are associated with the $\pi(e_{1g})\rightarrow $np excitation, then the former must correspond to the transition $^{1}A_{1g} \rightarrow {}^{1}A_{2u}$ and the latter must correspond to $^{1}A_{1g}\rightarrow {}1^{E}_{1u}$. The MCD of hot bands in the vicinity of the $3R$ origin is consistent with a recent Jahn-Teller analysis so Vitenberg et $al.^{2}$ which supports the above assignments of the origins. The $3r’’$ and $3r’’$ origins also appear to show strong A terms. We tentatively assign these origins to $^{1}A_{1g}\rightarrow ^{1}E_{1u}$ transitions associated with the $\pi(e_{1g})\rightarrow $nf excitation. The location of the $^{1}A_{1g}\rightarrow ^{1}A_{2u}$ transition which should also accompany this excitation is not clear, and a definitive assignment of the $R^{\prime\prime}$, $R^{\prime\prime}^{\prime}$ series requires higher resolution data. These measurements mark the first use of a synchrotron radiation source to make vacuum ultraviolet MCD measurements and suggest that much useful spectroscopic information can be obtained in this way.
Description
$^{1}$ P. G. Wilkinson, Can. J. Phys. 34, 596 (1956). $^{2}$ R. Vitenberg, B. Katz and B. Scharf, Chem. Phys. Letters 71, 187 (1980).
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