POLYENE SPECTROSCOPY: PHOTOELECTRON, ELECTRON IMPACT, AND CIRCULAR DICHROISM
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Date
1975
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Publisher
Ohio State University
Abstract
STUDIES Photoelectron spectra of the diphenylpolyenes with 1,2,3,4,5,6, and 8 double bonds have been obtained by J.N.A. Ridyard of Perkin-Elmer Corporation. The lowest energy ionization peak converges toward a limiting energy as the number of double bonds increases. All of the major spectral features can be quantitatively understood on the basis of simple H\”{U}ckel theory. An electron impact excitation study of all trans-hexatriene has been conducted using 100 eV incident electrons and scattering angles from zero to 28$^{\circ}$ with a resolution of 0,3 eV. Transitions are observed at 5.2 ( $^{1}A_{g} \rightarrow ^{1}$B$_{u}$, 6.2, 6.9, 7.9, 9.3, 10.8, and 12.5 eV. These results will be compared to the recent optical results of Gavin and Rice. The variation of the relative intensity with angle of the peaks in the 6.2 to 10 eV range indicates that they have Small electric dipole transition moments compared to their higher transition moments. Tentative evidence for a weak transition at about A.5 eV ($^{1}A_{g}$ $\rightarrow$ $^{1}A_{g}$) will also be presented. A series of alkyl substituted conjugated polyenes have been prepared from natural sources. One example is the tetraene $CH_{3}CH_{2}(-CH = CH-)_{4} (CH_{2})_{7}OOOH$. These compounds can be incorporated into single crystals of the corresponding saturated fatty acid. The tetraene shows a very strong induced circular dichroism ([$\theta$]) $\sim$ 10$^{4}$ ) when bound to bovine serum albumin in aqueous solution. The spectrum consists of a negative transition at long wavelengths and a positive transition at shorter wavelengths giving clear evidence for the presence of a low energy $^{1}A_{g}$ $\rightarrow$ $^{1}A_{g}$ transition.
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Author Institution: Departments of Chemistry and Physics, Stanford University; Princeton Plasma Physics Laboratory, Princeton University