POLYEN PHOTOPHYSICS--RESONANCE RAMAN INTENSITY STUDIES

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Ultraviolet resonance Raman spectra, excitation profiles, and absolute cross sections will be measured for 1,3-butadiene, trans- 1,3,5-hexatriene, and trans-1,3-pentadiene in vapor and solution phases. The vapor phase resonance Raman and absorption spectra will be analyzed to map out the excited state potential surfaces for these polyeners, particularly with regard to out of plane distortions. The absolute cross sections will permit quantitation of the rate at which the verticall excited electronic state decays, while the Raman intensities in torsional modes will reveal the contribution to this rate from twisting around double bonds. Extension to the solution phase will quantitate the effect of an environment on the excited state potential surfaces and nonradiative decay rates in these polyenes as well as the amount of inhomogeneous broadening of the electronic absorption spectra. These small polyeners are the simplest model systems for the biologically important polyene aldehyde, retinal. Accurate knowledge of their excited state potential surfaces and photophysics, both in the isolated molecules and in solution is important for developing theories to describe cis-trans photoisomerization of the retinal-containing visual pigments and bacteriorhodopsin.