VIBRATIONALLY RESOLVED OPTICAL SPECTROSCOPY OF CIS,TRANS-1,3,5,7-OCTATETRAENE
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Date
1984
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Ohio State University
Abstract
Vibrationally resolved fluorescence and one photon fluorescence excitation spectra are measured for cis,trans-octatetraene in n-alkane matrices (hexane and octane) at 4.2K. These spectra are surprisingly similar to those measured for trans,trans-octatetraene. There is a weak $S_{0}$ to $S_{1}$ transition (0-0 at $28645 cm^{-1}$ in n-hexane) approximately $3400 cm^{-1}$ below the strong $S_{0}$ to $S_{1}$ transition at $32134 cm^{-1}$. The vibrational development of the $S_{0}$ to $S_{1}$ absorption and fluorescence is that of a symmetry allowed transition unlike the results for the trans,trans isomer. The weak nature of the lowest energy absorption testifies to the importance of multiply excited configurations in the description of $S_{1}$. Vibrational modes in $S_{1}$ are weakly coupled with $S_{2}$ due to the small energy gap; this coupling is energy dependent. Franck-Condon factors for the $S_{0}$ to $S_{2}$ transition are also estimated. Together with the vibrational development of the $S_{0}$ to $S_{1}$ transition, these show that neither of the two lowest excited singlet states are significantly distorted with respect to the ground state.
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Author Institution: Department of Chemistry, Wesleyan University