DEHYDROCYCLOOCTATETRAENE - PHOTOELECTRON-SPECTROSCOPY OF THE C8H6 ANION

The photoelectron spectrum of the dehydrocyclooctatetraene negative io n, C8H6-, is reported. The spectrum strongly resembles that previously reported for the cyclooctatetraene anion, indicating that the structu re of C8H6- is very similar to that of C8H8-. Two electronic states of dehydrocyclooctatetraene are observed in the photoelectron spectrum. The lowest energy feature is assigned to singlet 1,3,5-cyclooctatrien- 7-yne, while the higher energy band corresponds to a triplet state of dehydrocyclooctatetraene. The electron affinity of C8H6 is found to be 1.044 +/- 0.008 eV, and the energy difference between the singlet and triplet states is 0.708 +/- 0.006 eV. Vibrational activity is observe d in the photoelectron spectrum and assigned using a simple potential energy surface. Stretching of the triple bond in cyclooctatrienyne is found to have a frequency of 2185 cm(-1), essentially what is expected for a triple bond within an eight-membered ring. Ab initio and densit y functional molecular orbital calculations on dehydrocyclooctatetraen e and the corresponding ions are reported. Cyclooctatrienyne is calcul ated to have a planar or pseudoplanar structure, consistent with assig nments based on peak widths in the photoelectron spectrum.