Dehydrocyclooctatetraene. Photoelectron Spectroscopy of the C8H6 Anion

Abstract

The photoelectron spectrum of the dehydrocyclooctatetraene negative ion, C8H6-, is reported. The spectrum strongly resembles that previously reported for the cyclooctatetraene anion, indicating that the structure 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 observed 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 density functional molecular orbital calculations on...