(all‐ E )‐1,3,5,7‐Octatetraene: Electron‐Energy‐Loss and Electron‐Transmission Spectra

Electron‐energy‐loss and electron‐transmission spectra of (all‐ E )‐1,3,5,7‐octatetraene were recorded with a trochoidal electron spectrometer. The energy‐loss spectra reveal two triplet states at 1.73 and 3.25 eV (0,0‐transitions), the UV‐active 1 1 B u state at 4.40 eV, and a higher‐lying singlet state at 6.04 eV. The 2 1 A g state recently reported to be the lowest excited singlet state in this polyene, could not be observed. This failure is probably de to a small excitation cross section under the scattering conditions used and the presence of the second triplet sate in the pertinent energy region. The electron‐transmission spectrum revealed three resonances ( i.e. short‐lived anion states) at 1.5, 2.5, and 4.15 eV.