ELECTRON-ENERGY-LOSS SPECTROSCOPY OF THE LOW-LYING TRIPLET-STATES OF STYRENE

Low-energy electron-energy-loss spectra of styrene deposited on a thin film of solid argon are measured at a temperature of 15 K. The spectra show vibrationally resolved bands in the region of the lowest valence transitions thus allowing to locate the 0-0 transition to the lowest triplet state at 2.69 eV. The second triplet state of styrene is detected for the first time with a 0-0 transition at 3.98 eV. Semiempirical calculations are performed to characterize the bands observed in the spectrum considering the nomenclature of Platt. They suggest that the lowest triplet state has the same spacial wave function as the second singlet state and is closely related to 3L(a) benzene. The second triplet state which has most likely B(a) character cannot directly be related to a specific singlet state because the B(a) and B(b) states are found to mix strongly in the singlet manifold whereas among the triplets they do not.