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 spectr a show vibrationally resolved bands in the region of the lowest valenc e 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 dete cted for the first time with a 0-0 transition at 3.98 eV. Semiempirica l 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 tri plet state which has most likely B(a) character cannot directly be rel ated 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 triple ts they do not.