Generalized oscillator strength for the B-1(3u)<-(1)A(g) transition of anthracene, as determined by electron energy-loss spectroscopy

As part of a systematic quantitative study of the angular dependence of valence-shell electron-impact excitation of molecules, we have determined, for the first time, the absolute inelastic differential cross section and the generalized oscillator strength (GOS) for the B-1(3u) <-- (1)A(g) transition (5.2 eV) in anthracene (C14H10). A minimum in the GOS has been observed at a K-2 value of around 0.2 au. The GOS values were determined from the relative inelastic differential cross section, measured with an electron-impact spectrometer, which uses a Wien-filter velocity analyser. The incident electron energy was 1 keV, the energy resolution was 1.0 eV and the energy-loss spectra were obtained in the range of 1.75 degrees-6.75 degrees. The absolute elastic differential cross section was determined in the 0.5 degrees-20 degrees angular range.