Electron energy loss measurements on p-terphenyl (C18H14) single crystals and vapor

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Abstract
Electron energy loss spectra with 50 keV electrons were taken on p‐terphenyl single crystals and vapor from 0–40 eV and 0–25 eV, respectively. The orientation of the main axes of the dielectric tensor is determined by means of symmetry considerations and the energy loss functions Im(−1/εii) (i=x, y, z) are derived from energy loss spectra taken with transferred momentum of the scattered electrons parallel to the tensor main axes. From Im(−1/εii) the main axis elements εii of the dielectric tensor are calculated by Kramers–Kronig analysis. The lower crystal excitations (E≲8 eV) are discussed in terms of excited molecular states, derived from the vapor spectra and taken from optical absorption data given in the literature. Values for the crystal and solution shift of π–π* excitations are obtained.