Momentum-dependent dielectric functions of orientedtrans-polyacetylene

Abstract

The momentum-dependent dielectric functions parallel and perpendicular to the chain axis of highly oriented nonfibrous crystalline trans-polyacetylene were determined by electron-energy-loss spectroscopy in the energy and momentum range 0.2–30 eV and 0.05–1.2 A${̊}^{\mathrm{-}1}$, respectively. Information on the electronic structure of π and σ bands as well as on collective excitations was obtained. In particular, a total width of the π bands of 4$t_0$=12.8±0.5 eV is derived. In addition, from the sum rule for π-electron excitations the ratio of the correlation energy U to the total width of the π bands U/4$t_0$∼0.7 is estimated. Most of the experimental results can be explained in a single-particle picture. The momentum-independent absorption edge is most likely explained by excitonic transitions.