Core excitons and the dielectric response of polystyrene and poly(2-vinylpyridine) from 1 to 400 eV

Publisher Website
Google Scholar
Abstract
The complete spectra of valence and core electronic excitations of atactic polystyrene, PS, and poly(2‐vinylpyridine), PVP, from 1 to 400 eV were measured by electron energy loss spectroscopy. Energy losses of 80 keV electrons transmitted through 1000 Å thick films were measured with a resolution of 0.1 eV. The spectrum of PS contains several previously unreported broad peaks between 9 and 20 eV which coincide with structure observed in gas phase benzene spectra and which have been attributed to Rydberg states, but which are described here as valence molecular orbital excitations. The dielectric response function of PS and PVP from 1 to 100 eV is computed from energy loss data. The calculated reflectivity and refractive index are in excellent agreement with recent optical measurements. The spectrum of carbon core electron excitations above 285 eV consists of a series of sharp peaks due to transitions to empty molecular states (core excitons) followed by transitions to a free‐electron‐like continuum of states. The core exciton spectrum is quantitatively described in a model based on a molecular orbital ground state calculation (CNDO/S). The results show that such spectra provide a measurement of the distribution of empty molecular orbitals. In addition, shifted exciton peaks are observed which correspond to inequivalent core electron binding energies due to differences in net atomic charge.