A microscopic picture of the fast process in a polymer melt

The picosecond process in a polymer melt is interpreted in terms of modes with a localized core, having an elastic dipole coupling to the viscoelastic medium. Fits of recent neutron scattering measurements of the fast process in (1,4)-polybutadiene at room temperature provide the dipole strength, together with a core diameter of about 0.6 nm. The result for the dipole strength is in good agreement with soft-potential fits of the low-temperature anomalies of polybutadiene. The finding suggests similar eigenvectors for the modes of the fast picosecond process in the melt and the tunneling modes in the glass phase.