Neutron inelastic scattering from oriented and polycrystalline polyethylene: Observation and polarization properties of the optical phonons

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Abstract
The neutron inelastic scattering spectra of oriented and polycrystalline polyethylene have been recorded with a beryllium filter spectrometer between 40 and 450 meV, at two different temperatures: 80 and 300 K. At low temperature we find a good agreement between the observed spectra and the calculated one‐phonon distribution functions; the influence of the Debye–Waller factor is found negligible. At room temperature the multiphonon contributions are important; nevertheless, considerable structure in the frequency distributions is still visible contrary to existing calculations. The polarization of the vibrational modes is neatly evidenced, even for the CH stretching modes situated at 360 meV.