Study of the low‐frequency motions in poly(ethylene terephthalate) (PET) by neutron inelastic scattering

By neutron inelastic scattering, a complex low-frequency spectrum is obtained for PET. This is attributed to the complicated structure of the monomer unit, a large number of intramolecular modes being possible. Most of them were identified using infrared and Raman data. Some indication of the presence of intermolecular modes below 200 cm−1 was found in the dependence of resolution and intensity on temperature in this frequency domain. The existence of these intermolecular modes was further supported by the spectra obtained from oriented or annealed crystalline samples.