INELASTIC NEUTRON-SCATTERING STUDIES OF POLYETHYLENE AND N-ALKANES

High quality inelastic neutron scattering (INS) spectra of randomly or iented polycrystalline polyethylene, perdeuteropolyethylene and highly oriented polyethylene are presented. The instrumental resolution was significantly better than previous work and has revealed increased det ail in the 0 - 600 cm(-1) region. For the polycrystalline sample, comp arison with the best available dispersion curves shows that these qual itatively reproduce the INS spectrum, apart from the energy of the max imum in the in-plane C-C bending mode vg. For the oriented samples, co mparison with calculated INS spectra show fair, but not exact, agreeme nt with the experimental spectra. For n-C18H38 the INS spectrum shows all of the low frequency CCC inplane bends and the out-of-plane skelet al torsions. To the author's knowledge, this is the first observation of all of these modes for an alkane longer than similar to C-10.