Longitudinal Acoustical Vibrations of Finite Polymethylene Chains

Abstract

The low-frequency Raman scattering spectra of finite polymethylene chains, observed utilizing laser excitation, show a band progression whose frequencies vary inversely and continuously as a function of chain length. It was established that these transitions arise from the longitudinal acoustical vibration of the chain skeleton and its overtones. These results are related to recent theoretical calculations for crystal vibrations of the infinite chain and are found to be in excellent quantitative agreement. An accurate spectroscopic value is derived for the elastic modulus of polyethylene.