Overall mobility of polymethylene chains in the solid state: A spectroscopic study

Abstract

Vibrational spectroscopy is used to characterize the molecular phenomena involved in pretransitional processes in polymethylene systems. — It is shown that the “soliton-like” model proposed to justify the mechanism of molecular mobility is consistent with different experimental data from vibrational spectroscopy and other techniques, namely, diffusion, transport of matter, and surface disordering. — By use of spectroscopic “probes” such as Raman band width, frequency shifts, and intensity changes, it is predicted that, if solitons exist, we should observe in the IR/Raman spectra narrow band width and a possible upward shift of a few specific vibrational modes. Moreover, an intensity behavior different for distinct modes is predicted as a consequence of their different coupling with the torsional modes which, in turn are activated by the conformational soliton-like distortion of the chain. Vibrational spectra agree with what is predicted. — A test case (n-alkanes included in urea clathrate) is provided to support the predictions.