Excess Density of Vibrational States at Terahertz Frequencies in the IR Spectra of Glassy Polymers

Abstract

The IR spectra of glassy polymers were studied in the terahertz range 0.27 − 6 THz (9–200 cm−1), where absorption appears due to both individual and collective torsional (libration) vibrations preceding the manifestation of relaxation dynamics. It is shown that collective torsional-vibrational modes, caused by the correlation of librational vibrations in a section of the chain commensurate with its thermodynamic segment, are responsible for the excess density of vibrational states at terahertz frequencies in the IR spectra of glassy polymers.