QUASIHARMONIC TREATMENT OF INFRARED AND RAMAN VIBRATIONAL FREQUENCY-SHIFTS INDUCED BY TENSILE DEFORMATION OF POLYMER-CHAINS

Stress‐induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains are interpreted theoretically on the basis of the quasiharmonic lattice dynamical treatment. The calculated frequency shifts are in good agreement with experiment for planar‐zigzag polyethylene and helical polyoxymethylene. The anharmonic terms of the force constants are estimated numerically in order to obtain the parameters of anharmonic potential functions such as the Morse potential. The close relationship between stress‐induced frequency shifts and molecular deformation mechanisms is discussed in terms of the force field and the geometry of the polymer chain. Copyright © 1990 John Wiley & Sons, Inc.