The Intramolecular Force Field and Normal Vibrations of Isotactic Polypropylene and Deuterated Derivatives

The infrared active normal vibrations of isotactic polypropylene and its deuterated derivatives in the crystalline state have been treated. The modified Urey-Bradley-Shimanouchi force field has been used for the calculations. A total of 23 potential constants have been adjusted by the method of least squares with reference to a total of 166 frequencies observed by Peraldo and Farina. The standard errors of the potential constants have also been calculated. The r. m. s. deviation of the calculated frequencies from the observed ones is as small as 0.9%. The potential energy distributions have also been calculated for the discussion of the nature of the observed infrared bands. Vibrational assignments of the liquid bands of isotactic polypropylene have also been made.