Crystal Vibrations and Intermolecular Forces of Polymethylene Crystals

Normal frequencies of crystalline polymethylene have been calculated for various phase differences along the c axis of the crystal. Intermolecular hydrogen—hydrogen force constants have been evaluated from the splitting of the spectroscopically active modes. The results of the calculations explain almost satisfactorily the splitting of the progression bands in the infrared spectra of long-chain n-paraffins as well as one lattice vibration band in the far-infrared spectrum of polyethylene.