BAND-STRUCTURE IN THE C-H STRETCHING REGION OF THE RAMAN-SPECTRUM OF THE EXTENDED POLYMETHYLENE CHAIN - INFLUENCE OF FERMI RESONANCE

The C-H stretching region of the Raman spectrum of the extended polymethylene chain is unexpectedly complex. This complexity is derived in large part from Fermi resonance interaction between the symmetric C-H stretching fundamental and a near continuum of overtones of the methylene 〈HCH scissors fundamentals. The Fermi resonance interaction equation is set up and solved for this system. Two unknown parameters are involved: the Fermi resonance interaction constant for an isolated methylene group and the frequency of the unperturbed symmetric C-H stretching fundamental. With adjusted values for these parameters and a reasonable form for the 〈HCH scissors dispersion curve, the observed positions and relative intensities of bands associated with the stretching fundamental can be accounted for quantitatively. © 1979 American Institute of Physics.