Band structure in the C–H stretching region of the Raman spectrum of the extended polymethylene chain: Influence of Fermi resonance

Abstract

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.