Characteristic curve Chemical sensitization

Some branches of the dispersion curve of the helical conformations will be insensitive to the environment of the chemical groups. These are referred to as the characteristic modes, and they correspond to the uncoupled vibrational modes. These characteristic modes have a very flat dispersion curve, and their frequencies do not depend on the phase angle (i.e., the conformation). Other branches of the dispersion curve are sensitive to the phase angle, and the frequencies of the modes depend on the pitch of the helix of the repeating units. Generally, the observed spectra will have modes that have the same frequency (characteristic modes) regardless of the helix type, as well as modes that have different frequency positions because of the helix form. These latter modes are useful for characterizing the helical conformation of a polymer in the solid state. 

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