Hyperpolarizability of Helical Polymer Molecules and the Sampling of the ir‐Active Optical Phonon Dispersion Curves

The selection rules for the inelastic three‐photon scattering of light by helical molecules is obtained from group theoretical analysis. It is shown that the dispersion curve (frequency vs wave vector) for ir‐active optical phonons may be sampled at four points throughout the Brillouin zone by measuring the frequency of the scattered light as a function of the polarization of both the incident (laser) and the scattered light provided that proper orientation of the laser light relative to the helix axis is maintained.