Antiresonance of Raman cross-sections for nonpolar phonons in CdS

The nonpolar optic phonons of E₂ symmetry in CdS are shown to exhibit a pronounced decrease in Raman cross-section at certain excitation energies. For the E₂ phonon branch at 43 cm⁻¹ the minimum cross-section occurs for laser excitation ∼0.18 eV below the band gap, and cross-section vs. excitation energy near this antiresonant minimum can be described by an equation of the form used by Ralston et al. for transverse polar phonon cross-sections. For the E₂ mode at 256 cm⁻¹ the antiresonance occurs at wavelengths longer than 6328 Å.