Breakdown of Infrared-Raman Complementarity in the Low-frequency Region in Condensed Matter

Abstract

Infrared absorption and Raman scattering are well known as complementary measurement methods, but this complementarity generally breaks down below a few cm⁻¹ (about 100 GHz). For infrared and Raman to be complementary, it is necessary that discrete energy levels are determined when the vibrational modes are treated quantum mechanically. Breakdown of the complementarity means that the energy levels are continuous. Spectral assignment based on the infrared and Raman selection rules is limited to regions of tens of cm⁻¹ (about 1 THz) or more.