Zone-center (q=0) optical phonons in CuO studied by Raman and infrared spectroscopy

We have conducted polarized Raman and infrared-reflectance measurements on CuO single crystals. Group theory predicts nine optical vibrations, of which three (Ag+2Bg) are Raman active and six (3Aᵤ+3Bᵤ) are infrared active. We have observed all nine frequencies. Infrared-reflectance spectra are modeled by a modified three-parameter dielectric-function method adapted to a monoclinic crystal. The nine optical zone-center (q=0) frequencies are fitted by a lattice-dynamical model based on Wilson's FG matrix method.