Optical constants of single crystal of thiourea in the paraelectric and ferroelectric phases from infrared reflectance spectra

Infrared reflectance spectra at nearly normal incidence, parallel to the three crystallographic axes, were obtained at room temperature (Phase V) and at T = 85°K (Phase I). The dispersion parameters and the optical constants were calculated from the Kramers-Kronig relation. The results are in good agreement with previous studies of infrared absorption and Raman scattering.The optical data are interpretible in terms of C_2v molecular symmetry, but that a slight distortion to C_s, resulting in spectral modifications too small to be observed, is also possible.