Measurements of far-infrared optical constants of liquids with a synchrotron radiation source

Abstract

The far-infrared optical constants of liquid acetonitrile, carbon disulfide, and carbon tetrachloride were determined from transmission measurements with a synchrotron radiation source at the Institute for Molecular Science (Okazaki). The small size of the synchrotron radiation source was of benefit to measurements of transmittances that were suited for an analysis based on an optical theory. From the transmittances of liquid acetonitrile at temperatures ranging from 238 to 343 K, both the absorption coefficients and the refractive indices were obtained by using the subtractive Kramers–Kronig relation proposed by Jones and co-workers. The dipole moment of liquid acetonitrile calculated from the optical constants, 4.5 ± 0.1 D, is nearly independent of temperature. The spectra of carbon disulfide and carbon tetrachloride were measured at pressures in the ranges 1–1800 bar and 1–1100 bar, respectively. The absorption coefficients were obtained from the transmittances by neglecting the dispersion of the refractive indices. The zeroth and second moments of the collision-induced absorption bands were obtained as a function of pressure, after resolving the overlap of intramolecular vibrational bands. Key words: far-infrared, optical constants, pressure, liquid, synchrotron radiation source.