Far-Infrared Spectra of Gaseous and Liquid SF6

The far-infrared absorption spectrum of SF6 in the gaseous state was measured at 25°C at pressures from 3 to 19 atm in the wavelength region 12–250 cm−1. The absorption of liquid SF6 in this region was measured at 0°C and −40°C. The strongest bands in the gas phase are centered roughly at 50 cm−1, and approximately at 94 and 173 cm−1. Bands centered at approximately 55, 90, and 150 cm−1 were observed in the liquid phase. Since the intensity of the band at 50 cm−1 varies as density squared, it is ascribed to collision induction. The bands at 94 and 173 cm−1 in the gas phase (considered to be the same bands at 90 and 150 cm−1 in the liquid phase) vary linearly with density and are ascribed to the difference vibrations, respectively, ν4 − ν5 and ν5 − ν6. The hexadecapole moment of SF6 was estimated from the integrated intensity of the collision-induced band in the gas.