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, ${\nu }_4{\mathrm{\hspace{0.17em}-\hspace{0.17em}\nu }}_5$ and ${\nu }_5{\mathrm{\hspace{0.17em}-\hspace{0.17em}\nu }}_6$ . The hexadecapole moment of SF₆ was estimated from the integrated intensity of the collision‐induced band in the gas.