Absorption spectra of cold dilute solid solutions

Infrared absorption spectra have been obtained for some compounds trapped in crystalline solids by freezing liquid Xe, Kr, Ar, or CH4 solutions. The optical quality of the solid solutions is good, and they have been cooled to ∼80 K in 1.35 cm sample thicknesses to study the absorption in fundamental vibrational bands of the solutes. In the cases discussed, the bands are narrow, with observed full widths at half-maximum absorbance 0.05–0.30 cm−1 greater than the instrumental resolution (0.18–0.29 cm−1). The spectra appear to be free of ‘‘multiple site’’ and solute aggregate absorptions. Spectra displaying isotropic splitting in bands of natural BCl3, SeF6, OsO4, TiCl4, and MoF6 are presented, and band frequencies are compared with some results obtained in evaporative matrices, in the gas phase, and in liquid solutions. For this comparison we have obtained some spectra of SeF6 and BCl3 gas.