Far-infrared spectra of t-butyl bromide-h9 and -d9 in the liquid and three solid phases

The far-infrared spectra of the liquid and three solid phases of t-butyl bromide-h9 and -d9 have been recorded between 200 and 10 cm−1. Strong absorption only occurs below 100 cm−1, where the liquid and the two plastic crystal phases, I and II, show a broad featureless band, whose frequency of maximum absorption increases with decreasing temperature. Relaxation processes and mixed translational-rotational vibrations contribute to the band, but the vibrations determine the frequency of maximum absorption. The spectra of solid phase III at 90°K show eight features that are assigned to lattice modes and indicate that the solid is ordered with at least two molecules per primitive unit cell. At 195°K phase III is orientationally disordered.