Infrared spectra of solid trifluoroiodomethane, CF3I, at temperatures
between 12 and 125 K in both the lattice and internal mode regions are
presented and discussed. A reversible phase transition at (115+/-3) K
is confirmed. The upper phase exhibits broad spectral features, chara
cteristic of a disordered or highly anharmonic crystal. At 12 K, the s
pectra are typical of an ordered harmonic molecular crystal, and are c
ompatible with a centrosymmetric unit cell containing at least four mo
lecules.