Infrared absorption spectra of liquid methyl iodide (CH 3 I) and its solutions in CCl 4 , CS 2 , heptane, benzene, chloroform and deuterated acetone-d 6 have been studied. Infrared spectra in the regions 3400-2700, 1700-1100 and 1000-750 cm −1 were fitted by the sum of components, with the form of multiplication of the Lorentzian and Gaussian functions. E-Type bands under investigation (v 4 = 3047, v 5 = 1428, and v 6 = 885 cm −1 ) were reproduced by the sums of two components: the narrower (n) and the broader (b) ones. A different temperature behaviour of the components has been found: the integrated intensity of the narrower component (I n ) decreases with the temperature, while the intensity of the broader one (I b ) increases. The narrower components of v 5 and v 6 were attributed to CH 3 l molecules moving according to the orientational diffusion mechanism; the broader ones were attributed to molecules, freely rotating about the C 3v axis. Some additional mechanism (probably the interactions between CH stretching vibrations with single particle and collective motions of molecular dipoles) was proposed to play a part in forming the v 4 bandshape. The enthalpy difference between freely rotating molecules and those moving via an orientational diffusion mechanism (ΔH) have been determined by the slopes of the dependencies of ln(I n /I b ) upon T −1 : ΔH = 0.8 ± 0.1 kcal mol −1 . The temperature behaviour of δ n has been studied in the 210–340 K temperature range, and Rakov's approach has been used to determine the activation enthalpy (ΔH∗) and entropy (ΔS∗) of parallel orientational diffusion in the pure liquid: ΔS∗ = −4.5 ± 0.2 cal mol−1 K−1, ΔH∗ = 0.1 ± 0.1 kcal mol−1. The CH 3 stretching range was found to be strongly affected by a solvent. Total integral absorption coefficients of v 1 and v 4 bands increase two-fold when going from CCl 4 to acetone-d 6 solution, while δ n values decrease by 3–9 cm −1 . The observed effects were explained in terms of the existence of complexes with weak ICH 3 · acetone hydrogen bonding. The strength of the hydrogen bonding was characterized by enthalpies of specific interaction ΔHint.CH 3 I/S (sp.). These values were estimated by the “intensity rule”: ΔH int. CH 3 I/S (sp.) = 0.13 kcal mol −1 for self-association in pure CH 3 I and 0.4 kcal mol −1 for solution in acetone-d 6 .