Infrared spectra and spinning diffusion of methyl bromide in solutions

Abstract

Infrared absorption spectra of methyl bromide (CH3Br) dissolved in carbon tetrachloride (CCl4) and carbon disulfide have being studied in wide temperature ranges. IR absorption in the regions of degenerate (E-type) bands belonging to CH3-stretching (ν4) and deformational (ν5, ν6) vibrations were fitted by the sum of Cauchy-Gauss components. Each E-type band was reproduced by the two components: the narrower (n) and the broader (b) one. The narrower components of the bands belonging to deformational CH3-vibrations were interpreted within the framework of the orientational diffusion mechanism. The broader components of these bands were attributed to the unresolved gas-like vibration-rotational absorption of the molecules. The different temperature behaviour of the components has been found: the integrated intensities of the narrower components (In) decrease with temperature, while the intensities of the broader ones (Ib) increase. The enthalpy differences between the molecules absorbing via two different mechanisms ΔH) were determined from the dependencies of ln(In/Ib) upon T-1: 0.87 ±0.28 (ν5) and 0.65 ±0.10 kcal mol-1 ν6). These values are close to those determined previously for CH3I and CD3I. The narrower components' band widths were used for evaluating the spinning diffusion constants for CH3Br in solutions. © 1997 Elsevier Science B.V.