The infrared absorption of dilute solutions of HC1 and HBr in benzene, chlorbenzene, carbon tetrachloride, and tin tetrachloride, was investigated by a prism grating spectrograph of high dispersion with effective slit widths of between one and two wave numbers. There was found a single absorption band for all solutions with the exception of tin tetrachloride which showed a double band for HC1 and a single band for HBr located at the position of one of the HC1 bands. These results for tin tetrachloride are attributed to the formation of H 2 SnCl6 in the case of the HC1 solution, and to the formation of a compound in such a manner that free HC1 was liberated in the case of the HBr solution. From the experimental values of the areas under the curves, their half-widths, and the maximum extinction, it is concluded that the dissolved molecules could be treated as a dilute gas composed of damped simple harmonic oscillators. From the half-widths of the bands the damping constants of the dissolved molecules are calculated, and the force constants are determined from the position of the peaks of the absorption bands. In all cases the value of the force constant is diminished from its value for the molecule in the vapor state. The ratio of the change in the force constant of HC1 to the change in the constant of HBr in the solvents, benzene, chlorbenzene, and carbon tetrachloride, is close to 1.32 which is the ratio of the dipole moments of the two substances in the vapor state. Likewise, the ratio of the half-widths of the bands for the two molecules is close to 1.32. Values of the Einstein coefficient of absorption and values of e in the equation, i* = no-\-€(r -r 0 ) for the electric moment of the molecules are calculated. I T is evident that the forces existing between molecules in the liquid state affect the dynamical properties of the individual molecules. These properties, in many cases, can be investigated by means of infrared absorption measurements, and the experimentally simplest of such are probably those that can be made on dilute solutions of diatomic polar molecules. Experiments on such solutions will yield information concerning the interaction of the dissolved polar molecules with their environment. The effect of the environment, in general, will be to alter the dynamical behavior of the solute molecules as evidenced, in the case of infrared absorption measurements, by.shifts in position of the absorption bands and by changes in their shape and in tensity. West and Arthur 1 have shown by Raman photographs, Plyler 2 and Williams, 3 and West and Edwards, 4 by infrared absorption measurements, with solutions of HC1, that the position of the band due to HC1 is shifted by amounts which depend upon the solvent. Now, most solvents which do not dissociate HC1 have strong bands in the region of the HC1 fundamental . absorption band, and this fact necessitates the use of an instrument of large dispersion and resolving power if it is desired to study the position of the infrared absorption bands and particularly their ...
