Absolute infrared absorption intensities of liquid chlorobenzene and toluene

The optical constants of liquid toluene and chlorobenzene were measured across the entire mid-infrared region at 25;The optical constants and the molar absorption coefficient spectra of toluene and chlorobenzene, together with those of liquid benzene and dichloromethane measured separately, were used to establish secondary infrared intensity standards for liquids. These standards have been published by the International Union of Pure and Applied Chemistry.;Molecular properties are more directly reflected in the imaginary molar polarizability spectrum than in the imaginary refractive index spectrum or the molar absorption coefficient spectrum. In order to calculate the integrated intensities, the imaginary molar polarizability spectrum must be separated into contributions from different transitions. The separation was achieved by curve fitting the imaginary molar polarizability spectra with bands of classical damped harmonic oscillator shape, then calculating the integrated intensities from the parameters of the fitted bands. The accuracy of the integrated intensities is estimated at 3-5% for strong bands and 5-10% for weak bands. The results of this work are corrected for liquid dielectric effects and agree usually within a factor of two with literature values for the gas obtained by experimental or by ab initio calculation. In these cases the agreement must mean that the vibrations in question have very similar intrinsic intensities in the liquid and gas phases.;The procedure used to determine the optical constants of the liquid from transmission measurements is exact but computationally complex. A simpler, approximate method was developed and the conditions under which it yields results of sufficient accuracy were explored.;Finally, a method for data reduction and presentation is given. The data is reduced and incorporated into a format that allows a spectrum to be tabulated in about 1/10 of the space required for a traditional table. The format allows direct retrieval of specific values, and also the retrieval, through a recovery program, of the entire spectrum without loss of intensity and line shape information.