Absolute Infrared Intensities Of Water-Alcohol Mixtures

Abstract

ABSTRACT The Circle cell method for measuring absolute infrared absorption intensities has been used to study mixtures of water and methanol over the entire concentration range. We have determined values of the real and imaginary refractive indices and dielectric constants in the infrared region between 8000 and 700 cm1 , of the molar conductivity in the same region, and of the integrated areas under the molar conductivity bands. Apart from a discontinuity between 0 and 1% methanol, the latter are linear functions of mole fraction, a result that is expected for ideal solutions but not for mixtures of molecules that interact as strongly as water and methanol. INTRODUCTION AND METHOD The Circle cell method of measuring absolute infrared absorption intensities has been described1 > 2. Its precision and accuracy have been explored2'3, and measurements of liquid h^O1 D2O2> 3, and manyprimary4* 5 and secondary alcohols have been made. The method transforms the multiple ATR spectra from the cylindrical CIRCLE cell to the optical constants. It uses the known optical constants of benzene2, the Kramers Kronig transform and the real refractive index of the sample liquid at 8000 cm1 . The optical constant spectra yield the dielectric constant spectra, and the imaginary dielectric constant spectrum, e(v) Vs. v, yields the molar conductivity spectrum3, Vm VE(V) Vs. v.Under the classical damped harmonic oscillator model for a liquid, the molar conductivity spectrum is related to molecular properties via