Knowledge Bank

Absolute infrared absorption intensity spectra have been obtained between 4500 and $700cm-1$ for water, acetonitrile, and water-acetonitrile mixtures over the whole range of compositions. The spectra of the imaginary molar polarizability, $\alpha m\prime \prime$, have been calculated for each mixture. The $\alpha m\prime \prime$ spectrum of an ideal mixture is the sum of the $\alpha m\prime \prime$ spectra of the components weighted by the mole fraction of the component. The measure of integrated intensity that has the greatest theoretical significance is the area under a band in the spectrum of $v~\alpha m\prime \prime$. The area under band $j$ in this spectrum is designated $Cj$. Thus for each band, a graph of $Cj$ versus molt fraction is linear if the mixture is ideal. Such graphs have been constructed for the acetonitrile-water system. The observed non-linearities have been analyzed to obtain the number of free and hydrogen-bonded acetonitrile molecules at each composition, and the number of free. O-H---O bonded, and O-H---N bonded, OH groups at each composition.