Knowledge Bank

Previous $measurements1$ of quantitative intensity spectra of $CH3OH,CH3OD,CD3OH$ and $CD3OD$ have been analysed. Gaussian and Classical Damped Harmonic Oscillator bands were fitted to the imaginary molar polarizability spectra. The minimum number of bands was used and the integrated intensities of the fundamentals were obtained from the fitted bands. These were compared with the integrated intensities previously $determined1$ by a more subjective comparison of the spectra of different isotopomers, and a set of accepted intensities was determined for nearly all vibrations of all isotopomers. To analyse the accepted intensities, a normal coordinate calculation was guided by an earlier ab initi $calculation2$ but was modified to require reproduction of the experimental fact that the wavenumbers and intensities of the CO stretching mode in $CH3OH$ and $CH3OD$ are identical. The eigenvectors so determined were used with the directions of the dipole moment derivatives calculated recently by Torii and $Tasumi3$ to fit the intensities of all four isotopomers by a complete set of dipole moment derivatives with respect to symmetry coordinates, from which the complete set of dipole moment derivatives with respect to internal coordinates was obtained. The results will be compared with those calculated for the isolated CH3OH molecule by Torii and $Tasumi3$. Although there is room for considerable improvement, the quantities presented are believed to be the most accurate and complete set determined so far for a liquid molecule of low symmetry.