Abstract :
We have previously reported accurate absolute infrared intensities of liquid benzene-h6 between 6225 and 500 cm21, of liquid benzene-d6
between 5000 and 450 cm21, and of liquid benzene-d1 between 6200 and 500 cm21. The absolute intensities of benzene-h6 were reported as
spectra and tables of the real refractive index, n; the imaginary refractive index, k; and the molar absorption coefficient, Em; and also as tables
of the average areas under, and average peak heights of, bands in the imaginary refractive index and molar absorption coefficient spectra.
For benzene-d6 and benzene-d1, the absolute intensities were reported as spectra and tables of the real and imaginary refractive indices, and as
spectra of the molar absorption coefficient and the imaginary molar polarizability ða00 mÞ under the Lorentz local field. Further, the
contributions from the different bands to the imaginary molar polarizability spectrum below 5000 cm21 were separated by fitting the
spectrum with Classical Damped Harmonic Oscillator (CDHO) bands. The integrated intensities Cj were then obtained from the parameters
of the CDHO bands as the areas under the corresponding ~va00 m bands. The integrated intensities gave the transition dipole moments and also,
for the fundamentals that are infrared-active in the gas phase, the dipole moment derivatives with respect to the normal coordinates under the
double harmonic approximation. The present paper completes the experimental study of benzene-h6 by presenting the results of the following
work. The imaginary refractive index spectrum of C6H6 was extended to 11.5 cm21 from its previous lower limit of 500 cm21. The real
refractive index spectrum between 8000 and 11.5 cm21 was obtained by Kramers–Kronig transformation of the imaginary refractive index
spectrum. It agrees excellently with the real refractive index spectrum directly measured below 100 cm21, which suggests that the accuracy
of the k spectrum is very good, particularly at low wavenumbers. The imaginary molar polarizability spectrum of C6H6 between 6200 and
11.5 cm21 was calculated from the n and k spectra and was fitted with 226 CDHO bands and 1 Gaussian band. No baseline was required in
the fit and the baseline absorption was described accurately by the bands used. The integrated intensity, Cj;of each band used to fit the
spectrum was calculated analytically from the band’s parameters. The transition dipole moments were then calculated for the clearly assigned
transitions, and the dipole moment derivatives with respect to the normal coordinates were calculated under the double harmonic
approximation for the fundamentals that are infrared-active in the gas phase. The values obtained are related to literature values for the liquid
and the gas, and are very close to those published previously and compared with the intensities of C6D6 and C6H5D.
q 2004 Elsevier B.V. All rights reserved.
