Infrared intensities of liquids. XVII. Infrared refractive indices from 8000 to 350 cm−1, absolute integrated absorption intensities, transition moments, and dipole moment derivatives of methan-d3-ol and methanol-d4 at 25 °C

Abstract

This paper reports absolute infrared absorption intensities of liquids methan-d3-ol (CD3OH) and methanol-d4 (CD3OD) at 25 °C between 8000 and 350 cm−1. Measurements were made by multiple attenuated total reflection spectroscopy with the CIRCLE cell, and by transmission spectroscopy with transmission cells fitted with calcium fluoride windows. In both cases, the spectra were converted to infrared real and imaginary refractive index spectra. The refractive indices obtained by these two methods agreed excellently and were combined to yield an imaginary refractive index spectrum k(ν̃) between 7244 and 350 cm−1 for CD3OH and between 5585 and 350 cm−1 for CD3OD. The imaginary refractive index spectrum was arbitrarily set to zero from 8000 to 7244 cm−1 (CD3OH) or 5585 cm−1 (CD3OD), where k is always less than 4×10−6, in order that the real refractive index can be calculated below 8000 cm−1 by Kramers–Krönig transformation. The results are reported as graphs and tables of the refractive indices between 8000 and 350 cm−1, from which all other infrared properties of the two liquids can be calculated. The estimated accuracy, not precision, of the imaginary refractive index is ±3%, except for ±10%, where k is less than 4×10−5. The estimated accuracy of the real refractive index is better than ±0.5%. In order to obtain molecular information from the measurements, the spectra of the imaginary polarizability multiplied by wave number ν̃αm″ were calculated under the assumption of the Lorentz local field. The area under these ν̃αm″ spectra was separated into the integrated intensities of different vibrations. The magnitudes of the transition moments were calculated from the integrated intensities, and the double harmonic approximation was used to calculate the magnitudes of the dipole moment derivatives of the liquid-state molecules with respect to the normal coordinates. Dipole moment derivatives with respect to internal coordinates were calculated under the simplest approximations, the validity of which is demonstrated by the experimental data in many cases. The consistency of the dipole moment derivatives with respect to internal coordinates obtained for different isotopomers is shown through their relative rotational corrections. Results are presented for the O–H, O–D, C–H, and C–D stretches; the C–O–H in-plane bending; and the D–C–O–H and D–C–O–D torsion vibrations.