Structure of liquid hydrogen fluoride studied by infrared and Raman spectroscopy

Infrared and Raman spectra of hydrogen fluoride, deuterium fluoride, and their isotopic mixtures at various temperatures from 293 to 77 K have been recorded and analyzed in comparison with calculated data obtained from the classical G.F. matrix method applied to hypothetical structures chosen a priori. The best fit lead to the most probable structure of HF at 293 K which is a zig–zag chain with six or seven molecules having an angle of 42° with the average axis. At a lower temperature (190 K), just before solidification, the chains become longer, n=8 with an angle θ≂35 °. These structures fit well with the high dielectric constant of liquid hydrogen fluoride and lead to a calculated Kirkwood factor g1=3.65 at 293 K and g1=5.36 at 190 K which are in perfect agreement with known experimental values.

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