The Water-Hydrogen Fluoride Complex

The complex HjO HF belongs to the best studied hydrogen bonded systems in the vapor phase. The fairly high association constant (Table 5) allows direct gas-phase studies to be performed in mixtures of hydrogen fluoride and water vapor. 

By this technique an average value cos 0 is measured. From this the authors calculated a mean amplitude 02 = 18.3° in H20 HF which is lower than the corresponding values for rare gas atom HF complexes Ar HF, 02 = 41.1° and Kr HF, 02 = 39.2°49,50). As expected, hydrogen bonding introduces some rigidity into the complex However, the isotope effect on 02 in H20 HF is not yet clear48 . 

Vibrational frequencies of H20 HF were calculated by means of a quasilinear model which neglects angular modes. Nuclear motions are restricted to variations 

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In an earlier paper Bevan, Legon, Millen and Rogers 84) presented the microwave spectrum of the water-hydrogen fluoride complex. For the O... F distance they obtain d 2.68 0.01 A and for the dipole moment component along the symmetry axis 3.82 0.02 D. For v they gave, as a preliminary value, 198 cm-1 and for the out-of-plane and in-plane bridge vibrations 94 and 180cm-1, respectively. A full paper has been announced. 

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