Infrared reflection of NaHF2 and KHF2 and the dipole derivatives of the HF−2 ion
1978; American Institute of Physics; Volume: 69; Issue: 1 Linguagem: Inglês
10.1063/1.436345
ISSN1520-9032
AutoresRodney D. Cooke, Christine Pastorek, Robert E. Carlson, J. C. Decius,
Tópico(s)Advanced Chemical Physics Studies
ResumoThe infrared reflection spectra of crystals of NaHF2 and of KHF2 have been studied in the internal mode region, i.e., from about 1100 to 1700 cm−1. Observations were made at oblique incidence angles in the range up to 45°, and both TE and TM polarized reflectivity were recorded for KHF2. Infrared transmission experiments were performed with polycrystalline mulls of both the sodium and potassium salts, in each case over a wide range of hydrogen–deuterium ratios. This spectral information was used to deduce ∂μ/∂Q2 in NaHF2 and both ∂μ/∂Q2 and ∂μ/∂Q3 in KHF2. For each of these anisotropic crystals, an appropriate dipole lattice sum was used to evaluate the effective internal field. It is demonstrated that the transition strength—a dielectric parameter, used to fit the observed reflection, and from which the dipole derivatives were calculated—is rather insensitive to the proportion of quadratic and quartic terms in the potential function. The values found for the dipole derivatives were analyzed in the context of the equilibrium charge–charge flux model of the molecular dipole moment. It is also shown that the dipole–dipole intermolecular coupling model is inadequate to account for the frequency ν2 in an isotopically isolated sample.
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