Hydrogen bonds harmonic vibrations

Eq. (3.8) assumes harmonic vibrational motion, a satisfactory approximation for the range of momentum transfers covered by the neutron data. NVR adjusted the OD distance, its rms-variation, and the rms-variation in the intramolecular DD distance by least-squares. The DD distance itself was computed from the OD distance and an assumed DOD angle of 104.5°, because its value, 1.58 A, is too close to the hydrogen-bonded D2O...D distance expected near 1.8 A. The molecular structure function 5m(s) calculated from these parameters is compared with the total structure function BN(s) in Fig. 7d. 

Harmon and Lovelace (1982) studied the ir spectrum of -toluidinium bifluoride and tetramethylammonium bifluoride and concluded that the hydrogen bonds are different from that of KHF. The first is different because it is known to be unsymmetrical, but the second was claimed to be even stronger than the hydrogen bond in KHFj. For the tetramethylammonium salts of HFj and DFj the isotope ratios were 1.40 (V2) and 1.41 (Vj). Clearly, the final word on the vibrational analysis of FHF has still to be written. Calculations of ionic force fields based on ir data have been carried out (Matsui et al., 1986), but since these are based on V3 it is probably unwise to read too much into them. 

Section VI. It is possible to unblock the first drawback (i), if to assume a nonrigidity of a dipole—that is, to propose a polarization model of water. This generalization roughly takes into account specific interactions in water, which govern hydrogen-bond vibrations. The latter determine the absorption R-band in the vicinity of 200 cm-1. A simple modification of the hat-curved model is described, in which a dipole moment of a water molecule is represented as a sum of the constant (p) and of a small quasi-harmonic time-varying part p(/j. 

Abstract The problem of the low-barrier hydrogen bond in protonated naphthalene proton sponges is reviewed. Experimental data related to the infra-red and NMR spectra are presented, and the isotope effects are discussed. An unusual potential for the proton motion that leads to a reverse anharmonicity was shown The potential energy curve becomes much steeper than in the case of the harmonic potential. The isotopic ratio, i.e., vH/VD (v-stretching vibration frequency), reaches values above 2. The MP2 calculations reproduce the potential energy curve and the vibrational H/D levels quite well. A critical review of contemporary theoretical approaches to the barrier height for the proton transfer in the simplest homoconjugated ions is also presented. 

Not only is the fundamental frequency of the OH vibration 3500 cm-1) displaced towards lower values, but also the harmonic vibrations at 7000 cm4 and 10500 cm4 show the same change on the formation of hydrogen bonds. 

Craven BM, Swaminathan S (1984, publ. 1985) Neutron diffraction carbon-hydrogen bond lengths corrected for harmonic and anharmonic thermal vibration. Thins Am Cryst Assoc 20 133-135... 

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