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Tentative study of strong hydrogen bond dynamics:Part II. Vibrational frequency considerations

Journal of Molecular Structure
Publication Date
DOI: 10.1016/0022-2860(90)85046-l
  • Mathematics


Abstract Experimental data on the O⋯O equilibrium distances R e (2.40 ⩽ R e ⩽ 2.69 Å) and the proton and deuteron stretching vibrational frequencies ( v H and v D) for compounds with short hydrogen bonds OHO and ODO are tabulated. Data is included for compounds in which the proton (deuteron) moves in a potential having a symmetry centre. For compounds with 2.60 ⪅ R e ⩽ 2.69 Å both symmetric and asymmetric hydrogen bonds are included. The earlier suggested (but slightly modified) mathematical model of the OHO (ODO) fragment potential-energy surface with a new set of fitting parameters was used for calculations of the proton and deuteron adiabatic terms E H υ and E D υ, as well as the Franck-Condon transition frequencies v H and v D as functions of R e. Simultaneously, the isotopic frequency ratio γ= v H/ v D was calculated depending on v H. These dependencies are compared with respective distributions of the ca. 100 experimental points in order to assign the observed frequencies to respective transitions. The non-monotonic γ dependence on v H, as well as the low (⪅1) and high ( > 1.37) γ values are also interpreted. The same model was used to compute the following quantities as functions of R e: (a) the O⋯O equilibrium distance change on isotopic substitution Δ R R D e − R H e; (b) the δ H distance between two points of maximum proton density in the double-well OHO potential: and (c) the isotopic difference Δδδ D−δ H. A qualitative and in some cases semi-quantitative agreement with experiment was obtained.

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