Rev.Adv.Mater.Sci. (RAMS)
No 1, Vol. 20, 2009, pages 14-20


Alexander I. Melker and Maria A. Vorobyeva


In this contribution we have analyzed main ideas and principles lying at the basis of mechanical models of molecule vibrations. We considered advantages and drawbacks of well-known models, such as the central force model, the valence force model and Urey-Bradley's model based on purely mechanical and volitional suggestions. A sketch of a newly developed electronic theory of molecule vibrations is also given. It is shown that the electronic theory clarifies the physical sense of vague parameters used in mechanical models and allows exclude excess ones. Besides of excluding excess parameters, the electronic theory of molecule vibrations has shown that valence vibrations are not independent and connected with deformation vibrations through electronic degrees of freedom. For example, in triatomic molecules ABA the interaction of valence and deformation vibrations through electronic degrees of freedom leads to changing of elastic constants and frequencies. As a consequence, the rigidity of elastic constant ks for symmetric longitudinal vibrations, and hence the corresponding frequency ωs respectively, is increased whereas those, ka and ωa, for asymmetric ones are decreased in the following manner ks=k+2kθ, ka=k-2kθ , . Here k and kθ is a usual force constant of valence and deformation vibrations, respectively, and kθ can be expressed in terms of effective electron charges of covalent bonds. As a result, calculated frequencies coincide practically with experimental data.

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