Mixed quadratic interaction terms

This last interaction term is harmonic becanse it is quadratic in the vibrational coordinates and harmonic terms are by definition those that are of degree less or eqnal to 2. go is defined in eq. (7.A5) of the appendix. The effect of this harmonic interaction term is to shift the centre of the band by a quantity eqnal in wavennmber to -( > (gg WqI c), with c the velocity of light. In the case of a mixed dimer the effect of this last term is, as already mentioned, negligible, because the two vibrations are not resonant. The magnitude of this term can conseqnently be taken equal to 110 cm in the case of (CD3COOH)2 and 80 cm in the case of (CD3COOD)2. These are values that are consistent with eq. (7.A7). The comparison of the bands of these mixed dimers with those of homodimers conseqnently conveys usefnl information on these stretching vibrations of H-bonds, more particnlarly on their harmonic interactions. 

Hansch-Free-Wilsoo mixed models were also proposed [Kubinyi, 1976a] by combining the two approaches in a single model. A quadratic term accounting for hydro-phobic interactions (usually logP or n Hansch-Fujita constant) can be added to the Free-Wilson (or Fujita-Ban) model as ... 

Fig. 1. Orientational dependence of the dispersion (multipole) interaction energy between two pyra-zine molecules at R = lOa (from ref. ). Different 2 -pole contributions to eqn. (21) are labelled by (Ij Iglg) quadratic terms 1 = 1, lg = 1 mixed pole terms 1 + 1 or lg + i ...

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