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We have studied the vibronic absorption spectra of thin submicron interlayers of anisole and nitrobenzene solutions as a function of the concentration and thickness of the interlayer. We have observed isosbestic points in a series of spectra obtained for different concentrations and thicknesses. This in turn is due to the existence in the system of two types of absorbing centers, which we connect with monomers and molecular associates (dimers). We discuss the relative contribution of different types of interactions leading to dimer formation.Introduction. Wall layers of organic liquids consisting of polar anisometric molecules are orientationally ordered like nematic liquid crystals under the action of the field of a lyophilic solid substrate. Therefore in these systems, as previously in nematics [1], we should expect the appearance of an associate formation effect due to dipole-dipole molecular interaction. The results of an experimental study of this effect in interlayers of nonmesogens by spectroscopy and dielectric constant measurements have been reported in [2]. Obviously the appearance of an associate formation effect is due to the action of an asymmetric surface force field and intermolecular dispersion interaction between monomer-dimer and dimer-dimer pairs, and also dipole interaction between monomer-monomer pairs.It is of interest to estimate the relative contribution of each of these interactions to the observed effects. In other words, we need to determine whether only one intermolecular interaction between liquid particles is sufficient to form dimers, or if a major role is played in the dimerization process by the surface force field.Experiment. The associate formation effect has been studied for nonmesogenic preparations such as polar monosubstituted benzene-nitrobenzene (C 6 H 5 -NO 2 ) and anisole (C 6 H 5 -O-CH 3 ), the dipole moments of which are equal to 4.2 D and 1.35 D respectively. In order to study the relative contribution of each type of interaction, they must be varied independently. By varying the thickness of the liquid interlayer, we can vary the contribution from the surface force field; and by varying the concentration of the solution of the test preparation, we can affect the contribution of the second factor.The characteristic features of the molecular structure of the wall layers were studied by investigating the shape of the bands in the electronic absorption spectra for submicron interlayers of solutions of the samples. The spectra were recorded in the region of the atmospheric UV range: in the frequency interval 34000-42000 cm -1 for anisole and 30000-50000 cm -1 for nitrobenzene. In the indicated frequency range for anisole there is a band connected with one vibronic transition, and for nitrobenzene we observe a number of overlapping bands due to several vibronic transitions [3].In the low concentration range, the spectra were recorded in standard cuvets for a planar layer with variable

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