UDC 535.37:541.6:543.422 One of the problems of modern molecular spectroscopy is to establish a relation between the structure of molecules and their spectral-luminescent properties. Heteroatoms havea considerable effect on the rate constants of electron transfers, and the energy and nature of the electron states. An investigation of the dependence of the spectral-luminescence properties of molecules on the nature of a heteroatom is necessary in view of the recent rapidly developing use of element-organic compounds in different areas of science and technology. The present paper investigates the change in the spectral-luminescence characteristics as a function of the contribution of the orbitals of the heteroatom to the electron shell of the molecule. We investigated molecules with the general formula Ph3M, where Ph is C6H5, and M is N, P, As, Sb, and Bi. The molecules are characterized by the fact that the electrons of an unshared pair of the heteroatom situeted in l-orbitals participate in ~-delocalization. The electron transitions of such molecules can be regarded as the superposition of transitions of an aromatic system and transitions with (l, v*) charge transfer [i]. The electron absorption and luminescence spectra of derivatives of group V elements are characterized by displacement of the maxima of the bands towards the short-wave end in a number of N, P, As, and Sb derivatives, and the complete absence of a vibrational structure, which indicates a considerable degree of perturbation of the v-system by the l-orbitals of the heteroatom. In Fig. 1 we show the fluorescence spectra of the molecules investigated. Photodissociation occurs when the Ph3P, Ph3As, PhsSb and PhsBi molecules are irradiated with ultraviolet light. The fluorescence spectrum of the products of photodissociation is shown by the broken curve in Fig. i. When the unshared pair of electrons of the heteroatom in the electron-acceptor solvent becomes coupled, there is a considerable reduction in the extinction coefficient, and a vibrational structure of the benzene-type occurs in the absorption spectrum (Fig. 2). This confirms the suggestion that the unshared pair of electrons of the heteroatom (l-orbitals) participate in the form of the electron spectra of the molecule. An investigation of the temperature dependence of the absorption spectra of the molecules with heteroatoms leads to the same conclusions [2]. To solve the problem of the participation of the l-orbital of the heteroatom in the formation of the electron shell of a molecule we used the CMDO method with a limited configurational interaction. We took into account up to 60 single excited configurations in the configurational interaction. As the atomic number of the heteroatom increases, for a correct description of the excited states of the molecules investigated it was necessary to take into account a large number of configurations. Thus, for the Ph3Sb molecule we used 52 configurations~ a further increase in the number of configurations did not lead to any change in the spectral-luminescent characteristics calculated. At the same time, for the Ph3N molecule it was possible to confine ourselves to 33 configurations. The Ph3P and Ph3As molecules occupy an intermediate position. No general criterion is at present available for choosing the parameters for carrying out a CMDO calculation, and the parameters proposed by different authors differ considerably [3]. We used the spectroscopic parameters (CMDO/S) proposed in [4], which gives an adequate description of the electron spectra. The parameters of the heteroatoms used for the calculation are shown in Table I.