Chemically active or toxic molecules of the man-made origin, such as hydrogen halides, fluorides, chlorides, hydrides, oxides, etc., interact easily with the basic molecular gases of atmosphere and, first and foremost, with water, whose content in atmosphere at small altitudes is from 0.02 to 4% mass. In addition to the products of chemical reactions, the feasibility of which is high only for particles present in relatively high concentrations, there is a high probability of the formation of molecular complexes with the energy from several tens of calories up to several kilocalories in atmosphere. The optical activity of such complexes may be fairly large. Therefore these compounds may become a source of additional radiation losses in atmosphere of industrial regions (for example, with developed radiochemical, chemical and electronic industries, metal manufacture, etc.) and of a disbalance of solar radiation fluxes. Gas-phase complexes are, as a rule, characterized by several kinds of motions of large amplitude, which bring out a transformation of vibrational spectra of their constituents (the spectral shift in respect to free molecules can reach several tens cm-1) and an appearance of new bands corresponding to intermolecular vibrations. The indicated factors, in their turn, result in serious methodological difficulties in detection and evaluation of the concentration of molecular complexes in atmosphere with the application of the state-of-the-art remote laser sounding technique.