Organic molecules of cometary substance

Unidentified emissions are observed in spectra of most comets. These separate lines and bands were not possible to be identified earlier by standard methods. A great number of narrow lines of unknown nature were tabulated [11]. For solving the problem of unidentified cometary emissions, had developed the theoretical model of frozen hydrocarbon particles of icy halos of comets and described the mechanism of FHPs photoluminescence [6]. The comparison of laboratory and observed data showed that hundreds of cometary emissions not identified earlier are the photoluminescence of frozen hydrocarbon particles. In [6] particularly suggested that the mixture of frozen polycyclic aromatic hydrocarbons and alkanes can be among the ices of cometary nuclei. These mixtures are the solid solutions of substance – solvent type; here the substance means polycyclic aromatic hydrocarbon (PAH), and the solvent – acyclic hydrocarbons. The optical properties of the solution are determined by the properties of a solvent, by the conditions of crystallization of the solution, by the existence of luminescent component, by the character of interaction between the components of the solution and by the content of additional impurities in the solution. The surface layers of icy cometary nucleus are the sources of frozen hydrocarbon particles of different sizes ejected and carried to the circumnuclear area as the comet approaches the Sun. The size of individual FHP can vary from micron to millimeter. FHP can has the characteristic color inherent in frozen mixture of PAH and acyclic hydrocarbons. Simonia assumed that the solar ultraviolet radiation excites the photoluminescence of icy particles of halo. Low albedo of particles that consist of the mentioned mixtures, and the high quantum yield of photoluminescence of PAHs make it possible to register the corresponding luminescent emissions. The quantum yield of photoluminescence of FHPs can really be rather high. In favor of this assumption speaks the results of laboratory investigations. For the case of small grains containing the frozen organic mixture obtained the quantum yield of photoluminescence in the range of 90-100% [8]. UV photons of solar origin cause the photoluminescence of cometary FHPs in the range of 3800-7000 Å. We presented in this chapter results of studies of several comets.