ИСТИНА

Small molecules (typically, 3 to 6 atoms) of both natural and anthropogenic origin widely occur in Earth and planetary atmospheres as well as in planetary and interstellar ices, where they are continuously affected by solar and galactic radiation. The understanding on the mechanisms of their radiation-induced transformations in cold environment is of considerable significance for different areas, ranging from ecology and climatic aspects to extraterrestrial prebiotic evolution of matter. The matrix isolation technique was applied for characterization of intermediates resulting from the molecules of atmospheric and astrochemical importance during several decades. However, most of these studies were related to photochemistry and focused on spectroscopic aspects rather than reaction kinetics and mechanisms. This presentation gives an overview of very recent model studies on the radiation-induced degradation and reactions of a number of small molecules presenting interest for astrochemistry and atmospheric chemistry (such as H2O, CO2, CH3OH, C2H2, HCN, and simple freons) carried out in our laboratory [1–4]. The matrix isolation experiments using X-ray irradiation in solid Ne, Ar, Kr and Xe matrices were performed with an original complex of closed-cycle helium cryostats based on a combination of FTIR and EPR spectroscopy. In addition to characterization of intermediates and molecular products, we have paid special attention to the studies of their dynamics and reaction kinetics at low temperatures, which is particularly relevant to the simulation of reactions in planetary and interstellar ices. According to the results, in many cases, the X-ray-induced degradation is significantly different from the photochemical processes under the action of UV/VUV light. The basic features of the high-energy reactions are (i) involvement of “hot” ionic channels; (ii) population of optically unattainable excited states (particularly, higher triplet states); (iii) predominating role of positive hole and energy transfer. It was found that the reactions of mobile radiation-induced hydrogen and oxygen atoms could play an important role in mixed systems containing different kinds of isolated molecules. We have also investigated the peculiarities of the radiation-induced transformations of “frozen” intermolecular complexes (e.g., H2O...CO2, HCN...CO2, CH3OH...H2O), which demonstrated dramatic effect of weak molecular interaction on the radiation-chemical evolution at low temperatures in certain systems [2]. The preliminary results of more complex molecules (like C2H5OH) are also presented. Finally, we discuss possible implications of our approach for astrochemistry and atmospheric chemistry and directions of future studies. This work was supported by a grant from the Russian Science Foundation (project 14-13-01266). References : [1] Ryazantsev S.V. & Feldman V.I., J. Phys. Chem. A, 119, 2578 (2015). [2] Ryazantsev S.V. & Feldman V.I., Phys. Chem. Chem. Phys., 17, 30648 (2015). [3] Kameneva S.V., Tyurin D.A., & Feldman V.I., Rad. Phys. Chem., in press (2015). [4] Feldman V.I. et al., Rad. Phys. Chem., in press (2015).