ИСТИНА

Hydrogen cyanide and related species observed in interstellar medium attract attention of researchers as possible precursors for synthesis of prebiotic molecules occurring under high energy irradiation at extreme temperatures [1]. Essential features of such processes may be revealed by model matrix isolation studies [2]. Meanwhile, this method is also useful for investigation of the radiation-induced transformations of weakly interacting complexes, such as H2O-CO2 [3], using double doped matrices. Such investigations may provide interesting information relevant to astrochemical ices and reveal unique spectroscopic features of the complexes formed by unstable species. Here we report a FTIR spectroscopic study of the radiation-induced processes in solid noble gas matrices containing different concentrations of HCN (DCN) and CO2. The matrix samples were irradiated with X-rays (maximum energy 33 keV) at 6 K and then annealed carefully in the temperature range from 6 to 50 K. The IR spectra were recorded at 6 K. Absorption bands assigned to the HCN-CO2 complexes of different geometry were observed in the deposited samples. The CO2-induced bands in the H-C stretch region of HCN were particularly prominent, if the deposition was carried out at higher temperatures. The identification was confirmed by the quantum-chemical calculations at the CCSD(T)/L2 level. Irradiation results in decomposition of both HCN and CO2 molecules. It is worth noting that addition of carbon dioxide makes the radiation-induced decomposition of HCN significantly less effective. The principal products of the radiolysis of triple systems are H, CN, HNC and CO. No evidence for the reactions of mobile O atoms produced from CO2 with HCN molecules was found. The thermally induced reactions of H atoms were studied in a krypton matrix. These reactions result in appearance of the known absorptions of H2CN, HCNH, HCO and HKrCN). In addition, we observed some new CO2-induced absorptions, which can be tentatively assigned to the HCNH-CO2 and HKrCN-CO2 complexes. The quantum-chemical calculations predict three stable HKrCN-CO2 complexes characterized by significant blue shift of the H—Kr stretching bands in the IR spectra. The blue shift is in qualitative agreement with the experimental observations, however, additional arguments are required for an unequivocal assignment. This work was supported by the Russian Science Foundation (project no. 14-13-01266). 1. R. Glaser et al., Astrobiol. 7, 3, 465-475 (2007). 2. S.V. Kameneva et al., Rad. Phys. Chem., 124, 30-37 (2016). 3. S.V. Ryazantsev, V.I. Feldman, J. Phys. Chem. 119, 2578-2586 (2015).