ИСТИНА

Fluoroform is one of the 'haloforms', a class of compounds with the formula CHX3 (X = halogen). Due to low reactivity and low toxicity it is used as refrigerant and fire suppressant. In particular, the application of fluoroform is considered as an ecologically acceptable alternative to chlorofluorocarbons (CFCs). It is worth noting that fluoroform yields hydrogen-bonded complexes with different substances [1, 2]. Fluoroform is supposed to be photochemically rather stable, but its radiation chemistry is poorly studied. Carbone monoxide CO is the simplest molecule, which can form complexes with CHF3, but such intermolecular adducts are unknown. Actually, the impact of weak intermolecular interactions on the processes induced by high-energy radiation is poorly studied, and this is an important issue for atmospheric chemistry, astrochemistry and basic chemical physics. Matrix isolation in solid noble gases (Ng) is a suitable approach to elucidate possible mechanisms of such transformations. In this work we report a FTIR spectroscopic study on the radiolysis and postradiation thermal reactions of CHF3 and CHF3/CO systems in solid Ne, Ar, Kr and Xe. The matrix deposited samples (typically, CHF3/Ng = 1/1000 and CHF3/CO/Ng = 1/1/1000) were irradiated with X-rays at ca. 6 K. It is known that the VUV photolysis of CHF3 in the gas phase at room temperature yields CF2 and HF, which are separated due to huge kinetic energy [3]. However, a quite different situation is observed, when fluoroform is irradiated with the X-rays in solid noble gas matrices [4]. It was found that the matrix ionization energy (IE) value crucially affected the composition of radiolysis products. Ionic processes dominate in neon and argon (IENg > IECHF3) and partially occur in krypton (IENg ~ IECHF3), but only neutral dissociation channels are observed in xenon (IENg < IECHF3). Thus, radiolysis of fluoroform in solid xenon may provide a stabilization of CF2…HF complex. In the case of CHF3/CO/Ng systems, the formation of CHF3...CO complexes is expected. According to the experimental data there are some shifted satellites close to C-H and C-F fundamentals of fluoroform and CO fundamental in Ar and Kr matrices. The quantum chemical calculations predict the existence of 3 intermolecular adducts, corresponding to H...O, H...C and C...O interactions between CHF3 and CO molecules respectively. Calculated shifts of harmonic frequencies of monomers upon the formation of complexes are in satisfactory agreement with the experimental findings. Since the main product of radiolysis of fluoroform is CF3 radical [4], it is logical to assume that radiolytic decay of CHF3…CO complexes should lead to formation of CF3...CO complexes. We observed some experimental evidences for stabilization these radical-molecular structures. Firstly, there is CO induced splitting of CF3 in the IR spectrum after irradiation in comparison with pure CHF3 sample. Secondly, we performed quantum chemical calculations, which also predicted splitting of CF3 fundamental upon the complexation. Finally, we discuss the influence of complexation on the mechanism of fluoroform radiolysis. This work was supported by a grant from Russian Science Foundation (project no. 14-13- 01266). References 1 R. Gopi, N. Ramanathan, K. Sundararajan, Chemical Physics, 2016, 476, 36–45. 2 N. Ramanathan, K. Sundararajan, Journal of Molecular Structure, 2013, 1034, 257–264. 3 M. Suto, and N. Washida, The Journal of Chemical Physics, 1983, 78, 1007–1011. 4 I. S. Sosulin, E. S. Shiryaeva, V. I. Feldman, Radiation Physics and Chemistry, 2017. DOI: 10.1016/j.radphyschem.2017.03.016.