ИСТИНА

Reactions of atomic oxygen with chemically inert molecules present considerable interest for atmospheric chemistry, gas-phase kinetics, and chemical dynamics. Considering the modern ecological challenges, one should pay special attention to fluoromethanes (CH2F2 and CHF3), which are widely used as an alternative to chlorinated freons supposed to be responsible for the depletion of the ozone layer. Indeed, in contrast to chlorinated analogs, CH2F2 and CHF3 are chemically and photochemically stable, but they can be activated by ionizing radiation or reactions with oxygen atoms produced from highly abundant atmospheric compounds. The radiation chemistry of isolated CHF3 and CH2F2 molecules and some of their atmospherically relevant complexes was recently investigated in our group using a matrix isolation approach [1–3]. As a next step, we applied this approach to simulate the reactions of fluoroform and products of its degradation with “hot” and thermal O atoms, which could be crucially important for the evolution of this compound in upper atmospheric layers, using different sources of O atoms. In the present work, we report an experimental and theoretical study on the radiation-induced and post-irradiation thermal reactions occurring in the CHF3/N2O/Ng or CHF3/H2O/Ng (Ng = Ar, Xe) systems irradiated with X-rays at 6 K. It was found that two products of the fluoroform oxidation were stabilized under these conditions: COF2 and its intermolecular complex COF2…HF. The latter species (a hydrogen-bonded complex) was first characterized in this work on the basis of a comparison between theoretical and experimental complexation-induced shifts in the IR spectra. The reaction pathways were analyzed from the theoretical point of view on the basis of consideration of potential energy surface (PES). Generally, there are two possible channels, corresponding to the insertion of oxygen atoms into C-H or C-F bonds. It appears that both channels exhibit a significant barrier, which can be overcome only due to involvement of “hot” oxygen atoms produced upon the radiolysis of oxygen-containing precursor molecules. Indeed, according to the experimental results, the oxidation products were produced only in the course of radiolysis and they were not formed upon annealing at appropriate temperatures when the trapped oxygen atoms become thermally mobile. In addition, we have found an indication of the reactions between O(1D) atoms and fluoroform radiolysis products, such as CF2 and CF3. The implications of the results for atmospheric chemistry are discussed.