Reversible photochemical transformations of cis- and trans-2,3-dimethyloxirane radical cations in freonic matrices at 77 K

† CFCl 3 (Freon 11, ~99%, Aldrich), CF3CCl3 (Freon 113a, obtained syn­ thetically 5 from Freon 113, 99%, Aldrich; the main product constituted more than 99% of the mixture) were used; in certain cases, Freons were purified additionally using a standard procedure. Commercial cis­ and trans­2,3­dimethyloxiranes (97%, Aldrich) were used as received. The dimethyloxirane/Freon solutions (0.3–0.5 mol%) were inserted into quartz or SK­4B glass tubes, evacuated to ~0.1 Pa and irradiated with X­rays at 77 K to doses of 2–4 kGy. A 5BHV6­W X­ray source (33 kV, 80 mA) was used. The EPR spectra of paramagnetic species were recorded on a Varian E­3 spectrometer. The absolute error in the concentration of paramagnetic species determined by EPR was within ±20%. The EPR spectra were simulated with the use of the PEST WinSim and Simfonia 6 standard soft ware packages.