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| - EPR and DFT Study on the Stabilization of Radiation-Generated Methyl Radicals inDehydrated Na-A Zeolite
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| - Electron paramagnetic resonance (EPR) spectroscopy was applied to study paramagnetic species stabilizedin Na-A zeolite exposed to gaseous methane and γ-irradiated at 77 K. Two types of EPR spectra were recordedduring thermal annealing of zeolite up to room temperature. Owing to the results for the zeolite exposed to13CH4 the multiplet observed at 110 K was assigned to a •CH3···Na+ complex. After decay of the multiplet,the isotropic quartet of methyl radical was recorded in the temperature range of 170−280 K. On the basis ofthe EPR parameters it is postulated that •CH3 radicals in this temperature region are able to freely rotateinside the zeolite cage. The structures of the •CH3···Na+ adsorption complex and respective hyperfine couplingconstants were calculated by applying DFT quantum chemical methods. Two different models were appliedto represent the zeolite framework: the 6T structure of one six-membered ring and the 3T cluster. The hyperfinecoupling constants calculated for the •CH3···Na+ adsorption complex for both applied models show verygood agreement with those obtained experimentally.
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