EPR and DFT study on the stabilization of radiation-generated methyl radicals in dehydrated Na-A zeolite.
EPR and DFT study on the stabilization of radiation-generated methyl radicals in dehydrated Na-A zeolite.
复制标题
EPR 和 DFT 研究脱水 Na-A 沸石中辐射产生的甲基自由基的稳定性。
DOI：
10.1021/jp063506y
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
J. Michalik
中科院分区：
文献类型：
--
作者：
M. Danilczuk;D. Pogocki;A. Lund;J. Michalik
用电子顺磁共振（EPR）谱研究了Na-A沸石在77 K甲烷和γ射线辐照下的稳定顺磁物种。在沸石热退火至室温的过程中，记录到两种类型的EPR谱。由于暴露于（13）CH（4）的沸石的结果，在110 K下观察到的多重峰归属于（.-）CH（3）... Na（+）络合物。在170-280 K温度范围内，记录到甲基自由基的各向同性四重峰。在EPR参数的基础上，假设（.-）CH（3）自由基在该温度范围内能够在沸石笼内自由旋转。（.-）的结构CH（3）.用DFT量子化学方法计算了Na（+）的吸附络合物和相应的超精细耦合常数。采用两种不同的模型来表示沸石骨架：一个六元环的6 T结构和3 T簇。计算了（.-）CH（3）... Na（+）的吸附络合物的两个应用模型显示出非常好的协议与实验获得的。
Electron paramagnetic resonance (EPR) spectroscopy was applied to study paramagnetic species stabilized in Na-A zeolite exposed to gaseous methane and gamma-irradiated at 77 K. Two types of EPR spectra were recorded during thermal annealing of zeolite up to room temperature. Owing to the results for the zeolite exposed to (13)CH(4) the multiplet observed at 110 K was assigned to a (.-)CH(3)...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 of the EPR parameters it is postulated that (.-)CH(3) radicals in this temperature region are able to freely rotate inside the zeolite cage. The structures of the (.-)CH(3)...Na(+) adsorption complex and respective hyperfine coupling constants were calculated by applying DFT quantum chemical methods. Two different models were applied to represent the zeolite framework: the 6T structure of one six-membered ring and the 3T cluster. The hyperfine coupling constants calculated for the (.-)CH(3)...Na(+) adsorption complex for both applied models show very good agreement with those obtained experimentally.