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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >H_2 Cracking at SiO_2 Defect Centers
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H_2 Cracking at SiO_2 Defect Centers

机译：SiO_2缺陷中心处的H_2开裂

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The interaction of H_2 with the defect sites of the SiO_2 surface has been studied by means of gradient-corrected density functional theory calculations on cluster models. The mechanism of hydrogen dissociation, the energy of reactants and products, and the corresponding activation energies and transition states have been determined for the following defect sites: Si singly occupied sp~3 dangling bonds (E' centers), ≡Si~·; nonbridging oxygen centers (NBO), ≡Si-O~·; divalent Si, =Si:; and neutral oxygen vacancies, ≡Si-Si≡. H_2 cracking on the NBO sites is exothermic by ～0.4 eV and has an energy barrier of ～0.1 eV (or less considering nonadiabatic effects) which suggest the occurrence of the process even at low temperature. On Si dangling bonds the formation of ≡Si-H and neutral H atom is endothermic and occurs with an activation energy of less than 0.5 eV; the reaction can occur at room temperature. The interaction of molecular hydrogen with the diamagnetic oxygen deficient centers, =Si: and ≡Si-Si≡, leads to the formation of stable ≡Si-H groups with exothermic processes and relatively high activation energies of about 2 eV. Thus, H_2 cracking is predicted to occur at room temperature on paramagnetic defects and only at high temperatures on the diamagnetic centers.
机译：利用簇模型上的梯度校正密度泛函理论计算研究了H_2与SiO_2表面缺陷位点的相互作用。已经确定了以下缺陷位点的氢离解机理，反应物和产物的能量以及相应的活化能和过渡态：Si单占据的sp〜3悬挂键（E'中心），≡Si〜·;非桥接氧中心（NBO），≡Si-O〜·;二价Si，＝ Si ：;和中性氧空位，≡Si-Si≡。 NBO位点上的H_2裂纹以〜0.4 eV放热，并具有〜0.1 eV的能垒（考虑到非绝热效应，该能级更低），这表明该过程即使在低温下也会发生。在Si悬空键上，≡Si-H和中性H原子的形成是吸热的，且活化能小于0.5 eV。该反应可以在室温下发生。分子氢与抗磁性缺氧中心= Si：和≡Si-Si≡的相互作用导致形成稳定的≡Si-H基团，并具有放热过程和相对较高的约2 eV活化能。因此，预计在室温下顺磁性缺陷会发生H_2裂纹，而在反磁性中心只会发生高温。

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