铝原子簇上化学吸附的尺度效应及其理论模型

对铝原子簇Al_n(n=1～10,12,13)已报导过的理论预测几何构型进行合理选择, 用量子化学CNDO/2法研究了单分子一氧化碳在这些簇上取不同吸附位形时的吸附作用。结果表明吸附强度随簇尺度的变化呈“幻数”特性: Al_2、Al_6、Al_(12)簇具有特别高的吸附能, 与实验观测结果相符。采用作者建议的推广电子壳模型可合理解释这一尺度效应。对Al_(12)和Al_(13)簇电子结构的分析进一步支持了壳模型的观点。随着簇的增大, 尺度效应逐步减弱并趋向于体相铝的性质。

SIZE-DEPENDENCE OF CHEMISORPTION ON ALUMINUM CLUSTERS AND ITS THEORETICAL MODEL

Theoretical investigations have been made on the monomolecular adsorption of carbon monoxide on aluminum clusters Al_n(n=1-10, 12, 13). The equilibrium adsorption positions and the binding energies of various CO sites have been evaluatedby using the quantum chemical method of CNDO/2 with properly choosing the optimalgeometries of aluminum clusters from the reported data. The results reveal that theadsorption of CO on Al_n remarkably depends upon the number of metal atoms in thecluster and exhibits a notable "magic number" behavior, viz. the adsorption energieson Al_2, Al_6 and Al_(12) appear in particularly large values, which are in encouragingagreement with the experimental observations and that predicted by our ExtendedElectron-Shell Model proposed previously. The analysis of the electronic structureof Al_(12) and Al_(13) puts the model on a still solid basis. It can also be seen that sucha size-dependence goes down with the increasing cluster size and the behavior ofcluster gradually approaches that of bulk aluminum.