分子态氧在银表面吸附的理论分析

Theoretical Analysis of Molecular State Adsorption of Oxygen on Ag Surface

本文用含分子片计算的EHMO方法计算了氧在具有银[110]面特征的不同大小原子簇上吸附位能面和吸附态的电子结构等,得到氧在银表面分子态吸附最佳构型为<110>方向槽位卧式吸附,离晶面高度约为O.9A;原子态吸附最佳位置是槽内两个第一层银原子之间高度约0.6A处;吸附时电子由Ag向O_(2p)轨道和分子氧的π_g~*轨道转移,同时存在部分电子由分子氧的π_u和3σ_g轨道向Ag的5p轨道反馈形成反馈键;吸附物种为O^(-1.5)和O_2^(-1.38)。并根据计算结果和各种实验事实对银的表面结构与氧的分子态吸附特性关系进行了分析,认为较小的银原子簇具有较高的分子态吸附活性和稳定性。

The potential surface and electronic structures of adsorption states of oxygen on various Ag clusters in character of [110] face have been calculated with EHMO method.The computed potential surfaces show that the oxygen molecules are laid in the troughs of <110> direction at height of 0.9 A for the molecular state adsorption of oxygen on Ag [110] surface and the oxygen atoms are situated in the troughs between the two first layer silver atoms at a height of 0.6A for the atomic state adsorption.The calculation of electronic strucure indicates that the oxygen adsorption on Ag leads some of electron densities to flow from silver into atomic orbitals 2p and antibonding molecular orbitals σ_g~* of oxygen and simultaneously a part of them to flow backward from bonding molecular orbitals π_u and 3σ_g into atomic orbitals 5p of silver.The resulting adsorbed species are O^(-1.5) and O_2^(-1.38).The dependence of molecular state adsorption properties of oxygen on the surface structure of silver has been investigated and discussed with the combination of computed results and various experimental facts.