咪唑在银表面吸附的理论分析

本文用EHMO紧束缚方法计算了咪唑在银(1,1,1)面上吸附的四种构型和吸附态的电子结构,得到咪唑在银表面上的优化构型为直立桥位吸附.按该方式,咪唑环上吡啶型氮原子的P轨道和邻近Ag原子s轨道之间形成多中心σ键.咪唑环上各原子的电荷布居在吸附后有较大的变化,表现出电子由银表面向咪唑转移,并进而使得环上N-H键解离能从吸附前的519.4kJ·mol^-1降低到吸附后的70.34kJ·mol^-1.这与实验中观察到的咪唑N-H键在Ag表面极易断裂的事实相符.

Theoretical analysis of adsorption of imidazole on ag(1,1,1)surface

Four imidazole adsorption geometries and their electronic structures were studied on Ag (111) by EHMO tight-binding calcns. (representing the Ag surface as a monolayer slab). The most favored configuration is standing-up at bridge sites with imidazole bound to Ag via pyridine ring N lone pair electrons. This results in formation of a multi-center s bond between N p and adjacent Ag s orbitals. The electron d. change induced by adsorption indicates that some electrons flow from the Ag into a p antibonding MO of chemisorbed imidazole. The calcns. also indicate that the chemisorbed imidazole tends to undergo facile cleavage of the N-H bond (in agreement with experimental observations).