二十面体对称
星团(航天器)
幻数(化学)
镍
化学
结合能
分子
化学物理
氨
Atom(片上系统)
协调数
结晶学
原子物理学
离子
计算化学
电子结构
物理
计算机科学
嵌入式系统
程序设计语言
有机化学
作者
E. K. Parks,Bernd Winter,T. D. Klots,S. J. Riley
摘要
The reactions of nickel clusters with ammonia and with water are used to probe cluster geometrical structure. Ammonia uptake experiments allow the determination of the number of preferred binding sites on cluster surfaces. This number shows pronounced minima in the 50- to 116- atom size range for many of the cluster sizes that appear as magic numbers in mass spectra of rare gas clusters. Since these magic numbers arise from closings of shells and subshells of the Mackay icosahedra, the correlation suggests that ammoniated nickel clusters in this size region also have icosahedral structure. Similar structure is found for ammoniated clusters smaller than ∼30 atoms, but is not seen for room temperature clusters in the vicinity of the third shell closing at 147 atoms. Icosahedral features do appear for the larger clusters at elevated temperatures. For many clusters above 50 atoms, prolonged exposure to ammonia causes a conversion from the icosahedral structure to some other structure that binds more ammonia molecules, and often the two structures are seen together. The equilibrium reaction of a single water molecule with the bare clusters probes the strength of the cluster–water bond. Enhanced water adsorption is often seen for clusters one atom larger than those showing minima in ammonia uptake, suggesting that these bare clusters likewise have icosahedral structure. The reasons for minima in ammonia uptake and maxima in water binding are discussed.
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