Adlayer structure dependent ultrafast desorption dynamics in carbon monoxide adsorbed on Pd (111)
Adlayer structure dependent ultrafast desorption dynamics in carbon monoxide adsorbed on Pd (111)
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DOI：
10.1063/1.4954408
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发表时间：
2016-07-07
影响因子：
4.4
通讯作者：
Camillone, Nicholas, III
中科院分区：
文献类型：
--
作者：
Hong, Sung-Young;Xu, Pan;Camillone, Nicholas, III
本文报道了我们对钯（111）表面一氧化碳吸附层中基底-吸附质能量转移的覆盖度依赖性的超快光诱导脱附研究。随着CO覆盖度的增加，吸附位点群从所有三重中空（高达0.33 ML）转移到桥和近桥（> 0.5至0.6 ML），最后转移到混合的三重中空加顶部位点（在0.75 ML处饱和）。我们发现，在0.24和0.75 ML之间的结合位点图案的进展是伴随着两个显着的特点，在超快光致解吸的吸附物：（i）的解吸概率增加约两个数量级，和（ii）在两个脉冲相关实验中观察到的吸附物-基板能量转移率的变化非单调，在中间覆盖率有一个最小值。模拟使用的唯象模型来描述吸附物-基板的能量转移的摩擦耦合方面表明，这些功能是一致的吸附位点依赖的电子介导的能量耦合强度，η（el），降低与结合位点的顺序：三重空心>桥和近桥>顶部网站。这种弱化的eta（el）在很大程度上抵消了解吸活化能的下降，伴随着吸附位点基序的这种进展，缓和了解吸概率的几个数量级的上升。在这个框架内，所观察到的能量转移速率增强饱和覆盖是由于interradsorbate能量转移的分子结合在三倍中空的顶部网站邻居的共同群体。由AIP出版社出版。
We report our ultrafast photoinduced desorption investigation of the coverage dependence of substrate-adsorbate energy transfer in carbon monoxide adlayers on the (111) surface of palladium. As the CO coverage is increased, the adsorption site population shifts from all threefold hollows (up to 0.33 ML), to bridge and near bridge (> 0.5 to 0.6 ML) and finally to mixed threefold hollow plus top site (at saturation at 0.75 ML). We show that between 0.24 and 0.75 ML this progression of binding site motifs is accompanied by two remarkable features in the ultrafast photoinduced desorption of the adsorbates: (i) the desorption probability increases roughly two orders magnitude, and (ii) the adsorbate-substrate energy transfer rate observed in two-pulse correlation experiments varies non-monotonically, having a minimum at intermediate coverages. Simulations using a phenomenological model to describe the adsorbate-substrate energy transfer in terms of frictional coupling indicate that these features are consistent with an adsorption-site dependent electron-mediated energy coupling strength, eta(el), that decreases with binding site in the order: three-fold hollow > bridge and near bridge > top site. This weakening of eta(el) largely counterbalances the decrease in the desorption activation energy that accompanies this progression of adsorption site motifs, moderating what would otherwise be a rise of several orders of magnitude in the desorption probability. Within this framework, the observed energy transfer rate enhancement at saturation coverage is due to interadsorbate energy transfer from the copopulation of molecules bound in three-fold hollows to their top-site neighbors. Published by AIP Publishing.