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Ultrafast Spectroscopy and Interface Femtochemistry of Adsorbed Molecules on a Metal in Liquid

液体中金属上吸附分子的超快光谱学和界面飞化学

基本信息

批准号：
11450322
负责人：
HARATA Akira
金额：
$ 9.47万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

This study aims to clarify main factors dominating interfacial femtochemistry at a sold/liquid interface. We have applied ultrafast transient reflectivity measurements for investigating ultrafast interaction of photoexcited electrons in metal with molecules adsorbed on the metal immersed in liquid solutions. A well-defined surface of Au(111) was investigated in an aqueous solution of perchloric acid or sulfuric acid, under electrochemical potential control and with/without interface modification by alkanethiols having a long alkyl chain of different lengths.We successfully developed an experimental setup to observe ultrafast transient reflectivity of metal in liquid with a high precision. Transient reflectivity of the Au(111) surface showed rapid decrease followed by rapid increase and a remaining constant offset for an initial 4 picosecond after photoexcitation. Decay rate constants of the rapid reflectivity change ranged from 3 to 10 (1/ps) depending on the interface conditions but there observed no dependence on excitation light intensity. The rapid decay was attributed to electron relaxation by electron-electron and electron phonon couplings, while the constant offset was due to phonon temperature rise.The transient reflectivity showed small but apparent dependence on electrochemical potential, kind of solute electrolytes in the liquid side, existence of surface modification, and hydrocarbon chain length of the alkanethiol interface modifiers. The experimental results are considered in connection with atomic and molecular structure of the solid/liquid interface. It is concluded that molecules adsorbed on the interface, including water molecules and adsorbed ions, play significant rolls in dominating ultrafast electron relaxation at the liquid/solid interface.

本研究的目的是澄清在固体/液体界面的界面飞秒化学的主要因素。我们应用超快瞬态反射率测量研究了金属中光激发电子与金属表面吸附分子的超快相互作用。在高氯酸或硫酸水溶液中，在电化学电位控制下，用不同长度的烷基硫醇对Au（111）表面进行了修饰，成功地建立了一套高精度测量金属在液体中超快瞬态反射率的实验装置. Au（111）表面的瞬态反射率在光激发后的最初4皮秒内表现出快速下降，然后快速上升和保持恒定的偏移。衰减速率常数的快速反射率的变化范围从3到10（1/ps）取决于界面条件，但没有观察到依赖于激发光强度。快速衰减归因于电子-电子和电子-声子耦合引起的电子弛豫，而恒定的偏移归因于声子温度的升高.瞬态反射率表现出小但明显的依赖于电化学电位，在液体侧的溶质电解质的种类，表面改性的存在，和烃链长度的烷基硫醇界面改性剂。实验结果被认为与固/液界面的原子和分子结构。它的结论是，吸附在界面上的分子，包括水分子和吸附的离子，在主导超快电子弛豫在液/固界面发挥显着的轧辊。