表面吸附剂上速度分辨激光诱导解吸动力学

IF 6.1 Q1 CHEMISTRY, MULTIDISCIPLINARY
Kim Papendorf, Dr. Kai Golibrzuch, Tianli Zhong, Dr. Sven Schwabe, Prof. Dr. Theofanis N. Kitsopoulos, Prof. Dr. Alec M. Wodtke
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引用次数: 0

摘要

大多数研究表面反应动力学的实验方法,例如程序升温脱附(TPD)、分子束弛豫光谱法(MBRS)和速度分辨动力学(VRK),都采用了需要热脱附的检测方案。然而,许多吸附质——例如反应中间体——在反应条件下永远不会离开表面。在本文中,我们提出了一种测量催化表面吸附质浓度的新方法,并证明了它在研究热解吸动力学方面的实用性。在短脉冲分子束将CO或NH3沉积在Pt(111)上之后,用诱导解吸的超短激光脉冲照射表面。另一个紧密聚焦的超短激光脉冲通过非共振多光子过程电离气相分子,并检测离子。然后在给药分子束脉冲之后将该双激光信号记录为时间的函数,并呈指数衰减。在一定温度范围内获得了一阶热解吸速率常数,并发现其与过去的报道非常一致。离子检测是通过离子成像进行质量选择性检测,通过气相分子的速度分散气相分子。由于激光诱导解吸(LID)产生高温气相分子,因此可以在很少或没有背景的情况下检测到它们。这种方法具有高度的表面特异性,并且显示出低于10-4ML覆盖范围的灵敏度。因为信号与吸附质浓度成线性比例,所以该方法可以在比VRK更低的温度下使用,VRK的信号与反应速率成比例。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Velocity-resolved Laser-induced Desorption for Kinetics on Surface Adsorbates

Velocity-resolved Laser-induced Desorption for Kinetics on Surface Adsorbates

Most experimental methods for studying the kinetics of surface reactions – for example, temperature programmed desorption (TPD), molecular beam relaxation spectrometry (MBRS) and velocity-resolved kinetics (VRK) – employ detection schemes that require thermal desorption. However, many adsorbates – for example reaction intermediates – never leave the surface under reaction conditions. In this paper, we present a new method to measure adsorbate concentrations on catalytic surfaces and demonstrate its utility for studying thermal desorption kinetics. After a short-pulsed molecular beam deposits CO or NH3 on Pt (111), the surface is irradiated with an ultrashort laser pulse that induces desorption. Another tightly focused ultrashort laser pulse ionizes the gas-phase molecules by a non-resonant multiphoton process and the ions are detected. This two-laser signal is then recorded as a function of time after the dosing molecular beam pulse and decays exponentially. First-order thermal desorption rate constants are obtained over a range of temperatures and found to be in good agreement with past reports. Ion detection is done mass selectively with ion-imaging, dispersing the gas phase molecules by their velocities. Since laser-induced desorption (LID) produces hyperthermal gas phase molecules, they can be detected with little or no background. This approach is highly surface-specific and exhibits sensitivity below 10−4 ML coverage. Because the signals are linearly proportional to adsorbate concentration, the method can be employed at lower temperatures than VRK, whose signal is proportional to reaction rate.

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CiteScore
7.30
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