Highly sensitive infrared studies on supported metal cluster adsorbates by infrared cavity ringdown spectroscopy

本项目旨在开发一种高灵敏度的红外光谱技术--红外空腔衰荡光谱(IR-CRDS)，用于研究反应物、中间体和产物分子在尺寸选定的负载型金属团簇上的吸附。振动指纹不仅可以识别吸附剂和团簇上的反应机理，而且随着团簇大小的变化和各种团簇S捕获中心的测量，相对于气相的振动位移对于阐明吸附剂与团簇的键合机制具有重要意义。CRDS非常灵敏，可以探测到低至1010/cm2(约10-5单层，ML)的星团覆盖率的微弱光学跃迁(？=0.1ä2)。这是首次将这种方法用于研究表面的化学过程。它的极端灵敏度将允许扩展红外研究，以表征C-H键，这是很难用传统技术完成的。这类研究将为详细研究碳氢化合物在不可伸缩尺寸范围内的小团簇的化学提供了可能性。我们计划研究甲烷的活化，脂肪烃或芳香烃的加氢，烯烃的选择性脱氢，或乙炔在小金属簇合物上聚合的可能反应机理。

This project aims to develop a highly sensitive infrared spectroscopic technique, the infrared cavity ringdown spectroscopy (IR-CRDS), for studying reactants, intermediates and product molecules adsorbed on size-selected, supported metal clusters. Vibrational fingerprints will not only allow for identification of the adsorbents and reaction mechanisms on clusters, but vibrational shifts with respect to the gas phase, as a function of cluster size and measured for various types of cluster¿s trapping centers are of fundamental interest for elucidating the bonding mechanism of the adsorbents to the clusters. CRDS is extremely sensitive allowing the detection of weak optical transitions (¿= 0.1 Å2) for cluster coverages as low as 1010 /cm2 (~10-5 monolayer, ML). This is the first time this method will be used to study chemical processes on surfaces. Its extreme sensitivity will allow to extend infrared studies for the characterization of C-H bonds, which is difficult to perform by using conventional techniques. Such studies will open up the possibility to investigate in detail the chemistry of small clusters in the non-scalable size regime with respect to hydrocarbons. We plan to study e.g. the activation of methane, the hydrogenation of aliphatic or aromatic hydrocarbons, the selective dehydrogenation of alkenes, or the possible reaction mechanisms of the polymerization of acetylene on small metal clusters.