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

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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.