Action spectroscopy with inert gas messenger atoms/molecules is commonly used for the characterization of clusters in the gas phase. With this method vibrational spectra of the clusters are measured via detection of inert gas desorption following excitation of cluster vibrational modes. We have constructed an apparatus for the application of action spectroscopy to surfaces of solids using light from the infrared free electron laser of the Fritz Haber Institute.<br/>There are two channels leading to inert gas desorption in surface action spectroscopy. One channel is bulk sensitive and reflects the sample's infrared absorption cross section. In this channel warming up processes induce inert gas desorption. The other, more interesting channel is surface sensitive – here energy of an excited surface vibrational mode breaks the bond between the inert gas messengers and the surface via vibrational coupling. This channel permits to get surface vibrational spectra without having to measure reference data as in the case of conventional infrared absorption spectroscopy. The sensitivity of the method depends on the messenger gas – the more weakly the atoms/molecules are bound, the more readily the bond may be broken by a vibrational excitation at the substrate surface. A relevant difference between infrared absorption spectroscopy and the surface action spectroscopy method is probably the possibility to selectively decorate surface features with messengers since in this case the signal comes only from the decorated surface features.<br/>Examples for the application of this method will be shown and discussed.

Surface action spectroscopy: A new tool for the spectroscopy of surface vibrations

2019 Spring National Meeting

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