Laser Spektroskopie an desorbierenden Molekülen

Chemical reactions based on heterogeneous catalysis are of enormous technological importance. The investigation of the single processes taking place in catalytic reactions (adsorption, diffusion, reaction, desorption) is the subject of surface science. In this project the internal state distribution (rotation, vibration) of desorbing particles following a surface reaction are investigated. The experiments are carried out in an ultrahigh vacuum apparatus, equipped with the standard surface analytical tools (Auger spectrometer, mass spectrometer, ion gun). Hydrogen molecules (and its isotopes) as well as hydrogen atoms can be supplied to well defined single crystal surfaces (nickel, aluminum, tungsten). The desorbing reaction products (H2, HD, D2) are then analyzed using the REMPI (resonance enhanced multiphoton ionization) technique. A tunable laser radiation in the 200 nm range is used to resonantly excite and ionize the molecules from distinct rotational and vibrational states. Calibration of the experimental data is accomplished by comparing the data with the spectra obtained from a thermalized hydrogen beam originating from a Knudsen source. The aim of the project is to investigate the correlation between the specific chemical reaction type and the population distribution of the reaction products. In particular the Langmuir-Hinshelwood (LH) reaction and the Eley-Rideal (ER) reaction are the topic of this work.