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Zusammenfassung:
Using in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) and conventional IRAS techniques the adsorption of NO on Pd(111) was studied from ultra-high vacuum (UHV) conditions to 400 mbar. New monomeric and non-monomeric high coverage NO adsorption states were observed at 400 mbar. Initial NO adsorption at 600 K and subsequent cooling in the presence of 400 mbar NO lead to a new high coverage monomeric adsorption state. For NO adsorption at room temperature the formation of NO dimer as well as dinitrosyl states was observed, which upon heating transformed into the high coverage monomeric adsorption state. In contrast, under UHV conditions, NO dimers were only stable at low temperatures up to 60 K, above which they transformed into a monomeric NO adsorption state with a (2×2)-3NO structure. Our results demonstrate that stable NO dimeric and dinitrosyl species can be formed on Pd(111) at elevated pressure conditions emphasizing their potential role in catalysis.
