Photoemission of Adsorbates Data Treatment

Photoemission experiments have been shown to provide much insight into the electronic structure of the adsorbate/adsorbent interaction [64, 97, 118]. Thus, this section is dealing with the peculiarities and problems of these techniques for the study of adsorbate interaction and approaches used in this thesis. General choices for data treatment are presented and explained, the interpretation is subject of the following section. The considerations are based on the general knowledge on PES/EES, the (experimental) principles are briefly introduced in the Chap. 3 in Sect. 3.2.5. 

Within this work also CO was dosed on the surface and the resulting UP spectmm revealed the expected CO MO peaks, which were shifted about -H).5 eV compared to of single crystal data thus indicating a possible cluster induced effect [108]. 

Using lower coverages additionally characterized by means of STM. 

With the intention to study the adsorbate-substrate/catalyst interactions the occurrence of adsorbate peaks originating from the corresponding MOs are of paramount interest. In particular, a comparison with gas phase PE spectra of the free molecule can yield information on the MO interaction with a surface, which manifests itself as a shift in the IP of the adsorbate s MO [97, 99, 120, 121]. Further, the changes in the WF of the adsorbent can reveal more information on the nature of the interaction as well as corroborate conclusions reached by studying the shift of IPs. 

In gas-phase studies the electron BEs are commonly referenced to the vacuum level and plotted on an ionization potential (IP) scale, whereas in the study of solids, Ep provides the experimental reference point on a BE scale (with Ep = 0) [101]. Thus, in order to compare gas phase spectra with spectra of adsorbed molecules 

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