Synchrotron radiation photoelectron sources

Synchrotron radiation (SR) sources provided a welcome boost to photoelectron spectroscopy in the late 80s. In fact, the switch from conventional discharge sources to SR induced a major revolution. Consequently, we now provide a brief description of the advantages and disadvantages of synchrotron radiation sources. Should the reader be interested in further details, a number of excellent reviews12-14 are available. 

Ultraviolet photoelectron spectroscopy (UPS) is a variety of photoelectron spectroscopy that is aimed at measuring the valence band, as described in sectionBl.25.2.3. Valence band spectroscopy is best perfonned with photon energies in the range of 20-50 eV. A He discharge lamp, which can produce 21.2 or 40.8 eV photons, is commonly used as the excitation source m the laboratory, or UPS can be perfonned with synchrotron radiation. Note that UPS is sometimes just referred to as photoelectron spectroscopy (PES), or simply valence band photoemission. 

As we have seen, the most advanced photoelectron techniques, especially those which necessitate the use of synchrotron radiation sources, have been applied until now only to U and Th systems. Application on Pu and Am systems as well as to heavier actinides is to be expected in the future. The same development is likely to occur as for neutron experiments, where more and more these hazardous actinides are investigated at high levels of instrumental sophistication. Difficulties arising from handling and protection problems are, of course, much greater for photoelectron spectroscopy. 

The majority of recent PES studies of the halomethanes has concerned photoionization dynamics, and has employed synchrotron radiation sources. Halomethanes are aptly suited for such studies because they exhibit a relatively small number of well-resolved PES bands and contain atoms of very different atomic number, Z. This variation of Z permits fine tuning of the molecular ion potential and opens a window for the study of photoelectron-ion interactions. In addition, the Br3d and I4d shells have large photoionization cross-sections in the SXR region, thus extending the scope of PES studies from the valence to the outer-core electrons. 

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