Photoelectron spin structure measurement

The results of a spin-polarization measurement of xenon photoelectrons with 5p5 2P3/2 and 5p5 2P1/2 final ionic states are shown in Fig. 5.21 together with the results of theoretical predictions. Firstly, there is good agreement between the experimental data (points with error bars) and the theoretical results (solid and dashed curves, obtained in the relativistic and non-relativistic random-phase approximations, respectively). This implies that relativistic effects are small and electron-electron interactions are well accounted for. (In this context note that the fine-structure splitting in the final ionic states has also to be considered in... 

The first prerequisite for measurement of photoelectron spin-polarization is the ability to separately detect the photoelectrons ejected from the different fine-structure levels (e.g., 2n3/2 and 2n1/2 for HX+ X2n). When the molecule contains a heavy atom (e.g., large spin-orbit splitting), it becomes easier to use the electron kinetic energy to distinguish the photoelectrons ejected from the different fine structure channels. For spin-polarization analysis, the accelerated electron beam (20-120 keV) can be scattered by a thin gold foil in a Mott-detector. The spin-polarization is determined from the left-right (or up-down) asymmetry in the intensities of the scattered electrons (Heinzmann, 1978). Spin polarization experiments, however, are difficult because the differential spin-up/spin-down flux of photoelectrons is typically one thousandth that obtained when recording a total photoionization spectrum. 

For closer elaboration of the numerous radical cation states of molecules on energy and time scales (Figure 2a and c), photoelectron (PES)3,5,16 and electron spin resonance (ESR/ENDOR)10,25 spectroscopic techniques have complementary time ranges Vertical ionization energy patterns are measured with a time resolution of less than 10 15 s (Figure 2c) without any vibrational structural changes on electron ejection and can therefore be correlated to the eigenvalues calculated for the neutral molecule by... 

Magnetic samples are exposed to ultraviolet radiation and the energies and spin orientation of the emitted photoelectrons are measured to reveal information about the spin resolved valence band electronic structure of the material. Range of operation typically 10—200 eV. This technique is similar to ultraviolet photoelectron spectroscopy but SPUPS is also sensitive to the polarisation of the electrons as well as their energy. 

Aluminum clusters have been investigated using a variety of experimental techniques, providing abundance spectra [164, 165], spin multiplicities [166], IPs [164, 167], EAs, and static polarizability [105]. Reactivity studies have been reported for size-selected A1 clusters in contact with a variety of small molecules (see, for instance, [167]), and the presence of different isomers in a population of clusters has been investigated by measuring the mobility of clusters in a buffer gas [168]. Finally, the electronic structure of these clusters has been probed by photoelectron spectroscopy on the anion species Al [169, 170]. As mentioned above, bulk aluminum is remarkably close to a nearly... 

During the coming years, one can expect the activity in this field to become even more intense, in part because of the increase in the number of synchrotron facilities and techniques for photoelectron spectroscopy. It is expected that there will be very extensive measurements of photoionization with excitation including resonance structure and double photoionization over wide energy ranges including studies of inner shells. There will be measurements of partial cross sections, angular distributions, and spin polarizations. This last topic, which has recently received considerable attention,was deferred to the paper by W. Johnson in this volume since it depends on relativistic effects. 

---