Photoelectron spectroscopy angular distribution

In conventional photoelectron spectroscopy, angular distributions are known to provide valuable insight into the underlying dynamics. A few groups have, moreover, recently reported measurements of angular distributions in pump-probe photoelectron spectra [332, 406]. Althorpe and Sei-deman have also examined the angular distributions of photoelectrons in the pump-probe ionization for a rigid diatomic molecule NO [8]. 

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

These may be generated by irradiating an atom with a beam of monochromatic X-rays or ultraviolet rays. X-ray and electron spectroscopy is one of the main methods used for studying the structure of atomic electronic shells, particularly inner ones, as well as the role of relativistic and correlation effects. A wealth of such information may also be obtained from the studies of angular distribution of photoelectrons. It is interesting to notice that with increase of the energy of X-rays the dipole approximation fails to correctly describe the angular distribution of electrons. 

Another factor influencing band intensities in photoelectron spectroscopy is the angular distribution of photoelectrons. This means that band areas in the photoelectron spectrum depend on the angle (a) between the directions of photon and electron propagation. These photoelectron distributions depend on the energy of the electrons and on the nature of the orbital from which they are ejected. The number of electrons Nj ejected per unit solid angle in a specific direction by unpolarized radiation is given by... 

MDAD Magnetic dichroism in the angular distribution of photoelectrons MDS Metastable de-excitation spectroscopy... 

An interesting technique for measuring hyperfine splittings of excited atomic levels by quantum-beat spectroscopy has been reported by Leuchs et al. [876]. The pump laser creates a coherent superposition of HFS sublevels in the excited state that are photoionized by a second laser pulse with variable delay. The angular distribution of photoelectrons, measured as a function of the delay time, exhibits a periodic variation because of quantum beats, reflecting the hfs splitting in the intermediate state. 

In this Subsection we apply the above theory of time-resolved photoelectron spectroscopy to the study of wavepacket motion on the nonadiabatically coupled ionic (Na+1 ) and covalent (Nal) states of sodium iodide. Here we show results of calculations of the energy and angular distributions... 

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. 

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