Photoelectron spectroscopy electronic shell structures

Most of what we know about the structure of atoms and molecules has been obtained by studying the interaction of electromagnetic radiation with matter. Line spectra reveal the existence of shells of different energy where electrons are held in atoms. From the study of molecules by means of infrared spectroscopy we obtain information about vibrational and rotational states of molecules. The types of bonds present, the geometry of the molecule, and even bond lengths may be determined in specific cases. The spectroscopic technique known as photoelectron spectroscopy (PES) has been of enormous importance in determining how electrons are bound in molecules. This technique provides direct information on the energies of molecular orbitals in molecules. 

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. 

When UV photons are used, the available energy provides only the possibility of studying the outer electron shells. Therefore UPS (Ultraviolet Photoelectron Spectroscopy) studies the valence band structures of materials. 

X-ray photoelectron spectroscopy Mossbauer spectroscopy X-ray singlecrystal diffraction XPS (ESCA) Inner-shell electron transitions. Excitation of nuclear spin by y rays. Fourier transform of diffraction data reveals location of electron density. Oxidation state of metal. Oxidation and spin state. Antiferromagnetic coupling (Fe only). Precise three-dimensional structure, bond distances and angles for small molecules. Lower resolution and precision for proteins. 

Venezia et al. [260] s)mthesized pumice-supported Ag-Pd bimetallic particles and characterized them by XRD and X-ray photoelectron spectroscopy (XPS). Huang et al. [261] s mthesized Ag-Pd bimetallic alloy particles by a chemical reduction method, characterized them by elemental analysis and XRD, and further used these particles for electronic component fabrication. Rao and co-workers synthesized FCC structured Ag-Pd and Cu-Pd nanoscale alloys in bulk quantities and characterized them with various techniques such as transmission electron microscopy and XRD [262]. It was also reported that that Pt-Pd nanobimetallic particles having a core-shell structure can be prepared in a single-step process using silanes as stabilizers [258]. 

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