[Explanation]: Concept of Photoelectron Spectroscopy (PES)

Photoelectron Spectroscopy (PES) is an excellent technique for determining atomic and molecular electronic energy levels. When an atom or molecule is subjected to high energy radiation, electrons are ejected due to collision with photon. (This experiment proves particle nature of electrons.)

Monochromatic X-ray or UV-rays fall on the sample and ejected electrons pass between a pair of electrically charged hemispherical plates which acts as a filter of kinetic energy.

Figure: UVPES and XPES

Types of PES:

Generally PES are of two types-

 1.  UVPES

In UVPES, UV radiation (a He lamp of wavelength 58.4nm and energy 21.2 eV) falls on the atoms and eject electrons. Since, UV has a very low energy, it can eject only the valence electrons.
 2. XPES

X-rays (K line of Aluminium and Magnesium of energy 1486.6 eV and 1536.2 eV) fall on the metal or atom and eject electrons. Since, X-rays are highly energetic, it can eject core electrons also.
Both these techniques are used to study different properties of catalytic surfaces. That is why both these techniques are known as Electronic Spectroscopy for Chemical Analysis, ESCA.
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