What is the formula for calculating the kinetic energy (Ek) in PES?

The kinetic energy (Ek) of electrons ejected from a material in photoelectron spectroscopy (PES) is calculated using the formula Ek = hv - Ei. Here, hv represents the energy of the incoming photon, which is the product of Planck's constant (h) and the frequency (v) of the photon. Ei is the ionization energy, which is the minimum energy required to remove an electron from an atom or molecule.

When a photon strikes an electron, it provides energy hv. Once the electron absorbs this energy and overcomes the ionization energy (Ei) necessary to free itself from the atom, the excess energy becomes the kinetic energy of the emitted electron. Thus, the ejected electron's kinetic energy is the total energy from the photon minus the energy needed to ionize the electron from its original state, leading to the correct equation Ek = hv - Ei. This relationship demonstrates how energy conservation principles apply in PES, where the total energy provided by the photon must encompass both the ionization energy and the kinetic energy of the emitted electron.