Ultraviolet photoelectron spectroscopy

Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by molecules that have absorbed ultraviolet photons, in order to determine molecular orbital energies in the valence region. == Basic theory == If Albert Einstein's photoelectric law is applied to a free molecule, the kinetic energy ( E k {\displaystyle E_{\text{k}}} ) of an emitted photoelectron is given by E k = h ν − I , {\displaystyle E_{\text{k}}=h\nu -I\,,} where h is the Planck constant, ν is the frequency of the ionizing light, and I is an ionization energy for the formation of a singly charged ion in either the ground state or an excited state.

Source: Wikipedia — Ultraviolet photoelectron spectroscopy (CC BY-SA 4.0)