 Ultraviolet photoelectron spectroscopy

Ultraviolet photoelectron spectroscopy (UPS) refers to the measurement of kinetic energy spectra of photoelectrons emitted by molecules which have absorbed ultraviolet photons, in order to determine molecular orbital energies in the valence region.If Albert Einstein's photoelectric law is applied to a free molecule, the kinetic energy (formula_1) of an emitted photoelectron is given by

where "h" is Planck's 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.