Photoelectron Spectroscopy

a method of studying the structure of a substance by measuring the energy spectra of electrons ejected during photoemission. According to the Einstein photoelectric law, the sum of the binding energy or work function of an ejected electron and the kinetic energy of the electron is equal to the energy hv of an incident photon, where h is Planck’s constant and v is the frequency of the incident radiation. The binding energy and the energy levels of the electrons in a substance that is being studied may be determined from the substance’s electron spectrum.

Photoelectron spectroscopy employs monochromatic X- or ultraviolet radiation with photon energies ranging from tens of thousand to tens of electron volts, which correspond to radiation wavelengths in the range from tenths of an angstrom to hundreds of angstroms. A photoelectron spectrum is analyzed by means of high-resolution electron spectrometers; the resolution may be as high as tenths of an electron volt in the X-ray region and as high as hundredths of an electron volt in the ultraviolet region.

The technique of photoelectron spectroscopy is applied to substances in the gaseous, liquid, or solid state and makes it possible to study both the outer and the inner electron shells of atoms and molecules as well as the electron energy levels in a solid, particularly the electron distribution in the conduction band. For molecules, the binding energies of the inner-shell, or core, electrons of the constituent atoms depend on the type of bond or on the chemical shift. Therefore, photoelectron spectroscopy is used in analytical chemistry to determine the composition of substances and in physical chemistry to study chemical bonds. In chemistry, the technique of photoelectron spectroscopy is known as electron spectroscopy for chemical analysis, or ESCA.