PHOTOELECTRON SPECTROSCOPY

Gas phase photoelectron spectroscopy (PES) involves the illumination of a molecular target species with photons of sufficient energy to cause photoionisation and the corresponding emission of photoelectrons. The photoelectrons are collected by an energy analyser and the measured kinetic energy distribution provides information on the electronic structure, or partial density of states, of the molecule under investigation. Vacuum-ultraviolet and soft X-ray sources, with photon energies of up to 100eV, are suitable for valence band PES studies. However, such low photon energies are insufficient to initiate photoemission from core levels, the study of which requires hard X-ray sources with photon energies of typically 1500eV or more.