= Photoemission spectroscopy
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= Photoelectron spectroscopy
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<Photoelectron spectroscopy> measures the <kinetic energies> of <photoelectrons> produced by illuminating matter with <photons> of known <energy>. The <photoelectric effect> supplies the emission mechanism; <spectroscopy> turns the distribution of emitted <Electron> energies into information about occupied <energy levels> and <chemical bonds>. A broad survey helps identify <chemical elements>, while small shifts within one element's lines can distinguish different chemical surroundings. These are different questions: finding <carbon> does not establish which <chemical bonds> its <chemical atoms> form.
The useful inversion is an <energy> balance. A known incoming <photon> energy pays for removal of an <Electron> and for its outgoing <kinetic energy>. To apply that balance to a <solid>, specify the zero of <energy> and the <work function> of the instrument. <Photoelectron binding energy reference> derives the conversion for a conducting sample in electrical contact with its analyzer. A free <molecule> instead has an <ionization energy> referenced to an <Electron> at rest in <vacuum>; it need not share a <Fermi level> with the analyzer.
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