Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Appearance energy

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Appearance energy (also known as appearance potential) is the minimum energy that must be supplied to a gas phase atom or molecule in order to produce an ion.[1] In electron ionization, this is the minimum electron energy that produces an ion.[2] In photoionization it is the minimum photon energy.


  1. International Union of Pure and Applied Chemistry. "Appearance energy". Compendium of Chemical Terminology Internet edition.
  2. Kerwin, Larkin; Marmet, Paul (1960), "Recent Appearance Potential Measurements Using an Electrostatic Electron Selector", Journal of Applied Physics 31: 2071, doi:10.1063/1.1735504