Appearance energy

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. In mass spectrometry, it is accounted as the voltage to correspond for electron ionization. {{GoldBookRef|title=Appearance energy|file=A00421}} This is the minimum electron energy that produces an ion.{{citation | last = Kerwin | first = Larkin | year = 1960 | title = Recent Appearance Potential Measurements Using an Electrostatic Electron Selector | journal = Journal of Applied Physics | volume = 31 | issue = 12 | pages = 2071 | doi = 10.1063/1.1735504 | last2 = Marmet | first2 = Paul|bibcode = 1960JAP....31.2071K }} In photoionization, it is the minimum photon energy of a photon that produces some ion signal. For example, the indene bromide ion (IndBr+) only loses bromine at an incident photon energy of 10.2 eV, so the product, indenyl, has an appearance energy of 10.2 eV.{{Cite journal |last=Hemberger |first=Patrick |last2=Steinbauer |first2=Michael |last3=Schneider |first3=Michael |last4=Fischer |first4=Ingo |last5=Johnson |first5=Melanie |last6=Bodi |first6=Andras |last7=Gerber |first7=Thomas |date=2010-04-15 |title=Photoionization of Three Isomers of the C 9 H 7 Radical |url=https://pubs.acs.org/doi/10.1021/jp9068569 |journal=The Journal of Physical Chemistry A |language=en |volume=114 |issue=14 |pages=4698–4703 |doi=10.1021/jp9068569 |issn=1089-5639|url-access=subscription }}