Electron capture ionization

Electron capture ionization is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form ${\displaystyle {\ce {A^-}}}$. The reaction is

${\displaystyle {\ce {A + e^- ->[M]A^-}}}$

where the M over the arrow denotes that to conserve energy and momentum a third body is required (the molecularity of the reaction is three).

Electron capture can be used in conjunction with chemical ionization.