auto-ionization

in mass spectrometry
https://doi.org/10.1351/goldbook.A00526
This occurs when an internally supra-excited atom or molecular @M03968@ loses an electron spontaneously without further interaction with an energy source. (The state of the atom or molecular @M03968@ is known as a pre-@I03183@ state.)
Sources:
Orange Book, 2nd ed., p. 206 [Terms]
PAC, 1991, 63, 1541. (Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)) on page 1547 [Terms] [Paper]