This refers to a process whereby gaseous molecules are ionized when they interact with other internally excited gaseous molecules or molecular moieties. Chemi-@I03183@ and chemical @I03183@ are two terms which should not be used interchangeably.
See also:
associative ionization (in mass spectrometry)
chemical ionization (in mass spectrometry)
Orange Book, 2nd ed., p. 204 [Terms] [Book]
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]