Editing Ion source (section)

===Associative ionization===
Associative ionization is a gas phase reaction in which two atoms or molecules interact to form a single product ion.<ref>{{GoldBookRef|title=associative ionization|file= A00475}}</ref><ref>*{{cite journal |vauthors=Jones DM, Dahler JS |title=Theory of associative ionization  |date=April 1988 |pmid=9900022 |journal=[[Physical Review A]]|volume=37|issue=8 |pages=2916–2933|doi= 10.1103/PhysRevA.37.2916|bibcode = 1988PhRvA..37.2916J }}</ref><ref>{{Cite journal | last = Cohen | first =  James S. | date = 1976 | title = Multistate curve-crossing model for scattering: Associative ionization and excitation transfer in helium | journal = Physical Review A | volume = 13 | issue =  1 | pages = 99–114 | doi = 10.1103/PhysRevA.13.99 |bibcode = 1976PhRvA..13...99C }}</ref> One or both of the interacting species may have excess [[internal energy]].

For example,

:<chem>A^\ast{} + B -> AB^{+\bullet}{} + e^-</chem>

where species A with excess internal energy (indicated by the asterisk) interacts with B to form the ion AB<sup>+</sup>.