lower than the internal energy of the excited-state atom or molecule. Associative Penning ionization can also occur: Fragmentation There are many important dissociation reactions that take place in the gas phase. Collision-induced dissociation CID (also called collisionally activated dissociation - CAD) is a method used to fragment molecular ions in the gas phase. The molecular ions collide with neutral gas molecules such as helium, nitrogen or argon. In the collision some of the kinetic energy is converted into internal energy which results in fragmentation. Charge remote fragmentation Charge remote fragmentation is a type of covalent bond breaking that occurs in a gas phase ion in which the cleaved bond is not adjacent to the location of the charge. Charge transfer reactions There are several types of charge-transfer reactions (also known as charge-permutation reactions): partial-charge transfer , charge-stripping reaction , and charge-inversion reaction positive to negative and negative to positive . Applications Pairwise interactions between alkali metal ions and amino acids, small peptides and nucleobases have been studied theoretically in some detail. See also Adiabatic ionization Mass-analyzed ion kinetic energy spectrometry Plasma (physics) Michael T. Bowers R. Graham Cooks Helmut Schwarz References Bibliography Fundamentals of gas phase ion chemistry, Keith R. Jennings (ed.), Dordrecht, Boston, Kluwer Academic, 1991, pp. 226–8 Gas Phase Ion Chemistry, Michael T. Bowers, ed., Academic Press, New York, 1979 Gas Phase Ion Chemistry Vol 2.; Bowers, M.T., Ed.; Academic Press: New York, 1979 Gas Phase Ion Chemistry Vol 3., Michael T. Bowers, ed., Academic Press, New York, 1983 External links http://webbook.nist.gov/chemistry/ion/ Mass spectrometry