Field of science concerning ions and molecules in the gas phase
Gas phase ion chemistry is a field of science encompassed within both
chemistry and
physics. It is the science that studies
ions and
molecules in the gas phase, most often enabled by some form of
mass spectrometry. By far the most important applications for this science is in studying the
thermodynamics and
kinetics of reactions.[1][2] For example, one application is in studying the
thermodynamics of the
solvation of ions. Ions with small
solvation spheres of 1, 2, 3... solvent molecules can be studied in the gas phase and then extrapolated to bulk solution.
Transition state theory is the theory of the rates of elementary reactions which assumes a special type of
chemical equilibrium (quasi-equilibrium) between reactants and activated complexes.[3]
The process of converting an
atom or
molecule into an
ion by adding or removing charged particles such as
electrons or other ions can occur in the gas phase. These processes are an important component of gas phase ion chemistry.
In chemical ionization, ions are produced through the reaction of ions of a reagent gas with other species.[6] Some common reagent gases include:
methane,
ammonia, and
isobutane.
where G is the excited state species (indicated by the superscripted asterisk), and M is the species that is ionized by the loss of an
electron to form the
radicalcation (indicated by the superscripted "plus-dot").
Penning ionization refers to the interaction between a gas-phase excited-state atom or molecule G* and a target molecule M resulting in the formation of a radical molecular cation M+., an electron e−, and a neutral gas molecule G:[7]
Penning ionization occurs when the target molecule has an
ionization potential 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.
CID (also called collisionally activated dissociation - CAD) is a method used to fragment molecular
ions in the gas phase.[8][9] 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 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.[10][11]
Charge transfer reactions
There are several types of charge-transfer reactions[12] (also known as charge-permutation reactions[13]): partial-charge transfer
^Rogers, Mary T.; Armentrout, Peter B. (2016). "Chapter 4. Discriminating Properties of Alkali Metal Ions Towards the Constituents of Proteins and Nucleic Acids. Conclusions from Gas-Phase and Theoretical Studies". In Astrid, Sigel; Helmut, Sigel; Roland K.O., Sigel (eds.). The Alkali Metal Ions: Their Role in Life. Metal Ions in Life Sciences. Vol. 16. Springer. pp. 103–131.
doi:
10.1007/978-3-319-21756-7_4.
PMID26860300.
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