Charge Transfer

Synonyms

Charge exchange

Definition

Charge transfer is a chemical process whereby electric charge is transferred from a positive or negative ion (cation or anion) to a neutral atom or molecule.

Overview

Simple charge transfer reactions between atomic or molecular ions and neutral atoms and molecules are important in many astronomical environments, ranging from planetary nebulae to comets, to dark molecular clouds. Reactions of the type

$$ {\mathrm{H}}^{+}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{H}}_2{\mathrm{O}}^{+}+\mathrm{H} $$

and

$$ {\mathrm{C}}_2{{\mathrm{H}}_2}^{-}+\mathrm{C}\mathrm{N}\to {\mathrm{C}\mathrm{N}}^{-}+{\mathrm{C}}_2{\mathrm{H}}_2 $$

are exothermic, rapid, and proceed with no molecular rearrangement. On the other hand, dissociative charge transfer reactions involve the breaking of chemical bonds, examples of which are:

$$ {\mathrm{He}}^{+}+\mathrm{C}\mathrm{O}\to {\mathrm{C}}^{+}+\mathrm{O}+\mathrm{He} $$

and

$$ {\mathrm{C}}_2{\mathrm{H}}^{-}+\mathrm{N}\to...