Unimolecular Dissociations in Mass Spectrometry

Abstract

Gaseous reactions can be categorized as (a) thermal reactions in which activation and deactivation of a molecule proceed via molecule/molecule collisions, and (b) unimolecular reactions of highly excited molecules or ions taking place without collisions:

$$ \begin{array}{lll} \mathrm{ A}+\mathrm{ M}\;\xrightarrow[{{k_1}}]{}{{\mathrm{ A}}^{*}}+\mathrm{ M}\quad (\mathrm{ collisional}\;\mathrm{ activation}) \hfill \\{{\mathrm{ A}}^{*}}+\mathrm{ M}\xrightarrow[{{k_{-1 }}}]{}\mathrm{ A}+\mathrm{ M}\quad (\mathrm{ collisional}\;\mathrm{ deactivation}) \hfill \\{{\mathrm{ A}}^{*}}\xrightarrow[{{k_2}}]{}\mathrm{ Product}\quad (\mathrm{ unimolecular}\;\mathrm{ reaction}). \hfill \end{array} $$