The Role of Ion Dissociation Dynamics in the Study of Ion and Neutral Thermochemistry
Various thermochemical cycles involving dissociative photoionization onsets, electron affinities, and radical ionization energies are described in terms of their accuracy and information content. The information content of spectroscopic methods which yield spectral information and thus structural information are stressed. These ionic cycles are compared to traditional methods involving primarily chemical kinetics for obtaining free radical heats of formation. The ion methods are illustrated by thermochemical cycles involving the CH2CN radical and its positive and negative ions. Dissociative ionization is one of the most powerful methods for obtaining energetics of free radicals and ions. However, the information can only be accessed by carefully modeling the data with the statistical RRKM theory of unimolecular dissociation. Examples are illustrated for various molecular ions including the dissociation of ICH2CN which leads to CH2CN+ ions, and various organic esters, R’COOR+ which dissociate to various distonic and enolic isomers of methyl acetate.
KeywordsMethyl Acetate Dissociation Limit Kinetic Shift Methyl Butanoate Photoionization Mass Spectrometry
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