Fifty years of ion and neutral thermochemistry by mass spectrometry

•Historical review of advances in measuring ion and neutral thermochemistry.•Discussion of advances in the determinations of ionization and appearance energies.•Advances in the measurement of electron affinities.•Several methods for measuring dissociation energies and their advances are discussed.•The ability to measure both ion and neutral thermodynamics using mass spectrometry. Originating with the appearance potentials for “positive rays”, the ability of mass spectrometry to obtain quantitative information about the energetics of both ions and neutrals has evolved dramatically. About 50 years ago, many of the techniques that are now common place were first implemented; the interim has seen significant advances in both instrumentation and analysis tools. In this review, a short historical perspective of mass spectrometric approaches to ion and neutral thermochemistry is provided. Included are determinations of ionization and appearance energies, electron affinities, and dissociation energies. The latter are explored via techniques utilizing metastable decomposition, visible and VUV photodissociation, infrared photodissociation, collision-induced dissociation, and electron-induced dissociations, as well as applications of equilibrium methods and association processes. Although many of these techniques focus on ion thermochemistry, the ability to measure the thermodynamics of neutrals via mass spectrometric approaches is also highlighted.