Ion dissociation dynamics and thermochemistry by photoelectron photoion coincidence (PEPICO) spectroscopy

Photoelectron photoion coincidence (PEPICO) is a technique that permits the mass spectrometric investigation of energy-selected ions. Dissociation rates and accurate dissociation onsets can be measured. Such data provide not only rigorous tests of the statistical theories for unimolecular reactions, but also provide benchmark heats of formation for anchoring the gas-phase proton affinity scale. When combined with other mass spectrometric methods and quantum calculations of ionic structures, PEPICO provides a means to place the field of ion structures on a firm quantitative basis. Ions are produced by dispersed vacuum ultraviolet radiation in a small electric field in which electrons and ions are extracted in opposite directions. By measuring only ions in coincidence with energy-selected electrons, the ion internal energy is established by conservation of energy [E(ion) = hv - IE - E(el)]. Recent results as well as new developments in pulsed-field ionization and velocity map imaging are discussed. (C) 2000 Elsevier Science B.V.