Mass spectrometry in connection with electrospray ionization can be used for investigation of compositions of reaction mixtures. A reaction solution is directly introduced into a mass spectrometer and components of the reaction mixture are detected as ions. Favorably for mass spectrometric studies, intermediates in organometallic reactions are often in the ionized form due to a metal present in the catalyst. The reaction intermediates are isolated by the transfer to the gas phase and therefore their properties can be effectively studied. Investigation of unimolecular reactivity provides information about the structure of the ions and about the bonding energies between their components. For example, we can determine bonding energy between organometallic catalyst and a substrate. We can also study reactivity of ions with other reactants and determine kinetics of a given reaction.
Ion spectroscopy is a novel method, which experiences a large development in the last three years. We use a multiuser facility CLIO, infrared free-electron laser nearby Paris, for measurements of infrared multiphoton dissociation (IRMPD) spectra. Reaction intermediates are generated exactly as in the laboratory experiments and isolated in an ion trap. Fragmentation of ions is induced by irradiation by the IR photons and detected by means of mass spectrometry. The IRMPD spectra of reaction intermediates are obtained from the dependence of the fragmentation on the wavelength of the photons. Ion spectroscopy is a very sensitive method, because mass spectrometry in principle allows to study even a fragmentation of only several ions.
Spectroscopy and reactivity studies are accompanied by theoretical calculations. Combination of all experimental and theoretical results provides a comprehensive picture of a given reaction and its reaction mechanism.