Review

Bond-Forming Chemistry in the Gas-Phase Reactions of Atomic and Molecular Dications and Trications

“…This improving understanding of the properties of isolated dications led logically, in the 1990s, to a series of investigations to study the chemistry of these species when they were involved in low-energy collisions with atoms or molecules. 7,[19][20][21][22][23][24][25][26] Collisions of dications with neutrals had been studied before this date, but almost invariably at high collision energies in adapted conventional MSs, conditions where bond-forming chemistry is unlikely. [27][28][29][30] Although there were a few pioneering studies of dicationic reactivity at low collision energies, 31,32 it was not until the 1990s that the low-energy collisions of dications, collisions where conventional chemistry might be expected to occur, were investigated systematically.…”

“…Such a spectrum clearly reveals the different bimolecular reactions that generate pairs of monocations following the collision of the selected dication with the neutral. 24 Under appropriate voltage conditions, given the particular geometry of the TOF-MS (which involves a large detector), it can be shown from the form of the coincidence data that all the product ions are being detected. Thus, the relative intensities of the different peaks in the two-dimensional mass spectrum directly yield the relative cross sections for the different reactive channels.…”

“…For more experimental details of the coincidence experiments, and the subtleties of the data processing, the reader is referred to Refs. [24,69,76].…”

“…23,76,81 The scattering dynamics of dication reactions are most readily revealed by constructing scattering diagrams from the experimental data. As described in detail before, 24 such scattering diagrams can be in the CM frame or in the internal frame. A CM scattering diagram is a radial histogram where, for each ion plotted, the radial coordinate is the magnitude of that ion's CM velocity |w i |, and the angular coordinate is the scattering angle (0 y 180 ) between w i and the direction of the velocity of the center of mass, which, under the experimental conditions, is usually very close to the direction of the velocity of the reactant dication.…”

“…A simple model that accounts for the majority of experimental observations was proposed by Herman 25,42 and has been extensively utilized by others. 23,24,63 The prototypical potential energy surfaces in this model are illustrated in Figure 10. This model recognizes that the dication and neutral approach each other on a potential energy surface dominated by polarization attraction.…”