Spectroscopy and chemical dynamics of weakly bound alkaline-earth metal ion-H2 and alkaline-earth metal ion-hydrocarbon complexes

The activation of hydrocarbon bonds by metal atoms are among the most vital processes in chemistry. This review focuses an the spectroscopy and chemical dynamics of weakly bound alkaline-earth metal ion-H-2 and alkaline-earth metal ion-hydrocarbon bimolecular complexes using mass-resolved photodissociation spectroscopy techniques. The photodissociation spectroscopy of isolated clusters, in concert with translational energy spectroscopy of the products, gives unique and detailed insight into the fundamental metal-hydrocarbon interactions. Measurements of the product yield, translational energy release and photofragment anisotropy as a function of the photolysis laser wavelength give quantitative information about the structure, lifetime and bonding of the complex and insight into the nuclear motion dynamics and the electronic non-adiabatic interactions which determine the product branching and energy partitioning. The experimental techniques of photodissociation spectroscopy are reviewed. Several examples are discussed including examples of the photoactivation of H-H and C-H sigma bonds and of C=C pi bonds by Mg+. In each case, a strong electronic orbital alignment selectivity is observed. The quenching mechanism can be explained by a bond-stretch process leading to rapid but non-adiabatic dissociation of the complex through a conical intersection or narrowly avoided surface crossing with the ground electronic surface. Additional examples of the photoactivation of C-O bonds and of photoinduced charge transfer chemistry are also discussed.