Transition metal ions, potential energy surface

Considerable interest in the subject of C-H bond activation at transition-metal centers has developed in the past several years (2), stimulated by the observation that even saturated hydrocarbons can react with little or no activation energy under appropriate conditions. Interestingly, gas phase studies of the reactions of saturated hydrocarbons at transition-metal centers were reported as early as 1973 (3). More recently, ion cyclotron resonance and ion beam experiments have provided many examples of the activation of both C-H and C-C bonds of alkanes by transition-metal ions in the gas phase (4). These gas phase studies have provided a plethora of highly speculative reaction mechanisms. Conventional mechanistic probes, such as isotopic labeling, have served mainly to indicate the complexity of "simple" processes such as the dehydrogenation of alkanes (5). More sophisticated techniques, such as multiphoton infrared laser activation (6) and the determination of kinetic energy release distributions (7), have revealed important features of the potential energy surfaces associated with the reactions of small molecules at transition metal centers. [Pg.16]

These results indicate that the transition from surface state III to surface state II is thermodynamically favorable. The redox potential of the trapped site coordinated with one carboxyl groups is less negative than the redox potential of the site coordinated with two carboxyl groups simultaneously. On this basis the energy level diagram of the electron trapped sites was proposed (Fig. 6). Such temperature transformations are typical for Pb doped and pure aqueous colloidal solutions. When the temperature is raised to room temperature for Pb ion doped solution, all photogenerated electrons are scavenged by metal ions,... [Pg.10]

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