Subject potential energy surface

Should a complete potential energy surface be subjected to outer and inner effects, then a new potential energy surface is obtained on which the corresponding rection paths can be followed. This is described in part 4.3.1 by the example of the potential energy surface of the system C2H5+ jC2H4 under solvent influence. After such calculations, reaction theory assertions concerning the reaction path and the similarity between the activated complex and educts or products respectively can be made. 

Fig. 3. Vibrational population distributions of N2 formed in associative desorption of N-atoms from ruthenium, (a) Predictions of a classical trajectory based theory adhering to the Born-Oppenheimer approximation, (b) Predictions of a molecular dynamics with electron friction theory taking into account interactions of the reacting molecule with the electron bath, (c) Born—Oppenheimer potential energy surface, (d) Experimentally-observed distribution. The qualitative failure of the electronically adiabatic approach provides some of the best available evidence that chemical reactions at metal surfaces are subject to strong electronically nonadiabatic influences. (See Refs. 44 and 45.)...

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. 

An alternative and more costly approach is to actually follow the reaction from transition state to both the reactants and (independently) the products. In practice, this involves optimization subject to a fixed position along the reaction coordinate. A number of schemes for doing this have been proposed, and these are collectively termed Intrinsic Reaction Coordinate methods. Note, that no scheme is unique while the reactants, products and transition state are well defined points on the overall potential energy surface, there are an infinite number of pathways linking them together, just like there are an infinite number of pathways leading over a mountain pass. 

We shall now focus on our results of modelling the potential energy surfaces for photodissociation for three metal carbonyls, Cr(C0)6, 2( 0) , and Fe(CO)5. One common feature of these carbonyls from experiment is that they are known to eject one CO ligand on an ultrafast timescale (2,4-7,34). Although the nature of the initial states that lead to this are still under discussion (vide supra), the mechanism of relaxation of the unsaturated metal carbonyl that remains has also been the subject of much investigation (2,5-7,34,48,78,79). 

Although the novelty of observing chemically produced vibrational excitation provided an initial impetus, the main purpose of the studies to date has been to determine in detail the relative proportions of excited molecules in the various energy states, the fraction of the reaction energy that goes into internal excitation, which products are excited, and the fate of the excited molecules. Such data are used as aids in the construction of potential energy surfaces to be used, in turn, to describe the dynamics of the reactions. In short, the studies have been in the hands of kineticists. As interest in the subject has spread, more attention has been paid to applications laser action and the reactions of the excited molecules. 

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