Potential energy surface, for reaction

Fig. 3. Schematic potential energy surfaces for reaction of FeH+, CoH+, and NiH+ with CH4 (93).

Another major, future advance in the quantum chemical computation of potential energy surfaces for reaction dynamics will be the ability to routinely compute the energies of molecular systems on the fly . The tedious and time-consuming process of fitting computed quantum chemical values to functional forms could be avoided if it were possible to compute the PES as needed during a classical trajectory or quantum dynamics calculation. For many chemical reactions, it should be practical in the near future to prudently select a sufficiently rapid and accurate electronic structure method to facilitate dynamics computations on the fly. 

A number of minima corresponding to oxonium ylides and H-bonded structures were found on the potential-energy surface for reaction of singlet carbenes with water and alcohols." Laser flash photolysis revealed that the rates of reaction between cyclopentadienylidene or fluorenylidene and alcohols increased with alcohol acidity and had linear Bronsted plots with slopes of 0.061 and 0.082, respectively.100 These results point to protonation with a very early transition state or to concerted OH insertion. For tetrachlorocyclopentadienylidene, the results showed that ylide formation (100) is predominant. 

S. Lorenz, A. Gross, M. Scheffler, Representing high-dimensional potential-energy surfaces for reactions at surfaces by neural networks, Chem. Phys. Lett. 395 (4-6) (2004) 210-215. 

Figure 6.3 Potential energy surface for Reaction 6.2. The energies are in kilocalories per mole and the reaction coordinate (defined as the difference between the two C-Cl distances) is in angstrom.

An ultrafast intermolecular electron transfer (ET) from electron donating solvent to an excited dye molecule was found. A temperature-dependent non-exponential time dependence was observed in aniline, and a temperature-independent single exponential process for Nile blue (160 fs) and oxazine 1 (260 fs) was observed in N,N-Smethylaniline. The solvation times of solvent anilines were obtained by dynamic Stokes shift measurements. The rate of ET in some systems was observed to be much greater than the solvation time of anilines. The dynamic behavior was simulated by the 2-dimen ional potential energy surface for reaction, taking into account of the effects of both solvent reorientation and nuclear motion of reactants. 

Fig. 2.29. Potential energy surface for reaction (6) adapted from Ref. [91].

Fig. 2.33. Possible potential energy surfaces for reaction (49). Solid line from Ref. [108).

In order to obtain a pictorial idea of the origin of isotope effects we shall now consider potential-energy surfaces for reactions. The potential energy of the bond C-H varies with the length according to the Morse curve (Fig. 1). If the molecule... 

Figure 7.2 Schematic potential energy surfaces for reactions with and without a saddle point.

Because of the difficulties involved in ab initio calculations of potential-energy surfaces for reactions, it would be highly desirable to have a semiempirical method that gives reliable reaction PES results. The MNDO, AMI, and PM3 methods have been widely applied to calculate relevant portions of PESs for chemical reactions (often with inclusion of solvent effects) so as to elucidate reaction mechanisms and transition-state structures. 

Contour drawing of the potential energy surface for reaction of 113. (Adapted from reference 220.)... 

Quantum mechanics (QM) calculations commonly produce potential energy surfaces for reactions at O K. In recent years, there has been an increasing effort to include entropy effects in the models, through a combination of QM and molecular mechanics (MM) methods, and thereby to calculate free energy surfaces at a particular temperature. Examples of the calculated entropic effects in inorganic systems can be found in the work of Ziegler and co-woikers. ... 

Leopoldini M, Marino T, Russo N, Toscano M (2009) Potential energy surfaces for reaction catalyzed by metalloenzymes from quantum chemical computations. In Russo N, Anton-chenko VY, Kryachko ES (eds) Self-organization of molecular systems from molecules and clusters to nanotubes and proteins, NATO Science for Peace and Security Series A Chemistry and Biology. Springer, New York, p 275-313. doi 10.1007/978-90-481-2590-6 13... 

D. G. Truhlar, Multiple potential energy surfaces for reactions of species in degenerate electronic states, J. Chem. Phys. 56 3189 (1972), 61 440(E) (1974). 

Soto, M.R., and M. Page (1990), Features of the potential energy surface for reactions of hydroxyl with formaldehyde, J. Phys. Chem., 94, 3242-3246. 

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