Potential surface for reactions

VB POTENTIAL SURFACES FOR REACTIONS IN SOLUTIONS 2.2 1. General Considerations... 

Figure 2. Two-dimensional potential surface for reaction in the Sumi-Maicus scheme along the coordinate X for diffusive Brownian motions and the coordinate q for much faster intramolecular vibrational motions, and an example of reactive trajectories there.

Figure B3.4.10. Schematic figure of a ID double-well potential surface. The reaction probabilities exliibit peaks whenever the collision energy matches the energy of the resonances, which are here the quasi-bound states in the well (with their energy indicated). Note that the peaks become wider for the higher energy resonances—the high-energy resonance here is less bound and Teaks more toward the asymptote than do the low-energy ones.

Silicon cluster reactions are an example of a newly emerging field of research which is very amenable to study with electronic structure methods. This exercise will examine the potential surface for silicon cation reacting with silane (SiH4). Such reactions are central to the growth of large silicon clusters, which occurs by sequential additions of -SiHj ... 

The potential surface for such a reaction has the following general shape ... 

The main features of the chemical bonding formed by electron pairs were captured in the early days of quantum mechanics by Heitler and London. Their model, which came to be known, as the valence bond (VB) model in its later versions, will serve as our basic tool for developing potential surfaces for molecules undergoing chemical reactions. Here we will review the basic concepts of VB theory and give examples of potential surfaces for bond-breaking processes. 

Exercise 1.9. Evaluate the potential surface for the H+H2— H2 + H exchange reaction and determine the energy of the transition state obtained with r12 = r23 = 1.4 A relative to the minimum energy of the system when one hydrogen atom is at infinity. 

Exercise 2.1. Evaluate the ground-state potential surface for the CH3OCH3—> CH3 + CH30- reaction using the reaction field model, with a cavity radius a = R/2 + 1.5. 

VB Potential Surface for Proton Transfer Reactions in Solutions... 

FIGURE 6.9. Potential surface for a general acid-catalysis reaction in solution r3 and r4 are the Ob -H and C-O distances, respectively. Regions of the potential surface with more than 50% ionic character are dotted (see Ref. 6 for more details). 

FIGURE 7.6. Comparing the potential surfaces for the catalytic reaction of trypsin (upper figure) to the corresponding reaction in solution (lower figure). The different configurations that define the corners of the potential surface are drawn on the upper left portion of the figure. 

FIGURE 9.1. The potential surface for proton transfer reaction and the effect of constrainir the tiA B distance. The figure demonstrates that the barrier for proton transfer increasi drastically if the A — B distance is kept at a distance larger than 3.5 A. However, in solutic and good enzymes the transfer occurs through pathway a where the A - B distance is arour 2.7 A. 

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