Minimum energy crossing point mecp

Figure 10. Arrhenius plot of the thermal rate constants for the 2D model system. Circles-full quantum results. Thick solid (dashed) curve present nonadiabatic transition state theory by using the seam surface [the minimum energy crossing point (MECP)] approximation. Thin solid and dashed curves are the same as the thick ones except that the classical partition functions are used. Taken from Ref. [27].

A and A = 0.1 eV. The adiabatic ground potential energy surface is shown in Fig. 11. The present results (solid line) are in good agreement with the quantum mechanical ones (solid circles). The minimum energy crossing point (MECP) is conventionally used as the transition state and the transition probability is represented by the value at this point. This is called the MECP approximation and does not work well, as seen in Fig. 10. This means that the coordinate dependence of the nonadiabatic transmission probability on the seam surface is important and should be taken into account as is done explicitly in Eq. (18). 

Figure 24. Electron-transfer rate versus electronic coupling strength. The temperature is T = 500 K. Solid line with circle-present results from Eq. (126) with the transition probability averaged over the seam surface. Solid line with square-present results with the transition probability taken at the minimum energy crossing point (MECP). Dashed line-Bixon-Jortner theory Ref. [109]. Dotted line-Marcus s high temperature theory. Taken from Ref. [28].

SCHEME 10.15 Qualitative examples for reactions taking place with different spin states involved. Dashed curves indicate reaction paths with higher spin state. Black dots indicate minimum energy crossing points (MECPs). 

The termination of the polymerization reaction by BHE to the chromium center and subsequent dissociation of the resulting olefin is found to require about 25 kcal mol and to be thermodynamically much less feasible than the alternative termination process by BHT to a monomer. The latter process involves spin change two minimum-energy crossing points (MECPs) and further transition states and intermediates have been identified [39]. The termination reaction may also be controlled by the use of polymerization additives [40]. 

The reaction was completed via a readily accessible triplet-singlet minimum energy crossing point (MECP) to give the symmetrieally bound singlet il -02 adduct. The 0-0 distance of 1.43 A in this speeies was eonsistent with the presence of a peroxide ligand. 

Proposed mechanistic pathway for bis(imidazolium) formation (MECP = minimum energy crossing point).-... 

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