Process isoenergetic

Internal conversion A photophysical process. Isoenergetic radiationless transition between two electronic states of the same multiplicity. When the transition results in a vibrationally excited molecular entity in the lower electronic state, this usually undergoes deactivation to its lowest vibrational level, provided the final state is not unstable to dissociation. 

The conversion from St to S, is an isoenergetic process that is followed by vibrational relaxation of the new vibrationally hot state. 

Adib, A. B., Entropy and density of states from isoenergetic nonequilibrium processes, Phys. Rev. E 2005, 71, 056128... 

A natural question is In which temporal order do the reorganization processes and the proper electron transfer take place The answer is given by the Frank-Condon principle, which in this context states First the heavy particles of the inner and outer sphere must assume a suitable intermediate configuration, then the electron is exchanged isoenergetically, and finally the system relaxes to its new equilibrium... 

Radiationless transitions (internal conversion and intersystem crossing) between electronic states are isoenergetic processes and are drawn as wavy arrows from the v = 0 level of the initial state to a vibrationally-hot (v > 0) level of the final state. 

The transthiolesterification reaction took place efficiently under mild conditions in aqueous media by simply mixing all the components. The library generation process was initiated by mixing equimolar amounts of all acyl components with five equivalents of each thiol. Since thiol component (7) is connected to the five different acyl functionalities at t, this ensured equal quantities of all thiol components in the system. Thus, the resulting concentrations of the formed constituents were relatively comparable, and the library showed close to isoenergetic behavior. 

Fig. 7. Energetics of a bimolecular rate process. Top Representation of the potential energy surface along coordinate axes corresponding to the interatomic distance of B-to-C and A-to-B, where incremental displacements along the potential energy axis are shown as a series of isoenergetic lines (each marked by arbitrarily chosen numbers to indicate increased energy of the transition-state (TS) intermediate relative to the reactants). Bottom Typical reaction coordinate diagram for a bimolecular group transfer reaction.

A term in photochemistry and photophysics describing an isoenergetic radiationless transition between two electronic states having different multiphcities. Such a process often results in the formation of a vibrationally excited molecular entity, at the lower electronic state, which then usually deactivates to its lowest vibrational energy level. See also Internal Conversion Fluorescence... 

Dipole-dipole coupling, in which the transition moments of donor and acceptor are strongly coupled.142 Such interactions can occur over large distances if both of the moments are large and the transition energies are matched so that the overall process is isoenergetic. 

One of the major questions that remains to be answered is the detailed mechanism of charge transfer. For redox couples which lie in the gap of the semiconductor, isoenergetic electron transfer would require the existence of an appropriate surface state. While such states have been postulated, little direct evidence of their existence is available. An alternate possibility is an inelastic (non-isoenergetic) electron transfer process such as is commonly observed in solid state dev ices.(18)... 

That surface interactions play such a role clearly demands that some sort of surface state concept be invoked. However, no simple techniques have yielded direct information about the nature of such states. To explain charge transfer, isoenergetic electron or hole processes are normally invoked with a subsequent thermalization of the electron or hole in the semiconductor. This unfortunately necessitates the existence of a surface state at the level of the redox potential. This may of necessity occur when strong chemisorption is present. However, in those cases,... 

Figure 1 illustrates different modes of electron transfer between electrolyte states and carriers in the bands at the semiconductor surface. If the overlap between the electrolyte levels and the semiconductor bands is insufficient to allow direct, isoenergetic electron transfer, then an inelastic, energy-dissipating process mustnbe used to explain experimentally observed electron transfer. Duke has argued that a complete theory for electron transfer includes terms that allow direct, inelastic processes. The probability of such processes, however, has not been treated quantitatively. 

In the case of a metal-semiconductor junction the semiconductor surface is closely coupled to the metal. As a result electrons in the conduction band at the surface see a high density of empty metal states into which they can cross the interface isoenergetically. Similarly, valence band holes see a high density of filled electron states in the metal. As a result, electron transfer is usually treated as direct transfer in a thermionic process and surface states a re-rjs legated to a minor role in surface generation and recombination effects. -1—... 

Does bimolecular substitution on tricoordinate sulfur involve the formation of an intermediate, or is it a one-step process The evidence is somewhat inconclusive. For example, when sulfite ester (14) is hydrolyzed with HO containing 180, 180 is found in the product but no significant amount is present in the recovered unreacted ester.70 Bunton and co-workers interpreted this to mean that the mechanism shown in Reaction 4.37 in which the intermediate 15 is formed in a rapid equilibrium prior to the transition state for the reaction, is ruled out. If 15 were so formed, they reasoned, it would rapidly equilibrate with isoenergetic 16. Then loss of HO- from 16 would result in lsO in recovered... 

Non-radiative processes can also be distinguished on the basis of the spin multiplicity of the initial and final electronic states. Internal conversion (IC) is the non-radiative crossover between two states of identical multiplicity, while intersystem crossing (ISC) is a process in which spin is not conserved. In both instances, crossover between the states is isoenergetic, regardless of the multiplicity. Subsequent vibrational relaxation (VR) occurs to release excess vibrational energy (see Figure 2.12). 

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