Energy transfer electronic

Detailed balance relates the rates of a particular activation and deactivation energy transfer process. Detailed balance thus provides a quantitative exact relation between rate constants that correspond to the same gap. This is unlike the principle of exponential gap tiiat provides an estimate of how the rate constants vary when the gap changes. The quahtative implication of detailed balance is that on a quantum state-to-quantum state basis, the rate constant for the activation process is always smaller than the rate constant for the reverse deactivation process. Take as an example the V—T process that we started this section with, A -I- BC(v = 0) A -I- BC(v = 1) and the reverse deactivation process, A -I- BC(v = 1) A -I- BC(v = 0). Detailed balance states that at equilibrium the rates of these two detailed ways of transferring populations between BC(v = 1) and BC(v = 0) must be equal. This is to be so even though there may be other processes that can transfer populations, such as transitions in the IR. Therefore, using the subscript eq to designate concentrations at equilibrium, 

Detailed balance therefore determines the exact ratio of the two rate constants A (v = 0 v=l) [BC(v=l)]gq 

The principle of exponential gap tells us that either one of the two rate constants in Eq. (9.18) is small if the gap in a V—T process is large. It does not however imply that the two rates are equal, meaning that they depend only on the magnitude, I A l and not on the sign of the translational release, see Problem J. 

There is considerable interest in the collision dynamics of electroiucally excited species not only due to their practical importance but also because such processes raise novel theoretical points. Since the electronic excitation energy is usually quite large, the adiabatic criterion would seem to rule out the efficient conversion of electronic to vibrational (or translational) energy upon collision. Yet, as we have already seen, such processes do occur, often with reasonable efficiency. Thus 

Our purpose in this section is to suggest what special features in the electronic structure of the reagents allow electronically non-adiabatic processes, with their nominally very high gap, to occur efficiently. The required feature is not invariably present. Many processes are electronically adiabatic. The exponential gap principle is valid. We will sketch a mechanism that, if present, allows the gap to be smaller than what you would expect. 

In passing to conversion of electronic excitation energy in molecular collisions, consider first the transfer of electronic to electronic energy in atomic collisions 

Yet another type of quasi-resonant processes corresponds to the so-called intramultiplet mixing, i.e. to transitions between fine-structure components of 

When sodium vapor is excited by one of the D-lines, the fluorescence spectrum is known to exhibit another line of an intensity increasing with the efficiency of collisional mixing 

Many experimental data concerning processes of the above type are now available [240]. Some of these, particularly those for processes involving alkali metals, have obtained extensive theoretical interpretation [341]. 

A different kind of energy conversion corresponds to the quenching of excited atoms when the electronic energy of the order of 1 eV is transformed into translational energy 

If an excited donor molecule D reverts to its ground state with the simultaneous transfer of its electronic energy to an acceptor molecule A, the process is referred to as electronic energy transfer  

The acceptor can itself be an excited state, as in triplet-triplet annihilation. (Cf. Section 5.4.5.5.) The outcome of an energy-transfer process is the quenching of the emission or photochemical reaction associated with the donor D and its replacement by the emission or photochemical reaction characteristic of A. The processes resulting from A generated in this manner are said to be sensitized. 

Energy transfer can occur either radiatively through absorption of the emitted radiation or by a nonradiative pathway. The nonradiative energy transfer can also occur via two different mechanisms—the Coulomb or the exchange mechanism. 

Radiative energy transfer is a two-step process and does not involve the direct interaction of donor and acceptor  

This clearly reflects the fact that J is not connected to the oscillator strengths of the transitions involved. 

2 Nonradiative Energy Tiransfer The nonradiative energy transfer D + A D + A  

At this point, we have to consider yet another very important process that is likely to go hand in hand with photoinduced electron transfer reactions—the electronic energy transfer. 

In a supramolecular system, electronic energy transfer, as depicted in Fig. 3.1, can be viewed as a radiationless transition between two locally, electronically excited states. Similarly to the electron transfer described above, we deal with two different states. Nevertheless, these states are local excitations lacking any charge transfer. 

3 Concepts of Photoinduced Electron and Energy Transfer Processes 

the rate constant for the energy transfer process is given by a golden rule expression  

//() is the electronic coupling between the two excited states intercon-verted by the energy transfer process and FCWDen is an appropriate Franck-Condon factor. 

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In this chapter we shall first outline the basic concepts of the various mechanisms for energy redistribution, followed by a very brief overview of collisional intennoleciilar energy transfer in chemical reaction systems. The main part of this chapter deals with true intramolecular energy transfer in polyatomic molecules, which is a topic of particular current importance. Stress is placed on basic ideas and concepts. It is not the aim of this chapter to review in detail the vast literature on this topic we refer to some of the key reviews and books [U, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, and 32] and the literature cited therein. These cover a variety of aspects of tire topic and fiirther, more detailed references will be given tliroiighoiit this review. We should mention here the energy transfer processes, which are of fiindamental importance but are beyond the scope of this review, such as electronic energy transfer by mechanisms of the Forster type [33, 34] and related processes. 

Resonant processes of some importance include resonant electronic to electronic energy transfer (E-E), such as the pumping process of the iodine atom laser... 

Jean J M, Chan C-K and Fleming G R 1988 Electronic energy transfer in photosynthetic bacterial reaction centers Isr. J. Chem. 28 169-75... 

Lamola, A. A. (1969). Electronic energy transfer in solutions theory and application. In Leermakers, P. A., and Weissberger, A. (eds.), Energy Transfer and Organic Photochemistry, Technique of Organic Chemistry 14 17-132. Interscience Publishers, New York. 

Enolate anions (4e) that have been heated by infiared multiple photon absorption for which torsional motion about the H2C-C bond, which destabilizes the 7t orbital containing the extra electron, is the mode contributing most to vibration-to-electronic energy transfer and thus to ejection. 

Chiorboli C, Indelli MT, Scandola F (2005) Photoinduced Electron/Energy Transfer Across Molecular Bridges in Binudear Metal Complexes. 257 63-102 Coleman AW, Perret F, Moussa A, Dupin M, Guo Y, Perron H (2007) Calix[n]arenes as Protein Sensors. 277 31-88... 

Not all sensitized photochemical reactions occur by electronic energy transfer. Schenck<77,78) has proposed that many sensitized photoreactions involve a sensitizer-substrate complex. The nature of this interaction could vary from case to case. At one extreme this interaction could involve a-bond formation and at the other extreme involve loose charge transfer or exciton interaction (exciplex formation). The Schenck mechanism for a photosensitized reaction is illustrated by the following hypothetical reaction ... 

A. A. Lamola, Electronic Energy Transfer in Solution Theory and Applications, in Techniques of Organic Chemistry, XIV, P. A. Leermakers and A. Weissberger, eds., Interscience, New York (1969), pp. 17-132. 

Eastman, R. H., 158, 166 Eaton, P. F., 460 Eigen, M., 80 Eisenberg, W., 125 Electrocyclic addition, 46 Electrocyclic reaction rules, 339 Electrocyclic reactions, 402,408 4n-examples, 408 (4n + 2)-examples, 410 Electron impact spectroscopy, triplet energy, 220-223 Electronic energy transfer, 267 Electronic integral, 21 Electronic transitions /-a ,16 n -Mr, 16... 

Wilkinson, F. and Ho, W.-T. 1978. Electronic energy transfer from singlet molecular oxygen to carotenoids. Spectrosc. Lett. 11 455-463. 

Microanalysis of the three PET-4,4 -SD copolymer yarns for sulfur yielded concentrations in agreement with the theoretical values. Since the 4,4 -SD comonomer was definitely incorporated into the three copolymer yarns, the absorption and luminescence characteristics of the copolymers point towards a co-absorption process between 4,4 -SD and PET rather than an electronic energy transfer process. 

Nonradiative transfer of excitation energy requires some interaction between donor and acceptor molecules and occurs if the emission spectrum of the donor overlaps the absorption spectrum of the acceptor, so that several vibronic transitions in the donor must have practically the same energy as the corresponding transitions in the acceptor. Such transitions are coupled, i.e., they are in resonance, and that is why the term resonance energy transfer (RET) or electronic energy transfer (EET) are often used. 

Ermolaev VL, Bodunov EN, Sveshnikova EB et al (1977) Nonradiative electronic energy transfer. Nauka, Leningrad... 

Chattoraj M, Chung DD, Paulson B et al (1994) Mediated electronic energy transfer effect of a second acceptor state. J Phys Chem 98 3361-3368... 

Next we shall show that the electronic energy transfer rate can be put into the spectral overlap form. Notice that by ignoring the super-exchange term we have... 

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