Mechanism of Energy Transfer

Excited electronic states can be formed as a result of high temperatures, highly exothermic chemical reactions (chemiluminescence), radiative recombination of electrons 

Both the molar absorption coefficient and the absorption cross sections are measures of the electronic transition probability. A further important measure of this is the oscillator strength, /, given for the transition between a lower state 1 and an upper state 2, which is proportional to the area of the absorption band. 

An excited atom may decay spontaneously to the ground state with the emission of a photon of energy 

Einstein obtained a relation between spontaneous and stimulated emission, using the relation between the number of atoms in the two states 

When an atomic system is in equihbrium with the radiation field, as many transitions occur in the direction 1 — 2 as in the opposite direction, 2 1. In this case, the equihbrium condition will be 

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Given such a reference, we can classify various mechanisms of energy transfer either by the probability tiiat a certain energy transfer process will occur in a Leimard-Jones reference collision , or by the average energy transferred by one Leimard-Jones collision . 

C3.4.6 EXCHANGE MECHANISM OF ENERGY TRANSFER IN FORBIDDEN TRANSITIONS... 

Discuss and compare the mechanisms of energy transfer using high-pressure steam, microwaves and ultrasound. Discuss the role and limitations of solvents for carrying out a chemical reaction using these energy sources. 

The second light-requiring step ultimately leading to the tetraphenyl methane was shown to occur by energy transfer from triplet benzophenone to the fuchsone, resulting in triplet fuchsone. The mechanisms of energy transfer will be discussed in a later chapter. 

The slope divided by the intercept gives the rate ratio kjket. Table 6.7 gives the results for compounds (7), n = 2-4 in benzene solution. The detailed mechanism of energy transfer must be able to account for the 25-fold decrease in ket in going from n = 2 to n = 4. While inspection of molecular models shows that the average distance between chromophores... 

The exact mechanism of energy transfer can vary from one complex to another, and is still the subject of some debate. The possibilities are discussed in the following sections. 

Whatever the particular mechanism of energy transfer is, the fluorescence lifetime of the donor center, xd, is affected as a result of any energy transfer process to an acceptor. Therefore, expression (1.20) must be rewritten for the lifetime of the donor ions as follows ... 

Mechanism of Energy Transfer, in Mercury Photosensitization (Gunning... 

Perhaps enzyme-substrate recognition and interaction are facilitated by an oscillating active site Its correlated motion could position more readily and reliably the catalytically essential groups of atoms. Recognition of the substrate could be visualized as a nonlinear resonance phenomenon, perhaps providing the mechanism of energy transfer from the entatic active site region to the substrate. An off-resonance condition could characterize an enzyme-inhibitor interaction. 

Mercury Photosensitization, Isotopic Effects and the Mechanism of Energy Transfer in (Gunning and Strausz). 1 209... 

H.E. Gunning and O.P. Strauss, Isotope effects and the mechanism of energy transfer in mercuty photosensitization , Reference W, 1, 1963, 209. 

An attractive vehicle for study of the detailed mechanism of energy transfer is observation of the intramolecular process. The most straightforward approach involves use of a system such as the following ... 

Enhancement of Eu3+ fluorescence has also been observed [612] when incorporating Tb3+ ion in Eu3+ doped tungstate host lattice. The degree of enhancement is proportional to the Tb3+ ion concentration. The mechanism of energy transfer in this case may probably involve interaction with Tb3+ affecting the cohesive force operating on Eu3+. 

Figure 3.36 The Dexter mechanism of energy transfer through simultaneous electron exchange.

Figure 3.37 The Forster mechanism of energy transfer through transition dipole interaction.

This formula was first derived in ref. 6 when calculating the kinetics of donor luminescence decay in the presence of the randomly, i.e. chaotically, located acceptors under the condition n N and on the assumption of the resonance exchange mechanism of energy transfer. Similar equations were later used for the analysis of experimental data on the kinetics of electron tunneling reactions obtained under conditions of the chaotic distribution of the reagents and at n < N. As a rule, only the first term of the exponent in eqn. (23) has been taken into account, which is equivalent to employing the previously mentioned (see Sect. 2.1) stepwise approximation of the function 0(R,t) = exp[- 1V(jR)(]. In this case, one obtains... 

Quenching the luminescence of TMPD by phthalic anhydride (PA) and of pyromellitic dianhydride (PMA) by hexamethyl triindan (HMTI) in vitreous MTHF at 77 K has been discussed by Miller et al. [34]. The donors were the excited molecules of TMPD or molecules of HMTI in the ground state while PA molecules in the ground state or the excited molecules of PMA served as the electron acceptor. Quenching of both the fluorescence and the phosphorescence of excited molecules was observed. The authors deny the possibility of quenching the luminescence of TMPD and PMA via the mechanism of energy transfer since the luminescence has been quenched by mol-... 

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