Cross self-quenching

Notice that this is the same as the mechanism written in Section II except that step (9), self-quenching, has been added. If we assume that the quantum yield of intersystem crossing for the sensitizer is unity and that all the sensitizer triplet is quenched either by the acceptor or by ground state sensitizer, then the following expression for 4>a, the actual quantum yield for reaction of the substrate triplet, can be derived ... 

The self-quenching rate constant of 21 x 10 cm /molecule s that was measured in these studies is unusually large (69). Quenching by various gases and collision induced rotational transitions have also been measured (68,69). The quenching cross sections by He and Ar in a supersonic jet increase at very low temperature (70), indicating the formation of collision complexes. ... 

As a matter of fact, the collisional cross-sections exhibit a clear dependence on the Franck-Condon factor. Their variation is relatively weak in the case of the very efficient self-quenching (a varying between 55 and 90 A ) and much more pronounced in the case of hght atoms. For He a varies from 0.3 A for 0= 15 to 1.8 A for v=25 and to 1.34 A for = 43 (an intermediate value of the Franck-Condon factor). 

Nd " ion has a disadvantage, which is called self-quenching of emission, due to its complex electronic stmcture. Por downconversion, an excited Nd " ion in the " p3/2 level could transfer part of the excitation to an unexcited Nd " ion. At room temperature, the process is dominated by the cross-relaxation process, i.e., (%3/2, " 19/2) C Ii5/2> " Ii5/2). Iti itiost Nd-doped laser materials, the final levels of the... 

The experimental results of Degenkolb et al. are shown in Table 1 together with self-quenching cross sections from other experiments. Their results indicate that the magnetic predissociation rises slowly and falls nearly... 

Exciting wavelength (A) Self-quenching cross sections (A ) b (see G )... 

Figure 5 Poly(ethylene)oxide lamella crystals grown within thin layers of melt (the white bar correspon

Several studies of bimetallic complexes in which the donor and acceptor are linked across aliphatic chains have demonstrated that these are generally weakly coupled systems. " Studies of complexes linked by l,2-bis(2,2 bipyridyl-4-yl)ethane (bb see Figure 5), indicate that these are good models of the precursor complexes for outer-sphere electron-transfer reactions of tris-bipyridyl complexes. A careful comparison of kinetic and spectroscopic data with computational studies has led to an estimate of //rp = 20cm for the [Fe(bb)3pe] + self-exchange electron transfer. In a related cross-reaction, the Ru/bpy MLCT excited state of [(bpy)2Ru(bb)Co(bpy)2] + is efficiently quenched by electron transfer to the cobalt center in several resolved steps, equations (57) and (58). ... 

At this stage QCM applications in aqueous media are still a vivid research area. Further sensitivity improvements can be obtained by an STW resonator. However, the real time observation of the incorporation processes, either specific or nonspecific, in comparison to a non-imprinted device is performed much more easily utilising QCMs than with optical devices. In particular, non-specific adsorption of cross-sensitive substances can be excluded by the use of suitable materials, such as polyurethanes, for mass-sensitive devices. In the case of optical sensing, the responses might be influenced by quenching or self-absorption. 

Since the EFG vanishes at cubic symmetry and the symmetry around the ions can be high, the negative amplitude of the cross EFG-TCE represents the static quenching of the individual contributions to the EFG. The cross correlation in the molecular contributions to the EFG does not necessarily results in a quenching, in a very inhomogeneous media the individual contributions could add on to enhance the self EFG-TCF. However, the cross correlation can never have a more positive amplitude than the self EFG-TCF, since when they are equal the total EFG-TCF cancels. There is both a static quenching of the amplitude of the... 

Figure 12 The molecular contributions to the electric field gradient (EFG) can be correlated. Hence the EFG-TCF can be divided into molecular self-EFG-TCF and cross-EFG-TCF terms (See equation (25)). The static quenching of the EFG is due to the momentary symmetry in the solvation shell. The cross EFG-TCF has a different decay that the self-EFG-TCF which results in a dynamic quenching of the molecular contributions.

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