Quenching cycle, dynamic

For sodium, such reactions become energetically favorable for the excited states. Moreover, they appear to be sufficiently fast ki-netically to reach a steady state during the initial part of the laser pulse. Their overall effect is to drain off elemental sodium or lithium from the dynamic excitation/physical quenching cycle into these chemical sinks. The actual extent depends on the relative magnitudes of the production and loss fluxes. 

As will be apparent in Chapter 4, MD simulations have made major contributions to our understanding of the structures and dynamical properties of solids. Problems and processes simulated include phase transitions (e.g. Impey et al., 1985 Meyer and Ciccotti, 1985), orientation dynamics in molecular crystals (e.g. Dove and Pawley, 1984) and ionic and diffusion (e.g. Gillan and Dixon, 1980 Vashishta and Rahman, 1978). In addition, they have been used to study melting and, as noted above, to prepare glass structures by a simulated melt-quench cycle as described by Vessal in Chapter 12. 

In an alternative mechanism, the substrate molecule is again coordinated to tetrahedral Zn, with the coordinated water molecule now serving as a site for transient proton transfer, thereby generating a penta-coordin ated zinc intermediate. Formation of this intermediate during substrate turnover was supported by time-resolved freeze-quenched X-ray absorption fine spectroscopic analysis of the thermophilic bacterium Thermoanaerobaaer brockii alcohol dehydrogenase (TbADH). These results thus provided further evidence for the dynamic alteration of the Zn from a tetrahedral to a penta-coordinated form with detection of two new penta-coordinated intermediate states these included the water molecule in the zinc coordination sphere during a single catalytic cycle. 

Farber A, Young AJ, Ruban AV, Horton P and Jahns P (1997) Dynamics of xanthophyll-cycle activity in different antenna subcomplexes in the photosynthetic membranes of higher plants. The relationship between zeaxanthin conversion and nonphotochemical fluorescence quenching. Plant Physiol 115 1609-1618... 

For to = S = 0, the initial wavepacket is considered to be prepared instantaneously at maximum intensity. In contrast, if to is set equal to T/4 (T = In/co), corresponding to 5 = tt/2, the initial state preparation occurs at the start of an optical cycle, i.e., at zero-field infensity. The two situations result into completely different dynamics, the former leading to dissociation quenching, while the latter is monitored by a barrier suppression mechanism. This distinction can best be understood by viewing the dynamics as taking place on the time-dependent adiabatic potential surfaces W R,t) which arise from diagonalizing the potential energy operator of Eq. (61). 

One should note that the CRAMPS technique is not necessarily a panacea for H NMR studies on surfaces, or for any other type of sample. Dynamics associated with motion and/or chemical reactions with a time constant that is comparable to the cycle time of the multiple-pulse sequence interferes with a multiple pulse averaging of H- H dipolar interactions [3b,4f]. Of course, an analogous problem can also arise with MAS, for which the critical period is i as. where v as is the MAS frequency [26]. To quench this kind of dynamic interference with the linenarrowing efficiency of any cyclic technique, like MAS and/or a multiple-pulse sequence, one would have to... 

The Forster cycle and the fluorescence titration methods assume that the dynamic equilibrium between prototropic species is established in the excited state. When fast proton-induced fluorescence quenching (k ) competing with proton transfer process (k ) is involved (see Scheme 2.1), dynamic analysis as described below is required to determine the accurate pK values. 

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