Quench requirements

An empirical point in support of the strong velocity dependence is the rule of thumb for quenching, requiring a high relative velocity [>60 m/s (200 ft/s)]. 

This type of static quenching requires relatively high quencher concentrations and it follows the Perrin action sphere model [64]. According to this model, each emitter molecule is surrounded by an active volume (in the general case it needs not be a sphere), such that if there is one quencher molecule at least within this volume, then quenching takes place instantly but molecules which have no quencher within the active volume emit just like those in a sample devoid of quencher. The Perrin model leads to two observable results ... 

Figure 6. Minimum quench requirements. One-inch bed dry MISP, 105 mm.

From a practical standpoint, it is essential to design and operate the reactor in such a way that the maximum cycle life for the reactor is achieved while minimizing the number of quenches required. This means that the quenching position(s) and the variation of feed temperature with time must be optimized to achieve the maximum cycle life. 

Figure 4-8 Effect of feed temperature on quench requirement, reactor cycle life, and optimum quench location (after Shah et at. ).

Figure 4-11 Effects of desulfurization level on quench requirement and reactor cycle life as a function of quench location (after Shah ei al. 1").

The recording of the rising part of the fluorescence transient (the decrease of photochemical quenching) requires a time resolution of the order of 100 ps per curve. A sequence this fast cannot be recorded in a single-shot experiment. Therefore, the recording of the sequence must be repeated and the data accumulated until enough photons have been collected. A suitable setup is shown in Fig. 5.33. 

Huorescence quenching requires a close approach of the quencher to the fluorophore and hence it can be used for smdying various structural problems and dynamie processes. When both the fluorophore and quencher are dissolved in a solution, the time-resolved data report on the rate of diffusion. When the... 

Shetlar, M. D. Mol. Photochem. 1974,6,191 reported a general form of the Stem-Volmer equation for a system with multiple excited states. Green, N. J. B. Pimblott, S. M. Tachiya, M. /. Phys. Chem. 1993,97,196 presented generalizations for cases in which the quenching requires description with a time-dependent rate constant. 

Lower quench requirement reduces the recycle gas compressor utilities. 

In accordance with the model it is assumed that the rate of geminate recombination of the CT state to the first excited singlet state follows Eq. (5) under the constraint that E >E. This implies that the CT state is always above the singlet exciton state. In single component molecular systems this condition is usually fulfilled as evidenced by the observations that (1) the fluorescence spectra are mirror-symmetric with absorption and (2) fluorescence quenching requires a high electric field [53]. Obviously, the present theory is limited to cases in which E y > Ecoui-... 

Both static and dynamic quenching require contact of the luminophore with a quencher molecule. This requirement is the basis of the many applications of luminescence quenching. Because there are so many molecules that can act as luminescence quenchers, an appropriate quencher can be selected for any luminophore under study in order to investigate specific properties of the luminophore. An example of biochemical applications of luminescence quenching is given later in this section. 

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