Radiation quenching

Bimolecular deactivation (pathway vii, Fig. 1) of electronically excited species can compete with the other pathways available for decay of the energy, including emission of luminescent radiation. Quenching of this kind thus reduces the intensity of fluorescence or phosphorescence. Considerable information about the efficiencies of radiative and radiationless processes can be obtained from a study of the kinetic dependence of emission intensity on concentrations of emitting and quenching species. The intensity of emission corresponds closely to the quantum yield, a concept explored in Sect. 7. In the present section we shall concentrate on the kinetic aspects, and first consider the application of stationary-state methods to fluorescence (or phosphorescence) quenching, and then discuss the lifetimes of luminescent emission under nonstationary conditions. 

Effects of Radiation Quenching, Ion-Bombardment, and Annealing on Catalytic Activity of Pure Nickel and Platinum Surfaces. II. Hydrogenation of Ethylene (continued). Hydrogen-Deuterium Exchange f... 

These results suggest that the high activity for the above reaction, following radiation quenching or argon-ion bombardment, is due to the presence of surface lattice defects which are largely removed by subsequent annealing. The results for nickel are consistent with the accepted view that the natures of the defects in the two cases are not the same. 

Samples were investigated in a cast (arc-melted) as well as in annealed condition, a) 1000°C, 65 h in high vacuum, radiation quenched, b) 500°C, 750 h in evacuated silica tubes. Starting materials were 99.9% pure. Congruent melting behavior was confirmed by metallographic analysis. 

Hiebl et al. (1981) studied the superconducting behavior for 1.5K in the pseudoternary system YRh4B4-LuRh4B4-ThRh4B4 on 30 samples in as-cast as well as annealed condition (1250°C, 48 h, radiation quench). 

Hydroxybenzophenones represent the largest and most versatile class of ulbaviolet stabilizers that are used to protect materials from the degradative effects of ulbaviolet radiation. They function by absorbing ultraviolet radiation and by quenching elecbonically excited states. 

In tbe first attempt to prepare a two-dimensional crystalline polymer (45), Co y-radiation was used to initiate polymerization in monolayers of vinyl stearate (7). Polymerization at the air—water interface was possible but gave a rigid film. The monomeric monolayer was deposited to give X-type layers that could be polymerized in situ This polymerization reaction, quenched by oxygen, proceeds via a free-radical mechanism. 

Through radiation also, the arc plasma di.ssipates a part of its heat which supplements the quenching. But this is too meagre a contribution, as heat dissipation occurs only through the outer surface of the arc plasma. Nevertheless, it is the major cause of gas impediment giving rise to the phenomenon of clogging, discussed later, and which helps in arc extinction. 

Short-wavelength UV radiation (A = 254 nm) is employed for excitation. This allows aromatic organic compounds, in particular, to be detected by fluorescence quenching. Uranylacetate may also be excited at A = 366 nm. 

However, the optical train illustrated in Figure 22B allows the determination of fluorescence quenching. The interfering effect described above now becomes the major effect and determines the result obtained. For this purpose the deuterium lamp is replaced by a mercury vapor lamp, whose short-wavelength emission line (2 = 254 nm) excites the luminescence indicator in the layer. Since the radiation intensity is now much greater than was the case for the deuterium lamp, the fluorescence emitted by the indicator is also much more intense and is, thus, readily measured. 

This is also (see [R 6]) a commercial chip ( Radiator ), provided by MCS, Micro Chemical Systems Ltd., The Deep Business Center [20]. A bottom plate contains an extensively wound serpentine channel. A top plate covers this microstructure. The two reactant solutions enter via capillary tubing through holes in the top plate. The first reactant is fed at the start of the serpentine path and the second enters this path in a short distance. Shortly before the end of the serpentine, a third stream can enter which may serve, e.g., for dilution and thus quenching of the reaction. After a very short passage, the diluted streams enter via a fourth port analytics. Commercially available capillary connectors were employed. 

Norrish RGW, MacF SW (1940) The quenching of the resonance radiation of sodium. Proc R Soc A176 295-312... 

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