Chemical effects during irradiation

The lifetime of the excited state shown in eqn. (59e) should, in consequence, be much larger for large band-gap oxides such as A1203 or Si02 on MgO, than for oxides having smaller band gaps. The former will thus have greater possibilities for interaction of the excited state (prior to its non-radiative decay) with an adsorbate, e.g. with cyclohexane via an 

I — Under f- irradiation- — After irradiation Under f irradiation After irradiation  

A diminution in TPC yield when methane was added after, rather than during, irradiation [cf. Fig. 15(c)] was taken to indicate that the first step and at least part of the second take place during irradiation, as would be consistent with a radiation-assisted Eley—Rideal or VCI-type process. 

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A large number of studies in the last decade have been concerned with primary processes in irradiated polymers. Unstable intermediates have been trapped and identified at low temperatures or detected by pulse radiolysis. In some cases, reactions of these intermediates have been identified and workers have attempted to correlate such reactions with the chemical effects of irradiation observed at room temperature. Some of the conclusions drawn will be summarized below. The elementary processes during irradiation at 77°K will be discussed first. The reactions of charged species, excited states and neutral radicals will be outlined successively. 

The effects of ultrasonic irradiation on photochemical reactions have been also reported. In those papers, effects of cavitation were demonstrated. Cavitation means the process in which micro bubbles, which are formed within a liquid during the rarefaction cycle of the acoustic wave, undergo violent collapse during the compression cycle of the wave.5) The dissociation of water to radicals is an example of these effects. Since activated chemical species such as free radicals have high reactivity, chemical reactions proceed. In other words, this phenomenon is a chemical effect of ultrasonic waves. 

As discussed previously, an optional postexposure, predevelopment bake can reduce problems with the standing-wave effect in DNQ-novolac positive resists. However, such a postexposure bake step is indispensable in the image reversal of positive resists (37-41) and certain resists based on chemical amplification of a photogenerated catalyst (64-67, 77, 78). For both types of resists, the chemistry that differentiates between exposed and unexposed areas does not occur solely during irradiation. Instead, differentiation occurs predominantly during a subsequent bake. Therefore, to obtain acceptable CD control in these systems, the bake conditions must be carefully optimized and monitored. 

Research on the chemical effects of ultrasound has undergone a renaissance during the past decade and has had a significant impact in a variety of areas [1, 2], Applications of sonochemistry have been developed in virtually all areas of chemistry and related chemical technologies [3, 4]. We can conceptually divide the effects of ultrasonic irradiation on heterogeneous catalysis into those that alter the formation of heterogeneous catalysts, those that perturb the properties of previously formed catalysts, and those that affect catalyst reactivity during catalysis. In practice, these three classes of effects are often deeply intertwined in reported experimental results. 

Hydrolysis at the glycosidic bond occurs also during irradiation of sucrose in aqueous solution, and acid is produced. " Changes in the ultraviolet absorption spectrum have also been noted, and the over-all change in optical rotation accompanying inversion was proposed by Wright for use as a pile-radiation dosimeter. The chemical effects of radiation on sucrose solutions have been investigated by Wolfrom, Binkley, and McCabe ... 

Physical or chemical separation of the analyte from its matrix avoids interelemental effects but is time-consuming, expensive, or tedious. Physical methods have the general advantage that interelement effect can be calculated. In x-ray fluorescence spectroscopy this is performed by taking the absorption of the primary beam and of the secondary fluorescence radiation into account. Figure 6.27 shows a profile of a sample during irradiation. 

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