Radiation chemistry solid-phase

Spectroscopy is basically an experimental subject and is concerned with the absorption, emission or scattering of electromagnetic radiation by atoms or molecules. As we shall see in Chapter 3, electromagnetic radiation covers a wide wavelength range, from radio waves to y-rays, and the atoms or molecules may be in the gas, liquid or solid phase or, of great importance in surface chemistry, adsorbed on a solid surface. 

Evidence indicates [28,29] that in most cases, for organic materials, the predominant intermediate in radiation chemistry is the free radical. It is only the highly localized concentrations of radicals formed by radiation, compared to those formed by other means, that can make recombination more favored compared with other possible radical reactions involving other species present in the polymer [30]. Also, the mobility of the radicals in solid polymers is much less than that of radicals in the liquid or gas phase with the result that the radical lifetimes in polymers can be very long (i.e., minutes, days, weeks, or longer at room temperature). The fate of long-lived radicals in irradiated polymers has been extensively studied by electron-spin resonance and UV spectroscopy, especially in the case of allyl or polyene radicals [30-32]. 

In general, however, the effect of phase is much less marked than for ionic species and results for different phases will not be considered separately in this section. Since, in fact, more experiments have been carried out on the radiation chemistry of liquids than of gases or solids, most of the results discussed in this section refer to the liquid state. 

The atmosphere is a complex medium in which several phases coexist gas, aerosol particles, condensed water, liquid, and ice particles. All of the interactions that may occur between these various phases are included in the term multiphase or heterogeneous chemistry. Clouds favor the development of atmospheric multiphase chemistry, as they are composed of all three atmospheric phases (i.e., gas, liquid, and solid phases that stimulate a full set of reactions). Moreover, clouds modify radiative properties by diffusion of short-wavelength radiation coming from... 

In summary, in this first era of radiation chemistry it was discovered that the medium absorbs the energy and the result of this energy absorption leads to the initiation of the chemical reactions. The role of radium in these systems was not as a reactant or as a catalyst, but instead as a source of radiation. Most quantitative work was done with gases. It was learned that there was a close correspondence between the amount of ionization measured in a gas and the yield of chemical products. Solid and liquid-phase radiolysis studies were primarily qualitative. 

This narrative echoes the themes addressed in our recent review on the properties of uncommon solvent anions. We do not pretend to be comprehensive or inclusive, as the literature on electron solvation is vast and rapidly expanding. This increase is cnrrently driven by ultrafast laser spectroscopy studies of electron injection and relaxation dynamics (see Chap. 2), and by gas phase studies of anion clusters by photoelectron and IR spectroscopy. Despite the great importance of the solvated/ hydrated electron for radiation chemistry (as this species is a common reducing agent in radiolysis of liquids and solids), pulse radiolysis studies of solvated electrons are becoming less frequent perhaps due to the insufficient time resolution of the method (picoseconds) as compared to state-of-the-art laser studies (time resolution to 5 fs ). The welcome exceptions are the recent spectroscopic and kinetic studies of hydrated electrons in supercriticaF and supercooled water. As the theoretical models for high-temperature hydrated electrons and the reaction mechanisms for these species are still rmder debate, we will exclude such extreme conditions from this review. 

Since phenols are solid under ambient conditions, few studies were concerned with the radiation chemistry of phenols in the gas phase. An early study demonstrated the acetylation of phenols when irradiated in a specific gaseous mixture. Gas-phase y-irradiation of a mixture of CH3F and CO was found to form the acetyl cation, CHsCO , and to lead to acetylation of substrates . Gaseous phenol, cresols and xylenols present in such a mixture were acetylated mainly at the OH group to form 80-97% aryl acetate. The remaining products, hydroxyacetophenones, were mainly the ortho and para derivatives. 

Radiation chemistry 1097 gas-phase 1104, 1105 in alkane solvents 1102, 1103 in aqueous solution 1098-1100 in organic halogenated solvents 1100-1102 in solid matrices 1103, 1104 of aqueous phenol solutions 1113 of neat phenols 1103 Radical anions,... 

In addition to emitting various types of radiation, nuclear waste materials are commonly mixtures of different compounds and even different phases. Energy transfer between phases and interfacial chemistry will affect the yields and types of products formed in these systems. Interfacial effects in radiation chemistry have long been observed, but the detailed mechanisms involved are not understood [3-5], Recent studies of water adsorbed on ceramic oxides clearly show that energy can migrate from the solid oxide phase to the water phase and lead to excess production of H2 [6, 7], This process complicates dosimetry because energy... 

Paramagnetic species, generated in the vapor phase in a crossed-beam experiment by irradiation with 1 Mev. He ions, have been trapped at 77 °K. and detected by electron spin resonance (ESR). This paper describes the results obtained from irradiated methyl-, ethyl-, and tert-butyl alcohol, acetone, and ethylene. Trapped electrons together with the radicals CH2OH, CHsCHOH, and (CHa)2C(OH)CH2- and (CH i).tC are formed in methyl-, ethyl-, and tert-butyl alcohol respectively. Ethyl radicals are formed from ethylene. Acetone gives rise to CHjCOCH, and CHS radicals and appears to form trapped electrons in the deposit. The results are compared with the radiation chemistry of these systems in the solid and vapor phase. 

Our results are consistent with the radiation chemistry data for most of these systems in the solid phase and with the occurrence of reactions well established in vapor phase radiolysis. In the alcohols (and to some extent in acetone) the formation of the principal radical species seems best explained on the basis of ionization, followed by an ion-molecule reaction and subsequent trapping of the appropriate radicals in the frozen matrix at 77°K. As in the case of water (34), electrons can be stabilized in a non-glassy matrix. 

T he aggregation state is known to exert a great influence on radiation chemistry processes. In the gas phase, active species formed by decomposition of a parent molecule can easily escape recombination. In the liquid phase, diffusion competes with recombination in the cage formed by the surrounding molecules. In the solid phase, diffusion is very limited, and the most probable fate of fragments issued from a parent molecule is recombination. 

The experiments with 5,6-dihydrothymine are a preliminary attempt to compare rates of formation of transients by addition and by abstraction. Dihydrothymine is the saturated analog of thymine. The transient species which it forms by reaction with OH have an absorption maximum at 400 n.m. at pH 7 and at 320 n.m. or lower at pH 12.4. The rate of formation of these transients appears to be slightly less than one-third of the rate of formation of transients by addition to thymine. At pH 7, OH adds to the 5,6 double bond of thymine. The aqueous solution radiation chemistry of dihydrothymine has not been investigated, but electron paramagnetic resonance (EPR) studies in the solid phase show that H atoms abstract... 

Protein radiation chemistry has been studied for more than 30 years and a wealth of data has been accumulated. In the solid phase, only modifications of the polypeptidic backbone were shown. They concern the surface. More precisely it seems that weak points are turns and loops. Nothing is known concerrung modifications of residues. The knowledge about radiation chemistry of membrane proteins is also extremely poor. Efforts in this field would be relevant for biology. Let us mention that one of the most important free radical producer systems of living cells is partly buried in a membrane (NADPH oxidase) (see for instance 238). 

In the following, first the interaction of the high-energy radiation with the medium is briefly discussed in Section II. Both the nature of the events and the spatial distribution in the track is dealt with. In Sections III, IV and V the chemistry in the gas, liquid and solid phase is discussed. 

Mansour M, Parlar H, Korte F. 1975. Ecological chemistry. Cl. Reaction behavior of 3,4-dichloraniline and 3,4-dichlorophenol in solution as a solid and in gas phase during UV radiation. Chemosphere 4 235-240. 

The principal impediment to effective process design and analysis is the limited understanding of synergistic effects due to ion, photon, and electron bombardment of solid surfaces during etching and deposition. Fundamental relationships must be established between the gas-phase chemistry the surface chemistry as modified by radiation and etch profiles, rates, selec-tivities, and film properties. 

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