Radiation halides

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

The complexed halide atoms are produced by high energy radiation in solutions of colloids that contain halide anions X and are saturated with nitrous oxide. Hydrated electrons formed in the radiolysis of the aqueous solvent react with NjO according to NjO -f e -f H O - Nj -t- OH -I- OH to form additional OH radicals. Ions X are oxidized by OH, the atoms X thus formed react rapidly with X to yield XJ radicals. 

Koplitz and co-workers have studied the photolysis of C2H5 via the A2A (3s) state by using 248-nm photolysis radiation and hot ethyl radicals generated from photolysis of ethyl halides.125,126 Chen and co-workers have investigated the photodissociation of jet-cooled ethyl (produced by flash pyrolysis of ethyl iodide and n-propylnitrite) in the region of 245-264 nm... 

In 1899, the Curies first reported the coloration of glass and porcelain and the formation of ozone from oxygen by radioactive radiation. Giesel (1900) noted that the coloration of alkali halides under these radiations was similar to the effect of cathode rays he also observed the decomposition of water. R Curie and Debierne (1901) observed continuous evolution of hydrogen and oxygen... 

Silver halide fibres (AgClxBri x) have the widest spectral range in the mid-IR, well into the fingerprint range. Due to their crystalline nature, they have a superior flexibility. Problematic is their tendency to decompose upon contact with UV radiation or base metals. Also sulphides will chemically destroy the fibre material. Other points against are the high intrinsic attenuation due to absorption by impurities or scattering at inclusions or micro-crystals and the non-availability of (applicable) core-clad fibres. 

Other detection modes in bright CL or BL reactions are multichannel detectors, which provide simultaneous detection of the dispersed radiation and produce a permanent image of a wide area. Photographic films or plates are emulsions that contain silver halide crystals in which incident photons produce stable clusters of silver atoms within the crystals. Internal amplification is provided in the development process by an electron donor that reduces the remaining silver ions to silver atoms within the exposed crystals. A complexing agent is used to remove the... 

Our latest results in this field stem from a matrix-spectroscopic study of the isomerization of nitrosyl halides (152) and isonitrosyl halides (153).201 Irradiation of nitrosyl bromide (152 X = Br) and nitrosyl chloride (152 X = Cl) leads to the corresponding isomers isonitrosyl bromide (153 X = Br) and isonitrosyl chloride (153 X = Cl). Both compounds, NOBr and NOC1,202 have again been identified by comparison of the experimental and calculated (BLYP/6-311+G ) IR spectra. The back-reactions 153 - 152 can be initiated by UV, visible or IR light. Astonishingly, this retransformation also occurs spontaneously even in the matrix at 10 K under exclusion of any UV/VIS or IR radiation. 

These defects were first produced by exposing alkali halide crystals to high-energy radiation such as X rays. This causes the crystals to become brightly colored with fairly simple bell-shaped absorption spectra. The peak of the absorption curve, rn lx, moves to higher wavelengths as both the alkali metal ion size and halide ion... 

In the mid-1960s the first measurements of propagation rate-constants for unsaturated monomers became available, from polymerisations initiated by y-radiation [5]. The circumstances of these experiments were such that it was immediately clear that these very high rate constants (106 to 108 1 mol"1 s 1) were those of unpaired cations, kp. All these reactions were carried out with bulk monomer, i.e., the polymerisations occurred in a medium of very low polarity (e c. 2 for hydrocarbons and 5 to 6 for alkylvinylethers). Unfortunately, the y-radiation method is not applicable to polymerisations in solution, especially in polar (usually alkyl halide) solvents. The methods which have been used to... 

The rate-constants, kp, calculated for polymerisations by H2S04 and HC104 from R = pmc0, (with c0 = [initiator], m = [monomer], R = rate) are very similar, but much smaller than the kp for polymerisations by radiation or some metal halides hence kp = R/ra[HA]0 is actually the kpE [3, 9, 27, 38]. 

Normal glass will only transmit radiation between about 350 nm and 3 /rm and, as a result, its use is restricted to the visible and near infrared regions of the spectrum. Materials suitable for the ultraviolet region include quartz and fused silica (Figure 2.28). The choice of materials for use in the infrared region presents some problems and most are alkali metal halides or alkaline earth metal halides, which are soft and susceptible to attack by water, e.g. rock salt and potassium bromide. Samples are often dissolved in suitable organic solvents, e.g. carbon tetrachloride or carbon disulphide, but when this is not possible or convenient, a mixture of the solid sample with potassium bromide is prepared and pressed into a disc-shaped pellet which is placed in the light path. 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

Later, Tieke reported the UV- and y-irradiation polymerization of butadiene derivatives crystallized in perovskite-type layer structures [21,22]. He reported the solid-state polymerization of butadienes containing aminomethyl groups as pendant substituents that form layered perovskite halide salts to yield erythro-diisotactic 1,4-trans polymers. Interestingly, Tieke and his coworker determined the crystal structure of the polymerized compounds of some derivatives by X-ray diffraction [23,24]. From comparative X-ray studies of monomeric and polymeric crystals, a contraction of the lattice constant parallel to the polymer chain direction by approximately 8% is evident. Both the carboxylic acid and aminomethyl substituent groups are in an isotactic arrangement, resulting in diisotactic polymer chains. He also referred to the y-radiation polymerization of molecular crystals of the sorbic acid derivatives with a long alkyl chain as the N-substituent [25]. More recently, Schlitter and Beck reported the solid-state polymerization of lithium sorbate [26]. However, the details of topochemical polymerization of 1,3-diene monomers were not revealed until very recently. 

Rocket propulsion oxidizers, 18 384-385 Rocks, weathering of, radiation and, 3 299 Rocksalt, crystal structure of, 2 6, 29 Rock-salt-type alkali halide crystals, dissolution process, 39 411 19 alkali chlorides, 39 413, 416 alkali fluorides, 39 413-415... 

See, for example, reviews by Asmus, K.-D. von Sonntag, C. Schuchmann, H.-P. Houee-Levin, C. Sicard-Roselli, C. In Radiation Chemistry Present Status and Future Prospects, Jonah, C.D. Rao, B.S.M., Eds. Elsevier Amsterdam 2001 pp. 341, 513, and 553, respectively. See, for example, Brede, O. Res. Chem. Intermed. 2001,27, 709 and references therein for pulse radiolysis of phenols liquid halocarbons and alkyl halides and Lomoth, R. Brede, O. Chem. Phys. Lett. 1998, 288, 47 for pulse radiolysis of DNA bases in liquid acetone. 

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