Excited radical anions, pulse radiolysis

Hayon23 studied the yields of ions and excited states in pulse radiolysis of liquid DMSO using anthracene as a solute to determine the yield of free ions and naphthalene as a solute to measure the yield of triplet excited states. Anthracene is known to react with solvated electrons to give the anthracene radical anion, A T... 

Aqueous alkaline luminol solutions can be excited to chemiluminescence by pulse radiolysis, the only additional requirement being oxygen 119h The suggested mechanism is that hydroxyl radicals attacking luminol monoanions, followed by reaction of the luminol radical anion thus formed with oxygen ... 

The absorption spectrum observed in the pulse radiolysis of solid films of polystyrene is shown in Figure 5. The absorption spectrum around 540 nm is also very similar to the absorption spectrum of polystyrene excimer observed in irradiated polystyrene solutions in cyclohexane as reported previously (2,3). The absorption with the maximum at 410 nm was reported previously and was assigned to anionic species (13,14). The longer life absorptions, attributed to triplet excited polystyrene repeat units and nonidentifiable free radicals, were observed in a wave length region < 400 nm. The absorption spectrum of CMS films obtained in pulse radiolysis showed a peak around 320 nm and a very broad absorption around 500 nm as shown in Figure 6. 

Spectra and kinetics were also determined for many other species. The solvated electron was observed and its spectrum was determined in a wide variety of solvents, from ethers and alcohols to hydrocarbons and even supercritical fluids. Other radicals, including the benzyl radical, the first species studied in pulse radiolysis, were observed. Excited states, both singlet and triplet, anions and cations, were determined for aromatic species. The number and variety of species is large. The importance of these studies was that it was now possible to observe the intermediate states in the radiation-chemical reactions and thus confirm or refute reaction mechanisms that had been proposed based on product yield data. 

Reactive states of aromatic molecules in solution may be observed directly by the pulse radiolysis method. Extensive investigations of both aromatic molecule ions (particularly the radical anions) and electronically excited states have provided new information about not only the radiation chemical processes but also the general kinetic behavior of these reactive intermediates. Absolute rate constants have been determined for many elementary processes such as energy transfer and electron and proton transfer reactions. 

The question whether or not radical ions are formed upon irradiation of liquids and stabilized enough for detection or engagement in bimolecular chemical reactions has moved radiation chemists ever since the early days of this research field. This was particularly exciting with respect to low polarity solvents, but even for aqueous solutions conclusions had to rely mainly on indirect evidence. A real breakthrough came with the experimental discovery of the hydrated electron and other powerful one-electron reductants (e.g., a-hydroxyalkane radicals such as (CH3)2C OH). Applying these new tools a large number of organic radical anions were detected and characterized with respect to their optical and chemical properties, particularly by pulse radiolysis. 

Pulse radiolysis of penicillamine in aqueous solution gives thiyl radicals RS% Amax 330 nm, and the radical anion RSSR-, Amax 450 nm, formed from RS and RS / Photolysis of propanethiol tritiated at SH, in the presence of a hydrogen donor, results in tritium scrambling in the propyl group and in the hydro n donor, suggesting that such a system is a useful source of H atoms in solution. In eased yields of the products of sensitized photodecarboxylation of R X CHj COaH (X = O, S, or NH) are obtained in the presence of thiophenol as hydrogen donor. Butane-thiol quenches triplet acetophenone only slowly (At = 1.4 x 10 1 mol s ), and it can be included in the reaction systems of ketone photo-reactions as a radical trap without interfering with the photo-excited substrate. ... 

The anion radicals of the metal complexes were observed by pulse radiolysis in aqueous solutions saturated with N2O. Excitation of the CT band for the zinc complex in the presence of methylviolgen (MV ) results in the oxidation of the complex... 

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