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1

Historic landmarks in radiation chemistry since early observations by Marie Skłodowska-Curie and Pierre Curie

Belloni J.

Nukleonika

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2011

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Vol. 56, No. 3

203-211

EN

The origin of the radiation chemistry history is contemporary with the X-rays and uranic rays discoveries. The complexity of the phenomena induced by the radiation effects, which involve electrons, ions and free radicals and a specific spatial distribution of the energy deposit along the tracks, was progressively understood, particularly when pulse radiolysis and time-resolved detection permitted to observe the short-lived transient species and to explain the chemical or biochemical mechanims. This short review summarizes the most important landmarks of the concepts and their applications.

2

Free-radical chemistry of thiourea in aqueous solution, induced by OH radical, H atom, a-hydroxyalkyl radicals, photoexcited maleimide, and the solvated electron

Schuchmann M., Schuchmann H., Knolle W., von Sonntag J., Naumov S., Wang W., von Sonntag C.

Nukleonika

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2000

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Vol. 45, nr 1

55-62

EN

Hydroxyl radicals react with thiourea (and its tetramethyl derivative) yielding dimeric radical cations which are characterized by strong absorptions at 400 nm (450 nm). An analysis of the kinetics of the buildup of these absorptions gives evidence for the intermediacy of OH-adducts and the monomeric radical cations. The dimeric radical cations are also generated in the reactions of triplet-excited maleimide with these thioureas. Moreover, in acid solutions even reducing radicals such as the H atom and a-hydroxyalkyl radicals give rise to these intermediates in full yields, albeit displaying different kinetics. Potential mechanistic implications are discussed. The dimeric thiourea radical cations are strong oxidants and readily oxidize the anions of phenol and 2’-deoxyguanosine. The solvated electron gives rise to an intermediate which is rapidly protonated by water (pKa > 11). Quantum-mechanical calculations support the assignment of the 400 nm (450 nm) absorption to the respective dimeric thiourea radical cation.

3

Femtosecond internal conversion and solvation dynamics of the solvated electrons in neat water and aqueous solution

Laenen R., Assel M., Laubereau A.

Bulletin of the Polish Academy of Sciences. Chemistry

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1999

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Vol. 47, No. 4

283-301

EN

Transient pump-probe spectroscopy of equilibrated solvated electrons is car-ried out in neat water and in an aqueolls NaCl solution (5.9 M) in the visible and near infrared using pulses of 100-170 fs duration and polarization resolution. Excitation is per-formed by a pump pulse at 620 nm in the blue wing of the electronic absorption band of the e- promoting electrons from the Is ground state to the highest of the 2p-substates. Transient bleaching is observed in a broad interval around the maximum of the band at 720 nm, accompanied by induced absorption at longer wavelengths. No holeburning features are observed within our experimental time resolution suggesting a time constant T1<80 fs for rapid solvent relaxation and/or population redistribution among the excited 2p-substates. The relaxation dynamics clearly involves a first intermediate that is strongly proposed to be a modified excited. state .p' and the lifetime of which is determined to be T2 = 190:= 40 fs. After 500 fs an isosbestic point develops in the transient spectrum that is related to a second intermediate that is assigned to a modified ground state s". A fur-ther time constant T = 0.9:=: 0.15 ps accounts for the final recovery of the population to the original ground state 1s. Evidence for stimulated emission in the probe absorption of the first intermediate allows its assignment as p' and suggests a distinct red shift of the transition p' ~ ground state to 760 nm, while the transient absorption band of electrons in the longer-lived s"-level is centered at 810 nm. The negligible net anisotropy < 0.01 of the probe absorption measured during and after the excitation process indicates that the observed distribution of solvent cavities of hydrated electrons is close to spherical symmetry. Comparison with similar observations for NaCl solution is also reported.

4

Electron localization in liquid methanol. Quantum Path-Integral simulation

Bartczak W.M., Sopek M.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 7S

1798-1825

EN

An excess electron o liquid methanol at room temperature was studied using the method of Path-Integral Molecular Dynamics simulation. A compact charge distribution of an excess electron, suggesting a localized electron state, was found. The charge distribution is centred in a cavity built of methanol according to the traditional picture of the solvated electron. Various radial distribution functions were calculated reflecting the correlations between the cavity centre or the electron charge density and the sites of the methanol molecule. The correlations are stronger than in the case of the hydrated electron. Interpretation of the radial distribution functions as well as the bond-angle distribution functions leads to a picture of 4 methanol molecules forming the solvation shell of the solvated electron. The molecules are oriented towards the centre of the electron density by the OH bonds. The coordination number of the solvated electron agree with the conclusions from electron magnetic resonance experiments.