International Journal for Radiation Physics and Chemistry最新文献

The influence of electron acceptors on the yield of trapped electrons in frozen aqueous solutions is examined, and the results of picosecond radiolysis is discussed. It has been shown that the correlations observed cannot be explained if thermal electrons only take part in reactions occurring in such matrices, whereas they can be correctly interpreted assuming that epithermal electrons are also capable of reacting with acceptors in a condensed medium.

Experimental data obtained are discussed on the basis of these concepts. The times needed for thermalization, solvation and capture have been evaluated, and the rate constants of the reactions of epithermal electrons computed.

The reaction of OH radicals with aqueous tris(1,10-phenanthroline)iron(II) leads to the formation of an adduct, which exhibits a broad absorption band at rmpH = 6, λ_{max = 460 nm}, and ϵ₄₆₀ = 6700 (molar, decadic, 1 mol⁻¹ cm⁻¹). The rate of formation of the adduct is first order in complex concentration with a bimolecular rate constant $\text{k = (1 >}\text{s}\text{̇}\text{;05±0 >}\text{s}\text{̇}\text{;03)× 10}{}^{10}\text{1 mol}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-1}}$ independent of pH in the range pH 3–11. The adduct decays by mixed-order kinetics, but at 310 nm a second-order formation of a decay product can be directly observed.

The reaction of OH radicals with aqueous 1,10-phenanthroline leads also to the formation of an adduct which absorbs in the whole visible region with a maximum at 425 nm and ε₄₂₅ = 2612 (molar, decadic, 1 mol⁻¹ cm⁻¹) in neutral solution. The adduct exhibits a red shift in acidic and alkaline media. The formation is first order in 1,10-phenanthroline with a bimolecular rate constant $\text{k = (8 >}\text{s}\text{̇}\text{;6±0 >}\text{s}\text{̇}\text{;7)×10}{}^9\text{1 mol}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-}}$ at pH = 6; the rate of formation is pH dependent. The adduct decays according to second-order kinetics leading to the formation of a product that exhibits the presence of an additional functional group. A similar product, determined to have pK⋟4 > ṡ;2 and pK₂⋟8 > ṡ;1, has been isolated after γ-radiolysis of 1,10-phenanthroline.

The mechanism of cyclohexane radiolysis in the condensed phase is discussed with particular attention paid to the cleavage of CC bonds. The contribution of ions and various neutral excitation states to the formation of radiolysis end-products is analysed. As follows from the experimental data shown, short-lived (≈10⁻¹²) superexcited states (S.E.S.) take part in the cyclohexane radiolysis reactions in the liquid phase. The basic process accompanying the decay of S.E.S. molecules is the formation of hydrogen atoms which may acquire excess kinetic energy (“hot atoms”). It is assumed that inspection of hot H atoms along the CC bond constitutes the main source of saturated products formed by cleavage of the cyclohexane ring (C.R.C.P.=cyclohexane ring cleavage products): CH₄, C₂H₆, C₆H₁₄ and so on. In condensed medium, the cleavage of two or more CC bonds in the same molecule, giving rise to unsaturated C.R.C.P. (C₂H₄, C₃H₆, etc.), originates mainly from S.E.S. A smaller amount of unsaturated C.R.C.P. is probably formed via the decay of excited molecular ions. Cleavage of a single CC bond with formation of hexene proceeds effectively from lower excited states which derive particularly from ion-recombination.

Experimental data concerning the incidence of polymorphous transformation in cyclohexane on the C.R.C.P. yields are given. A general scheme for cyclohexane radiolysis, based on the cleavage of CH bonds, is postulated.

The experimental arrangements used by the authors for the study of optical vacuum ultra-violet and electron energy loss spectra of organic compounds are described and some theoretical aspects of studies of higher excited states are considered. Results for alkanes, benzene, naphthalene, anthracene and some more complex hydrocarbons are reviewed. Recent results obtained by reflection and electron energy loss spectroscopy for single crystals of anthracene are included and their relevance for gas phase work as well as for the understanding of exciton effects in organic solids is described.

When alkane containing a small amount of toluene is irradiated by γ-ray or X-ray in the solid state at 77 K, luminescence from excited toluene is observed. The formation of the excited toluene is not due to direct excitation of toluene by γ-ray or Čerenkov light, but to the rapid energy transfer from the irradiated alkane to toluene. The intensity of luminescence from the excited toluene in the cyclopentane matrix does not correspond at all to the amounts of toluene ions, which are formed by pre-irradiation. The energy transfer is not caused by a free hole and an electron, but by an exciton. Furthermore, the effect of additives on the fluorescence suggests that the Wannier exciton or mobile ion-pair is responsible for the energy transfer in cyclopentane containing toluene in the solid phase at 77 K.

Experiments on H atom scavenging by alkanethiols in γ-irradiated aqueous solutions have confirmed that the reaction products depend on thiol structure. The percentage of H abstraction decreases with increasing branching at the carbon atom α to sulfur while -SH abstraction simultaneously increases. Methyl and ethyl radicals appear to react only by H abstraction from the thiol group since the yields of methane and ethane are independent of thiol structure. There is no significant temperature dependence of the H₂ and H₂S yields over the range 0–50°C for aqueous solutions of cysteine and penicillamine.

An investigation into the formation and characterization of the transients arising from the reactions of hydroxyl radical with the complexes bis(ethylenediamine)platinum(II) perchlorate and chloride, chloro(diethylenetriamine)platinum(II) chloride and chloro(1,1,7,7-tetraethyldiethylenetriamine)platinum(II) chloride in aqueous media saturated with nitrous oxide has been carried out using the technique of pulse radiolysis. In general, the transients exhibit absorption bands with either a single, intense peak below 300 nm (ϵ ⪞ 400 m² mol⁻¹) or for the longer-lived species, two peaks of lesser intensity at about 350 and 500 nm. For the bis(ethylenediamine)-platinum(II) system, the transients are interrelated by acid-base reactions and in the presence of free chloride ion by substitution process. The disappearance of the longer-lived intermediate, which obeys second-order kinetics, does not lead to the formation of detectable amounts of ammonia (or free ethylenediamine). This feature in conjunction with other results indicates that the transients are not those arising from the degradation or loss of the co-ordinated amine ligand. Some of the intermediates exhibit reactivity towards either copper(II) perchlorate, an oxidant, or the reducing agent potassium ferrocyanide. The flash photolysis of trans-dichlorobis(ethylenediamine)platinum(IV) perchlorate has been used to generate and further characterize some of the transients encountered in the pulse radiolysis study. It is concluded that the intermediates are platinum(III) amine complex ions. For the Pt(III) species with absorption peaks below 300 nm, their structures are proposed to be distorted octahedra with substitutionally labile co-ordination sites. It is suggested that the products absorbing above 300 nm may be structurally different from those absorbing below 300 nm.

Pulse radiolysis of adrenaline in acid aqueous solutions (pH 1–3) was carried out. The rate constants for the reactions of adrenaline with H and OH were determined: k(H + adr.) = (0·9±0·1) × 10⁹ dm³ mol⁻¹ s⁻¹; k(OH + adr.) = (1·65±0·15) × 10¹⁰ dm³ mol⁻¹ s⁻¹. The H-adduct of adrenaline has two λ_max, at 280 and 355 nm, with ϵ₂₈₀ = 420 m² mol⁻¹ and ϵ₃₅₅ = 390 m² mol⁻¹, which disappears according to a first order reaction, k₁ = 1·4 × 10³ s⁻¹. The spectra formed by OH attack was assigned to the corresponding benzoxy radical with absorption maxima at 285 and 365 nm and ϵ₂₈₅ = 620 m² mol⁻¹ and ϵ₃₆₅ = 105 m² mol⁻¹. Due to the overlapping of the intermediates, no decay kinetics could be obtained.

Competition between CH and CC bond ruptures has been established and attributed largerly to ion-electron recombination.