a Sorbonne Universités, UPMC Univ Paris 06, UMR 8235, Laboratoire Interfaces et Systèmes Electrochimiques, F-75005 Paris, France. e-mail: emmanuel.maisonhaute@upmc.fr b Sorbonne Universités, CNRS, UMR 8235, Laboratoire Interfaces et Systèmes Electrochimiques, F-75005 Paris, France. c Laboratoire de Chimie Physique, CNRS UMR 8000, Université Paris-Sud, Bat 350, 91405 Orsay Cedex, France. e-mail: jean-louis.marignier@u-psud.fr.

We follow the reactivity of a guanosine radical created by a radiolytic electron pulse both by spectroscopic and electrochemical methods. This original approach allows us to demonstrate that there is a competition between oxidation and reduction of these intermediates, an important result to further analyse the degradation or repair pathways of DNA bases.

The possibility to couple a transient electrochemical detection of the redox intermediates produced by a picosecond electron accelerator is explored. The principle is demonstrated with the well-behaved methylviologen radical cation that can be reoxidised at the electrode and simultaneously detected by transient absorption.

Absorption spectra and absorption cross sections of gaseous acetylene, C2H2, at 298 and 85 K were measured in the wavelength range 110–155 nm with a slit–jet system coupled to a synchrotron as a source of vacuum ultraviolet light. Using published spectral parameters of C2H2, we simulated the absorption profile for the Rydberg transition to state 4R0 in the range 124.6–125.1 nm, according to which the temperature of the jet-expanded sample at stagnation pressure 200 Torr is 85 ± 5 K. Our cross sections of C2H2 are applicable for determining properties sensitive to temperature for diagnostic work on Saturn and Titan.

Measurement of H(2) production from electron irradiation (10 MeV) on SBA-15 materials has shown that adsorbed water is attacked preferentially. Silanol groups are only attacked when they are in the majority with respect to adsorbed water, however they are much less efficient at producing H(2). The comparison between water content before and after electron irradiation and the corresponding H(2) production indicates that water desorption is the main route to adsorbed water loss for SBA-15 materials. On the other hand, surface silanol groups are more susceptible to attack, leading to H(2) production when SBA-15 samples have undergone extensive thermal treatment. Electron irradiation of SBA-15-Cu materials has shown that the presence of Cu(II) on the surface reduces and inhibits the production of H(2.) This inhibiting power affects adsorbed water bonded to grafted copper but not surface silanol groups.

Hydrogen production by radiolysis of water absorbed on solid is a major problem for nuclear waste management. In the present study, we demonstrate that controlling extreme surface properties of the irradiated material allows a direct tuning of the hydrogen production under irradiation. We achieve this control on a model system (silica fibers) using liquid phase atomic layer deposition (ALD) of titanium or zirconium oxide. The hydrogen production is strongly inhibited by the deposition of a subnanometric layer of titanium oxide, whereas it is amplified upon zirconium oxide grafting.

The rate constants of the reactions of eaq− and the OH· radical with the oxalate ion in a neutral aqueous solution were measured by means of the pulse radiolysis technique. They were found to be (3.5 ± 0.5) × 107 and (1.5 ± 0.2) × 107 l mol−1 s−1, respectively. The radical anion −OOC-C·OO2− is characterized by an optical absorption band that has a maximum at 270 nm and a molar absorption coefficient of (2400 ± 200) l mol−1 cm−1. The radical anion ·OOC-COO−, the product of the reaction with the OH· radical, exhibits absorption that has no maximum and increases in intensity with a decrease in the wavelength extending to the UV region (ɛ220 = 1800 l mol−1 cm−1). The mechanism of radiation-chemical transformations in aqueous oxalate solutions is discussed.

Laboratory measurements of the photoabsorption cross section of 15NH3 at wavelengths between 140 and 220 nm are presented for the first time. Incorporating the measured photoabsorption cross sections of 15NH3 and 14NH3 into a one-dimensional photochemical diffusive model, we find that at 400 mbar, the photolytic efficiency of 15NH3 is about 38% greater than that of 14NH3. In addition, it is known that ammonia can condense in the region between 200 and 700 mbar, and the condensation tends to deplete the abundance ratio of 15NH3 and 14NH3. By matching the observed ratio of 15NH3 and 14NH3 at 400 mbar, the combined effect of photolysis and microphysics produces the ratio of (2.42 ± 0.34) × 10-3 in the deep atmosphere, in excellent agreement with the Galileo spacecraft measurements. The usefulness of the isotopic composition of ammonia as a tracer of chemical and dynamical processes in the troposphere of Jupiter is discussed.

The formation and disappearance of O− in oxygen-free aqueous solution at pH 13 has been studied and its spectrum has been re-determined utilizing pulse radiolysis optical measurements in the UV region. The rate constant for the reaction H+OH− is determined to be 2.5×107dm3mol−1s−1. A determination of the rate constants for the equilibrium OH+OH-⇔O- was not possible; the pK value for this equilibrium was determined to be 11.9. The rate constant for the demerisation O−+O− was measured at 325nm to be 2k=2×109dm3mol−1s−1. The absorption spectrum of O− differs significantly from that in the literature below 250nm.

In this research work, a mathematical model for simulation of the solar radiation system has been developed by using a system dynamics methodology. Bangladesh is used here for model validation. The simulated results obtained from this model have compared with the experimental results and found reasonably a good agreement. Therefore the performance of the model is to be expected as satisfactory.

In a plasma display panel (PDP) He–Xe or Ne–Xe gaseous mixtures are subjected to electric discharge between two glass panels, so to generate VUV light. Red, green and blue phosphors absorb this VUV radiation and re-radiate the energy as visible light to produce the colors that appear on the screen. The phosphor plays an important role in the working of a PDP. To improve the efficiency of phosphors, we have established a photoluminescence end station coupled to the beam line of a synchrotron to study the luminescence of PDP phosphors. This luminescence is analyzed with a 0.32m monochromator having maximum resolution 0.04nm, and is monitored with a photomultiplier tube operated in a photon-counting mode. Preliminary data demonstrate the powerful performance of this end-station for studying PDP phosphors.

The rate constant for the reaction of H with tert-butyl alcohol in aqueous solution has been re-determined utilizing pulse radiolysis optical measurements. Special care was taken to avoid the formation of isobutene as a competitive species. A value of 1.5 × 105 dm3 mol−1 s−1 was thus obtained, which is in good agreement with previous values.

Two new procedures were employed for studying the reaction of hydrogen atoms with hydrogen peroxide. The absorption in the UV-range was observed either for an acidic aqueous solution containing only hydrogen peroxide or for a similar solution but also containing an aliphatic alcohol. From the increase in absorption of various alcohol radicals, a rate constant of 3.5×107dm3mol−1s−1 was determined. In addition, the rate constant for the reaction of hydroxyl radicals with hydrogen peroxide was determined to be 3.0×107dm3mol−1s−1.

There have been a number of reforms in the power sector in Bangladesh since her independence, but these reforms failed to bring desired improvements in the power sector. Among the three main components of the power system, recent reform activities were centered around generation and transmission. The most pressing problem in the power sector has been with the distribution system, which is characterized by heavy system loss and poor collection performance; however, the distribution system seldom got the priority in reform initiatives. Thus, it becomes very difficult to derive benefits from the reforms while leaving the distribution system untouched. This implies that priority in reform must be given to the distribution. To make it efficient and effective, its administration must be restructured. At the same time, its performance should be monitored continually on the basis of particular performance indicators. It is found that system loss in any power distribution system in Bangladesh should not exceed 10%, i.e. collection–import (CI) ratio should be kept above 90%. To maintain the system loss and the CI ratio at the recommended level, the malpractice by the utility personnel must be stopped fast. This will help to achieve economic sustainability.

The kinetics of the reactions of hydroxyl radicals with aliphatic alcohols in aqueous solution were studied using pulse radiolysis. Based on the optical absorption observed in the UV region, the rate constants for the reaction of hydroxyl radicals with methanol, ethanol, 2-propanol and tert-butyl alcohol were determined to be 9.0×108, 2.2×109, 2.0×109 and 6.2×108dm3mol−1s−1, respectively. The values obtained here by direct observation of the alcohol radicals basically confirm the values which were earlier determined indirectly by competition.

The kinetics of the reactions of hydrogen atoms with aliphatic alcohols in aqueous solution were studied by pulse radiolysis. The rate constants for the reaction of hydrogen atoms with methanol, ethanol, 2-propanol and tert-butyl alcohol were determined from the increase in optical absorption in the UV region to be 1.1 × 106, 1.75 × 107, 5.3 × 107 and 2.3 × 105 dm3 mol−1 s−1, respectively. The bimolecular decay rate constants of the first two alcohol radicals were evaluated to be 2.4 × 109 and 1.5 × 109 dm3 mol−1 s−1.

Reactions of OH, O−, N3 and SO4− and eaq− radicals with furazan and its dimethyl and diamino derivatives were studied by radiation chemical methods. The OH radical reaction is selective with the rates following the order furazan<3,4-dimethylfurazan (3,4-DMF)<3,4-diaminofurazan (3,4-DAF), the k values being <107, 3.5×108, 3.9×109 dm3 mol−1 s−1, respectively. The transient absorption spectra measured in the OH radical reaction with 3,4-DMF and 3,4-DAF exhibited maxima at 270 and 290 nm, respectively, which are assigned to the benzylic and anilino type radicals. The same intermediates are also formed in the O− reaction by H abstraction. All three derivatives showed lack of reactivity with N3 radical and was only 3,4-diaminofurazan found reactive with SO4− (k=3.6×109 dm3 mol−1 s−1). The rates of eaq− with all the three derivatives are diffusion controlled k=(0.8–1.9)×1010 dm3 mol−1 s−1 and its reaction mechanism involves very fast protonation of the initially formed radical anions by water (k≥107 s−1) followed by tautomerisation of the N-atom protonated C-centred radical to the C-atom protonated N-centred radical. The transformation is catalysed by OH− and the rates for the spontaneous transformation in neutral solution are 5.4×104 and 1.5×105 s−1 with furazan and 3,4-diaminofurazan, respectively.