[en] Platinum(III) is no longer an uncommon oxidation state. Numerous binuclear platinum(III) complexes have been prepared and structurally characterized over the past eight years. These include sulfate-bridged dimers of Dsub(4h) symmetry, [Pt₂(S0₄)₄L₂]^2-, L = H₂O, DMSO; phosphate-bridged complexes [Pt₂(HPO₄]₄→(H₂O)₂]^2- and [Pt₂(H₂PO₄)(HPO₄]₃(py)₂]; POP H₂P₂O₅^2--bridged ions [Pt₂→(POP)₄X₂]^2- X = halide; an extensive series of α-pyridonate (C₅H₄NO^-)-bridged head-to-head and head-to-tail complexes, [Pt₂(NH₃)₄(C₅H₄ NO)₂XY]^- X, Y = NO₃, NO₂, H₂O, Cl, Br; n = 2, 3; and organometallic derivatives such as [PT₂(CH₃)₄→(CF₃CO₂)₂(4-Mepy)₂]. In all cases there is a Pt-Pt single bond of length 2.47-2.7A, pseudo-octahedral geometry about platinum, and two or more bridging ligands. The complexes are stable in solution and some undergo quasi-reversible two-electron redox reactions. Mononuclear platinum(III) complexes are less well characterized structurally, but have been stabilized in diamagnetic host lattices in the solid state and by macrobicyclic cage ligands in solution following pulse radiolytic or γ-irridation of precursor platinum(II) complexes. The first unequivocal, crystallographically characterized mononuclear platinum(III) complex, [Pt(C₆Cl₅)₄], has just been reported

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[en] In this work, laser-induced breakdown spectroscopy was applied to determining the elemental composition of a set of ancient bronze artefacts dated from the Late Bronze Age and Early Iron Age (14^th – 10^th century BC). We used a Nd:YAG laser at 1064 nm with pulse duration of 10 ns and energy of 10 mJ and determined the elemental composition of the bronze alloy that was used in manufacturing the samples under study. The concentrations of tin and lead in the bulk of the examined materials was estimated after generating calibration curves for a set of four standard samples. The preliminary results of the analysis will provide information on the artefacts provenance and on the production process. (paper)

[en] The complexity of the interaction of radiation with large biological structures makes understanding their photochemistry a challenging exercise. In this article, the optimal initiation of quantum dynamics of N-H photodissociation of pyrrole on the S₀- ¹πσ*(¹A₂) coupled electronic states by UV-laser pulses in an effort to guide the subsequent dynamics to dissociation limits, is studied theoretically. Specifically, the task of designing optimal laser pulses that act on initial vibrational states of the system for an effective UV-photodissociation is considered by employing optimal control theory. The associated control mechanism(s) for the initial state dependent photodissociation dynamics of pyrrole in the presence of control pulses is examined and discussed in detail. The initial conditions determine implicitly the variation in the dissociation probabilities for the two channels, upon interaction with the field. The optimal pulse corresponds to the objective fixed as maximization of overall reactive flux subject to constraints of reasonable fluence and quantum dynamics. The simple optimal pulses obtained by the use of genetic algorithm based optimization are worth an experimental implementation given the experimental relevance of πσ*-photochemistry in recent times

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[en] Recent NOVA laser experiments featuring ablatively-generated data on very small liquid deuterium samples have shown an unexpected degree of compressibility in deuterium as it undergoes molecular dissociation to a metallic phase above 25 GPa. To test these controversial results under somewhat different shock loading conditions, we have developed a cryogenic target system on the Sandia Z pulsed radiation source for precision EOS studies of liquid deuterium using radiation-driven shocks. Experiments am underway to develop a constant pressure drive of 10-20 ns duration spatially uniform over a relatively large area (3-4 mm diameter) with minimal preheat effects. Techniques are also being developed to perform fiber-optic-coupled VISAR interferometry, active shock breakout and optical spectroscopy measurements on the stepped Al pusher plate and liquid deuterium sample in the Z bremsstrahlung environment. Initial VISAR measurements have been able to track the highly reflective metalized shock front propagating in deuterium at pressures of about 55 Gpa

[en] The use of pulse radiolysis to learn about processes which occur before the beginning of chemical times is discussed. Two examples, the distance distribution of positive and negative ions in hydrocarbons, and the state of the dry electron are discussed in detail

[en] The site of attack of OH radicals on dihydrouracil and five methylated derivatives was determined by pulse radiolysis using N,N,N',N'-tetramethylphenylenediamine (TMPD) to detect oxidizing radicals and tetranitromethane (TNM) as well as K₃Fe(CN)₆ to detect reducing radicals. In dihydrouracil OH radicals abstract preferentially an H atom at C(6) giving the 6-yl radical (>= 90 %) which at pH equivalent to 6.5 reduces TNM and K₃Fe(CN)₆ at almost diffusion-controlled rates. Only a small fraction of OH radicals abstract the H atom at C(5) (<= 10%). The resulting 5-yl radical oxidizes TMPD to TMPD⁺ at pH 7-8. With the methylated derivatives of dihydrouracil, OH radicals react less selectively, especially in the case of N(1)-methyl derivatives. This methyl group is activated to a similar degree as the methylene group at C(6). In 1-Medihydrouracil the yield of N(1)-CH₂ radicals is about 29%. Radicals at the other methyl substituents are generated to a lesser extent (<= 10%) and are relatively unreactive towards oxidizing agents such as TNM and K₃Fe(CN)₆ as well as towards the reducing agent, TMPD. Although methyl substitution opens new routes for OH attack the preferred site of H abstraction remains C(6) (> 60%). (author)

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