Effect of substrate temperature on MAPLE deposition of synthetic eumelanin films

Eumelanin is an important pigment almost ubiquitous in animals and plants exhibiting interesting charge transport capabilities. Its poor solubility in common solvents represents a severe limitation for preparing thin films. It was recently demonstrated that eumelanin films can be successfully deposited with the MAPLE (Matrix Assisted Pulsed Laser Evaporation) technique starting from a frozen water suspension, using infrared laser radiation. The low laser absorption of ice together with the high absorption of eumelanin suggests that the target ablation is due to laser energy absorbed by the eumelanin molecules, followed by thermal energy transfer, and ejection of ice/water/vapor containing undamaged eumelanin molecules and supramolecular structures.     

High-spin excitations of 81, 82, 83, 85Se : Competing single-particle and collective structures around N = 50

The ^{81, 82, 83, 85}Se nuclei have been produced as fission fragments in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Their high-spin level schemes have been built from the triple -ray coincidence data and - angular correlations have been analyzed in order to assign spin and parity values to many observed states. The lowest-spin states of the two-neutron and three-neutron configurations are strongly mixed with two-proton excitations among the fp orbits. On the other hand, the highest-spin states of these neutron configurations are found to remain almost pure. Neutron excitation across the N = 50 gap is observed both in ⁸³Se₄₉ and in ⁸⁵Se₅₁ .     

Glass breaks like metal,but at the nanometer scale

We report in situ atomic force microscopy experiments which reveal the presence of nanoscale damage cavities ahead of a stress-corrosion crack tip in glass. Their presence might explain the departure from linear elasticity observed in the vicinity of a crack tip in glass. Such a ductile fracture mechanism, widely observed in the case of metallic materials at the micrometer scale, might be also at the origin of the striking similarity of the morphologies of fracture surfaces of glass and metallic alloys at different length scales.     

New excited superdeformed bands in heavy Pb nuclei: Clue for an octupole softness near the N = 118 gap at large deformation

We report the identification of six new superdeformed (SD) bands in ^197,198Pb observed with the EUROBALL IV spectrometer. The results are interpreted in the framework of cranked Hartree-Fock calculations with approximate projection on the particle number by means of the Lipkin-Nogami method. A mixing between quasi-particle excitations and an octupole vibration is suggested in the two SD isotopes. We have estimated the ordering of the neutron valence orbitals and confirm indirectly a N = 118 SD gap. Received: 20 December 2000 / Accepted: 24 January 2001     

High oxygen pressures and the stabilization of six-coordinated Ir(VI) in an oxygen lattice

Abstract

During these last twenty five years a great efforts have been made in the Laboratoire de Chimie du Solide du CNRS in order to develop high oxygen pressure for the stabilization of unusual oxidation state of transition elements.

The aims of such research works was to correlate the increase of the Mⁿ⁺-O bond covalency versus the increase of the oxidation state n+ to the physicochemical properties of resulting oxides [1].

Iridium was an interesting element due to its position (5d) in the Periodic Table. In 1980 Ir(V) (d⁴) was stabilized in La₂LiIrO₆ in the perovskite structure [2]. Such a study had underlined the strong value of the spin-orbit coupling associated to Ir(V) [3].

The stabilization of Ir(VI) is interesting from two points of view : (i) its isotropic electronic configuration (d³), (ii) such a high oxidation state could lead to the strongest M-O bond in an oxygen lattice.

Selecting, through a specific methodology, the most appropriate local structural and chemical factors and with the help of high oxygen pressure, Ir(V1) was stabilized in the perovskite Ba₂CaIrO₆. Structural, magnetic and Mössbauer studies have been carried out in order to characterize the physicochemical properties induced by this unusual oxidation state.     

Benchmark values for the Soret,thermal diffusion and diffusion coefficients of three binary organic liquid mixtures

With the aim of providing reliable benchmark values, we have measured the Soret, diffusion and thermal diffusion coefficients of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4 tetrahydronaphthalene for a concentration of 50 wt% at a temperature of 25C. The experimental techniques applied by the five participating laboratories are transient holographic gratings, annular and parallelepipedic thermogravitational columns, and vertical parallelepipedic columns with velocity amplitude determination by laser doppler velocimetry. The systems have also been studied in a annular thermogravitational column filled with a porous medium in the gap. There is a good agreement between the different experiments with deviations of the order of a few per cent in most cases (8.5% at most). The numerical values are tabulated in the paper.     

Coloring of universal graphs

LetG be a graph andr a cardinal number. Extending the theorem of J. Folkman we show that if eitherr or clG are finite then there existsH with clH = clG andH (G) _r ¹ . Answering a question of A. Hajnal we show that countably universal graphU ₃ satisfiesU ₃ (U₃) _r ¹ for every finiter.     

Heterocyclic and acyclic derivatives of F-N-isopropylacetimidoyl chloride

$\text{F}$-N-Isopropylacetimidoyl chloride, CF₃CClNCF(CF₃)₂, has been used as a precursor for a variety of heterocyclic and acyclic compounds. Reaction with azide ion yields a mixture of the imidoyl azide, CF₃(N₃)CNCF(CF₃)₂, and the 1,5-tetrazole, CF₃$\text{CNNN}$CF(CF₃)₂. Hexafluoropropylideniminolithium produces as a minor product the conjugated diimine, (CF₃)₂CNC(CF₃)NCF(CF₃)₂, from nucleophilic attack at the imidoyl chlorine and as a major product the triimine, (CF₃)₂CNC(CF₃)NC(CF₃)₂NC(CF₃)₂, from further attack at the isopropyl fluorine. A thio-amide, CF₃C(S)NHCH(CF₃)₂, and a Δ³-1,2,4-dithiazoline, $\text{SSC(CF}{}_3\text{)NC}$(CF₃)₂, are produced upon reaction of hyrogen sulfide with the imidoyl chloride. Pathways are proposed for each of the reactions.     

A mass spectral study of some symmetric and unsymmetric sulfides,disulfanes, and trisulfanes

The low-resolution mass spectra of 13 trifluoromethyl and/or methyl sulfur-containing compounds (CF₃S_nCF₃, CF₃S_nCH₃, CH₃S_nCH₃, CF₃S_mCl, and CH₃S_mCl; n = 1, 2, 3; m = 1, 2) are reported and discussed. There is a considerable similarity between the fragmentation pattern of compounds with the same terminal groups. However, with a fluorinated and a non-fluorinated methyl group, the major fragmentation products produced are similar to those for the dimethyl compounds.