E0 andM1 excitations in56Ni

The centroid energy and the decay width of the giant monopole resonance in the unstable nucleus⁵⁶Ni are predicted. The resulting 0⁺, ΔT=0 strength distribution, including the escape and the spreading width, displays a structure centered at around 18 MeV with the total width of about 5 MeV. We also study theM1 response in this nucleus which shows a strong isovector transition at 9.6 MeV and a weak isoscalar one at 7.5 MeV.     

Imaging-XPS/Raman investigation on the carbonization of polyimide after irradiation at 308 nm

The laser ablation of polyimide was studied using 308 nm laser irradiation 𙜡 mJ cm^-2. Confocal Raman microscopy revealed the deposition of carbon surrounding the ablation crater, which consists of amorphous carbon with some crystalline features. Inside the crater, graphitic material was detected on top of the cones, very similar to the material from cw-Ar⁺ ion laser irradiation. FT-Raman measurements reveal the presence of intermediates of the polyimide decomposition. Imaging-X-ray photoelectron spectroscopy confirmed the deposition of carbon material surrounding the ablation crater and showed that the oxygen and nitrogen contents of the remaining material decrease.     

Dynamics of single-particle and collective excitations in heavy nuclei

The propagation of single-particle and small-amplitude collective excitations in a heavy nucleus is considered. We calculate perturbatively corrections to the mean-field approximation induced by the coupling of one-particle and collective motion via the residual particle-hole interaction. Special attention is paid to the energy variation of the quasiparticle effective mass near Fermi energy. We conclude from the calculation that particles and holes excited in low multipolarity giant resonances have average effective masses of the order of 0.8 m rather than m. The mechanism for the decrease is provided by the enforced decoupling of the quasiparticles from surface oscillations due to the high frequency of the giant resonances. We also study the role of surface modes in the decay of giant resonances. Considerable reduction of the damping into 2p-2h states expected from the absorptive part of the optical potential is found. The correlated particle-hole pairs interact with each other by exchanging surface oscillations which adds a destructive interference term to the decay widths of giant resonances. The reduction depends on the multipolarity of the mode and is only large for low angular momenta.     

New cyclopentenyl-linked [NPN] ligands and their coordination chemistry with zirconium: synthesis of a dinuclear side-on-bound dinitrogen complex

The synthesis and characterization of two 1,2-cyclopentyl-bridged diiminophosphine proligands, (CY5)[NPN](DMP)H(2) (CY5 = cyclopentylidene; DMP = 2,6-Me(2)C(6)H(3)) and (CY5)[NPN](DIPP)H(2) (DIPP = 2,6-(i)Pr(2)C(6)H(3)), are presented, and tautomerization to the corresponding 1,2-cyclopentenyl-bridged enamineimine phosphine precursors is reported. These two new proligands are obtained by deprotonation of N-DMP- or N-DIPP-cyclopentylideneimine (N-DMP, 2,6-dimethylphenyl; N-DIPP, 2,6-diisopropylphenyl) and the subsequent addition of 0.5 equiv of dichlorophenylphosphine. Each ligand precursor exists as a mixture of isomers that consist of the diimine, enamineimine, and dienamine tautomers and corresponding stereoisomers, each of which could be identified. The bis(dimethylamido)zirconium complexes (CY5)[NPN](DMP)Zr(NMe(2))(2) and (CY5)[NPN](DIPP)Zr(NMe(2))(2) were prepared directly from the neutral proligands and Zr(NMe(2))(4) via protonolysis. Exchange of the dimethylamido ligands in the latter complexes for chlorides and iodides takes place upon reaction with excess Me(3)SiCl and Me(3)SiI, respectively. A dinuclear zirconium-dinitrogen complex, {(CY5)[NPN](DMP)Zr(THF)}(2)(μ-η(2):η(2)-N(2)), was obtained via KC(8) reduction of (CY5)[NPN](DMP)ZrCl(2) under 4 atm of N(2). On the basis of single-crystal X-ray analysis, N(2) has been reduced to a side-on-bound hydrazido (μ-η(2):η(2)-N(2)(4-)) unit. This dinitrogen complex is thermally unstable and decomposes in solution.     

Isoscalar dipole coherence at low energies and forbidden E1 strength

In ¹⁶O and ⁴⁰Ca an isoscalar, low-energy dipole transition (IS-LED) exhausting approximately 4% of the isoscalar dipole (ISD) energy-weighted sum rule is experimentally known, but conspicuously absent from recent theoretical investigations of ISD strength. The IS-LED mode coincides with the so-called isospin-forbidden E1 transition. We report that for N = Z nuclei up to ¹⁰⁰Sn the fully self-consistent Random-Phase Approximation (RPA) with finite-range forces, phenomenological and realistic, yields a collective IS-LED mode, typically overestimating its excitation energy, but correctly describing its IS strength and electroexcitation form factor. The presence of E1 strength is solely due to the Coulomb interaction between the protons and the resulting isospin-symmetry breaking. The smallness of its value is related to the form of the transition density, due to translational invariance. The calculated values of E1 and ISD strength carried by the IS-LED depend on the effective interaction used. Attention is drawn to the possibility that in N 1 \neq Z nuclei this distinct mode of IS surface vibration can develop as such or mix strongly with skin modes and thus influence the pygmy dipole strength as well as the ISD strength function. In general, theoretical models currently in use may be unfit to predict its precise position and strength, if at all its existence.     

Hadrons in hot and dense matter

I discuss our current understanding of the properties of hot and dense hadronic matter in equilibrium and its excitation spectrum. The latter allows for an experimental study of matter under extreme conditions through ‘in-medium spectroscopy’.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

Experimental calibration and field investigation of the oxygen isotopic fractionation between biogenic aragonite and water

Marine molluscs have long been recognised as potential records of palaeoclimate change using the patterns and differences in the stable isotopic composition of the carbonate shells. The aim of this study is to improve the robustness of this approach for aragonitic molluscs by completing the first experimental calibration of the fractionation between water and biogenic aragonite. Fractionation factors were calibrated by growing specimens of the freshwater mollusc Lymnaea peregra under controlled conditions of water temperature and isotopic composition. Fifteen populations of L. peregra were maintained at constant temperature and isotopic conditions for five months (at five different temperatures and using three different water compositions). Water samples and temperature measurements were taken regularly throughout the experiment. The temperature dependence of the fractionation factor, between 8 and 24 degrees C, is given by: 1000 ln alpha=16.74x(1000T(-1))-26.39 (T in Kelvin) and the relationship between temperature (T), delta(18)O(carb) and delta(18)O(wat) is given by: T=21.36-4.83xdelta(+ degrees )O(carb)-delta(+ degrees )O(wat) (T is in degrees C, delta(18)O(carb) is with respect to Vienna Pee Dee Belemnite (PDB), the International Atomic Energy Agency (IAEA) replacement standard for PDB, and delta(18)O(wat) is with respect to Vienna standard mean ocean water (VSMOW)) The outcome of the controlled experiment is compared with previous studies on synthetic, and biogenic, calcite and aragonite from field and laboratory investigations. These comparisons suggest that although a vital offset exists between the fractionation of isotopes in synthetic and biogenic aragonite for molluscs in general, there is no vital effect that is specific either to freshwater, or to individual, genera. Therefore, the calibrated relationship may be used for any freshwater or marine mollusc to derive palaeotemperatures providing the isotopic composition of the environmental water can be reliably constrained. Copyright 1999 John Wiley & Sons, Ltd.