Core-level Auger spectroscopy of the 4d metals

We report some of the results of extensive experimental and theoretical studies by our group of the high energy Auger spectra of the 4d metals and some of their alloys. We consider, separately, three aspects of these spectra: comparison of experiment with atomic theoretical calculations; the relationship between the Auger kinetic energies and the screening mechanisms in these metals; and the unique properties of satellites associated with these spectra, especially with the L_1,2,3M_4,5M_4,5 spectra. Comparison with atomic theory yields some discrepancies that should be taken into account in the formulation of the theories. Consideration of the Auger kinetic energies yields insight into screening mechanisms and suggests methods for extracting electronic structure changes in alloys from XPS and XAES shifts. Systematic studies of the satellites permit their identification as arising from shake-up processes without contributions from of Coster–Kronig processes, in contrast to studies of 3d metals, such as Cu. Synchrotron studies allow the observation of the transition from the adiabatic approximation regime to that of the sudden approximation.     

ESCA determination of the electronic structure of PtCu alloys

A systematic series of ESCA measurements in Pt_1?xCu_x manifest observable shifts for only the Cu core levels. These shifts are linearly related to the corresponding centroids of the valence band spectra. Physical arguments permit extraction of electronic valence structure changes induced by alloying from the measured quantities. Changes in Fermi energy are not related to differences in work function. The Pt valence structure appears unchanged and the Cu structure exhibits dehybridization. There is little charge transfer.     

LIDAR multiple scattering from clouds

Multiple-scattering LIDAR return calculations obtained by seven different models for the same specified numerical experiment are compared. This work results from an international joint effort stimulated by the workshop group called MUSCLE for MUltiple SCattering Lidar Experiments. The models include approximations to the radiative-transfer theory, Monte-Carlo calculations, a stochastic model of the process of multiple scattering, and an extension of Mie theory for particles illuminated by direct and scattered light. The model solutions are similar in form but differ by up to a factor of 5 in the strength of the multiple-scattering contributions. Various reasons for the observed differences are explored and their practical significance is discussed.     

Optical and photophysical properties of light-harvesting phenylacetylene monodendrons based on unsymmetrical branching

The optical and photophysical properties of phenylacetylene dendritic macromolecules based on unsymmetrical branching are investigated using steady-state and time-dependent spectroscopy. Monodendrons, up to the fourth generation, are characterized with and without a fluorescent perylene trap at the core. The higher generation monodendrons without the perylene trap exhibit high molar extinction coefficients (>10(5) M(-1) cm(-1)) and high fluorescence quantum yields (65-81%). When a perylene trap is placed at the core, then the monodendrons typically exhibit high energy transfer quantum yields (approximately 90%), as well as subpicosecond time scale excited-state dynamics, as evidenced by ultrafast pump-probe measurements. The photophysical properties of the unsymmetrical monodendrons are compared to those of phenylacetylene monodendrons with symmetrical branching, which have been described recently. The high fluorescence quantum yields and large energy transfer quantum efficiencies exhibited by the unsymmetrical monodendrons suggest they have potential for applications in molecular-based photonics devices.     

Gorenstein algebras, symmetric matrices, self-linked ideals, and symbolic powers

Inspired by recent work in the theory of central projections onto hypersurfaces, we characterize self-linked perfect ideals of grade as those with a Hilbert-Burch matrix that has a maximal symmetric subblock. We also prove that every Gorenstein perfect algebra of grade can be presented, as a module, by a symmetric matrix. Both results are derived from the same elementary lemma about symmetrizing a matrix that has, modulo a nonzerodivisor, a symmetric syzygy matrix. In addition, we establish a correspondence, roughly speaking, between Gorenstein perfect algebras of grade that are birational onto their image, on the one hand, and self-linked perfect ideals of grade that have one of the self-linking elements contained in the second symbolic power, on the other hand. Finally, we provide another characterization of these ideals in terms of their symbolic Rees algebras, and we prove a criterion for these algebras to be normal.

     

Efficient energy transfer via the cyanide bridge in dinuclear complexes containing Ru(II) polypyridine moieties

We report the synthesis, structure and properties of the cyanide-bridged dinuclear complex ions [Ru(L)(bpy)(μ-NC)M(CN)(5)](2-/-) (L = tpy, 2,2';6',2'-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2'-bipyridine, M = Fe(II), Fe(III), Cr(III)) and the related monomers [Ru(L)(bpy)X](2+) (X = CN(-) and NCS(-)). All the monomeric compounds are weak MLCT emitters (λ = 650-715 nm, ? ≈ 10(-4)). In the Fe(II) and Cr(III) dinuclear systems, the cyanide bridge promotes efficient energy transfer between the Ru-centered MLCT state and a Fe(II)- or Cr(III)-centered d-d state, which results either in a complete quenching of luminescence or in a narrow red emission (λ ≈ 820 nm, ? ≈ 10(-3)) respectively. In the case of Fe(III) dinuclear systems, an electron transfer quenching process is also likely to occur.