We report a combined experimental and theoretical investigation of the magnetic structure of the honeycomb lattice magnet Na2IrO3, a strong candidate for a realization of a gapless spin-liquid. Using resonant x-ray magnetic scattering at the Ir L3-edge, we find 3D long range antiferromagnetic order below TN =13.3 K. From the azimuthal dependence of the magnetic Bragg peak, the ordered moment is determined to be predominantly along the a-axis. Combining the experimental data with first principles calculations, we propose that the most likely spin structure is a novel "zig-zag" structure.

We investigate the high-energy magnetic excitation spectrum of the high-T(c) cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8+δ) (Bi-2212) using Cu L(3) edge resonant inelastic x-ray scattering. Broad, dispersive magnetic excitations are observed, with a zone boundary energy of ∼ 300 meV and a weak dependence on doping. These excitations are strikingly similar to the bosons proposed to explain the high-energy "kink" observed in photoemission. A phenomenological calculation of the spin response, based on a parametrization of the the angle-resolved photoemission spectroscopy derived electronic structure and Yang-Rice-Zhang quasiparticles, provides a reasonable prediction of the energy dispersion of the observed magnetic excitations. These results indicate a possible unified framework to reconcile the magnetic and electronic properties of the cuprates and we discuss the advantages and disadvantages of such an approach.

A key issue in heavy fermion research is how subtle changes in the hybridization between the 4f (5f) and conduction electrons can result in fundamentally different ground states. CeRhIn_{5} stands out as a particularly notable example: when replacing Rh with either Co or Ir, antiferromagnetism gives way to superconductivity. In this photoemission study of CeRhIn_{5}, we demonstrate that the use of resonant angle-resolved photoemission spectroscopy with polarized light allows us to extract detailed information on the 4f crystal field states and details on the 4f and conduction electron hybridization, which together determine the ground state. We directly observe weakly dispersive Kondo resonances of f electrons and identify two of the three Ce 4f_{5/2}^{1} crystal-electric-field levels and band-dependent hybridization, which signals that the hybridization occurs primarily between the Ce 4f states in the CeIn_{3} layer and two more three-dimensional bands composed of the Rh 4d and In 5p orbitals in the RhIn_{2} layer. Our results allow us to connect the properties observed at elevated temperatures with the unusual low-temperature properties of this enigmatic heavy fermion compound.

The room temperature rate constant of the reaction F + N, -NF + N2 has been determined by monitoring the time dependence of laser-induced fluorescence from the intermediate N3 radicals in the presence of a large excess of F atoms. Experiments were performed with CF4, SF,, and F2 as precursors of the F atoms. The results indicate that the F + N, rate constant is (5.8 f 0.6) X lo-" cm3 s-' at 298 K. Rate constants for the reactions of N, with H, Cl, and Br atoms were determined from competitive rate studies in which N, was allowed to react with mixtures of each of these atoms with F atoms. The data indicate rate constants of (1.0 f 0.1) X and (3 f 2) X 1O-Io cm3 s-l for H + N,, C1 + N3, and Br + N,, respectively.(2.8 f 0.4) X IntroductionOver the past several years, a considerable amount of information has been published in the literature concerning reactions of the N3 radi~al.l-~ These processes are of interest because of the large amounts of energy liberated, angular momentum constraints on the distribution of this energy among product states, and the potential utility of such processes for pumping new lasers. The rate constants of N3 reactions have been found1+' to vary over a range from lo-'* to cm3 s-l. The most commonly used method for generating N3 radicals

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