The first (pentamethylcyclopentadienyl)gaUium compounds Ga(C5Me5)2Cl and Ga(C5Me5)Cl2 have been prepared and fully characterized by elemental analyses, cryoscopic molecular weight measurements, IR and NMR data, Lewis acid-base studies, and X-ray structural studies. The derivative Ga(C6Me5)2Cl can be readily prepared from GaCl3 and LiC5Me5 in diethyl ether. When the stoichiometry of the reagents LiC5Me5/GaCl3 was 3.2 or 2.2, the only gallium-containing product was Ga(C5Me5)2Cl. The identical product was isolated when the solvent was THF or the reaction mixture was refluxed. An X-ray structural study of a colorless crystal of bis(pentamethylcyclopentadienyl)gallium chloride demonstrates that the crystal consists of discrete isolated dimeric molecules of [Ga(C6Me=)2Cl]2. The compound crystallizes in the triclinic space group Pi with unit cell dimensions o = 7.825 (3) A, b = 14.341 (4) A, c = 23.853 (6) A, a = 79.20 (3)°, ß = 86.28 (3)°, 7 = 84.93 (3)°, and dcalcd = 1.28 g cm"1 23 for Z = 3. Full-matrix leas-squares refinement led to a final R value of 0.061 for 2007 observed reflections. The dimeric molecules have chlorine bridges, and the planar pentamethylcyclopentadienyl rings exhibit 1 coordination. In benzene solution, the dimeric molecule dissociates and only monomers are observed according to the concentration independent cryoscopic molecular weight data. The dichloro derivative Ga(C5Me5)Cl2 is readily prepared from Ga(C5Me5)2Cl and GaCl3 by a standard ligand redistribution reaction. An X-ray structural study of a light yellow crystal of [Ga(C5Me5)Cl2]2 demonstrates that the compound crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 8.804 (4) A, b = 8.337 (4) A, c = 17.086 (5) A, ß = 94.59 (5)°, and dcaicd = 1.465 g cm"3 for Z = 2. Full-matrix least-squares refinement led to a final R value of 0.052 for 1009 observed reflections. This dimeric molecule also contains chlorine bridges with planar ^-pentamethylcyclopentadienyl rings. Consequently, these new compounds have provided the first structural studies of organogallium halides and permit useful comparisons with the structural data for [GaCl3]2.

The ARGO-YBJ experiment detects extensive air showers in a wide energy range by means of a full-coverage detector which is in stable data taking in its full configuration since November 2007 at the YBJ International Cosmic Ray Observatory (4300 m a.s.l., Tibet, People's Republic of China). In this paper the measurement of the light-component spectrum of primary cosmic rays in the energy region * Corresponding author. mari@fis.uniroma3.it PHYSICAL REVIEW D 85, 092005 (2012) 1550-7998= 2012=85(9)=092005 (10) 092005-1 Ó 2012 American Physical Society ð5 Ä 200Þ TeV is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment.

The EPR g factors g // and g ⊥ for the six-coordinated Cu 2+(1) site in YBa 2 Cu 3 O 6+x are theoretically investigated from the perturbation formulas for a 3 d 9 ion in tetragonally elongated octahedra. The related tetragonal crystal-field parameters Ds and Dt are determined from the superposition model and the structural data for the Cu 2+(1) site, by considering the effective elongation of the oxygen octahedron due to the Jahn-Teller effect of the Cu 2+ cluster. Based on the calculations, the effective elongation (≈ 15%) of the ligand octahedron is obtained for the signals at 100K. As for the EPR signals at room temperature, the elongation declines to merely 4%, corresponding to the smaller anisotropy Δ g (= g // - g ⊥). The theoretical results for the g factors are in good agreement with the observed values, and the local tetragonal distortion due to the Jahn-Teller effect is discussed.

The superhyperfine parameters A′ and B′ for Cr 3+ ions in K 2 NaGaF 6 , K 2 NaCrF 6 , KMgF 3 and CsCdF 3 are theoretically studied from the cluster approach. In the present treatments, the orbital admixture coefficients and the unpaired spin densities in 2s, 2p s and 2p p 2 fluorine orbitals are obtained in a uniform way. The experimental A′ and B′ are reasonably explained, and the unpaired spin densities for the 2s, 2pσ and 2pπ orbitals of the ligand F − are also compared with those in the previous works.

The spin Hamiltonian parameters (g factors g , g ⊥ and the hyperfine structure constants A , A ⊥ ) and the local structures for the two tetragonal Cu 2+ centers I and II in Ca(OH)2 are theoretically studied from the perturbation formulae of these parameters for a 3d 9 ion under tetragonally elongated octahedra. The [Cu(OH)6] 4− clusters on the substitutional Ca 2+ site are found to suffer the relative elongations by about 0.083 Å and 0.065 Å for centers I and II, respectively, along the C4 axis due to the Jahn-Teller effect. The above tetragonal elongations may entirely depress the original trigonal distortion of the host Ca 2+ site in Ca(OH)2. The calculated spin Hamiltonian parameters based on the above Jahn-Teller elongations show good agreement with the experimental results. The EPR spectra and the local structures for the two centers are compared with one another.