Asymptotic Regge Trajectories of Non-strange Mesons

We analyze the asymptotic behavior of Regge trajectories of non-strange mesons. In contrast to an existing belief, it is demonstrated that for the asymptotically linear Regge trajectories the width of heavy hadrons cannot linearly depend on their mass. Using the data on masses and widths of rho_J, omega_J, a_J and f_J mesons for the spin values J \leq 6, we extract the parameters of the asymptotically linear Regge trajectory predicted by the finite width model of quark gluon bags. As it is shown the obtained parameters for the data set B correspond to the cross-over temperature lying in the interval 170.9-175.3 MeV which is consistent with the kinetic freeze-out temperature of early hadronizing particles found in relativistic heavy ion collisions at and above the highest SPS energy.Comment: 14 pages, 3 figure

Beta-agostic silylamido and silyl-hydrido compounds of molybdenum and tungsten.

Reactions of bis(imido) compounds (RN)(2)Mo(PMe(3))(n) (n = 2, R = (t)Bu; n = 3, R =2,6-dimethylphenyl (Ar') and 2,6-diisopropylphenyl (Ar)) and (RN)(2)W(PMe(3))(3) (R = 2,6-dimethylphenyl and 2,6-diisopropylphenyl) with silanes afford four types of products: the beta-agostic silylamido compounds (RN)(eta(3)-RN-SiR'(2)-H...)MCl(PMe(3))(2) (M = Mo and W), mono(imides) (RN)MCl(2)(PMe(3))(3) (M = Mo and W), silyl hydride bis(imido) derivative (ArN)(2)W(PMe(3))(H)(SiMeCl(2)), and Si-Cl...W bridged product (ArN)(eta(2)-ArN-SiHMeCl-Cl...)WCl(PMe(3))(2). Reactions of molybdenum compounds (RN)(2)Mo(PMe(3))(m) (m = 2 or 3) with mono- and dichlorosilanes HSiCl(n)R'(3-n) (R' = Me, Ph; n = 1,2) afford mainly the agostic compounds (RN)(eta(3)-RN-SiR'(2)-H...)MoCl(PMe(3))(2), accompanied by small amounts of mono(imido) derivatives (RN)MoCl(2)(PMe(3))(3). In contrast, the latter compounds are the only transition metal products in reactions with HSiCl(3), the silicon co-product being the silanimine dimer (RNSiHCl)(2). The reaction of (ArN)(2)W(PMe(3))(3) with HSiCl(2)Me under continuous removal of PMe(3) affords the silyl hydride species (ArN)(2)W(PMe(3))(SiMeCl(2))H, characterized by NMR and X-ray diffraction. This product is stable in the absence of phosphine, but addition of catalytic amounts of PMe(3) causes a fast rearrangement into the Si-Cl...W bridged product (ArN)(eta(2)-ArN-SiHMeCl-Cl...)WCl(PMe(3))(2). The mechanism of silane addition to complexes (RN)(2)Mo(PMe(3))(n) has been elucidated by means of density functional theory calculations of model complexes (MeN)(2)Mo(PMe(3))(n) (n = 1-3). Complex (MeN)(2)Mo(PMe(3))(2) is found to be the most stable form. It undergoes facile silane-to-imido addition reactions that afford silylamido hydride complexes stabilized by additional Si...H interactions. The ease of this addition increases from HSiMe(2)Cl to HSiCl(3), consistent with experimental observations. The most stable final products of silane addition are the agostic complexes (MeN)(eta(3)-MeN-SiR(2)-H...)MoCl(PMe(3))(2) (R(2) = Me(2), MeCl, Cl(2)) and Cl-bridged silylamido complexes (MeN)(eta(2)-MeN-SiRH-Cl...)MoCl(PMe(3))(2) (R = Me or Cl). In the case of HSiMeCl(2) addition the former is the most stable, but for HSiCl(3) addition the latter is the preferred product. In all cases, the isomeric silyl hydride species (MeN)(2)Mo(PMe(3))(H)(SiClR(2)) are less stable by about 6 kcal mol(-1). Silane additions to the imido ligand of the tris(phosphine) (MeN)(2)Mo(PMe(3))(3) afford octahedral silylamido hydride derivatives. The different isomers of these addition products are destabilized relative to (MeN)(2)Mo(PMe(3))(3) only by 7-24 kcal mol(-1) (for the HSiMe(2)Cl additions), but since the starting tris(phosphine) is 14.8 kcal mol(-1) less stable than (MeN)(2)Mo(PMe(3))(2), silane addition to the latter is a more preferred pathway. A double phosphine dissociation pathway via the species (MeN)(2)Mo(PMe(3)) was ruled out because this complex is by 24.7 kcal mol(-1) less stable than (MeN)(2)Mo(PMe(3))(2)

Synthesis and molecular and electronic structure of an unusual paramagnetic borohydride complex Mo(NAr)2(PMe3)2(eta2-BH4).

Reaction of Mo(NAr)2Cl2(DME) (Ar=2,6-C6H3iPr2, DME=1,2-dimethoxyethane) with NaBH4 and PMe3 in THF formed the paramagnetic Mo(V) d1 borohydride complex Mo(NAr)2(PMe3)2(eta2-BH4) (1). Compound 1, which was characterized by EPR spectroscopy and X-ray diffraction analysis, provides a rare example both of a paramagnetic bis(imido) group 6 compound and a structurally characterized molybdenum borohydride complex. Density functional theory calculations were used to determine the electronic structure and bonding parameters of 1 and showed that it is best viewed as a 19 valence electron compound (having a primarily metal-based SOMO) in which the BH4- ligand behaves as a sigma-only, 2-electron donor

Measurement of the beam asymmetry in η photoproduction off the proton

The beam asymmetry, Sigma, was measured at ELSA in the reaction gamma p -< eta p using linearly polarised tagged photon beams, produced by coherent bremsstrahlung o ff a diamond. The crystal was oriented to provide polarised photons in the energy range E-gamma = 800 to 1400MeV with the maximum polarisation of P-gamma = 49% obtained at 1305MeV. Both dominant decay modes of the eta into two photons and 3 pi(0) were used to extract the beam asymmetry from the azimuthal modulation of the cross- section. The measurements cover the angular range circle minus cm similar or equal to 50-150 degrees. Large asymmetries up to 80% are observed, in agreement with a previous measurement. The eta- MAID model and the Bonn- Gatchina partial wave analysis describe the measurements, but the required partial waves differ significantly