Study of the reactione + e −→K + K − in the energy range1350 \leqq \sqrt s \leqq 2400 MeV

Thee ⁺ e ^?→K ⁺ K ^? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ^± form factor |F _F ^±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment.     

Detection and measurement of noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor using multifrequency powder EPR spectroscopy: application to cis-[(NH(3))(2)Pt(1-MeU)(2)Cu(H(2)O)(2)](SO(4)) x 4.5H(2)O (1-MeU = monoanion of 1-methyluracil)

Multifrequency continuous wave EPR spectra (4-34 GHz) on a powder of the title compound are consistent with a spin-triplet state. This arises from interaction between centrosymmetrically related pairs of copper(II) ions in the solid. The spectra at all frequencies have been simulated with a single set of spin-Hamiltonian parameters. The results show that there is noncoincidence between the principal axes of the g-matrices on each copper center and those of the zero-field splitting (D) tensor. This noncoincidence is a single rotation of 33 degrees +/- 2 degrees. The parameters from the powder spectra have been verified by a subsequent single-crystal EPR study which yielded the spin-Hamiltonian parameters g(XX) = 2.074, g(YY) = 2.093, g(ZZ) = 2.385, D(XX) = +/-0.0228 cm(-1), D(YY) = +/-0.0211 cm(-1), D(ZZ) = -/+0.0439 cm(-1) with Euler angles of alpha = 179 degrees, chi = 33.4 degrees, and gamma = 328 degrees. Analysis of the zero-field splitting tensor in terms of exchange indicates that the interaction between the pairs of copper(II) ions is almost entirely dipolar in origin. This study shows that multifrequency EPR spectroscopy on powders, coupled with spectrum simulation, can detect and measure noncoincidence between the principal axes of the g-matrix and zero-field splitting tensor, and does not necessarily require the presence of metal hyperfine interactions.     

Radiative decay ofJ/ψ into γ π+ π−

The radiative decayJ/ψ → γ π⁺ π^? has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe ⁺e^? storage rings at Orsay. The π⁺ π^? mass spectrum shows a cleanf ₂ (1270) signal, and the possible presence of two other states at thef ₂ (1720) andf ₄ (2030) masses. For thef ₂ (1270), the branching ratio BR(J/ψ →γf)xBR(f→π⁺ π^?) is measured to be (7.50±0.30±1.12)×10^?4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.     

Non-planar smoulder propagation governed by diffusion

The steady propagation of a thin smouldering front in a half-spacehas been considered. A suitable coordinate transformation hasallowed the region near the leading edge of the front to beexamined for both a maintained planar surface and with surfacecollapse due to material shrinkage. The change in the oxidizerconcentration for a small increment in the propagation speedfor large time and surface collapse has been determined. Theinfluence of two types of nonlinear diffusion on the shape ofthe smouldering front has been found; other cases can be dealtwith in a similar manner.     

Mixed metal PtxMyLz complexes of L = 1-methyluracil and 1-methylthymine: Preparation and spectroscopic studies

The reactions of cis-(NH₃)₂PtL₂ (L = 1-MeT or 1-MeU, the anions of 1-methylthymine or 1-methyluracil respectively) in water with various salts of Fe(II), Fe(III), Co(II), Ni(II), Cu(II) or Ag(I) have produced 14 new heteronuclear complexes of the general types: cis-[(NH₃)₂PtL₂ML₂Pt(NH₃)₂]X_n·mH₂O or cis-(NH₃)₂PtL₂MX_n·mH₂O, and also with silver(I) perchlorate a complex of stoichiometry cis-{(NH₃)₂Pt(1-MeU)₂}₂· 3AgClO₄·6H₂O. Comparisons are made with previously reported heteronuclear species derived from cis-(NH₃)₂PtL₂ and factors influencing the type of heteronuclear complex formed are discussed, particularly the versatility of binding patterns with Ag(I). A tetranuclear structure is suggested for the compound of stoichiometry cis-(NH₃)₂Pt(1-MeU)₂·FeSO₄·3H₂O involving iron(II) ions linked by sulphate bridges. The electronic spectra of the trinuclear complexes cis-[(NH₃)₂Pt(1-MeU)₂M(1-MeU)₂Pt(NH₃)₂] (NO₃)₂·mH₂O (M = Fe, Co or Ni) are reported. They show that the trans-MO₄Pt₂ geometry results in a very severely trans-elongated ligand field about the central metal ion, M. This conclusion is supported by the Mössbauer spectrum in the case of the iron(II) complex. The X- and Q-band EPR spectra of the Fe(III) analogue are also reported.     

Intraatomic exchange and the violation of Hund's rule in twisted ethylene

It is demonstrated that the reason the singlet state lies below the triplet state in twisted ethylene (in violation of Hund's rule) is because there remains a significant component of the antiferromagnetic coupling of two triplet methylenes optimal for the methylene—methylene separated limit. We find that this effect can be completely described using a simple generalized valence bond wavefunction.     

Crystal and molecular structures of 5,7-dimethyl-1,8-naphthyridine-2-ol (=LH) and of its mercury (II) complex HgL2 and synthesis of some lanthanide/HgL2 heterometallic complexes

The crystal structures of the title compounds have been determined by single crystal diffraction methods. Crystals of 5,7-dimethyl-1,8-naphthyridine-2-ol (1) are monoclinic, space groupP2₁/n witha=7.336(2),b=8.989(2),c=13.125(3)Å,=95.72(3)°,V=861.2(4)ų,Z=4,D _c =1.34 g cm^–3, finalR=0.052. The molecules are linked in pairs by two N-HO hydrogen bonds, and these dimers are stacked in a discontinuous, stepped fashion. Crystals of HgL₂ (2) are monoclinic space groupP2₁,/c witha=4.044(2),b=12.147(2),c=18.093(5)Å,=93.32(2)°,V=887.3(4)ų,Z=2,D _c =2.05 g cm^–3, finalR=0.051. In2 the mercury binds to N(1) to form a linear N-Hg-N coordination geometry, and the HgL₂ molecules form a continuous stacked structure. The syntheses of the compounds ML₄(NO₃)₃·H₂O (M=Nd, Gd, and Er), PrHg₂L₄(NO₃)₃, andM ₂Hg₃L₆(NO₃)₆ (M=Gd, Er) are also reported.