Absolute γ-decay rates of the fc(3.55) from tensor meson dominance and QCD-potentials

We compute the coupling gf_c of the 2⁺⁺ cc? meson f_c(3.55) to the energy-2-momentum tensor, 〈0|T_μν|f_c〉·√ = gf_c?μν, from the QCD-potential of Barbieri, Gatto, Kögerler and Kunszt. Vector meson and tensor dominance then imply, including color, Γ(Ψ' → γf_c) = 20 keV in good agreement with experiment. Other potentials available in the literature yield widths which are larger by up to a factor 2. A naive formulation of vector meson dominance for both γ's in f_c → γγ yields A width which is an order of magnitude above the experimental limit.     

Electronic properties of D4h d complexes through a crystal-field model: an appraisal

The crystal-field model recently used by Huang et al. [J. Phys. Chem. Solids 64 (2003) 523] for explaining some optical transitions and the g and hyperfine tensors of the CuCl₄²⁻ unit placed in K₂PdCl₄ is critically reviewed. It is firstly pointed out that using accurate 〈r⁴〉₀=2.7 a.u. and 〈r²〉₀=1.0 a.u. values for free Cu²⁺ the d-d transitions of CuCl₄²⁻ calculated in a rigorous crystal-field framework are much smaller than experimental ones. The agreement with experimental values when an approximated 3d wavefunction is used (leading to 〈r⁴〉₀=44.8 a.u. should then be taken as meaningless. The neglect of charge transfer (CT) transitions for explaining the experimental EPR parameters is shown to be against the onset of these excitations in CuCl₄²⁻ observed at about 25,000 cm⁻¹ and the 40% delocalization of the unpaired electron in the b_1g (≈x²−y²) level. Finally it is pointed out that the experimental g tensor for similar units like AgBr₆⁴⁻ or CuBr₄²⁻ involving a higher covalency cannot be explained by a model where the contribution of CT transitions and ligand spin-orbit coupling is ignored.     

Two and three pion-cut contributions to nucleon-nucleon scattering

Examining information from NN forward scattering in terms of discrepancy functions, we show that the 2π cut contributions as calculated via dispersion methods from πN scattering are in perfect agreement with NN scattering. Furthermore, we demonstrate the need for 3π cut contributions which are quantitatively well described by a nucleon exchange model. Finally, in addition to the 2π and 3π cut contributions, we determine the coupling constants of the ω and A₁ to be: g_Vω²/4π = 8.1 ± 1.5, g_Tω/g_Vω = 0.14 ± 0.20 and g_A1²/4π = 7.3 ± 3.0. The coupling of the η turns out to be zero.     

Electric-magnetic duality in non-abelian gauge theories

The duality transformation of the vacuum expectation value of the operator which creates magnetic vortices (the 't Hooft loop operator in the Higgs phase), is performed in the radial gauge (x_uA_u^a(x) = 0). It is found that in the weak coupling region (small g) of a pure Yang-Mills theory the dual operator creates electric vortices whose strength is $\text{1}\text{g}$. The theory is self-dual in this region, and the effective coupling of the dual Lagrangian is $\text{1}\text{g}$. (It is self-dual also in the extreme strong coupling region.) Thus the above duality transformation reduces to electric-magnetic duality where the electric field in the 't Hooft loop operators transforms into a magnetic field in the dual operator. In a spontaneously broken gauge theory these results are valid only within the region where the vortices (or the monopoles) are concentrated, or in directions of the algebra space of unbroken symmetry, as self-duality holds only for this subset of fields. Noting that the 't Hooft loop operator project into the subspace of these field configurations we find that it is an electric-magnetic duality for the spontaneously broken theory as well. In the strong coupling region a strong coupling expansion in powers $\text{1}\text{g}$ is suggested.     

Sublimation Study of Six 5-Substituted-1,10-Phenanthrolines by Knudsen Effusion Mass Loss and Solution Calorimetry

The vapor pressures of six solid 5-X-1,10-phenanthrolines (where X = Cl, CH₃, CN, OCH₃, NH₂, NO₂) were determined in suitable temperature ranges by Knudsen Effusion Mass Loss (KEML). From the temperature dependencies of vapor pressure, the molar sublimation enthalpies, Δ_cr^gH_m⁰(⟨T⟩), were calculated at the corresponding average ⟨T⟩ of the explored temperature ranges. Since to the best of our knowledge no thermochemical data seem to be available in the literature regarding these compounds, the Δ_cr^gH_m⁰(⟨T⟩) values obtained by KEML experiments were adjusted to 298.15 K using a well known empirical procedure reported in the literature. The standard (p⁰ = 0.1 MPa) molar sublimation enthalpies, Δ_cr^gH_m⁰(298.15 K), were compared with those determined using a recently proposed solution calorimetry approach, which was validated using a remarkable amount of thermochemical data of molecular compounds. For this purpose, solution enthalpies at infinite dilution of the studied 5-chloro and 5-methylphenantrolines in benzene were measured at 298.15 K. Good agreement was found between the values derived by the two different approaches, and final mean values of Δ_cr^gH_m⁰(298.15 K) were recommended. Finally, the standard molar entropies and Gibbs energies of sublimation were also derived at T = 298.15 K. The volatilities of the six compounds were found to vary over a range of three orders of magnitude in the explored temperature range. The large difference in volatility was analyzed in the light of enthalpies and entropies of sublimation. The latter was tentatively put in relation to the rotational contribution of the substituent group on the phenanthroline unit.     

Deeply virtual and exclusive electroproduction of ω-mesons

The exclusive ω electroproduction off the proton was studied in a large kinematical domain above the nucleon resonance region and for the highest possible photon virtuality (Q²) with the 5.75 GeV beam at CEBAF and the CLAS spectrometer. Cross-sections were measured up to large values of the four-momentum transfer (- t < 2.7 GeV²) to the proton. The contributions of the interference terms σ_{TT} and σ_{TL} to the cross-sections, as well as an analysis of the ω spin density matrix, indicate that helicity is not conserved in this process. The t-channel π⁰ exchange, or more generally the exchange of the associated Regge trajectory, seems to dominate the reaction γ^*p↦ωp, even for Q² as large as 5 GeV². Contributions of handbag diagrams, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract for this process. Remarkably, the high-t behaviour of the cross-sections is nearly Q²-independent, which may be interpreted as a coupling of the photon to a point-like object in this kinematical limit.     

Studies of the crystal field energy levels and g factors for Ce in LiYF4 crystal

The five observed crystal field energy levels and EPR g factors g_//and g_⊥ for Ce³⁺-doped LiYF₄ crystal are calculated together from a complete diagonalization (of energy matrix) method. In the method, the contributions to g factors of ground Kramers doublet from all the rest doublets within the ground and excited manifolds ²F_5/2 and ²F_7/2 are included. The calculated results show reasonable agreement with the experimental values. The calculations suggest that the crystal field parameter B₂₀ > 0 in LiYF₄: Ce³⁺ crystal. The opinion of the parameter B₂₀ < 0 in the previous paper is not correct. Since this opinion is based on the calculation of g factors using a very simple method where only the contributions to g factors from the doublets within the ground manifold ²F_5/2 are considered, it is suggested that this simple method is not effective in the calculation of g factors for 4f¹ ions in crystals.     

Semi-empirical analysis of magnetic moments of single-particle (or-hole) states around the 208Pb core

Magnetic moments of single-particle (or-hole) states around the ²⁰⁸Pb core were fitted by three state-independent parameters δg_l^(p), δg_l⁽ⁿ⁾ and α, where α is a parameter that is connected closely with δg_S and g_p. The analysis was performed under the assumptions that (i) the state-dependence of radial integral I((nl)²(n'l')²) involved in δg_s and g_p is calculated by the harmonic-oscillator potential, and (ii) δg_s is taken as being equal to ?4g_p, as expected from the δ-force type core polarization. An excellent fit was obtained when δg_l^(p) = 0.10(2), δg_l⁽ⁿ⁾ = ?0.05(1) and α = 1.2(1), which show that the main contributor to δg_s is the M1 core polarization and δg_l⁽ⁿ⁾ is certainly smaller than 0. B(M1)'s for allowed transitions calculated with the use of the same parameters as above are smaller than the observed B(M1)'s whereas α = 1.01(1) explains well the observed B(M1)'s.     

Modified expression for permeability tensor in partially magnetised ferrites

Green and Sandy's experimental results [IEEE Trans Microwave Theory Tech.MTT-22 641 (1974)] for μ', the permeability tensor element of the partially magnetised ferrites, show systematic discrepancies with the values computed by them from their formula for large values of the normalised average magnetisation. It has been shown that a good agreement is possible if Schlömann's expression for μ'₀ occuring in this formula is replaced by another expression originally given by Sandy provided the average demagnetisation factor N of the domains is taken as a linear function of the magnetisation. This modification is also able to interpret the author's experimental results on Magneto-Microwave Kerr Effect successfully, which are not at all explained by the original Green and Sandy formula.     

Calculation of spin-dependent parameters in the Landau-Migdal theory of nuclei

Contributions to the spin-dependent parameter G'₀, the coefficient of σ₁·σ₂τ₁·τ₂δ(r₁?r₂) in the Fermi-liquid interaction, and to the tensor invariants, are related back to elementary-particle exchange. Once finite-range pion-nucleon interactions are used, almost all of G'₀ comes from theρ-exchange nucleon-nucleon potential. Using modern parameterizations of the strength in the ρ-channel, we find G'₀ to be in the region of 1.5 to 2.4 which agrees well with an empirical determination.     

The AΠu state of : Electric properties, fine and hyperfine coupling constants, and magnetic moments (g-factors). A theoretical study

Several properties are calculated for A²Π_u of —the majority for the first time—including electric and magnetic moments, and fine/hyperfine structure (fs/hfs) parameters. The new results are compared with our previous ones for X² and B² of [P.J. Bruna, F. Grein, J. Mol. Spectrosc. 227 (2004) 67–80]. The electric quadrupole Θ and hexadecapole Φ moments, polarizability α, and hfs constants a, b, c, d, eQq₀, eQq₂ are evaluated at the density functional theory (DFT) level [B3LYP/aug-cc-pVQZ]. The fs constants (spin–orbit coupling A_Π, Λ-doubling p, q, spin-rotation γ_Π), and magnetic moments (g-factors) are obtained via 2nd-order sum-over-states expansions, using wavefunctions and matrix elements obtained with a multireference configuration interaction (MRDCI) method, and the Breit–Pauli Hamiltonian. At equilibrium, 2nd-order properties of A²Π_u are dominated by its coupling with B². For the A state, two independent components are reported for traceless tensor properties (multipoles Θ and Φ; hfs parameters c/d and q₀/q₂) and three for traced properties (polarizability α and g-factors), i.e., one more component than for axially symmetric Σ states. The currently available experimental data on — limited to A_Π, p, and q—are well reproduced by our theoretical results.     

Enhancement of the Debye frequency due to a charged-boson exchange model of high temperature superconductors

A simple model of 1-2-3 superconductors in which electrons (holes) in CuO₂ planes interact via exchange with two kinds of bosons is considered. Namely, via one-phonon exchange (weak coupling-Cooper pairing), and via paired holes on oxygen O⁰ from Cu-O chains. The mechanisms of paired holes exchange (“charged bosons”-“O⁰” exchange) considered here in strong coupling leads to the enhancement of the Fröhlich constant g_f (g²_F→Kg²F), and as a consequence to the enhancement of the Debye frequency ω_D^K=f^Kω_D, f^K 1. In the proposed model the exact expression for the constant K is derived.     

Measurement of NO22B2 state g values by optical radio frequency double resonance

The g values for some selected levels of the NO₂ 6126 and 5933 Å bands were measured using optical radio frequency double resonance. The g values are found to be well described by the Hund's case (b) coupling scheme.     

Magnetic properties and EPR spectra of [Cu(L-arginine)2](NO3)2·3H2O

Magnetic and EPR data have been collected for complex [Cu(L-Arg)₂](NO₃)₂·3H₂O (Arg=arginine). Magnetic susceptibility χ in the temperature range 2-160 K, and a magnetization isotherm at T=2.29(1) K with magnetic fields between 0 and 9 T were measured. The observed variation of χT with T indicates predominant antiferromagnetic interactions between Cu(II) ions coupled in 1D chains along the b axis. Fitting a molecular field model to the susceptibility data allows to evaluate g=2.10(1) for the average g-factor and J=−0.42(6) cm⁻¹ for the nearest neighbor exchange coupling (defined as H_ex=-∑J_ijS_i·S_j). This coupling is assigned to syn-anti equatorial-apical carboxylate bridges connecting Cu(II) ion neighbors at 5.682 Å, with a total bond length of 6.989 Å and is consistent with the magnetization isotherm results. It is discussed and compared with couplings observed in other compounds with similar exchange bridges. EPR spectra at 9.77 were obtained in powder samples and at 9.77 and at 34.1 GHz in the three orthogonal planes of single crystals. At both microwave frequencies, and for all magnetic field orientations a single signal arising from the collapse due to exchange interaction of resonances corresponding to two rotated Cu(II) sites is observed. From the EPR results the molecular g-tensors corresponding to the two copper sites in the unit cell were evaluated, allowing an estimated lower limit |J |>0.1 cm⁻¹ for the exchange interaction between Cu(II) neighbors, consistent with the magnetic measurements. The observed angular variation of the line width is attributed to dipolar coupling between Cu(II) ions in the lattice.     

Single-phonon contribution to the hopping Hall effect in amorphous solids and glasses

Full single-phonon contribution to the tensor of the electronic d.c. hopping conductivity in external magnetic field? is found and its first derivative (with respect to?) is shown to vanish at?=0. Thus the Hall mobilityμ _H is found to be proportional to the squared electron-phonon coupling constantg ² at least, in accordance with extremely low values ofμ _H in amorphous semi-conductors and glasses.     

Neutron spectroscopy study of magnons in the austenite and martensite phases of a Ni-Mn-Ga Heusler alloy

The low energy region of magnon excitations of an off-stoichiometric Ni_49.1Mn_29.4Ga_21.5 single crystal has been investigated by neutron spectroscopy. The lowest magnetic exchange stiffness constant D of 97±2 meV Å² has been found in the cubic austenite phase. In the two martensitic phases the exchange stiffness constants are significantly larger with values of 149±4 meV Å² in the tetragonal phase and 198±7 meV Å² in the low temperature martensite. The large value of D in the low temperature phase compared to the other phases cannot be explained solely by renormalization effects due to magnon-magnon interaction and is attributed to a stronger magnetic coupling. In both the martensitic phases a gap of magnon excitation at the Γ-point of about 0.2 meV was observed.     

High order vibrational matrix elements for diatomic molecules; dipole moment function and transition moments of CO

The fifth and sixth-order contributions to the vibrational matrix elements are obtained for the transitions v→v'(v'?v+4) using an eight power internuclear Dunham potential and a quartic power series expansion of the dipole moment function. The results for the dipole moment coefficients M₀ to M₄ of CO and the transition moments R_v^v' (with v=5, 10, 20) deduced from a calculation including succesively third, fourth, fifth and sixth-order perturbation theory are compared. The validity of these results is discussed.Using a quintic dipole moment function, general expressions for the vibrational matrix elements corresponding to the transitions v→v'(v'? v+5) are also presented and the influence of these contributions on the calculation of the dipole moment coefficients as well as the hot band transition moments of CO is shown.     

Transition metal ions in crystals: A refined treatment and deduction of coulomb and exchange interaction constants

Making use of Racah's irreducible tensor operator technique a refined treatment for the 3d-transition metal ions in crystals has been presented. The refined theory has been applied to analyse the recently observed fine optical spectra of MgF₂:Co²⁺ and MgF₂:Mn²⁺. Important differences have been noticed in the assignments of the optical lines obtained from the present analysis and from the conventional three-parameter theory. First numerical values of the exchange and Coulomb integrals in these systems have also been given.     

Far infrared absorption of Fe2+ in KMgF3

Far infrared absorption in cubic KMgF₃ doped with Fe²⁺ is reported . A line is observed at 87cm^?1, which is assigned to the (Γ_5g → Γ_3g, Γ_4g) transition in the Fe²⁺. The reduction in the spin-orbit coupling from the free ion value has been predicted by Ham, Schwarz and O'Brien.     

Deviation from Kittel's magnetic resonance formula near Tc of CdCr2Se4

Approaching the Curie temperature of the cubic ferromagnet CdCr₂Se₄ from above, the g-factor increasingly shifts from the value predicted by Kittel's formula. In the exchange critical region (susceptibility χ ?1) the g-shift is consistent with δg/g ≈ χ² following from the complex self-energy.