Dynamical effects in finite nuclei and their importance in giant resonance calculations

Dynamical effects on the single-particle self-energy Σ_m(ω), i.e., its ω dependence, are studied microscopically using realistic finite-range NN interactions. In heavy nuclei the coupling of particles to high collective low-lying surface vibrations causes dynamical effects much stronger than in nuclear matter. This result can resolve the discrepancies in previous calculations of giant dipole resonance energies.     

Second order self-energy of the two-dimensional Hubbard model

The self-energy Σ(k; ω) of the 2D Hubbard model on the square lattice is calculated numerically in second order perturbation theory. In the limit of small frequencies the imaginary part of Σ(k; ω) is also obtained analytically. We find that at half filling ImΣ(k; ω) ～ ω for k on the Fermi surface, with a logarithmically divergent prefactor close to the corners k = (0,±π) and (±π,0) in agreement with the numerical results.     

Quasiparticle lifetime in graphite studied by ultrahigh-resolution ARPES

We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy (ARPES) to elucidate the nature of quasiparticle dynamics in graphite. We found fairly sharp quasiparticle peak of π band around K(H) point in the vicinity of the Fermi level, together with the strong mass renormalization of the band (kink). The imaginary part of electron self-energy (ImΣ) shows a sudden drop below 0.18 eV, indicative of a strong electron-phonon coupling. The linear energy dependence of ImΣ at higher binding energies provides an evidence for the deviation from the conventional Fermi liquid theory.     

Oxygen isotope effect in optimally doped Bi2Sr2CaCu2O8+δ studied by low-energy ARPES

Using angle-resolved photoemission spectroscopy (ARPES) with low-energy tunable photons, we studied the oxygen isotope effect in optimally doped Bi₂Sr₂CaCu₂O_8+δ (Bi2212). We found the oxygen isotope shift in the real part of the electron self-energies [ReΣ(ω)s] along the nodal direction derived not only from the momentum distribution curves (MDCs) but also from the energy distribution curves (EDCs). Present results indicate straightforwardly the coupling between the nodal electrons and the phonons.     

High-resolution study of the bΣ(b0)→XΣ(X10) transition of PI

Emission spectra of the b¹Σ⁺(b0⁺)→X³Σ⁻(X₁0⁺) transition of phosphorus iodide have been measured with a high-resolution Fourier-transform spectrometer. The PI radicals were generated and excited in a fast-flow system by reaction of phosphorus vapor (P_x) with iodine and microwave-discharged oxygen. Four sequences, Δv=0,+1,−1,−2, of the b¹Σ⁺(b0⁺)→X³Σ⁻(X₁0⁺) transition of PI comprising 28 bands were observed. Six bands were measured at high spectral resolution. Vibrational and rotational analyses have yielded accurate spectroscopic constants of the X₁0⁺ and b0⁺ states (in cm⁻¹): X₁0⁺: ω_e=371.296(4), ω_ex_e=1.3302(9), B_e=0.1194117(2), α_B=−0.0005676(7), D_e=4.56(2) ×10⁻⁸; b0⁺: T_e=11136.921(4), ω_e=400.165(6), ω_ex_e=1.345(2), B_e=0.1239237(2), α_B=−0.0005540(2), D_e=4.84(5) × 10⁻⁸, where the numbers in parentheses are the standard deviations of the parameters. No emissions of the b0⁺→X₂1 sub-system nor of the a¹Δ(a2)→X³Σ⁻(X₂1) transition have been observed leaving PI the only group Va halide for which the spin splitting in the X³Σ⁻ ground state is still unknown.     

Third-order optical harmonic coefficients of atomic hydrogen at low frequencies

The analytical expression is derived for the third-order optical harmonic coefficients χ⁽³⁾₁₁₁₁ (ω, ω, ω) = χ⁽³⁾₂₂₂₂ (ω, ω, ω) = χ⁽³⁾₃₃₃₃ (ω, ω, ω) of the atomic hydrogen at very low frequencies ω → 0.     

Selective effects of homogeneous and heterogeneous reactions in the system N21-CO

In the system N₂¹-CO, effects arising only from the reactions in the homogeneous phase have been isolated in a reactor with inert walls. After an induction period of 0.13 s, they involve a stationary rate of enhancement of N₂(B³Π_g) and N(⁴S) concentrations according to the reactions N₂(X¹Σ_g⁺)_v¹+CO→ CO(X¹Σ⁺)_v1 + N₂(X¹Σ_g⁺ and CO(X¹Σ⁺)_v1 + N₂(A³Σ_u⁺) → N (⁴S) + N(⁴S) + CO(X¹Σ⁺).In a reactor with active walls, both the above reactions in the homogeneous phase and heterogeneous reactions due to CO adsorbed on the walls are involved according to CO_ads + N₂(X¹Σ_g⁺)_{v1 ads or not} → CO(X¹Σ⁺)_v1 + N₂(X¹Σ_g⁺ and N(⁴S) + N(⁴S) + CO_ads → N₂(X¹Σ_g⁺) + CO(X¹Σ⁺)N(⁴S) + CO_ads → N₂(X¹Σ_g⁺) + CO(X¹Σ⁺). In this case, the rate of enhancement is not stationary. Furthermore, for cylindrical reactors with large diameters, the two types of reaction do not interact and their effects are additive.     

Self-consistent calculation of the optical potential and ground-state properties of nuclear matter

On the basis of the Green-function formalism, we performed a self-consistent calculation of the self-energy ∑(k, ω) of a particle interacting with the infinite nuclear medium. The function ∑(k, ω) was mapped out in the energy-momentum plane, and the single-particle energy ω(k), momentum distribution ?(k) and the “on-shell” part of the self-energy, ∑(k, ω(k)), were defined, from which all physical properties followed. In particular we investigated the ground-state properties of nuclear matter in two Λ-approximations of the T-matrix. In one, the intermediate two-particle propagator, Λ₀₀, represented free-particle propagation; in the other, called Λ₁₁, intermediate states included both interacting particles and holes. Pauli principle effects were included in both approximations. The second approximation was expected to be conserving because it included a large part of the rearrangement effects which, we found, contributed ～6 MeV per particle to the average energy and ～28 MeV to the singleparticle energy at zero momentum. The Hugenholtz-van Hove theorem was nearly satisfied, with only 1 MeV separating the chemical potential from the average energy. We also studied, in the Λ₀₀-approximation, the optical potential for the scattering of a particle by a large nucleus; it was directly related to the “on-shell” part of the self-energy. It was found that, below 100 MeV, the real part varied as (?90 + 0.584E) [MeV], and the imaginary part as (2.4 + 0.009 E) [MeV].     

Vibrational analysis of the a3Σ+-X1Σ+ and b3Π-X1Σ+ band systems of GeS

Spectra of GeS have been obtained in a chemiluminescent flame produced by the reaction Ge + OCS → GeS + CO. Neither of the known band systems, D¹Π-X¹Σ⁺ and E¹Σ⁺-X¹Σ⁺, was observed, but two new band systems in the regions 350–400 and 420–650 nm were obtained. By comparison with similar systems in isovalent molecules, these were assigned as b³Π₁-X¹Σ⁺ and a³Σ⁺-X¹Σ⁺, respectively. Vibrational assignments were made with the help of the germanium isotope effect and vibrational constants were obtained for the states involved. Approximate Morse potential Franck-Condon factors were computed and were shown to fit the general trend of the intensity distribution for both systems. Addition of active nitrogen to the flame was shown to increase the intensity of the b-X system by an order of magnitude while hardly affecting the a-X system. Constants (in cm^?1) obtained for the two new states are: a³Σ⁺: T_e = 21986.3 ± 2.3, ω_e = 388.9 ± 1.0, ω_ex_e = 1.35 ± 0.11; b³Π₁: T_e = 27192.0 ± 1.8, ω_e = 435.4 ± 1.1, ω_ex_e = 1.68 ± 0.20.     

Influence of mobile space charges on electrical properties of ferroelectric Bi3.5La0.5Ti3O12 thin films

Lanthanum-substituted bismuth titanate, Bi_3.5La_0.5Ti₃O₁₂ (i.e., x=0.5 in Bi_4−xLa_xTi₃O₁₂), thin films have been grown on Pt/Ti/SiO₂/Si substrates using pulsed laser deposition. The frequency dependence of the real part ε′(ω) and the imaginary part ε″(ω) of the dielectric constant has been studied. The ε′(ω) does not show any sudden change within the frequency range of 10²-10⁶ Hz. In contrast, the ε″(ω) shows a large dispersion as frequency decreases. The observed relaxation behavior in ε″(ω) can be explained in terms of a migration of oxygen vacancies in (Bi₂O₂)²⁺ layers, not in Bi₂Ti₃O₁₀ perovskite layers.     

Thermodynamics of superconducting Nb3Sn

Shen's experimental data on α²(ω)F(ω) and μ¹ in superconducting Nb₃Sn is used to calculate its thermodynamic properties. It is found to exhibit the same size strong coupling corrections to BSC as does Pb. Comparison with experimental data shows satisfactory agreement.     

Theoretical study of the spin-orbit coupling in the X2Π state of OH

The spin-orbit coupling constant, A(r), as a function of internuclear distance (r) was computed for the X²Π state of OH, using the microscopic spin-orbit Hamiltonian, extended basis sets, and extensive configuration-interaction wavefunctions. Our best theoretical results are in excellent agreement with the “experimental” A(r) functions deduced from an inversion of the observed A_v. Our calculated first-order contributions to A_v, v ≤ 10, obtained by vibrationally averaging our theoretical A(r) function using the X²Π RKR potential, differ from experiment by less than 0.12%. A minimum occurs in the A_v at v = 7 in agreement with experiment, reflecting the local minimum in A(r) near 2.8 bohr. The second-order contributions to A_v are only about 0.1% for v ≤ 10. They arise mainly from the A²Σ⁺ state for the lower vibrational levels, but each of the A²Σ⁺, B²Σ⁺, (1)²Σ^?, (1)⁴Σ^?, and (1)²Δ states contributes significantly for higher vibrational levels. Spin-orbit centrifugal distortion parameters, A_Dv and a_Dv, are reported for v ≤ 6. The theoretical A_Dv are also in excellent agreement with experiment when the “experimental” A(r) function has the same slope at the equilibrium separation as that obtained from the effective spin-rotation constants of OH, OD, and OT.     

Measurement of the surface density of states by field ionization

It is shown that recent measurements of field ion energy distributions from clean tungsten surfaces probe the density of metal states in the vicinity of the surface. We find j(ω) = (2π/kh)Σ_m| ∫ d³rψ_m(r)γ_z|²δ(ω??_m), where j(ω) is the ion current a ω, ψ_mand ?_m are electronic metal eigenfunctions and eigenvalues in the presence of the external electric field used in field ionization and γ(z) is a function which is large near the noble gas atom. An explicit expression for γ(z) is given in the text. It is estimated that tungsten metal states with values of k₆ at least as large as 0.5 Å^?1 make an appreciable contribution to j(ω) where k₆ is the electron momentum parallel to the surface.     

Spectral function and self-energy of the one-dimensional Hubbard model in the U →∞ limit

The interpretation of the k dependent spectral functions of the one-dimensional, infinite U Hubbard model obtained by using the factorized wave-function of Ogata and Shiba is revisited. The well defined feature which appears in addition to low energy features typical of Luttinger liquids, and which, close to the Fermi energy, can be interpreted as the shadow band resulting from 2k _F spin fluctuations, is further investigated. A calculation of the self-energy shows that, not too close to the Fermi energy, this feature corresponds to a band, i.e. to a solution of the Dyson equation ω-ε(k)-ReΣ(k,ω) = 0.     

First observation of the production and decay of the Σc+

An event with the decay chain Σ_c⁺ → Λ_c⁺ + π⁰, Λ_c⁺ → K^? + p + π⁺, has been observed in an exposure of BEBC, equipped with a track sensitive target, to the wide band neutrino beam from the SPS at CERN. The event has a unique three constraint kinematic fit to the ΔS = ?ΔQ reaction v + p → μ^? + p + K^? + π⁺ + π⁺ + π⁰ with both gammas from the π⁰ decay detected. The proton and other final state particles are identified. The masses are M(Λ_c⁺) = 2290 ± 3 MeV/c², M(Σ_c⁺) = 2457 ± 4 MeV/c² and M(Σ_c⁺) ? M(Λ_c⁺) = 168 ± 3 MeV/c². Including other data one obtains M (Σ_c⁺⁺) ? M(Σ_c⁺) = 0 ± 4 MeV/c².     

Spectroscopic studies on Pb3O4-ZnO-P2O5 glasses doped with transition metal ions

Optical absorption, Electron Paramagnetic Resonance (EPR) studies are carried out on lead zinc phosphate glass systems doped with Cr³⁺ and VO²⁺. From optical absorption investigations the crystal-field parameters Dq, B and C are evaluated. EPR measurements on Cr³⁺ systems indicate that Cr³⁺ ions are located at sites with low symmetry. EPR spectra of vanadyl doped system revealed the characteristic nature of vanadyl ion. Spin-Hamiltonian and hyperfine values are evaluated for both the systems. Optical absorption spectra of vanadyl doped system revealed three bands that are characteristic of VO(II) ion in tetragonally distorted octahedral site. By correlating both EPR and optical data, the dipolar coupling constant (P) and Fermi-constant coupling parameter (κ) and molecular orbital coefficients β^?2, e_π^?2 are evaluated. Electron Paramagnetic Resonance and optical absorption studies showed that the chemical bonds of Cr³⁺ ions and VO²⁺ ions with the ligands have more covalent nature. From these studies it is also observed that lead spinals are playing major key role in sustaining the covalent nature of bonding.     

CrHn(n=0,+1,+2)分子及离子的势能函数

用原子分子反应静力学原理推导出CrHⁿ(n=0，+1，+2)的电子状态及其离解极限. 对H原子采用6-311++G^**基组，对Cr原子采用SVP(split valence polarization)全电子基组，用B3PW91方法计算了它们的平衡几何、电子状态，在此基础上分别计算CrH，CrH⁺的Murrell-Sorbie解析势能函数和CrH²⁺的解析势能函数及其对应的力常数、光谱参数，理论计算值与实验值和文献计算值符合较好. 从离解极限和通道解释了不同的势能函数形状. 计算表明：CrH⁺的势能曲线均具有对应于稳定平衡结构的极小点，说明CrH⁺可稳定存在. 而CrH²⁺离子的势能曲线对应于不稳定的排斥态，说明CrH²⁺是不稳定的. 关键词： n(n=0')" href="#">CrHⁿ(n=0 +2) 势能函数 光谱参数 稳定性     

Inclusive production of Σ±(1385) in pp interactions at 12 and 24 GeV/c

The inclusive production of Σ^±(1385) is studied in pp interactions at 12 and 24 GeV/c. In this energy range, the inclusive cross sections for Σ⁺(1385) and Σ^?(1385) rise from 0.20 ± 0.03 mb to 0.28 ± 0.03 mb and from 0.07 ± 0.02 mb to 0.12 ± 0.02 mb. The decays of Σ^±(1385) account for ～20% of all observed Λ hyperons. The p_T² distributions are compatible with an exponential decrease and the slopes are in agreement with a common value of B ～ 3 (GeV/c)^?2. The longitudinal spectra are significantly different: Σ^?(1385) is mainly produced in the central region, whereas proton fragmentation contributes strongly to Σ⁺(1385) production.     

Structural, electronic and optical calculations of CaxZn1−xO alloys: A first principles study

First principles density functional calculations, using full potential linearized augmented plane wave (FP-LAPW) method, have been performed in order to investigate the structural, electronic and optical properties of Ca_xZn_1−xO alloy in B1 (NaCl) phase. Dependence of structural parameters as well as the band gap values on the composition x have been analyzed in the range 0?x?1. Calculated electronic structure and the density of states of these alloys are discussed in terms of the contribution of Zn d, O p and Ca p and d states. Furthermore, optical properties such as complex dielectric constants ε(ω), refractive index including extinction coefficient k(ω), normal-incidence reflectivity R(ω), absorption coefficient α(ω) and optical conductivity σ(ω) are calculated and discussed in the incident photon energy range 0-45 eV.