Plasmon dispersion in Al atk≦k F using electron energy loss spectroscopy

We find a quasi quadratic dispersion of the plasmon up to _p = 28 eV atk=1.77 Å^–1 with no levelling off contrary to other measurements. We usedk-scans at constant energy loss andE-scans at constant wave vector, which yield different dispersions of the plasmon peak maximum because of the finite halfwidth. The levelling off in plasmon dispersion observed previously is due to multiple scattering events, which obscure the plasmon dispersion inE-scans.We confirmed the anisotropy of the dispersion coefficient by investigating polycrystalline samples of different orientation.     

Low temperature Mössbauer spectra and magnetic ordering of lithiated ferric molybdate: Li2Fe2(MoO4)3

Powder x-ray diffraction, variable temperature magnetic susceptibility, and zero field Mössbauer spectroscopy measurements were used to characterize the new phase Li₂Fe₂ (MoO₄)₃. This material is obtained topochemically simply by the mixing of solutions of lithium iodide in acetonitrile with solid Fe₂(MoO₄)₃ at ambient temperature. Li₂Fe₂(MoO₄)₃ possesses the high temperature orthorhombic ferric molybdate $$\begin{gathered} Fe_2 (MoO_4 )_3 + 2LiI\xrightarrow{{CH_3 CN}}Li_2 Fe_2 (MoO_4 )_3 + I_2 \hfill \\ (solid)(solution)(solid)(solution) \hfill \\ \end{gathered}$$ structure. Guinier photographs were completely indexed in space group Pnca. Magnetic hyperfine splitting of the zero field Mössbauer spectrum below 12.5 K indicates a three-dimensional magnetically ordered state which susceptibility results show to be weakly ferromagnetic owing to probable canting of antiferromagnetically coupled sublattices.     

Gaussian modification of neutrino energy loss on strongly screening nuclides ~（55）Co and ~（56）Ni by electron capture in stellar interior

Gaussian modifications of the neutrino energy loss (NEL) by electron capture on the strongly screening nuclides ⁵⁵Co and ⁵⁶Ni are investigated. The results show that in strong electron screening (SES), the NEL rates decrease without modifying the Gamow-Teller (G-T) resonance transition. For instance, the NEL rates of ⁵⁵Co and ⁵⁶Ni decrease more than two and three orders of magnitude for ρ₇=5.86, T₉≤5, Y_e=0.47, Δ=6.3, respectively. In contrast, due to Gaussian modification, the NEL rates increase about two orders of magnitude in SES. Due to SES, the maximum values of the C-factor (in %) on NEL of ⁵⁵Co, ⁵⁶Ni are of the order of 99.80%, 99.56% at ρ₇=5.86 Y_e=0.47 and 99.60%, 99.65% at ρ₇=106 Y_e=0.43, respectively.     

Effect of pseudohalides in pentadentate-iron(III) complexes studied by DFT and Mössbauer spectroscopy

Mononuclear iron complexes in which the iron(III) ion is coordinated by a pentadentate Schiff base ligand L⁵ with two phenolate, two imino and one amino group can exhibit a spin crossover. In this contribution experimental results are presented for complexes with cyanate and thiocyanate as co-ligands. Furthermore, theoretical results of quantum chemical calculations of energies and entropies for the low-spin and high-spin state are shown and compared with Mössbauer results. We also demonstrate how the ligand field of the monodentate co-ligand influences the spin crossover energies and entropies in [Fe^IIIL⁵NCY] complexes.     

Crystal-chemistry aspects and electric-field-gradient (EFG) dispersion in Ca-gallogermanate-type structures studied by Mössbauer spectroscopy

The crystal field disorder in some trigonal germanates of the type X_3-yLn_yFe_2+yGe_4-yO₁₄ (X = Ba, Sr; Ln = La, Nd; y = 0, 1) is studied by ⁵⁷Fe M?ssbauer effect. The dispersion of the electric field gradient (EFG) at the octahedral sites of these compounds is investigated. A correlation of the experimental and calculated EFG data with some crystal-chemistry aspects is presented. Received 3 February 1999     

The growth of ice clusters on the Si(100)(2 × 1)-H(D) surface: Electron energy loss spectroscopy and thermal desorption studies

The growth of ice clusters on the Si(100)(2 × 1)-H surface has been investigated mainly by the use of high-resolution electron energy loss spectroscopy and thermal desorption spectroscopy. At 90 K, H₂O molecules are adsorbed on the (2 × 1)-H surface to form ice clusters by the hydrogen-bonding interaction. Four H₂O peaks are observed at 165, 185, 215 and 270 K in the thermal desorption spectra for the ice-covered surface. The peaks at 165 and 185 K correspond to the ice clusters and the peaks at 215 and 270 K to the strongly-bound H₂O species which play a role as the nucleation centers of the ice clusters desorbing as H₂O at 185 and 165 K, respectively.     

Production ofH(2s) andH(2p) by electron detachment fromH − in collisions with nitrogen and oxygen

¹⁹⁹Hg Fourier Transform NMR studies of various solutions of diverse mercury salts in H₂O and D₂O or in the appropriate protonated and deuterated acids are reported for both Hg ₂ ⁺⁺ and Hg⁺⁺. In the different solutions investigated the¹⁹⁹Hg line positions depend on the concentration of the solution, on the solvents and their isotopic composition and on the temperature of the sample. A ratio of the Larmor frequency of¹⁹⁹Hg and of²H in a Hg(NO₃)₂ solution in dilute DNO₃ is given. Using this ratio and the measured chemical shifts, a ratio of the Larmor frequencies of¹⁹⁹Hg for infinite dilution relative to²H in pure D₂O is given. From this a g_I-factor for¹⁹⁹Hg is derived and compared with the g_I-factor of an optical pumping experiment. The resulting shielding constant is σ^* (hydrated¹⁹⁹Hg⁺⁺ versus¹⁹⁹Hg atom)=?24.32(5) · 10^?4. This yields an atomic reference scale for all measured NMR line shifts of mercury.     

Time-resolved spectroscopy and energy transfer in Pr3+-doped Gd2(SO4)3·8H2O

The luminescence of Pr³⁺ in gadolinium sulfate hydrate is reported for 195 nm laser excitation. the Pr³⁺ ion acts as a sensitizer of the host lattice emission. The Pr³⁺Gd³⁺ energy transfer occurs in two different ways. In the octahydrate the transfer occurs from the lowest component of the 4f5d configuration of Pr³⁺, but in the samples with less water there is energy transfer from the¹ S _o level of Pr³⁺ to several Gd³⁺ levels. The Pr³⁺ emission in the two modifications is, of course, also strikingly different.Deceased 24 December 1994     

Electronic structure of bis(benzo)pentathienoacene in gas and solid phase: ultraviolet photoemission spectroscopy and energy band calculation

Ultraviolet photoemission spectroscopic measurements of bis (benzo)pentathienoacene were carried out in gas and solid phase. For the measurements of solid phase, vacuum deposited films in both amorphous and crystalline phase were prepared on different substrates of HOPG and polycrystalline Au, respectively. The adiabatic ionization energies were determined to be 6.8₄, 5.3₂, and 5.0₈ eV, for gas, amorphous, and crystalline phases, respectively. The spectral lineshapes were interpreted with the aid of the density functional calculations for both isolated molecule and single-crystal structure. The calculated electronic structures were further analyzed in terms of the energy band dispersion and the transport properties of charge carriers.     

A study of the reaction (π+, π+ p) in 12C and 6Li

We have measured the angular and momentum distributions of the scattered pions from the reaction ¹²C(π⁺, π⁺p)¹¹B and ⁶Li(π⁺, π⁺ p)⁵He in a coincidence experiment. We compare our results with the plane and distorted wave impulse approximations.     

InAs quantum dots on different Ga(In)As surrounding material investigated by photoreflectance and photoluminescence spectroscopy: electronic energy levels and carrier’s dynamic

In this article, comprehensive combination of photomodulated optical spectroscopy (PR) and temperature-dependent photoluminescence (PL) is carried out to investigate the electronic energy levels and carrier dynamics in nanometers’ size InAs quantum dots (QDs) in different surrounding material. Depending on the temperature range, the integrated PL intensity as a function of temperature, correlated to a rate equation model reveals two thermal escape channels for the InAs QDs in a pure GaAs matrix and three thermal escape channels for InAs/InGaAs dots-in-a-well structure. The extraction of the electronic energy levels by room temperature PR allow analyzing the impact of the surrounding material composition on the thermal activation energies and resulting PL quenching process.     

Renormalization of the electron spectrum by confined and interface phonons in a spherical nanoheterosystem (β-HgS/CdS)

The mechanisms of the electron spectrum renormalization by confined (L) and interface (I) phonons in a spherical quantum dot (QD) embedded in a semiconducting sphere are studied for the specific case of the β-HgS/CdS nanosystem. It is shown that, in view of the absence of interaction between an electron in spherically symmetric states and interface phonons forming only one bound state in a small-size QD, the shift Δ of this single level is formed only by confined phonons. As the size of the QD increases, the contribution of L and I phonons to Δ changes accordingly (L phonons slightly dominate), and the shift varies from Δ _CdS ^3D to Δ _HgS ^3D .     

Spectrophotometric determination of copper(II) in pharmaceutical,biological and water samples by 4-(2′-benzothiazolylazo)-salicylic acid

A highly sensitive method is proposed to determine copper(II) ions by forming a stable complex through their interaction with 4-(2′-benzothiazolylazo)-salicylic acid (BTAS) at room temperature and pH of about 5.0. The complex gave a maximum absorption at λ = 485 nm with a molar absorptivity coefficient of 2.35·10⁴ l/(mol·cm). The linear range for the copper determination is 0.63–5.04 mg/l. The method can be applied to determine copper ions in different biological specimens like some drugs and water samples.     

Surface structure of In2O3(111) (1 × 1) determined by density functional theory calculations and low energy electron diffraction

The surface structure of In₂O₃(111) has been investigated by dynamical analysis of low energy electron diffraction data, in conjunction with first principles calculations using density functional theory. The experimental data set consisted of eight independent beams whose intensities were measured for incident energies in the range between 25 eV and 250 eV. In fitting the experimental data it was essential to treat the radii of In and O spheres as variable parameters: following this procedure a final Pendry R factor of 0.31 was obtained. The LEED results are compatible with the calculations and both analyses suggest that the surface structure involves only small vertical relaxations in the outermost of the {[O^2?]₁₂^24?[In³⁺]₁₆⁴⁸⁺[O^2?]₁₂^24?} quadrupolar units that define the (111) surface. The ab initio slab calculations also confirm that lateral relaxations not considered in fitting the experimental data are of very minor importance.     

New determination of the astrophysical 13C( p, γ) 14N S(E) factors and reaction rates via the 13C(7Li, 6He) 14N reaction

The ¹³C(⁷Li, ⁶He) ¹⁴ N_0,1 reactions were measured at E (⁷Li) = 34 MeV with the Q3D magnetic spectrometer of the HI-13 tandem accelerator, and the first peaks of the angular distributions were obtained for the first time. The ¹⁴N_0,1 proton spectroscopic factors were extracted to be 0.67±0.09 and 0.73±0.10 , respectively. Using the ¹³C(p, ??) ¹⁴N direct capture S _dc(E) factors derived by the spectroscopic factors, the direct measurement data for both 1^? and 0^? resonances were well fitted via updating the resonance parameters, and then the total astrophysical ¹³C(p, ??) ¹⁴N S(E) factors and reaction rates were determined at stellar energies. The present work offers an independent examination to the existing results of the ¹³ C(p, ??) ¹⁴N reaction.     

Study on the spin crossover transition and glass transition for Fe(II) complex film, [Fe(II)(H-triazole) 3 ]@Nafion, by means of M?ssbauer spectroscopy

[Fe(II)(H-trz)₃]@Nafion (trz = triazole) is a transparent spin crossover complex film, where the spin crossover transition between the low-spin (S = 0) and the high-spin (S = 2) states takes place between 225?K and 300?K. In this film, two doublets corresponding to the low-spin and high-spin states were observed in the ⁵⁷Fe M?ssbauer spectra, reflecting the spin crossover transition. From the analysis of ⁵⁷Fe M?ssbauer spectra, the Debye temperatures of the low-spin and high-spin sites were estimated at 185?K and 176?K, respectively, in the temperature range between 10?K and 150?K. In this film, the total intensity of the M?ssbauer spectra corresponding to the low-spin and high-spin sites drastically decreases above 200?K, reflecting the glass transition of Nafion, where the lattice vibration of [Fe(H-trz)₃] $_{\rm n}^{\,\,\rm 2n+}$ is softened just as in solution due to micro-Brown motion of the segment of Nafion polymer membrane.