Mass measurements far from stability around theN=Z line (100Sn,100In,100Cd)

Secondary ions of¹⁰⁰Ag,¹⁰⁰Cd,¹⁰⁰In and¹⁰⁰Sn were produced via the fusion-evaporation reaction⁵⁰Cr+⁵⁸Ni at an energy of 5.1 MeV/nucleon. TheA=100 secondary ions were accelerated in the second cyclotron of GANIL, which was used as a high-resolution mass spectrometer. The masses of the three latter isobars were measured with respect to the abundantly produced¹⁰⁰Ag. The known mass of¹⁰⁰Cd was very well reproduced and the masses of¹⁰⁰In and¹⁰⁰Sn were determined for the first time with precisions of 3×10^?6 and 10^?5, respectively.     

Excited states of100Tc from100Mo(p,nγ)100Tc reaction and the parabolic rule

γ-spectra and excitation functions of the¹⁰⁰Mo(p, nγ)¹⁰⁰Tc reaction were measured in the 1.2–3.6 MeV proton energy range by using thick, enriched targets, Ge(Li) and low energy photon (hyperpure Ge) spectrometers. These detectors were used inγγ-coincidence experiments, too. Conversion electron spectrum measurements were performed by means of a superconducting magnet transporter Si(Li) spectrometer (SMS) atE _p =4 MeV and multipolarities of some transitions have been determined. Based on the experimental results a level scheme of¹⁰⁰Tc has been constructed. Level energies of¹⁰⁰Tc were calculated on the basis of the parabolic rule, derived from the cluster-vibration model.     

Uptake,transport, and release of hydrogen from Pd(100)

Understanding the interactions of hydrogen atoms with the surface and the subsurface regions of Pd is critical to the development of advanced energy technologies for hydrogen storage, hydrogen separations, and catalytic conversion processes. While many of the physical and chemical characteristics of the H₂–Pd system are known, the kinetics and thermodynamics of H atom absorption into the bulk, transport from the bulk back to the surface, and desorption from the surface remain unclear. In this work, the kinetics of D₂ release from Pd following exposure to D₂ over a range of pressures and temperatures were measured using temperature programmed desorption. To accurately simulate the kinetics of D₂ release, the continuum-based model of Mavrikakis, et al. (J. Chem. Phys 105, 8398, 1996) was extended to include activation barriers for desorption and transport that depend on D atom concentration in the surface, subsurface and bulk regions of the Pd. The use of concentration dependent barriers improves the ability of the model to predict the hydrogen uptake and release kinetics observed across temperatures ranging from 100 to 600 K.     

Adsorption studies of trichloroethylene (TCE) on MgO(100)/Mo(100)

Employing ultraviolet photoelectron spectroscopy (UPS, He I), the more surface sensitive metastable impact electron spectroscopy (MIES) and temperature programmed desorption (TPD) measurements of the adsorption properties of the pollutant trichloroethylene (TCE) on thin MgO(100) films, grown on a Mo(100) single crystal, have been investigated. From TPD spectra of different coverages it is concluded that TCE interacts only weakly with MgO, which is attributed to physisorption. For increasing coverages a change from one peak to two peaks in the TPD spectra, one at higher, the second at lower temperatures with respect to the single peak is detected. Additionally, the observation of a local minimum for the work function (WF) for both MIES and UPS spectra is presented. Such a local minimum has been reported previously for the adsorption of metals with outer s valence electrons on transition metal substrates and adsorption of metals with outer s valence electrons on metal oxide films. Herein, we present the first WF minimum observed for a system of organic molecules adsorbed on an insulating surface. Two different models are discussed in order to understand the presented results.     

Li(p,pd)He reaction at 100 MeV

An angular correlation experiment of the ⁶Li(p, pd)⁴He reaction at 100 MeV has been performed using a symmetric and coplanar geometry and covering an angular range from 45.5 to 57°. In addition to the conventional ΔE-E telescope systems for the detection of both protons and deuterons, a 14° analyzing magnet was employed to select deuterons of a given momentum range. The results for the ground state transition are consistent with those obtained at other incident energies. The angular distribution for the transition to the 20 MeV excited state of the recoiling α-particle was also obtained and the overall magnitude of the differential cross section is at least an order of magnitude smaller than that of the ground state transition. The plane wave impulse approximation (PWIA) was used to analyze the experimental results. A form factor was generated using the Saxon-Woods potential as the d-α inter-cluster potential. Satisfactory agreement between theory and experiment was obtained. A value of 0.45 ±0.08 was extracted for the deuteron clustering probability on ⁶Li. The exchange and the optical distortion effects were also discussed.     

The superstructures of the clean Pt(100) and Ir(100) surfaces

The clean and reconstructed surfaces of Pt(100) and Ir(100) were investigated by low energy electron diffraction (LEED). It is shown that two superstructures can be observed in the case of platinum. The structure Pt(100)-hex, which is commonly called Pt(100)-(5 × 20), transforms to Pt(100)-hex-R0.7° above 1100 K. It is shown that this stable phase differs from the first one by a slight rotation of the hexagonal surface layer by 0.7°. For Ir(100) only the well known (1 × 5) superstructure is observed without any rotation of the outer layer. The rotation angle of 0.7° for platinum and the stability of the unrelated structure for iridium can be interpreted by simple calculations of the coordination of surface atoms with those of the second layer. The method assumes that the surface layer is of ideal hexagonal structure in the case of platinum and nearly hexagonal in the case of iridium. The results are in good agreement with the experiment.     

Low energy electron spectroscopy of Pt (100) and Pt (100)/CO

Fine structure in the n_vi, _VIIVV spectrum of clean Pt (100) has been observed, and interpreted as “band like” in origin rather than quasi-atomic. Differences in the dependence of the Auger yield on primary beam energy are observed between the N_VI, _VIIVV and O_IIIVV peaks, and are associated with anomalies in the dependence of the inner shell ionization crossection of the 4f level. Low energy electron loss spectra on the clean surface have been investigated at primary energies in the range 71–774 eV and at angles of incidence of the beam 0–60°. The results are related to high energy loss and optical data, and assignments are given for inter-band and plasmon losses. With approximately $\text{3}\text{4}$ of a monolayer of CO on the surface there is a prominent additional loss at around 13.5 eV, which is interpreted as a one electron transition from a σ state below the d band to available states several electron volts above the Fermi level.     

XPS and XAES study for oxidation of V/Cu(100) and V,Na/Cu(100) surfaces

Oxidation states of vanadium overlayers ( 0.1 to 2.0 ML) on a Cu(100) surface with and without sodium on the surface were investigated by XPS and XAES. The vanadium overlayers gave a V₂O₃-like surface oxide after exposure up to 600 L O₂, showing a chemical shift of the V2p_3/2 peak by 3.5 eV without coverage dependence. The surface vanadium oxide was easily oxidized further to V⁵⁺ to give a chemical shift of 5.5 eV after addition of sodium atoms on the oxide and heating at 530 K for 5 min. The high oxidation state was interpreted by a mixing of vanadium oxide and oxidized sodium. This mixing is affirmed by spectral changes showing a separation of sodium ions from the oxide during the formation of sodium acetate by adsorption of acetic acid.