Cu/ZnO(0001̄) and ZnOx/Cu(111): Model catalysts for methanol synthesis

In an attempt to understand the relative importance of the various constituents of copper-zinc oxide catalysts for methanol synthesis (2H₂ + CO → H₃COH), we have prepared and characterized a number of single-crystal surface structures of Cu-ZnO. The model catalysts have also been tested in terms of their activity for methanol synthesis. The growth of vapor-deposited Cu overlayers on a ZnO(0001&#x0304;) (O face) single crystal has been investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), He⁺ ion scattering spectroscopy (ISS) and low-energy electron diffraction (LEED). The results are consistent with a growth model in which, at room temperature, the first monolayer spreads uniformly across the surface in a p(1 × 1) structure. As more Cu is added, thick Cu(111) islands grow and these are separated by large regions of the p(1 × 1)-Cu monolayer. The Cu(111) islands are rotationally aligned with the ZnO substrate, and at high enough coverages grow together to cover the ZnO. Increasing temperature favors more agglomeration. A clean Cu(111) crystal and one containing a ZnO_x (x ⋍ 3) monolayer were also studied. None of these model catalysts gave rates of methanol production which were measurable in our present experimental limits (TOF < 2 × 10⁻³ molecules site⁻¹ s⁻¹) at 500–600 K and CO + H₂ pressures up to 1500 Torr. Under these “reaction” conditions, the Cu in direct contact with ZnO may be slightly oxidized; all the other Cu is completely metallic. The Cu does not change its character between deposition and reaction conditions, even if heavily oxidized to CuO in between. The addition of CO₂ at very high levels under reaction conditions does not change the character of a Cu(111) model catalyst surface, and no surface oxygen is ever observable after treatment under reaction conditions.     

Exchange interaction and spin dynamics in pentanuclear clusters, Cu3Ln2(ClCH2COO)12(H2O)8 (Ln = Nd3+, Sm3+, Pr3+)

New compounds, [Cu₃Ln₂(ClCH₂COO)₁₂(H₂O)₈]·2H₂O with Ln = Nd³⁺ (I), Sm³⁺ (II), Pr³⁺ (III), built up of pentanuclear clusters were synthesized and studied by means of X-ray analysis and electron paramagnetic resonance (EPR). X-ray data show that all compounds are isostructural and the pentanuclear clusteres may be considered as a linear system with alternating Cu(II) and Ln(III) ions: Cu(2)-L¹-Ln-L²-Cu(1)-L²-Ln-L²-Cu(2) with L¹ and L² being bridging fragments and Cu(1) and Cu(2) being structurally nonequivalent copper complexes. EPR studies demonstrate that in the temperature range of 100–293 K the signals due to only one type of the copper complexes are observed in the spectra of I–III. AtT<100 K the spectral temperature dependence is nontrivial. AtT<30 K new signals are detected in the spectra of I and II. The temperature dependence of the EPR spectra is interpreted under the assumption that the parameter of the exchange interaction Cu(2)-Ln considerably exceeds the parameter of the interaction Cu(1)-Ln. EPR spectra are calculated for the fragments of five paramagnetic centers in the frames of the model taking into account the nonequivalence of two copper complexes, short longitudinal and transverse paramagnetic relaxation times of the rare-earth ions at room temperature and the change of the relaxation rates when the temperature decreases. The results of the calculations show that it is possible to obtain information about the interactions in the system on the basis of the analysis of the temperature dependence of the EPR spectra of the central copper complex. The parameter of the isotropic part of the exchange interaction between copper and neodymium ions (for the interaction Cu(2)-Nd) is estimated as about 15 cm⁻¹. A considerable rearrangement of the spin states when the temperature changes is found for all complexes.     

ISS measurement of surface composition of AuCu alloys by simultaneous ion bombardments with Ar+ and He + ions

Surface composition of Au-Cu(43 at%) alloy under 1.5–5 keV argon ion bombardment has been investigated by ion scattering spectroscopy (ISS). In this experiment, we adopted a specific technique to use mixed He⁺ and Ar⁺ ions as primary beam in order to perform sputtering (Ar⁺) and ISS measurement (He⁺) simultaneously. The outermost atom layer of Au-Cu alloys under Ar⁺ ion bombardment is Au-rich leading to the conclusion that Ar⁺ ion bombardment of AuCu alloys causes the preferential sputtering of Cu atoms, resulting in a Au-rich outermost atom layer and a depletion layer of Au atoms beneath the outermost atom layer due to ion-beam-enhanced surface segregation. This result explains the experimental results obtained by AES as well.     

Interactions of relativistic heavy ions in thick heavy element targets and some unresolved problems

Interactions of relativistic heavy ions with total energies above 30 GeV in thick Cu and Pb targets (≥ 2 cm) have been studied with various techniques. Radiochemical irradiation experiments using thick Cu targets, both in a compact form or as diluted “2π-Cu targets” have been carried out with several relativistic heavy ions, such as 44 GeV ¹²C (JINR, Dubna, Russia) and 72 GeV ⁴⁰Ar (LBL, Berkeley, USA). Neutron measuring experiments using thick targets irradiated with various relativistic heavy ions up to 44 GeV ¹²C have been performed at the JINR. In addition, the number of “black prongs” in nuclear interactions (due to protons with energies less than 30 MeV and emitted from the target-like interaction partner at rest) produced with 72 GeV ²²Ne ions in nuclear emulsion plates has been measured in the first nuclear interaction of the primary ²²Ne ion and in the following second nuclear interaction of the secondary heavy (Z > 1) ion. Some essential results have been obtained. (1) Spallation products produced by relativistic secondary fragments in interactions ([44 GeV ¹²C or 72 GeV ⁴⁰Ar] + Cu) within thick copper yield fewer products close to the target and many more products far away from the target as compared to primary beam interactions. This applies also to secondary particles emitted into large angles (Θ > 10°). (2) The neutron production of 44 GeV ¹²C within thick Cu and Pb targets is beyond the estimated yield as based on experiments with 12 GeV ¹²C. These rather independent experimental results cannot be understood within well-accepted nuclear reaction models. They appear to present unresolved problems. The text was submitted by the authors in English.     

Level structure of the doubly odd nucleus 112In from the (p,nγ) reaction

Properties of the levels in ¹¹²In have been studied with the reaction ¹¹²Cd(p, nγ)¹¹²In. The level scheme of ¹¹²In below 1300 keV was constructed from the γ-ray excitation functions and γγ coincidences. In ¹¹²In, 22 excited states were observed and spins and parities of 8 excited states were newly assigned or restricted by comparing the measured angular distributions and linear polarizations of the deexciting γ-rays as well as the excitation functions of the residual levels with the predictions of the statistical compound nucleus model. Possible configurations of the low-lying levels are discussed in terms of their decay properties and the systematics of the excited states in the neighbouring doubly odd In isotopes.     

Excitation of discrete levels of <Superscript>63</Superscript>Cu and <Superscript>65</Superscript>Cu nuclei in (<Emphasis Type="Italic">e,e′</Emphasis>) reactions

Inelastic electron scattering on ⁶³Cu and ⁶⁵Cu nuclei at excitation energies of up to 5 MeV was studied. Information about the reduced probability and multipolarity of transitions was obtained for 11 low-lying levels and groups of levels of the ⁶³Cu nucleus and for 17 such levels and groups of levels of the ⁶⁵Cu nucleus. It was shown that the experimental form factors for inelastic scattering accompanied by the excitation of discrete levels and group of levels of these nuclei with a nonzero spin can be described in terms of a single multipolarity, even though the law of angular-momentum conservation admits the existence of several more multipolarities yielding the same parity of an excited state.     

Some lifetimes and transition probabilities in Cu(I)

Radiative lifetimes of 7 levels in the Cu(I) 3d⁹ 4s4p configuration have been measured using a delayed coincidence technique; copper vapor was excited in an argon buffer gas and cross sections for collisional destruction of copper levels by argon were also obtained. Transition probabilities of the lines originating from these levels have been determined using the measured lifetimes and branching ratios.     

Absorption and fluorescence spectroscopy of 3-hydroxy-3-phenyl-1-o-carboxyphenyltriazene and its copper (II), nickel (II) and zinc (II) complexes: a novel fluorescence sensor

Absorption and fluorescence spectroscopic properties of 3-hydroxy-3-phenyl-1-o-carboxyphenyltriazene (HT) are studied. The mechanism of photo-induced electron transfer (PET) followed by energy transfer process of the ligand and the Cu (II), Ni (II) and Zn (II) metal complexes have been investigated. The excited state photo induced intramolecular hydrogen transfer from N-OH to triazene 1-nitrogen atom is explained. The effect of pH, solvent and concentration on the absorption and fluorescence of the ligand is studied and it has been found that the absorption and fluorescence of HT is highly pH, solvent and concentration dependent. Participation of the N-OH proton of HT in the solvent assisted O to N-proton transfer has also been proposed. The fluorescence band shift and changes in intensity is modulated by protonation and complexation with metal ions. This fluorophore can thus be used as a pH dependent and M⁽ⁿ⁺¹⁾⁺/Mⁿ⁺ redox on/off switchable molecular sensor.     

Studies of EPR and ENDOR spectra of14N and15N label bis(2-hydroxyacetophenyl ketoxime)-63Cu(II) and-65Cu(II) complexes in disordered system

The EPR spectra of isotopic label bis(2-hydroxyacetophenyl ketoxime)-Cu(II) [N?Cu-HAP] complexes, such as¹⁴N?⁶³Cu-HAP,¹⁵N?⁶³Cu-HAP and¹⁴N?⁶⁵Cu-HAP in frozen THF solution below 77 K, and their ENDOR spectra in frozen DMSO/EtOH (5∶1) solution below 20 K were studied. The exact values of the components ofg-tensor, of hyperfine tensors of copper isotopes, and of superhyperfine interaction tensors of copper with nuclei of nitrogen isotopes and¹H nuclei, and of the¹⁴N nuclear quadrupolar moment coupling tensor were obtained. The bond parameters α, β, δ, γ and the corresponding energy levels of N?Cu-HAP complexes were calculated by using EPR and ENDOR data. It was shown that the unpaired, electron is delocalized not only to the nearest N atom but also to the H atom, of ligands, which is more far from the Cu ion.     

Population densities and optical gain of VUV transitions of Cu II in Cu−He hollow cathode discharges

Population densities of excited Cu II-levels between 16 and 25 eV in Cu–He hollow cathode discharges were determined by emission spectroscopy. Population inversion was detected for several 6s-4p transitions. Investigation of the enhancement of Cu II vuv lines in He compared to Ne discharges showed that the excitation of the 6s levels by charge transfer is up to 100 times higher in He than in pure Ne discharges. Using the population densities and known transition probabilities, a single pass gain of 55% m^–1 at 780.8 nm and 1.2% m^–1 at 154.17 nm at a current density of 0.4 A cm^–2 was calculated.This paper is dedicated to Prof. Dr. H. Gobrecht on the occasion of his 75th birthday     

A Chemosensing Ensemble for the Detection of Cysteine Based on the Inner Filter Effect Using a Rhodamine B Spirolactam

A fluorescent chemosensing ensemble for the detection of cysteine is designed based on the fluorescence inner filter effect. The method employs the coordination of Cu²⁺ ion with salicylaldehyde rhodamine B hydrazone (I), a colorless and non-fluorescent rhodamine B spirolactam derivative to form I-Cu(II), a pink color but weakly fluorescent complex. When rhodamine B was introduced to the I-Cu(II) complex solution, the fluorescence signal of rhodamine B is dramatically decreased because of the fluorescence inner filter effect (IFE). Upon adding cysteine to the above solution, it can complex preferentially to Cu²⁺ compared to I, and the I-Cu(II) complex dissociates, which thus decreases the fluorescence IFE of the solution, and in turn leading to the fluorescence increase of the chemosensing system. Based on the above mechanism, a fluorescent chemosensing ensemble for cysteine is developed. The fluorescence increase is linearly with cysteine concentration up to 10.0 μ mol L⁻¹, with a detection limit of 1.4 × 10⁻⁷ mol L⁻¹ (3σ). The optimal conditions of the proposed method were studied and the selectivity of the proposed method was investigated in this paper.     

Gamma-ray spectroscopy of61Zn

The⁶¹Zn decay scheme and level properties have been investigated up to the 2,269.6 keV level by the⁵⁸Ni(α, n γ)⁶¹Zn reaction using enriched targets. Excitation functions,γ ray spectra andn-γ coincidence spectra have been measured as well as angular distributions and angular correlations in Litherland II geometry. Gamma ray energies, excited state spins andγ ray branching ratios have been determined.     

Mass measurement and spectroscopy of57Cu with the58Ni(14N,15C)-reaction

The mass of⁵⁷Cu has been measured with the⁵⁸Ni(¹⁴N,¹⁵C)-reaction at 150 MeV incident energy with theQ 3D-spectrometer. The reaction has been selected after a careful inspection of the DWBA-expression for the cross section with respect to the highest weighting factors for spins andl-transfer. Cross sections of several μb/sr have been obtained. TheQ-value has been measured to beQ ₀=?19.90 (4) MeV and the⁵⁷Cu mass excess is ?47 340 (40) keV. Four lines of excited states have been observed up to 5.7 MeV. These states have a structure of single particle character, since⁵⁷Cu consists of a doubly closed core with N=Z=28 and a proton outside, and states up to the 2d 5-shell are observed.     

Gamma-ray spectroscopy of62Cu

A spectroscopy study has been made of the⁶²Ni(p,nγ)⁶²Cu reaction, allowing levels in⁶²Cu to be investigated up toE _x=1.843 MeV. Ten new levels and eleven spins are given.     

Exchange interaction and Jahn—Teller correlations in novel tetranuclear supramolecular Cu(II) grid complexes: an ESR study

Novel tetranuclear Cu(II) complexes in which four Cu(II) ions are arranged in a square planar fashion by four bis(bipyridyl)pyrimidine ligands were investigated by X and Q band ESR in the temperature range 4.2-300 K. The ESR spectra of this grid-like structure were well simulated as rising from triplet species. Analysis of their intensities allowed the spectra to be assigned to the first excited triplet state, and revealed intramolecular antiferromagnetic coupling of the Cu(II) spins. The isotropic exchange interaction J was determined as ?47 K and reducing to about ?5 K on functionalizing the bridging pyrimidine ring at the 2-position by methyl or phenyl. For comparison an ESR investigation was also carried out on the mononuclear analogue Cu(II)—(terpyridine)₂ complexes with substituted terpyridine ligands at the 5′ and 5″ position. Depending on the substitutent, the spectra exhibit a static or dynamic Jahn—Teller effect at room temperature. The temperature dependence of their g-values is examined by a modified Silver—Getz model which includes cooperative Jahn—Teller interactions. There is evidence that both an anisotropic spin exchange contribution to D = 0.0159 cm^?1 and a coupled (static) Jahn—Teller effect are responsible for efficient coupling between the four Cu(II) ions in the grid complexes with non-substituted pyrimidine bridges.     

The (t, α) reaction on 121Sb and 123Sb

Angular distributions of α-particles from the (t, α) reaction on ¹²¹Sb and ¹²³Sb have been measured for incident tritons of 12 MeV. Levels up to excitation energies of 5.2 and 4.9 MeV in ¹²⁰Sn and ¹²²Sn, respectively, have been identified and analysed by the DWBA. Values of orbital angular momenta of the transferred protons have been assigned and spectroscopic factors deduced for all strongly excited levels. The extracted ground-state wave functions of the target nuclei have been compared with the calculated ones. A mixture of collective degrees of freedom is present in the low-lying states, weakly excited by the above very selective proton pick-up reaction. These states are populated by the pick-up of external protons (outer shells). At higher excitation energy (between 4 and 5 MeV) there are many strongly excited states populated by the proton pick-up from the Z = 50 proton core (inner shells); a predominantly 1p-1h character has been assigned to these states.     

Excitation of single proton states in (p, α) reactions

A high resolution experiment, using the BIG KARL spectrometer has been made to identify the levels of ¹⁴¹ Pr excited in the ¹⁴⁴ Nd(p,α) reaction at 25 MeV. It has been found that only levels with a dominant single proton component are populated with appreciable intensity.     

Energy levels of 94Ru observed with the 96Ru(p,t) reaction

The level structure of the neutron-magic nucleus ⁹⁴Ru, up to an excitation energy of 4 MeV, has been studied by means of the (p, t) reaction. Particular emphasis was placed on a search for excited 0⁺ levels, none of which have been reported previously. Among new levels observed in this study are 0⁺ levels at 2.995, 3.615 and 3.770 MeV, and the 3^? octupole vibration at 2.965 MeV.     

Low-lying levels, γ-ray transitions,and vibrational structure in 198Pt from (n,n'γ) reaction spectroscopy

Low-lying states in ¹⁹⁸Pt have been studied by (n, n'γ) reaction spectroscopy at incident neutron energies below 2.5 MeV. Using detailed γ-ray excitation functions and angular distribution measurements, we have established a level scheme which includes 16 excited levels and is believed to include all levels below an excitation energy of 1.5 MeV. The positive-parity structure is similar to that expected for an anharmonic vibrator; however, difficulties in asserting that the first 0⁺ excited level is a collective excitation are encountered. Only two negative-parity states are observed, and they are adequately described in the semi-decoupled model.     

Molecular orbital study of the interaction of carbon monoxide and carbon dioxide with copper (100)

A molecular orbital study is made of the structures and energy levels of CO and CO₂ on Cu(100). The importance of self-consistency is discussed. CO is found to occupy fourfold indentations, in agreement with the semiempirical results of Doyden and Ertl. The C-surface distance is 1.0 Å and the CO bond stretches less than 0.1 Å. Large models of the surface show convergence of the electronic structure with four CO molecules on a twelve Cu atom cluster model of the surface. At coverages up to c(2 × 2) half monolayer, calculated energy levels match Demuth and Eastman's phase I photoemission spectrum. Phase II, as observed by them, has no analog in the calculations. No evidence is found for CO deviating from perpendicular to the surface when tightly bound. CO₂ is found to adsorb more weakly to the surface. This molecule rests in a μ bridging position, bonded through mixing of Cu d with CO₂ π¹ orbitals. It bends, with an angle of 120°, which is significantly similar to 122° for the ¹B₂ excited state of free CO₂, which has an electron promoted to the π¹ orbital. On the basis of this molecular orbital study, extrapolations to Ni and Zn surfaces and OCS, CS₂, CSe₂ and CTe₂ are made.