Optical properties and electronic structure of copper atoms adsorbed on a platinum electrode

The optical properties of Cu atoms deposited in the underpotential region from electrolytic solution onto a polycrystalline Pt electrode have been studied by differential reflectance spectroscopy. Spectra of the normalized reflectance change ($\text{ΔR}\text{R}$) have been obtained in the photon energy range between 1.5 and 5.5 eV for p- and s-polarized light as a function of coverage θ and angle of incidence ?₁. Evaluation of the adsorbate optical constants by a simple 3-phasemodel reveals three absorption bands in the range studied, one of them being strongly angular dependent. From an assignment of these transitions the positions of the 3d-, 4s- and 4p-derived levels in the energy level diagram of the Cu adatom is determined. As expected these levels are considerably shifted and broadened in comparison to their unperturbed atomic counterparts. Optical evidence for the occurrence of a structural change in the adsorbate layer at about θ = 0.6 is also presented.     

Absence of magnetic field influences on the rate of Ni(CO)4 formation on Ni(100) under various surface conditions

Using UHV techniques and a flow system with continuous monitoring of the reaction rate, we have investigated the rate of Ni(CO)₄ formation, R, on Ni(100) in an external magnetic field up to 1000 G, under various surface conditions. No magnetic field effect ($\text{ΔR}\text{R}\text{< 0.01}$) has been found under any conditions (clean surface with or without roughness ;precoverage with C, S, Hg; temperatures up to 200°C; different B orientation; darkness or illumination).     

Copper monolayer formation on platinum single crystal surfaces: Optical and electrochemical studies

The formation of a Cu monolayer on Pt(100), (110) and (111) was investigated by optical and electrochemical techniques. The adsorption isotherms as obtained by cyclic current-potential curves clearly show that the monolayer is deposited in various steps at underpotentials. Differential reflectance spectroscopy at normal incidence was used to detect structural changes of the adsorbate as the coverage increases. For Cu on Pt(110) a pronounced anisotropy in $\text{ΔR}\text{R}$was observed as the electric field vector of the linearly polarized light was rotated. From these measurements it was deduced that Cu in the submonolayer range is deposited onto Pt(110) in rows along the [11&#x0304;0] direction of the substrate. No such anisotropy was found for Cu on Pt(100) and Pt(111) and for surface oxide formation on all three low index faces of Pt. The spectral dependence of the normalized reflectance change,$\text{ΔR}\text{R}$, for the Cu monolayer on Pt(hkl) is shown and discussed.     

Franck-condon factors for diatomic molecules and the factorization method

By means of the factorization method, recurrence relations for the matrix elementS$\text{<ψ}{}_{\mathrm{<mtext>v\text{'}</mtext>}}\text{¦r}{}^{\mathrm{N}}\text{¦ψ}{}_{\mathrm{<mtext>v</mtext>}}\text{<}$ for an arbitrary positive integer N are obtained in the framework of α-averaging for the Morse potential. The method of calculating the matrix element$\text{<ψ}{}_{\mathrm{<mtext>v\text{'}</mtext>}}\text{¦R}{}_{\mathrm{<mtext>e</mtext>}}\text{¦ψ}{}_{\mathrm{<mtext>v</mtext>}}\text{<}$ is outlined, provided a dependence of the electronic transition moment R_e on the internuclear distance r can be approximated by the polynomial R_e(r)=a₀+a₁r+a₂r²+…+ainNr^N. Recurrence relations are also obtained for the case of the exponential dependence R_e(r).     

Thermal changes in the optical properties of SnSxSe2−x crystals

Optical measurements on crystals in the series SnS_xSe_2?x for 0 ? x ? 2, have yielded information on the changes in the ordinary refractive index $\text{Δn}\text{ΔT}$ and the energy gap $\text{ΔEg}\text{ΔT}$ in the temperature range 125–425 K. The coefficient $\text{Δn}\text{ΔT}$ has values +40 to +160 × 10^?6K^?1 and this confirms that covalent bonding predominantly exists in these materials. The coefficient $\text{ΔEg}\text{ΔT}$ remains fairly consistent for all values of x with an average value of -8.0×10^-4eV K^-1.     

The change of conductivity of erbium films caused by the sorption of hydrogen and oxygen

Films of erbium were evaporated onto the inside wall of a pyrex glass reaction vessel at 1O^?9 torr. Their mean thickness (200–600 Å) was deduced from their mass and geometrical area. Estimates of their surface areas were made from the physical adsorption of krypton at 78 °K (BET method) giving a mean specific surface area of 71 m^?2 g^?1. The number of surface sites was calculated from a relationship given by Brennan et al.¹⁾. The sorption of hydrogen and oxygen was studied separately, by measuring the changes in the electrical resistance of the films as a function of the amount of pure gas admitted to the reaction vessel in measured doses ～ 10¹⁸ atoms per dose. The experiments were repeated at 295 °K, 200 °K, 130–140 °K for both gases (measurements at 78 °K were not reproducible, probably because of a magnetic phase change). Hydrogen at 295 °K [as reported²⁾] caused an initial increase ΔR in the original resistance R to a maximum $\text{ΔR}\text{R}$ ～ 20 %, which was followed by a decrease to $\text{ΔR}\text{R}\text{= 0}$ and then to $\text{ΔR}\text{R}\text{< 0.}$ A similar pattern of resistance changes was observed at 200°K and 130–140°K with smaller changes of $\text{ΔR}\text{R}$, i.e. 16 % and 8 % respectively, but no significant differance in surface (θ) and bulk atomic ratios at which the maxima occurred, e.g. $\text{ΔR}\text{R}$ was a maximum for 1.6?θ?1.9.     

Site-selective adsorption of xenon on a stepped Ru(0001) surface

The adsorption of xenon has been studied with UV photoemission (UPS), flash desorption (TDS) and work function measurements on differently conditioned Ru(0001) surfaces at 100 K and at pressures up to 3 × 10^?5 Torr. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) served to ascertain the surface perfectness. On a perfect Ru(0001) surface only one Xe adsorption state is observed, which is characterized by$\text{Xe}\text{5}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$,$\text{1}\text{2}$ electron binding energies of 5.40 and 6.65 eV, an adsorption energy of E_ad≈ 5 kcal/mole and dipole moment of μ'_T ≈ 0.25 D. On a stepped-kinked Ru(0001) surface, the terrace-width, the step-height and step-orientation of which are well characterized with LEED, however, two coexisting xenon adsorption states are distinguishable by an unprecedented separation in$\text{Xe}\text{5}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$,$\text{1}\text{2}$ electron binding energies of 800 meV, by their different UPS intensities and line shapes, by their difference in adsorption energy ofΔE_ad ≈ 3 kcal/mole and finally by their strongly deviating dipole moments of μ_S = 1.0 D and μ_T = 0.34 D. The two xenon states (which are also observed on a slightly sputtered surface) are identified as corresponding to xenon atoms being adsorbed at step and terrace sites, respectively. Their relative concentrations as deduced from the UPS intensities quantitatively correlate with the abundance of step and terrace sites of the ideal TLK surface structure model as derived from LEED. Furthermore, ledge-sites and kink-sites are distinguishable via E_ad. The E_ad heterogeneity on the stepped-kinked Ru(0001) surface is interpreted in terms of different coordination and/or different charge-transfer-bonding at the various surface sites. The enormous increase in Xe 5p electron binding energy of 0.8 eV for Xe atoms at step sites is interpreted as a pure surface dipole potential shift. —The observed effects suggest selective xenon adsorption as a tool for local surface structure determination.     

Operator formulation of Regge asymptotic behavior

If the appropriate high-energy limits of the amplitudes $\text{W ≡ ?}\text{d}\text{x}\text{e}{}^{\mathrm{<mtext>i</mtext><mtext>q\; ·\; x</mtext>}}\text{<b|j(x)j′(0)|b′ >}$ are Regge pole dominated, then the large distance (x₀ → ∞, x²fixed) behavior of the current product is completely characterized by an operator expression $\text{R}\text{(x : 0)}$, involving only local operators at 0, which is such that $\text{R ≡ ?}\text{d}\text{x}\text{e}{}^{\mathrm{<mtext>i</mtext><mtext>q\; ·\; x</mtext>}}\text{<b|}\text{R}\text{|b′ >}$ and W have the same high-energy behavior. In the only case (|b> a single particle stateand |b′> the vacuum) where W is not Regge behaved, it is shown that R is identical to W, and so the relation $\text{jj′ →}\text{R}$ is established as a large distance operator expansion, valid between all states. $\text{R}$ is expressed as a differential operation B(□_x, ?_x · ?₀, □₀) on the light-cone expansion and some of its properties are deduced by carrying out the differentiations. A second form of $\text{R}$ is given in terms of non-local “reggeon” field operators R_αm(0) (α is a (fixed) spin index and m is a (variable) helicity index) which might be useful coordinate in reggeon field theories. These operators can be used to define reggeon-particle amplitudes and if conventional double-Regge and triple-Regge behaviors are further assumed, the large distance behaviors of the current-reggeon and reggeon-reggeon field products are specified in terms of other reggeon fields.     

High-resolution photoemission study of adatom bonding effects: Cl (√2 × √2) R 45° on Cu (100)

We have investigated photoemission from an ordered $\text{(}\text{2}\text{×}\text{2}\text{) R 45°}$ Cl-overlayer on Cu (100) at good angular (Δθ ? 1°) and energy (ΔE = 100 meV) resolution. We observe two prominent adsorbate- induced features at 1.95 eV (FWHM ≈ 100 meV) and 5.4 eV (0.65 eV) below E_F. By determination of their angular momentum character, their spatial orientation and their energy dispersion, they are identified as “antibonding” and “bonding” resonances, respectively. Significant modification of the Cu d-band emission is observed and interpreted in terms of substrate orbitals which are involved in bonding.     

Electronic transition-moment variation in the B 2ϵ+−X 2Пr system of the AsO molecule

The spectrum of AsO was excited in a quartz discharge tube and the relative band intensities were measured by using photographic photometry. It was found that the electronic transition moment varies as R_e(r) = constant x (1–0.575r) in the range $\text{1.46}\text{A}\text{?}\text{< r < 1.66}\text{A}\text{?}$. Smoothed relative band strengths are derived for the 11 bands.     

The resistance jump in the pure type-I superconductors tin,indium and lead

It is shown that for tin, indium and lead samples of sufficiently high purity, sufficiently large diameter (2–3mm), and sufficiently close to the critical temperature (ΔT<0.15K), there exists a common value close to $\text{2}\text{3}$(0.64?R(i_c)/R_n ? 0.69) of the resistance jump at the transition from the superconducting to the intermediate state.     

Majorana masses,photon gas heating and cosmological constraints on neutrinos

Non-vanishing Majorana masses generally lead to flavor-changing neutral currents in the neutrino sector. It is shown that when both right- and left-handed neutrinos have non-vanishing Majorana masses (M_R≠0 and M_L≠0), flavor-changing neutral currents could be as large as flavor-diagonal ones. However, when only right-handed neutrinos have non-vanishing Majorana masses (M_R≠0 but M_L=0), flavor-changing neutral currents are small. If M_R?D (Dirac masses), they are of $\text{O}\text{((}\text{D}\text{M}{}_{\mathrm{<mtext>R</mtext>}}\text{)}{}^2\text{)}$. If M_R?D, they are $\text{?(}\text{m}{}_{\mathrm{<mtext>L</mtext>}}\text{m}{}_{\mathrm{<mtext>H</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, where m_L and m_H are masses of light and heavy neutrinos appearing in a flavor-changing process.By using these results we examine cosmological implications of non-vanishing flavor-changing neutral currents. Heavy neutrinos can decay into three light neutrinos at an appreciable rate by exchanging a Z-boson. It is demonstrated that owing to this decay mode, heavy neutrinos of mass larger than 70 keV but less than 2m_e give rise to no contradiction with the standard big bang cosmology in the most general case.We also show that if there exist heavy neutrinos of mass m_H2m_e, their decay at an early era of the universe induces photon gas heating, which alters Cowsik and McClelland's constraint on light neutrino masses to Σm_L < k · 100 eV with the sum running over all Majorana eigenstates. Here the constant k, representing the heating effect of the photon gas, is restricted by the deuterium abundance of the present universe. For instance, Σm_L < 240 eV for m_H ～ 25 MeV and the present baryon density = 3.4 × 10^?31 g · cm^?3.     

New evaluation of muon (g − 2) hadronic anomaly

The hadronic part a_H of the muon g-factor anomaly $\text{a ≡}\text{(g ? 2)}\text{2}$ is evaluated from latest data on σ(e⁺e^? → hadrons). For a p-wave ππ scattering length of a₁ = 0.04±0.005 we calculate a_H = (66±10) × 10^?9, compared to a(experiment) ? a(QED) = (60±29) × 10^?9. Half of the uncertainty on a_H is associated with the energy interval $\text{0.92 <}\text{s}\text{< 2}\text{GeV}$.     

Theoretical studies of chemisorbed oxygen on Ag(110)

The interaction of an oxygen atom with a 26-atom cluster model of the (110) face of Ag has been investigated with ab initio self-consistent-field and configuration-interaction theory. The SCF results for the bridge site (C_2v) predict $\text{r = 0.3}\text{A}\text{?}$ and ω_e = 327 cm^?1, in good agreement with the available experimental evidence. The calculated binding energy (D_e = 9 kcal/mole) is roughly an order of magnitude too small. The inclusion of electron correlation increases r_e and ω_e only slightly, but should have a dramatic effect on D_e. The ground state corresponds to a “surface oxide” state. The theoretical projected density-of-states curves exhibit “bonding” and “anti-bonding” O(2p) peaks, separated by ~ 6 eV, in good agreement with recent angle-resolved photoemission data.     

Search for heavy isosinglet neutrinos in e+e− annihilation at 130

《Physics letters. [Part B]》1999,461(4):397-404

The chemisorption of sulphur on W(100)

The interaction of sulphur vapour with a W(100) surface is studied in detail with Auger Electron Spectroscopy (AES), LEED, work function difference (Δ?) measurements and thermal desorption spectroscopy (TDS). The dissociative adsorption of S occurs on the W surface without reconstruction. Several LEED structures are observed which indicate repulsive adatom interactions. TDS shows that the desorption energy of atomic S decreases from about 8 eV at θ = 0.1 ML to about 3 eV near saturation in close vicinity of 1 ML. Above $\text{θ =}\text{3}\text{4}$ ML, S₂ desorbs in addition to S in a high temperature peak which saturates at about 1 ML. Sulphur in excess of about 1 ML is desorbed in two low temperature peaks of which the lower one consists not only of S and S₂ but also of S₃ and S₄.     

A study of the (00) LEED beam intensity at normal incidence from CdS(0001), Cu(001), Cu(111), and Ni(111)

A Faraday cage apparatus is used for the measurement of the (00) LEED beam intensity, I₍₀₀₎, and the total secondary emission coefficient, δ(E_k), for angles of incidence from 0° ± 2° to 8° ± 2°, with an energy resolution of ± 0.037 of the incident beam energy, in the energy range 1 to 200 eV. The data are normalized and expressed as a fraction of the incident beam intensity. The basic principle of operation is the separation of the incident and specularly diffracted beams in a uniform magnetic field. Monolayer, or in-plane, resonances associated with the emergence of nonspecular beams, as well as beam threshold minima, are observed in I₍₀₀₎ at normal incidence from clean CdS(0001), Cu(111), and Ni(111). Some major differences are observed in the I₍₀₀₎ profiles for the clean (111) surfaces of nickel and copper. All secondary Bragg peaks, except the 2$\text{2}\text{3}$ order, have greater intensities for Ni(111) in the energy range 50–150 eV, thus indicating that the atomic scattering cross-section for electrons in this energy range is larger for nickel than for copper. For the (111) surface of nickel, the (11) resonance is missing, but the (10) resonance and all $\text{1}\text{3}$ order secondary Bragg peaks between the second and fifth orders are observed. For Cu(111) both the (10) and (11) resonances are observed, but the $\text{1}\text{3}$, $\text{2}\text{3}$, 1$\text{2}\text{3}$, and 3$\text{1}\text{3}$ order secondary Bragg peaks are missing in this energy range. These data indicate that multiple scattering with evanescent intermediate waves, or “shadowing”, is predominate on the (111) surfaces on nickel and copper for energies above 30 eV, and that below 30 eV multiple scattering with propagating intermediate waves is predominate on Cu(111). Correlation of the (00) beam intensity profiles from clean Ni(111) at 0°, 2°, and 6° with the intensity profiles of the (10). (1&#x0304;0), and (11) non-specular beams is nearly one-to-one from 30 eV to 100 eV, thus supporting the dynamical theories of LEED in which peaks in the (00) beam are expected to occur at nearly the same energies as peaks in the non-specular beams.     

A spectrum of rhenium oxide

The arc emission spectrum of the ReO molecule has been photographed in the region 590–860 nm and three bands of a single electronic transition have been rotationally analyzed. The separation of lines of the isotopic molecules ¹⁸⁵ReO and ¹⁸⁷ReO leads to the conclusion that the vibrational assignments for these bands are 1-0, 0-0, and 0–1. It is conceivable that an electronic isotope shift of ～0.08 cm^?1 exists. The following vibrational and rotational data (cm^?1) have been determined: ν₀(0-0) = 14 038.42, $\text{Δ}\text{G′(}\text{1}\text{2}\text{) = 867.85}$, $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 979.14}$; B′_e = 0.3889, α′_e = 0.0019, B″_e = 0.4257, α″_e = 0.0043. It is concluded that Λ′ ? Λ″ = +1 with Λ″ ≥ 2.