Interaction of O2 with Pt(100): I. Equilibrium measurements

Two newly discovered phases on the Pt(100) surface produced by the adsorption of oxygen have been investigated using Rutherford baekscattering (RBS), nuclear microanalysis (NMA), work function changes (Δφ) and LEED. One phase is associated with the oxygensaturated surface (0.63 ± 0.03 monolayers0.81 × 10¹⁵ O atoms cm^?2), where a very complex LEED pattern is observed; the other is observed at an average coverage of 0.44 ± 0.05 monolayers and gives rise to a (3 × 1) LEED pattern (when observed at room temperature). For both surfaces, RBS measurements indicate large (? 0.025 nm) Pt atom displacements. Also discussed is a new method for preparing the “clean” (1 × 1)-Pt(100) surface without the need for NO adsorption/decomposition.     

Absolute coverages of CO and O on Pt(111); Comparison of saturation CO coverages on Pt(100), (110) and (111) surfaces

Nuclear microanalysis (NMA) has been used to determine the absolute coverages of oxygen and CO adsorbed on Pt(111). The saturation oxygen coverage at 300 K is 3.9 ± 0.4 × 10¹⁴ O atoms cm^?2 (θ = 0.26 ± 0.03), confirming the assignment of the LEED pattern as p(2 × 2). The saturation CO coverage at 300 K is 7.4 ± 0.3 × 10¹⁴ CO cm^?2 (θ = 0.49 ± 0.02). The low temperature saturation CO coverages on Pt(100), (110) and (111) surfaces are compared.     

Investigation of third-order optical nonlinearity in KBe2BO3F2 crystal by Z-scan

The third-order optical nonlinearity of deep-ultraviolet (DUV) nonlinear optical (NLO) crystal KBe₂BO₃F₂ (KBBF) was investigated using single-beam Z-scan technique for the first time. The Z-scans were performed on a c-cut KBBF crystal and a KBBF prism-coupling device (PCD) with picosecond pulses at 355?nm. No two-photon absorption was observed in the experiment. The measured nonlinear refraction index n ₂ showed positive signs, indicating self-focusing Kerr effects. The n ₂ values were estimated to be (1.75±0.35)×10^?15?cm²/W with the c-cut sample and (1.85±0.37)×10^?15?cm²/W with the PCD, corresponding to the third-order nonlinear optical susceptibilities $\chi_{\mathrm{eff}}^{(3)}$ of (0.99±0.20)×10^?13?esu and (0.94±0.19)×10^?13?esu, respectively. The results are expected to promote the investigation of frequency conversion processes with ultra-short laser in KBBF crystal.     

The chemisorption of Co on Rh(111)

The adsorption of CO on Rh(111) has been studied by thermal desorption mass spectrometry and low-energy electron diffraction (LEED). At temperatures below 180 K, CO adsorbs via a mobile precursor mechanism with sticking coefficient near unity. The activation energy for first-order CO desorption is 31.6 kcal/mole (ν_d = 10^13.6s^?1) in the limit of zero coverage.As CO coverage increases, a (√3 ×√3)R30^u overlayer is produced and then destroyed with subsequent formation of an overlayer yielding a (2 × 2) LEED pattern in the full coverage limit. These LEED observations allow the absolute assignment of the full CO coverage as 0.75 CO molecules per surface Rh atom. The limiting LEED behavior suggests that at full CO coverage two CO binding states are present together.     

The adsorption of Xe and CO on Ag(111)

The adsorption of Xe and CO on Ag(111) in the range 66 to 123 K and 10^?7 to 10^?1 Pa has been studied by surface potential, low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and electron energy loss spectroscopic (EELS) measurements. Isotherms derived from both surface potential and AES measurements for submonolayer Xe adsorption reveal successive stages and a two-dimensional phase change. Isosteric heats were 18 ± 1 kJ mol^?1. Temkin isotherms were observed for CO, the heat falling linearly with coverage from an initial value of 27 ± 1.5 kj mol^?1. No ordered CO overlayer structure could be detected. EEL spectra of clean Ag(111) agree with previous studies. Additional loss peaks were recorded for Xe and CO overlayers, and the assignment of the substrate loss features is discussed in relation to the effects of adsorption.     

Effects of adsorbates on electron spin polarization in low energy electron diffraction from tungsten (001): II. Ordered CO overlayer

Electron spin polarization and intensity profiles have been measured in low electron diffraction (LEED) for the (00) beam at θ = 13° and ø = 0° from a W(001) surface exposed to CO and annealed to obtain an ordered c(2 × 2) CO overlayer. The annealed surface with additional CO adsorbed was also studied. The polarization was found to be sensitive to the surface condition and the very distinct P?V profile corresponding to the c(2 × 2) overlayer is believed to be a very sensitive indicator of CO in the β₃ phase. The properties of the annealed surface exposed to further CO suggest the use of this surface as a low energy electron spin polarization analyzer.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Swift heavy ion provoked structural, optical and electrical properties in SnO2 thin films

SnO₂ thin films grown on glass substrates at 300 ^°C by reactive thermal evaporation and annealed at 600 ^°C were irradiated by 120 MeV Ag⁹⁺ ions. Though irradiation is known to induce lattice disorder and suppression of crystallinity, we observe grain growth at a certain fluence of irradiation. X-ray diffraction (XRD) revealed the crystalline nature of the films. The particle size estimated by Scherrer’s formula for the irradiated films was in the range 10–25 nm. The crystallite size increases with increase in fluence up to 1×10¹² ions?cm^?2, whereas after that the size starts decreasing. Atomic force microscope (AFM) results showed the surface modification of nanostructures for films irradiated with fluences of 1×10¹¹ ions?cm^?2 to 1×10¹³ ions?cm^?2. The UV–visible spectrum showed the band gap of the irradiated films in the range of 3.56 eV–3.95 eV. The resistivity decreases with fluence up to 5×10¹² ions?cm^?2 and starts increasing after that. Rutherford Backscattering (RBS) reveals the composition of the films and sputtering of ions due to irradiation at higher fluence.     

New measurement of (g−2) of the Muon

The g-factor anomaly, a≡(g?2)/2, has been measured for μ⁺ in the new Muon Storage Ring at CERN. The result is a = (1 165 895 ± 27) × 10^?9. This is (13 ± 29) × 10^?9 below the theoretical value which includes sixth-order QED terms and a hadronic contribution of (73 ± 10) × 10^?9.     

The Massachusetts Toxics Use Reduction Act: a model for nanomaterials regulation?

Polyvinylimidazole (PVIm)-grafted superparamagnetic iron oxide nanoparticles (SPION) (Si-PVIm-grafted Fe₃O₄ NPs) were prepared by grafting of telomere of PVIm on the SPION. The product identified as magnetite, which has an average crystallite size of 9?±?2?nm as estimated from X-ray line profile fitting. Particle size was estimated as 10.0?±?0.5?nm from TEM micrographs. Mean particle size is found as 8.4?±?1.0?nm which agrees well with the values calculated from XRD patterns (9?±?2?nm). Vibrating Sample Magnetometer (VSM) analysis explained the superparamagnetic nature of the nanocomposite. Thermogravimetric analysis showed that the Si-Imi is 25?% of the Si-PVIm-grafted SPION, which means an inorganic content is about 75?%. Detailed electrical and dielectric properties of the properties of the product are also presented. The conductivity of the sample increases significantly with temperature and has the value in the range of 1.14?×?10^?7?C1.78?×?10^?4?S?cm^?1. Analysis of the real and imaginary parts of the permittivities indicated temperature and frequency dependency representing interfacial polarization and temperature-assisted reorganization effects.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

Quenching kinetics and small signal gain spectrum of the ZnI photodissociation laser

By photodissociation ZnI₂ with 193 nm (ArF) laser radiation, the rate constants for quenching of the upper and lower energy levels of the ZnI (B → X) laser by ZnI₂ have been measured to be (1.7 ± 0.2) × 10^-9 and (1.4 ± 0.4) × 10^-9 cm³ s^-1, respectively. Although the former rate constant was found to be laser intensity-dependent for I ? 10⁵ W cm^-2, the ZnI(B) state radiative lifetime was determined to be 26 ± 4 ns. Also, the small signal gain coefficient, g₀, of this molecular laser has a peak value of ? 15% cm^-1 at λ ? 602 nm and exceeds 5% cm^-1 for 591 nm ≤ λ ≤ 608 nm for a potential tuning range of at least 170 Å.     

The adsorption of Xe and CO on a Cu (311) single crystal surface

LEED, electron energy loss spectroscopy and surface potential measurements have been used to study the adsorption of Xe and CO on Cu (311). Xe is adsorbed with a heat of 19 ± 2 kJ mol^/t-1. The complete monolayer has a surface potential of 0.58 V and a hexagonal close-packed structure with an interatomic distance of 4.45 ± 0.05 Å. CO gives a positive surface potential increasing with coverage to a maximum of 0.34 V and then falling to 0.22 V at saturation. The heat of adsorption is initially 61 ± 2 kJ mol^?1, falling as the surface potential maximum is approached to about 45 kJ mol^?1. At this coverage streaks appear in the LEED pattern corresponding to an overlayer which is one-dimensionally ordered in the [011̄] direction. Additional CO adsorption causes the heat of adsorption to decrease further and the overlayer structure to be compressed in the [011̄] direction. At saturation the LEED pattern shows extra spots which are tentatively attributed to domains of a new overlayer structure coexisting with the first. Electron energy loss spectra (EELS) of adsorbed CO show two characteristic peaks at 4.5 and 13.5 eV probably arising from transitions between the electronic levels of chemisorbed CO.     

Selective Fluorescence Sensing of Deoxycytidine 5��-Monophosphate (dCMP) Employing a Bis(diphenylphosphate)diimine Ligand

A new bis(diphenylphosphate)diimine ligand (BP1) was prepared and evaluated for its ability for selective detection of deoxycytidine 5??-monophosphate (dCMP). BP1 exhibited off-type fluorescence in the presence of dCMP. The fluorescence of BP1 was significantly quenched upon the addition of 2.5?×?10^?4 M dCMP and the detection limit was 1.25?×?10^?5 M in MeCN-H₂O (1:1, v/v). The binding ratio between BP1 and dCMP was determined to be 1:1 with the binding constant of 3.98?±?0.60?×?10^?3 M^?1.     

The adsorption of CO on Cu(110)

The adsorption of CO on Cu(110) has been studied by LEED, surface potentials and infrared spectroscopy. With increasing surface coverage the s.p. passes through a maximum value of 0.29 V and than falls to 0.17 V at saturation. The heat of adsorption is nearly constant (~55 kJ mol^?1) up to the maximum s.p. but then falls rapidly. A ( 2× 1) structure is formed near the s.p. maximum, followed by a structure which is compressed in the [11?0] direction and poorly ordered in the [001] direction but tending towards c(1.3 × 2). At low coverage two infrared bands appear at 2088 and 2104 cm^?1; their relative intensity is similar at 77, 195 and 295 K. As the coverage increases, the bands shift in frequency and merge into a single band at 2094 cm^?1. The origin of the two bands is discussed in relation to the overlayer structure. Strong interaction between CO molecules is shown by the spectra of mixtures of ¹³CO and ¹²CO.     

Kinetics of the gas‐phase homogeneous unimolecular elimination of selected ethyl esters of 2‐oxo‐carboxylic acids

The gas‐phase elimination kinetics of selected ethyl esters of 2‐oxo‐carboxylic acid have been studied over the temperature range of 270–415 °C and pressures of 37–114 Torr. The reactions are homogeneous, unimolecular, and follow a first‐order rate law in a seasoned static reaction vessel, with an added free radical suppressor toluene. The observed overall and partial rate coefficients are expressed by the following Arrhenius equations:

• Ethyl oxalyl chloride
• log k_overall (s^?1) = (13.22 ± 0.45) ? (179.4 ± 4.9) kJ mol^?1 (2.303 RT)^?1
• Ethyl piperidineglyoxylate
• log k_(CO2) (s^?1) = (12.00 ± 0.30) ? (191.2 ± 3.9) kJ mol^?1 (2.303 RT)^?1
• log k_(CO) (s^?1) = (12.60 ± 0.09) ? (210.7 ± 1.2) kJ mol^?1 (2.303 RT)^?1
• log k_t(overall) (s^?1) = (12.22 ± 0.26) ? (193.4 ± 3.4) kJ mol^?1 (2.303 RT)^?1
• Ethyl benzoyl formate
• log k_(CO2) (s^?1) = (12.89 ± 0.72) ? (203.8 ± 9.0) kJ mol^?1 (2.303 RT)^?1
• log k_(CO) (s^?1) = (13.39 ± 0.31) ? (213.3 ± 3.9) kJ mol^?1 (2.303 RT)^?1
• log k_t(overall) (s^?1) = (13.24 ± 0.60) ? (205.8 ± 7.6) kJ mol^?1 (2.303 RT)^?1

The kinetic and thermodynamic parameters of these reactions, together with those reported in the literature, lead to consider three different mechanistic pathways of elimination. Copyright © 2010 John Wiley & Sons, Ltd.     

Magnetization behaviour of DyAl2 single crystals

We report the theoretical interpretation of the magnetization and the magnetocrystalline anisotropy of ferromagnetic DyAl₂ single crystals between 4.2 and 60 K and magnetic fields up to 15 T. Good agreement between theory and experiment is obtained by using three temperature independent parameters: the two crystal field parameters B₄ = (?0.50 ± 0.05) × 10^?4 meV, B₆ = ? (0.51 ± 0.05) × 10^?6 meV and the Curie temperature T_c = (62 ± 2) K.     

An estimation of surface vibration excitation cross sections of CO,O and H adsorbed on tungsten

A simple model is described for the evaluation of adatom loss spectra of dipole vibrations perpendicular to the substrate. It considers the inelastic electron scattering before and after specular reflection on the substrate. By comparing the loss to elastic peak area the total cross section σ of the inelastic electron scattering can be estimated. The model was used for evaluating experimental results published in the literature by Ibach, Froitzheim, Adnot, Backx and Barnes on the systems WCO, WO and WH. The main results are: for the CO 258 meV loss peak, σ = (11.6?18.3)×10^?18cm²; for the O 78 meV loss peak, σ = (8.4?16.2) × 10^?18cm²; and for the H 130 and 155 meV loss peaks, σ =(0.73?2.2) × 10^?18cm². They are close to the theoretical values. A reasonable agreement was found between σ values determined on WO and WβCO (dissociated) systems.     

Precision bond lengths for Rydberg Matter clusters K19 in excitation levels n =4, 5 and 6 from rotational radio-frequency emission spectra

Several long series of up to 40 equally spaced lines are observed in the radio-frequency range 15–90?MHz that are attributed to stimulated emission from the electronically excited condensed matter called Rydberg Matter (RM). These frequencies are more than a factor of 1000 smaller than for most ordinary molecules, and if they did not agree with RM clusters they would indicate extremely large and heavy molecules that are unlikely to exist in the gas phase at room temperature. Theoretical predictions for RM clusters agree within 2% with the observed frequencies. Such clusters are planar, six-fold symmetric oblate rotors. The most prominent series with B?=?0.9292?±?0.0001?MHz (3.067?×?10^?5?cm^?1) agrees accurately with the theoretically predicted B value for the cluster K₁₉ in excitation level n?=?4, thus with a K–K bond length of 2.4074?nm. Two other prominent long series agree accurately with K₁₉ at n?=?5 and 6, with bond lengths of 3.804 and 5.518?nm, respectively. The ratio between the interatomic distance and the electron orbit radius for n?=?4 is found to be 2.8433?±?0.0003, a considerable improvement in precision over the theoretical value of 2.9.     

Measured collisional radiative coefficients of the 4p groups of the argon I and argon II systems

We determine the r¹ (p) coefficients of the argon I 4p ¹P₁ state (2p₂ with Paschen notation) with the λ = 696.5 nm line and of the argon II 4p ²D_{$\text{5}\text{2}$} state with the λ = 488.0 nm line in a highly ionized, low temperature (T_{e = 3?4 eV}), magnetically confined (0.2 T) plasma of a hollow cathode arc with electron densities n_e between 10¹⁹ and 10²⁰ m^?3. The neutral density n₀ is 10¹⁹ m^?3 or less. The r¹ (4p) values are (6 ± 2) × 10^?5 for argon I and (5 ± 2) × 10^?4 for argon II.