Absolute cross sections of electron attachment to molecular clusters. Part II: Formation of (H2O) N? , (N2O) N? , and (N2) N?

Absolute cross sections σ⁻(E, N) of electron attachment to clusters (H₂O) _N , (N₂O) _N , and (N₂) _N for varying electron energy E and cluster size N are measured by using crossed electron and cluster beams in a vacuum. Continua of σ⁻(E) are found that correlate well with the functions of electron impact excitation of molecules’ internal degrees of freedom. The electron is attached through its solvation in a cluster. In the formation of (H₂O) _N ⁻ , (N₂O) _N ⁻ , and (N₂) _N ⁻ , the curves σ⁻(N) have a well-defined threshold because of a rise in the electron thermalization and solvation probability with N. For (H₂O)₉₀₀, (N₂O)₃₅₀, and (N₂)₂₆₀ clusters at E = 0.2 eV, the energy losses by the slow electron in the cluster are estimated as 3.0 × 10⁷, 2.7 × 10⁷, and 6.0 × 10⁵ eV/m, respectively. It is found that the growth of σ⁻ with N is the fastest for (H₂O) _N and (N₂) _N clusters at E → 0 as a result of polarization capture of the s-electron. Specifically, at E = 0.1 eV and N = 260, σ⁻ = 3.0 × 10⁻¹³ cm² for H₂O clusters, 8.0 × 10⁻¹⁴ cm² for N₂O clusters, and 1.4 × 10⁻¹⁵ cm² for N₂ clusters; at E = 11 eV, σ⁻ = 9.0 × 10⁻¹⁶ cm² for (H₂O)₂₀₀ clusters, 2.4 × 10⁻¹⁴ cm² for (N₂O)₃₅₀ clusters, and 5.0 × 10⁻¹⁷ cm² for (N₂)₂₆₀ clusters; finally, at E = 30 eV, σ⁻ = 3.6 × 10⁻¹⁷ cm² for (N₂O)₁₀ clusters and 3.0 × 10⁻¹⁷ cm² for (N₂)₁₂₅ clusters. Original Russian Text ? A.A. Vostrikov, D.Yu. Dubov, 2006, published in Zhurnal Tekhnicheskoĭ Fiziki, 2006, Vol. 76, No. 12, pp. 1–15.     

Spin exchange and chemi-ionization during collisions of polarized metastable helium atoms with ground-state cesium atoms

The kinetics of the optical orientation of atoms in a helium-cesium gas-discharge plasma are considered, and kinetic equations describing the optical orientation of atoms in the case of two simultaneously occurring processes, viz., an elastic process (spin exchange) and an inelastic process (chemi-ionization), are derived. The rate constants of these processes are determined experimentally: C _se=(2.8±0.8)×10⁻⁹ cm³s⁻¹, C _ci=(1.0±0.3)×10⁻⁹ cm³s⁻¹. Zh. Tekh. Fiz. 69, 36–40 (September 1999)     

Measurement of the spin-exchange and chemical ionization rate constants in collisions of polarized metastable 23 S 1 helium atoms with 32 S 1/2 sodium atoms

Experimental data on the spin-exchange rate constants for the He(2³ S ₁)-Na(3² S _1/2) system are reported for the first time. Measurements show that the spin-exchange rate constant is C _se = (23 ± 11) × 10⁻¹⁰ cm³ s⁻¹ and the chemical ionization rate constant is C _si = (29 ± 14) × 10⁻¹⁰ cm³ s⁻¹ at a temperature of 420 K. The results are compared with the data calculated from the rate constants.     

Addition and spin exchange rate constants by longitudinal field μSR: The Mu+NO reaction

The addition reaction Mu+NO+M→MuNO+M and the spin exchange reaction Mu(↑) +MO(↓)→Mu(↓)+NO(↑) have been measured by longitudinal field μSR at room temperature in the presence of up to 58 atm of N₂ as inert collider. The pressure dependence of the longitudinal relaxation rate due to the addition reaction (λ_c) demostrates that the system is still in the low pressure regime in this pressure range. The corresponding termolecular rate constant has been determined ask _0,Mu =(1.10±0.25)×10⁻³² cm⁶ molecules⁻² s⁻¹, almost 4 times smaller than the corresponding H atom reactionk _0,H=3.90×10⁻³² cm⁶ molecules⁻² s⁻¹ [I.M. Campbell et al., J. Chem. Soc. Faraday Trans. 1.71 (1975) 2097]. The average value of the spin exchange rate constants in the 2.5–58 atm pressure range,k _SE=(3.16±0.06)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, is in good agreement with previous values obtained by transverse field μSR [D.G. Fleming et al., J. Chem. Phys. 73 (1980) 2751].     

Kinetics of the formation of gas bubbles during polarization of copper and graphite electrodes in electrolytic aqueous solutions

The adsorption and kinetic processes of the formation of gas bubbles passivating the surface during polarization of copper and graphite electrodes in 1% aqueous solution of sulfuric acid have been investigated. Three stages of the process related to the recharging of the double electric layer—adsorption accumulation of the gas escaping from the surface, the critical nucleation of the gas bubbles, and their subsequent growth—have been revealed, distinguished, and quantitatively estimated. It has been shown that potential leveling at the steady-state value specified by the Tafel equation is unambiguously associated with achievement of the limiting surface area screened by the gas bubbles for each particular current density. The surface diffusion constants D _H = (1.5–4.4) × 10⁻⁴ and (0.1–3.8) × 10⁻⁵ cm²/s of hydrogen on copper and graphite, respectively, and D _O = (1.8–4.5) × 10⁻⁷ cm²/s of oxygen on graphite during the motion toward the drain (the gas bubbles) have been calculated.     

One-dimensional ionic conduction in solid Ag2 Tl6I10

The ionic and electronic conductivities of Ag₂Tl₆I₁₀ single crystals have been studied as a function of crystallographic orientation and temperature from 20 to 135°C. EMF as well as AC and DC techniques have been employed. The highly anisotropic material is predominantly an Ag⁺-ion conductor parallel toc-direction, with the Ag⁺ ions moving through linear channels that are not interconnected. The conductivity σ_‖c =1.6×10⁻⁷Ω⁻¹cm⁻¹ at 25°C, with an activation enthalpy for σ_‖c of 0.38 eV. The conduction perpendicular toc-direction has been found to be predominantly electronic with a value of σ_⊥c =3×10⁻⁹Ω⁻¹cm⁻¹ at 25°C and an activation enthalpy for σ_⊥c of 0.64 eV. This is the first observation of one-dimensional Ag⁺ conduction and this type of orientation-dependent change from ionic to electronic conduction. On leave from Institute of Physics, Academia Sinica, Peking, China.     

EPR of Fe3+ ion and symmetry of [AIF5·H2O]2? complex ion in (NH4)2AIF5·H2O single crystals

We used the spin-Hamiltonian method for the analysis of the electron paramagnetic resonance (EPR) spectrum of Fe³⁺ as a probe ion in (NH₄)₂AlF₅·H₂O single crystalline basic material. The theoretical expressions for the magnetic field (at which the fine structure transition lines appear) versus the angle between the magnetic field and the axis of symmetry of the magnetic complex are also given. These values were calculated by applying the perturbation theory to the second-order terms. From the experimental results (at 300 K and 9.21 GHz), the spin-Hamiltonian parameters were deduced:D=(668±10)·10⁻⁴ T,E=(−56±10)·10⁻⁴ T,a=(−54±10)·10⁻⁴ T,F=(30±10)·10⁻⁴ T. An isotropic superhyperfine structure was evidenced for the five fluorine ions. The obtained EPR data were used to determine the local symmetry of the Al³⁺ ion. A good agreement with X-ray diffraction measurements was found.     

Implantation doping of germanium with Sb,As, and P

The ions of Sb, As, and P have been implanted into germanium at energies ranging from 200 keV to 700 keV. Annealing was performed at 400°C, 550°C, and 650°C. The doping profile was determined by differentialCV-measurements. Strong outdiffusion (80%) and diffusion into the bulk material was observed after annealing. The remaining doping concentration and the diffusion constants were determined by a computer fit at 650°C. We foundD _Sb=1.8×10⁻¹³ cm²/s,D _As=9×10⁻¹⁴ cm²/s andD _P=4×10⁻¹⁴ cm²/s. Lower values of the diffusion constant were determined when the samples were covered with a SiO₂ layer.     

EPR of trivalent iron ions in a LiCaAlF6 crystal

The orientational dependences of the EPR spectra of Fe³⁺-doped LiCaAlF₆ single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail. The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B ₂₀=40.072×10⁻⁴ cm⁻¹, B ₄₀=−5.799×10⁻⁴ cm⁻¹, B ₄₃=−4.281×10⁻⁴ cm⁻¹, A _s=24.33±1, A _p=6.13±1, g _∥=g _⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F⁻). Fiz. Tverd. Tela (St. Petersburg) 39, 488–490 (March 1997)     

Fundamental absorption edge of evaporated amorphous WO3 films

The fundamental absorption edge of evaporated WO₃ films is investigated. The optical gap of the virgin film is estimated to be 3.41 eV at room temperature and it decreases with increase of annealing temperature up to 200°C. Annealing at 300°C leads to change in the spectral shape, which is caused by crystallization. For the films annealed at 200°C, temperature coefficient of the optical gap is estimated to be −2×10⁻⁴ eV/K and the slope of Urbach's tail is found to be independent of measuring temperature up to 200°C. With electrolytic coloration, shift of the optical gap toward higher energy is observed. Magnitude of this shift is estimated to be 0.05 eV at the color center concentration of 7.5×10²¹ cm⁻³ when H⁺ electrolyte is used. If Li⁺ electrolyte is used, the magnitude of this shift is about three times larger than in the case of H⁺ electrolyte. This fact is interpreted by a small change in the host matrix structure owing to the injection of proton or Li⁺ during coloration.     

Comparative Raman study of the Ti complex Cp2Ti(η2-C60) · C6H5CH3 and TixC60 films

Raman spectra from the first Ti fullerene complex Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ are presented. Compared to spectra of pure C₆₀, the spectra of the Ti complex exhibit a number of new peaks due to the symmetry lowering for C₆₀. The A _g(2) mode is downshifted by 12 cm⁻¹ compared to C₆₀, which corresponds to a charge transfer of one electron per Ti-C₆₀ bond. This value (6 cm⁻¹ for one transferred electron) is identical to the downshift of the A _g(2) mode in alkali metal fullerides with ionic bonding. The spectra of Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ were compared to the spectra of evaporated Ti_xC₆₀ films. The A _g(2) mode in Ti₄C₆₀ showed a downshift of about 25 cm⁻¹ compared to pure C₆₀, which corresponds to a charge transfer of one electron per Ti atom; this is similar to the ionic alkali metal fullerides and different from η²-C₆₀-type bonding. From Fizika Tverdogo Tela, Vol. 44, No. 3, 2002, pp. 483–485. Original English Text Copyright ? 2002 by Talyzin, Jansson, Usatov, Burlakov, Shur, Novikov. This article was submitted by the authors in English.     

Pentacene thin film transistors using La2O3 as gate insulator

A study of Pentacene OTFTs using La₂O₃ as gate insulator is presented. The device characteristics were studied and analyzed. The OTFTs exhibit p-type conductivity with field effect mobility 6.5 × 10⁻⁸ m²/V.s, ON/OFF ratio 1.4 × 10², sub-threshold swing 2 mV/decade and hole concentration 4.5 × 10¹⁷ cm⁻³. The SEM and XRD analysis on the semiconductor film are also reported.     

Influence of Ar, Ne, Xe, and CCl4 impurities on luminescence kinetics of Cd II ions (5s22D5/2-5p2P3/2 transition, λ = 441.6 nm) in He-Cd mixture

The luminescence kinetics of the Cd II ion at a wavelength of 441.6 nm has been studied experi-mentally in a high-pressure He-Cd mixture in the presence of Ar, Ne, Xe, and CCl₄ impurities. Cadmium ions were excited through the bombardment of a cadmium foil heated up to 240°C by a pulsed electron beam with an electron energy of 150 keV, a pulse duration of 3 ns, and a current of 500 A. The constants of collisional quenching of the Cd II 5s ^{2 2} D _5/2 level by Ar, Ne, and Xe atoms and CCl₄ molecules and the integral luminescence quenching constants of this level in the helium medium by these impurity gases have been determined. The constants of collisional quenching appeared to be 8.1 × 10⁻¹² (Ar), 1.2 × 10⁻¹² (Xe), 1.5 × 10⁻¹³ (Ne), and 1.8 × 10⁻¹⁰ cm³/s (CCl₄, for λ = 325 nm), while the integral constants were found to be, respectively, 4.1 × 10⁻¹¹, 3.4 × 10⁻¹¹, 9.5 × 10⁻¹², 1.4 × 10⁻⁹ cm³/s for Ar, Ne, Xe, and CCl₄ at a buffer gas pressure of 1 atm. Original Russian Text ? A.I. Miskevich, Liu Tao, 2009, published in Optika i Spektroskopiya, 2009, Vol. 107, No. 1, pp. 45–49.     

Structural phase transitions in Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 alloys observed by pac

The phase transition in the alloys Pd_0.8 Si_0.2 and Pd_0.75 Si_0.20 Ag_0.05 have been investigated through the quadrupole interaction of¹¹¹Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about 870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT ^3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10⁻⁵ K^−3/2 andB=3.70(15)·10⁻⁵ K^−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric field gradients observed in the alloy PdSi,V _zz (1)=3.47(54)·10¹⁷ V/cm² andV _zz (2)=2.29(36)·10¹⁷ V/cm², indicates that there are two different¹¹¹Cd sites. The corresponding fractionsf ₁ andf ₂ strongly depend on temperature. Below 520 K, most¹¹¹Cd nuclei are subject to the higher EFGV _zz (1) (f ₁≈70%), whereas above 520 Kf ₁ falls rapidly to zero andV _zz (2) becomes dominant. The temperature dependences of thef ₁ andf ₂ reveal a picture of the phase transition between the two crystal structures.     

ESR study of exchange coupled pairs in copper diethyldithiocarbamate

ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)₂, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g _‖=2.1025,g ₊=2.031,A=75.1×10⁻⁴ cm⁻¹,B=14.8×10⁻⁴,D=276.0×10⁻⁴ cm⁻¹ andE=46.7×10⁻⁴ cm⁻¹. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm⁻¹. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)₂—direct exchange and superexchange through the bridging sulphurs—are discussed.     

Incorporation of Sn into epitaxial GaAs grown from the liquid phase

The incorporation of Sn into LPE GaAs was studied as a function of the atomic fractionx _Sn ^l of Sn in the liquid (1.6×10⁻⁴≤x _Sn ^l ≤0.54), the growth temperatureT _K and the cooling rate α. The diffusion coefficient of As in Ga for moderate Sn-doping was deduced from the growth velocities to beD _As (760° C)=(3.3±1.0)×10⁻⁵ cm²/s. The epitaxial layers were analyzed after van der Pauw with special emphasis on the sources of experimental error. With the aid of current mobility theories the concentrations of the ionized donors and acceptors were derived. From their dependence onx _Sn ^l , on α and onT _K combined with the Schottky-barrier model of Sn incorporation it can be concluded that the melt and the growing crystal surface were in thermal equilibrium. The diffusion coefficient of Sn in GaAs is about 8×10⁻¹⁴ cm²/s at 760° C. The distribution coefficient for Sn increases from 4.4×10⁻⁵ to 12.3×10⁻⁵ in the temperature range from 690 to 800° C. The total Sn incorporationx _Sn ^s was measured using the atomic absorption spectroscopy for the first time down tox _Sn ^s =10¹⁷/cm³. From these data it can be concluded that up tox _Sn ^l =0.54 the dopant Sn is incorporated as donor and as acceptor only and that within the experimental scatter there is no indication of incorporation as a neutral species.     

Improved absolute frequency measurement of the 115In+ 5s2 1S0-5s5p3P0 narrowline transition: Progress towards an optical frequency standard

We report on an improved absolute frequency measurement of the 5s ^{2 1} S ₀0-5s5p ³ P ₀ narrowline clock transition at 236.5 nm, for a single, trapped, and laser-cooled ¹¹⁵In ion. Using a narrowline laser as the local oscillator, a linewidth of 43 Hz for the transition is resolved. The uncertainty of the transition frequency’s centroid is 18 Hz, leading to a fractional uncertainty of 1.4 × 10⁻¹⁴. For absolute frequency measurement, we use an optical frequency comb locked to a cesium clock as the reference. The transition frequency is found to be 1267402452900967(63) Hz, averaged over 13 days of separate measurements. The accuracy is about 5.0 × 10⁻¹⁴. We discuss possibilities for further improvement. Original Text ? Astro, Ltd., 2007.     

Indication of asymptotic scaling in the reactions dd → p3H, dd → n3He, and pd → pd

It is shown that the differential cross sections of the reactions dd → n ³He and dd → p ³H measured at a c.m.s. scattering angle θ_cm = 60° in the interval of the deuteron beam energy 0.5–1.2 GeV demonstrate the scaling behavior dσ/dt ∼ s ⁻²², which follows from constituent quark counting rules. It is found also that the differential cross section of the elastic dp → dp scattering at θ_cm = 125°–135° follows the scaling regime ∼s ⁻¹⁶ at beam energies 0.5–5 GeV. These data are parameterized here using the Reggeon exchange. From Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, Vol. 81, No. 7, 2005, pp. 387–390. Original English Text Copyright ? 2005 by Uzikov. This article was submitted by the author in English.     

Cross sections for slow ion production and charge transfer in H+3(D+3)−H2(D2) collisions

Slow ion production cross sections for collisions of H⁺₃ and D⁺₃ ions with H₂ and D₂ have been measured at collision energies between 100 eV and 500 eV. The values vary from 2 × 10^-17 cm² to 6 × 10^-17 cm². The smaller cross sections for D₃ projectiles may be explained as an internal energy effect.     

Analysis of Bs→φ?+?? decay with new-physics effects

The rare B _s →φ ℓ ⁺ ℓ ⁻decay is investigated by using the most general model-independent effective Hamiltonian for ℓ=μ,τ. The calculated value of Br(B _s →φ μ ⁺ μ ⁻)=1.92×10⁻⁶ is consistent with the experimental upper bound. The dependencies of the branching ratios and polarization asymmetries of leptons and combined lepton–antilepton asymmetries on the new Wilson coefficients are presented. The analysis shows that the branching ratios and the lepton-polarization asymmetries are very sensitive to scalar- and tensor-type interactions. The results obtained in this work will be very useful in searching new physics beyond the standard model.