bluuebunny/crossref_metadata_2025 huggingface dataset:
The Statistical-Mechanical Theory of Transport Processes. VIII. Quantum Theory of Transport in Gases
Authors: Ross John , Kirkwood John G.
Published: April 2005

The quantum-mechanical analog of the Maxwell-Boltzmann equation of transport in gases of low density is derived from the quantum-mechanical equation for the motion in phase space of the Wigner function. The derivation is based upon the theory of phase-space transformation functions which is developed in this article. Although the present treatment resembles the derivation of Mori and Ono, it is simpler and more general. Particularly, the assumption of random a priori phases, an integral part of Mori and Ono's work, need not be applied explicitly. The Uhling and Uhlenbeck equation is verified in the Born collision approximation.
Frequency Spectrum and Specific Heat of a Face-Centered Cubic Lattice. II. Low Temperature Region
Authors: Garland Carl W. , Jura George
Published: April 2005

From the Born-von Kármán treatment of a face-centered cubic lattice a simplified secular equation valid for low frequencies has been obtained. The frequency spectrum of low frequency normal modes of vibration has been calculated using the root sampling technique of Blackman. From this distribution function a T3 law is obtained for Cv at low temperatures. The effect on the low temperature specific heat of including interactions with neighbors more remote than the next nearest neighbors is discussed. Numerical results are presented for silver.
Equilibrium Constant, Infrared Spectrum, and Thermodynamic Properties of Bromine Chloride
Authors: Mattraw H. C. , Pachucki C. F. , Hawkins N. J.
Published: April 2005

The equilibrium constant of 0.15 for the gaseous system 2BrCl = Br2+Cl2 has been determined by means of a mass spectrometer. The fundamental vibration frequency of BrCl was observed at 439.5 cm-1 wave numbers in the infrared spectrum. The thermodynamic properties — (F — E00), S, and Cp were calculated for one mole of gas at atmospheric pressure from 100—1000°K. From the thermodynamic properties, equilibrium constant and known standard state properties of Br2 and Cl2, the standard state properties of BrCl were computed. There was no evidence for the existence of BrCl3.
Inter- and Intramolecular Energy Transfer Processes. 4. Hydrogen-Hydrocarbon Systems
Authors: Moodie Margaret M. , Reid C.
Published: April 2005

Extensive experiments have confirmed our earlier conclusion that long-range energy transfer does not occur between pairs of molecules in solution. Evidence is brought forward to show that the transfer of excitation energy from terphenyl to diphenyl hexatriene under x-ray bombardment in liquid scintillators must be due to a short-range process which occurs after the formation of a molecular complex between diphenyl hexatriene and either a positive terphenyl ion or a very highly excited terphenyl molecule.

Results of experiments in heterogeneous systems, in which transfer of excitation energy from adsorbed component to host crystal, and vice versa sometimes occurs, are summarized.
Effect of Pressure on Diffusion in Polymer Solutions
Authors: Emery A. H. , Tung L. H. , Drickamer H. G.
Published: April 2005

Diffusion measurements have been made using two molecular weights of polysulfide polymer at 25°C and 59°C in toluene solution. One isotherm for the low molecular weight was obtained in chloroform solution.

The results indicate that there are two mechanisms of motion in solution. At low pressure the dominant mode involves the expulsion of a solvent molecule from the coiled polymer. At high pressure the motion is segmental.
Structures of the Boron Hydrides
Authors: Lipscomb William N.
Published: April 2005

Evidence for the structures of B2H6, B4H10, B5H9, B5H11, and B10H14 is reviewed. Correlations of the boron arrangements with known structures have been pointed out, and a systematic discussion of the boron-hydrogen distances is given.
The Electrical Properties of Some Complex Compounds. Part 1
Authors: Fielding P. E.
Published: April 2005

Electrical measurements on dicobalt decamine-μ-peroxy complex (Vortmann's salt) are described. The current formulation contained CoIII and CoIV in crystallographically equivalent positions and hence it was thought that the complex might be an intrinsic semiconductor. An apparent dielectric constant K of 106 was found to be due to chemical polarization caused by traced of acid on the material. It is concluded on the basis of conductivity measurements that the material is not an intrinsic semiconductor.
Infrared Spectra of Thionyl Chloride and Sulfuryl Chloride
Authors: Martz Dowell E. , Lagemann Robert T.
Published: April 2005

The infrared spectra of thionyl chloride and sulfuryl chloride have been investigated from 400 cm—1 to to 5000 cm—1 with a prism spectrometer. Three of the fundamentals of SOCl2 have been found and four for SO2Cl2. They and the various additional bands have been assigned to their appropriate symmetry species assuming SOCl2 has C8 symmetry and SO2Cl2 has C2v symmetry.
Rotational Magnet Moments of KClFeCl2 and KBrFeBr2
Authors: Kusch P.
Published: April 2005

The molecules KClFeCl2 and KBrFeBr2 have rotational magnetic moments much larger than those found in other heavy molecules with large moments of inertia. The maximum magnetic moment of the state of most probable J at a temperature of 935°K is about 72 nuclear magnetons for the first of the molecules and about 50 nuclear magnetons for the second of these molecules.
The Fluorescence of Biacetyl Vapor at 4358A
Authors: Coward Nathan A. , Noyes W. Albert
Published: April 2005

The fluorescence efficiency of biacetyl vapor when excited by radiation of wavelength 4358A is independent of the number of quanta absorbed per cubic centimeter per second, almost if not quite independent of biacetyl pressure, and decreases with increase in temperature but there seems to be a transition from one type of variation with temperature to another between 60° and 100°. Oxygen quenches the fluorescence strongly, and isobutylene quenches the fluorescence little or not at all.

The marked difference in fluorescence behavior of biacetyl when excited by 4358A radiation from that when excited by 3660A radiation as pointed out by previous authors makes desirable an attempt to correlate fluorescence with photochemical behavior. Some suggestions are made with regard to mechanism.
Infrared Spectrum and Thermodynamic Functions of Formamide
Authors: Evans J. C.
Published: April 2005

The infrared spectra of formamide in the vapour and liquid states, and in solutions in CHCl3, CCl4, CH3CN, H2O, and D2O, and of sodium formamide and formamide hydrochloride were observed between 650 cm—1 and 3800 cm—1. The effect of association on the bands was examined, where possible, in solution and in the vapor state. These infrared results were taken in conjunction with the available Raman data and an assignment of the frequencies to the fundamental modes of vibration of the molecule has been made. Thermodynamic functions have been calculated.
The Application of the Debye-Hückel Theory to Polyions. Part I. The Range of Applicability of the Debye Limiting Law
Authors: Hayman H. J. G.
Published: April 2005

The Debye limiting law has been used to deduce an expression for the electrical work which must be done to build up a polyion from the corresponding single ions in extremely dilute solutions containing various (appreciable) concentrations of 1 — 1 electrolyte. The case of an infinite straight rigid polyion having charges at equal intervals along its length was treated in greater detail, and a corrected expression was obtained for the above-mentioned electrical work, which makes allowance for the finite size of the polyion charges and takes some account of the steric effects due to the remainder of the polyion molecule. The error due to the high electric potential ψ surrounding such a polyion which invalidates the Debye approximation of replacing sinh (εψ/kT) by εψ/kT was evaluated by numerical integration of the Poisson-Boltzmann equation. The integration was started at a considerable distance from the polyion on the assumption of cylindrical symmetry and continued at closer distances on the assumption of spherical symmetry surrounding each polyion charge. The results obtained indicated that the error involved in using the simple Debye limiting law formula would seldom be more than a few percent, provided the concentration of the 1 — 1 electrolyte was rather low (not more than about N/100).
Virial Expansion of the Osmotic Pressure in the Donnan Membrane Equilibrium
Authors: Hill Terrell L.
Published: April 2005

Two methods for refining the usual Donnan treatment of the Donnan membrane equilibrium are introduced and compared. One method is to apply the McMillan-Mayer solution theory while the second method involves modifying the Donnan treatment to include Debye-Hückel corrections to activity coefficients and osmotic pressure expressions.
A Note on the Flow of Gases through Very Fine Tubes
Authors: Sears G. W.
Published: April 2005

It is shown that Knudsen's laws of flow for rarefied gases must be modified for very fine tubes. Gas flow occurs by diffusion of molecules in the adsorbed layer on the tube walls as well as in the gas phase. When the tube dimension is comparable to the mean free path in the gas film, the two flow mechanisms become comparable in effectiveness.
The Effect of Pressure on Thermal Diffusion in n-Paraffin Hydrocarbon-CS2 Mixtures
Authors: Rutherford W. M. , Drickamer H. G.
Published: April 2005

Thermal diffusion measurements have been made to 10 000 atmospheres at 40°C and 78°C pressure for the systems. n−hexane (20 percent)−CS2 (80 percent),n−heptane (20 percent)−CS2 (80 percent),n−octane (20 percent)−CS2 (80 percent),at 40°C and 78°C. The data are interpreted in terms of a modified regular solution theory presented previously. The results are consistent with the theory and the regularities indicate that a general quantitative theory of thermal diffusion is possible.
Thermal Diffusion in Binary Mixtures of CS2 and Hexane Isomers
Authors: Rutherford W. M. , Dougherty E. L. , Drickamer H. G.
Published: April 2005

Thermal diffusion measurements have been made for binary mixtures of CS2 and the five isomeric hexanes at atmospheric pressure and under pressure to 10 000 atmospheres. The data, measured in two different types of apparatus, are consistent. The results indicate that the further the deviation from spherical symmetry, the larger the value of the steric correction factor ψ. Thus, for mixtures of molecules of the same size and cohesive energy, the more spherically symmetrical will concentrate at the cold wall.
A Treatment of Chemical Kinetics with Special Applicability to Diffusion Controlled Reactions
Authors: Noyes Richard M.
Published: April 2005

If a molecule is produced in a medium containing molecules able to react with it, its instantaneous reactivity is a function of the time since its formation. At very short times the reactivity is determined by the conventional ``true'' rate constant k, which is the product of the rate constant for encounters and the probability of reaction during an encounter. At long times (10—9 sec or greater in many liquids), the reactivity falls to a value determined by the ``long-time'' rate constant k′. The constants k and k′ differ by the factor 1 — β′, where β′ is the probability that a specific pair of molecules separating from a nonreactive encounter will ultimately react with each other. If β′ is small either because there is little chance of reaction per encounter (activation control), or because there is little chance the specific pair will undergo a subsequent encounter (as in gas phase), the two rate constants are virtually identical and conventional kinetics apply.

Equations are developed for the time dependence of the reactivity of a molecule in such a system, and a model is suggested for evaluating the necessary parameters in terms of the relative diffusion coefficient, the encounter diameter, and the root-mean-square displacement distance during diffusion. Application of available kinetic data indicates that diffusive displacements in liquids are of the order of a molecular diameter and take place with a frequency of the order of 1011 sec—1.

In the quenching of fluorescence and other processes where reactive molecules are produced singly, experimental measurements have given the ``long-time'' rate constant, k′. When reactive molecules are produced in pairs, the recombination process in a thermal equilibrium is described by the ``true'' rate constant, k; but k′ has been obtained from all rate measurements on the recombination of pairs produced photochemically. Experiments are suggested for obtaining information on systems during the short time in which the apparent rate constant in changing.
Chemical Synthesis from Free Radicals Produced in Microwave Fields
Authors: McCarthy R. L.
Published: April 2005

Although much attention has been given to the physics of a microwave glow discharge, substantially less information is available regarding the chemical effects upon a gas undergoing such excitation. We have studied the chemical effects of a 2450-Mc/sec glow discharge on several gases and have made quantitative measurements on a few simple molecular systems, e.g., N2, H2, O2, air, CH4. A fundamental relationship has been found to exist between the yield in simple chemical systems and the controllable variables of electric field strength, contact time, and pressure. Analytical expressions for these relationships have been obtained.
The United Atom-Separated Atom Treatment of H2+
Authors: Streetman J. R. , Matsen F. A.
Published: April 2005

A trial wave function consisting of a linear combination of 1S orbitals centered on the nuclei and on a point half-way between them was used in a variational treatment of H2+. A one-electron three-center integral with nonequal charges which arises in the course of this treatment was evaluated. The effective nuclear charges for minimum energy were found approximately by calculating energies for a range of values of the separated atom charge and of the united atom charge. The lowest energy calculated, —0.5969 au, occurred where both effective nuclear charges are equal at 1.25. The energy value should be compared with —0.6031 au, the exact value, and with —0.6001 au obtained by hybridizing 1S and 2Pz orbitals on the separated nuclei. The ratio of the united atom coefficient to separated atom coefficient was found to be 0.3501 for the energy value mentioned.
The Germanium-Oxygen System
Authors: Hoch Michael , Johnston Herrick L.
Published: April 2005

High-temperature x-ray diffraction patterns of germanium plus germanium oxide GeO2 between 750° and 1400°C, showed that germanium monoxide GeO is not a stable compound. At elevated temperatures germanium can dissolve up to 60 atom percent of oxygen. The oxygen causes first a slight expansion and then a contraction of the Ge lattice. At 850° and 930°C, the x-ray pattern of a germanium-oxygen compound, consisting of equimolecular quantities of germanium and oxygen, showed only the germanium pattern. At 1000° and higher (above the melting point of pure germanium, 965°C), the germanium pattern disappears, and liquid-like structure is visible, though the sample is still solid (melting point 1430°C). When the temperature is lowered again to 930°C, the germanium pattern reappears. The electrical resistivity of the Ge and GeO2 mixture shows a sharp break at 970°C. In the germanium-oxygen compound we thus have a disordering of the germanium lattice above the melting point of pure germanium.
Stark Effect in the Microwave Spectra of KCl and NaCl
Authors: Tate P. A. , Strandberg M. W. P.
Published: April 2005

Some further lines in the microwave spectrum of KCl have been observed at frequencies predicted by the rotational constants given by recent molecular beam work. Measurements have been made on the Stark patterns of the J=2→3, v=0 line of K39Cl35 and the J=1→2, v=0 line of Na23Cl35. The dipole moments of these molecules have been determined to be 10.1±0.2 Debye units for KCl and 8.5±0.2 Debye units for NaCl. The KCl value is in fair agreement with the results of molecular beam investigations.
The Photographic Latent Image. III. Dimensional Changes in Silver Bromide Following Exposure
Authors: Huggins Maurice L.
Published: April 2005

Using previously tested equations and constants, calculations are made of the dimensional changes to be expected in AgBr crystals as a result of the presence of varying proportions of uncharged bromine atom and silver-ion vacancy defects. The results depend to a considerable extent on the unknown degree of ordering of these defects. With reasonable assumptions as to this degree of ordering and as to the magnitudes of the other unknown and approximately known quantities involved, the experimentally observed behavior—a lattice constant decrease, followed by a return to approximately the original value on further exposure—is quantitatively accounted for.
Approximate Method of Evaluating Lattice Sums of r—n for Graphite
Authors: Crowell A. D.
Published: April 2005

The graphite lattice is approximated by a set of planes in which the carbon atoms are assumed to be distributed with uniform density. It is shown that the lattice sums of r—n taken over the graphite planes can then be expressed directly in terms of tabulated functions. The results of the approximation are compared with the results obtained by direct summation.
Hydrogen Bonding in Sodium Trifluoroacetate-Trifluoroacetic Acid Compounds
Authors: Klemperer William , Pimentel George C.
Published: April 2005

The dissociation pressure of trifluoroacetic acid over two compounds with sodium trifluoroacetate has been measured from 25° to 40°C. One compound is CF3COONa·2CF3COOH, and the other is probably CF3COONa·CF3COOH. The infrared spectra of CF3COONa·2CF3COOH, CF3COONa·2CF3COOD, and CF3COONa have been measured in the spectral region 4000 to 650 cm—1. The stability of these salt-acid compounds is attributed to strong hydrogen bonding. The heat of dissociation of CF3COONa·2CF3COOH is +14 kcal per mole of monomeric trifluoroacetic acid, and the OH stretching frequency is found 1150 cm—1 below its location in the monomeric acid.
High-Temperature Equation of State by a Perturbation Method. I. Nonpolar Gases
Authors: Zwanzig Robert W.
Published: April 2005

A theoretical study is made of the equations of state of argon and nitrogen, at high temperatures and densities. The intermolecular potential used is of the Lennard-Jones form, with an adjustable rigid sphere cutoff. A perturbation theory is developed, by which the thermodynamic properties of one system may be related to those of a slightly different system and to the difference in the intermolecular potentials of the two systems. In this article, the unperturbed system is a rigid sphere fluid, and the Lennard-Jones potential is the perturbation. The results are in fair agreement with experiment, and also lead to an experimental test of the theoretical rigid sphere equation of state.
Conjugation of Several Phenyl Radicals Bonded to a Single Central Atom
Authors: Jaffé H. H.
Published: April 2005

Spectroscopic evidence is used to show that phenyl radicals are only weakly conjugated with central atoms (S, P, As, Sb, Si, Sn, Pb) not having unshared valence electrons. No resonance interaction is encountered between several phenyl radicals attached to such a central atom, and each phenyl radical makes an independent contribution to the molar extinction coefficients. If the central atom (S, N, P, As, Sb, Bi) has an unshared pair of electrons, extensive conjugation between the phenyl radicals occurs and leads to spectra in sharp contrast to those of simple benzene derivatives. No simple relation exists between the spectra of closely related compounds with different numbers of phenyl radicals attached to the same central atom. The near ultraviolet absorption spectra of dimethylaniline, methyldiphenylamine, triphenylamine, triphenylarsine, triphenylstibine, triphenylbismuthine, triphenylarsine oxide, and triphenylstibine dichloride are reported and compared with those of related compounds of phosphorus, sulfur, and group IVA elements.
Appearance Potential Studies. I. Determination of Excess Kinetic Energy
Authors: Kandel Richard J.
Published: April 2005

The metastable ion suppressor on the Consolidated Engineering Corporation Model 21—103 mass spectrometer has been used as a retarding potential device to determine the excess kinetic energies possessed by the ions formed during appearance potential measurements. The suppressor setting at which an ion beam is extinguished is compared with the extinction setting for an ion beam with no excess energy. These settings are studied as a function of ionizing voltage, extrapolated back to the appearance potential, and converted into units of energy.

N+ from N2 was found to have no excess kinetic energy at the appearance potential. CH3+ from C2H6, CH3+ from C3H8, CN+ from C2N2, and CH3+ from C6H5CH3 were all formed with excess kinetic energy. The following quantities were deduced after taking the excess energy into account: D(CH3–CH3)=3.87 volts; D(CH3–C2H5)=3.70 volts; I(CN)=15.13 volts; I(C6H5)=9.90 volts; D(C6H5–CH3)=3.80 volts; D(C6H5–H)=4.64 volts.
Thermal Relaxation in Gases
Authors: Brout Robert
Published: April 2005

The solution of the linearized equations appropriate for sound dispersion is presented. The limiting cases as the sound frequency becomes large or small is examined. The two state gas is exhibited as a special case and shown equivalent to previous work in the field when the appropriate assumptions are made.
Dissociation Energy of N2
Authors: Hendrie J. M.
Published: April 2005

An attempt has been made to observe the thermal dissociation of N2 in order to choose between the two values, 7.385 ev and 9.765 ev, for the dissociation energy of N2. At the highest available temperatures no dissociation could be observed, and a lower limit of 8.80 ev is set for D(N2).
Decomposition of Methanol Induced by Methoxy Radicals
Authors: Takezaki Yoshimasa , Takeuchi Chisato
Published: April 2005

Kinetical studies were made at 167°C on the decomposition of methanol induced by methoxy radicals, by pyrolyzing a small amount of dimethyl peroxide in methanol. A considerable amount of ethylene glycol was found. The following mechanism was proposed, and the kinetical equations derived therefrom could express the most part of the reaction quantitatively: CH3OOCH3    →2CH3O,CH3O+CH3OH→CH3OH+CH2OH,  (a)CH3O          →CH2OH,CH3O+CH2OH→CH3OH+HCHO,2CH3O         →CH3OH+HCHO,CH3O+HCHO  →CH3OH+CHO,  (b)CH3O+CHO   →CH3OH+CO  or  2CHO→HCHO+CO,2CH2OH        →CH2OH−CH2OH.The dissociation rate constant of dimethyl peroxide is represented by 4.1×1015 exp (—36.9 kcal/RT) sec—1, and the activation heat of (a) is 3.0∼4.3 kcal higher than that of (b).
Ion-Pair Yield of the Tritium-Oxygen Reaction
Authors: Dorfman Leon M. , Hemmer B. A.
Published: April 2005

The rate of reaction of tritium and oxygen, initiated by the tritium beta radiation, has been investigated at 25°C, in the absence of mercury vapor, by using a sensitive Bourdon gauge as the manometer. The rate is not linear with time, but shows a small continual decrease as the reaction proceeds. The initial reaction rate was found to be directly proportional to the tritium pressure, and hence proportional to the radiation intensity. It was independent of the oxygen concentration over the range investigated. The reaction rate shows a slight dependence on the isotopic composition of the hydrogen reactant, tending to rise with increase in the mole fraction of protium. The initial reaction rate may be represented by R0=1.19×10−4CT2(1+0.3mH),where Ct2 is the tritium concentration in moles/liter or other absolute concentration units, and mH is the mole fraction of protium in the hydrogen reactant. On the basis of a requirement of 33 ev per ion pair in the reactant mixture, the initial ion-pair yield for tritium disappearance or water formation is (M/N)0=3.25 for the reaction of pure tritium with oxygen. Material balance measurements indicate that little or no peroxide appears in the product.
Temperature Dependence of Ultrasonic Velocity in Plastics
Authors: Subrahmanyam S. V.
Published: April 2005

The composite piezoelectric oscillator method has been employed to study the temperature dependence of the velocity of ultrasonic waves in Perspex and polystyrene plastics. While confirming a previously reported transition in Perspex at 60°C, the results show the existence of a transition in polystyrene also at 70°C for the first time.
Influence of Rate of Shear on the Apparent Viscosity of A—Dilute Polymer Solutions, and B—Bulk Polymers
Authors: Bueche F.
Published: April 2005

The measured viscosity of bulk polymers and their solutions varies with the magnitude of the applied shearing stress. In this paper we show that this is a natural consequence of the fact that the molecules are caused to rotate by the shearing action. This rotation gives rise to sinusoidal forces which alternately stretch and compress the molecules. The viscous behavior of such a system is shown to be analogous to that of a spring immersed in a viscous medium and being acted upon by sinusoidal viscous forces. We have treated the problem quantitatively using the method of a previous paper. Good agreement is obtained between theory and experiment without the aid of adjustable parameters. It is found that, if the molecule is considered shielded, the theory accurately represents the experimental data for dilute solutions. The behavior of the bulk polymer is well represented by means of the free draining approach. It is pointed out that the variation of the viscosity of dilute polymer solutions with the rate of shear may provide a convenient method for determining molecular weights of coiling type polymers.
Absolute Yield of the Ferrous Sulfate Oxidation Reaction
Authors: Weiss J. , Bernstein W. , Kuper J. B. H.
Published: April 2005

The absolute yield of the ferrous sulfate oxidation reaction, under the influence of ionizing radiation, has been determined. A polystyrene, parallel plate ionization chamber, filled with argon, nitrogen, or air, was used to measure the energy absorbed per unit volume of the solution through the application of the Bragg-Gray principle. The ionization current was extrapolated to zero changer spacing. In related experiments the average ionization potential of polystyrene was determined to be approximately 61.0 v; the value of W for air for electrons was determined to be 34.3 ev by comparison with argon and nitrogen. The G value obtained in this experiment using the three gases was 15.9±0.5 ions/100 ev, in good agreement with calorimetric and cathode-ray bombardment measurements.
Cation Distribution and g Factors of Certain Spinels Containing Ni++, Mn++, Co++, Al+++, Ga+++, and Fe+++
Authors: Greenwald Selma , Pickart Stanley J. , Grannis Frederick H.
Published: April 2005

X-ray measurements on NiOAl2O3, MnOAl2O3, and CoOAl2O3 show that the Ni spinel is almost completely inverted, the Mn partially so, and the Co compound almost completely normal. This information combined with the magnetic susceptibility vs temperature data yields a g-value of approximately 4.0 for both tetrahedrally coordinated Ni++ and for octahedrally coordinated Co++. X-ray measurements indicate that the Ni++ ion also prefers the octahedral site in NiOGa2O3, NiOFe1.00Al1.00O3, and NiOFe0.25Al1.75O3.
Magnetism and electronic structure of triplet binuclear niobium complexes in inorganic glasses, organic ligand environment, and polymers
Authors: Rakhimov R. R. , Arrington S. A. , Jackson E. M. , Hwang J. S. , Prokof'ev A. I. , Alexandrov I. A. , Aleksandrov A. I.
Published: April 2005

We investigated paramagnetic properties of binuclear niobium complexes Nb–O–Nb with two nonequivalent Nb4+ ions in lithium–niobium phosphate glasses (LNPG), in the environment of catechol/ortho-quinone ligands and in polyethylene. Experimental electron paramagnetic resonance spectrum analysis revealed nonequivalent distribution of the charge and electron spin density between two Nb atoms. Mechanochemical interaction of LNPG with an organic donor–acceptor mixture catechol/ortho-quinone followed by organic solvent extraction leads to the formation of a new binuclear complex with catechol/ortho-quinone ligands. This complex can be further incorporated into polyethylene matrix to form the complex with properties close to the complex in LNPG.
The role of grain boundaries in determining the transport properties of magnetite
Authors: Mertens D. C. , Montfrooij W. , McQueeney R. J. , Yethiraj M. , Honig J. M.
Published: April 2005

We present magnetoresistance and Hall-effect measurements on single-crystal magnetite (Fe3O4) close to the Verwey transition TV=123.8K. We show that the formation of grain boundaries accompanying the reduction in crystal symmetry plays a significant role in the electron-scattering mechanism, and that grain boundaries can account for the apparent change in sign of the charge carriers below TV.
Ultrafast demagnetization of Co25Ni75∕Pt multilayers with perpendicular anisotropy at elevated temperatures
Authors: Wilks R. , Hicken R. J. , Ali M. , Hickey B. J.
Published: April 2005

Ultrafast demagnetization has been studied in Si∕Pt(160Å)∕[Co25Ni75(x)∕Pt(8Å)]20 (x=3, 4.5, and 6 Å) multilayers with perpendicular anisotropy by magneto-optical pump-probe measurements in the polar geometry. Time-resolved measurements made in the saturated state showed that maximum demagnetization was achieved within 300 fs. Hysteresis loops were measured at a time delay of 1.3 ps for temperatures from 20 to 300 °C. The Curie temperature was found to increase from 150 to 250 °C with increasing Co25Ni75 thickness. By comparing the loops obtained with and without pump excitation, the increase in electron temperature due to the pump was estimated to be about 60 K.
Inhibition of Nd magnetic order in NdFe1−xCoxO3 by magnetic vacancies
Authors: Bartolomé F. , Bartolomé J.
Published: April 2005

The low-temperature specific heat of NdFe1−xCoxO3 (x=0, 0.03, 0.1, 0.25, and 0.5) has been measured to study the magnetic ordering of the Nd sublattice as a function of Co content. The results, satisfactorily explained by a mean-field model, show the inhibition of the Nd cooperative ordering for x⩾0.1.
Spin reorientation of Fe film with an ultrathin Co underlayer on Cu (001) substrate
Authors: Ren Y. , Gao C. L. , Zhang Z. Z. , Ma B. , Jin Q. Y. , Ahmad E. , Xu Y. B.
Published: April 2005

The magnetic properties of the ultrathin Fe∕Co∕Cu(100) films grown at 110K with Co underlayer thickness below 2 monolayers (ML) are investigated by means of the in situ magneto-optical Kerr effect. The spin reorientation transitions (SRT) from out-of-plane to in-plane influenced by the Co underlayer are observed. A simplified bilayer growth mode of Co is introduced to fit the experiment results, obtaining that the true critical Fe thickness of a SRT if without structural transformation for a fct Fe on Cu(001) is about 4.6 ML, the same value as the previous Co capping experiment.
Dependence of spatial coherence of coherent suppression of magnetization precession upon aspect ratio in Ni81Fe19 microdots
Authors: Barman A. , Kruglyak V. V. , Hicken R. J. , Scott J. , Rahman M.
Published: April 2005

Coherent suppression of magnetization dynamics in circular microdots of Ni81Fe19 has been observed by time-resolved scanning Kerr effect microscopy. The applied pulsed field rose sharply, stimulating precession, and then exhibited an oscillatory behavior. For certain values of the static magnetic field the precession was suppressed at the point at which the magnetization lay in the sample plane. Time resolved images confirmed that coherent suppression had occurred at the center of the element, but nonuniformity was observed at the edges of the element, which became greater with decreasing aspect ratio. The nonuniform magnetization dynamics result from the dephasing of confined spin wave modes, suggesting that a more involved pulse shaping scheme may be required to coherently suppress the full mode spectrum.
Exchange coupling in pure hcp Gd and magnetostructural transition in Gd5(Si2Ge2)
Authors: Samolyuk G. D. , Antropov V. P.
Published: April 2005

The electronic structure and magnetic properties of Gd and Gd5(Si2Ge2) systems were studied using the band structure approach. Multiple-scattering formalism of exchange coupling calculation was implemented and Curie temperature was calculated in pure Gd. The decrease of exchange coupling in Gd5(Si2Ge2) through structural transformation leads to first-order magnetostructural phase transition with large value of ∣∂H∕∂T∣ and giant magnetocaloric effect.
Ferromagnetic phase boundary in the bond frustrated Heisenberg model
Authors: Beath A. D. , Ryan D. H.
Published: April 2005

We determine the ferromagnetic phase boundary for the short range ±J bond frustrated Heisenberg model in three dimensions using a very efficient Monte Carlo algorithm which eliminates the critical slowing down usually experienced at a second order phase transition. The phase boundary is identified by measuring the correlation length directly, a method which we show to be superior to more conventional methods such as the crossing of the Binder cumulant. The critical concentration of antiferromagnetic bonds beyond which ferromagnetism is lost is xc=0.208(2).
Study of the electronic structure of CaFeO3
Authors: Yang J. B. , Kim M. S. , Cai Q. , Zhou X. D. , Anderson H. U. , James W. J. , Yelon W. B.
Published: April 2005

We have studied the charge disproportionation phenomenon in CaFeO3 using the local-spin density approximation with the on-site Coulomb interaction parameter U and exchange parameter J. The calculation reveals that the total number of the 3d electrons is about 5.1 for both Fe(1)(Fe5+) and Fe(2)(Fe3+) atoms, and that there are about 0.25 electron holes in the O-2p band. Therefore, the charge disproportionation can be more accurately described as 2d5L(Fe4+)=d5L2(Fe5+)+d5(Fe3+), where L denotes a hole in the oxygen 2p band, instead of 2d4(Fe4+)=d3(Fe5+)+d5(Fe3+). The hybridization between the Fe-3d and O-2p orbitals is stronger for Fe(1) than for Fe(2) due to the shorter Fe(1)–O bond. The hyperfine magnetic field contributed from conduction electron polarization is larger for Fe(2), resulting from a stronger s-d hybridization between the s orbital of Fe(2) and the d orbitals of its neighboring Fe(1) atoms. The on-site Coulomb repulsion and the exchange interaction increase the splitting between the occupied spin up and unoccupied spin down bands of Fe atoms. Fe-3d electrons become localized and the occupied d-band shifts to a lower energy range, even below the O-2p level. The calculated magnetic moments, hyperfine fields, and electron charge density agree well with the experimental data.
Spin polarization of electrons in Landau spin orbit coupling semiconductor system
Authors: Tan S. G. , Jalil M. B. A. , Teo K. L. , Liew Thomas
Published: April 2005

We present a device model that couples electron spin to the crystal field, external magnetic, and transverse electric field Ey, such that current jx transport in the ballistic regime is produced. As Ey modulates jx and its polarization P at a particular distance y, our model shows that the Landau spin-orbit system can implement the functions of a spin-field-effect transistor. We have found that a net P can be obtained in the z axis, thus allowing resistance detection to be performed in that axis. Further calculations show spatial variation of P across the cyclotron diameter that increases with higher Landau levels.
Electronic and magnetic phase diagram of La0.5Sr0.5Co1−xFexO3(⩽x⩽0.6) perovskites
Authors: Phan The-Long , Yu Seong-Cho , Van Khiem Nguyen , Phan Manh-Huong , Rhee Jang Roh , Phuc Nguyen Xuan
Published: April 2005

Spin dynamics and magnetic frustration effects in La0.5Sr0.5Co1−xFexO3 (0⩽x⩽0.6) compounds were systematically studied by means of resistivity, dc magnetization, ac susceptibility, and electron-spin-resonance spectra. The Fe substitution caused a metal-semiconductor transition for x⩽0.3 compositions whereas the only semiconducting state behaved for x>0.3 compositions. With increasing Fe-doping levels, the ferromagnetic–paramagnetic transition temperature, TC, decreased from 250 (x=0) to 166K (x=0.4). A spin-glass behavior was observed for x>0.4 compositions and is attributed to the frustration of random competing exchange interactions, namely, the ferromagnetic Co3+–Co4+ double-exchange interaction and the antiferromagnetic interactions such as Co–O–Fe and Fe–O–Fe. The internal dynamic properties of the samples were elucidated by the electron-paramagnetic-resonance spectra. An electronic and magnetic phase diagram of La0.5Sr0.5Co1−xFexO3 is drawn up.
Spin dynamics and magnetic frustration effects in La1−xSrxCoO3 (<x⩽0.5) compounds
Authors: Khiem Nguyen Van , Phuc Nguyen Xuan , Phan The-Long , Yu Seong-Cho , Phan Manh-Huong
Published: April 2005

La 1 − x Sr x Co O 3  (0<x⩽0.5) have been thoroughly studied by means of dc magnetization, ac susceptibilities, and electron-spin-resonance (ESR) spectra. Spin-glass behavior and its transition process for x<0.2 compositions appeared to occur at temperature Tg ranging from 14.6to68K, whereas for further strontium substitution the system was characterized by growing ferromagnetic clusters. The frequency dependence of the spin-glass freezing temperature Tf has been analyzed using the conventional critical slowing-down scaling law. The temperature dependence of Ta with respect to the external magnetic field Hex obeyed an exponential function of θa=Ta∕TC∝−Hexn. A complete magnetic phase diagram of La1−xSrxCoO3 is drawn up. Besides, the internal dynamics in the samples are elucidated by the ESR spectra. The results obtained provide more insights into the nature of spin dynamics and so-called magnetic frustration phenomena in such a cobaltate system.
Inductive time-domain measurement of magnetization dynamics in epitaxial Fe1−xCox single and double layers
Authors: Martin T. , Becker B. , Ganzer S. , Hagler T. , Sperl M. , Bayreuther G.
Published: April 2005

A pulsed inductive microwave magnetometer (PIMM) is used to examine magnetization dynamics. The thin film sample is brought into close proximity to the coplanar waveguide, which allows for simple changing of samples. The angle between the easy axis (e.a.) and field direction can easily be varied by rotation of the sample on the waveguide. The magnetization dynamics, i.e., precessional frequency, decay time, and precessional amplitude, are determined with respect to this angle or the bias field for epitaxial Fe1−xCox films with different anisotropies. The two precessional motions of a magnetic double layer (FeCo∕Au∕Ni80Fe20) where resolved with the PIMM, which is promising for future investigations on exchange coupled layers.
Absence of Kondo lattice coherence effects in Ce0.6La0.4Pb3: A magnetic-field study
Authors: Pietri Richard , Rotundu Costel R. , Andraka Bohdan , Daniels Bryan C. , Ingersent Kevin
Published: April 2005

The specific heat of polycrystalline Ce0.6La0.4Pb3 has been measured in magnetic fields ranging from 0to14T. After subtraction of a lattice contribution, the specific heat between 1K and 10K is well described by the S=12 single-impurity Kondo model with just one adjustable parameter: the zero-field Kondo temperature. In particular, the variation in the temperature and the height of the peak in C vs T is captured with good accuracy. This fit suggests that lattice coherence effects play no significant role in the magnetic-field response of this concentrated Kondo system.
Magnetic properties of YIG (Y3Fe5O12) thin films prepared by the post annealing of amorphous films deposited by rf-magnetron sputtering
Authors: Kang Young-Min , Wee Sung-Hun , Baik Seong-Il , Min Seong-Gi , Yu Seong-Cho , Moon Seung-Hyun , Kim Young-Woon , Yoo Sang-Im
Published: April 2005

We report magnetic properties of Y3Fe5O12 (YIG) films on thermally oxidized Si (100) and (Gd3Ga5O12) GGG (111) substrates. Amorphous YIG films with the cation ratio Y:Fe=3.04:4.96, deposited by rf-magnetron sputtering at room temperature in pure argon atmosphere, were crystallized by postannealing (600–900 °C) of amorphous films in air and in 500 ppm oxygen. While postannealed YIG films on GGG substrates were well textured, those on Si (100) were randomly oriented. High-quality YIG films could be better obtained in the reduced (500 ppm O2) oxygen atmosphere than air since more effective YIG growth during annealing process and lower FMR linewidth (ΔH) of films could be achieved.
Universal scaling functions and multi-critical points in the site frustrated Heisenberg model
Authors: Beath A. D. , Ryan D. H.
Published: April 2005

Recently, the ordering scenario of three-dimensional site frustrated Heisenberg models has been challenged. The existence of a decoupled tetracritical point (DTP) where ferromagnetic (FM) and antiferromagnetic (AF) order occur simultaneously has been modified to include a line of multicritical points where both FM and AF occur simultaneously. In addition, numerous studies claim that, within the mixed phase, critical exponents are altered from Heisenberg values. Here we show that within the narrow region of proposed multicritical points, the transition temperatures away from the tetracritical point are indeed distinct, confirming the occurrence of a DTP. In addition, we show a universal scaling collapse of the magnetization both away from, and within, the mixed phase using Heisenberg exponents, demonstrating that the stable fixed points are within the Heisenberg universality class.
Theory of solvent influence on reaction dynamics
Authors: Neufeld A. A.
Published: April 2005

A generalization of the recently published quantum-classical approximation [A. A. Neufeld, J. Chem. Phys., 119, 2488 (2003)] for the purposes of reaction dynamics in condensed phase is presented. The obtained kinetic equations treat a solvent influence in a nonphenomenological way, account for the change of the free energy of the surrounding media, allow for different solvent dynamics in each reaction channel, and constitute a powerful framework for an accurate modeling of solvent effects, including ultrafast processes. The key features of the approach are its differential form, which considerably facilitates practical applications, and well defined wide applicability limits. The developed methodology fully accounts for an arbitrary long memory of the canonical bath and covers solvent-induced processes from a subpicosecond time scale.
Penning ionization of N2O molecules by He*(2S3,1) and Ne*(P2,3) metastable atoms: A crossed beam study
Authors: Biondini Francesco , Brunetti Brunetto G. , Candori Pietro , De Angelis Filippo , Falcinelli Stefano , Tarantelli Francesco , Moix Teixidor Marc , Pirani Fernando , Vecchiocattivi Franco
Published: April 2005

The energetics of [Rg⋯N2O]* autoionizing collision complexes (where Rg=He or Ne) and their dynamical evolution have been studied in a crossed beam apparatus, respectively, by Penning ionization electron spectroscopy (PIES) and by mass spectrometry (MS) techniques in the thermal energy range. The PIES spectra, detected by an electron energy analyzer, were recorded for both complexes at four different collision energies. Such spectra allowed the determination of the energy shifts for Penning electron energy distributions, and the branching ratios for the population of different electronic states and for the vibrational population in the molecular nascent ions. For the [Ne⋯N2O]* collision complex it was found, by MS, that the autoionization leads to the formation of N2O+, NO+, O+, and NeN2O+ product ions whose total and partial cross sections were measured in the collision energy range between 0.03 and 0.2eV. The results are analyzed exploiting current models for the Penning ionization process: the observed collision energy dependence in the PIES spectra as well as in the cross sections are correlated with the nature of the N2O molecule orbitals involved in the ionization and are discussed in term of the Rg–N2O interaction potentials, which are estimated by using a semiempirical method developed in our laboratory.
Growth processes and surface properties of diamondlike carbon films
Authors: Liu Dongping , Zhang Jialiang , Liu Yanhong , Xu Jun , Benstetter Günther
Published: April 2005

In this study, we compare the deposition processes and surface properties of tetrahedral amorphous carbon (ta-C) films from filtered pulsed cathodic arc discharge (PCAD) and hydrogenated amorphous carbon (a-C:H) films from electron cyclotron resonance (ECR)-plasma source ion implantation. The ion energy distributions (IEDs) of filtered-PCAD at various filter inductances and Ar gas pressures were measured using an ion energy analyzer. The IEDs of the carbon species in the absence of background gas and at low gas pressures are well fitted by shifted Maxwellian distributions. Film hardness and surface properties show a clear dependence on the IEDs. ta-C films with surface roughness at an atomic level and thin (0.3–0.9 nm) graphitelike layers at the film surfaces were deposited at various filter inductances in the highly ionized plasmas with the full width at half maximum ion energy distributions of 9–16 eV. The a-C:H films deposited at higher H∕C ratios of reactive gases were covered with hydrogen and sp3 bonded carbon-enriched layers due to the simultaneous interaction of hydrocarbon species and atomic hydrogen. The effects of deposited species and ion energies on film surface properties were analyzed. Some carbon species have insufficient energies to break the delocalized π(nC) bonds at the graphitelike film surface, and they can govern film formation via surface diffusion and coalescence of nuclei. Dangling bonds created by atomic hydrogen lead to uniform chemisorption of hydrocarbon species from the ECR plasmas. The deposition processes of ta-C and a-C:H films are discussed on the basis of the experimental results.
Breathers and thermal relaxation as a temporal process: A possible way to detect breathers in experimental situations
Authors: Castrejón Pita A. A. , Castrejón Pita J. R. , Sarmiento G. A.
Published: April 2005

Breather stability and longevity in thermally relaxing nonlinear arrays is investigated under the scrutiny of the analysis and tools employed for time series and state reconstruction of a dynamical system. We briefly review the methods used in the analysis and characterize a breather in terms of the results obtained with such methods. Our present work focuses on spontaneously appearing breathers in thermal Fermi–Pasta–Ulam arrays but we believe that the conclusions are general enough to describe many other related situations; the particular case described in detail is presented as another example of systems where three incommensurable frequencies dominate their chaotic dynamics (reminiscent of the Ruelle–Takens scenario for the appearance of chaotic behavior in nonlinear systems). This characterization may also be of great help for the discovery of breathers in experimental situations where the temporal evolution of a local variable (like the site energy) is the only available/measured data.