bluuebunny/crossref_metadata_2025_split huggingface dataset:
Capacitance and Conductance Effects in Photoconducting Alkali Halide Crystals
Authors: Macdonald James Ross 
Published: April 2005

Measurements of the ac and dc response of illuminated F-centered potassium bromide single crystals have been carried out. The dependence of crystal capacitance and conductance on frequency, light intensity, electrode character and separation, F-center concentration, applied voltage, temperature, and optical bleaching time have been investigated. Most of the measurements were made on crystals containing both U and F centers, but a few were also made on additively colored and plain untreated crystals for comparison.
It was found that F centers in U-centered crystals bleached much slower under strong illumination than did those in additively F-centered crystals. The frequency response of the crystals depended significantly upon whether the electrodes were blocking or rectifying, but in both cases it was characterized by a single relaxation time given by the quotient of a series capacitance C0 and G∞, the normal conductance of the crystal. C0 was found to be independent of all variable parameters except dark storage and bleaching time and is thought to arise from a charge-free layer located at one or both electrodes. Space-charge capacitance effects were apparently largely hidden by C0 but did probably produce a small voltage-dependent non-linearity observed at low frequencies with high applied voltages. G∞, and thus the conduction-band electron concentration, depended linearly on light intensity over a wide range but underwent a transition from linear dependence on F-center concentration to independence thereof at high concentrations. Partly bleached crystals in total darkness exhibited appreciable conductivity, probably electronic in character. Most of the results on U-centered crystals can be tentatively explained in terms of electron trapping by negative-ion vacancies, F centers, interstitial hydrogen atoms, and hydrogen atoms in negative-ion vacancies.
Infrared Emission and Absorption in an Ammonia-Oxygen Diffusion Flame
Authors: Dows David A. , Whittle Eric , Pimentel George C. 
Published: April 2005

An ammonia-oxygen diffusion flame has been studied spectroscopically in the infrared region using a flat diffusion flame of the kind described by Wolfhard and Parker. The emissions of OH, NH3, and H2O and the absorptions of NH3 and H2O have been studied as a function of position in the flame. Combined with the information obtained earlier by Wolfhard and Parker concerning the distributions of OH, NH, NH2, and O2, a complete description of the flame is possible. Evidence is presented that OH is in vibrational as well as rotational equilibrium in the flame.
No evidence of infrared emission by NH or NH2 could be found.
On the Electronic Structure and Electronic Spectra of Ethylene-Like Molecules
Authors: Parr Robert G. , Pariser Rudolph 
Published: April 2005

A previously given theory of the electronic spectra and electronic structure of complex unsaturated molecules is applied to ethylene-like molecules, molecules such as ethylene itself, propylene or formaldehyde, which have two π electrons and two atomic π orbitals available for π-bond formation. Relations are derived among electronic excitation energies, intensities of electronic transitions, extra-ionic resonance energies and dipole moments of such molecules. Relative electronegativities are shown to play an important role in these relations, where the effective electro-negativity of an atom is Mulliken's electronegativity (the mean of the appropriate atomic valence-state ionization potential and electron affinity) plus the total attraction of the valence electron of the atom for all other atoms in the molecule.
The analysis yields the result that the dipole moment due to a slight bond heteropolarity is proportional to the electronegativity difference of the bonded atoms, the extra-ionic resonance energy to its square. Proportionality factors are given absolutely by the theory. It is pointed out that the theory of a two-electron σ bond is formally the same, moreover, so that a derivation is provided for the familiar electronegativity relations of Pauling. Theoretical and empirical values for the proportionality factors are found to agree reasonably well for both π bonds and σ bonds.
The formulas given cover multiple perturbations of any type which may be considered not to add (or subtract) π electrons or π orbitals. They thus provide a scheme for quantitative evaluation of inductive effects in ethylene-like molecules. Systematic consideration of mesomeric effects is deferred, but an outline of the procedure which may be used for their study is given, using mono-substituted ethylene as an example.
To illustrate the use of the formulas, to bring out the relationships between the method and the work of other authors, and to see whether the method has promise for σ-electron systems, calculations are made of the electronic spectrum of ethylene, the twisting force constant of ethylene, the ionization potential and electron affinity of ethylene, the electronic spectrum and dipole moment of formaldehyde, and the electronic spectrum, ionization potential, and binding energy of the hydrogen molecule.
Measurement of the Magnetic Susceptibility of Manganese Nitride Mn5N2 by a Microvibration Method
Authors: Yousef Y. L. , Girgis R. K. , Mikhail H. 
Published: April 2005

The susceptibility-temperature relationship of carefully prepared manganese nitride Mn5N2 was measured over the temperature range —180°C to 530°C. The Curie-Weiss law χ=C/(T—θ) was found to hold, with θ=—1070 and C=0.0316 emu deg/g. The effective Bohr magneton number is 3.94 per Mn, and is in reasonable agreement with the theoretical value 3.87 for 3 unpaired electrons. This suggests that Mn5N2 behaves as a coordination compound with 4 electron-pair bonds.
A new microvibration technique, particularly suitable for susceptibility investigations of materials available in small amounts, has been developed for the present work. The underlying principle is to modulate the magnetic field and to translate the periodic force on the material into a periodic displacement of an elastic strip. The force is measured dynamically in terms of a compensating electrostatic force, an electronic circuit being used as a null detector. Accuracy to 10—4 dyne is claimed.
Analysis of Spin-Spin Multiplets in Nuclear Magnetic Resonance Spectra
Authors: McConnell H. M. , McLean A. D. , Reilly C. A. 
Published: April 2005

A systematic procedure is developed for the analysis of the spin-spin multiplets that are observed in the high-resolution NMR (nuclear magnetic resonance) spectra of liquids. It is shown how the symmetry properties of nuclear spin functions can be used to simplify the interpretation of NMR multiplets in terms of the empirical quantities, chemical shifts, and spin-spin coupling constants. It is also pointed out that when NMR multiplets have been properly interpreted in terms of these empirical quantities, it is then possible to predict theoretically relative intensities of multiplets to the same degree of precision as that involved in the measurement of multiplet frequency separations.
As an example the multiplet splittings of the H1 and F19 resonances in 1,1-difluoroethylene are analyzed using the procedure proposed in the present paper.
Infrared and Raman Spectra of Nitrogen Trifluoride
Authors: Pace E. L. , Pierce Louis 
Published: April 2005

The infrared spectrum of gaseous nitrogen trifluoride has been investigated with prism instruments in the range from 400 cm—1 to 3000 cm—1. The Raman spectrum of liquid nitrogen trifluoride has been investigated in the range from 400 cm—1 to 2000 cm—1. The fundamental frequency assignment made from the infrared data is ν1(A1) = 1031 cm—1, ν2(A1) = 642 cm—1, ν3(E) = 907 cm—1, and ν4(E) = 497 cm—1. The corresponding Raman shifts in the liquid are ν1(A1) = 1050 cm—1, ν2(A1) = 667 cm—1, ν3(E) = 905 cm—1, and ν4(E) = 515 cm—1.
Differences from the results of previous investigators appear either in the assignment of the fundamental frequencies or in the interpretation of the overtone and combination bands in the infrared spectrum. The present results are considered more reliable because of (1) the added weight of an investigation of the Raman spectrum and (2) the use of a sample of known high purity.
Coupling of the Out-of-Plane Bending Mode in Nitrates and Carbonates of the Aragonite Structure
Authors: Decius J. C. 
Published: April 2005

The infrared absorption of polycrystalline samples of KNO3 and BaCO3 in the form of Nujol mulls has been observed between 11.3 and 12.5 microns under conditions such that the rotational lines of the NH3 spectrum separated by 1.5 cm—1 could be clearly resolved. When the N15 or C13 content is increased to the order of 50 percent, fine structure is observed which is not present e.g., in NaNO3, which possesses a crystal structure similar to calcite. The fine structure is interpreted by postulating a force constant which couples the out-of-plane vibrations of nearest neighbors in the aragonite-type lattice.
Very satisfactory agreement between the calculated and observed spectra is then found; in the case of BaCO3, the vibrations of CO3 ions which occur in isotopic isolation, as pairs, triplets, and quadruplets are resolved. The significance of the coupling constant is discussed; in principle, it may be used to evaluate the dipole derivative for the mode under consideration.
Phase Diagram of Liquid Ozone-Oxygen System
Authors: Brown Callaway , Berger Abraham W. , Hersh Charles K. 
Published: April 2005

Vapor pressure composition data for liquid ozone-oxygen mixtures were obtained at —195.5°, —183°, and —180°C. The vapor pressure isotherms were used to construct the boiling point-composition line at one-atmos pressure. The vapor pressure of pure liquid ozone defines an upper limit for the partial pressure of ozone in the vapor in equilibrium with boiling liquid.
The vapor pressure of ozone-oxygen solutions deviates markedly from Raoult's law in a positive direction. It is suggested that the apparent boiling point maximum reported by Schumacher, which implies negative deviations, may be due to difficulties in analysis of ozone at high concentrations where it is subject to decomposition at ordinary temperatures.
Liquid-liquid equilibrium data are reported which indicate —180°C as an upper bound for the consolute temperature. The region of two liquid phases extends from 9 to 91 percent ozone by weight at —195.5°C, 29.8 to 72.4 percent at —183°.
Inertial Effects and Dielectric Relaxation
Authors: Gross E. P. 
Published: April 2005

The study of dielectric relaxation in compressed gases requires an extension of existing theory. As the gas pressure is lowered below several hundred atmospheres, the inertial response of the dipoles gives rise to large deviations from the Debye equations. The absorption and dispersion depend on collision time and frequency of applied field in a manner which is sensitive to the molecular constants and to the state of dynamical order of the compressed gas.
These phenomena are investigated by studying the response to an alternating electric field of a dilute solution of dipolar molecules in a nonpolar compressed gas. The dipoles are described by a classical distribution function which is a function of angular velocity, orientation, and time. We assume that the duration of collision may be neglected compared to the time between collisions, the period of the applied field, and the mean thermal period. The distribution function satisfies a kinetic equation; the effects of collisions are described by a collision kernel. One kernel yields a soft impact theory which is a generalization of Debye's Brownian motion treatment to include inertial effects. The complex polarization is given in the form of a convergent infinite continued fraction. Other models studied involve strong collisions and partial specular reflection.
A common feature of all models is that the Debye relaxation shape is found at high pressures. Inertial corrections are important in the region between one and a few hundred atmospheres; the corrections depend on the model. Another common feature is the way in which the discrete rotational lines are linked with the Debye spectrum. The collision frequency 1/τ increases with increasing gas pressure; at low pressures it is proportional to the width of a rotation line. At high pressures when the Debye shape is found, the relaxation time t* is given by t* = 1/τ(I/kT). Here I is the moment of inertia of the dipole, k is Boltzmann's constant, and T is the temperature of the reservoir. Thus the relaxation time varies inversely with time between collisions. The physical reason is that collisions hinder the drift motion of the dipoles which is the cause of the relaxation of the polarization.
At lower pressures the main contribution to the polarization arises from dipoles rotating with an angular frequency close to that of the applied field. This is related to the known result that the main contribution to the static polarization is from librating dipoles.
Thermodynamics of Sorption by Solids under Finite Strain with Particular Reference to Fibers
Authors: White Howard J. 
Published: April 2005

Equations have been derived expressing the conditions of equilibrium for a strained solid absorbent in contact with fluid absorbates. The results are more general than any previously derived and are not limited to infinitesimal strains or isotropic absorbents; it is necessary that the principal axes of stress and of strain coincide. The results are applied to a few cases involving various states of strain in fibrous absorbents such as might be encountered in the textile industry.
One result was obtained which was uniquely different from the usual thermodynamic relations involving hydrostatic pressure. Essentially, three different forms of Gibbs free energy appear. These differ in accordance with the way in which the extensive variable for the absorbent was defined.
Mechanism of Potential Inversion of the Joshi Effect
Authors: Mohanty S. R. 
Published: April 2005

The positive Joshi effect +Δi (i.e., the photoincrease of the current i) increases initially with the exciting ac potential V(&lt;Vm the ``threshold potential'') to a maximum at Vm, decreases precipitously and changes sign (to the negative effect—Δi, i.e., photosuppression of i) at an inversion potential ViI. Beyond ViI, —Δi first increases rapidly and diminishes slowly thereafter. A second inversion, —Δi→+Δi, obtains, in certain systems, at ViII in the region of high V. Oscillographic studies reveal simultaneous occurrence, at V&gt;Vm, of intrinsic (+Δi) and intrinsic (—Δi); the integrating current indicator shows the balance.
The initial +Δi at V&lt;Vm, and its enhancement with V, results from photoelectron emission from the (momentary) cathode of field diminished work function. At Vm, consequent to the continuous discharge and an electron residuum from the antecedent half-cycle, largely enhanced emission and space accumulation of negative ions (from attachment of the electrons) lead to incipience of (—Δi) due to inhibition of γ and ηθg processes. Electrons able to cross the barrier cause (+Δi). The observed co-occurrence of (+Δi) and (—Δi) follows. Beyond Vm, increase in emission due to field reduction of surface work function enhances space charge density and therefore (—Δi). Observed diminution in +Δi follows from the above, and the reduction in the number of photoelectrons able to cross the barrier. At ViI, (+Δi)=(—Δi) and therefore, ±Δi=0. Increase of —Δi above ViI also follows from the above considerations. The decrease in attachment probability P=f(p/F), where p is the gas pressure and F the field, leads to subsequent diminution of (—Δi) at large V. Increase in the associated (+Δi) is a contributory factor, and above ViII causes the observed positive effect.
Magnetic Annealing in Perminvar. II. Magnetic Properties
Authors: Nesbitt E. A. , Heidenreich R. D. 
Published: April 2005

Previous work on Alnico single crystals (permanent magnet alloy) showed that magnetic torque reversals are associated with an inhomogeneous structure. More recently, it has been found that alloys of iron, nickel, and cobalt in the Perminvar region also exhibit these torque reversals although the alloys are considered to be solid solutions. An inhomogeneous structure occurs simultaneously with the torque reversals in some of these alloys. The inhomogeneous structure has been observed by means of electron diffraction, and the observations have been interpreted to mean that there are faults in the lattice normal to [111] directions. The faults form in the temperature region where the magnetic field heat treatment is effective and their density is roughly proportional to the response of the magnetic field treatment. When the crystals are not heat treated in a field, the faults are arranged to have cubic symmetry and their magnetic anisotropy has cubic symmetry. When the crystals are heat treated in a magnetic field, electron diffraction indicates that the faults are usually affected also.
Evidence has been obtained that small amounts of oxygen as an impurity in Perminvar cause both the faulting and the heat treatment in a magnetic field. An extremely small amount of oxygen (0.0014%) is sufficient to cause such effects.
In a more detailed sense we feel that the magnetic anisotropy introduced by heat treatment in a magnetic field probably arises either from short range order within the faults or from the arrangements of the faults each of which is parallel to a (111) into regions whose shape anisotropy is along the direction of the magnetic field.
Magnetoreflection Experiments in Intermetallics
Authors: Wright George B. , Lax Benjamin 
Published: April 2005

Magnetoreflection experiments involving both intraband and interband transitions can provide valuable information about the electronic band structure of semiconductors. In the intraband experiments, performed near the plasma reflection edge, the application of a magnetic field splits the edge and results in the formation of two minima separated by the cyclotron frequency. It is thus possible to determine the cyclotron frequency directly, at room temperature, and for high carrier concentrations. When scattering losses are taken into account in the theory, it becomes possible to determine the carrier concentration, scattering time, and effective mass from the optical measurements alone. The theory of the effect is discussed for applied magnetic field transverse and parallel to the direction of propagation, and experimental results are presented for InSb, InAs, and HgSe. A consistent fit to Kane's theory for the variation of mass with concentration in InSb is obtained when previously published data have been corrected for reststrahl dispersion.
Interband magnetoreflection experiments can be useful in cases where high absorption coefficients or difficulty of preparing thin samples make transmission experiments unfavorable. This type of experiment yields information on energy band gaps, effective masses, and g factors. Experimental data for the direct transition in InSb are presented.
Optical Absorption Edge in GaAs and Its Dependence on Electric Field
Authors: Moss T. S. 
Published: April 2005

Values of absorption constant covering the range 1 cm−1 to 104 cm−1 have been derived from transmission measurements made on single-crystal gallium arsenide. The absorption edge is very steep up to ∼4000 cm−1, where there is a knee beyond which the absorption increases relatively slowly with photon energy. The energy bands have been calculated using Kane's theory. From these a theoretical absorption curve has been obtained which shows very good agreement with the experimental data.
Using semi-insulating material, it has been possible to measure the shift of the edge with applied electric field. The effect is small (∼200-μ ev shift for 5000-v/cm field) but is in good agreement with theory.
Energy of Spectrum and Scattering of Current Carriers in Gallium Arsenide
Authors: Nasledov D. N. 
Published: April 2005

Conductivity in impurity bands is observed in gallium arsenide at low temperatures. The impurity banding phenomena observed in n- and p-type crystals are markedly different due to the wide divergence in their effective masses. In the temperature interval where the crystal conductivity is determined by conduction in the impurity band, resistivity of n-type material decreases with increasing magnetic field.
The temperature dependences of carrier mobility indicate that at low temperature the impurity ions play the dominant role of the scattering centers. In order to investigate scattering processes more thoroughly, studies were made of the thermomagnetic Nernst-Ettingshausen effects which are very sensitive to the scattering mechanism. It was found that, in the case of nondegenerate specimens at low temperatures, scattering by impurity ions dominates, and at high temperatures by acoustical lattice vibrations; scattering by acoustical lattice vibrations becomes dominant even at low temperature in specimens of high degeneracy. Scattering was also investigated in indium arsenide and indium antimonide.
Production of High Ion Densities in Helium by Means of High Explosives
Authors: Seay G. E. , Seely L. B. , Fowler R. G. 
Published: April 2005

Temperatures of about 20 000°K with ion densities ranging from 1017 to 1018 cm−3 have been produced in helium by means of explosive-driven shocks. Helium was used because of its relatively simple structure, but this choice eliminated usual shock methods because of the high sound speed and high ionization potential. Shock waves having sufficient strength and planarity were obtained by reflecting against a glass plate initially strong shock waves produced by high explosives. Equilibrium calculations based on smear camera velocities of accurately plane shocks were used to determine the state of the gas behind the reflected shock wave.
The light emitted consisted of a continuum on which were superimposed shifted and broadened lines of the normal helium spectrum and forbidden lines as well. Time-resolved spectrograms showed evidence of a measurable relaxation time at the shock front but no evidence of significant radiative cooling of the gas behind the shock.
Under the conditions of these experiments, it was demonstrated that a quantitative prediction of the behavior of the helium states with principal quantum numbers 2, 3, and 4 requires consideration of the effects of electrons as well as ions.