bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropy, Heat Capacity, and Heats of Transition of 1,3,5-Trimethylbenzene
Authors: Taylor R. Dean , Kilpatrick John E.
Published: April 2005

The heat capacity and the heats and temperatures of fusion of 1,3,5-trimethylbenzene have been determined experimentally. This substance exhibits three melting points: at 228.424°K, at 223.346°K, and at 221.462°K. The only solid phase having reproducible heat capacities was found to be the one having the highest melting point. The entropy of the ideal gas at 25°C and one atmos pressure has been found to be 92.09±0.15 cal/deg mole.
Critical Isotherm and the Equation of State of Liquid-Vapor Systems
Authors: Widom B. , Rice O. K.
Published: April 2005

Pressure-volume-temperature data on xenon, carbon dioxide, and hydrogen are analyzed. Special attention is paid to the regions fairly close to, but not in the immediate neighborhood of, the critical point. It is shown that in each case the critical isotherm is of the fourth degree, one degree higher than that of the coexistence curve, as is required by the theorem of Rice. However, the relation between the critical isotherm and the coexistence curve is determined by the almost constant value of ∂2P/∂T∂ρ in the PVT region considered, and this is different from its value at the critical point. The critical isobar is also considered and it is shown that it is of the fourth degree near the critical point, but of lower degree further away. A general equation of state is deduced for the PVT region under discussion, and the implications of this equation of state with respect to the coexistence curve and the critical isotherm are considered.
Molecular Orbitals for the Hydrogen Molecule Ground State
Authors: Wallis Richard F.
Published: April 2005

The ground-state energy of the hydrogen molecule has been calculated using a wave function constructed from LCAO molecular orbitals. The effective nuclear charge in the MO for one electron is taken to be different from that for the MO for the second electron. The best value of the dissociation energy is found to be 3.565 ev for values of the effective nuclear charge equal to 1.5 and 0.9. A physical interpretation of these values of the effective nuclear charge is given. Calculations have also been made using a wave function having a variable ratio of homopolar terms to ionic terms and having two effective nuclear charges. The best value of the dissociation energy for this case is found to be 4.08 ev.
Conductances of Trimethylphenylammonium Chloride and Iodide in Water and in Dimethylformamide at 25°C
Authors: Sears Paul G. , Wilhoit Eugene D. , Dawson Lyle R.
Published: April 2005

The conductances of trimethylphenylammonium chloride and iodide in water and in dimethylformamide have been measured at 25°C. Solute concentrations ranged from 0.6 to 30×10—4N. Limiting equivalent conductances for the salts in both solvents have been evaluated by the Shedlovsky extrapolation method. Trimethylphenylammonium chloride and iodide are more conducting but only slightly more highly dissociated in water than in dimethylformamide. A possible explanation for the reversal of the magnitude of the conductance of the iodide and the chloride ions in very dilute solutions in these two solvents is given.
Vibrational Relaxation Times of Diatomic Molecules and Rocket Performance
Authors: Penny H. C. , Aroeste Henry
Published: April 2005

Computations are presented for the variation of vibrational excitation probabilities with temperature for mixtures of O2 and N2, and of HF and H2. The values of six different excitation probabilities in each mixture are reported for temperatures up to 3000°K. For each of the probabilities there is a lower temperature limit given, below which the theory of Schwartz, Slawsky, and Herzfeld, which is used here, is not applicable. Using the results for H2–HF mixtures, we present some considerations which suggest that the expansion through the de Laval nozzle for representative H2–F2 rocket motors may be taken as vibrational near-equilibrium flow.
Heat Capacity of NiF2 from 12 to 300°K. Thermodynamic Functions of NiF2. The Thermal Anomaly Associated with the Antiferromagnetic Ordering
Authors: Catalano Edward , Stout J. W.
Published: April 2005

The heat capacity of NiF2 has been measured calorimetrically between 12 and 300°K. There is an anomaly in heat capacity rising to a maximum of 9.23 cal deg—1 mole—1 at 73.22°K. The anomaly is associated with the antiferromagnetic ordering of the magnetic moments of the nickel ions. Values of heat capacity, entropy, enthalpy, and free energy are tabulated at selected temperatures. The entropy at 298.16°K is 17.59±0.04 cal deg—1 mole—1. For the reaction NiF2+H2=Ni+2HF, ΔH00=29.56±0.20 kcal and ΔH0=30.06±0.20 kcal at 298.16°K.
Self-Diffusion of Ions in Molten Electrolyte under the Influence of an Electric Field
Authors: Yang Ling , Simnad M.
Published: April 2005

By taking into account both self-diffusion and electric migration of the radioactive ions formed by the electrolytic dissolution of a radioactive metal anode, an equation has been derived for the distribution of the radioactivity as a function of the distance from the anode surface along the diffusion path. Based on this equation, the error involved in the direct determination of ionic mobility by measuring the distance of spreading of the radioactivity and neglecting the role of self-diffusion is analyzed. It is shown that for a system with a given diffusivity, the error decreases with the increase of the time of electrolysis, t, and the applied potential, E. To obtain the true ionic mobility, it is suggested that measurements should be made for a number of ``t'' or ``E'' values. The apparent ionic mobility obtained is then plotted against 1/t or 1/E and extrapolated to 1/t=0 or 1/E=0 to give the true value.
Effect of Isotopic Substitution on the Mass Spectra of Molecules. III. Carbon Dioxide, Theoretical Interpretation
Authors: Schaeffer Oliver A.
Published: April 2005

The relative changes in pattern for O18 and C13 substituted carbon dioxide are calculated. The frequencies for the isotopic carbon dioxide molecules and the associated normal coordinates are obtained for a harmonic potential function. These are then used as the basis for the ground-state vibrational wave functions. The bond breaking probability integrals are evaluated for various values of the ``critical'' internuclear separation rc, and a study is made of the change in predicted bond breaking ratios as a function of rc. The values of rc are chosen which give the experimental pattern for O16C12O16 and then the relative changes in pattern are calculated for the other molecules and are compared with experimental values. Especially striking is the fact that the calculation faithfully reproduces the change in pattern for the case of a heavier molecule, which is more likely to fragment than a lighter one, as well as for the reverse case. It is concluded that a Franck-Condon type calculation adequately describes the electron impact process in carbon dioxide.
Theory of Dielectric Relaxation for a Single-Axis Rotator in a Crystalline Field. II
Authors: Hoffman John D.
Published: April 2005

Previous work on the relaxation times associated with a polar single-axis rotator where the dipole may occupy three or four orientational sites by turning in a lattice point has been extended to include the more general case where the energies of the sites (as well as the intervening barriers) are all different. The results for these more general models tend to confirm the view that the presence of barriers of different magnitudes between the equilibrium orientations of a dipole can be the source of a set of discrete dielectric relaxation times.

The dielectric properties of some specialized three- and four-position models are then considered in detail. A very narrow or an extremely wide set of relaxation times can be obtained depending on the nature of the barrier system, and accordingly, a wide range of dielectric behavior can be accommodated. Despite the wide range of behavior, certain qualitative features (noted in Sec. VII in italics) appear to persist in many of the models. These features may be useful in applying the theory in a general way.

The equations given will facilitate the calculation of the properties of three- and four-position models not already considered.
Reaction of Oxygen Atoms with Ethylene
Authors: Cvetanović R. J.
Published: April 2005

Reaction of O-atoms, produced by mercury photosensitized decomposition of nitrous oxide, with ethylene has been studied at room temperature and 123°C. The primary step of the process appears to be a direct addition of the atom to the double bond to form an energy-rich intermediate which undergoes further reactions. The following products are formed: aldehydes (CH3CHO, C2H5CHO, and C3H7CHO), CO, CH4, C2H6, C3H8, C4H10, H2, very small amounts of some other substances and traces of HCHO. At 24°C O-atoms react with ethylene 22±5 times as readily as with n-butane. Assuming comparable pre-exponential factors for the two processes ΔE= — 1.9 kcal/mole, so that the activation energy of addition of oxygen atoms to the double bond in ethylene is estimated at close to 3 kcal/mole. In the presence of molecular oxygen the character of the reaction is profoundly changed.
Use of Molecular Quantum-Mechanical Approximations Exemplified in the Energy Calculation of the H3— System
Authors: Barker Roland S. , Eyring Henry , Baker Don A. , Thorne Charles J.
Published: April 2005

Certain approximations of molecular quantum mechanics are examined. The size of the resultant error due to approximate methods for specific multicenter integral evaluations are cited. Examination of the Sklar approximate multicenter electron repulsion formula together with the generalizations and extensions of Vroeland and Löwdin allow application of the underlying approximation principle to three center nuclear attraction integrals. Specific approximate formulation of these integrals is given.

The accumulation of computational errors arising from the many individual integral approximations in the energy evaluation of the linear H3— system is specifically examined. The ground state energy of this system found from the Heitler-London and Wang-like treatments were — 70 kcal/mole and — 84 kcal/mole for the Sklar type approximations, — 1 kcal/mole and — 19 kcal/mole for the Mulliken type approximations, and — 26 kcal/mole and — 41 kcal/mole for exact integral evaluations.

It is concluded that the Sklar type approximations, while preferable to the Mulliken type in a few specific evaluations lead like that formulation to considerable discrepancy between the over-all energy obtained for a polyatomic system. The Sklar approximations have the further disadvantage of requiring two-center integral evaluations not needed in the over-all energy calculations. However, both the Sklar and the Mulliken approximations do give a rapid method for evaluating ``best'' distance and effective charge parameters for use with more extensive exact integral variational method calculations.
Intramolecular Charge Transfer Spectra Observed with Some Compounds Containing the Nitro or the Carbonyl Group
Authors: Nagakura Saburo
Published: April 2005

A new method, which proved to be useful for the theoretical study of electron migration for the monosubstituted benzene molecule, is employed to interpret strong absorption bands observed with various unsaturated compounds containing the nitro or the carbonyl group. Consequently, it is shown that these absorptions correspond to the transition between two energy levels produced by the interaction of the highest occupied level of the electron donating group with the lowest vacant one of the electron accepting group, and that theoretical values of transition energies and oscillator strengths evaluated by use of the present method are in very good agreement with the observed values. Furthermore, the present interpretation of these absorptions is discussed in comparison with the earlier resonance viewpoint.
Perturbation Method for the Calculation of Molecular Vibration Frequencies. II. Generalization of the Theory
Authors: Higgs P. W.
Published: April 2005

The perturbation theory developed previously for calculating frequencies by Wilson's F and G matrix method is now generalized in two respects: the effects, on the one hand, of degeneracy amongst the approximate frequencies and, on the other, of interaction constants coupling the two classes of vibration are considered.
Perturbation Method for the Calculation of Molecular Vibration Frequencies. III. Skeletal Stretching Vibrations of Normal Paraffins
Authors: Higgs P. W.
Published: April 2005

The perturbation theory developed in a previous paper is applied to the skeletal vibrations of the zigzag configuration of the n-paraffins. By treating the CCC bending force constant as small compared with the CC stretching force constant the first-order correction to the stretching frequencies is obtained in closed form. It is compared with the corresponding term in the Kirkwood-Pitzer formula for the frequencies of long-chain paraffins.
Heat of Formation and Entropy of Titanium Tetrachloride from an Investigation of the Equilibrium: TiO2(s)+4HCl(g) = TiCl4(g)+2H3O(g)
Authors: Farber Milton , Darnell A. J.
Published: April 2005

The equilibrium, TiO2(rutile)+4HCl=TiCl4(g)+2H2O(g), was studied in the temperature range of 800—1400°K by means of a flow method in which HCl was passed over a sample of rutile. The heat of reaction was found to be 12.9 kcal/mole in this temperature range. This leads to a value of —182.9±0.5 kcal/mole for ΔHf of TiCl4(g) and —192.5±0.5 kcal/mole for ΔHf of TiCl4(l). The entropy of TiCl4(g) at 1100°K is found to be 124 cal/°/mole.
Infrared Spectra of Oxonium Halides and the Structure of the Oxonium Ion
Authors: Ferriso C. C. , Hornig D. F.
Published: April 2005

The monohydrates of the hydrogen halides exist as ionic crystals. The infrared spectra of OH3F, OH3Cl, OH3Br, OH3I, and OD3Cl at —195°C showed the four fundamental frequencies expected for a symmetrical pyramid at about 1100 cm—1 (ν2), 1700 cm—1 (ν4), 2600 cm—1 (ν1 or ν3), and 3200 cm—1 (ν1 or ν3). The high-frequency bands, which are very broad at —195°C, did not sharpen on cooling to 8°K, indicating that their breadth is caused by some frozen-in disorder.
Magnetism on Optical Excitation of Manganese-Activated Zinc Sulfide Phosphors
Authors: Oshima Keichi , Nagano Hiroshi
Published: April 2005

Changes of magnetic susceptibility accompanying the optical excitation of manganese-activated zinc sulfide phosphors were measured. It was found that there was some change in susceptibility for phosphors containing manganese more than 9.0×10-4 g Mn/g ZnS. While there was concentration quenching for manganese emission intensity at high manganese concentration, the value of susceptibility change increased monotonically with concentration. From these results it is concluded that the nonradiative process in concentration quenching does not affect much the excitation probability and the lifetime of the excited state which is of the multiplicity giving rise to the susceptibility change.
Structure and Internal Motion of C2F6 and Si2Cl6 Vapors
Authors: Swick D. A. , Karle I. L.
Published: April 2005

The molecular structure and internal motion of C2F6 vapor and of Si2Cl6 vapor have been investigated by means of the sector-microphotometer method of electron diffraction. Both molecules exhibit hindered internal rotation, with equilibrium in the trans position. The interdependence of the potential barrier and the modes of vibration other than the torsional is presented graphically. The values for the bonded distances are: C – F = 1.32±0.01 A, C – C = 1.56±0.03 A with ∠ CCF = 109½°±1½° and Si – Cl = 2.01±0.01 A, Si – Si = 2.24±0.06 A with ∠ SiSiCl = 109½°±1°.
Catalytic Activity Induced by Neutron Irradiation of Inert Silica
Authors: Weisz P. B. , Swegler E. W.
Published: April 2005

In pure silica gel, irradiation with 2 to 8×1018 fast neutrons/cm2 produced a significant increase in catalytic activity for the double-bond isomerization in hexene. The effect is believed to be due to lattice dislocations.
Second Approximation to the Thermal Diffusion Factor on the Lennard-Jones 12 :6 Model
Authors: Saxena S. C. , Srivastava B. N.
Published: April 2005

Several collision integrals useful for the calculation of the second approximation to the thermal diffusion factor have been evaluated for the Lennard-Jones 12:6 model and utilized to calculate [RT]2, the second approximation to the thermal separation ratio from the expressions developed by Mason for the exp-six model. It has been shown that the difference between [RT]1 and [RT]2 for the 12:6 model is very small and does not vitiate the method developed by us elsewhere for calculating the force constants from the thermal diffusion data. These considerations have been applied to argon and the results compared with the experimental data. A simple empirical relation connecting [RT]1 and [RT]2 has been derived for the Lennard-Jones 12:6 model.
Electronic States of the Naphthalene Crystal
Authors: McClure Donald S. , Schnepp Otto
Published: April 2005

The existing experimental data on the low-temperature fluorescence and absorption of naphthalene crystal is reviewed and correlated with our own data. Some preliminary work on crystals of C10D8 is included. A vibrational analysis of the first moderately strong absorption region, 31 476—33 700 cm—1 is made on the basis of the corresponding absorption of naphthalene in solid solution with durene. Some constants of the exciton theory of molecular crystals are obtained for the first and second excited singlet molecular states. Some discrepancies with the theory are pointed out; one of these is removed by calculating the crystal induced mixing of the two excited molecular states. Factor group splitting is found for certain vibronic levels of the ground and first excited state, but most vibronic levels of these states do not split appreciably.
Thermal Conductivities of Organic Vapor Mixtures
Authors: Bennett L. A. , Vines R. G.
Published: April 2005

The thermal conductivities of binary mixtures of organic vapors have been investigated in the temperature range 60—125°C. When nonpolar vapors of similar viscosity and molecular weight are used, the variation of conductivity with composition of the mixture is roughly linear. Mixtures of nonpolar and strongly polar vapors, on the other hand, exhibit pronounced maxima in the conductivity vs composition curves. The difference in behavior is due to the strong interaction between polar molecules on collision.
Absorption Cross Sections of Carbon Dioxide and Carbon Monoxide in the Vacuum Ultraviolet
Authors: Sun H. , Weissler G. L.
Published: April 2005

Absorption cross sections of CO2 and CO in the region from 1306 A to 374 A have been measured. The absorption spectrum of CO2 consists of strong resonance bands between 1306 A and 700 A, with one of them at 923 A showing an unusually large cross section of 117×10—18 cm2. A continuum with bands superimposed on it was observed to start at about 860 A or 14.4 ev which corresponded to the first ionization potential of CO2. From 700 A toward shorter wavelengths, the contour of the continuum was better defined and smooth with a broad maximum of 36×10—18 cm2 at 550 A and a total f-value of 4.4. The CO absorption between 1306 A and 955 A was less than 10—18 cm2. Prominent resonance bands appeared at 924 A and extended to 600 A. An absorption continuum could be identified between 876 A and 374 A showing maximum values of σ≃19×10—18 cm2 between 750 A and 550 A with perhaps a small dip of 15×10—18 cm2 at 644 A. The f-value of this continuum was 2.8.
Rate of Convergence of Madelung Series by the Method of Bertaut
Authors: Templeton David H.
Published: April 2005

A calculation is made of the correction to be applied to the Madelung constant when computed by a method given by Bertaut with a finite number of terms.
Nuclear Magnetic Resonance: Structure of the Amino Group I
Authors: Kromhout R. A. , Moulton W. G.
Published: April 2005

Line widths and second moments of the proton magnetic resonance absorption line of ten amines, amides, and amino acids have been measured. It is shown that hydrogen bonds in the amides and amino acids strongly affect the structure. New evidence for the existence of glycine in the dipolar form in the solid state is presented. The N–H bond distances in urea and glycine are calculated from observed second moments and are found to be 1.077±0.007 A and 1.074±0.014 A, respectively. The bond angles of the amino group are assumed tetrahedral in both cases in making the calculation.
Binary Diffusion of Similar or Isotopic Molecules in Three Component Systems
Authors: Senett William P. , Gollob Fred , Taylor T. I.
Published: April 2005

The application of Maxwell's equations to obtain the diffusion coefficient for the mixing of two gases in the presence of a fixed concentration of a third leads to an inconsistency so that only an approximate solution may be obtained. Since the approximation becomes better as the diffusing species become similar, isotopic species are a favorable case. The two bulb mixing problem for isotopic gradients in each of two molecular species but no molecular gradient as a whole is now solved as two independent three component systems leading to relatively simple equations. The validity of the treatment is confirmed by a series of experiments in which agreement between the calculated relaxation time and observed one is well within the estimated error of about 5%.
Raman and Infrared Spectra and Structure of 2,6-Dioxaspiro (3,3)heptane
Authors: Sirkar S. C. , Voelz Fred L. , Cleveland Forrest F.
Published: April 2005

The Raman spectrum of 2,6-dioxaspiro (3,3)heptane in the molten state and infrared spectra of CS2 and CCl4 solutions have been investigated. The polarization of the Raman lines of the liquid also has been studied. The results indicate a symmetry D2d for the molecule. The appearance of two extra strongly polarized Raman lines near the 2874K (kayser, cm—1) line, which corresponds to the totally symmetric C–H stretching oscillation, has been accounted for by assuming Fermi resonance between overtones of C–H bending vibrations and the symmetric C–H stretching mode.
Proton Magnetic Resonance of the CH3 Group. III. Reorientation Mechanism in Solids
Authors: Powles J. G. , Gutowsky H. S.
Published: April 2005

The proton magnetic resonance absorption has been reported to change with temperature in a manner suggesting hindred C3 rotational motions of the CH3 groups in several solid compounds. In this paper, the reorientation mechanism is considered more closely. The second moments of the absorption lines are calculated as a function of temperature for three types of motion. Similar predictions are obtained for two classical models, a Brownian type rotation by random angles and a random jumping between fixed positions 2π/3 apart. The results are different for the third model, a quantum-mechanical tunnel effect, for which approximate calculations are given.

The experimental data for methyl chloroform, 2,2-dinitropropane, and 2-chloro-2-nitropropane can be fitted either to a classical model or to the tunnel effect by adjusting the potential barrier to the reorientations. However, the activation energies for classical rotation are low, about 2.2 kcal mole—1 and the observed frequency factors of 107 are unexplained. The tunnel effect gives larger barriers, about 5 kcal, and the predicted frequency factors agree well with experiment. In the case of 2,2-dichloropropane a classical motion is indicated by the large frequency factor of 1012.
Force Constants, Infrared Spectrum, and Thermodynamic Properties of TiCl4
Authors: Hawkins N. J. , Carpenter D. R.
Published: April 2005

The spectrum of gaseous titanium tetrachloride was obtained in the rock salt and potassium bromide regions of the infrared. The thermodynamic functions Cp0, S0, and — (F0—E00)/T were calculated. The orbital valence force field constants were computed, and lead to the conclusion that hybridization changes may be significant in the F2-vibrations.
Magnetic Properties of Uranium Hydride
Authors: Gruen Dieter M.
Published: April 2005

The magnetic susceptibility of β UH3 has been measured in the temperature range 191°K to 603°K. From the high-temperature portion of the χ—1 versus T curve one calculates a magnetic moment of 2.79 Bohr magnetons, with Δ = —137°K. A ferromagnetic transition occurs in the neighborhood of 173°K. Magnetic moment measurements made in the temperature range 63°K to 196°K in fields of 1550 to 8700 oersteds can be extrapolated to yield a saturation magnetic moment of about one Bohr magneton.
Transient Response of Grain Boundaries and Its Application for a Novel Light Sensor
Authors: Mueller Rolf K.
Published: April 2005

Grain boundaries in n-type germanium and silicon carry a negative surface charge and constitute a potential barrier for electrons. The height of this barrier can be increased by applying an electrical pulse across the boundary or decreased by injecting holes. The relaxation time with which the perturbed barrier returns to its equilibrium value is for sufficiently low temperatures very large compared to the time necessary to change the barrier height. A theory of the transient response of a grain boundary to a pulse is given for the low temperature region. It is shown that the application of a pulse of given height results in a barrier height φs which is practically independent of the barrier height φa prior to the pulse. The transient current, however, depends markedly on φa. A novel photosensor based on this phenomenon is described, and preliminary experimental results are reported.
Microwave Techniques in Measurement of Lifetime in Germanium
Authors: Ramsa A. P. , Jacobs H. , Brand F. A.
Published: April 2005

New techniques are proposed for the measurement of lifetime in semiconductors by utilizing the absorption of microwave power by charge carriers. The densities of holes and electrons are varied by irradiation with light or the conduction mechanism. Agreement is found when the microwave absorption methods are compared with the more established photoconductivity decay techniques. One of the new methods offers an advantage in that electrode attachments are no longer required.
Ruby as a Maser Material
Authors: Kikuchi Chihiro , Lambe John , Makhov George , Terhune Robert W.
Published: April 2005

The reasons for the initial choice of ruby as a maser material are outlined and some measurements of the parameters in the spin Hamiltonian and of spin relaxation times are reported. The relative merits of single- and double-pump modes of operation of a four-level maser are discussed and measurements of the oscillator power for the two cases are included.
Synthesis of a (110) [001] Type Torque Curve in Silicon Iron
Authors: Dunn C. G. , Walter J. L.
Published: April 2005

The orientations and sizes of all the grains in a polycrystalline disk specimen of high-purity 3.25% silicon iron are measured to determine a calculated magnetic torque curve and the texture of the specimen. The torque results agree with the experimentally determined values. The curves approximate a (110) [001] single crystal torque curve, which is reduced about 75%, and thus indicate a possible texture consisting of about 25% (110) [001] and 75% random. The true texture obtained from the orientation data is found to have more than ten components, none of which is (110) [001]. Illustrations showing how a (110) [001] type torque curve may be synthesized from non-(110) [001] type components in the texture are given.
Electron Metallographic Evidence of Diffusion of Hydrogen through Tin Plate Containers
Authors: Lanterman Elma
Published: April 2005

Electron metallographs evidenced rupture and blistering of the exterior tin surface of containers which had failed prematurely due to excessive hydrogen formation by corrosion processes within the container when packed with grapefruit juice. The enlargement of grain boundaries of the base steel of tin plate due to hydrogen diffusion has been illustrated.
Dissociation of Solid SrO by Impact of Slow Electrons
Authors: Moore George E.
Published: April 2005

Dissociation of solid SrO by impact of electrons having energy below 400 v was measured by a mass spectrometer method. Positively and negatively charged dissociation products were observed with equal sensitivity; no uncharged products were observed with an arrangement having poorer sensitivity. The fundamental dissociation products are Sr+, Sr++, and O+ with essentially no O−. Surface impurities such as CO, Cl, F, and H were also abundant. The only source of chlorine found was an impurity in the original SrCO3, of about 1 part in 105. However, its abundance in the ion current is about equal to that of oxygen, and the yields of Cl+ and Cl− are about equal. All particles must come essentially only from the surface layers.

Yields of Sr+ and Sr++ increase with the square of electron density; yields of O+, Cl+, and Cl− increase, respectively, with the 1.5, 1.0, and 1.0 power of electron current density. The process is quite inefficient, the impact of 107 electrons giving about 1 fundamental dissociation product for 20 to 30 ma per cm2 of bombarding current. Yields are independent of electron energy from slightly above threshold to beyond 200 v, above which they decline slowly. Yields increase slightly with temperature, corresponding to activation energies of a few tenths of a volt.

At least some of the chlorine on the surface probably exists in the uncharged form; threshold energies are too low to convert a Cl− on the surface to a Cl+ in the vacuum. Removal of O+, Sr+, and Sr++ ions is discussed in terms of a crystal composed of singly charged Sr+ and O− ions; a process involving two incoming electrons in rapid succession on a minute area is apparently required for removal of an O+, Sr+, or Sr++ ion.
Electron Mirror Microscopy of Magnetic Stray Fields on Grain Boundaries
Authors: Mayer Ludwig
Published: April 2005

Experimental evidence is presented that electron mirror microscopy is particularly well suited for direct visual observation of magnetic stray fields at grain boundaries in magnetic materials. Silicon-iron disks were used as specimens. By mounting these specimens on a special magnetic stage of axial symmetry, the appearance and the growth of magnetic stray fields with increasing external applied magnetic fields could be observed directly, and motion picture recordings were taken from the viewing screen of the microscope. A series of electron mirror micrographs shown demonstrates that grain boundaries behave quite differently stray field-wise. The fact that magnetic stray fields on grain boundaries are now accessible to direct visual observation is considered valuable for many magnetic investigations. The still controversial subject of grain size effects on the magnetic properties of such important magnetic materials as silicon-iron is one subject which might profit from these potentialities inherent in electron mirror microscopy. This electronic observation method might also be helpful in grain boundary studies concerned with the basic physics of magnetics in such narrow regions of distorted order.
Spectrum of Thin Target Bremsstrahlung Bounded by a Forward Circular Cone
Authors: Hubbell J. H.
Published: April 2005

The Schiff expression for the cross section per nucleus, for thin-target bremsstrahlung into the angular and energy ranges dθ0 and dk, is integrated analytically over angle from zero to θ̄0. Results are shown for the case Z=78, E0 − mc2=40 Mev and x̄=0.5, 1, 2, 4, and 8, where E0 − mc2 is the kinetic energy of the incoming electron and x̄ is the reduced angle θ̄0E0/mc2. The fraction of the total cross section included in a cone of angle θ̄0 can be approximated to within 20% by x̄2/(1+x̄2). At x̄=1, or θ̄0=0.723°, the ratio of energy delivered by photons above (E0 − mc2)/2 to that below is 9% greater than for the limiting spectral shape at θ̄0=0, or that given by the Schiff expression at θ0=0, and 13% greater than for the spectrum integrated over all angles. For a target of finite thickness, multiple electron scattering should partially suppress the spectral dependence on x̄.
Magnetic Annealing in Perminvar. I. Structural Origin
Authors: Heidenreich R. D. , Nesbitt E. A. , Burbank R. D.
Published: April 2005

This paper deals with the results of an electron diffraction investigation of the structure of soft magnetic materials which exhibit magnetic annealing. The property of heat treatment in a magnetic field has been found to depend upon the oxygen content present as an impurity and is associated with distinct diffraction phenomena. A structural model based on an interpretation of diffraction results, magnetic properties, and oxygen content is presented.

The pertinent conclusions from this study are:

1. The ability of soft magnetic alloys containing Fe, Co, and Ni to exhibit magnetic annealing properties is due to oxygen present as an impurity.

2. An oxygen content of about 0.001% is sufficient to produce magnetic annealing with the proper heat treatment. An alloy containing only 0.0001% oxygen fails to respond to field heat treatment or is ``dead.''

3. The oxygen impurity produces magnetic activity in the alloy crystal (with proper heat treatment) by condensing into the (111) planes of the crystal, thus giving rise to a stacking disorder or fault. The term ``impurity fault'' has been introduced to describe this structural irregularity.

4. The oxygen impurity faults are presently thought to be aligned by magnetic annealing and are intimately connected with field heat treatment properties. If sufficient oxygen is available in the crystal, the faults thicken and organize to yield metal oxides.
Galvanomagnetic Properties of InSb
Authors: Weiss H.
Published: April 2005

In discussing the galvanomagnetic effects of semiconductors with high electron mobility one has to distinguish four main groups of parameters which influence these effects: (1) For InSb with practically no magnetoresistive effect on a long rod, an increase in resistance by a factor 38 can be reached in 10 000 gauss with appropriate shape (field disk). (2) Layers periodically changing their electron concentration produce an anisotropy of magnetoresistance. For certain specimen orientations the Hall coefficient depends on the magnetic field and a planar Hall effect is observed. Near a step of concentration one measures apparent negative resistances which are caused not by a retrograde current, but merely by rotation of the current lines. (3) If there are more than one type of charge carriers, it is difficult to know the concentration and mobility characteristic of a special type. Because of the high mobility ratio in InSb it is possible to state a hole mobility of 620 cm2/v sec in 150 000 gauss for pure material at room temperature. (4) After elimination of the influences of the above-mentioned points 1 to 3 one cannot find in InSb any magnetoresistive effect of electrons in the conduction band up to 150 000 gauss. The Hall coefficient is magnetic field independent up to this value of the magnetic induction for n-type InSb.
Band Structure Parameters Deduced from Tunneling Experiments
Authors: Hall R. N. , Racette J. H.
Published: April 2005

Measurements of the voltage and temperature dependence of tunneling in Ge and GaSb are presented which confirm the close proximity of the (000) and (111) conduction band edges in these materials. In the case of Ge, the energy separation of these edges is found to increase with increasing donor concentration.

Tunneling in the indirect semiconductor GaP shows no evidence for indirect (phonon-assisted) tunneling transitions. It is believed that tunneling in the junctions which we studied proceeds via deep-level impurities rather than between conduction and valence bands directly, thereby eliminating the requirement of wave number conservation.

Revised values for the zone-center longitudinal optical phonon energies as deduced from tunneling data in 3–5 and lead salt semiconductors are presented.
Energy Band Structure of Gallium Antimonide
Authors: Becker W. M. , Ramdas A. K. , Fan H. Y.
Published: April 2005

Resistivity, Hall coefficient, and magnetoresistance were studied for n- and p-type GaSb. The infrared absorption edge was investigated using relatively pure p-type, degenerate n-type, and compensated samples. Infrared absorption of carriers and the effect of carriers on the reflectivity were studied. The magnetoresistance as a function of Hall coefficient for n-type samples at 4.2°K gave clear evidence for a second energy minimum lying above the edge of the conduction band; the energy separation is equal to the Fermi energy for a Hall coefficient of 5 cm3/coulomb. The shift of absorption edge in n-type samples showed that the conduction band has a single valley at the edge, with a density-of-state mass md1=0.052 m. By combining the results on the edge shift, magnetoresistance, and Hall coefficient, it was possible to deduce: the density-of-states mass ratio md2/md1=17.3, the mobility ratio μ2/μ1=0.06, and the energy separation Δ=0.08 ev between the two sets of valleys at 4.2°K. Anisotropy of magnetoresistance, observed at 300°K, showed that the higher valleys are situated along (111) directions. The infrared reflectivity of n-type samples can be used to deduce the anisotropy of the higher valleys; tentative estimates were obtained. Infrared reflectivity gave an estimate of 0.23 m for the effective mass of holes. The variation of Hall coefficient and transverse magnetoresistance with magnetic field and the infrared absorption spectrum of holes showed the presence of two types of holes. Appreciable anisotropy of magnetoresistance was observed in a p-type sample, indicating that the heavy hole band is not isotropic; this was confirmed by the infrared absorption spectrum of holes. The results on the absorption edge in various samples seemed to indicate that the maximum of the valence band is not at k=0. However, it appears likely that transitions from impurity states near the valence band produced absorption beyond the threshold of direct transitions.
Galvanomagnetic Effects in III–V Compound Semiconductors
Authors: Beer A. C.
Published: April 2005

The influence of various structural characteristics in the III–V compounds on galvanomagnetic properties is discussed. Evidence for the scattering of charge carriers by polar optical modes is reviewed, and the behavior of Hall and magnetoresistance coefficients is examined in regard to the conduction band structure. Unique characteristics, imparted by light masses in certain bands, include high mobilities and large magnetoeffects associated either with transport in the band or with ionization energies of the impurity centers. The importance of avoiding inhomogeneities, either in specimen or in magnetic field, when measuring Hall coefficient or magnetoresistance in high-mobility materials is emphasized. Illustrations are given of the effects of nonuniformities in carrier concentration or in applied magnetic field on various galvanomagnetic phenomena.
Interband Faraday Rotation in III–V Compounds
Authors: Lax Benjamin , Nishina Yuichiro
Published: April 2005

Experimental investigation of Faraday rotation in III–V compounds has exhibited a striking singularity at photon frequencies just below the energy gap. A quantum theoretical result associated with the direct transition has been developed to explain the phenomenon. The treatment has been extended to include forbidden transitions which are readily applicable to such materials as InAs, GaAs, and GaSb where interband transitions between the split-off valence bands have been observed. The treatment for observing Faraday rotation by reflection has also been considered and experimental results in InSb at optical frequencies will be presented. The calculations have also been performed for degenerate semiconductors at low temperature.
Fundamental Reflectivity Spectrum of Semiconductors with Zinc-Blende Structure
Authors: Cardona Manuel
Published: April 2005

The fundamental reflectivity spectrum of several III–V and II–VI semiconductors is discussed and compared with the reflectivity spectrum of the group IV semiconductors. A general feature of these spectra is the presence of two peaks within the fundamental absorption region. The lower energy peak, which corresponds to a maximum in the refractive index, can be split into a doublet. This peak is probably due to direct transitions between the valence band extrema in the [111] direction at the edge of the Brillouin zone (L point) and the corresponding conduction band minima. The splitting of this peak corresponds to the spin-orbit splitting of the valence band extrema (L3). The second peak corresponds to a maximum in the combined density of states for the transitions. The temperature dependence of these peaks is also discussed.
Oscillatory Magnetoresistance in the Conduction Band of PbTe
Authors: Cuff K. F. , Ellett M. R. , Kuglin C. D.
Published: April 2005

Oscillatory behavior of the transverse magnetoresistance has been used to investigate the conduction band structure of PbTe. From the oscillatory periods, it is established that the minima in the conduction band consist of four equivalent 〈111〉 prolate ellipsoids with a mass anisotropy of approximately 5.5 and located at the Brillouin zone edge. The decay of the oscillation amplitudes with temperature yields a transverse ellipsoid mass of mT*=(0.030±0.005)m0. High field oscillations have been detected that point to the existence of a second band located at the center of the zone, having a mass of about 0.08 m0, and lying within ±0.002 ev of the ellipsoid minima. The phase of the oscillations suggests that spin splitting of the Landau levels may be quite large in PbTe.
Valence Bands in Lead Telluride
Authors: Allgaier R. S.
Published: April 2005

The magnetic field dependence of the Hall coefficient at 296° and 77°K, and the temperature dependence of the weak-field Hall coefficient and the resistivity between 296° and 77°K were studied in single-crystal samples of p-type PbTe having carrier concentrations ranging from 4.9×1017 to 1.7×1019 per cm3. The Hall data at 77°K are quantitatively consistent with magnetoresistance data which have previously established the presence of 〈111〉 ellipsoids in the valence band. They are not consistent with a low-temperature two-band model, proposed by Stiles from de Haas-van Alphen data at 4.2°K, unless the band edges lie at approximately the same energy (as Stiles found) and unless the carrier mobilities in the two bands are nearly alike. On the other hand, both the Hall and resistivity data above about 150°K do exhibit two-carrier effects suggesting the presence of a lower mobility band at an energy about 0.1 ev below those bands which are occupied at low temperatures.
Magnetotunneling in Lead Telluride
Authors: Rediker R. H. , Calawa A. R.
Published: April 2005

Rotation of a large magnetic field (∼60 kgauss) in a plane perpendicular to the direction of junction current in PbTe tunnel diodes produces a periodic behavior of this current. Diodes in which the junction current flow is along the [100], [110], or [111] crystallographic axis have been investigated. The observed anisotropies are consistent with a crystal with cubic symmetry whose constant energy surfaces in k space are ellipsoids of revolution oriented along the 〈111〉 crystalline axes. The magnetotunneling results are interpreted in terms of the effective motion of each ellipsoidal valley as the magnetic field is increased, valleys oriented at different angles to the electric field contributing with different weights to the tunneling current. Quantitative comparison awaits theory. Heavier mass bands close in energy to these ellipsoids, although unimportant by themselves in tunneling, may be necessary to explain the apparent position of the Fermi level with respect to the band edges. The excess current has the same anisotropy as the tunneling current; however, the thermal current does not show this anisotropy and therefore must be of different origin. Hump current, which was observed in two diodes, disappeared in magnetic fields above 3 kgauss.
Recent Studies of Bismuth Telluride and Its Alloys
Authors: Goldsmid H. J.
Published: April 2005

This paper reviews the work which has been carried out in these Laboratories during the past two years on single crystals of bismuth telluride and its alloys.

The combination of experiments on Faraday rotation with those performed previously on galvanomagnetic effects has established that there are 3- and 6-valley band structures associated with p- and n-type Bi2Te3, respectively. However, observations of the anisotropy ratio for the electrical conductivity and of the galvanomagnetic coefficients for heavily doped n-type material have shown that the shape of the equal-energy surfaces is dependent on carrier concentration. Similar conclusions have been drawn from the behavior of the Seebeck coefficient at low temperatures.

Measurements on Bi2Te3 at low temperatures and on alloys of Bi2Te3 have shown that the lattice thermal conductivity is particularly sensitive to the substitution of atoms of I, Se, or S for those of Te. It has also been shown that the anisotropy ratio for the lattice thermal conductivity is almost the same for the alloys as for pure Bi2Te3.
Model for the Electronic Transport Properties of Mixed Valency Semiconductors
Authors: Miller R. C. , Heikes R. R. , Mazelsky R.
Published: April 2005

It is shown that the simple ``hopping model'' for the transport processes of mixed valency semiconductors is inadequate for impurity concentrations [similar or greaterthan]1%. In particular, it is necessary to redefine (1) the number of free charge carriers, and (2) the density of available states because of the dominant role played by the impurities in the high concentration range.
Recent Studies on Rutile (TiO2)
Authors: Frederikse H. P. R.
Published: April 2005

A review is made of the work on reduced and ``doped'' rutile performed since the appearance of Grant's survey article in the Reviews of Modern Physics (1958). Measurements of electrical and optical properties, and of electron spin resonance spectra are discussed. A model of electronic bound states and conduction levels is suggested that is compatible with the results of these experiments. There is strong evidence that the defects in reduced rutile are interstitial Ti3+ ions. At very low temperatures, nearly all electrons are self-trapped on cation sites (polarons). As the temperature increases, some of these trapped electrons will be excited into the conduction band. The activation energy for this process is approximately 0.007 ev below 50°K, and about one order of magnitude higher around room temperature. It is concluded that conduction takes place in a narrow 3d band associated with Ti ions; the effective mass at the bottom of this band is ∼25m0. If one assumes that the polaron binding energy can be described with a hydrogenic model, one calculates an effective dielectric constant close to the static value. This result is at variance with the commonly accepted ideas concerning electron lattice coupling.
Heitler-London Approach to Electrical Conductivity
Authors: Yamashita Jiro
Published: April 2005

A Heitler-London approach to electrical conductivity is proposed in order to discuss conduction in semiconductors with incomplete d shells, in which the mobility of carriers is very low. The physical conditions which make the hopping motion of the electrons predominant is examined in detail.
Electrical and Optical Properties of the II–V Compounds
Authors: Turner W. J. , Fischler A. S. , Reese W. E.
Published: April 2005

The noncubic II–V semiconductors have been studied recently by several workers. A review will be given of the present situation. The energy gaps of these materials range from 0.13 to over 1 ev. Room temperature mobilities of 10–15 000 cm2/v sec have been observed. Anisotropy of electrical and optical properties have been reported for several of the compounds. For CdAs2 it has been possible to explain the anisotropy of Hall mobility by a simple energy band model.