bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of oxygen and copper on the defect cluster in neutron-irradiated p-type silicon
Authors: Usami Akira , Tokuda Yutaka
Published: February 2004

The effect of the oxygen and acceptor concentration and Cu contamination on the defect clusters, found to be produced in p-type silicon by neutron irradiation at room temperature without enclosing the samples by Cd plating, was investigated by using electrical conductivity and Hall effect measurements. The insulating volumes of the defect clusters and the barrier heights formed by the cluster-space charge regions were obtained by Gossick's cluster model. The insulating volumes and barrier heights depended on neither oxygen concentration nor Cu contamination. The insulating volumes decreased with the 0.72 power of the acceptor concentration and the barrier heights increased with the 0.28 power of the acceptor concentration. The acceptor concentration dependency of the insulating volumes could be simply explained by Gossick's cluster model. The recovery of the barrier height was similar to that of the light-sensitive defects by Stein and the trap centers by Nakashima and Inuishi. From the isothermal annealing of the barrier height, the activation energy was found to be about 1.1 eV for both the noncontaminated and Cu-contaminated samples. This activation energy corresponds to the liberating energy of vacancies from clusters. In isochronal annealing above 210°C, the recovery of the carrier concentration showed the effect of the Cu contamination which could not be observed after irradiation.
Charge dynamics for electron-irradiated polymer-foil electrets
Authors: Gross B. , Sessler G. M. , West J. E.
Published: February 2004

Charge buildup, storage, and decay in 25-μm polyfluoroethylenepropylene (Teflon type A) foils due to irradiation with partially penetrating monoenergetic electron beams in the 10–50-keV range are investigated. Currents from the irradiated front surface and the nonirradiated rear surface are measured separately by means of 1000-Å evaporated aluminum electrodes. Charge storage due to irradiation and a charge recall effect caused by irradiation of previously charged samples are observed. Discharge currents measured after termination of the irradiation indicate the importance of the delayed component of radiation-induced conductivity. Measurements of the spatial depth of the charge are also reported. A mathematical model is developed which takes into account the radiation-induced conductivity and the electrical and geometrical parameters of the sample. It allows for the calculation of current transients during and after irradiation.
Nonsaturating velocity-field characteristic of gallium arsenide experimentally determined from domain measurements
Authors: Riginos Vasilis E.
Published: February 2004

A new method is presented for the measurement of the average electron drift velocity as a function of the electric field (velocity-field characteristic) for semiconductor materials which exhibit bulk negative differential conductance. The characteristic is determined from capacitive probe measurements made on high-field Gunn-effect domains. This method is most applicable for values of E > 20 kV/cm, where very little information exists. The method was applied to the measurement of the velocity-field characteristic of GaAs. The characteristic found is nonsaturating and slowly decreasing up to 100 kV/cm, the maximum measured electric field. The results correlate well with the velocity-field characteristic theoretically calculated by Heinle.
Infrared reflection of ion-implanted GaAs
Authors: Kachare A. H. , Spitzer W. G. , Euler F. K. , Kahan A.
Published: February 2004

Gallium arsenide has been implanted with nitrogen ions at 1–3 MeV and fluences between 3.3×1013 and 2.0×1017 ions/cm2. Room-temperature infrared spectra are presented which show major changes in the reststrahl region. A sample having the highest fluence was isochronally annealed with 2-h 100°C steps from 200 to 600°C, and the implantation-induced reflectivity changes are annealed by 600°C. Changes of the dispersion parameters were determined by Kramers-Kronig analysis as well as by curve fitting with classical dispersion (CD) analysis. Examples of dispersion parameters obtained by different analyses are compared and their validity is discussed. The data of nonimplanted and samples implanted with fluence up to 3.3×1014 ions/cm2 can be satisfactorily fitted with CD analysis assuming the material to be optically homogeneous. With this assumption, attempts to fit the data of samples with fluences ≥3.3 ×1015 ions/cm2 were unsuccessful. By extending the CD analysis to a layer model a reasonable fit was achieved. The analyses indicate changes in the transverse- and longitudinal-optic-mode frequencies. The latter changes were confirmed by Raman scattering measurements. Both the analyses and interference fringes observed in the near-infrared reflection spectra indicate some implantation-induced increase in the high-frequency dielectric constant.
Small and quasineutral domains in negative-differential-conductivity materials
Authors: Torrens A. B.
Published: February 2004

A theoretical analysis shows that for a small quasineutral domain porpagating steadily in a negative-differential-conductivity (NDC) material, the domain field ED and outside field EU obey the relation ED-EU = 3(Ep-EU), and the domain excess voltage is proportional to [(Ep-EU)/N]1/2, where Ep and N are, respectively, the field for peak velocity and the doping concentration. Within its range of validity, this analysis is confirmed by computations, which also extend the results to domains which are not small or quasineutral. The length and excess voltage of a quasineutral domain are found to be proportional to N−1/2 even if the domain is not small. The new shape obtained from this theory for the domain characteristic near the peak field indicates the possibility of small domains. The velocity of these domains is very near vp, which is approximately twice that of large domains. The small oscillations which have sometimes been observed near the threshold may be attributed to these small domains.
Excitation spectra of magnetic bubble lattices
Authors: Sokoloski M. M. , Tanaka Tomoyasu
Published: February 2004

The excitation spectra of a hexagonal lattice of magnetic bubbles is calculated using the methods of lattice dynamics. The bubbles are allowed one internal zero-mode radial degree of freedom and two translational degrees of freedom of the center of mass. This results in three branches of free oscillation, one optical and two acoustical. The equations of motion of the system are obtained from a Lagrangian with a Rayleigh dissipative function. The Fourier transform of these equations yields a secular determinant of order three corresponding to the three branches. The secular equation is a polynomial equation of sixth degree in the complex frequency. This is solved for the directions kx and ky. The interbubble potential is approximated by a dipole-dipole potential, and restricted to nearest neighbors. The magnetostatic bubble self-energy is replaced by the analytic approximation of Josephs and Callen. For a close-packed lattice with no coupling between the radial and translational degrees of freedom, the optical and acoustical branches cross. The inclusion of coupling has drastic effects on the dispersion relationships. The acoustical branches consist of admixtures of translational and radial oscillations. Because of damping, a critical wave number exists below which no real part of the frequency exists. Changes in the acoustical branches can be brought about by changing the external magnetic field.
Correlation functions for predicting properties of heterogeneous materials. IV. Effective thermal conductivity of two-phase solids
Authors: Corson Peter B.
Published: February 2004

The Beran bounds on the effective thermal conductivity of a statistically homogeneous and isotropic heterogeneous material require a knowledge of several three-point correlation functions. These bounds are evaluated here for two-phase materials, using the correlation functions developed in Paper II of this series. The resultant bounds are compared with experimental data on the effective thermal conductivity of air-saturated porous sandstone (phase thermal conductivity ratio of 80 : 1) and air-saturated firebrick (ratio of 60 : 1), and with the less restrictive Hashin-Shtrikman bounds which do not require any knowledge of correlation functions. It is shown that the Beran bounds are a significant improvement over the Hashin-Shtrikman bounds, with the greatest improvement occurring for low-phase thermal conductivity ratios.
Kinetics of silicide formation by thin films of V on Si and SiO2 substrates
Authors: Kräutle H. , Nicolet M-A. , Mayer J. W.
Published: February 2004

The reaction rate of vacuum-evaporated films of V of the order of 1000 Å thick is investigated by MeV He backscattering spectrometry. On substrates of single-crystal Si and for anneal times up to several hours in the temperature range 570–650°C, VSi2 is formed at a linear rate in time. The activation energy of the process is 1.7±0.2 eV. The presence of oxygen in amounts of 10% can significantly decelerate the reaction. On substrates of SiO2 in the temperature range 730–820°C and anneal times of several hours or less, V3Si is formed at a square-root rate in time. The activation energy of this process is 2.0±0.2 eV.
Application of NMR to the study of molecular motion in SBS copolymers
Authors: Wardell G. E. , McBrierty V. J. , Douglass D. C.
Published: February 2004

NMR T1 and T2 data are presented for two styrene-butadiene-styrene block copolymers along with results for homopolymers of polystyrene and polybutadiene. The relaxation processes in both polymers are discussed. The results indicate that the glass transition temperature for polystyrene is lower in the SBS copolymer than for the homopolymer, in agreement with earlier findings. It is concluded that the vigorous motions in the polybutadiene phase of the copolymer instigate motion in the polystyrene phase prematurely. The data further indicate that motion in polybutadiene is more hindered in SBS than in the pure polymer as a result of the cross-linking effect of the polystyrene domains; however, there is little effect on Tg for polybutadiene. Finally, the T1 results indicate that spin diffusion is operative between the two phases in the SBS block copolymer. The principal features of this effect are satisfactorily explained in terms of a simple model which neglects the geometry of the interface between the two phases.
Gallium arsenide field-effect transistors by ion implantation
Authors: Welch B. M. , Eisen F. H. , Higgins J. A.
Published: February 2004

Gallium arsenide Schottky-barrier field-effect transistors have been fabricated in an n-type film produced by sulfur implantation in a Cr-doped semi-insulating GaAs substrate. The conditions of the implantation and the resulting electrical properties of the film are presented. The FET devices are described and the measured current-voltage characteristics of this device are discussed.
Refractive indices of congruently melting lithium niobate
Authors: Nelson D. F. , Mikulyak R. M.
Published: February 2004

The ordinary and extraordinary refractive indices of congruently melting LiNbO3 in the wavelength range 0.40463–3.05148 μm are reported.
Size effect in low-temperature electrical resistivity of Al–Al3Ni in situ composites
Authors: Simoneau R. , Bégin G.
Published: February 2004

Fiber composites have been grown in situ by unidirectional solidification of Al–Al3Ni eutectic. The interfiber distance has been changed by more than an order of magnitude through variation of the solidification rate. The electrical resistivity, measured in directions perpendicular and parallel to the Al3Ni fiber axis, exhibited an important anisotropy and a marked dependence on the interfiber distance at 77 and 4.2 K. These experimental results are explained in term of partial specularity of reflections of conduction electrons on internal Al–Al3Ni interfaces.
Positive column of Na–Ar and Na–Ne–Ar dc low-pressure discharges
Authors: van Tongeren H. , Heuvelmans J.
Published: February 2004

Measurements are reported of the electron temperature, electric field, and electron density in the positive column of low-pressure Na–Ar and Na–Ne–Ar dc discharges. The production of light at the sodium D resonance lines was also measured. The experimental data were obtained for a tube radius of 1.4 cm, and a noble gas filling of 10 Torr. The sodium density varied from 1×1019 to 6×1019 m−3, and the discharge current from 0.1 to 3.0 A. Depletion of sodium ground-state atoms was found to have a decisive effect on the discharge properties at the higher discharge currents. Calculations on a model of the discharge were performed in addition to the measurements. In this model deviations from the Maxwell electron energy distribution were included. The results of the calculations for the electron temperature as a function of current were found to be in good agreement with the experimental data. However, the calculated electric field as a function of current showed qualitative agreement only.
Stimulated emission from carbon monoxide transitions below 5 μm excited in supersonic electric discharge
Authors: Shirley J. A. , Hall R. J. , Bronfin B. R.
Published: February 2004

Low-power cw laser emission from carbon monoxide excited by an rf discharge maintained directly within a supersonic (M ≈2.5) flow has been observed to consist predominantly of the lower-lying vibrational transitions. Optical power is extracted before the quasi-steady-state vibrational population distribution (dominated by vibrational-vibrational energy exchange) is achieved. P-branch laser emission has been observed on the ν=4→3, 5→4, and 6→5 vibrational transitions (λ = 4.89−5.04 μm) with a shifting to the higher vibrational transitions as the optical axis is translated downstream. A theoretical model coupling the effects of electron-impact pumping, molecular energy transfer, multiline laser emission, and nonequilibrium gas dynamics has been developed descriptive of this system. Representative model calculations are compared with experimental data.
Analysis of distributed-feedback and distributed-Bragg-reflector laser structures by method of multiple reflections
Authors: Wang Shyh , Cordero Rodolfo F. , Tseng Cheng-Chung
Published: February 2004

A new method based on multiple reflections is proposed here for analyzing thin-film Bragg devices in integrated optics. Expressions are derived for reflection and transmission coefficients at the interface between a uniform and periodic waveguide. The method is used to find the response of distributed-feedback laser amplifiers and the noise output of distributed-Bragg-reflector lasers.
Anomalous hysteresis loss in superconducting wire due to flux jump
Authors: Shiiki Kazuo , Kudo Mitsuhiro
Published: February 2004

A sudden increase in the hysteresis loss of nonideal type-2 superconductors having high critical current density was observed in the ac magnetic fields for frequencies from 35 to 100 Hz. This anomaly, which is reproducible in the sample, occurs at a peak field of about 2500 Oe in the transverse configuration and depends slightly on the frequency. It can be understood on the basis of the limited flux jump. The diameter dependence of the anomaly for Nb-60.2 Ti-2.8 Zr superconducting wires is studied over a range from 45 to 508 μm. It follows that the critical diameter necessary for adiabatic stability is about 27 μm.
Numerical analysis of vortex motion on Josephson structures
Authors: Nakajima Koji , Onodera Yutaka , Nakamura Tadao , Sato Risaburo
Published: February 2004

The one-dimensional and two-dimensional sine-Gordon equations with dimensionless loss factors and unitless normalized bias are numerically calculated by computer. The results are presented for accelerations, velocities, collisions, coupled states, and two-dimensional propagation of solitons.
Studies of the Nitrogen Afterglow. I. Surface Catalytic Efficiency and Diffusion-Controlled Decay of Atomic Nitrogen
Authors: Lund R. E. , Oskam H. J.
Published: February 2004

The temporal behavior of the afterglow light intensity in decaying nitrogen plasmas, as well as that of the number density of N+, N2+, N3+, and N4+ ions, was studied in the pressure range of about 0.1 to 1.7 torr. The analysis of the light intensity decay curves resulted in a method of measuring the surface catalytic efficiency γN for the recombination of nitrogen atoms at the plasma boundary. The simultaneous identification of the ions present in the plasma by means of a quadrupole mass spectrometer ensures that the data relate to pure nitrogen as well as to extremely clean surfaces. The values obtained for γN of molybdenum sputtered on a glass surface decreased with pressure from a value of 0.22 at 0.09 torr to 0.04 at 1.35 torr. The studies also showed that part of the afterglow light emission is due to collisions between metastable nitrogen molecules which are produced in the afterglow by the atomic volume recombination process.
Analysis of the Paramagnetic Resonance and Optical Spectra of d3,7 Ions in Tetragonal Crystal Fields. I. Orbitally Nondegenerate Ground States
Authors: Jesson J. P.
Published: February 2004

The ligand-field Hamiltonian, including spin–orbit coupling and all states of the configuration, has been diagonalized for the d3,7 ions in tetragonal environments. The g-tensor components have been determined within the lowest two Kramers doublets in cases where the ground state is orbitally nondegenerate. The variation of D, g‖, and g⊥ with the parameters of the tetragonal potential has been investigated for parameter values appropriate to the Co2+ ion in D2d symmetry. The results are compared with those obtained from simple perturbation expressions which have been used in the literature. Parameters for the extended spin Hamiltonian are evaluated directly. Matrices for the tetragonal potential are used to discuss optical and paramagnetic resonance data for Cs3CoCl5 and Co2+ in CaF2. Polarized single-crystal optical data for Cs3CoCl5 at 4.2°K are described for the T14(4F) and T14(4P) states.
Direct Visual Observation of Concentration Fluctuations in a Critical Mixture
Authors: Debye P. , Jacobsen R. T.
Published: February 2004

The statistical concentration fluctuations in a solution of polystyrene in cyclohexane near its critical temperature have been directly observed by means of a specially thermostatted phase-contrast optical microscope. A technique which may be of use in the determination of the spatial and temporal persistence of these fluctuations is also described.
Photolysis of Methyl Iodide in Matrices of Organic Compounds at 20° and 77°K. Reactions of Hot Methyl Radicals
Authors: Rebbert R. E. , Ausloos P.
Published: February 2004

Methyl iodide-hydrocarbon and methyl iodide-alcohol matrices have been photolyzed with 2537-Å radiation both at 20° and 77°K. The probability of abstraction of an H atom by the hot CH3 radical formed upon photodissociation of CH3I is at least a factor of 10 larger in the solid phase than in the gas phase. However, the relative probabilities of abstracting an H atom from various organic compounds are about the same in both phases. Also, hot CH3 radicals are more reactive than CD3 radicals in both phases. Photolysis of CH3I or CD3I in the presence of (a) equimolar mixtures of perprotonated and perdeuterated hydrocarbons and (b) partially deuterium labeled hydrocarbons shows that the hot methyl radical abstracts an H atom or D atom with equal probability. The hot methyl radical does, however, exhibit a certain selectivity in the site of reaction. For instance, a secondary H atom is abstracted more readily than a primary H atom. This nonstatistical behavior is, however, less important in the solid phase than in the gas phase. When the matrix consists of an unsaturated hydrocarbon, the hot methyl radical can add to the double bond as well as abstract a H atom. It is shown that a hot methyl radical adds to ethylene to form a n-C3H7 radical which subsequently reacts with the I atom with which it is in juxtaposition. At 20°K about one-fourth of the hot methyl radicals add to C2H4.
Molecular Structure of XeF6 and IF7
Authors: Falconer W. E. , Büchler Alfred , Stauffer James L. , Klemperer William
Published: February 2004

The deflection of molecular beams of XeF2, XeF4, XeF6, and IF7 in an inhomogeneous electric field has been examined. From the defocusing behavior of each of these species, it is concluded that the electric dipole moment μ is less than 0.03 D for XeF4, XeF6, and IF7 if these molecules have rigid structures. The upper limit for the polarity of nonrigid (inverting) structures is (μ / Δ1 / 2) < 0.1 D / (cm−1) / 2, where Δ is the separation between inversion doublets. These results imply molecular structures with symmetry-forbidden electric dipole moments for XeF4, XeF6, and IF7.
Ion Cyclotron Resonance Study of the Secondary Ion-Molecule Reactions in Hexafluoroethane
Authors: King J. , Elleman D. D.
Published: February 2004

The mechanism of secondary ion production in the electron impact decomposition of C2F6 has been determined using ion cyclotron double-resonance techniques. The secondary formation of CF3+ occurs primarily from the decomposition of C2F5+ and charge transfer from CF2+. The reaction CF3++C2F6→CF2++ neutral products is postulated to account for secondary CF2+ production.
Theoretical Σg+1–Σu+1 Dipole Strengths of Some Homonuclear Diatomic Molecules: Configuration Interaction
Authors: Marchetti M. A. , LaPaglia S. R.
Published: February 2004

The dipole strengths of the homonuclear diatomic molecules Li2, C2, Be2, N2, and F2 have been calculated for high- and low-energy transitions of the type Σg+1–Σu+1. Increasingly accurate approximations to the ground-state wavefunction are used, including configuration interaction. A frozen-core approximation is used for the excited state. Comparison of dipole strengths calculated from dipole-moment and dipole-momentum operators stresses the importance of configuration interaction to obtain agreement between these two methods. Population analysis of the C2 and Be2 molecular orbitals reveals an interesting analogy with the resonance transition of the Be atom in the role of (2s)2→(2p)2 nondynamical correlation.
Nuclear Magnetic Relaxation of 19F Due to Cu(II) in Aqueous Solutions of F− and HF
Authors: Eisenstadt Maurice , Friedman Harold L.
Published: February 2004

The effect of Cu + +  on T1 and T2 of aqueous fluoride has been measured over a range of fluoride concentrations and from pH 0.5–6. A strong interaction due to electron overlap in the complex CuF+ dominates both the T1 and T2 effects. The T2 data have been treated by a three-site analog of the Swift–Connick equation, taking explicit account of T1 and T1e, the spin–lattice relaxation time of the unpaired electron, as well as allowance for chemical effects on the lifetime of the complex. The hyperfine tensor in CuF+ has an anisotropic part as well as an isotropic part, equal to 8 × 108 and 1 × 109 rad/sec, respectively. The former controls the T1 process with a correlation time determined by the tumbling motion, while the latter, the familiar scalar-contact interaction, controls the T2 process in a way modified by various correlation time effects. T1e seems too long to give a measurable effect on either process. The following results were obtained for the rate constants of the chemical processes which control the lifetime of the CuF+ complex: CuF+→Cu++ + F− k = 1 × 108 / sec, CuF+ + H+→Cu++ + HF k = 5 × 109 / sec·M, CuF+ + F−→F− + CuF+ k = 1 × 108 / sec·M, CuF+ + HF2−→HF2− + CuF+ k = 1 × 109 / sec·M. The last two are F− exchange reactions. These parameters all depend on the assumption that the CuF+ complex with the contact interaction has the molar-scale association constant K = 2. In addition to the processes which involve CuF+ there is one involving CuHF + +  which dominates T1− 1 at the lowest pH. The contribution of this species to the relaxation processes is accounted for by the dipole–dipole interaction of the unpaired electron with the 19F, and an association constant little different from that of random collisions.
Nuclear Magnetic Resonance of the Solid Phases of HCl, HBr, and HI
Authors: Genin D. J. , O'Reilly D. E. , Peterson E. M. , Tsang T.
Published: February 2004

Proton relaxation times, second moments, and deuteron line splittings have been measured in the solid phases of HCl, HBr, and HI from 50° to 200°K. In solid I of each hydrogen halide two types of molecular motion have been detected: (1) a rapid rotational reorientation and (2) translational diffusion of the molecules. Solid III of HBr shows an intermediate plateau in the proton second moment and both HBr and HI have a well-defined minimum in the rotating-frame relaxation time T1ρ. These effects are interpreted as due to a single-plane reorientation process. Similar minima of T1ρ are observed in solid II of HI and the intermediate solid of HBr, which are ascribed to two-plane and three-plane reorientation processes. The splitting of the deuteron resonance of DBr and DI is quite dependent on temperature but not as strongly dependent as expected for equal site occupational probability. It is proposed that in the ferroelectric solid II of HCl the molecules undergo a single-plane reorientation process but with nonequal orientational site probabilities. Correlation times for these motions are compared with correlation times derived from dielectric loss measurements. The two sets of correlation time data are generally in order-of-magnitude agreement.
Kinetics of Unimolecular Breakdown. VIII. The Lindemann–Hinshelwood Mechanism
Authors: Levine R. D.
Published: February 2004

A quantum-mechanical theory of thermal unimolecular breakdown based on the Lindemann–Hinshelwood mechanism is presented. The kinetic equation is derived on the basis of the averaged density operator of Karplus and Schwinger [Phys. Rev. 73, 1020 (1948)]. The kinetic equation is solved under stationary experimental conditions, and the pressure dependence of the rate of formation of products is related to the detailed time evolution of activated molecules.
Dielectric Studies. XXI. Relaxation Processes of Some Haloethanes in p-Xylene Solution
Authors: Crossley J. , Walker S.
Published: February 2004

The dielectric absorption of several haloethanes in p-xylene solution has been determined at microwave frequencies and the static dielectric constant at 2 Mc/sec. The dielectric data have been used to yield mean relaxation times and apparent dipole moments. All of the compounds which have been measured exhibit an appreciably longer measured relaxation time in p-xylene than in cyclohexane solution. This indicates that the free energy of activation for molecular reorientation is increased, probably by weak hydrogen bonds formed between the hydrogen of the substituted ethane and the π-electron cloud of the p-xylene. Interaction is also apparent from the difference between their apparent dipole moments in the two solvents and may be dependent upon the volume of the molecule and the protonic character of the hydrogen atoms within the haloethane.
Viscosity of Entangled Polymers; Theory of Variation with Shear Rate
Authors: Bueche F.
Published: February 2004

The very high viscosity of melt polymers caused by entanglements decreases with shear rate. A theory for this effect, based on the ideas of Graessley, is presented. It uses the fact that, at high shear rates, the time needed to form entanglements is larger than the transit time of a group of segments over a potential entanglement site. As a result, entanglements do not have time to form and the viscosity is decreased. Account is taken of the fact that entanglements of various complexity have different formation times. This effect is combined with previous viscosity theory to give an equation relating viscosity to shear rate. It agrees well with the literature data for monodisperse polystyrenes and gives the same general shear-rate dependence as Graessley has found by a somewhat different method.
Anderson–Grüneisen Parameter δ for a General Interatomic Potential
Authors: Mathur V. K. , Singh S. P. , Vij D. R.
Published: February 2004

Assuming a general type of interatomic potential for a diatomic crystal, an expression is derived for Anderson–Grüneisen parameter. This expression is then specialized for alkali halides. The value of δ is calculated for NaCl-type alkali halides.
Charge Distribution of the NO2- Radical in Ferroelectric Sodium Nitrite
Authors: Marino R. A. , Bray P. J.
Published: February 2004

The 14N nuclear quadrupole resonance spectrum of ferroelectric sodium nitrite is interpreted to yield the charge distribution of the nitrite radical. Contributions to the electric field gradient due to lattice changes are estimated by performing a lattice sum, while the local electrons are treated using the approximations of the Townes and Dailey theory. Occupation numbers for the N–O sigma- and pi-bond wavefunctions are obtained, and the effective charge on the nitrogen is deduced. The latter quantity is found to be very close to zero.
Absorption Spectrum and Zeeman Effect of the Transitions “5I8” → “3K8” and “5I8” → “5G4” in Holmium Ethylsulfate
Authors: Spedding F. H. , Rothwell M. T. , Haas W. J. , Sutherland W. L.
Published: February 2004

The absorption spectrum and Zeeman effect of the ground term and two excited terms of Ho3 + were measured in the C3h point symmetry of hexagonal single crystals of holmium ethylsulfate. Magnetic-field strengths from 0 to 27 900 G were employed for studying the behavior of the energy levels in both the HsC (magnetic field perpendicular to c axis) and HpC (magnetic field parallel to c axis) crystal orientations. When the single crystals were rotated about the c axis in the HsC case, a 60° periodicity was observed in the energies of some of the Zeeman components and in the intensities of some of the lines. The angle φ defined by Murao, Spedding, and Good (MSG), which describes the angle between the a and x axes in the basal plane of the crystal was found to be 5° ± 2° for both holmium ethylsulfate and 10 mole % holmium in yttrium ethylsulfate. At high magnetic-field strengths, since the magnetic splitting could no longer be considered small compared to the crystal-field splitting, the second-order perturbation treatment of MSG was not sufficient to account for the periodic energy behavior of the levels or the intensity behavior of the lines. The energy behavior was in good agreement with a more recent theoretical treatment for the case where the crystal and magnetic splittings are comparable and with calculations performed in this work in which the observed crystal-field levels were perturbed by approximate matrix elements of the Zeeman interaction. These matrix elements were calculated using the approximate wavefunctions obtained by diagonalizing the parameterized C3h crystal-field matrix which gave the best agreement with the crystal-field splittings of the “3K8” as observed in this paper. Due to the large nuclear moment and high J values of the holmium ion, we were able to resolve the nuclear hyperfine structure in a number of absorption lines. When the magnetic field was along the c axis of the crystal, it was found that an apparent change in the selection rules, and a distinct change in the hyperfine patterns occurred in the neighborhood of field strengths where levels in the ground term with different crystal quantum numbers were expected to cross. This behavior was explained theoretically by including the effects of matrix elements of hyperfine interaction which are not diagonal in μ. These elements prevent the crossing, and patterns calculated in this way were, within the limits of our resolution, in good agreement with the experimental results.
Magnetic Shielding of a Hydrogen Molecule in an Electric Field
Authors: Gruninger J. , Hameka H. F.
Published: February 2004

We evaluate the effect of an electric field F along the molecular axis on the magnetic shielding constants σa and σb of a hydrogen molecule. It was found that the two shielding constants can be represented as σa,b(F) = σ ∓ C1Fz − C2Fz2 − C′2(Fx2 + Fy2) if the z axis is taken as the molecular axis. We found that σ = 1.40114σ0 and C1 = 2.19171σ0 if F is expressed in atomic units e / a02; σ0 = e2 / 3mc2a0. It is concluded that the splitting is observable if F is of the order of 106 to 107 V/cm.
Valence Structure from Coherent X-Ray Scattering: Fourier Difference Synthesis
Authors: Stewart Robert F.
Published: February 2004

The one-electron density function for a molecule of first-row atoms is partitioned into core-electron and valence-electron density pieces. The SCF 1s AO's are used to define the core-electron density pieces. The residual density, after removal of the core density, constitutes the valence density, which is assumed to be chemically interpretable. The partitioning is explored in reciprocal space to provide insight into x-ray diffraction experiments. The contribution from valence scattering within the CuKᾱ sphere is 10%–30% of the total scattering. Valence-electron density maps have been Fourier synthesized from x-ray diffraction data of uracil. The density maps reveal trigonal bonding for the nitrogen atoms and bridge densities in the middle of the C(5)–C(6) and C(4)–C(5) bonds. The densities near the time-average nuclear positions are unreliable.
Atomic Wavefunctions and Diamagnetic Susceptibilities
Authors: Dehn J. T. , Mulay L. N.
Published: February 2004

The predictions of early and modern wavefunctions concerning the diamagnetic susceptibilities of the elements up to Z = 83 are compared with experiment. It is concluded that self-consistent-field wavefunctions with optimized orbital exponents give the best over-all description.
Laser Raman Spectrum and Force-Constant Calculation of Co(CO)3NO
Authors: Mann R. H. , Hyams I. J. , Lippincott E. R.
Published: February 2004

The laser-excited Raman spectrum of liquid Co(CO)3NO is presented and, in addition, the infrared spectrum of the liquid. A reassignment of fundamentals is made, and symmetry force constants are calculated using reported vapor-phase frequencies.
Molecular Orbitals for Large Molecules. V. Parameterization from SCF Matrices of Related Small Molecules
Authors: Boyd Donald B. , Lipscomb William N.
Published: February 2004

A new method for obtaining molecular orbitals in large molecules is described within the LCAO framework. After evaluation of overlap and kinetic integrals exactly, parameters are obtained from self-consistent-field calculations on small, chemically similar molecules for the potential-energy parts of the SCF matrices. These parameters are employed to generate both nonzero and zero overlap matrix elements of the large molecule of known geometry. No experimental parameters are introduced, and all electrons are included. Given the parameters (many are tabulated), the Hamiltonian matrix is readily constructed, so that very large systems (40 atoms and 140 AO's) can be handled. Total energies, eigenvalues, overlap populations, atomic charges, and dipole moments are compared with results from rigorous SCF calculations.
Error Bounds for the Energy and Overlap of Approximate Wavefunctions
Authors: Gordon R. G.
Published: February 2004

A sequence of variational principles for upper and lower bounds to the energy of the ground state of a quantum-mechanical system is constructed. The first approximations in the sequence are simply the Ritz upper bound and the Temple lower bound. Higher approximations give improved upper and lower bounds, at the cost of computing additional integrals of the form 〈φ | Hm | φ〉 over the approximate wavefunction. As in the Temple formula, the lower bounds to the ground-state energy also depend on a knowledge of the energy of the first excited state. If in addition one knows an accurate energy for the ground state (say from experiment), then it is shown that one can construct a sequence of upper and lower bounds to the overlap between the approximate function and the true (but unknown) ground-state wavefunction. The first approximation in this sequence is the Eckart lower bound to this overlap, and the higher approximations provide improved upper and lower bounds to the overlap.
Quadratic Zeeman Effect in Asymmetric Rotors
Authors: Levy Donald H.
Published: February 2004

The Hamiltonian for a diamagnetic molecule rotating in a magnetic field is derived in spherical tensor form and is shown to contain terms both linear and quadratic in magnetic field. The matrix elements of this Hamiltonian are derived, and the constants appearing in these matrix elements are related to the molecular quadrupole moment tensor. It is shown that the effect of a magnetic field on the rotational spectrum of a molecule should provide a way of measuring molecular quadrupole moments.
Steady-State Thermal Conductivity of Rotationally Degenerate Gases
Authors: Monchick L.
Published: February 2004

By a formal partitioning of the collision operator, the coupling of the fluxes of energy and angular momentum is broken. An effective thermal conductivity appears that is simpler in structure than the usual thermal conductivity. The relevance to experiment is discussed.
Nuclear Magnetic Resonance of Ti in Ti–H Systems
Authors: Frisch Ronald C. , Forman Richard A.
Published: February 2004

The nuclear magnetic resonance spectrum of 47,49Ti in powder samples of metallic titanium hydride TiHx has been studied over the range of hydrogen concentrations corresponding to 1.7 ≤ x ≤ 2.0. For TiH2 the Knight shift is found to be +0.26 ± 0.04%, and there is no change in the Knight shift as a function of hydrogen concentration over the range studied. The titanium resonance in all samples was quite broad, 20 Oe, so that the lines from the two isotopes were not resolved. As a function of hydrogen concentration, the line shape was found to remain constant, but a rapid decrease of line intensity was noted. In order to investigate the possibility of magnetic ordering suggested by earlier studies of the magnetic susceptibility of TiH2, studies of the magnetic-field dependence and temperature dependence of the resonance were also performed. No dependence of Knight shift or line shape on magnetic field was observed over the range 9.0–15.0 kOe. No changes in Knight shift or line shape were observed in the temperature region 170°–525°K, thoroughly encompassing the region of the magnetic susceptibility maximum at approximately 300°K. These results strongly suggest that the cause of the maximum in the magnetic susceptibility is not magnetic ordering. Results on hydrogen and deuterium resonances in these samples are also reported.
Environmental Effects on Phosphorescence. II. “Activation Volumes” for Triplet Decay of Aromatic Hydrocarbons
Authors: Baldwin B. A. , Offen H. W.
Published: February 2004

The rate of triplet decay k has been measured to 32 kbar for 20 aromatic hydrocarbons at room temperature. The measured lifetimes are generally shortened by high pressure. The slope of lnk-vs-P plots were all linear above 15 kbar. This slope is positive except for terphenyl, and can be related to “activation volumes” ΔV‡ for this kinetic process. The values −1.0 < ΔV‡ < 0.2 Å3 / molecule are found for this class of compounds. The perdeuterated compounds have a larger negative “activation volume” than the corresponding perprotonated aromatics. Hence, environmental perturbations are most effective for slow processes which arise from weak intramolecular perturbations in the solute.
Momentum and Temperature-Slip Coefficients with Arbitrary Accommodation at the Surface
Authors: Loyalka S. K.
Published: February 2004

Accurate theoretical expressions for momentum and temperature-slip coefficients for monatomic gases with arbitrary accommodation at the surface are derived by applying a variational technique to the full linearized Boltzmann equation. In the jump regimes, the use of these expressions appears preferable to the use of the previous results based on mean-free-path theory or numerical methods. As an example, a correction in the reported values of accommodation coefficients is suggested.
Fluorescence of Doped Crystals of Anthracene, Naphthalene, and Phenanthrene under High Pressures: The Role of Excimers in Energy Transfer to the Guest Molecules
Authors: Jones Peter F. , Nicol Malcolm
Published: February 2004

Fluorescence spectra of crystals of anthracene, naphthalene, and phenanthrene doped with other polycyclic aromatic hydrocarbons have been studied at pressures as great as 50 kbar. The most significant effects of pressure on the spectra of the host crystals are a loss of intensity of the normal fluorescence with increasing pressure and the almost simultaneous appearance of a broad, featureless emission at energies about 3000–6000 cm−1 lower than that of the normal fluorescence. This emission is assigned as the fluorescence of excimers formed upon optical excitation of the crystals under high pressure. The growth of the intensity of the excimer emission with increasing pressure, relative to the intensity of the normal fluorescence, is the same in doped crystals as in pure crystals. The intensities of the guest molecule fluorescence relative to the intensity of the normal host fluorescence in the various doped crystals increase with pressure at about the same rate as the intensity of the excimer emission. These observations are interpreted as indicating that excimers are the lowest-energy excited singlet species of aromatic molecular crystals at these pressures and that when the excimer concentration is appreciable, the path of energy transfer is from the host via excimers to the guest.
I. Kinetics of Reactions of Electrons during Radiolysis of Liquid Methanol. II. Reaction of Electrons with Liquid Alcohols and with Water
Authors: Jha K. N. , Freeman G. R.
Published: February 2004

The gamma radiolysis of liquid methanol has been studied over the temperature range from its melting point ( − 98°) to its critical temperature (240°). The value of G(H2) varies from 4.95 at −98° to 5.45 at 25° and 8.0 at 240°. Sulfuric acid and nitrous oxide were added as electron scavengers at −97°, 25°, and 150°. The nitrogen and hydrogen yields were calculated as functions of the nitrous oxide concentration at each of the three temperatures. The calculations were based on a proposed mechanism. Homogeneous kinetics were used for the reactions of the free ions and nonhomogeneous kinetics were used for the reactions in spurs. At −97°, G(total ionization) = 4.6 and the value is assumed to be independent of temperature. The yield of free ions is G(esolv−)fi = 2.0 ± 0.2, independent of temperature from −97° − 150°. The reaction esolv−→CH3Osolv−) + H has a rate constant of 4.6 × 105 sec− 1 at 25° and an activation energy equal to that of dielectric relaxation (3.7 kcal/mole); the entropy of activation of the reaction is −21 cal/deg·mole. In each of the liquids methanol, ethanol, isopropanol, and probably also water, the reaction esolv−→ROsolv− + H has an activation energy approximately equal to that of dielectric relaxation and has a large negative entropy of activation. The large negative entropy of activation indicates that the transition state has a relatively specific structure. It is suggested that solvated electrons are liquid-structure breakers in water and relatively weak structure formers in the alcohols.
Conformation Parameter and Gradient Dependency of Poly-γ-benzyl-l-glutamate by Viscometry
Authors: Byerley A. J. , Jennings B. R. , Jerrard H. G.
Published: February 2004

Measurements are reported of the viscosity of a sample of poly-γ-benzyl-l-glutamate (M = 467 000) in solutions of mixed solvents of dichloroacetic acid and m-cresol. Solutions over the concentration (c) range 0.1–0.4 g/100 ml have been studied when subjected to a velocity gradient (G) range of 0–1500 sec−1 at 30°C. A concentric-cylinder-type viscometer was employed. The change in reduced viscosity at zero values of c and G, i.e., the limiting viscosity number [η]0,0, with solvent composition suggests a two-stage conversion of the polypeptide from its randomly coiled to its helical form. The viscosity of solutions in m-cresol, a helix-promoting solvent, was accounted for by the theory of Saito for rigid ellipsoids. In all the mixed solvents studied, the viscosity, after an initial period during which G had no effect, obeyed a relationship of the form [ηsp / c]c,0 − [ηsp / c]c,G = A′G2, where [ηsp / c]c,0 and [ηsp / c]c,G are the reduced viscosities at finite concentration and zero and finite gradients, respectively. A′ is a constant. From a theoretical analysis by Peterlin, A′ depends upon the cube of the reduced viscosity at zero gradient, some constants of the system and a parameter K. The latter is a measure of the molecular flexibility and also is dependent on the anisotropy of hydrodynamic interaction. The results here indicate that the coil-to-helix transition is effected in two stages, one of which has been studied in detail and is manifest in changes of A′ and K. The change with solvent composition of reduced viscosity and A′ were similar, but the latter was more sensitive to molecular conformation than the former and was also very concentration dependent. K on the other hand varied considerably with solvent composition yet in a very different manner from A′. It also was probably independent on concentration.
Spin Contamination in Spin-Unrestricted INDO Molecular-Orbital Wavefunctions
Authors: Beveridge David L. , Dobosh Paul A.
Published: February 2004

The effect of contaminating spin components in spin-unrestricted valence-electron molecular-orbital wavefunctions calculated at the INDO level of approximation is considered with reference to the calculation of unpaired spin populations and isotropic hyperfine coupling constants in organic molecules.
Deuteron Magnetic Resonance Study of Potassium Binoxalate
Authors: McGrath J. W.
Published: February 2004

A DMR single-crystal study of KDC2O4 was done. It was found that there are two equivalent pairs of identical sites per unit cell. The coupling constants and asymmetry parameters at room temperature are 115.9 ± 0.7 kc/sec and 0.175 ± 0.010, 115.8 kc/sec and 0.194 ± 0.010. The major principal axes for the EFG lie in the bc plane making angles of ±5° with the c axis. Results are consistent with placing the deuteron on certain O–O line segments between neighboring oxalate groups, thus resolving a previous uncertainty. The coupling constant fits an empirical functional relation of coupling constants versus O–O bond lengths. The values are much closer to the theoretical value obtained by Weissmann than to that of Bersohn. The coupling constant increased from 114.1 to 120.2 kc/sec in the range −37.3– + 137.7°C. Such an increase is rare; it may be due to vibration of the deuteron along the O–D···O bond or to thermal expansion of the crystal.
Semiclassical Theory of Satellite Bands Produced in the Spectra of Alkali Metals by Interaction with Foreign Gases
Authors: Kielkopf John F. , Gwinn Joel A.
Published: February 2004

A 6–12 potential is used to describe the interaction of an alkali atom in any state with a foreign gas molecule or atom. The hydrogenlike nature of the alkali combined with knowledge of the polarizability of the foreign gas atom allows an explicit semiclassical expression for the force constants to be given. This potential is used to relate the equilibrium separation of an alkali atom–noble gas collision pair to the position of the red satellite band produced. Within a series of levels of the same l and j, this separation is seen to vary linearly with the square of the effective principal quantum number. This permits an expression to be written for the line–band separation. As a check, positions of the bands are calculated. The results are in good agreement with previously reported experimental values.