bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Circular Dichroism in Tetrahalo Cobaltate Ions
Authors: Denning R. G.
Published: January 2005

The magnetic-circular-dichroism spectra of the ions CoX4=(X=Cl, Br, I) have been measured in the region of the 4A2→4T1(P) transition. Available theoretical treatments are incapable of detailed explanation of the data. Mixing of the 4A2 and 4T2 states under the magnetic field is not the main contribution to the activity. Other possibilities are discussed.
On the Correlation of the Motion of a Polyion and Its Ionic Atmosphere
Authors: Mazo Robert M.
Published: January 2005

A generalization of the Nernst—Einstein equation is derived. It is shown how this equation, together with data on self-diffusion and electrophoretic mobility, enables one to calculate a measure of the magnitude of the correlation of an ionic atmosphere current with a polyion velocity, relative to the autocorrelation of the polyion with itself. The case of sodium dodecyl sulfate micelles is presented as an example. It is found that the relative magnitudes are large, varying from about ⅗ to ⅘ over the range of salt concentrations studied.
Motions of Water Molecules in Potassium Ferrocyanide Trihydrate, Water, and Ice: A Neutron Scattering Study
Authors: Rush J. J. , Leung P. S. , Taylor T. I.
Published: January 2005

The motions of H2O molecules in ferroelectric potassium ferrocyanide trihydrate, water, and ice have been investigated by total cross section and differential inelastic scattering measurements with cold neutrons. The results show no significant change in the average rotational or translational freedom of the water molecules in KFCT at or near its ferroelectric transition. The inelastic neutron spectra for KFCT exhibit broad peaks at about 425 and 160 cm−1, both above and below the transition, which are assigned primarily to the librational and optic translational modes of the H2O molecules, respectively. Moreover, both the total cross section and inelastic scattering results indicate a greater freedom of motion of the H2O molecules in the KFCT lattice than in either water or ice. In addition, a decrease in the total cross section of H2O, and in its variation with neutron wavelength is observed at the water—ice transition, indicating a significant change in the frequency distribution. The neutron results are compared with the results of NMR and infrared measurements.
Higher Polarizability of the Helium Atom
Authors: Boyle L. L. , Buckingham A. D. , Disch R. L. , Dunmur D. A.
Published: January 2005

The electric dipole moment induced in a helium atom by a uniform electric field F can be expressed by αF+⅙γF3+···, where α is the well-known electric polarizability, and γ is a higher polarizability describing the initial deviation from a linear polarization law, and is sometimes called the hyperpolarizability. An experimental determination of γ has been made by observation of the Kerr electro-optical effect in helium. The result is γ = (2.6±0.4) × 10−38 esu. An analytic calculation has been carried out by a perturbation procedure, with the results γ = 1.57×10−38 esu, α = 0.2027 Å3. The observed value of α is 0.2051 Å3. Approximate calculations of the quadrupole moment of helium induced by an electric field and a field gradient are also described.
Electron Spin Resonance Analysis of a γ-Irradiated Single Crystal of Pentafluoropropionamide
Authors: Lontz Robert J.
Published: January 2005

Electron spin resonance data indicate that irradiation of pentafluoropropionamide at 300°K produces the stable free radical CF3ĊFCONH2. The hyperfine interaction of the unpaired electron with the alpha-fluorine nucleus has the characteristic values observed in other cases of the CF fragment. The unpaired electron also interacts equally with each of the three methyl-group fluorine nuclei at room temperature, implying free rotation of this group about the Cα–Cβ bond. Two of the principal elements for the beta-fluorine tensor (36 and 14 G) are located in the plane perpendicular to the maximum alpha-fluorine hyperfine element, and the third (17 G) is perpendicular to this plane. Also presented is evidence that the free rotation of the methyl group may be stopped by cooling the crystal to 77°K. Preliminary room-temperature data indicate attack of the free radical by oxygen to produce the radical R–O–Ȯ, and the possible existence of a second free radical, CF3CF2COṄH, resulting from N–H bond rupture.
X-Ray Photoconductivity of Anthracene
Authors: Kramer G. , Ghalla M. , Canfield J.
Published: January 2005

The excess currents generated in anthracene crystals under x radiation have been measured as a function of x-ray intensity, electric field, and temperature. The currents were linear with respect to absorbed dose rate and electric field. A sensitivity of 7.1±0.7×10−12 C/cm2·rad at a field strength of 630 V/cm was obtained. The mobility, lifetime product, μτ, was 9.9±0.9×10−8 cm2/V. The photocurrent was observed to increase with increasing temperature and exhibited two different activation energies, one below 250°K and a second above 250°K. The magnitude of these energies decreased with increasing dose rate. The temperature behavior may be explained in terms of exciton theory or may be due to changes in carrier mobility.
Electronic Spectra and Structure of Sulfur Compounds
Authors: Thompson S. D. , Carroll D. G. , Watson F. , O'Donnell M. , McGlynn S. P.
Published: January 2005

The lower-energy electronic states of a series of saturated sulfur compounds have been investigated theoretically and experimentally. The compounds investigated fell into two categories: the monosulfide series ABS in which the substituents A and B were varied, and the polysulfide series R2Sn, where n=1, 2, 3, and 4 and where R was usually CH3. The data collected included ultraviolet vapor spectra, solution spectra, solvent shifts, and vibrational data. Computations followed an approach related to that of Wolfsberg and Helmholz. This theoretical method closely approximates the experimentally observed energies in the compounds containing a single sulfur atom but encounters difficulties when two or more sulfurs are present because of the large 3dS−3dS and 4sS−4sS interactions which are predicted. It is indicated that the lower-energy excited electronic states of all the monosulfide compounds investigated are of a molecular nature in which the 4sS and 3dS atomic orbitals of sulfur play particularly dominant but by no means exclusive roles. The lower-energy excited states of the molecules R2Sn, n=2, 3, and 4, also contain significant 4s and 3d character; additionally, however, they are of S–S antibonding nature.
Calculation of the Lowest Energy Configurations of Nucleotide Base Pairs on the Basis of an Electrostatic Model
Authors: Nash H. A. , Bradley D. F.
Published: January 2005

In this report we have taken as a point of departure the idea that the principal force acting between two nucleotide bases is the Coulomb law force between the localized formal charges on each atom of one base and each atom of the other base. The charges were computed by semiempirical quantum-mechanical methods for both σ and π electrons separately and added together. The energies of attraction between all possible pairs of the four common bases adenine, uracil, cytosine, and guanine in all possible coplanar orientations were computed automatically on a Honeywell 800 digital computer. Twenty-seven deep potential-energy minima were found. Although it was not possible to find gas-phase geometries and energies with which to compare these computed stable states, the energies in solution and known geometries in crystals, cocrystals, and polymer fibers were, with a single possible exception, completely consistent with the predicted structures and relative energies. Examination of the computed structures showed that, with few exceptions, the N–H···O and N–H···N short contacts are essentially linear, so that although the forces which led to these geometries were purely electrostatic in nature, the complexes may for convenience be thought of as being ``hydrogenbonded complexes.'' In several of the computed structures, nonlinear N–H···O and N–H···N close contacts were observed and these can be conveniently thought of as ``bifurcated hydrogenbond complexes'' which have been observed in nature although not, as yet, in purine and pyrimidine complexes.

The need for employing formal charges to reproduce the electrostatic forces was demonstrated by showing that dipole—dipole forces do not lead to potential minima and/or stable structures. Tests with a variety of computed charge densities showed that variation in the charges does not affect the equilibrium geometries or their relative stabilities although it does affect the absolute energies.

The method described therefore appears to be a satisfactory method for obtaining trial geometries for x-ray-diffraction analyses of crystals and fibers, and for estimating relative stabilities for use in predicting which pairings can occur where choice is possible, i.e., in codon—anticodon complexes, in hairpin-folded RNA complexes, as well as in cocrystals.
Infrared Spectrum of Crystalline CH2I2. Crystal Structure and Phase Transition
Authors: Marzocchi M. P. , Schettino V. , Califano S.
Published: January 2005

The infrared spectra of two crystalline modifications, I and II of CH2I2, have been measured at various temperatures ranging from 3° to −196°C between 4000 and 400 cm−1. The transition between the two crystal forms I→II has been demonstrated to be monotropic.

The absence of the A2 fundamental in Form I allows a C2v site symmetry to be established, while for Form II the activity of the A2 fundamental and the observed factor-group splitting for A1, B1, and B2 fundamentals is consistent only with trivial site symmetry.

Among the multiplicity of factor groups consistent with the observed crystal spectra, a choice is possible using packing considerations. Orthorhombic, (D2h5) or (D2h13), and monoclinic (C2h5) structure are proposed for Forms I and II, respectively, which are consistent with the ir crystal spectra and densities of the two crystalline solids.
Paramagnetic Relaxation and Crystal-Field Theory for the Ground Manifold of Chromium in Rutile
Authors: Lampe Donald R. , Wagner Peter E.
Published: January 2005

Paramagnetic relaxation within the ground manifold of chromium in rutile is studied experimentally and theoretically. Relaxation proceeds solely by direct transitions between two Kramers doublets and, at low temperatures, approaches the behavior identified with the usual Orbach mechanism. The three characteristic decay times in this four-level system are expressed in terms of two temperature-independent parameters, which are evaluated from measurements of the longest two time constants. The decay times are independent of Zeeman field and chromium concentration and show the expected temperature variation. Strong-field crystalline-field theory is applied to the microwave spectrum and the relaxation process; theory explains the spectrum satisfactorily but is only marginally successful in explaining the behavior of the relaxation times.
Electronic Energy Integrals Arising from a Correlated Wavefunction for Three-Electron Atoms
Authors: Roberts P. J.
Published: January 2005

A three-electron wavefunction containing exponential correlation factors for each pair of electrons is proposed for the ground state of three-electron atoms. A scheme for reducing the electronic energy matrix elements to a form suitable for numerical computation is described.
Some Considerations of Unimolecular Rate Theory. II. Aspects of the General Theory
Authors: Buff Frank P. , Wilson David J.
Published: January 2005

The rate constant for a unimolecular reaction is obtained in alternative ways from the Liouville equation supplemented by the strong collision assumption. The final expression for the rate constant explicitly includes the details of the interactions between the collision process and intramolecular processes. The ``new-approach'' formula, obtained by Slater on intuitive grounds, is recovered when the collisional relaxation time is evaluated from the kinetic theory collision constant.

With this assumption, the rate constant is expressed in terms of the eigenvalue problem generated by the Liouville operator of the isolated molecule in its interesting states. This expression provides a basis for a perturbative evaluation of the rate constant.

Statistical arguments are used to develop consistency theorems for checking experimental data. Reversible isomerization reactions are discussed, and a transmission coefficient which monotonically increases with pressure is deduced.
Some Flow Characteristics of Mesophase Types
Authors: Porter Roger S. , Barrall Edward M. , Johnson Julian F.
Published: January 2005

Characteristic flow properties for each of the three nominal mesophase types have been empirically established. Results are given for the nematic, smectic, and cholesteric types of mesophase. Discussion is centered on mesophases or liquid crystals exhibited by pure compounds within defined temperature intervals between the regular solid and the isotropic liquid. For nematic mesophases, the prominent flow orientation, consequent low viscosity, and the unusual flow behavior near the nematic—isotropic transition are discussed. The remarkably high and shear-dependent viscosities of cholesteric mesophases are contrasted to the simple flow properties of these cholesterol derivatives at temperatures for their respective isotropic liquids. Descriptions of flow properties for smectic mesophases are based essentially upon data on a single compound, ethyl-p-azoxybenzoate. Viscosity data on this compound from several sources are intercompared for the first time. Some of the new empirical conclusions given here are at variance with those reported previously in several reviews.
Nuclear Magnetic Resonance and Relaxation of Hexafluoride Molecules in the Solid
Authors: Blinc R. , Pirkmajer E. , Slivnik J. , Zupančič I.
Published: January 2005

The 19F magnetic resonance absorption spectra and spin—lattice relaxation times of polycrystalline UF6, PuF6, WF6, OsF6, PtF6, MoF6, and XeF6 have been studied as a function of temperature and magnetic field. In all investigated metal hexafluorides the chemical shifts were found to be quite large, exceeding the dipole—dipole broadening in the solid and allowing an unambiguous determination of the tetragonal distortion of the hexafluoride octahedra in the low-temperature orthorhombic phase. The fluorines can thus occupy either axial or equatorial sites. The chemical shifts of the axial and equatorial fluorines (σ0, axial=−5350 ppm, σ0, equatorial=−2800 ppm) with respect to HF, and the anisotropies of the 19F screening tensors in PtF6, |σ∥—σ⊥ |a=1300±100 ppm and |σ∥—σ⊥ |e=1380±100 ppm seem to be the largest of all known fluorine compounds. A slow, thermally activated motion where each fluorine atom is alternatively axial and equatroial, and which consists of a hindered rotation and subsequent distortion of the octahedron in the crystalline field of its neighbors, produces at higher temperatures a coalescence of the spectrum into a single, narrow line.

The same fluorine motion was found to influence the spin—lattice relaxation both by a direct modulation of the resonance fields due to anisotropic chemical shifts tensors as well as by a modulation of the dipole—dipole coupling. The solid—solid transitions to the cubic phase in PtF6, WF6, and MoF6, were found to be accompanied by a very sharp increase in T1 and a lowering of the activation energy for molecular motion.
Energy and Entropy Parameters for Vacancy Formation and Mobility in Ionic Crystals from Conductance Measurements
Authors: Beaumont J. H. , Jacobs P. W. M.
Published: January 2005

A new technique for the evaluation of defect parameters (enthalpy and entropy of creation of a pair of vacancies, enthalpy and entropy of migration of these vacancies, and the free energy of formation of divalent cation—cation vacancy complexes) has been developed. Unlike all previous approaches this method of analyzing conductance data does not make any approximations other than those inherent in the Teltow nearest-neighbor model. The application of this technique to new measurements of the specific conductance of single crystals of pure KCl and of KCl+SrCl2 is described.
Thermal Accommodation Coefficients of Helium on Tungsten and Hydrogen on Hydrogen-Covered Tungsten at 325°, 403°, and 473°K
Authors: Wachman Harold Y.
Published: January 2005

Measurements have been made of accommodation coefficients of helium and hydrogen from 324° to 473°K on tungsten under conditions designed to minimize amounts of adsorbable impurities from the experimental system.

The helium accommodation coefficient values, lying between 0.0194 and 0.0228, compare favorably with measurements at lower temperatures, obtained by Thomas et al., which are probably the best available. The data are also correlated with results of theories on accommodation.

Values of hydrogen accommodation coefficients have been associated with the population of atomic hydrogen on the surface estimated from the adsorption studies of Hickmott. To a first approximation, hydrogen accommodation coefficients are found to be independent of coverage at the high coverages of these experiments and inversely proportional to hydrogen temperature.
On the Stereoregularity of Vinyl Polymer Chains
Authors: Frisch H. L. , Mallows C. L. , Bovey F. A.
Published: January 2005

We explore quantitatively the kind and extent of information concerning the distribution of configurational sequences in vinyl (and related) polymer chains obtainable from data such as presently available high-resolution NMR spectroscopy measurements. After finding the number of observationally distinguishable types of sequences, containing n monomer units [n(ads)], we obtain the necessary consistency relations which must hold between the observed proportions of n(ads), explicitly for all n≤5. Geometrically, the possible regions accessible to the n(ad) proportions form certain simplexes in a space of D(n) dimensions. The extreme points always correspond to repeating polymers. The computed dimensionality number D(n) plays a central role in fixing the number of free parameters of the polymer propagation model determinable by an n(ad) analysis. We discuss in some detail certain Markovian and the non-Markovian Coleman—Fox propagation model in relation to n(ad) analysis. We introduce the concept of a completely reversible polymerization mechanism. We include in our discussion chains of alternating tacticity such as can be found on polymerizing α, β disubstituted monomers.

We present a number of actual examples based on available NMR spectra of certain polymer samples which illustrate how our formalism is useful in (1) checking the consistency of peak and (2) checking the consistency of peak proportion assignment, (3) predicting lower-order n(ad) frequencies (unobtainable because of spectral complexity) from higher-order n(ad) frequencies, (4) ruling out certain propagation mechanisms, etc.
Nonresonant Absorption and Spin Relaxation in Polyatomic Gases
Authors: Gordon R. G.
Published: January 2005

A theory is developed for nonresonant dipolar absorption of microwaves and for spin-relaxation times in polyatomic gases. Molecular reorientation produced by independent binary collisions results in nonresonant absorption of the Debye shape. The correlated effects of two, three, etc., successive binary collisions produce corrections to the Debye form. These correlations are present because the amount of angular momentum transferred by a given collision depends on the initial rotational state, which in turn is determined by previous collisions. Keeping only correlations through two collisions gives a good account of the pressure and frequency dependence of nonresonant-absorption experiments. The collision cross sections and correlation parameters used in this description are defined in terms of the changes in rotational motion produced in collisions. These results permit quantitative study of intermolecular torques and molecular-collision dynamics by the methods of nonresonant microwave absorption and nuclear resonance.
Calculated Ion-to-Molecule—Ion Ratios for Electron-Bombardment Studies of Molecular Hydrogen and Its Isotopes
Authors: Cashion J. K.
Published: January 2005

Recent accurate calculations of the H2+ and H2 potentials have been used in computing the ratios X+/X2+ (where X is H, D, or T) which arise from the electron bombardment of hydrogen and its isotopes. Values are given for a range of electron energies for the ground vibrational states. Values for 30-V electrons are given for those vibrationally excited states which would contribute to the ratio in shock-tube studies. All these values should be limited in accuracy only by the assumption of the Franck—Condon principle which underlies the calculation. Comparison with experiment shows discrepancies of +6%, −16%, and −11% for hydrogen, deuterium, and tritium, respectively.
Near-Ultraviolet Absorption Spectrum of Polyethylene
Authors: Partridge Roger H.
Published: January 2005

The apparent absorption spectrum of polyethylene is studied between 1μ and the onset of true polymethylene absorption (described in the following paper) at 1780 Å. The apparent absorption is found to be caused by surface and Rayleigh scattering, by unsaturation in the polymer chains, and by a number of products of oxidation reactions some of which consist of polycyclic aromatic molecules. The aromatic compounds are at least partially responsible for the fluorescence, phosphorescence, and thermoluminescence of polyethylene, for its various chemical reactions under uv irradiation, and probably also for much of its electrical conductivity; the same may be true also for solid and liquid alkanes. A simple method is found for removing most of the oxidation products from polyethylene, so increasing its chemical purity and enabling the oxidation products themselves to be studied separately in solution.
Electron Spin Resonance Identification of an N2− Defect in X-Irradiated Sodium Azide
Authors: Gelerinter Edward , Silsbee Robert H.
Published: January 2005

A defect is produced in sodium azide (NaN3) by exposing it to x rays and is studied using the ESR (electron spin resonance) technique in the frequency range of 10–70 kMc/sec. The observed spectrum agrees with the theoretical predictions made using a model of an N2− ion in the azide position with the surroundings frozen in a Jahn—Teller distortion. Since the azide ion is in a position of trigonal symmetry, there are three such distortions, and there is experimental evidence that these three distortions are equally populated. The absence of experimental evidence for tunneling does not necessarily imply correspondingly low tunneling matrix elements, but instead may be the result of stabilization of the static states by the strain which is known, from x-ray data, to be present. These strains are also responsible for some of the observed line broadenings. The available crystals are heavily twinned, so that it is necessary to correlate x-ray and ESR data in order to remove the ambiguities associated with this twinning.
Atom—Atom Ionization Mechanisms in Argon—Xenon Mixtures
Authors: Kelly Arnold J.
Published: January 2005

The atom—atom ionization process occurring in high-purity argon—xenon mixtures has been investigated by means of a conventional shock tube employing a microwave probe to monitor the electron-generation rate. All tests were conducted at approximately atmospheric pressure and at temperatures in the range between 5000° and 9000°K, corresponding to a neutral-particle density of 7.0×1017 cm−3. The cross-sectional slope constant for xenon ionized by collision with an argon atom is 1.8×10−20 cm2/eV±20%, that is, equal to that for xenon ionized by collision with another xenon atom. The data for the reaction of argon ionizing xenon are consistent with an activation energy of 8.315 eV, that is, of the xenon—xenon, atom—atom ionization process. No data were obtained for xenon ionizing argon. Good correlation was obtained between the cross sections for electron elastic momentum exchange derived from the microwave experiment and those obtained from beam experiments.

The argon—xenon ionization cross section implies that, for atom—atom processes in the noble gases at pressures ∼1 atm and temperatures ∼⅔ eV, the ionization cross section is independent of the electronic structure of the projectile atom.
Infrared and Raman Spectra of Carbon Suboxide in Condensed Phases
Authors: Smith Wm. Hayden , Leroi George E.
Published: January 2005

Infrared and Raman spectra of liquid, crystalline, and matrix-isolated carbon suboxide have been obtained in the region 20–4000 cm−1. A previously unreported solid—solid transition has been observed at 115°±5°K, and possible structures for both crystalline phases have been inferred from the spectroscopic results. The πu central-carbon bending mode ν7 has been identified in the liquid phase at 72±2 cm−1. The problem of ``disappearing'' sum bands is discussed, and a revised vibrational assignment and force-constant analysis for carbon suboxide is presented.
Infrared and Raman Spectra of Carbon Subsulfide
Authors: Smith Wm. Hayden , Leroi George E.
Published: January 2005

Infrared and Raman spectra of carbon subsulfide (C3S2) in various phases have been obtained in the region 30–4000 cm−1. Mass and ultraviolet spectra are also presented. Analysis of the vibrational spectra indicates a D∞h structure. Of particular interest is the 94-cm−1 band assigned as ν7, the central-carbon bending frequency, which lies at a higher frequency than the analogous band in C3O2. A vibrational analysis has also been performed.
Single-Center Calculation of NH3
Authors: Bishop David M.
Published: January 2005

A single-center molecular wavefunction for NH3 consisting of nine terms is obtained. Each term is a symmetry-adapted combination of Slater determinants which are composed of Slater-type orbitals of noninteger principal quantum number. Up to and including f orbitals are considered. The H–N–H angle is found to be 104°10′ (experimental: 106°46′) and the bond distance to be 1.86 a.u. (experimental: 1.916 a.u.).
14N Quadrupole Coupling Constants in N2O by High-Resolution Microwave Spectroscopy
Authors: Sancho Michael , Harmony Marlin D.
Published: January 2005

The J=1←0 microwave transition of 14N2O has been investigated under high resolution. Analysis of the hyperfine structure has given the values of the quadrupole coupling constants of the two nitrogen nuclei, viz., χend=−0.792±0.005 MHz and χcentral=−0.238±0.005 MHz. Spin—rotation energy terms were included, and with the assumption that the spin—rotation constants of the two nuclei were identical, a value of M=−0.003±0.001 MHz was obtained for the spin—rotation constant. These results have been interpreted in terms of other molecular properties.
Ionization Mechanism of Chromium in Cr–Ar Mixtures
Authors: Shackleford W. L. , Penner S. S.
Published: January 2005

Time-resolved emission measurements have been performed behind reflected shocks in mixtures of Cr(CO)6 and Ar, for wavelength regions including the 3421.2- and 3422.7-Å transitions of Cr(II) and the 3976.7-, 3983.9-, and 3991.7-Å transitions of Cr(I); a single measurement was performed for the 4254.4-Å resonance line of Cr(I). Under the experimental conditions used in our studies, self-absorption was not important, except possibly for the resonance line of Cr(I) at 4254.4 Å. The observed time—intensity data in the three spectral regions are consistent with the following excitation and ionization model of Cr in an Ar bath at temperatures of about 7000°K: (a) Cr(I) is excited by collisions with electrons and/or atoms to levels which lie approximately 3.1 eV above the ground level; (b) excitation to more highly excited levels of neutral chromium occurs very rapidly; (c) ionization occurs from the excited electronic states of Cr(I) by rate-controlling processes that involve inelastic collisions with either electrons or neutral atoms.
High-Pressure Decomposition of Synthetic Garnets
Authors: Marezio M. , Remeika J. P. , Jayaraman A.
Published: January 2005

The stability of synthetic garnets {Y3}[Fe2](Fe3)O12, {Y3}[Al2](Al3)O12, and {Y3}[Ga2](Ga3)O12 has been investigated at high pressures and high temperatures. Decomposition to the YXO3 compound (X=Fe or Al) with the perovskitelike structure and to the sesquioxide with the corundum structure has been found to occur in the former two garnets: {Y3}[X2](X3)O12→3 YXO3+X2O3, while in the case of yttrium—gallium garnet no breakdown was detected at pressures up to 44 kbar and 1000°C. The three garnets seem to behave differently at high pressure and high temperature. This appears to be related to the differences in the preference of the three cations for the tetrahedral site.

Results of preliminary studies of the effect of high pressure and high temperature on Li0.5Fe2.5O4 are presented.

The geophysical implications of the decomposition under high pressure and high temperature of the garnet structure are discussed.
Growth of Potassium Chloride Crystals from Aqueous Solutions. I. The Effect of Lead Chloride
Authors: Botsaris G. D. , Mason E. A. , Reid R. C.
Published: January 2005

Single crystals of potassium chloride were grown from aqueous solutions under carefully controlled conditions of supersaturation, agitation, and impurity lead chloride concentration. The growth rate of the (100) face was determined.

It was found that PbCl2 concentrations as low as 10−8 moles PbCl2/mole KCl decreased the rate of growth, and the retardation increased markedly with increasing PbCl2 concentration. The growth process changed from a layer type to a dendritic form over a small supersaturation range. Mass transfer rates of both KCl and PbCl2 from the solution to the crystal face were estimated and conditions delineated where each may be the rate-controlling step. A mechanism is proposed to account for the formation of crystal clusters on the surface of KCl at slow stirring rates.
Spectroscopic and Laser Properties of Europium α-Naphthoyltrifluoroacetonate in Solution
Authors: Riedel E. P. , Charles R. G.
Published: January 2005

Ultraviolet radiation absorbed by the organic ligands surrounding the europium ion in europium α-naphthoyltrifluoroacetonate Eu(α-NTF)4− is efficiently converted via intramolecular energy transfer to fluorescence characteristic of Eu3+. The quantum efficiency for this process is shown to be a constant from 2600 to 3900 Å in acetonitrile solution. Laser operation has been observed at temperatures up to −10°C. The effect of the relatively high scattering losses on both the threshold and the radiance of the laser are discussed.
Solubility of Naphthalene in Compressed Methane, Ethylene, and Carbon Dioxide. Evidence for a Gas-Phase Complex between Naphthalene and Carbon Dioxide
Authors: Najour Gerald C. , King Allen D.
Published: January 2005

The solubility of solid naphthalene in methane, ethylene, and carbon dioxide has been measured over ranges of pressure from 1 to 130 atm and of temperature from 23° to 73°C. Second virial coefficients calculated from the measurements indicate the existence of a complex between naphthalene and carbon dioxide in the gas phase.
Second-Order Perturbation Theory of the Mean-Square Radius of a Linear Polymer Molecule
Authors: Yamakawa Hiromi , Aoki Akihiro , Tanaka Genzo
Published: January 2005

A second-order perturbation theory of the expansion factor αS for the radius of gyration of a linear polymer molecule is presented. The result is αS2=1+1.276z−2.082z2+···,where z is the well-known excluded-volume parameter. A Ptitsyn-type closed expression for αS is also presented. Upon combining this and the corresponding expression for the expansion factor αR for the end-to-end distance, there is obtained the relation αR2/αS2=1.06 at large z. This is in excellent agreement with the Monte Carlo result obtained by Wall and Erpenbeck.
Microwave Spectrum, Structure, and Dipole Moment of Diazoacetonitrile
Authors: Costain C. C. , Yarwood J.
Published: January 2005

The microwave spectra of the normal species and of three isotopic species of diazoacetonitrile, N2:CH·CN, have been investigated between 14 and 31 kMc/sec. The following parameters have been obtained: r8(C≡N) = 1.165±0.005, r0(C–H) = 1.082±0.004 (assumed), r0(C–C) = 1.424±0.006, r0(C=N) = 1.280∓0.010, r0(N≡N) = 1.132±0.010 Å; ∠HCC=117°±1°30′, ∠CCN=119°32′±30′. The data are consistent with a planar model. The spectra of molecules in the first and second excited states of a low-frequency in-plane bending vibration have been observed (ν=150±30 cm−1). Least-squares analysis of the spectrum of the normal species yields the centrifugal-distortion constants DJ=1.55±0.5 kc/sec, DJK=−89.73±2 kc/sec. The dipole-moment components obtained are μa=2.75±0.06, μb=2.08±0.04 D giving a resultant dipole moment of 3.45±0.07 D at an angle of 37°6′±30′ to the a axis.
Correlation Effects in Complex Spectra. I. Term Energies for the Magnesium Isoelectronic Sequence
Authors: Zare Richard N.
Published: January 2005

We present a method for the ab initio calculation of configuration interaction in many-electron spectra. It is based on the expansion of the total electronic wavefunction in terms of Hartree—Fock—Slater determinants, as calculated by the programs of Herman and Skillman. This procedure has been applied to several of the low-lying excited configurations of the magnesium isoelectronic sequence which are noted for the presence of violent perturbations causing term values arising from a single configuration to be distorted and/or inverted. Convergence to the observed energy separation between multiplet term values appears to be quite rapid, and the method offers promise as a means of including electronic correlation in the calculation of atomic properties. For example the calculated energy difference between the 1D and 3D terms arising from the 3s3d configuration differs from the observed energy difference by 24 cm−1 out of 1554 cm−1 for Mg I, 720 cm−1 out of 14 540 cm−1 for Al II, and 1969 cm−1 out of 22 820 cm−1 for Si III. Following a discussion of the nature and degree of configurational mixing with increasing nuclear charge along the magnesium isoelectronic sequence, an examination is made of the significance that can be attached to configurational assignments. An alternative nomenclature is proposed.
EPR of Pentavalent Molybdenum in Liquid Solutions
Authors: Abraham M. M. , Abriata J. P. , Foglio M. E. , Pasquini E.
Published: January 2005

The paramagnetic resonance of Mo5+ in liquid solution with two different (chloride and thiocyanate) complexes has been observed. In each case, a hyperfine interaction due to the odd isotopes of molybdenum was observed, in addition to the contribution of the zero-spin isotopes which yield a single line at the center of the spectrum. Upon freezing the solutions, the resonance spectra may be described by spin Hamiltonians possessing axial symmetry. The averages of the g tensor and the hyperfine tensor agree very well with the measured values obtained with the liquid solutions.
Orthogonality to Lower States and the Hartree—Fock Method
Authors: Perkins J. F.
Published: January 2005

By a simple adaptation of a theorem regarding quadratic forms it is shown that imposition of the stationary-energy requirement on Rayleigh—Ritz, and in certain cases Hartree—Fock trial functions, has the effect of constraining the trial function to be orthogonal to lower-state functions which are ``most effective'' in raising the higher-state energy, rather than to the exact wavefunctions of the lower states. Hence these methods lead to energy overestimates arising both from improper orthogonalization and from limited flexibility of trial function. He 1s2s 1S was calculated by use of expansion-type Hartree—Fock trial functions which were constrained to be orthogonal to various approximate forms of the 1s21S function, including a ``most effective'' one. The energy overestimate arising from improper orthogonalization was small compared with that resulting from limited flexibility of trial function.
Inelastic Excitation Transfer in Helium
Authors: Teter M. P. , Robertson W. W.
Published: January 2005

When the positive column of a helium glow discharge is irradiated with intense 5016 Å (21S−31P) light, the population of the 31P state can be markedly increased without affecting the discharge parameters. The resulting enhancement of radiation from the n=3 states allows an upper limit of 4×10−17 cm2 to be placed on the cross section for transfer of excitation by neutral collision in the reaction He(31P)+He→He(33P)+He. This is to be compared on the one hand to reported values ranging from 1.3 to 7.8 times the gas-kinetic cross section, 1.5×10−15 cm2, and on the other to a different interpretation of similar experimental results that does not require the above reaction with its violation of the Wigner spin-conservation rule.
On an Asymptotic Solution of the Poisson—Boltzmann Equation—The Moderately Charged Cylinder
Authors: MacGillivray A. D. , Winkleman J. J.
Published: January 2005

The Poisson—Boltzmann equation is considered in the case of a uniformly charged circular cylinder in an environment containing added electrolyte. The problem is recognized to be a ``singular perturbation'' problem and a uniformly valid asymptotic approximation is found in the case of a ``moderately charged'' cylinder, with the surprising result that the solution to the Debye—Hückel equation is an appropriate approximate solution. Results of numerical integration of the Poisson—Boltzmann equation are included to verify the validity of the analytic results.
New Type of Molecular Perturbation Treatment
Authors: Hirschfelder Joseph O. , Silbey Robert
Published: January 2005

A new type of perturbation treatment is developed for molecular problems using a product of atomic or molecular orbitals as the zeroth-order wavefunction. A special feature of this procedure is that all of the quantum states arising from a single electronic configuration are treated simultaneously. The formulas are derived for a general molecular configuration. For the special case of H2+ where the 1s atomic orbital leads to both a symmetric and antisymmetric molecular state, our basic equation is Ha=12(Es+Ea)a+12(Es−Ea)bwhere the exact unnormalized wavefunctions for the symmetric and antisymmetric states are ψs=a+b and ψa=a—b, respectively. This basic equation is used to generate a set of perturbation equations, the zeroth order being the Schrödinger equation for a separated hydrogen atom. The interaction of three hydrogen atoms in their ground state is also considered as an example. In general, the energy through the first order agrees with the Heitler—London formalism.
Mössbauer Effect in Compounds of 127I
Authors: Perlow G. J. , Perlow M. R.
Published: January 2005

The Mössbauer effect of the 57.6-keV transition to the ground state of 127I, which follows the β decay of 127Tem, is used to measure the isomer shifts of a variety of compounds at 4.2°K. A comparison of the shifts with the quadrupole couplings in KICl2, KICl4, ICl, and I2 indicates no detectable contribution from iodine s orbitals to the bonds. A shift of 0.56 mm/sec is observed per p electron removed from the closed-shell I− configuration. With the aid of a shielding constant derived by Hafemeister, DeWaard, and DePasquali, one finds a shift of −2.8 mm/sec per s electron removed. With this, the orbital populations on iodine in IO4− and IO65− are determined from their shifts. It is found that localized sp3d2 hybrids for the latter lead to an unreasonable charge on the iodine while a delocalized description does not demand iodine 6d orbitals and can be made to give a reasonable result. For the tetrahedrally bonded IO4−, either description suffices and gives an acceptable answer. It is shown that frozen aqueous hydriodic acid is highly ionic while the condensed anhydrous substance is mainly covalently bonded. The substance produced when the Te in Te(OH)6 undergoes beta decay and subsequently emits the γ ray of interest is found to be mainly IO65− as shown by their relative shift. The large recoilless fractions found for telluric acid and the paraperiodate ion are attributed to the large ionic charge in a simple analysis.
Dependence of Sensitized Biacetyl Phosphorescence Intensity on Exciting-Light Intensity
Authors: Murov S. , McClure D. S. , Yang N. C.
Published: January 2005

The intensity of benzophenone-sensitized phosphorescent emission of biacetyl in solution was found to be dependent on the exciting-light intensity. The efficiency of emission decreases as the exciting-light intensity increases. The decrease in emission efficiency is attributed to the triplet—triplet annihilation of biacetyl.
Heats of Solution of Alkali Metals in Ammonia
Authors: Tuttle Thomas R. , Guttman Charles , Golden Sidney
Published: January 2005

The heats of solution of sodium and potassium in liquid ammonia are examined in terms of the redox model which has been proposed for the composition of these solutions. The heats of solution are shown to vary in an essentially linear manner with the spin paramagnetic susceptibility of the solutions, as expected from the model. Analysis of the data yields enthalpy changes for the redox equilibrium M++2S−⇌M−+2S,which are in reasonably good agreement with those obtained from the temperature variation of spin paramagnetic susceptibility. A temperature-dependent enthalpy is indicated for the redox equilibrium.
New Investigation of the 1SeAutoionizing States of He and H−
Authors: Holøien Erling , Midtdal John
Published: January 2005

The present investigation should provide some insight into the convergence properties of some particular upper roots of the full Hamiltonian. In this connection detailed calculations using the scaling-variation orthogonalization procedure with different subsets of the basis up to order 54 have been carried through both for He and H−.

Subsets including basic functions up to g—g are used, and a complete mapping of the ten lowest roots of the energy matrix by a continuous variation of the scale factor has been carried out within a definite range. The investigation clearly demonstrates the stabilizing ability of particular upper roots throughout the extension of the basis if the orthogonalization is properly achieved. These roots in the second-step solution may be associated with certain autoionizing states (quasi doubly excited, discrete states). The eigenvalues, obtained by optimizing the scale factor for these roots, are compared with those obtained for resonance positions in He+ and H elastic-scattering calculations by using other approximate methods, and by experiments.
Temperatures of Neutral Atoms in C-Stellarator Discharges and Charged-Particle Temperatures of the Afterglows
Authors: Hirschberg Joseph G. , Hinnov Einar
Published: January 2005

The kinetic temperatures of neutral helium and hydrogen atoms in ohmically heated discharges of the C stellarator were determined from measurements of spectral profiles of the λ4921, 21P−41D line of HeI and the Hβ line of hydrogen. The time resolution of the measurements was about 250 μsec, or about 110 of the duration of the discharge. It was found that the neutral atoms were at all times at a temperature much higher than the walls of the discharge vessel, with highest temperatures in the neighborhood of 2 eV. The results are interpreted in terms of energy transfer between electrons and ions through Coulomb collisions, between ions and neutral atoms through resonant charge exchange, and between neutral atoms and the walls through semielastic collisions. In addition, the temperature of the recombining ions in the afterglow of the discharges was determined by the same method, and found to be in good agreement with simultaneously measured electron temperatures.
Geminal Isotope Effects on the Proton Magnetic Resonance of Some First-Row Molecules
Authors: Bernheim R. A. , Batiz-Hernandez H.
Published: January 2005

Geminal substitution of H by D in first-row molecules generally causes upfield shifts in the proton magnetic resonance. These isotope shifts are sometimes explained in terms of intramolecular electrostatic effects. This work shows that they can also be considered as being due to the changes in bond rehybridization accompanying small changes in molecular geometry upon isotopic substitution. The diamagnetic part of the magnetic shielding at the protons in NH3, CH4, and CH3D was evaluated as a function of HNH or HCH bond angle using localized equivalent orbitals constructed from Slater atomic orbitals. The treatment for CH3D differed from that for CH4 in that the shorter experimental CH bond distance was used. The results of the calculation showed that the magnetic shielding at the proton in a NH or CH bond increased with decreasing bond angle, and with a decrease in bond distance. For small changes in geometry, similar to what is experimentally found upon isotopic substitution, the calculated change in shielding was the same order of magnitude as that experimentally observed. Consideration of isotope shift data on first-row molecules reveals that the magnitude of the shift is also a function of the initial molecular geometry, being larger for molecules with smaller HXH bond angles (X=C, O, N) and H–H internuclear distances. Isotope shifts were measured for CH2Cl2, CH2Br2, and CH2I2. Upon monodeuteration the proton magnetic resonance shifted upfield by 0.0125±0.0003, 0.0137±0.0002, and 0.0135±0.0002 ppm, respectively. The measured JHD spin—spin coupling constants were also measured for these molecules and found to be in agreement with previous work.
On the Symmetry of Slater Determinantal Wavefunctions
Authors: Gallup G. A.
Published: January 2005

A method involving the use of characteristic polynomials of irreducible representation matrices of groups and yielding the symmetry species of Slater determinantal functions is given. The necessary polynomials have been calculated for the commonly occurring symmetry groups and are listed to supplement the usual character tables.
Interaction of Triplet Excitons and the Line-Shape Function
Authors: Iguchi Kaoru
Published: January 2005

The general scheme of the interaction of triplet excitons is formulated to remove the degeneracy of spin energy levels of the system and predict the spread of each spin absorption line in the zero-field magnetic resonance spectra.

An approximate function of quasi-Lorentz type is derived for the shape of spectrum which represents the feature for different numbers of excitons interacting effectively. The maximum slope width is computed and it is proportional to the square of exciton density. Discussion is made in comparison with experimental data.
Pyrolysis of Ethylene in Shock Waves
Authors: Gay I. D. , Kern R. D. , Kistiakowsky G. B. , Niki H.
Published: January 2005

The pyrolysis of ethylene, highly diluted by neon, was studied in the temperature range 1710°—2170°K with reflected shock pressures of 225 to 1600 torr. The products are C2H2 and H2 with some diacetylene at higher temperatures. The rate law is −d[C2H4]/dt=k32[C2H4][Ne]12 over a threefold ethylene and sixfold neon pressure range and the rate constant is given by log10k32=(0.01±0.19)−(50 500±1700)/2.303RT (cc/molecule)12sec−1.

In experiments with equimolar C2H4+C2D4 mixtures the hydrogen formed initially contains as much HD as H2 although at the same temperatures the reaction H2+D2→2HD is found to be relatively slow. In experiments with C2H4+D2 mixtures as much HD as H2 is formed in pyrolysis. Some relatively slow isotopic exchange between ethylenes and between C2H4 and D2 occurs, forming mainly C2H3D in the latter case.

An unexpectedly high sensitivity of the mass spectrometer to hydrogen formed in the pyrolysis suggested that it may be formed in vibrationally excited states. A number of diagnostic experiments could neither confirm nor reject this possibility.

Both a simple unimolecular reaction C2H4+M→C2H4*→C2H2+ H2*+M (where H2* is a vibrationally excited molecule) and several free-radical chain mechanisms of the Rice—Herzfeld type can describe the observed kinetics, although in all cases the relatively low observed activation energy is very difficult to explain. Thus no clear-cut identification of the most probable reaction mechanism is possible.