bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymer NMR Spectroscopy. XI. Polystyrene and Polystyrene Model Compounds
Authors: Bovey F. A. , Hood F. P. , Anderson E. W. , Snyder L. C.
Published: January 2005

The high-resolution NMR spectra of isotactic and ``atactic'' polystyrene in tetrachloroethylene and o-dichlorobenzene are compared to the spectra of the model compounds, meso- and dl-2,4-diphenylpentane. Analysis shows that despite marked differences in the appearance of the polymer and model spectra—particularly in the β-methylene region—isotactic polystyrene has the same local conformation as the meso pentane. This conformation is a segment of the 31 helical conformation which isotactic polystyrene is reported to have in the crystalline state. It is probable that this conformation is quite strongly preferred for all isotactic vinyl polymers. This does not necessarily mean, however, that such polymers exist as 31 helices in solution (although polystyrene probably does) because the chains may deviate widely from a 31 helix by undergoing mirror inversions of the local conformation with little net expenditure of energy. Thus, NMR does not at present allow us to make any larger statement concerning the over-all polymer conformation (e.g., the end-to-end distance) in solution.

For the dl-pentane, two conformations are present, their proportions varying with temperature. This finding cannot, however, be readily related to the conformation of syndiotactic polystyrene (or of the syndiotactic sequences in ``atactic'' polystyrene) because the NMR spectrum of ``atactic'' polystyrene, unlike that of the isotactic, is too poorly resolved to give the necessary information. It appears that there may be other, more favorable cases for which this can be done.
Dipolar Broadening of EPR Spectra Due to Solute Segregation in Frozen Aqueous Solutions
Authors: Ross Robert T.
Published: January 2005

EPR spectra of Mn2+ and Gd3+ in a number of frozen aqueous solutions show that ice crystallization causes extensive segregation of solutes. The concentration of paramagnetic ions thus induced results in dipolar broadening of EPR spectra, and published spectra of frozen aqueous Mn2+ are reinterpreted accordingly. This segregation effect may be reduced by the addition of quantities of experimentally inert solute.
Thermoelectric Power of Some Organic Photoconducting Dyes
Authors: Petruzzella N. , Nelson R. C.
Published: January 2005

The thermoelectric effect in several cationic-dye photoconductors has been investigated. For all, there was an inverse relationship between illuminance and thermoelectric power. In the case of rhodamine-B, the magnitude of the effect could be calculated from published kinetic and ESR data for this substance, using a localized-process model. The effect of varying illuminance was ascribed to a logarithmic distribution of the characteristic trapping levels over a range of 0.12 eV. For crystal violet, the thermoelectric power calculated from a similar model is about 50% higher than that observed, for reasons unknown. Attempts to interpret the data in terms of a simple band model proved unsatisfactory.
Study of Molecular Orbital Degeneracy in C5H5
Authors: Liebling Gerald R. , McConnell Harden M.
Published: January 2005

The paramagnetic resonance of the cyclopentadienyl radical (C5H5) has been observed in a single oriented crystal of cyclopentadiene at temperatures ranging from 25° to 150°K. The spectra are of two types, high-temperature and low-temperature spectra, with the transition occurring reversibly between 70°K and 120°K. The high-temperature spectra consist of six equally spaced lines with a splitting of 6.2 G and can be accounted for in terms of a uniform spin distribution around the ring and rapid reorientation of the ring in its plane. The low-temperature spectra are slightly anisotropic and can be reasonably well accounted for by a distorted C5H5 radical with a nonuniform spin distribution undergoing rapid reorientation in its molecular plane.
New Rydberg Series in Molecular Oxygen near 500 Å
Authors: Codling K. , Madden R. P.
Published: January 2005

Previously unknown resonances in the continuous photoionization absorption of molecular oxygen have been observed spectroscopically in the 500–600-Å region, using the NBS 180-MeV electron synchrotron as a background source. These resonances form four Rydberg series, two converging to a level in O2+ at 24.564 (±0.004) eV, the others converging to a level in O2+ at 24.754 (±0.004) eV. The resonances are caused by high-lying autoionized states of neutral oxygen; the transitions involve the excitation of an inner σu2s electron to outer nsσ or ndπ orbitals. Additionally, this work confirms the LeBlanc analysis of the Hopfield emission bands at 2100 Å, as being due to transitions in O2+.
Condensation of Tungsten on Tungsten in Atomic Detail: Observation with the Field-Ion Microscope
Authors: Gurney Theodore , Hutchinson Franklin , Young Russell D.
Published: January 2005

Tungsten has been condensed onto a clean tungsten point in a field-ion microscope held at liquid-nitrogen and liquid-hydrogen temperatures. Stepwise field evaporation has been employed to observe the structure of the deposit in atomic detail. The first layer of deposited tungsten atoms above the substrate appears to contain one-fourth to one-third vacancies. A brief discussion is given of the possibility of extending the range of specimens observable in the field-ion microscope by employing a shadowing technique which would leave a highly detailed imprint of the specimen on the emitter surface. It is concluded that the imperfect first layer of deposited tungsten observed in these studies would reduce the fidelity with which the details of the specimen could be observed for high-resolution microscopy.
Observations of Negative Ions in Oxygen and Water Vapor by Ion Cyclotron Resonance
Authors: Wobschall Darold , Graham J. R. , Malone D. P.
Published: January 2005

Observations were made of the cyclotron resonance absorption of O—, O2—, H—, OH—, and H2O— in oxygen containing water vapor. A technique utilizing a circularly polarized rf electric field is described which allows the cyclotron resonance absorptions of negative and positive ions to be distinguished. The production of O2— was found to depend on the presence of water vapor as well as oxygen and is probably due to charge exchange with H—.
Evaluation of Parameters in Semiempirical Molecular Quantum-Mechanical Calculations
Authors: Brown Thomas H. , Taylor Robert L.
Published: January 2005

General analytic expressions are given for the partial derivatives of both eigenvalues and eigenvectors with respect to the various molecular integrals, or parameters, which appear in the secular equation in molecular quantum-mechanical problems. Since most physical properties of interest depend upon the various eigenvalues and eigenvectors in a straightforward manner, it is then possible to evaluate analytically the derivatives of the calculated values of these properties with respect to the various parameters associated with the problem. With the aid of nonlinear estimation procedures, it is therefore possible to readily find that set of parameters which gives the ``best fit'' to a particular set of experimental data. Thus a systematic procedure for evaluating these parameters is available.
Production of Aluminum Hydride by Hydrogen-Ion Bombardment
Authors: Appel M. , Frankel J. P.
Published: January 2005

An ultrapure aluminum target specimen was bombarded with 12.5-MeV deuterons for 300 μA·h. The specimen was sufficiently thick so that all the hydrogen was trapped within it. At no time did the temperature exceed 300°F.

X-ray diffraction studies of the specimen indicated the formation of a new phase with the hexagonal structure predicted for aluminum hydride and d spacings which coincide with those given for aluminum hydride in the literature. Least-squares analysis of 21 diffraction peaks shows a hexagonal structure with c/a=1.57±0.05, c=4.55±0.08 Å, and a=2.90±0.05 Å.
Theoretical Study of C–H Nuclear Spin—Spin Coupling Using a Constrained SCF Model
Authors: Bartow D. S. , Richardson J. W.
Published: January 2005

A constrained SCF model is used in an ab initio calculation of C–H nuclear spin—spin coupling constants. The C–H bond of some molecule of the general form, R≡C–H, is treated as a diatomic molecule in the molecular orbital approximation. The subsequent self-consistent-field calculation is performed subject to the constraint of orthogonality between the resulting molecular orbitals and the valence hybrid atomic orbitals centered on the carbon atom, representing the residue of the original R—C bond(s). Calculations are carried out for the sp3, sp2, and sp hybrid situations using both an optimized minimal basis set and an extended basis set. The further dependence of the coupling constant JCH on the C–H bond distance is examined. The extended-basis-set treatment is found to be preferable to the use of a minimal basis set from the standpoints of accuracy and of the efficiency of parameter variation. The computed coupling constants resulting from such extended-basis-set calculations differ from experimental JCH values for representative compounds of sp3, sp2, and sp hybridization by 11.2%, 13.7%, and 23.0%, respectively.
Orbital Theories of Electronic Structure. II. Molecularly Invariant Orbitals
Authors: Adams William H.
Published: January 2005

We express mathematically the question: Do orbitals for localized groups in molecules exist such that they are accurately the same in all molecules containing the same localized electron group? The advantage of giving the question mathematical form is that then the search for such molecularly invariant orbitals requires that accurate Hartree—Fock calculations be carried out only on a set of reference systems. Constructing the Hartree—Fock wavefunction of a molecule from the localized orbitals of subgroups in the reference systems, one can then test the accuracy to which the subgroup orbitals are molecularly invariant orbitals. Based on our quantitative approach, we present arguments and suggest conditions which favor the existence of molecularly invariant orbitals. The conditions favoring their existence are as follows. (a) The subgroup orbitals in general should not be orthogonal to the orbitals of any other subgroup in a molecule. (b) The subgroup orbitals should be well localized, in the sense that they are small in the neighborhood of the nuclei of the other subsystems. (c) The nuclear separations in the molecule from which the localized orbitals are taken, and the nuclear separations in the molecule to which the orbitals are transferred, should be identical. (d) If two molecules differ only through the substitution of one ion for another, the most favorable case will be that in which the two ions have the same net charge. (e) The differences between the eigenvalues of the orbitals of a subsystem in one molecule and those of the same subsystem in another molecule decrease at least as rapidly as the fourth power of the reciprocal of the separation of the subsystem from the rest of the system, for increasing separation.
Induced Infrared Absorption of Solutions of H2 and D2 in Liquid Neon
Authors: Ewing George E. , Trajmar Sandor
Published: January 2005

The induced infrared absorption spectra of solutions of H2 and D2 in liquid neon (27.2°K) have been studied. Absorption features were found which differed by less than 7 cm−1 from frequencies of vibration—rotation transitions expected for the freely rotating H2 or D2 molecule. Rotatory energy levels of H2 and D2 in neon solution are, therefore, essentially the same as for gas-phase molecules. Evidence for quantized translational energy levels for the solute was found. Broad absorption features which shift in frequency with isotope change in solute are assigned to vibration—translation combination bands in which the H2 (or D2) molecule, in addition to increasing its vibrational level, increases its translational level in its solvent cage. The spectroscopic determination of quantized-translational energy levels permits the estimation of a solute—solvent interaction potential. A harmonic-oscillator potential to describe the intermolecular interaction is consistent with the observation that the translational energy levels for D2 in neon are √2 smaller than those of H2 in neon. This quadratic potential is also in order-of-magnitude agreement with the potential calculated from the Lennard-Jones and Devonshire cell model of the liquid state. The problems of quantitative determination of translational energy levels from spectroscopic data are discussed. This study has provided a spectroscopic estimate of the liquid-state interaction potential for the H2 and D2 neon system and an approximate evaluation of all the types of energy of the solute: vibration, rotation, and translation.
Proposed Theory of Calculating the Energy of Negative-Ion Resonant Elastic Scattering States and of the Pre-Ionization States of Electronic Spectroscopy
Authors: Taylor Howard S. , Williams J. K.
Published: January 2005

In elastic electron-impact experiments, with the subsequent formation of negative ions and pre-ionization spectral theory, similar theoretical problems arise. In both, autoionizing states of lifetime 10−14 to 10−12 sec are of basic importance, and also the variation principle is not applicable to the problem of the calculation of the energy. We propose here an approximate variation principle for calculating their energies and wavefunctions. The ideas are based on physical and nonanalytic arguments and tested successfully on the problem of elastic scattering of electrons by the hydrogen molecule, with an explanation of the H2— resonances observed by Simpson et al. and the H— resonance observed by Schulz.
Use of Gaussian Functions in the Calculation of Wavefunctions for Small Molecules. III. The Orbital Basis and Its Effect on Valence
Authors: Reeves C. M. , Fletcher R.
Published: January 2005

Further calculations on N, H, NH, and NH3 are used as a guide for the selection, in general, of symmetry types and screening parameters of Gaussian atomic orbitals in an LCAO—SCF—CI scheme. The paper also examines the sensitivity of predicted valence properties to the choice of orbital basis and to the amount of configuration interaction included.
Crossed-Beam Investigation of N2D+ Production in N2+—D2 Collisions
Authors: Turner B. R. , Fineman M. A. , Stebbings R. F.
Published: January 2005

The reaction N2++D2→N2D++D has been studied in a crossed-beam experiment. The angular distribution of the secondary ions was determined with a movable quadrupole mass filter. Differential cross sections have been obtained within the energy range 7.5 to 57.5 eV.

Total cross sections for this reaction have been determined using another crossed-beam apparatus in which the product ions are collected in toto. Total cross sections were also derived from the angular measurements, but less reliance is placed in these values.
Calculation of the Total Cross Section from Angular Measurements in Crossed-Beam Experiments
Authors: Colwell J. , Fineman M. A.
Published: January 2005

The total cross section is written as the sum of an integral taken over the scattered intensity measured in the plane of the initial velocity vectors and a correction term which itself is the sum of two integrals of the center-of-mass (c.m.) differential cross section. One of these integrals is taken from 0 to ε, the other from π—ε to π, where ε is the angle between the center-of-mass velocity and the relative velocity. In certain atomic or molecular scattering experiments, the angle ε is small; for these cases, it is shown that only a small error is made by dropping this correction term. This error is estimated for the case of isotropic scattering and for the case of glory scattering. In the latter case, the range of parameters for which the method is useful is given. In the event that the shape of the differential cross section is known a priori, the correction term can be calculated and the total cross section found exactly.
Thermal Generation and Spectrometric Measurement of Ba and Ba+ in a Hot Flame
Authors: Maček Andrej , Simmons John A.
Published: January 2005

The object of this program was formulation and laboratory study of a combustion system whose products contain both neutral (Ba0) atoms and Ba+ ions. The system consists of tetracyanoethylene, hexanitroethane, and barium peroxide, all solids at room temperature. In a series of digital-computer calculations, a mixture containing 8.0% BaO2, 52.6% C2(NO2)6, and 39.4% C2(CN)4 by weight was found suitable and chosen for experimental work. The calculated extent of ionization of barium in that mixture is 7.9%, at the adiabatic flame temperature of 3780°K. The mixture was prepared and pressed into strands of 1.65 g/cc density; its stability, sensitivity, and burning rate were studied. Flame spectrometry of the mixture yields line-intensity temperature of 3310±50°K. The experimental extent of ionization of barium, determined by the relative intensities of the Ba+ and Ba0 lines, is 9.0%. The calculated equilibrium ionization at 3310°K is only 2.2%. The discrepancy between the measured and calculated degrees of ionization is ascribed to incomplete combustion of electron-absorbing species, especially those containing the CN radical, which promote ionization of barium. Relevance of these laboratory studies to the performance of a scaled-up burner releasing gaseous barium in the upper atmosphere is briefly discussed.
Orbital Radii of Atoms and Ions
Authors: Waber J. T. , Cromer Don T.
Published: January 2005

Radii corresponding to the principal maxima in the radial distribution functions r2ψi2(r) have been obtained for the ground states of all the atoms in the periodic table. The relativistic wavefunctions employed were solutions of the Dirac equations. Slater's ρ⅓ method for including exchange and Latter's method for the self-interaction correction were used in ``creating'' the potential.

The radii corresponding to these maxima are used as measures of the size of each orbital. The relation between the orbital radii of the valence electrons is shown as plots for the first, second, and third series of transition elements.

In the elements below nobelium, only four maxima occur in the total charge-density function. The relation of these maxima to the shell structure of the atom and the effect of shielding by outer electrons are discussed. The effect of the relativistic contraction on orbitals of low angular momentum is shown.
Matrix Elements for Vibration—Rotation Transitions in the HBr Overtone and Hot Bands
Authors: Babrov Harold J. , Shabott Abraham L. , Rao B. Sesh
Published: January 2005

The strengths of the vibration—rotation lines of the first overtone, first hot band, and fundamental band of HBr have been measured by a curve of growth method, applying a correction for two overlapping lines devised by Sakai. The squares of the electric-dipole matrix elements |M02(m) |2 and |M12(m) |2 for the lines have been calculated, and have been fitted, respectively, to a cubic and quadratic polynomial in m, using the method of least squares. The experimental results for all three bands are compared with the theory of Herman and Wallis. The fact that the experimental |M02(0) |2 is less than that calculated from a linear dipole-moment function clearly requires a positive value of M2, the second derivative of the dipole-moment function.

The squares of the matrix elements |M01(0) |2 and |M02(0) |2 are used to calculate M1 and M2, the dipole-moment coefficients, for Morse and anharmonic oscillators. Of all the possible sets of M1 and M2 obtained in each case, the one giving results in better agreement with |M12(0) |2 is chosen. The chosen values of the dipole-moment coefficients are M1=+4.56×10−11 esu and M2=+0.69×10−3 esu cm−1 for the Morse oscillator and M1=+4.63×10−11 esu and M2=−0.70×10−3 esu cm−1 for the anharmonic oscillator. Since the sign of M2 is positive, the Morse oscillator results are preferred.
Quadrupole Splitting of the Magnetic Resonance Spectrum of 9Be in Chrysoberyl
Authors: Reaves Harry L. , Gilmer Thomas E.
Published: January 2005

The quadrupole coupling constant, the asymmetry parameter, and the orientation of the principal axes of the electri cfield gradient tensor were determined for the 9Be sites in chrysoberyl. These values were found to be: η=0.90±0.01 and | eQφzz/h |=318±2 kc/sec. Two different types of sites were found for the beryllium. These two sites are equivalent. One of the principal axes was found to be parallel to the crystalline c axis.
Shear Dependence of the Intrinsic Viscosity of Rigid Distributions of Segments with Cylindrical Symmetry
Authors: Hearst John E. , Tagami Yukiko
Published: January 2005

The theory of Hearst for the intrinsic viscosity of any segment distribution of cylindrical symmetry is used to calculate the shear dependence of such a model. Results are applied to the rigid rod and an approximate model of the random coil.
Spin Hamiltonian for a Many-Center Imperfection with Applications to the VK Center
Authors: Casselman T. N. , Markham J. J.
Published: January 2005

A spin Hamiltonian containing the interaction of a one-electron defect center with the surrounding ions is derived. It is shown, by means of the gauge invariance of perturbation theory that for a many-center imperfection in a magnetic field, that one may choose a different gauge for each force center such that the orbital angular-momentum operators refer to the individual force centers. The above result is found to be a consequence of the gauge transformation properties when orbital angular-momentum operators occur in the Hamiltonian. The spin Hamiltonian is applied to the g shift of the VK center and some qualitative results are obtained for the case of nonorthogonal atomic orbitals.
Hypervirial Functions and the Positive Powers of the Radial Coordinate Operator in He and H—
Authors: Gordon Sidney L.
Published: January 2005

Ground-state He and H— trial functions are scaled to satisfy the hypervirial relations generated by the family of hypervirial operators Wn=r1np1. These one-parameter hypervirial functions are used to calculate expectation values of the positive powers of the radial coordinate operators, rt, for t=1 through 20. Accurate values of 〈rt〉, for this range of t, are calculated using 20-term Hylleraas functions. A comparison of results shows that simple hypervirial functions of the form exp[—K(r1+r2)] scaled to satisfy the hypervirial relations generated by W2, give a good over-all calculation of 〈rt〉 for both He and H—.

The hypervirial theorem is used to develop a variety of expectation value relationships for one- and two-electron central force problems in the Appendix.
Ultrasonic Attenuation in Ammonium Chloride
Authors: Garland Carl W. , Jones Joseph S.
Published: January 2005

The attenuation coefficient α of longitudinal ultrasonic waves propagating along the [100] direction in single-crystal ammonium chloride has been measured as a function of frequency from 5 to 55 Mc/sec and as a function of temperature from 200° to 270°K. A sharp maximum is observed in α at the order—disorder critical temperature. The results are analyzed in terms of a relaxation model with a highly temperature-dependent relaxation time.
Single-Configuration Calculations on Excited States of Helium. II
Authors: Davidson Ernest R.
Published: January 2005

The best one-configuration wavefunctions for the first 18 excited states of helium have been found. The error in the energy varies from 2% of the ionization energy for the 2s 1S state to 0.1% for the 4f 3F state. The electron-repulsion integral is consistently larger for triplet states than for singlet states, in contradiction to more näive theories.
Improved Measurement of the Electric-Dipole Moment of the Hydroxyl Radical
Authors: Powell F. X. , Lide David R.
Published: January 2005

The Stark effect of the J=72,2π32, Λ-doublet transition of OH at 13 438 Mc/sec has been resolved and accurate measurements taken. The dipole moment of OH was determined to be μ=1.660±0.010 D.
Spin-Echo NMR Studies of Chemical Exchange. IV. Intramolecular Exchange of a Coupled AB System
Authors: Allerhand Adam , Gutowsky H. S.
Published: January 2005

A mathematical and experimental study of the spin-echo amplitudes in a Carr—Purcell train of echoes is reported for a coupled AB system undergoing intramolecular exchange. The density-matrix approach was used to derive a set of four coupled recursion relations for the amplitudes of successive echoes. It seems unlikely that the set of equations can be reduced to a simple analytical function applicable to the general case, so a program was written to investigate the properties of the system numerically with a high-speed computer. Such an analysis predicts that when the exchange rate 1/2τ is small compared with the coupling constant A in rad sec−1, the amplitude of the echo train is modulated. The modulation frequency depends on A, 1/2τ, and on the chemical shift δω and the rf pulse separation tcp. The modulation diminishes as the exchange rate increases, and it disappears when 1/2τ≳3A. In the latter case, the train of echoes decays exponentially with an apparent decay constant 1/T2 which is described by the semiclassical equations derived previously for the uncoupled AB system. These predictions have been verified by 19F spin-echo experiments at 16.70 and 25.27 Mc/sec on 1,1-difluorocyclohexane in which axial and equatorial fluorines are interchanged by the chair—chair isomerization. The condition 1/2τ≳3A is satisfied at temperatures above about −40°C. The complex, modulated echo trains observed at lower temperatures are very sensitive to instrumental instabilities and adjustments, and no serious attempts were made to use them for determinations of 1/2τ, A, or δω. However, exchange rates were obtained from the exponential decays observed at temperatures from −40° to 42°C, and the results are compared with those from a previous high-resolution study. Exchange rates were determined to much higher temperatures in the spin-echo experiments because they are unaffected by the H–F coupling, but neglect of the coupling in the high-resolution line-shape analysis leads to erroneous results once the coalesced linewidth approaches 〈JHF〉ex.
Activation Energy for the Sublimation of Gallium Nitride
Authors: Munir Zuhair A. , Searcy Alan W.
Published: January 2005

Gallium nitride was found to sublime congruently from a torsion—effusion cell when the ratio of orifice area to sample area was about 1/30 and incongruently to yield nitrogen gas and liquid gallium when this ratio was about 1/100 or less. A mass-spectrometer investigation revealed no measurable concentrations of gallium nitride vapor molecules. The heat of activation for the reaction 2GaN(s)=2Ga(1)+N2(g) was calculated to be 39 kcal at 1300°K from the temperature dependence of the effusion data.

The rate of the reaction 2GaN(s)=2Ga(g)+N2(g) was measured by a torsion—Langmuir method. From the temperature dependence of sublimation the heat of activation for this reaction was calculated to be ΔH1300‡=218.6 kcal compared to 173 kcal for the equilibrium reaction, and the entropy of activation was calculated to be 74.3 cal/deg.
Singlet-to-Triplet Conversion in Gas-Phase Naphthalene, Phenanthrene, and Anthracene
Authors: Zahlan A. B. , Weisz S. Z. , Jarnagin R. C. , Silver M.
Published: January 2005

A new method is presented for studying the radiationless process of singlet-to-triplet conversion in systems demonstrating delayed fluorescence via triplet—triplet annihilation. The usefulness of the technique was illustrated through application to the gas-phase emission of anthracene, naphthalene, and phenanthrene. The ratio of the first-order conversion constant kST to the singlet decay constant k in the pressure regions examined was 0.3 for anthracene (1–3 mm) and 0.2 for naphthalene (10–50 mm). For phenanthrene, kST/k increased from 0.3 to about 0.9 with increasing phenanthrene pressure from 10 to 50 mm. In all cases addition of N2 showed no effect.
Localized Excitations in Condensed Ne, Ar, Kr, and Xe
Authors: Jortner Joshua , Meyer Lothar , Rice Stuart A. , Wilson E. G.
Published: January 2005

Experiments are reported which lead to the conclusion that electronic excitation energy in solid and liquid Ne, Ar, Kr, and Xe can be trapped by the formation of excimers. The consistency of this conclusion with other electronic properties of these substances is briefly discussed.
Reversible Phototransfer of Electrons between Rare-Earth Ions in CaF2
Authors: Welber Benjamin
Published: January 2005

This paper describes the observation of a charge-transfer phenomenon occurring between divalent and trivalent ions incorporated into the CaF2 lattice. It is shown that, in one of the two cases considered, the phenomenon is reversible at 4°K.
Kinetic Evidence Concerning the Geometry of Substituted Methyl Radicals
Authors: Benson S. W. , Golden D. M. , Egger K. W.
Published: January 2005

The result of Noyes et al. that cis or trans di-iodoethylene will rapidly exchange I atoms with I2* via an I-atom addition to the double bond (relative to much slower geometrical isomerization) is shown to be compatible with a planar structure for the intermediate free radical. A tetrahedral structure for the free-radical end would lead to nearly equivalent rates of exchange and isomerization. The recent suggestion by Skell et al. that the stable form of the β-iodo-alkyl radical is I bridged is shown to be incorrect. His observations are explained in terms of the I atom catalyzed, concerted addition of I2 to the olefin.
Interfacial Tension Effects in Finite, Periodic, Two-Dimensional Systems
Authors: Mayer Joseph E. , Wood Wm. W.
Published: January 2005

We consider a two-dimensional system whose pressure specific area (p—v) isotherm (the temperature T being held fixed throughout our discussion) displays a first-order phase transition in the thermodynamic limit, i.e., as the number of molecules N and the total area V both tend to infinity for various fixed specific volumes v=V/N. When N is large but finite we adopt a macroscopic description of the system in which the total Helmholtz free energy A is given by additive contributions from the bulk properties of the two coexisting phases and an interfacial term appropriate to periodic boundary conditions. At fixed N and V we minimize A with respect to variations in the specific areas and amounts of the two phases and with respect to the shape of the interface, making a number of simplifying assumptions. The resulting p—v isotherm is found to have ``loops'' involving jump discontinuities, with three different forms appearing, depending upon the value of a dimensionless parameter involving the number of molecules N and the interfacial tension, and with coexistent phases found to exist only in the two cases involving larger values of N. The amplitude of the loop obtained by Alder and Wainwright for a system of 870 hard disks is used to make a crude estimate of the interfacial tension between two phases.
Static and Dynamic Frequency Shifts in Electron Spin Resonance Spectra
Authors: Fraenkel George K.
Published: January 2005

A detailed theoretical analysis has been made of the factors which affect the positions of the hyperfine lines in electron spin resonance spectra. The deviations from the usual high-field-approximation formulas are found to depend on the relaxation and line-broadening interactions [H1(t)] as well as on the well-known corrections to the high-field approximation that result from the exact solution of the time-independent static Hamiltonian [Ho]. The time-dependent processes H1(t) make a direct dynamic contribution to the frequency shifts, and in addition they alter the frequency spectrum of the static Hamiltonian. This latter effect arises because the dynamics of the system are properly determined by the total Hamiltonian Ho+H1(t), not just by the time-independent part Ho. The theory is developed in terms of the Redfield—Abragam relaxation-matrix formulation, but simple models are also treated by a limited but more easily handled procedure based on the modified Bloch equations.

The most interesting results predicted by the theory occur when there is a large alternating linewidth effect arising from modulations of the isotropic hyperfine splittings. Usually, the dynamic frequency shifts are less than the linewidths, but, when there is a large alternating linewidth effect, the dynamic shift is large compared to the width of the narrow lines in the spectrum even though it is still small compared to the width of the broad lines. The alternating linewidth phenomenon also changes the static frequency shift, e.g., in the case of two nuclei of spin I=1 it causes the mean relative static shift in the positions of the sharp lines to be a factor of 3 greater than in the absence of an alternating linewidth effect. The theory indicates that experimental studies of the frequency shifts and linewidths in appropriate systems should make it possible to determine both the magnitude of the mean-square fluctuations in hyperfine splittings and the correlation time characteristic of the fluctuating motions. The experimental determination of these two quantities, which appear only as adjustable parameters in previous theories, should make it possible to obtain considerable information about the inter- and intramolecular factors which influence the instantaneous structure of free radicals.

It has been rigorously shown that, when the width variations among a group of degenerate or nearly degenerate transitions are small, the net shift is determined by the average value of the shifts, both static and dynamic, of all the components involved in the set of degenerate transitions. Unresolved shifts from proton splittings (or from other nuclei with spin I=½) usually cause all the hyperfine lines to be shifted by the same amount, independent of whether or not the width variations are small. Normally, the shifts arising from the effects of tumbling motions on the intramolecular, anisotropic, electron—nuclear, magnetic-dipole interactions are small, as are those arising from the cross term between the dipolar and g-tensor interactions.
On the Electrophoretic Term of the Limiting Law for Electrical Conductance in Solutions
Authors: Friedman Harold L.
Published: January 2005

The model to which the cluster theory of conductance was applied in an earlier paper is extended to allow for nonpairwise contributions to the interactions among the ions. When the nonpairwise parts of the long-range hydrodynamic interactions are included in the cluster theory calculation, then the electrophoretic term of the limiting law found by Debye, Hückel, and Onsager is recovered.
Relaxation Term of the Limiting Law of the Conductance of Electrolyte Mixtures
Authors: Friedman Harold L.
Published: January 2005

The calculation of the limiting-law terms from the cluster theory of conductance, as presented in recent papers, is extended to solutions of mixtures of electrolytes. The more general evaluation of one of the cluster integrals required for this purpose is achieved by using some results from the theory of symmetric polynomials. The resulting relaxation term is very different in form from that of Onsager and Kim but, at least for solutions of three solute species, the two theories give the same numerical results for the ionic conductances in a variety of systems.
M
4 Band in Colored KCl and KBr
Authors: Hirai Masamitsu , Scott Allen B.
Published: January 2005

The M4 band, one of the absorption bands of the M center, was observed free from any interfering absorption in additively colored KCl crystals. The band maximum was found to lie at 633 mμ, the half-height width was 0.059 eV, and the oscillator strength was 0.052 that of the M1 transition. In KBr, the M4 band was observed near 700 mμ as a shoulder on the long-wavelength side of the F band.
Microwave Absorption and Molecular Structure in Liquids. LX. Intramolecular Relaxation Mechanisms in Aromatic Ethers and Several Related Molecules
Authors: Anderson James E. , Smyth Charles P.
Published: January 2005

The dielectric constants and losses of 11 aromatic ethers and related compounds in dilute benzene solution have been measured at wavelengths between 1.25 and 50 cm at temperatures from 20° to 60°. The substances measured are dibenzyl ether, benzyl phenyl ether, dicyclohexyl ether, 2-nitrophenyl phenyl ether, m-diphenoxybenzene, 4-bromophenyl phenyl ether, 4-biphenyl phenyl ether, phenoxathiin, thianthrene, triphenylphosphine, and triphenylchloromethane. The dielectric relaxation times calculated from these data indicate that most of the seemingly small values obtained result from combination of short, coupled, ring rotations with over-all molecular rotation.

Comparison of the dipole moment values calculated for twenty-three substituted phenyl ethers with the observed values gives no evidence of the large mesomeric moments seemingly necessary to make mesomeric charge shift a generally important factor in lowering the relaxation times of these molecules. The low relaxation time found for phenoxathiin probably results from combination of dipole orientation by a ``butterfly motion'' of the nonplanar molecule with orientation by over-all molecular rotation.
Liquid—Vapor Equilibrium in the System Neon—Argon
Authors: Streett W. B.
Published: January 2005

Liquid—vapor equilibrium phase compositions for the binary system neon—argon have been determined at seven temperatures in the range 84.42°−129.93°K and at pressures up to 1050 psia. The vapor-recirculation method of obtaining equilibrium was used in conjunction with a vapor-pressure-controlled cryostat, in which both liquid nitrogen and liquid argon have been used as the bath fluid. The results are presented in both tabular and graphical form, and the general behavior of the system is discussed. A comparison with some earlier data is given.
Magnetic Susceptibility and Crystal Structure of (Pyridine N-Oxide)-Copper(II) Chloride
Authors: Schäfer H. L. , Morrow J. C. , Smith H. M.
Published: January 2005

Magnetic susceptibility of (pyridine N-oxide)-copper(II) chloride, C5H5NOCuCl2, has been measured by the Faraday method from 90° to 300°K. The magnetic moment decreases rapidly with temperature; the dimeric structure proposed on the basis of magnetic behavior has been confirmed by the results of crystal structure determination. The crystals are monoclinic, P 21/b—C2h5, with four copper atoms in the unit cell of dimensions: a = 5.844 Å, b = 10.049 Å, c = 13.643 Å (all ±0.005 Å), γ = 104° 52′±10′. Data were collected by Weissenberg photography. The structure was determined from Patterson projections on (100) and (010) and refined by two dimensional electron density difference syntheses. The Cu–Cu internuclear distance of 3.23 Å is quite a bit larger than that observed in a number of dimeric copper systems. Another novel feature of the dimer is that it has distorted tetrahedral environment for copper in a binuclear system and consists of two distorted bisphenoids which share an edge.
Light-Scattering Study of Bentonite Solutions when Subjected to Electric Fields
Authors: Jennings B. R. , Jerrard H. G.
Published: January 2005

A brief account of the theory is given, and the results presented for a light-scattering study of Wyoming sodium bentonite solutions in the absence and presence of applied electric fields. Measurements made without electric fields gave no indication of the side-by-side aggregates found by other workers. If it is assumed that the particles are flat disks, the data indicates a radius of 3400 Å, and a thickness of 9.4 Å. The application of alternating current fields to solutions of polar or electrically anisotropic particles results in a change in the angular scattering pattern, and moreover enables a distinction to be made between these two classes. Furthermore such fields introduce an alternating scattered intensity component of twice the frequency of the applied field. The solutions were subjected to fields up to 374 V cm−1 at frequencies up to 400 cps and were found to consist of at least two kinds of particles. Consideration of the frequency dependence of the intensity changes enabled rotary diffusion constants to be estimated, which in turn indicated the relative particle sizes of the two constituents. Measurements of the alternating intensity changes supported the results obtained from the data with the nonalternating changes, and this confirms the usefulness of detecting and measuring these components. x-ray diffraction studies have revealed the two constituents of the bentonite to be sodium montmorillonite, gypsum, and quartz.
Structural Symmetry Consideration in the Calculation of Unperturbed Dimensions of Polymer Chains
Authors: Nagai Kazuo
Published: January 2005

The possibility has been examined that structural symmetry may be utilized to reduce the order of matrices to be treated in the calculation of unperturbed mean-square end-to-end distances of polymer chains. It is found that this is the case for a class of polymers possessing such a symmetry that when all the skeletal bonds are forced to be in the trans conformation the chemical structure is symmetric with respect to the plane involving skeletal bonds. For this class of polymers, the order of matrices is shown to be reduced from 3s to 32s when the cis and trans states are forbidden to occur, and from 3s to 32(s+1) when the cis state is forbidden but the trans state is allowed. Here s is the number of rotational isomeric states of skeletal bonds. It is suggested that the method is equally effective in the calculation of higher even moments of end-to-end distances and optical anisotropies of polymer chains.
Spectrum and Structure of the He2 Molecule. I. Characterization of the States Associated with the UAO's 3pσ and 2s
Authors: Ginter Marshall L.
Published: January 2005

The He2 band systems 3pσ, 1,3Σg+→2s, 1,3Σu+ are described in detail. The rotational and vibrational constants of the 2s, a 3Σu+ and A 1Σu+ and 3pσ, c 3Σg+ states are improved and the data for the A and c states extended from v=1 to v=3 and 4, respectively. The 3pσ C 1Σg+ state (identified for the first time) has been characterized through v=5. The apparent dissociation energy of the c 3Σg+ state is found to be ∼0.7 eV too high to be consistent with the theoretical dissociation energy of He2+. If the D0 value for He2+ is correct, large maxima must be present in the potential curves of a number of electronic states of He2. Also discussed is the observed and expected behavior of states associated with npσ UAO's.
Interpretation of the Infrared Spectrum of Boehmite
Authors: Wickersheim K. A. , Korpi G. K.
Published: January 2005

The infrared-absorption spectrum of the mineral boehmite is interpreted in terms of the normal modes of a linear zigzag chain of OH— groups. The results of deuteration experiments confirming this interpretation are described. Hydrogen bond lengths, determined from the infrared spectrum, are used to evaluate available x-ray measurements. Bond angles, calculated on the basis of the zigzag chain model, are in general agreement with x-ray results. The extreme sensitivity of the infrared spectrum of this compound to small changes in hydrogen bond length, as might be caused by compositional variations, is discussed.
Symmetry Numbers and Reaction Rates. II. The Computation of the Reaction-Path Degeneracy for Bimolecular Reactions
Authors: Schlag E. W. , Haller Gary L.
Published: January 2005

The reaction path degeneracy n is a needed parameter in the computation of a rate constant based on absolute rate theory since it is only partially provided by the symmetry numbers. The previous group theoretical method for deriving n is examined for the case of bimolecular reactions. Furthermore, this method is compared to a direct count of the number of reaction possibilities, and it is seen, by comparison, that there are some difficulties in the application of the direct count method. Some direct count rules are derived which should avoid these difficulties. The computation of equilibrium constants and rate constants for reactions involving optically active species is discussed.
Mechanism of the Acetylene—Oxygen Reaction in Shock Waves
Authors: Glass G. P. , Kistiakowsky G. B. , Michael J. V. , Niki H.
Published: January 2005

The oxidation of acetylene has been studied using sufficiently high gas densities and concentrations of inert gas to keep the reaction isothermal and reduce boundary-layer effects. The induction periods and exponential time constants of the oxidation have been measured using the observations of: (a) chemiluminescence and gas conductivity in incident and in reflected shock waves, and (b) total ionization and product formation using a time-of-flight mass spectrometer in reflected shock waves. The results are internally consistent, and the time constants τ are best represented by the following equation: log10(τ[O2])=−11.29+17 000/4.58Tin units of seconds·moles/liter. Induction periods are about eight times longer. The following reaction mechanism is most consistent with the data: H+O2=OH+Ok1=1/(4τionization[O2]),O+C2H2=OH+C2Hk2,OH+C2H2=H2O+C2Hk3,C2H+O2=2CO+Hk4,C2H+O2=CO2+CHk5.

Reaction (1) is rate-controlling, the above-defined value of k1 agreeing well with the work of others. The time constants τ for CO, CO2, and H2O are identical, indicating that they are all formed in the branching chain reaction, but those of ionization and luminescence are half as large. Diacetylene formation is observed in acetylene-rich mixtures. Experiments with added CO indicate that Reaction (5) is initially the main source of CO2.

The reactionC2H+O=CH(A2Δ)+CO  k6explains the observed chemiluminescence well.

Experiments with the mass spectrometer show that C3H3+ is the first ion observed. Other experiments suggest that the simple reaction CH(A2Δ)+C2H2=C3H3++e— k7 is not responsible for the ionization. Other possible mechanisms for the formation of C3H3+ are discussed.
Spin Dipole—Dipole Interaction in O2
Authors: Kayama Kunifusa
Published: January 2005

The electron spin dipole—dipole interaction in O2 is calculated nonempirically by the use of several approximate wavefunctions of the HL and LCAO—MO types. It is pointed out that the experimental value determined by Tinkham and Strandberg can hardly be explained by simple LCAO-type approximations; the calculated value would agree with the experiment only if the wavefunctions of this molecule were almost completely ionic.
Correlation Function Theory of Dielectric Relaxation
Authors: Cole Robert H.
Published: January 2005

The Kubo formalism is developed for polarizable dipolar molecules treated as harmonic oscillators in the relaxation counterpart of Kirkwood's equilibrium theory. Treatment of reaction field induced moments as in Onsager's model gives a generalization of the relaxation time ratio 3ε0/(2ε0+ε∞) proposed by Powles. The correlation function expression for relaxation is evaluated for several models: rotational transition probabilities including diffusion, nonequivalent dipole orientation sites, and flexible molecules with internal dipole reorientations.