bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Relaxation Study of the Anisotropy of Rotational Reorientation in Liquid Boron Trichloride
Authors: Allerhand Adam
Published: February 2004

Boron-11 and chlorine-35 nuclear magnetic relaxation measurements were used to determine the anisotropy of rotational reorientation in liquid BCl3. If the classical diffusion model is used, then the ratio of the rotational diffusion constants parallel and perpendicular to the C3 axis in 11B35Cl3 is 0.75 + 0.25, independent of temperature in the range − 90 to 30°C. The error estimate includes the effect of uncertainties in the 11B and 35Cl quadrupole coupling constants for the liquid. It is also shown that the determination of the anisotropy of rotational motion in liquids from relaxation times dominated by a quadrupolar mechanism is very sensitive to errors in the nuclear quadrupole coupling constants. This problem is least serious when the motion is nearly isotropic, as in BCl3.
Adsorption of Activated Nitrogen on Tungsten
Authors: Matsushita Kun-Ichi , Hansen Robert S.
Published: February 2004

Adsorption and desorption of activated nitrogen on a polycrystalline tungsten filament were studied by the flash filament desorption technique incorporated with mass spectroscopy and field emission microscopy. Nitrogen in excess of the β-nitrogen structure on tungsten is conveniently prepared by the adsorption of atomic nitrogen resulting from electron impact on nitrogen gas, or, less effectively, from thermal activation. The structure thus prepared is shown to be equivalent in all major properties to that prepared by decomposition of ammonia on tungsten at 800°K. Specifically, the (β + x)-nitrogen structure, prepared by activated nitrogen adsorption, can contain nearly twice the nitrogen of the β-nitrogen structure. x-Nitrogen flash desorption can be resolved from β-nitrogen desorption and is found to be second order in x-nitrogen with activation energy about 47.6 kcal/mole. When a β 15N predose is followed by an activated 14N dose extensive isotopic mixing occurs in both x- and β-nitrogen flash desorption peaks. All of these properties are, within experimental error, properties of the (β + x) structure obtained by ammonia decomposition on tungsten. Work-function–flash-temperature curves and field emission pattern photomicrographs obtained from a tungsten tip dosed with ammonia at 600°K can be very nearly duplicated by dosing with activated nitrogen instead. A model involving electron impact dissociation of nitrogen, adsorption and desorption of atomic nitrogen on glass, and formation of x-nitrogen from adsorption of atomic nitrogen on β-nitrogen predosed tungsten surface provides a correct dependence of the amount of x-nitrogen on dosing pressure, time, and current with reasonable values of parameters.
Dielectric Friction on a Moving Ion. II. Revised Theory
Authors: Zwanzig Robert
Published: February 2004

The Born–Fuoss–Boyd–Zwanzig calculation of the dielectric friction coefficient on a moving ion is revised in two ways. The relative motion of the ion and its surrounding fluid is taken into account by standard hydrodynamic methods, with both sticking and slipping boundary conditions. Also, the electrostatic problem of finding the electric field due to a change in a moving medium is formulated and solved exactly. The magnitude of the resulting friction coefficient is smaller than in the B–F–B–Z calculation. When the slipping boundary condition is used, the maximum conductance predicted for a singly charged ion in water is about 46 conductance units.
Specific Heat of Amorphous Polymethyl Methacrylate and Polystyrene Below 4°K
Authors: Choy C. L. , Hunt R. G. , Salinger G. L.
Published: February 2004

Measurements of the specific heat of polymethyl methacrylate and polystyrene have been performed using the heat pulse method between 0.5 and 4.3°K. Above 2°K the specific heat is about double that expected on the basis of the Debye theory and acoustic measurements. Below 2°K the experimental data approach the Debye value. The excess specific heat can be fit by two Einstein modes. For polymethyl methacrylate the Einstein temperatures are 4.9 and 17.5°K containing 0.014% and 1.0% of all modes, respectively. For polystyrene the corresponding modes are 5.5 and 16°K with strengths of 0.038% and 1.8% respectively. The data support a model of pendant side groups near voids capable of independent low frequency torsional oscillations. The barrier to internal rotation of the pendant group is estimated.
Bulk Modulus and Grüneisen Parameters for Linear Polymers
Authors: Broadhurst M. G. , Mopsik F. I.
Published: February 2004

Expressions are derived for the isothermal bulk modulus BT and Anderson–Grüneisen parameter δ for a simple two-dimensional bundle-of-chains model where parallel nearest-neighbor chains are assumed to interact with a simple separation-dependent potential. Bulk modulus data for general linear polymers are examined and shown to be essentially temperature independent at constant volume in accord with the model. The theory is shown to predict quite accurately for reasonable assumed pair potentials both BT and δ of high-density polyethylene and n-paraffins with no adjustable parameters. The values of δ obtained for polyethylene from BT data are in excellent agreement with those reported from ultrasonic data. The analysis is also shown to provide a sensitive measure of the form of the effective chain pair potential near its minimum. Also, a close relationship between δ and the Grüneisen constant γ is derived for this model.
Proton-Transfer Reactions in the Simple Alkanes: Methane, Ethane, Propane, Butane, Pentane, and Hexane
Authors: Futrell J. H. , Abramson F. P. , Bhattacharya A. K. , Tiernan T. O.
Published: February 2004

Proton-transfer reactions from CHO+ and CDO+ to the simple alkanes, methane through hexane, have been investigated in a tandem mass spectrometer. Acetaldehyde is shown to be the molecular source yielding CHO+ reactant with the lowest internal excitation energy. The translational energy dependence observed for the reactions CHO++CH4→CX5++CO, CX5+→CX3++X2 (X=H or D) suggests that the interaction is better represented over the energy range considered as proton stripping rather than as proceeding through an intermediate [CXO+–CX4]* complex. In addition, there is no evidence from isotope effects for a transition in mechanism. A highly simplified model treating the protonated methane species as a collection of closely coupled harmonic oscillators permits application of the classic rate expression for unimolecular decomposition to the dissociation yielding CH3+, and this relation provides a reasonable semiempirical fit to the experimental data. The reaction of CHO+ with ethane at quasithermal energy yields C2H7+ in relatively large abundance. C2H5+ is the major product, but isotopic experiments indicate that the latter is not formed by a direct hydride ion abstraction but instead results from dissociation of the protonated ethane ion. Isotopic evidence also indicates that 1,1 elimination of hydrogen from protonated ethane is more probable by a factor of 1.5 than 1,2 elimination. Further, there is a slight preference for eliminating the added proton even at the lowest kinetic energy, a tendency which is more pronounced at higher energies. The extreme sensitivity to slight changes in internal energy which is demonstrated in the C2H7+ decomposition is shown to account for the failure to detect C2H7+ as an intermediate in the CH3+/CH4 reaction. For alkanes larger than ethane, no protonated molecular ion could be observed, although the reactions of these hydrocarbons with CHO+ can also be reasonably interpreted as proton transfer followed by decomposition. For the higher hydrocarbons a greater number of decomposition paths are evident, and there is an increased tendency to eliminate the added proton at low kinetic energies. Proton addition to the hexanes apparently occurs by a fairly random attack of the protonating agent on the carbon skeleton. The relative intensities of decomposition products in the latter case suggest that the protonated hexanes undergo rearrangement prior to dissociation.
Third Virial Coefficients. Three-Body Dispersion Interactions between Asymmetric Molecules
Authors: Stogryn Daniel E.
Published: February 2004

This work examines corrections to the third virial coefficient arising from three-body dispersion forces of the Muto–Axilrod–Teller type between asymmetric molecules. The corrections are derived for mixtures of gases composed of molecules of arbitrary asymmetry and are examined through the second order of a perturbation treatment. A Lennard-Jones (12–6) or (18–6) potential is assumed to describe the spherically symmetric component of the two-body potential for overlap and dispersion interactions. The first-order correction for asymmetric molecules is found to be identical in form to that previously found for spherical molecules. Examples of the second-order corrections are given for CO2, where they are large enough to require consideration in a comparison between theory and experiment, and for a more nearly spherical molecule, N2, where they are relatively small.
Reactions of Metal Atoms. II. The Combination of Mercury and Bromine Atoms and the Dimerization of HgBr
Authors: Greig G. , Gunning H. E. , Strausz O. P.
Published: February 2004

The combination reaction of mercury atoms with bromine atoms from the direct photolysis of CF3Br has been studied. The kinetics were followed by monitoring the band intensities of the Π3/2−22Σ and Π1/2−22Σ systems of the HgBr transient with kinetic absorption spectroscopy. The Π1/2−22Σ system has been analyzed and the following constants obtained: Te = 34 741 cm−1, ωe″ = 188 cm−1, and ωe′ = 274 cm−1. The extinction coefficient of the 2875-Å band of the Π1/2−22Σ system has been found to have the value 1.2 × 104 mole−1·cm−1. The second-order rate constant for the reaction is 1.7 × 108 mole−1·sec−1 in 200 torr CF3Br and is independent of temperature between 120 and 175°C. The rate constant for the removal of HgBr which is second order in [HgBr] is 1.25 ± 0.8 × 1010 mole−1·sec−1 in the same mixture.
Hyperfine Interactions in the Triplet State EPR of Quinoxaline
Authors: Vincent James S.
Published: February 2004

The anisotropic hyperfine interaction of nitrogen and the ring protons in the lowest triplet state of quinoxaline have been measured in single crystals of perdeuterodurene at temperatures close to 80°K. The spin densities determined from these experiments are ρn = +0.133, ρ2 = +0.088,ρ5 = +0.258 ρ6 = +0.071, ρ9 = −0.060. These results are compared with the experimental results for the quinoxaline negative ion.
Calculation of Proton Chemical Shifts
Authors: Katô Hajime
Published: February 2004

The proton chemical shifts are calculated using Ramsey's equation for the nuclear magnetic shielding constant. By using reasonable approximations to the molecular integrals and excitation energies, an attempt at assessing how well one can evaluate the proton magnetic shielding constants in molecules is made. In order to know what sorts of molecular integrals are important and how each term in Ramsey's equation makes significant contributions to proton chemical shifts, some molecular integrals are calculated exactly, and their properties are studied. This method is applied to acetylene and satisfactory agreement with experiment is obtained.
Uncertainties in Intermolecular Pair Potential Parameters Determined from Macroscopic Property Data. I. Virial Coefficients
Authors: Lin H.-M. , Robinson R. L.
Published: February 2004

The effect of experimental variables (temperature range, experimental uncertainty, and number of data points) on the uncertainties in intermolceular pair potential parameters derived from second virial coefficient data is described. A knowledge of these uncertainties is required when conclusions regarding combination rules for prediction of the unlike pair potential are made from comparison of “experimental” and predicted unlike pair parameters.
Dynamics of Some Lattice Models of Polywater
Authors: Bates John B. , Lippincott Ellis R. , Mikawa Yukio , Jakobsen Robert J.
Published: February 2004

Recent spectroscopic evidence suggests that the structure for a new material termed “polywater” is a layer network consisting of infinitely repeating (in two directions) unit cells. This planar network has D6h (hexagonal) symmetry. An additional structure having D3d (trigonal) symmetry has also been considered in which the oxygen atoms form a puckered lattice structure having a repeating unit similar to the D6h structure. We have calculated the normal modes for both the D6h and D3d structures using a simple modified valence force field and were able to obtain excellent agreement with the existing infrared and Raman data. The force constants obtained from both the D6h and D3d models are consistent with type of hydrogen bonding known for the FHF− (bifluoride) ion.
Three-Body Interactions and Short-Range Force Constants in Alkaline-Earth Fluorides
Authors: Ra O/ystein
Published: February 2004

By assuming the binding forces in CaF2, SrF2, and BaF2 to be predominantly ionic, the cohesive energies and short-range force constants are calculated on the basis of a semiempirical adaption of the Heitler–London approximation. While the model attributes the major part of short-range central force interactions to first neighbor M2+–F− pairs, the nonorthogonality of free-ion orbitals associated with second neighbor F−–F− pairs contributes significantly to three-body effects. These are estimated by multipole expansion of electrostatic potentials due to point-charge clusters representing the distribution of overlap charge throughout the lattice. A comparison with earlier Born–Mayer calculations is presented. For CaF2 the substitution of Huggins radii for Pauling radii improves the agreement of Born–Mayer theory with effective one-particle force fields inferred from the observed temperature dependence of neutron diffraction intensities. Simultaneously, this substitution brings the description closer to the present model crystal composed of essentially undeformed ions. Hence it is dubious whether the inadequacy of Pauling radii in this case provides valid evidence of deformations of crystal ions relative to their free states. However, the presently obtained 3%–4% discrepancies between predicted and observed cohesive energies probably indicate some deviation from the ideally ionic state.
Structure of the Pressure-Induced Phase of S 56Se0.44
Authors: Geller S. , Lind M. D.
Published: February 2004

The structure of the pressure-induced phase of S0.56Se0.44 has been determined from “single”-crystal x-ray diffraction data estimated from Weissenberg photographs. Crystals of this phase belong to space groups P31 or P32 but are 60° rotation twinned and thus give diffraction symmetry 6 / m. The lattice constants are a = 7.85, c = 4.62 ± 0.01 Å; each unit cell contains five S and four Se atoms. The structure contains three crystallographically nonequivalent helical molecules of different composition, namely 60%, 67%, and 40% sulfur, with the average equal to 56% sulfur. Best agreement between calculated and observed structure amplitudes is obtained by allowing disorder in position of one specific molecule.
Isomer Shift and Electronegativity in Compounds of Tin and Group-VI Elements
Authors: Baggio Elisa M. , Sonnino T.
Published: February 2004

Using the Mössbauer effect in 119Sn we have measured the isomer shift in compounds of divalent and tetravalent tin with elements of Group VI. The isomer shift is linearly dependent on the values of electronegativity in both series of compounds. The coefficient of this dependence is for tetravalent compounds nearly twice that of the divalent ones. This result is discussed in terms of electron structure of the chemical bonds of the compounds.
On the Heterogeneous Nucleation of Long-Chain Molecules
Authors: Devoy C. , Mandelkern L.
Published: February 2004

The critical conditions for the nucleation of long-chain molecules on a flat substrate and in conical cavities have been studied using methods and models previously reported for monomeric systems. It is found that the critical free energy for nucleation and the critical number of chains, or ordered sequences, required is reduced relative to homogeneous nucleation. However, the critical dimensions in the chain direction ζ* remain unaltered in many cases. The general condition for the latter result to hold is developed. From this study it can be seen why the appropriate interfacial free energy, calculated from homogeneous nucleation experiments, can be used successfully to predict crystallite sizes in bulk crystallized systems.
Polarizability and Second Dielectric Virial Coefficient of Interacting He Atoms
Authors: Lim Tiong-Koon , Linder Bruno , Kromhout Robert A.
Published: February 2004

The polarizability α of the pair of interacting He atoms has been calculated by Hartree–Fock perturbation theory, both coupled and uncoupled. A basis of 16 Gaussians was used, eight centered on each atom. Good convergence was obtained in the region of overlap between one and six atomic units internuclear separation, R. Values of α for large separations were obtained by extrapolation using an R−6 dependence as predicted by previous long-range calculations. The effect of the interatomic interaction on the second dielectric virial coefficient was then calculated using the radial distribution function based on empirical Lennard-Jones parameters. The results show that the effect of overlap and exchange do not sufficiently counteract the positive deviation caused by the van der Waals interaction to produce the substantial negative value as measured by Orcutt and Cole.
Molecular Structure of Cyclobutane from Its Proton NMR in a Nematic Solvent
Authors: Meiboom Saul , Snyder Lawrence C.
Published: February 2004

The molecular structure of cyclobutane has been deduced from its proton nuclear magnetic resonance spectra in the nematic phase of p, p′-di-n-hexyloxyazoxybenzene. The observed spectra include satellites due to molecules containing carbon-13 in natural abundance. Cyclobutane is found to be bent with a symmetry of D2d, but the molecule oscillates between the two equivalent bent conformers to give a spin Hamiltonian of symmetry D4h. From the observed spectra, it is not possible to determine both coordinates required to locate the carbon atoms, and an extra assumption must be made to determine the geometry. If the two C–H bond lengths to a carbon are assumed equal, then we find a bent geometry with a dihedral angle of 27°, with ∠HCH = 108.1°, with the methylene group tilted 4° in a way which brings axial protons on the same side of the ring together. If the size of cyclobutane is scaled by taking the C–C bond length to have the electron diffraction value of 1.548 Å, then we find a C–H bond length of 1.133 Å. Other assumptions to fix the undetermined coordinate are explored.
Infrared Spectrum of the NO2− Ion Isolated in an Argon Matrix
Authors: Milligan Dolphus E. , Jacox Marilyn E. , Guillory William A.
Published: February 2004

The molecular ion NO2− has been stabilized in an argon matrix in sufficient concentration for detection of its antisymmetric stretching fundamental, ν3, at 1244 cm−1 by electron bombardment or photoionization of matrix-isolated NO2 and by the interaction of an alkali-metal atomic beam with NO2 in an argon matrix. In contrast to the position of this fundamental in an inert, nonionic environment, a value of approximately 1275 cm−1 is characteristic of the crystalline material. Isotopic data are consistent with a 115° valence angle for NO2−, independent of environment. Irradiation of the sample with light of wavelength near 3150 Å leads to the destruction of the NO2− absorption in the studies of the electron bombardment and photoionization of NO2, but not in the experiments in which the alkali metal atoms provide a reservoir of photoelectrons.
Dissociation Energy and Long-Range Potential of Diatomic Molecules from Vibrational Spacings of Higher Levels
Authors: LeRoy Robert J. , Bernstein Richard B.
Published: February 2004

An expression is derived which relates the distribution of vibrational levels near the dissociation limit D of a given diatomic species to the nature of the long-range interatomic potential, in the region where the latter may be approximated by D − Cn / Rn. Fitting experimental energies directly to this relationship yields values of D, n, and Cn. This procedure requires a knowledge of the relative energies and relative vibrational numbering for at least four rotationless levels lying near the dissociation limit. However, it requires no information on the rotational constants or on the number and energies of the deeply bound levels. D can be evaluated with a much smaller uncertainty than heretofore obtainable from Birge–Sponer extrapolations. The formula predicts the energies of all vibrational levels lying above the highest one measured, with uncertainties no larger than that of the binding energy of the highest level. The validity of the method is tested with model potentials, and its usefulness is demonstrated by application to the precise data of Douglas, Mo/ller, and Stoicheff for the B 3Π0u+ state of Cl2.
Dynamic Model for Locally Stiff Ring and Straight Chain Polymers
Authors: Simon Eliot
Published: February 2004

The Rouse–Bueche bead–spring model for high polymers is extended to account for stiffness arising from local torsional and bending interactions. A mechanical model including second- and third-nearest-neighbor bead–spring interactions is developed. The effect of local stiffness is introduced into the normal-mode eigenvalue spectrum via second- and third-nearest-neighbor Hooke's law spring constants. A calculation is made of the effect of stiffness on both the free-draining and hydrodynamic interaction properties of linear and circular high polymers. Experiments for supercoiled circular DNA where local stiffness is expected to be large and circular DNA are compared with theory. The effect of local stiffness is sufficient to account for the differences in intrinsic viscosity between the two species.
Millimeter and Submillimeter Wave Spectrum and Molecular Constants of Aluminum Monofluoride
Authors: Wyse F. C. , Gordy Walter , Pearson Edwin F.
Published: February 2004

Rotational transitions of 27Al19F have been measured in the millimeter and submillimeter wave regions to frequencies of 461 Gc/sec. Vibrational states up to υ = 4 were observed. From analysis of the data the following Dunham rotational constants were obtained: Y01 = 16 562.930 ± 0.006 Mc/sec, Y11 = − 149.420 ± 0.009 Mc/sec, Y21 = 0.515 ± 0.004 Mc/sec, Y31 = 1.4 ± 0.6 kc/sec, Y02 = − 31.37 ± 0.02 kc/sec, and Y12 = 0.046 ± 0.014 kc/sec. The Dunham potential constants found are: a0 = 2.9167 ± 0.0019 × 105, a1 = − 3.1850 ± 0.0009, a2 = 6.82 ± 0.06, and a3 = − 11.6 ± 0.6 cm−1. The nuclear quadrupole coupling constants obtained are: eqQ(27Al) = − 37.59 ± 0.25 Mc/sec for υ = 0 and eqQ(27Al) = − 37.14 ± 0.6 Mc/sec for the υ = 1 vibrational state. Vibrational constants derived are ωe = 802.85 ± 0.25 cm−1 and ωexe = 4.86 ± 0.06 cm−1. The equilibrium internuclear distance re = 1.65436 ± 0.00002 Å was obtained.
Spectroscopic Behavior and Coordination of Nickel(II) in Liquid Mixtures of Zinc and Cesium Chlorides
Authors: Smith W. Ewen , Brynestad Jorulf , Smith G. Pedro
Published: February 2004

Optical absorption spectra of dilute solutions of NiCl2 in molten ZnCl2–CsCl mixtures were measured over the complete range of solvent compositions. The temperature extremes investigated were 260°C for melts containing 38 mole % CsCl and 1000°C for 75 mole % CsCl. At temperatures within 100–300°C of the liquidus (depending on melt composition) the spectra were highly composition and temperature dependent and consisted of relatively narrow absorption bands. Analysis of these spectra showed the presence under different conditions of six kinds of nickel(II) centers with well-defined coordination geometries. An equilibrium between octahedral and tetrahedral centers occurred in 0–8 mole % CsCl such that the octahedral form was favored with increasing CsCl content. A different octahedral–tetrahedral pair occurred in 20–50 mole % CsCl with the tetrahedral form favored by increasing CsCl content and temperature. In CsCl-rich melts tetrahedrally coordinated Cl3NiClZnCl33− and NiCl42− were found. In ZnCl2-rich melts at high temperatures the absorptions became broad and only mildly dependent on solvent composition. Suggestions are made regarding the relationships between these coordination effects and structure in the solvent.
Powder Line Shapes in the Electron Paramagnetic Resonance Spectra of High-Spin Ferric Complexes
Authors: Aasa Roland
Published: February 2004

The positions of powder lines in the electron paramagnetic spectra of high-spin ferric systems (d5, S = 52) have been calculated by solving the spin Hamiltonian H = gβB·S + 13D[3Sz2 − S(S + 1)] + E(Sx2 − Sy2) for a broad range of parameters. Powder lines are obtained for every transition when the magnetic field points along the principal axes of the fine structure tensor. However, it was found that for most transitions extra powder lines are often found when the field lies in any of the principal planes but not along the axes. Particular attention is directed to the transition responsible for the g′ ≈ 4.2 absorption in nearly rhombic (E / D∼13) ferric complexes. The calculations show that, depending on the value of the ratio between the microwave quantum and the parameter D, this transition may consist of 3–6 powder lines near g′ = 4.2. The g′ values for all these powder lines were also obtained from a third-order perturbation calculation which assumes nearly rhombic symmetry and D > gβB. The 9.2- and 34-GHz spectra of Fe(III)–EDTA diluted in the corresponding diamagnetic Co(III) compound and the 2.7-, 9.2-, and 34-GHz spectra of native human serum transferrin have been analyzed by the aid of the calculations. It was determined that for Fe EDTA | D | = 0.83 cm−1 and | E / D | = 0.31, while for transferrin | D | = 0.27 cm−1 and | E / D | = 0.31–0.32.
Possible Sources of Large Error in Determinations of Ion–Molecule Reaction Rates with Drift Tube–Mass Spectrometers
Authors: McDaniel E. W.
Published: February 2004

Drift tube–mass spectrometers are now used extensively to measure the rate coefficients of ion–molecule reactions. The accuracy which can be obtained in favorable cases is about 10%, but if careful attention is not paid to a number of factors, very large errors can result. The purpose of this paper is to call attention to this fact, which seems not to be widely known, and to enumerate the factors which can lead to these large errors.
Magnetothermodynamics of α-MnCl2·4H2O. III. Heat Capacity, Entropy, Magnetic Moment, from 0.3 to 4.2°K with Fields to 90 kG along the [100] Crystal Axis
Authors: Giauque W. F. , Hornung E. W. , Brodale G. E. , Fisher R. A.
Published: February 2004

The heat capacity and magnetic moment of a 3.934 cm diameter spherical single crystal of α-MnCl2·4H2O have been measured with stabilized solenoid fields of 0, 1, 5, 10, 14, 22, 25, 40, 65, and 90 kG, along the [100] crystal axis. The magnetic saturation value, 27 999 G·cm3 mole−1, obtained at both 65 and 90 kG, and 0.46°K, indicates that the temperature independent susceptibility is zero and the saturation moment of the temperature-dependent system is 27 999 G·cm3 mole−1, equivalent to g[100] = 2.005. At 90 kG the nuclear spins contributed a heat capacity term of 5.6 × 10−3 T−2gibbs mole−1. The amount of enthalpy required to remove quanta of angular momentum from the saturated condition at 90 kG was found to be 20.2 cal mole−1. This is less than gβH = 24.09 cal mole−1, the magnetic work, by 3.9 cal mole−1. This difference is the amount of stored internal energy contributed by the saturated condition to this limiting process, and is consistent with antiferromagnetic interactions. Extrapolation of the magnetic moment–temperature curves to the absolute zero yields the expression M = 0.9946H + 2.50 × 10−6H2G·cm3 mole−1 at 0°K. On this slightly curved line the saturation value, 27 999 G·cm3 mole−1, is reached at 26 400 G, and the work of magnetization to saturation, ∫HdM, is 9.02 cal mole−1. Temperature field observations on 26 isentropes were used to correlate the entropies along 10 isoerstedic heat capacity series. The zero of electronic and lattice entropy was located from the low temperature heat capacities at 90 kG. The upper limit of the electronic entropy was found to be 3.561 gibbs mole−1 in complete agreement with the Rln6 expected for an S = 52 state. Smoothed correlated values of the heat capacity, entropy, enthalpy, internal energy, magnetic moment and its isoerstedic temperature coefficient, and the work of magnetization have been tabulated.
Vibrational Energy Transfer in CO–He Lasers
Authors: Yardley James T.
Published: February 2004

Time-resolved fluorescence arising from Δυ = 2 transitions in CO has been observed in a flowing Q-switched CO laser containing only He and CO. The time for equilibration of the vibrationally excited states of CO at translational temperatures near 120°K has been found to be given by pCOτ = 208 ± 30 μsec·torr, where pCO is the partial pressure of CO. The relaxation time for loss of vibrational energy due to processes other than stimulated emission is typically 6–15 msec. The net rate of pumping energy into the vibrations of CO is estimated to be 2 × 1019 quanta sec−1·cm−3. This compares favorably with calculations based on direct vibrational excitation by electron impact. The observations of vibrational relaxation are consistent with vibrational energy exchange in binary CO–CO collisions subject to harmonic-oscillator selection rules.
Electron Paramagnetic Resonance Studies of VO2+ in Nitrate Single Crystals. II NH4NO3, NaNO3, and Ba(NO3)2
Authors: Rao K. V. S. , Sastry M. Dattatreya , Venkateswarlu Putcha
Published: February 2004

The electron paramagnetic resonance studies of VO2+ doped in NH4NO3, NaNO3, and Ba(NO3)2 single crystals have been performed over a wide temperature range. At room temperature an isotropic octet exhibiting mI dependence of linewidths is obtained in all the three crystals, which is thought to be due to a very fast readjustment of VO2+ ions which brings the system to an effective liquid with low viscosity. As the temperature is lowered below − 20°C an anistropic spectrum is obtained in VO2+-doped NH4NO3 which is presumably due to hindered rotation of VO2+ ions. The hindered motion of vanadyl ion below −20°C, in spite of volume expansion associated with a phase transition at that temperature, is attributed to the effect of oxygens of NO3− ions on VO2+ ions. The anisotropic spectrum is observed at and below − 80°C in Ba(NO3)2, and at − 196°C in NaNO3. A comparison of the present results with those of VO2+ in KNO3 and CsNO3 reported earlier by us is made, and the results are examined in relation to the recently reported low-temperature phase transitions in these crystals. A probable phase transition around − 110°C in CsNO3 is suggested. The mI dependence of linewidths for the room-temperature spectra is studied using Kivelson's formulism.
NMR Multiple Quantum Transitions by Second Quantization Formalism
Authors: Bucci P. , Cavaliere P. , Santucci S.
Published: February 2004

Single and multiple quantum transitions in NMR are calculated using a second quantization formalism. This leads to a great formal simplification with respect to the usual rotating frame treatment. The results strictly agree with the experimental data available for thiophene.
Absorption Spectrum of Tm3+:LaF3
Authors: Carnall W. T. , Fields P. R. , Morrison J. , Sarup R.
Published: February 2004

The absorption spectrum of Tm3+:LaF3 was measured in the region 0.2–2.0 μ which encompasses all but one of the excited states in the 4f12 configuration. Centers of gravity of the observed crystal-field components of each level were computed and used as the basis for determining the free ion energy level parameters. In addition to the electrostatic and spin–orbit interactions, the effects of configuration interaction and certain two-body magnetic interactions were considered. The theoretical analysis of the results yielded an excellent agreement between calculated and observed free ion levels.
Simple Collision Theory of Reactive Hard Spheres
Authors: Marron Michael T.
Published: February 2004

A hard-sphere model for reactive collisions is derived which is based on considerations of the energy and momentum of the reactants and the products. The conservation of energy and momentum equations completely determine the collision dynamics once the initial and final relative energies and reduced masses are specified. It is found that all collisions cannot be reactive and simultaneously satisfy the conservation equations. The differential and total reactive cross sections are given analytically. There is always a forward cone (in the center of mass) in which no products are found. The model is compared with the usual hardsphere model which requires a minimum energy component along the line of centers for reaction.
Double Resonance Studies of Anions Formed in Irradiated Succinic and Thiodiglycolic Acid
Authors: Wells James W.
Published: February 2004

Fast passage ENDOR techniques were applied to the study of the β-proton hyperfine splittings found in the initial carboxylic anions created in irradiated single crystals of succinic acid and thiodiglycolic acid. The associated tensors for each acid were found to be very similar and indicated both were essentially unchanged from the undamaged molecular conformation. For thiodiglycolic acid the hyperfine tensor associated with the polar proton was also determined and shown to be based primarily on hyperconjugation.
Self-Consistent Molecular Orbital Methods. V. Ab Initio Calculation of Equilibrium Geometries and Quadratic Force Constants
Authors: Newton Marshall D. , Lathan William A. , Hehre Warren J. , Pople John A.
Published: February 2004

Ab initio calculation of equilibrium geometries and quadratic force constants for a large group of first-row polyatomic molecules has been carried out, using the previously described [J. Chem. Phys. 51, 2657 (1969)] STO–3G approximation for STO basis functions. The average deviation of calculated and experimental bond lengths and angles is 0.035 Å and 1.7°, respectively. Nearly all important experimental trends are reproduced. For a few cases involving bonds between electronegative atoms, significant discrepancies are found. Quadratic force constants are evaluated for symmetric stretching and bending modes and are found to be overestimated, typically by 20%–30%. Nearly all experimental trends are satisfactorily accounted for. It is concluded that a minimal STO basis with properly chosen orbital exponents offers a useful and computationally efficient model for potential surface studies.
Behavior of Solutions of Linear Macromolecules in Steady Shear Flow with Superposed Oscillations
Authors: Evans D. Colin , Warner Harold R. , Ramakka William R. , Bird R. Byron
Published: February 2004

The rotational diffusion equation has been solved for a suspension of rigid dumbbells in a velocity field which is the superposition of steady shearing flow (large deformation) and an infinitesimal oscillatory motion (very small deformation). An expression is obtained for the associated shear stresses and the results are expressed in terms of a complex viscosity, appropriately modified for the superposed steady shearing flow. The rigid dumbbell model gives a maximum in the real part of the complex viscosity as well as negative values for the imaginary part at low frequencies. Such behavior has been observed experimentally. The elastic dumbbell model (two beads connected by a Hookean spring) does not give results which are qualitatively similar to the experimental data.
Theoretical Study of the MgH Molecule
Authors: Chan Arthur C. H. , Davidson Ernest R.
Published: February 2004

Within the Born–Oppenheimer framework, extended configuration-interaction calculations, involving the use of natural orbitals, are carried out to study the ground-state energy, wavefunction, and selected molecular properties at the experimental equilibrium internuclear separation of the MgH molecule. Electronic population analysis of the elaborate molecular wavefunctions is done to investigate the nature of the chemical bond involved. More limited configuration-interaction calculations are also carried out to study the low-lying excited states of the MgH molecule. Potential-energy curves are plotted, and transition probabilities are also considered. An estimated dissociation energy of 2.0 ± 0.2 eV has been deduced for the MgH molecule. A dipole moment of − 0.595 a.u. (− 1.511 D) was also obtained. The various results obtained confirmed the intuitive belief that the BeH and the MgH molecules are cogeners. Careful analysis of the accurate molecular wavefunctions reveals that the promotion of an s electron to the corresponding p orbital in bond formation is characteristic of the BeH and the MgH molecules. The calculated transition energy (A 2Π → X 2Σ+) for the MgH molecule was within 5% of the experimental value.
Noniterative Solutions of Integral Equations for Scattering. III. Coupled Open and Closed Channels and Eigenvalue Problems
Authors: Sams W. Neal , Kouri Donald J.
Published: February 2004

The homogeneous integral solution formalism developed by Sams and Kouri is applied to the problems of coupled open- and closed-channel radial equations and coupled radial eigenvalue equations. The problem of coupled eigenvalue equations is considered first. Because we deal with the integral equation form of the Schrödinger equation, the proper solutions may be obtained by integrating from the origin outward, rather than both outward from and inward toward the origin. For the case of eigenvalue radial equations, quantization arises from the fact that exponentially decaying solutions are obtained only when the eigenvalue of a certain matrix equals one. Next, we consider the coupled open- and closed-channel radial equations. Unlike the case of coupled open channels, we find it convenient to consider a column vector solution rather than a matrix. Just as in the open-channel case, however, the Volterra integral equations generated in solving the coupled open- and closed-channel equations are the same for the homogeneous and inhomogeneous integral solutions. Thus, the number of equations which must be solved is not as large as first appears. The method necessitates at most two matrix inversions, one for a n0 by n0 matrix and one for a nc by nc matrix, at the very end of the calculation. Here n0 is the number of open channels and nc the number of closed channels. Finally, application of the eigenvalue procedure is made to a Lennard-Jones (12–6) potential in order to illustrate the method.
Theory of the Pre-exponential Factor in Organic Semiconductors
Authors: Kemeny Gabor , Rosenberg Barnett
Published: February 2004

Tunneling through intermolecular barriers from activated energy levels of molecules is postulated to be the conduction mechanism in some organic semiconductors. The compensation rule follows immediately from this model. The relationship between the characteristic temperature on one hand, and the barrier shape, height, width, and the effective mass of the electrons on the other, is established. It is shown that the triangular barrier assumption gives a qualitative but not quantitative agreement with experiment. Estimates of the barrier height, width, and effective mass are given. Activated state effective masses of ∼ 100me result. The experimentally found correlation between σ0′ and the characteristic temperature acquires a physical basis.
Charge Exchange for H+ and H2+ in H2O, CO2, and NH3
Authors: Coplan M. A. , Ogilvie K. W.
Published: February 2004

Differential charge-exchange cross sections have been measured for H2+ and H+ incident on H2O, CO2, and NH3 in the incident ion energy range 30–500 eV. From retarding-potential and magnetic-deflection measurements the energy of the product ions was determined to be near thermal for all the systems. This is consistent with the narrow angular distribution of product ions and the observed asymmetry of the differential cross sections in the laboratory frame. Total cross sections were calculated from the differential results and compared with earlier measurements. Mechanisms for charge exchange for these systems are discussed in terms of the results.
Photolysis of Carbon Tetrachloride in the Presence of Ethyl Chloride at 25°C
Authors: Yu W. H. S. , Wijnen M. H. J.
Published: February 2004

The photolysis of CCl4 in the presence of C2H5Cl yielded at 25°C the following reaction products: CH3Cl; C2Cl6; 1,1,1,3-C2H3Cl4; 1,1,1,2-C3H4Cl4; meso- and racemic 2,3-C4H8Cl2, and 1,3-C4H8Cl2. The formation of these products is explained by recombination and disproportionation reactions of the radicals produced in the reactions CCl4+hv→CCl3+Cl, Cl+CH3CH2Cl→CH3CHCl+HCl, Cl+CH3CH2Cl→CH2CH2Cl+HCl. Data regarding various ratios of rate constants for recombination and disproportionation reactions of these free radicals are reported and discussed. Data on H atom abstraction by Cl atoms from ethyl chloride are also included.
Raman Scattering and Thermal Defects in Polytetrafluoroethylene
Authors: Koenig J. L. , Boerio F. J.
Published: February 2004

The Raman scattering of polytetrafluoroethylene has been studied as a function of temperature. The 575-cm−1 band is strong below the 19°C transition but weakens above 19°C, while the 595 band is absent below 0°C and increases in intensity with temperature. The 575- and 595-cm−1 bands are attributed to transplanar and gauche backbone linkages, respectively.
Lattice Vibrations of LiYF4
Authors: Miller S. A. , Rast H. E. , Caspers H. H.
Published: February 2004

The long wavelength phonon spectra of single crystal LiYF4 have been studied by means of Raman scattering and infrared emittance and absorption. The observed phonons have been assigned to the various irreducible representations of the point group of the crystal. Symmetry coordinates for these vibrations are given.
Raman Spectral Studies of the Effects of Perchlorate Ion on Water Structure
Authors: Walrafen G. E.
Published: February 2004

Raman contours corresponding to the OD and OH stretching vibrations from HDO, as well as from H2O and D2O, were obtained at 25°C from a series of ternary aqueous solutions containing HDO, ClO4− (Li+, Na+, K+), and H2O or D2O. The Raman spectra were obtained photoelectrically using 4880-Å argon-ion-laser excitation, as well as conventional 4358-Å mercury excitation. Quantitative Raman data were obtained from ternary solutions having NaClO4 concentrations from 1 to 4M, and stoichiometric concentrations of 5.51M D2O (H2O as solvent), or 5.53M H2O (D2O as solvent). Raman spectra were also obtained from solutions having lower (and higher) HDO or NaClO4 concentrations. In addition, binary solutions of NaClO4 and H2O or D2O were examined. Addition of ClO4− to solutions containing HDO, and H2O or D2O produces a pronounced splitting of the OD and OH stretching contours from HDO, as well as from D2O and H2O. The splittings are directly observable in the Raman spectra. Two principal peaks or components, having frequencies nearly identical to components uncovered previously in the absence of ClO4−, result in the HDO case (or four major components in the D2O and H2O cases). The Raman intensities of the high-frequency OD or OH components from HDO (or of the corresponding high-frequency D2O or H2O components) increase relative to the low-frequency components with addition of ClO4−. The effects are evident even at 0.5M ClO4− and below. In addition, isosbestic frequencies are observed from the binary and ternary perchlorate solutions for bands of HDO, D2O, and H2O, and the values compare favorably with isosbestic frequencies obtained previously at a series of temperatures. Examination of the OD and OH stretching contours from HDO at high ClO4− concentration, at which the high-frequency components are nearly isolated, also indicates that the component shapes are Gaussian. The Raman data indicate that the ClO4− ion is a strong structure breaker, and that it does not hydrate appreciably, in agreement with the recent infrared absorbance results of Kecki et al. The data also provide clear evidence in contradiction to spectroscopic continuum models of water and aqeuous solutions, but mixture models involving several major classes of interactions, e.g., hydrogen-bonded or non-hydrogen-bonded OD or OH groups, and OD or OH groups engaged in the hydration of cationic and anionic species, but excluding ClO4−, are in accord with the data.
Low-Frequency Vibrations of Molecular Crystals. VII. DMSO and DMSO-d6
Authors: Durig J. R. , Player C. M. , Bragin J.
Published: February 2004

The far-infrared spectra of polycrystalline dimethylsulfoxide and dimethylsulfoxide-d6 have been measured from 600 to 33 cm−1 at various temperatures from −30 to −194°C. Raman spectra of both compounds in the liquid and solid states have been recorded with 6328-Å helium–neon excitation. Assignments are made for internal and lattice vibrations in terms of the crystallographic unit cell P21 / c (C2h5) with four molecules per unit cell. A distinction between librational and translational lattice modes was made on the basis of the isotopic shift factors. The external fundamentals are readily explained in terms of a layer lattice unit cell with intralayer coupling between molecules being of greater significance than interlayer coupling. The interesting methyl torsion was observed in the infrared at 257 cm−1 in the “light” compound shifting to 189 cm−1 with deuterium substitution. The threefold barrier to internal rotation was calculated to have a value of 4.4 kcal/mole for the solid. This barrier is compared to that found in the vapor as well as those obtained for structurally similar phosphorous compounds. It appears that oxygen raises the barrier by about 1 kcal/mole. No evidence for short-range ordering could be found in the Raman spectrum of the liquid.
Prediction and Interpretation of Free-Ion and Crystal-Field Spectra of the Actinides. The Intermediate Crystal-Field Diagram for 5f2 Np5+ in Octahedral CsNpF6
Authors: Varga L. P. , Brown J. D. , Reisfeld M. J. , Cowan R. D.
Published: February 2004

The problem of identification and characterization of the many oxidation states of the actinide elements which give rise to f–f electronic spectra is treated both for free-ion and crystal-field spectra. For the free-ion, nonrelativistic self-consistent-field calculations on fn configurations of the actinides have yielded values for the Coulomb and spin–orbit interaction parameters from which electronic spectra may be predicted. Comparison of these calculated energy levels with the spectra observed for several actinides has been made. Crystal-field splitting of the free-ion levels was examined in detail for the case of 5f2Np5+ in CsNpF6. A complete intermediate crystal-field coupling diagram for this f2 configuration ion under Oh point-group symmetry was constructed and the observed spectrum was fit to the diagram confirming the predominant octahedral structure of NpF6−. The combined Coulomb, spin–orbit, and octahedral crystal-field spectroscopic parameters for NpF6− were: E1 = 3144, E2 = 16.75, E3 = 251.9, ζ = 2230, B04 = 1071, and B06 = 551 cm−1. Application of these techniques to other electron configurations and point-group symmetries is suggested.
Reactions of Trifluoromethyl Radicals with Monosilane and Monosilane-d4
Authors: Jakubowski E. , Sandhu H. S. , Gunning H. E. , Strausz O. P.
Published: February 2004

Arrhenius parameters for the reactions of trifluoromethyl radicals, produced by the photolysis of hexafluoroazomethane, with SiH4 and SiD4 have been measured. It has been found that CF3 radicals are more reactive than CH3, the difference in reactivity being due to lower activation energies, as the A factors are almost identical. A theoretical value of Ea obtained by the BEBO method using a simple three-mass-point model is compared with the experimental. The BEBO and LEPS methods have been used to predict kinetic isotope effects with and without tunneling corrections for comparison with experimental results.