bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Dye Sensitization. I. Selenium
Authors: Ing S. W. , Chiang Y. S.
Published: January 2005

Surface dye sensitization of amorphous Se has been studied. Maximum quantum efficiencies measured were in the range from 10−2 to 10−1. The dye coatings were deposited onto the surfaces from their respective methanol or benzene solutions. Five dyes were used for the sensitization: crystal violet, pinacyanole, methylene blue, phenosafranine, and nitrosobenzene. The enhanced photocurrents due to the dye coatings occured at wavelengths longer than those corresponding to the intrinsic bandgap energies of Se. The maximum enhanced response was in the range from 5500 to 7000 Å, depending on the dye. The enhanced photocurrents corresponded to injection of carriers from the surface into the bulk photoconductor, electrons for some dyes (crystal violet and pinacyanole) and holes for others (methylene blue, phenosafranine, and nitrosobenzene).
Thermally Stimulated Trap-Emptying Measurements in Phthalocyanine
Authors: Westgate C. R. , Warfield G.
Published: January 2005

Traps with a density of 1014/cm3 and an activation energy of 0.36 eV were found in both metal-free and lead phthalocyanine single crystals using thermally stimulated trap-emptying measurements. These traps were responsible for fast trapping observed in transient current measurements.
Intermolecular Forces in Globular Molecules. II. Multipolar Gases with a Spherical-Shell Central Potential
Authors: De Rocco A. G. , Spurling T. H. , Storvick T. S.
Published: January 2005

The integrals appropriate to the classical second virial coefficient for a molecule obeying a spherical-shell central potential and including either a dipole moment or a quadrupole moment are calculated for a wide range of values of r0*, T*. The functions Hk(r0*, T*) are available for k=6, 10, 12, 15, 18, 20, and 24. The results are used to investigate the intermolecular forces in methyl chloride and benzene. In both cases a significant improvement in fit with experimental data is noted upon inclusion of multipolar forces. For benzene, treated as an axial molecule, a quadrupole moment Θzz of ±15×10−26 esu is deduced.
Photochemical Decomposition of Sodium Bromate
Authors: Herley P. J. , Levy P. W.
Published: January 2005

The ultraviolet-induced photolysis of powdered NaBrO3 has been studied using both unirradiated crystals and materials subjected to 60Co gamma-ray irradiation. The rate against time curves for all samples show an initial deceleratory stage followed by a final constant rate stage. This final stage deviates from a second-order dependence on light intensity which is in a manner opposite to that reported in most previous studies. The different curvature is attributed to a photolytic generation of additional sites. Gamma-ray irradiation increases the variation from an exact second-order dependence, decreases the initial rate, and decreases the time required to reach the final stage. Irradiation also produces color centers and a shift in the apparent absorption edge. A phenomenological theory has been developed which is consistent with the observed dependence on intensity.
Spectrophotometric Study of Ytterbium(III) Cyclopentadienides at Liquid-Helium Temperature
Authors: Pappalardo R. , Jørgensen C. K.
Published: January 2005

The 2F7/2→2F5/2 transitions of green Yb(C5H5)3 and certain of its adducts with Lewis bases show beyond any doubt a fairly unperturbed 4f13 electron configuration. The green color is caused by a weak band showing a very pronounced fine structure at low temperatures. This absorption is probably due to an electron transfer from a linear combination of cyclopentadienide orbitals having particularly low ionization energy because of strong ligand—ligand repulsion. The MO treatment of M(C5H5)3 in trigonal symmetry is discussed.
One-Center Calculation of the He–He Repulsion
Authors: Morris B. M. , Present R. D.
Published: January 2005

Earlier one-center calculations have been extended, through the inclusion of additional configurations, to apply to internuclear distances of 0.75 and 1.0 a.u. The configurations investigated were 1s22s2, 1s22pσ2, 1s3dσ2s2, 1s22s3dσ, 1s3dσ2pσ2, 1s2s2pσ2, 1s5gσ2pσ2, 1sns2pσ2, and ns22pσ2. The best three-configuration mixture 1s22pσ2+1s3dσ2pσ2+3s22pσ2 gives the same energy as Ransil's two-center single-configuration LCAO MO calculation at R=0.75 a.u. but is 8 eV above the Ransil result at R=1 a.u. The two-center calculation of Buckingham and Duparc, using a mixture of (σg1s)2(σg2s)2 and (σg1s)2(σu1s′)2 configurations (the latter due to Huzinaga), gives better results than we have obtained at distances of 0.5 and 0.75 a.u.
Studies in Molecular Dynamics. IV. The Pressure, Collision Rate, and Their Number Dependence for Hard Disks
Authors: Hoover William G. , Alder Berni J.
Published: January 2005

The pressure for four, 12, and 72 hard disks determined dynamically from the virial theorem or the collision rate is shown to be identical to that determined by the Monte Carlo method. To show this equivalence, it is necessary to take into account that the center-of-mass velocity is kept fixed in the dynamic system. This numerical agreement suggests the validity of the quasiergodic hypothesis even for small systems. The (lnN)/N dependence of the phase-transition pressure on the number of particles N is simply explained in terms of the communal entropy.
Dielectric Constants of Imperfect Gases. III. Atomic Gases, Hydrogen, and Nitrogen
Authors: Orcutt R. H. , Cole R. H.
Published: January 2005

A modified cyclic-expansion method has been used to determine dielectric constants as a function of relative density with a precision of less than 1 ppm for He, Ne, Ar, Kr, H2, and N2 at 49°C and pressures below 150 atm, which with data at measured pressures below 7 atm determine the first and second dielectric virial coefficients, and can also be used to determine pressure second virial coefficients.

Dielectric second virial coefficients are for all six gases less than values predicted by present theories of fluctuations and pair polarizabilities, an effect believed to result from overlap interactions at short range. The low-density values of the Clausius—Mossotti function are in good agreement with other recent determinations.
On the Statistical Interpretation of Thermodynamic Entropy in a Strongly Coupled Gas
Authors: Nicolis G.
Published: January 2005

The first strong-coupling contribution to the canonical entropy of a classical gas is analyzed in the simple case of a Gaussian potential. In agreement with the results by Prigogine et al., it is shown that two different kinds of contributions appear and that only one of them can be identified with the thermodynamical entropy.
Some Theorems Concerning Symmetry, Angular Momentum, and Completeness of Atomic Geminals with Explicit r12 Dependence
Authors: King Harry F.
Published: January 2005

Several results are presented which have important implications for the calculation of many-electron wavefunctions. Electron-pair functions are constructed to be eigenfunctions of the two-electron inversion, permutation, and angular-momentum operators with quantum numbers L and M. For a given L and M there exist 2L+1 particular linear combinations of binary products of spherical harmonics called generators. These 2L+1 generators multiplied by members of a complete set of S-type geminals constitute a complete set of geminal basis functions with that angular momentum. This approach establishes a connection between a formulation in terms of Eulerian angles developed by Wigner and others, and analyses based on configuration interaction expansions. One of several possible forms for the complete set of S-type geminals employs only 1s-type orbitals and a correlation factor, R(r12).

Mixing of symmetry may occur when a strongly orthogonal geminal is projected out from a symmetry-adapted one. This problem is easily circumvented. It is shown that any geminal is annihilated by an operator which projects out the component strongly orthogonal to a particular geminal with exponential r12 dependence.
Thermoelectric Power of TlCl Containing PbCl2
Authors: Christy R. W. , Dobbs H. S.
Published: January 2005

Thermoelectric power of pure TlCl and TlBr was measured as a function of temperature between 275° and 400°C. Thallium metal electrodes were used. Measurements were also made on TlCl doped with PbCl2 in concentrations between 0.01 and 0.5 mole %, and on TlCl doped with Tl2S. The thermoelectric power of pure TlCl is about −0.2 mV/deg, and it becomes more negative as a result of adding PbCl2. The data for TlCl:PbCl2 are in excellent agreement with the thermodynamical theory of Howard and Lidiard for Schottky defects, if it assumed that there is no association between the cation vacancies and Pb+ + ions. With this assumption, the data are analyzed to give the following values for defect parameters in TlCl: enthalpy of formation of Schottky pair, 1.3 eV; entropy of formation of cation vacancy, 0.3 meV/deg (3.7 k); entropy of formation of anion vacancy, 0.6 meV/deg (6.6 k); heat of transport of cation vacancy, −0.9 eV; heat of transport of anion vacancy, −0.5 eV; activation energy for cation mobility, 0.5 eV; activation energy for anion mobility, 0.2 eV. The Tl2S impurity apparently does not enter the crystal in the form of unassociated anion vacancies and S− — ions.
Spectrum of Gaseous UCl4
Authors: Morrey J. R. , Carter D. G. , Gruber John B.
Published: January 2005

The spectra between 4000 and 23 000 cm−1 of gaseous UCl4 have been obtained for the temperature range 950° to 1250°K. These spectra have been compared with those of single-crystal UCl4 at 77°K and room temperature. Spectra of solid UCl4 were obtained over the temperature range 300° to 827°K in order to compare with the gas. In general, the molar absorptivities of the gas are a factor of 10 attenuated over the solid. The energy levels of the gaseous state do not shift appreciably with temperature but, in general, the spectrum of the gas is shifted to the red side of the high-temperature solid spectra. With the exception of a general shift, the spectrum of the vapor is remarkably similar to that of the solid.
Magnetic Moments of V2+, Cr3+, and Mn4+ Ions in Octahedral Ligand Fields
Authors: Elliott Norman
Published: January 2005

The magnetic susceptibilities of V (bipy)3(ClO4)2, K3Cr(CN)6, and K2MnCl6 have been measured in the temperature range of liquid-nitrogen to room temperature. The magnetic moments of the ions, V2+, Cr3+, and Mn4+ agree, within experimental error, with the spin-only moment, 3.87 β.
Significant Structure Theory Applied to Surface Tension
Authors: Lu Wei-Chen , Jhon Mu Shik , Ree Taikyue , Eyring Henry
Published: January 2005

An equation of surface tension has been derived from significant structure theory, by introducing the approximation that the surface of liquids consists of a monomolecular layer in which a molecular has a sublimation energy different from that for a bulk liquid molecule. The theory is successfully applied to simple liquids, polar liquids, and molten metals at various temperatures.
On the Origin of the Color of Magnus' Green and Related Salts
Authors: Anex Basil G. , Ross Michael E. , Hedgcock Marcus W.
Published: January 2005

The polarized single-crystal reflection spectra of Magnus' green salt and two of its tetra-alkylamine analogs have been determined and the corresponding absorption spectra obtained through Kramers—Krönig analyses. It is found that a strong ultraviolet transition exists with the proper polarization for the visible out-of-plane bands to gain their intensity from it through vibronic mixing of zero-order electronic wavefunctions. The correlation of the visible intensity with the nature of the ultraviolet band further confirms this mechanism. Possible assignments of the ultraviolet band are discussed.
Electronic-Absorption Spectra of Gaseous NiCl2, NiBr2, and NiI2. Axial Ligand Field Calculations Including Spin—Orbit Coupling
Authors: DeKock C. W. , Gruen D. M.
Published: January 2005

Electronic-absorption spectra of gaseous NiCl2, NiBr2, and NiI2 have been measured in the range 4000–20 000 cm−1. An interpretation of the low-intensity dn←dn transitions is given based on ligand field calculations for a 3d8 configuration in an axial field including spin—orbit coupling.

The main features of the spectra are due to transitions to 3Pπ and 1DΔ,π excited states which are strongly intermixed in the bromide and iodide. An analysis of the nephelauxetic effect in these levels leads to the conclusion that the F2 parameter decreases more rapidly than the F4 parameter in the series NiCl2–NiBr2–NiI2.
On the Gaussian-Lobe Representation of Atomic Orbitals
Authors: Harrison James F.
Published: January 2005

The reliability of angularly dependent properties calculated from wavefunctions constructed over a nonnuclear-centered Gaussian basis has been explored by examining the spherical harmonic expansion of the Gaussian-lobe function representation of a pz function. It is found that the component of pz in the Y10 subspace is similar to a double-zeta function while the component in the Y30 subspace is several orders of magnitude less than the Y10 component.

Expectation values for several angularly dependent operators are evaluated over the Gaussian-lobe function representation of a pz orbital and compared with the expectation value calculated over the corresponding double-zeta function. The small angular asymmetry in the Gaussian-lobe function representation of the atomic pz orbitals is reflected in the similarity between the two expectation values.
Single-Center Wavefunctions for H3+ and H3
Authors: Considine J. P. , Hayes E. F.
Published: January 2005

Wavefunctions for the H3+ molecule ion and the H3 molecule are reported for a linear symmetric configuration of the nuclei with a separation of 1.8 bohr between adjacent protons. The basis functions are Slater-type orbitals centered on the central proton. For H3+ a total energy of −1.24657 a.u. is found using a 21-term configuration-interaction wavefunction; for H3 a total energy of −1.61208 a.u. is found using a 52-term configuration-interaction function. These energies differ from exact energies by about 0.02 and 0.05 a.u., respectively. Some new single-center procedures are discussed, and some existing problems are pointed out.
Kinetics of the Oxygen—Tungsten Reaction at High Temperatures
Authors: Walsh Patrick N. , Quets Jean M. , Graff Robert A.
Published: January 2005

The rate of reaction of molecular oxygen with tungsten was measured from 2000° to 3300°K at pressures from 0.11 to 11.5 torr. High gas-phase mass transfer coefficients were obtained by impinging a high-velocity gas jet on the sample. A maximum reaction rate was observed at each O2 pressure, the temperature of maximum rate increasing with pressure. Below the temperatures of the maxima, an apparent activation energy near 23 kcal mole−1 was observed. These results are well described by the empirical equations of Perkins, Price, and Crooks, except that no transition to a regime of higher activation energy at lower temperatures was observed here and the maxima were found at slightly higher rates and temperatures than previously reported. Appreciable diffusion effects were found only near the observed maxima. These data and the 10−4 torr data of Schissel and Trulson were correlated in terms of the two-layer oxygen-atom adsorption model for tungsten oxidation kinetics proposed by the latter authors. Kinetic constants for a slightly modified version of this model were obtained.
Role of the 3(n—π*) State in the Photoreduction of Acridine
Authors: Donckt E. Vander , Porter G.
Published: January 2005

Photosensitization of acridine reduction by benzophenone is shown to occur via the ketyl radical of benzophenone rather than by an energy-transfer mechanism. The principal evidence for participation of an upper triplet n—π* state of acridine in the photoreduction reaction is therefore discounted and the reaction probably occurs via the lowest excited singlet level.
Absolute Infrared Intensities of Stannane
Authors: Levin Ira W.
Published: January 2005

The absolute gas-phase infrared intensities for the triply degenerate vibrations of SnH4 and SnD4 are determined using the nitrogen pressure-broadening technique. An analysis of the SnH4 intensities yields alternative sets for the dipole-moment derivatives in terms of the symmetry coordinates of the F2 species: For ∂Pz/∂S3, Set I is ±2.81±0.14 D/Å and Set II is ±2.66±0.14 D/Å; for ∂Pz/∂S4, Set I is ±1.68±0.09 D/Å and Set II is ∓1.85±0.09 D/Å. A comparison with data for the other Group IV hydrides suggests a possible preference for Set I, the positive ratio for the relative sign combination of the stretching and bending dipole-moment derivatives.
Solvent Effects on H–F Couplings: Dipole Orientation Requirements for Solvent Dependence of Coupling Constants
Authors: Smith Stanford L. , Ihrig Arthur M.
Published: January 2005

Solvent-dependent variations of 2JHF, cis 3JHF, and trans 3JHF have been observed in trifluoroethylene and vinyl fluoride. These data, in conjunction with previous observations, indicate that orientation of the solute dipole strongly affects the solvent dependence of geminal coupling constants. The electric field of the solvent appears to be the primary causative factor, but strong molecular associations (e.g., H bonding) may either enhance or decrease the observed effect. The limited results available suggest that the absolute sign of 2JHF may be obtained by observing the change of 2JHF as a function of solvent.
Nuclear Quadrupole Resonance in Solid Diazines
Authors: Schempp Ellory , Bray P. J.
Published: January 2005

Nitrogen−14 nuclear quadrupole resonance data are reported for pyridazine, pyrazine, and pyrimidine. The spectra are analyzed assuming sp2 hybridization of the nitrogen σ bonding and lone-pair orbitals. Coupling constants and asymmetry parameters are interpreted in terms of electron densities in σ and π orbitals and compared with values for pyridine. Evidence is presented indicating significant polarization of the σ bonds and strong localization of the lone-pair electrons. Good agreement is found with LCAO MO calculations of π-charge densities.
Reaction of Graphite Filaments with Hydrogen above 2000°K
Authors: Clarke J. T. , Fox B. R.
Published: January 2005

The reaction rate of graphite and hydrogen has been measured between 2000° and 3400°K and pressures of 0.01 to 1.0 atm using a heated filament. At the lower temperatures and higher pressures, the reaction occurs on the surface and its rate is proportional to the hydrogen pressure and the KD where KD is the dissociation constant of hydrogen. At high temperature and low pressure, the reaction occurs in the vapor phase and is proportional to the sublimation rate of graphite. The sublimation temperature of graphite as a function of carbon to hydrogen ratio has been experimentally investigated at 0.1 atm and shown to agree with the estimated thermodynamic calculations.
Electrical Properties and Electronic Configuration of the Monocarbide, Monophosphide, and Monosulfide of Plutonium
Authors: Kruger O. L. , Moser J. B.
Published: January 2005

The electrical properties of PuC, PuP, and PuS were measured over the temperature range of 300° to 1000°K. The monocarbide and monophosphide had resistivities of 257 and 752 μΩ·cm, respectively, at room temperature; these values did not change appreciably with temperature. Plutonium monocarbide is a p-type conductor with a low absolute thermoelectric power which is only slightly temperature dependent. The monophosphide is also a p-type conductor at room temperature, but it changes to an n-type conductor above 740°K. The quasimetallic conduction of PuC and PuP is essentially proportional to the mobility as indicated by thermoelectric power measurements.

Plutonium monosulfide was found to be an intrinsic semiconductor from 425° to 700°K with an activation energy for conduction of 0.240 eV. Calculations show that above 700°K PuS becomes degenerate as the carrier concentration exceeds 1019 cm−3 and a gradual transition to metallic conductivity is indicated. A peak in the absolute thermoelectric power of 115 μV°K−1 was observed for this compound which is an n-type conductor over the temperature range studied.

In these plutonium compounds and similar actinide compounds conduction appears to be governed by a systematic change of carrier concentration in the s+d valence band and scattering caused by s+d, f transitions. A split in the f states is proposed as the mechanism responsible for the semiconductor properties of PuS.

A comparison was made of the compound unit cell volumes and metal radii for the rare-earth and actinide mononitrides, monophosphides, and monosulfides. The data indicate effective valences of four electrons per atom for the actinide mononitrides and between three and four electrons per atom for the actinide monophosphides and monosulfides.

These plutonium compounds do not have much promise as thermoelectric materials because their figures of merit are all too low for acceptable power generation.
Molecular SCF Calculations on PH3, PO, PO−, and P2
Authors: Boyd Donald B. , Lipscomb William N.
Published: January 2005

Wavefunctions, Hamiltonian matrices, and population analyses are obtained for PH3, PO, PO−, and P2 from accurate self-consistent-field calculations in which multicentered basis sets of Slater orbitals have been employed. The P3d exponent was optimized at 1.40 in PO and 1.10 in PO−, assuming Slater exponents for other orbitals. These 3d orbitals were found to be important in the bonding in each of these molecules. Studies were also made of dipole moments, ionization potentials, and binding energies.
Optimized Minimum Basis Set for BH4−
Authors: Hegstrom Roger A. , Palke William E. , Lipscomb William N.
Published: January 2005

An LCAO SCF wavefunction for BH4− has been optimized with respect to variation of orbital exponents in a minimum basis set. The resulting charge distribution, quite different from that given by Slater exponents, yields Mulliken charges of +0.044 for B and −0.261 for each H atom. These results, and electron density maps, indicate that the unit negative charge is distributed among the four H atoms, which have an optimized exponent of 1.04.
Field Emission through Atoms Adsorbed on a Metal Surface
Authors: Duke C. B. , Alferieff M. E.
Published: January 2005

An exactly solvable one-dimensional pseudopotential model is employed to calculate the field-emission probability and current from a free-electron metal through both metallic and neutral absorbates. The adsorbate potential is taken to be atomistic in nature consisting of an attractive square well plus a delta-function (orthogonalization) core outside the surface of the metal. Metallic adsorbates lead to the wide (Δ∼1-eV) resonances in the emission probability, an additional peak or shoulder in the energy distributions, large (102−104) enhancements in the emission current, and reductions in the slope of the Fowler—Nordheim plots of In[current/(field)2] versus (field)−1 at fields F≳5×107 eV/cm. Neutral adsorbate potentials without bound states lead to reductions in both the emission probability and current, and to a simple scaling of the Fowler—Nordheim energy distributions. Neutral adsorbate potentials with bound states below the metallic conduction band lead to enhancements of the current for loose binding, additional asymmetry in the energy distributions for all strengths of binding, and to both reductions in the current and strong field reductions of the slope of the Fowler—Nordheim plots for tight binding. The reduction in the emission current by neutral adsorbates is used to interpret the simultaneous reduction of the work function and emission current by the adsorption of nitrogen on the (100) and (411) faces of tungsten. The prediction for metallic adsorbates of an extra peak in the energy distributions whose location shifts linearly in F distinguishes the results of the atomistic pseudopotential model from those of a surface-film model.
Calculation of Nuclear Magnetic Shielding Constants in Two Simple Systems
Authors: McKoy Vincent , Musher Jeremy I.
Published: January 2005

The nuclear magnetic shielding constants of two simple systems are calculated explicitly. These systems are (1) a nucleus μ at a distance R from a hydrogenic atom of charge ζe in the presence of an external electric field, and (2) a nucleus μ of a hydrogenic atom of charge ζe in the presence of a point charge at R with the result expanded in inverse powers of R. These calculations should prove useful in understanding the long-range contributions of functional groups and neighboring molecules to observed chemical shifts of molecules.
Reactions of 1D Oxygen Atoms. III. Ozone Formation in the 1470-Å Photolysis of O2
Authors: Sullivan J. O. , Warneck Peter
Published: January 2005

The extent of ozone formation in the 1470-Å photolysis of oxygen and 1:1 helium—oxygen mixture has been studied in a flow system as a function of pressure and temperature. A determination of the ozone quantum yield at atmospheric pressure gave φ = 2.0±0.2 in good agreement with previous values. At lower pressures, the production of ozone was found to decrease with pressure, and this effect has been interpreted as arising from the reaction of O(1D) with ozone. The quantitative evaluation of the ozone quantum yields in terms of O(1D) reactions provides ratios of rate constants for the reactions of O(1D) with ozone, oxygen, and helium. From the temperature dependence, the reaction with ozone is found to have an activation energy of 2.4±1.0 kcal/mole. Absolute rate constant estimates are obtained by the application of independent data.
On the Theory of Chemical-Reaction Cross Sections. II. Application to the H + H2 Reaction
Authors: Marcus R. A.
Published: January 2005

The statistical—dynamical model formulated in Paper I is applied to the H+H2→H2+H reaction and compared with the exact three-dimensional classical-mechanical computer calculations of reaction cross sections. Encouraging agreement is obtained in the low-to-moderate relative velocity range, without the use of adjustable parameters. At very high velocities the comparison indicates the occurrence of some vibrational nonadiabaticity. Calculations are presently in progress to see if this nonadiabaticity equals that expected from a companion paper on analytical mechanics of certain collisions. Applications are also made to several topics: relations between classical and quantum computer calculations of cross sections, between activation energy and the recently reported threshold energy of reaction (D+H2→DH+H), and tests of activated-complex theory.
Barrier Studies in the Halopropenes. II. Microwave Spectra, Molecular Structure, Dipole Moment, and the Barrier to Internal Rotation of the Methyl Group in 1,1-Difluoropropene
Authors: Weiss V. W. , Beak P. , Flygare W. H.
Published: January 2005

1,1-Difluoropropene has been synthesized and characterized by study of the 19F and H nuclear magnetic resonance spectra, infrared spectra, and mass spectra.

The microwave spectra in the ground and first excited torsional states are assigned giving the following rotational constants for the A-type torsional levels: Ground state, A = 10 154.30, B = 3742.19, and C = 2779.33; first excited torsional state, A = 10 098.00, B = 3741.80, and C = 2781.80 (all in megacycles per second). The barrier to internal rotation of the methyl group was determined from the rotational spectra to be V3 = 1252±20 cal/mole. The molecular-dipole components along the principal inertial axes are determined by the Stark effect to be ua = 0.836±0.005 and ub = 0.309±0.005 D with the total dipole being u = 0.889±0.007 D.

The barrier to the internal rotation of the methyl group is discussed in terms of the interaction of the methyl group and the cis substituent. It is concluded from the difference in the barriers between cis-fluoropropene and 1,1-difluoropropene that the barrier is insensitive to small changes in the distance between the cis-fluorine atom and the methyl group.
Quantum-Mechanical Kinetic Theory of Loaded Spheres. II. The Classical Limit
Authors: Mueller John J. , Curtiss C. F.
Published: January 2005

In a previous paper, the quantum-mechanical scattering amplitudes and collision cross sections of loaded spheres were obtained as power series in δ/σ, where σ is the diameter of the sphere and δ is the amount by which the center of mass is displaced from the geometrical center, and the coefficients of the zero, first, and second powers of δ/σ were evaluated explicitly. These results are used to obtain the classical limit of the relaxation time and the coefficients of shear viscosity, thermal conductivity, and diffusion. The results are found to agree with results obtained by purely classical methods.
Deuteron Magnetic Resonance and Proton Relaxation Times in Ferroelectric Ammonium Sulfate
Authors: O'Reilly Donald E. , Tsang Tung
Published: January 2005

The deuteron nuclear magnetic resonance of single crystals of (ND4)2SO4 has been studied from 77° to 300°K and particularly in the region of the first-order ferroelectric phase transition at 223°K. At high temperatures four closely spaced pairs of lines (10-G max separation) are observed, which shift abruptly as the crystal is cooled through the transition temperature (Tc). These lines are assigned to the two inequivalent ND4+ ions (I and II) in a unit cell, which are slightly distorted from the tetrahedral configuration and rapidly reorienting so as to average the quadrupolar splitting to a small value. At 130°K only two pairs of closely spaced lines are observed due to ND4+ (II); at 77°K eight pairs of widely spaced (400-G max separation) lines are observed corresponding to ND4+ (I). In the transition to the ferroelectric phase the principal coordinate system of the electric-field gradient (EFG) tensor rotates by about 30° for each ion with little change in the coupling constants or asymmetry parameters. The spontaneous polarization produced by the distorted ions has been calculated from the observed EFG tensors and is in reasonable agreement with the experimental value.

Proton spin—lattice relaxation times (T1) and proton relaxation times along the rf field (T1ρ) have been measured for polycrystalline (NH4)2SO4. T1 versus temperature (T) has two minima, and may be interpreted as due to the two inequivalent NH4+ tetrahedra reorienting at different frequencies and coupled to each other via dipole—dipole interaction. Correlation times τc at various temperatures have been obtained for the two inequivalent NH4 ions from the T1 and T1ρ measurements; above Tc and below 170°K, logτc is a linear function of T−1, with normal values of pre-exponential factors. The activation energies change only slightly at the transition, in agreement with recent neutron inelastic scattering data. τc is, however, anomalously short immediately below Tc due to the volume contraction of the crystal. Correlation times have also been estimated from deuteron resonance linewidths and proton second moments. The results are consistent with those derived from the proton T1 and T1ρ data.

An order—disorder mechanism is proposed for the phase transition in which NH4+ tetrahedra are disordered with respect to the crystal ab plane. A first-order transition is described by the molecular field approximation for a sufficiently strong dependence of the interaction parameter on the spontaneous polarization.
Rate of Dissociation of Chlorine in Shock Waves
Authors: Carabetta Ralph A. , Palmer Howard B.
Published: January 2005

Emission of light from the radiative recombination of chlorine atoms has been used to measure the rate of dissociation of molecular chlorine behind shock waves in 1:5 Cl2:Ar mixtures between 1735° and 2582°K. Assuming second-order kinetics for the dissociation, —d[Cl2]/dt=kd[Cl2][M], the rate constants kd are adequately expressed by the equation kd=1013.94exp(−48 300 cal/RT) cm3 mole−1·sec−1over the indicated temperature range.
Debye—Waller Factors of Copper and Gold
Authors: Gupta R. P. , Sharma P. K.
Published: January 2005

The temperature variation of the Debye—Waller exponents for copper and gold are calculated using the electron gas model for the lattice dynamics of metals propounded by one of us earlier. The results of the calculation are compared with available x-ray measurements. Good agreement with the experimental data is obtained for gold, but not in the case of copper.
Spectroscopic and Electrical Properties of Polymeric Donor—Acceptor Complexes
Authors: Klöpffer W. , Rabenhorst H.
Published: January 2005

The spectroscopic and electrical properties of poly (p-dimethylaminostyrene) complexes with a variety of electron acceptors have been measured. Weak electron acceptors yield charge-transfer complexes, whereas strong electron acceptors are partially converted into radical anions. As may be concluded from measurements of the Seebeck coefficient, charge transport is caused by electrons. The electrical conductivity of the complexes is critically dependent on acceptor concentration and is attributed to hopping processes between radical anions and neutral acceptor molecules.
Geometry of the Lowest Triplet State of Benzene
Authors: Nieman G. C. , Tinti D. S.
Published: January 2005

The phosphorescence, fluorescence, and absorption spectra of seven isotopic benzenes in a C6D6 host crystal were obtained at 4.2°K. The isotopes having less than D3h symmetry show splittings in their phosphorescence and singlet absorption spectra. Expected splittings in the fluorescence spectrum have not yet been observed because of the greater difficulty in obtaining the required high-resolution fluorescence spectra. The splittings are interpreted in terms of a distortion, which may arise either from extrinsic or intrinsic perturbations, in the 1B1u and 3B1u states of crystalline benzene. This distortion causes conformers of isotopic benzenes with less than trigonal symmetry to have different zero-point energies and leads to the observed line multiplicity. The vibronic structure of the phosphorescence and fluorescence emissions implies that the magnitude of the distortion is small.

Benzene molecules in the low-symmetry crystalline field are not expected to retain a hexagonal shape. However, the splittings in the fluorescence are only about ⅛ as large as those in the phosphorescence, implying that the distortion in the 3B1u state is larger than that in the 1B2u state. There is therefore some cause to believe that the distortion in the 3B1u state is partly intrinsic and thus has the significance attached to it by theorists. Our experiments, however, cannot actually distinguish between intrinsic and extrinsic distortions, but certainly give the impression that the distortion of the 3B1u state of benzene in the crystal is not very substantial and is either wholly or partly caused by the effect of the crystal field.

The relative intensities of the components of the multiplet structure in the phosphorescence are strongly concentration dependent because of trap-to-trap excitation migration in the crystal. At low guest concentrations, where little migration can occur, the intensity ratio gives the statistical weights of the components; at high concentrations a Boltzmann intensity ratio is obtained. The interpretation of the available optical data can be made to agree with the interpretation of ESR results by de Groot, Hesselmann, and van der Waals that a distorted 3B1u benzene is preferentially oriented in the site cavity of the solid phase, but the resulting picture is not a wholly satisfying one.
Mössbauer Studies of Ferro- and Ferricyanide Supercomplexes with 3d Transition Elements
Authors: Chandra K. , Raj Deo , Puri S. P.
Published: January 2005

The results of systematic Mössbauer studies of the ferro- and ferricyanide supercomplexes with 3d transition elements (Cr, Mn, Fe, Co, Ni, Cu, and Zn) are reported. It is concluded that the coordination number of Fe(II) remains six, and a metal—metal charge transfer is invoked to explain the data. The nearly double values of quadrupole splittings in ferricyanide supercomplexes, as compared to K3Fe(III) (CN)6 are explained.
Motion of a Vibrationally Coupled Exciton Wave Packet in an Infinite One-Dimensional Crystal
Authors: Bierman Arthur
Published: January 2005

It is shown that the rate of spreading of a vibrationally coupled exciton wave packet in a one-dimensional crystal is a constant, √2W | S | 2/ℏ, for all coupling strengths, if the initial state is a localized eigenstate of N noninteracting monomers. The utility of this initial condition is questioned in the light of the Franck—Condon principle, and another initial condition is proposed. The change in the second moment of a strongly coupled packet is calculated using perturbation theory. It is found that the new initial conditions combined with phonon—exciton coupling result in a time-dependent decrease of the rate of spreading. This decrease, for large t, goes as t, lnt, or a constant depending on whether ℏω<2W, ℏω=2W, or ℏω>2W. It has a maximum at some value of ℏω/2W which for t< <1 is given by the inequality π<ωt<32π and for large t is at ℏω≈2.2W.
Nuclear Magnetic Relaxation and Overhauser Effects in Liquid CHF3
Authors: Chaffin John H. , Hubbard Paul S.
Published: January 2005

The longitudinal nuclear magnetic relaxation, transient and steady-state Overhauser effects, and diffusion coefficient of the protons and fluorine nuclei in liquid CHF3 have been measured by pulsed magnetic resonance techniques at temperatures between 113° and 173°K. Interpretation of the data gives values of the contributions to the relaxation due to intra- and intermolecular dipole—dipole, and spin—rotational interactions. The effects of intermolecular dipole—dipole interactions are found to be larger than the effects of intramolecular dipole—dipole interactions. The intermolecular dipole—dipole contributions are larger, and the intramolecular contributions are smaller, than is predicted by the familiar theory that relates these contributions to the diffusion coefficient. The effects of the spin—rotational interactions of the fluorine nuclei are important, but the effects of the spin—rotational interactions of the protons are negligible. This investigation demonstrates that the use of Overhauser-effect data in addition to relaxation-rate data facilitates the determination of the effects of dipole—dipole and spin—rotational interactions.
Electronic Interaction Integrals for Atoms Calculated with Laguerre Polynomial Radial Wavefunctions
Authors: Brown Robert T.
Published: January 2005

Straightforward evaluation of electronic interaction integrals for many-electron atoms using Laguerre polynomial radial wavefunctions leads to sums of differences of large numbers. An alternate formulation is presented which does not have this disadvantage.
Effect of Deuteration of Durene on the Lifetime of the Phosphorescent Triplet State of Naphthalene in a Durene Host Crystal
Authors: Hirota Noboru , Hutchison Clyde A.
Published: January 2005

The observation of a pronounced increase in the lifetime of the lowest triplet state of naphthalene in a single crystal of durene produced by deuteration of the durene is reported. For naphthalene-d8 at ∼298°K the increase in mean life is from 0.8 to 10.8 sec. It is shown that the decay in question is an exponential triplet—singlet intramolecular transition.
Second-Order Nuclear Dipolar Contribution to Second Moment of Integer Spins
Authors: Choy W. T. P.
Published: January 2005

A formula has been derived for the second-order contribution of the dipolar broadening to the second moment of the resonance lines in pure quadrupole resonance experiments.

The following assumptions have been made: The nuclei undergoing the resonant transitions have spin ½; all resonant spins experience the same electric-field gradient which has a small amount of axial asymmetry; the dipolar interaction strength is small compared with the separation of the two resonance lines.
Approximate Theories of Chemical Shift
Authors: Hegstrom Roger A. , Lipscomb William N.
Published: January 2005

Starting from coupled Hartree—Fock perturbation theory, approximate expressions are derived for the magnetic shielding of a nucleus in a magnetic field. Some of these expressions are compared with existent approximate formulas which have been derived by other methods. The concept of localized contributions is explored and illustrated in the case of the diatomic molecules LiH and BH, for which exact coupled Hartree—Fock calculations have been performed.
Microwave Spectrum, Structure, and Barrier to Internal Rotation of Pentafluoroethane
Authors: Tipton Ann Baugh , Britt Chester O. , Boggs James E.
Published: January 2005

The rotational spectrum of CF3CHF2 has been studied in the 8.4- to 26.5-Gc/sec region, with c-type, R-branch transitions being assigned for both the ground vibrational state and the first excited torsional state. With the assumptions that rC–H=1.10 Å, ∠CCH=110°, rF–F=2.162 Å for the CF3 group, that the CF3 group is symmetrical and its axis and the C–C bond are collinear, and that the CHF2 fluorines are equivalent, an approximate structure of rC–F=1.335 Å, ∠FCF=108.14°, rC–C=1.520 Å, rC–F′=1.345 Å, ∠F′CF′=109.06°, and ÅCCF′=109.58° was found to fit the observed moments of inertia and to be consistent with determinations in other molecules. The primed F's refer to fluorine atoms of the CHF2 group. Relative intensity measurements gave a torsional frequency of 74 cm−1 compared with the infrared observation of 73.4 cm−1. From these data, the barrier to internal rotation is 1223±34 cm−1 or 3.51±0.10 kcal/mole.
Proton Magnetic Resonance Shifts in Aqueous Cobalt(II) Solutions Containing Various Monodentate Ligands
Authors: Horrocks William DeW. , Hutchison James R.
Published: January 2005

Isotropic PMR shifts for protons of water in aqueous solutions of cobalt(II) containing a variety of monodentate ligands have been measured. The results indicate that the magnitude of the shift in the bulk water resonance does not invariably decrease as water is diplaced from the primary coordination sphere. A marked increase in the shift upon complexation was observed for the system cobalt(II)—thiocyanate which was studied in detail. These results may be understood in terms of a significant contribution of the dipolar (pseudocontact) interaction to the total observed shift in these magnetically anisotropic cobalt(II) complexes. Relevant data in the literature concerning cobalt(II)—methanol—water complexes may also be interpreted in these terms. The present findings suggest that measurement of solvent NMR shifts in cobalt(II) solutions containing potential ligands may not be as useful in determining the average number of solvent molecules displaced from the first coordination sphere as previously suggested.
Study of Linear Stretch in Polyatomic Molecules: Accurate SCF MO Wavefunctions for CO2 and BeF2
Authors: Peyerimhoff Sigrid D. , Buenker Robert J. , Whitten Jerry L.
Published: January 2005

Accurate SCF MO calculations are carried out for CO2, BeF2, and various AH2 and AH3 molecules as a function of internuclear distance. It is noted that the resulting sum of orbital-energy curves show minima at much smaller internuclear distances than the corresponding total energy curves, even though it has previously been shown that derivatives of ET and ∑ εi with respect to internuclear angle quite generally vanish at approximately equal angles. This distinction emphasizes the point that the close correlation between angular derivatives of ET and ∑ εi is in large part caused by the lack of changes in internuclear distances between closely interacting atoms in the process of angular variations. It is further shown that an elementary application of Koopman's theorem enables one to make qualitative determinations of both relative bond angles and relative bond lengths by adding or subtracting various differentiating orbital-energy curves to an appropriate total-energy curve.
Fluorine Spin—Rotation Interaction and Magnetic Shielding in Fluorobenzene
Authors: Chan Sunney I. , Dubin Alan S.
Published: January 2005

The radio-frequency spectrum corresponding to the reorientation of the 19F nuclear moment in fluorobenzene has been studied by the molecular-beam magnetic resonance method. A molecular-beam apparatus with an electron-bombardment detector was used in the experiments. The 19F resonance is a composite spectrum with contributions from many rotational states and is not resolved. A detailed analysis of the resonance line shape and width led to the following diagonal components of the fluorine spin—rotational tensor in the principal inertial axis system of the molecule: CaaF = −1.0±0.5 kc/sec, CbbF = −2.7±0.2 kc/sec, and CccF = −1.9±0.1 kc/sec. From these interaction constants, the paramagnetic contribution to the 19F nuclear shielding in C6H5F was determined to be −284±10 ppm. It was further concluded that the 19F nucleus in this molecule is more shielded when the applied magnetic field is directed along the C–F bond axis. The anisotropy of the magnetic shielding tensor, σ∥—σ⊥, is +160±30 ppm.
Deuteron Magnetic Resonance Study of Potassium Oxalate Monodeuterate
Authors: McGrath J. W. , Ossman G. W.
Published: January 2005

Quadrupole splittings of the Larmor resonance for the deuteron in potassium oxalate monodeuterate (K2C2O4·D2O) were measured for single crystals at temperatures from −50° to 95°C. The D2O molecule is stationary at room and lower temperatures. The coupling constant and asymmetry parameter were determined to be 209.7±2.5 kc/sec and 0.090±0.020, respectively. The z field-gradient axis is within 4.8°±2.0° of parallelism with the O—D bond while the y axis is in the a—c plane and within 4.6°±2.0° of being perpendicular to the DOD plane.

The D2O molecule begins to 180° flip about its DOD bisector at 25°—50°C and higher. The coupling constant and asymmetry parameter of the flipping molecule are 114.2 kc/sec and 0.851, respectively. The z field-gradient axis is nearly perpendicular to the DOD plane while the y axis is nearly parallel to the D—D vector in its equilibrium position. Both axes are in the a—c plane and rotated away from perpendicularity and parallelism, respectively, by 4.6°±2.0°.

The coupling constants of this and three other deuterates differ among themselves and they are markedly lower than the computed and measured values for the isolated D2O molecule. Reasons for these differences are discussed including hydrogen bond strengths and D2O motion. For this crystal the field gradient due to nearby ions was estimated on the basis of a simple model and it was found to augment the measured coupling constant by about 9%.
Ternary Excess Enthalpies in Reciprocal Fused Salt Mixtures. IV. Effect of Charge Asymmetry
Authors: Meschel S. V. , Kleppa O. J.
Published: January 2005

Calorimetric measurements have been carried out on the enthalpies of mixing in the reciprocal systems Cd2+–Ag+–Cl−–NO3− and Cd2+–Tl+–Cl−–NO3−. The results, when compared with corresponding data for the binaries and for the metathetical reactions, enable us to evaluate the ternary excess enthalpies. In order to give the results in a simple algebraic form we have adopted the concept of the equivalent enthalpy of mixing, and have expressed compositions in terms of equivalent ionic fractions.

It is found that the ternary excess enthalpies for the system Cd2+–Ag+–NO3−–Cl− may be accounted for by a suitable adaptation of the quasichemical theory. This suggests that these excess enthalpies largely are due to deviations from random mixing in the relative arrangement of cations and anions. However, for the system Cd2+–Tl+–NO3−–Cl− the ternary excess enthalpies show orders-of-magnitude deviations from the predictions of our adaptation of the quasichemical theory.
Organic Scintillators with 2-Ethyl Naphthalene as a Solvent
Authors: Carter J. G. , Christophorou L. G.
Published: January 2005

The emission spectra and the integrated emission intensities for 11 efficient scintillator solutes in 2-ethyl napthalene excited by x rays are reported. Data are also presented on the quenching of scintillation emissions by various materials used for loading liquid scintillators. Pulse heights under β- and γ-ray excitation are also given, and new, efficient liquid scintillators are suggested. The role of solvent excimers in organic scintillators is discussed.