bluuebunny/crossref_metadata_2025_split huggingface dataset:
Association of CN in an Expansion Wave
Authors: Bauer S. H. , Watt W. S. 
Published: January 2005

The expansion wave generated by the simultaneous arrival of the ``contact'' surface and the reflected rarefaction wave was used for a direct kinetic study of a condensation process, the association of CN radicals generated by shocking C2N2/Ar mixtures to about 2000°K in the reflected-shock region. During the quenching-expansion phase the concentration of CN radicals decreases due to the concurrent chemical association and the lowering in total density. The CN concentration was followed spectrophotometrically at 3883 Å.
The results were reduced in three ways: (A) unidirectional association to C2N2 in the presence of a third body, (B) relaxation to the local equilibrium via a three-body process, and (C) bimolecular reaction with C2N2 and CmNm polymers (formed during the heating process) to produce higher polymers. The data show that at the onset of quenching, the removal of CN was sluggish. This is attributed to failure to attain equilibrium in the preparation of the sample. After ≈200 μsec the data were best fitted by the third mechanism. This conclusion is in agreement with results obtained by another method and is supported by a reaction scheme which accounts for the formation and decay of CN in the presence of CmNm species. For a 2% initial concentration of C2N2, an average polymer number of ≈10 was indicated.
Theory of the Origin of the Internal-Rotation Barrier in the Ethane Molecule. II
Authors: Wyatt Robert E. , Parr Robert G. 
Published: January 2005

In the previous paper, the total energy difference ΔW hindering internal rotation in the ethane molecule was shown to comprise a nuclear—nuclear repulsion energy difference plus an electronic energy change ΔE, which may be computed from the integral Hellmann—Feynman formula, ΔE=∫ρES(1)H′(1)dv(1). Here ρES(1) is the first-order spinless transition density between the eclipsed and staggered states, and H′(1) is the difference between the one-electron electron-nuclear attraction operators for the two forms. It was shown how ρES(1) and H′(1) both could be expanded in Fourier series in the electronic azimuthal angle φ about the CC axis, so that ΔE becomes the sum of contributions from successive Fourier components of the transition density.
In the present paper this analysis is continued. The threefold and ninefold components of ρES(1) are accurately computed from the LCAO—SCF wavefunctions of Pitzer and Lipscomb, thus eliminating several mathematical approximations made in the previous paper. The threefold contribution to the rotation barrier is found to be ΔE3≈−2.4 kcal/mole, the ninefold contribution ΔE9≈0.0 kcal/mole. The net barrier is ΔW≈2.4 kcal/mole. Contributions to ΔE3 from localized and corresponding orbital expansions of ρES(1) are evaluated, and contour maps are given of ρ3(r,θ) and ρ3(r,θ)A3(r,θ) over the whole molecule. From the orbital analyses and the density maps, the following conclusions are drawn: (1) The CC and carbon iS orbitals contribute insignificantly to ΔE. (2) Most of ΔE arises from CH orbitals. (3) The quantity ΔE can be interpreted as mainly arising from regions around protons; regions near the CC axis are unimportant. (4) The effects of changes of localized orbitals on rotation are probably not negligible, but their precise evaluation is particularly difficult.
The Pitzer—Lipscomb energy difference, 3.3 kcal/mole, is different from the integral Hellmann—Feynman result. A method for bringing the two methods into concordance is described, and it is reasoned that if this were carried through the common result would probably be very near the experimental value, 2.9 kcal/mole.
Various other theoretical questions are discussed, and a number of suggestions are made for further research on the internal-rotation problem.
Molecular Structures of Gaseous Hexabromo- and ortho-Dibromobenzene as Determined by Electron Diffraction
Authors: Strand Tor G. 
Published: January 2005

The molecular structures of hexabromo- and ortho-dibromobenzene have been studied by least-squares refinements based on gaseous electron-diffraction intensity data. The equilibrium conformation of ortho-dibromobenzene is found to be planar with C2v symmetry and with an angle of 63.6°±0.5° between the two carbon—bromine bonds. For hexabromobenzene, the ortho-bromine—bromine distance indicates a distorted structure possessing S6 symmetry with every second bromine atom above and below the plane of the benzene ring. The other bromine—bromine and the nonbonded carbon—bromine distances, however, are in better agreement with a planar and undistorted configuration. Possible structures of this molecule are discussed in the text. The most important molecular parameters and estimated standard deviations are listed in Table IV.
Accurate partial-wave scattering factors for the atomic scattering of 40-keV electrons have been applied in some refinements. The results are compared with the results obtained using scattering factors according to the first Born approximation, and a better agreement with the experimental data is observed for the former scattering factors.
Electrical Properties of Cobalt Monoxide
Authors: Fisher Bertina , Tannhauser D. S. 
Published: January 2005

The electrical conductivity of polycrystalline CoO1+x was measured as a function of temperature and partial pressure of oxygen, P(O2). The range of temperature was 900°—1450°C and the range of partial pressure was 1 − 10−12 atm. The plot of the conductivity against partial pressure of oxygen gave two distinct regions: Region A, where the conductivity is proportional to P(O2)¼, and Region B, where the conductivity is proportional to P(O2)⅙. From these results, together with considerations of ionic radii, we concluded that the dominant defects in CoO1+x at high temperatures are cation vacancies, with the majority being singly ionized in Region A and doubly ionized in Region B.
A combination of gravimetric and electrical measurements showed that the mobility of the holes contributed by these vacancies rises exponentially with temperature. The activation energy of mobility is Eu=0.3 eV. At 1350°C, the mobility is about 0.4 cm2 V−1·sec−1. These values are discussed in terms of polaron theory.
The sum of the enthalpy of formation of a neutral vacancy and the first ionization energy is Δhv+E1=0.56 eV. The second ionization energy was measured separately and found to be E2=0.65 eV. A rough estimate of the first ionization energy gives E1≅0.45 eV.
Analysis of Seebeck-coefficient measurements performed in the same range of temperature and oxygen pressure is consistent with the results of the conductivity measurements regarding the sign and number of charge carriers. The term Ap, the so-called heat of transport, was calculated on the assumption that p0, the molar concentration of available states for charge carriers, is about 1. This assumption gave negative values for Ap. The term dAp/d(kT)−1, which is independent of the value of p0, is about 0.24 eV in Range A, and 0.54 eV in Range B. The value of dAp/d(kT)−1 in range A is close to Eμ, as the theory suggests.
The resistivity of quenched samples of CoO1+x was measured at temperatures below 70°C for different x. Above the Néel temperature (tN≅19°C) the activation energy of the conductivity is ½E1+Eμ≅0.5 eV in a wide range of concentrations. This value is consistent with E1 and Eμ evaluated at high temperatures. At very low deviations from stoichiometry the activation energy increases, due perhaps to the appearance of electrons donated by interstitial cobalt atoms. Below the Néel temperature the activation energy ε decreases by about 0.1 eV, the difference between ε(t&gt;tN) and ε(t&lt;tN) depending on the departure from stoichiometry. This decrease is not understood.
The appendix contains a slight correction to the phase diagram that was previously published. This correction is due to a more refined analysis of the data.
Primary Processes in Ozone Photolysis
Authors: DeMore W. B. , Raper O. F. 
Published: January 2005

The photolysis of O3 dissolved in liquid Ar at 87°K has been studied at 2537 Å and at wavelengths near 3130 Å. Quantum yields of O3 photodecomposition were determined for O3 concentrations ranging from 5×10−4 to 0.3 mole/liter at 2537 Å and 0.03 to 0.67 mole/liter at 3130 Å. Disappearance of O3 is attributed to the reactions O3→ lim φIabsO2+O(1D),O(1D)+O3→2O2,where Φ is the quantum yield of O(1D) formation at a given wavelength. The limiting photodecomposition quantum yield at high O3 concentration is about 2 at 2537 Å and about ½ at 3130 Å.
Quantum yields were also determined at several wavelengths in the interval 2970 to 3340 Å for the photo-exchange reaction O3+36O2→52O3+O2.
The foregoing studies, together with previous work, show that the O(1D) quantum yield in O3 photolysis is unity below 3000 Å but falls to a value of 0.4±0.15 in the 3130-Å region. The exchange experiments show that the total quantum yield of atomic oxygen, including O(1D) and O(3P), retains a constant value of unity throughout the wavelength range studied, with onset of O(3P) formation occurring at 3000 Å.
From these results the rate of O(1D) production in the lower atmosphere is calculated to be 1.2±0.5 pphm/h (pphm is parts per hundred million), based on an assumed O3 concentration of 10 pphm and a solar zenith angle of 45°.
Theoretical Transition Probabilities
Authors: La Paglia S. R. , Sinanoğlu Oktay 
Published: January 2005

The contribution to the intensity of atomic and molecular electronic transitions beyond the Hartree—Fock, or independent-particle model, is examined by means of ``many-electron theory'' (MET). The contribution is of first order in the wavefunctions of the combining states.
MET analysis of the off-diagonal matrix element for the transition probability in the frozen-core approximation yields physically interesting expressions which are applied to atomic and molecular examples. Considerable improvement in calculated atomic (e.g., Be resonance transition) and molecular (e.g., π—π* transitions) intensities are obtained when analysis shows that ground-state ``hole pairs'' are strongly scattered into the orbital sea of the excited state.
The uses of energies and operators in the calculation of electronic intensities is also examined. The relation between the expectation values of operators ∇ and r which replaces the widely used off-diagonal hypervirial theorem in the absence of exact wavefunctions is given.
Kinetics of Unimolecular Breakdown. V. Mass-Spectral Patterns
Authors: Levine R. D. 
Published: January 2005

The measurement of mass-spectral patterns is discussed as a foundation for a formal theory. The formalism is developed in close correspondence with experimental information and concepts. The Morrison technique is discussed and expressions are derived for all measured quantities in terms of the matrix elements of relevant transition operators.
Rearrangement processes are discussed and isotope retention ratios are predicted in agreement with experiment.
Absorption Spectra of the Solvated Electron in Polar Liquids: Dependence on Temperature and Composition of Mixtures
Authors: Arai Shigeyoshi , Sauer Myran C. 
Published: January 2005

The effect of temperature on the absorption spectra of the solvated electron in various liquid alcohols is reported. From 25° to −78°C, the energy corresponding to the absorption maximum increases by 0.23, 0.35, 0.36, and 0.46 eV for methanol, ethanol, isopropanol, and n-butanol, respectively. Within experimental error there is no change in the width (in electron volts) of the absorption at half-maximum.
The absorption spectra of the solvated electron in several binary mixtures at room temperature are reported. In all mixtures examined the spectrum has only one peak at wavelengths intermediate to the absorption maxima of the pure components, and the exact position depends on the mixture composition. In 50:50 mixtures of many of the materials used, the absorption maxima and half-widths are closer to those of one pure component than of the other.
The fact that there is no evidence of two peaks in mixtures indicates that the solvation of the electron depends on the macroscopic properties of the solution in the sense that a particular electron interacts significantly with a large number of solvent molecules. However, the results indicate that at least in some mixtures the electron is associated on a microscopic scale preferentially with one component.
Partial spectra, at low temperature, of the solvated electron in the liquids diethyl ether, monomethylamine, and monoethylamine are also reported.
Molecular Structures of Gaseous Hexachloro- and 1,2,4,5-Tetrachlorobenzene as Determined by Electron Diffraction
Authors: Strand T. G. , Cox H. L. 
Published: January 2005

The molecular structures of hexachloro- and 1,2,4,5-tetrachlorobenzene have been determined by least-squares refinements based on gaseous electron-diffraction intensity data. The equilibrium configuration of hexachlorobenzene is found to be planar with D6h symmetry. The observed shrinkage for this molecule is compared with the shrinkage calculated from spectroscopic data for hexafluorobenzene. 1,2,4,5-Tetrachlorobenzene is planar with D2h symmetry; the repulsion between the neighboring chlorine atoms leads to an angle of 62.8°±0.4° between the ortho carbon—chlorine bonds. The most important molecular parameters and estimated standard deviations are listed.
Hartley's modification to the least-squares method was applied in refinements of the structure of 1,2,4,5-tetrachlorobenzene. It was found that the least-squares method modified in this fashion has a wider circle of convergence than the regular Gauss—Newton method, and that the regular method diverged even when the final parameters from the modified method were applied as a starting vector for the regular method.
Low-Lying Pi—Sigma Transition in the Spectrum of Norbornadiene
Authors: Robin M. B. , Kuebler N. A. 
Published: January 2005

A vibrational analysis of the first electronic band of norbornadiene (NBD), with origin at 45 120 cm−1, shows that the band is electronically allowed, the accompanying vibrations being totally symmetric. This is contrary to earlier theoretical work which assigned the band as N→V1, forbidden. A comparison with the spectra of cyclopentene and norbornene (NBE) suggests that the first band of norbornadiene is to be associated with the weak band of uncertain assignment found at approximately 45 000–50 000 cm−1 in all olefinic substances.
Gross changes in the vibrational spacing and shape of the vibronic envelope are observed on freezing the NBD and NBE molecules in low-temperature matrices. The spectral changes appear to be due to modifications of the upper-state potential surfaces as a consequence of the rigidity of the matrix.
There is some evidence in the NBD spectrum for weak vibronic coupling between the two halves of the diene molecule, and it is shown how the observed splitting pattern might be explained on such an assumption.
Transverse Relaxation in Systems of Two Nonidentical Spins
Authors: MacLean C. , Mackor E. L. 
Published: January 2005

Nuclear relaxation in molecules with two nonidentical spins may originate from intra- and intermolecular interactions between like and unlike spins. The various contributions to the relaxation may be determined from the longitudinal relaxation combined with the Overhauser effect.
Transverse relaxation rates are likewise related to the contributions of the possible interactions. We have derived the appropriate equations for transverse relaxation in systems consisting of scalar-coupled nuclear spins. The expressions have been applied to CHFCl2, both neat and diluted in COS.
The results on the neat liquid are in agreement with those obtained previously from longitudinal relaxation: at −142°C hydrogen and fluorine relax mainly by interactions between unlike spins. Dilution in COS barely affects the ratio of intra- to intermolecular interactions under conditions where the relaxation is of dipolar nature. This surprising finding must be related to nonviscous rotational behaviour of molecules in liquids of low viscosity like COS. The moment of inertia of the molecule rather than the viscosity of the liquid determines rotational relaxation.
Structure of Sodium Aluminosilicate Melts Containing at Least 50 mole % SiO2 at 1500°C
Authors: Riebling E. F. 
Published: January 2005

Viscosity and density data were obtained for several series of alkali aluminosilicate melts between 1200° and 1700°C with a counterbalanced sphere viscometer. Property comparisons are presented as functions of the SiO2 content, Na2O content, and constant Al/Na ratios at 1500° and 1700°C.
The viscosity and expansion information support the formation of three-dimensional cristobalitelike liquids on the Al/Na=1.0 line with some of the aluminum (III) in the form of AlO6 octahedra for Al/Na&gt;1.0 melts.
The molar volume models that coincide with experiment for Al/Na≤1.0 melts involve AlO4 tetrahedra and v̄Na2O values that increase with increase of the Al2O3 content. The model that best agrees with experiment for melts with Al/Na&gt;1.0 involves only some of the excess aluminum ions in octahedral coordination as well as a changing v̄Na2O. Melt molar volume dependencies on composition can resemble those observed for similar glasses, which suggests structural similarities. The present liquid structure picture differs somewhat from previous concepts of alumina-rich glass structures in this ternary system.
ESR of the Perinaphthenyl Radical in a Liquid Crystal
Authors: Glarum Sivert H. , Marshall James H. 
Published: January 2005

The electron spin resonance spectrum of the perinaphthenyl radical has been studied in the isotropic and nematic phases of p-azoxyanisole. The g tensor and hyperfine splitting tensors for the two proton couplings and three of the four carbon−13 couplings have been determined, and were found to agree in most cases with theoretical estimates. Ordering of the radical was also deduced as a function of temperature in the liquid-crystal range, and corresponded to the ordering of the solvent molecules.
A general expression for the effective spin Hamiltonian of a radical in a liquid crystal is derived. Zeeman anisotropy and dipolar electron—nuclear couplings are shown to result in g shifts and changes in the hyperfine splitting coefficients.
Infrared Spectra of HCl in Pure and Impure Noble-Gas Matrices. Absolute Intensities
Authors: Verstegen J. M. P. J. , Goldring Hanna , Kimel S. , Katz B. 
Published: January 2005

High-resolution spectra were taken of the 1–0 absorption band of HCl trapped in argon, krypton, and xenon matrices in the temperature range between 6° and 50°K. The influence of impurities on such spectra was studied by introducing small quantities of a different noble gas into the matrices.
A new spectral line, believed to be due to the combination of a ΔJ=0 transition with the constrained translational mode, is reported. Absolute intensities of the 1–0 band were measured and found to be 15 000, 18 500, and 18 000 darks in argon, krypton, and xenon, respectively. The spectra of HCl polymers are discussed.
Systematics of the Evaporation Coefficient Al2O3, Ga2O3, In2O3
Authors: Burns Richard P. 
Published: January 2005

The rate of evaporation from surfaces of Al2O3, Ga2O3, and In2O3 has been studied through a combination of thermal-imaging and mass-spectrometric techniques.
A discontinuity is observed in the rate of evaporation of Al2O3 and Ga2O3 at the melting point TM. The evaporation coefficient αv of the solid at the melting point is equal to 0.3±0.05 for all gaseous species over Al2O3, Ga2O3, and In2O3. The rate of evaporation from the surface of the liquid at the melting point is the equilibrium rate (αv=1) for all gaseous species. The evaporation coefficient αv over the solid is very nearly temperature independent for monatomic vapor species but depends strongly on temperature for polyatomic species.
It is shown that the data for the different systems can be directly correlated when they are plotted as logαv vs TM/T, where TM is the melting temperature. This correlation also applies to other systems and appears to be useful in predicting evaporation behavior in related systems.
The equilibrium rates of evaporation are used to calculate: D0°(AlO) = 116.0±3.0 kcal mole−1, D0°(Al2O) = 241.6±7.0 kcal mole−1, ΔH°v,298(Ga) = 64.2±2.0 kcal mole−1, D0°(GaO) = 90.2±3.5 kcal mole−1, D0°(Ga2O) = 206.8±7.0 kcal mole−1, D0°(In2O) = 179.2±4.0 kcal mole−1.
Polymorphism of LiMO2 Compounds and High-Pressure Single-Crystal Synthesis of LiBO2
Authors: Marezio M. , Remeika J. P. 
Published: January 2005

Single crystals of γ-LiBO2, which is the phase stable at high (P, T), have been grown at 15 kbar and at 950°C by using a flux technique. The crystals were retained metastably by quenching to room pressure and temperature.
γ-LiBO2 is tetragonal with four molecules per unit cell (a=4.1961±0.0004, c=6.5112±0.0007 Å), Space Group I4̄2d. The arrangement is that of a zinc-blende-like structure, with every atom tetrahedrally coordinated. The structure has been refined from single-crystal x-ray-diffraction data with a precision corresponding to an R factor of 0.028. The interatomic distances are B–O=1.483 Å and Li–O=1.957 Å.
The polymorphism of the LiMO2 compounds (M=B, Al, Ga, In, Tl) is discussed. It is shown that there is a common trend among these compounds. They tend to assume a NaCl-like structure. LiAlO2 and LiGaO2 have such an arrangement at high (P, T), while LiInO2 and LiTlO2 have a NaCl-like structure at room pressure and temperature. The only exception is LiBO2.
Two-State Model for the Free Volume of Vitreous B2O3
Authors: Macedo P. B. , Capps W. , Litovitz T. A. 
Published: January 2005

New data on the density of B2O3 from 25° to 230°C are given. A two-state equation of state for the volume is presented which fits the volume data from 350° to 1400°C. A specific structure for the two states is suggested and shown to be consistent with Raman data. Below 350°C and at high pressures the data indicated that the two-state expressions for free volume still hold but the volume of the close-packed structure becomes temperature and pressure dependent.
The viscosity of B2O3 from the glass transition up to 1400°C and at high pressure is consistent with the equation of state and the hybrid equation of Macedo and Litovitz. The viscosity values above 1400°C indicate a breakup of the two-state structures and the beginning of multistate behavior which results in a temperature-dependent activation energy. The onset of this effect causes the ``apparent'' activation energy to increase above 1400°C.