bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anomalous Effects in EPR Spectra of the Azulene Anion
Authors: Reddoch A. H. 
Published: January 2005

The proton hyperfine coupling constants of the azulene anion in dimethoxyethane with lithium ions show systematic variations of the order of 10% as temperature and concentration are changed. No splitting is observed from the lithium ion. As the concentration decreases, the variations of the five proton coupling constants are linearly related and the coupling constants approach those obtained by Bernal, Rieger, and Fraenkel for azulene in dimethylformamide with tetra-n-propyl ammonium ions. As the temperature is lowered, the coupling constants change rapidly until by about —40°C they are close to those of Bernal et al. At lower temperatures the change is small. At —40°C the peak heights of the lines are those predicted by the degeneracies of the nuclear spin states. At higher temperatures the peak heights become anomalous and the widths of the lines vary from line to line.
These effects are explained by a model involving a rapid chemical equilibrium between two states of the azulene—lithium ion system, having different degrees of association and different proton coupling constants. The less associated form has coupling constants similar to those of Bernal et al. and is more stable at low temperatures and concentrations. The anomalous linewidths are shown to result from the perturbation caused by the association and dissociation of the azulene—lithium ion pairs and are quantitatively related to the measured variations in the coupling constants.
Structure of Molten Oxides in the System: 0.25 Na2O·(0.75-x)GeO2·xSiO2
Authors: Riebling E. F. 
Published: January 2005

The counterbalanced-sphere technique was used to obtain high-temperature viscosity and density data for a series of Na2O·GeO2·SiO2 ternary melts. These compositions contained a fixed amount of Na2O (∼25 mole %). The effect of gradual SiO2 substitution for GeO2 was studied at 1300°C.
The data have been interpreted in terms of a model that involves no change for the partial molar volume of SiO2 (v̄SiO2). It is concluded that the elimination of GeO6 octahedra is not continuous with the gradual substitution of SiO2 for GeO2. A 0% to 10% replacement of GeO2 results in a slight decrease of the number of GeO6 octahedra. The partial molar volume results suggest that most of the GeO6 octahedra are transformed to GeO4 tetrahedra between 30% and 50% GeO2 replacement.
Single-Crystal X-Ray Diffraction Studies of α-N2 and β-N2
Authors: Jordan Truman H. , Smith H. Warren , Streib William E. , Lipscomb William N. 
Published: January 2005

The structure of α-N2 is cubic in the space group P213 with four molecules per unit cell. A total of 49 independent observed single-crystal x-ray diffraction maxima yield R=Σ ‖Fo|−|Fc ‖ /Σ|Fo|=0.13. Two faint reflections, (501) and (520), violate the space group Pa3, which yields R=0.21. Molecular centers are displaced by 0.1 to 0.2 Å from the centrosymmetric positions in Pa3 along the [111] directions so that the symmetry is reduced to P213.
Some corrections have been made in the Lorentz factors for upper levels and for the absorption of x rays in the experimental arrangement in the β-N2 study. The value of R improves from 0.09 to 0.04 for the freely rotating model, and the best precession angle is 56.0° rather than 54.5° (both ±2.5°) for the precession model, which we prefer.
Molecular Structures of PCl4F, PCl3F2, PCl2F3, and PF5: Infrared and Low-Temperature Raman Vibrational Spectra
Authors: Griffiths James E. , Carter Richard P. , Holmes Robert R. 
Published: January 2005

Molecular structures of PCl4F, PCl3F2, PCl2F3, and PF5 are derived from vapor-state infrared spectra (2000–250 cm—1) and low-temperature liquid-state Raman displacements (Δν=50–1200 cm—1) together with qualitative polarization measurements. All of the compounds appear to have a basic trigonal bipyramidal framework.
The spectra of PCl4F are best interpreted in terms of a C3v structure in which the fluorine atom occupies an axial site; in PCl3F2 (D3h point group) the fluorine atoms also assume axial positions. For PCl2F3, the symmetrical D3h structure is shown to be incorrect. Available evidence supports the C2v structure in which the fluorine atoms appear in one equatorial and two axial sites. Phosphorus pentafluoride is found to have a regular trigonal bipyramidal structure.
Complete vibrational assignments are made in terms of the normal modes and thermodynamic functions are evaluated for PCl5, PCl3F2, and PF5.
Conformation and Internal Rotation of Nitroaromatic Amines in Solution as Detected by Proton Magnetic Resonance
Authors: Heidberg Joachim , Weil John A. , Janusonis Gaile A. , Anderson Judith K. 
Published: January 2005

The 60-Mc/sec proton magnetic resonance spectra of N-methyl-2,4,6-trinitroaniline (I) and of N-methyl-2,6-dinitroaniline (II), as well as of the analogous N-diphenylamino compounds, show that the 3- and 5-phenyl protons are inequivalent at low temperatures in solution, but act as equivalent at sufficiently high temperatures. The N-unsubstituted anilines and N,N-dimethyl anilines corresponding to I and II show no such inequivalence. The coalescence with temperature of the AB quartet of the picryl protons in the picrylaniline (I) and diphenylpicrylhydrazine in dichloromethane solution could be described quantitatively by the line-shape equations for two coupled protons exchanging with each other. The analysis yielded the lifetimes of the ground state configurations of these molecules, with Arrhenius activation energies of 14.5±0.3 and 12.5 ± 0.2 kcal/mole and frequency factors of 1.4×1015 and 6×1010 sec—1, respectively, for the intramolecular exchange process. A model for these observations, including Hückel MO calculations, is presented in terms of the barrier to rotation about the amino nitrogen-ring carbon bond, the orientation of the nitro groups ortho to the amino group, and hydrogen bonding between the amino group and these nitro groups.
The chemical shift and spin—spin coupling parameters for these compounds and for the 2,4-dinitro analogs are tabulated and compared. The chemical shift values exhibit regularities in excellent agreement with the model introduced.
X-Ray Diffraction Study of Solid Argon
Authors: Barrett C. S. , Meyer Lothar 
Published: January 2005

Lattice constants for face-centered cubic argon determined on a precision x-ray diffractometer were found to be 5.3118 Å at both 4.2 and 15°K, 5.3187 at 21°K, 5.4033 at 64°K, with estimated errors of ±0.0005 Å, and 5.458 at 81°K. Least-squares fitting to a polynomial expression gives, for T≥21°K, a=5.29980+ 5.6389×10—4T+1.4231×10—5T2+3.552×10—8T3 (an expression not intended to be used below 21°K). Lattice constants for the close-packed hexagonal phase that sometimes coexists with the cubic may be taken as ahex=0.7071 acubic and chex=1.633ahex throughout the temperature range of solid argon. Evidence of rapid diffusion was seen near the melting point; at lower temperatures, cold work produced strain hardening. Agreement with published density measurements is good; values from some prior x-ray work lie slightly below these values.
Techniques were developed which permit plastic deformation and annealing of specimens to produce fine-grained strain-free samples suited to powder diffractometry. When grain growth could not be avoided (above about 65°K) a method of single crystal diffractometry was used.
Gaussian Correlation Functions: Two-Electron Systems
Authors: Lester William A. , Krauss Morris 
Published: January 2005

The correlated molecular orbital method is applied to the He isoelectronic sequence and H2 using a Gaussian basis set to explore the possible use of Gaussian basis function in wavefunctions containing explicit electron correlation for larger systems. The wavefunctions are analyzed in terms of the change in the electron-pair distribution and a comparison of the Coulomb holes is made for the atomic cases. The dependence of the correlation improvement on the accuracy of the orbital functions is discussed.
General formulas for Gaussian correlation integrals also are included.
Vapor Pressure of Neptunium
Authors: Eick H. A. , Mulford R. N. R. 
Published: January 2005

The vapor pressure of liquid neptunium metal in the temperature range 1700° to 1950°K, as determined by the Knudsen effusion technique, may be described by the equation logp(atm) = — (20 610±1280)/T+(5.10±0.70). The experimental heat and entropy of vaporization are ΔH°1800=94.3±5.9 kcal/mole, and ΔS°1800=23.3±3.2 cal/mole·deg, and the extrapolated normal boiling point of the metal is 4175°K.
The neptunium specimen contained 0.56 wt. % plutonium-239, and the partial pressure of that species over the solution may be described by the equation logp(atm) = — (19 051±538)/T+(3.29±0.30).
Z-Center Energy Levels
Authors: Johnson Wilbur V. , Scott Allen B. 
Published: January 2005

One of the centers proposed to account for Z-band absorption in alkali halide crystals consists of an electron trapped at the divalent cation. A calculation of the absorption energy has been made using the method of Simpson. This method, though not free of objections, has been surprisingly successful in predicting F-band absorption maxima.
For Ca++ in KCl and NaCl, the absorption maxima were found to lie at 3.92 and 3.70 eV, respectively, for Sr++ at 9.00 and 8.70 eV. These locations are far removed from the Z bands, which lie near 2.0 eV in both crystals. While the numerical accuracy of the calculations is not high, the possibility of a Z-type center absorbing in the far ultraviolet is raised; this has a bearing on recent thermodynamic arguments concerning the nature of Z centers.
Quenching of the 2537-Å Resonance Radiation of Mercury
Authors: Yarwood A. J. , Strausz O. P. , Gunning H. E. 
Published: January 2005

Cross sections for the quenching of the 2537-Å resonance radiation of mercury have been obtained by direct measurement of the resonance fluorescent intensities in an improved Zemansky-type apparatus. The data were evaluated on the basis of Zemansky's calculation (a) of the imprisonment time from Milne's theory, as well as using Holstein's experimentally verified formula (b) for the imprisonment decay constant, developed on modern imprisonment theory. The cross section values derived by (a) with the Samson ``equivalent opacity,'' by (b), and those obtained by Biberman from a numerical solution of the Holstein—Biberman transport equation all agree within 23%.
The trend observed in the measured cross section values of a number of substances including paraffins, olefins, silane and methyl silanes, alcohols, N2O, and some other inorganic molecules provides further evidence for the electrophilic character of Hg 6(3P1) atoms.
Behavior of Fused-Ring Aromatic Hydrocarbons at Very High Pressure
Authors: Aust R. B. , Bentley W. H. , Drickamer H. G. 
Published: January 2005

The effect of very high pressure has been studied on the electronic structure of some fused-ring aromatic hydrocarbons. The material most thoroughly studied is pentacene. Observations include optical absorption of the low-energy peaks and electrical resistance. The optical absorption peaks of tetracene and pentacene shift red at a rate which increases with density. Azulene peaks shift first blue, then red. The dipole moment of the excited state increases with increasing pressure. The electrical resistance decreases rapidly with increasing pressure, as a result of the decrease in activation energy for carrier production. Single-crystal pentacene becomes metallic at 270 kbar. The fused powder exhibits metallic behavior at somewhat higher pressures.
At pressures above about 180–200 kbar and temperatures above 180°—190°K an irreversible transition takes place in pentacene involving resistance increase and, at higher pressure, a transformation from metal to semiconductor. The low-energy optical absorption peaks have largely disappeared. It is proposed that this is a cross linking between adjacent molecules. A similar phenomenon is observed in violanthrene. The very sharp irreversible rise in resistance in single-crystal graphite above 150 kbar and 180°K may be an analogous cross-linking transformation.
Direct Determination of the Crystal Structure of Cornetite, Cu3PO4(OH)3, by the Monte Carlo Method
Authors: Fehlmann M. , Ghose Subrata , Finney J. J. 
Published: January 2005

The crystal structure of the peacock-blue mineral cornetite, Cu3PO4(OH)3, orthorhombic, with a0=10.845, b0=14.045, c0=7.081 Å, space group Pbca, has been determined. The phase problem has been solved by the direct determination of the heavy atom positions through the application of the Monte Carlo and optimal shift methods. Subsequent three-dimensional Fourier synthesis revealed all the light atom positions. The atomic parameters have been refined, using three-dimensional data, by the method of full-matrix least squares.
Two of the three independent copper atoms have essentially fivefold tetragonal pyramidal coordination, the coordination plane being curved in a boat shape towards the fifth ligand. The third copper atom has a highly distorted tetragonal bipyramidal coordination. Cornetite contains two sets of dimeric cupric complex ions. The first set [Cu2(OH)4O2] is formed by two different copper coordination planes sharing an edge, and the second [Cu2(OH)4O4] by two tetragonal pyramids, related by a center of symmetry, sharing a pyramidal edge. The [Cu2(OH)4O2] dimers are stacked upon each other along the c axis in a zigzag fashion, so that each dimer has two (OH) groups common with two other dimers above and below it. The dimeric chains thus formed are held together in a three-dimensional network, through isolated [Cu2(OH)4O4] dimers, PO4 groups, and O–H···O bonds.
Effect of Pressure on the Properties of TCNQ and Its Complexes
Authors: Aust R. B. , Samara G. A. , Drickamer H. G. 
Published: January 2005

The effect of very high pressure has been measured on the properties of TCNQ (tetracyanoquinodimethane) and three complexes. For all three complexes the electrical resistance at 296°K decreased with increasing pressure to about 140–150 kbar, beyond which pressure there was a very large rise accompanied by much drifting upward with time. This transformation was irreversible. At 78°K no rise was noted at high pressure, but if a sample was heated at high pressure the transformation initiated about 180°K.
It was found that the absorption peaks in the visible region had almost completely disappeared in the transformed material although the 280-mμ peak remained. The resistance of TCNQ was too high to permit electrical studies, but samples taken to high pressure also showed disappearance of absorption peaks in the visible. These and other related observations indicate that the TCNQ molecules are reacting, probably through the C≡N bond. The type of reaction seems in many ways similar to that obtained in pentacene and single-crystal graphite and discussed in a previous paper.
Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O
Authors: Carrington Tucker 
Published: January 2005

When water vapor absorbs light of wavelength less than 1350 Å, an electronically excited OH fragment may be produced. This process has been observed, using wavelengths 1216, 1236, and 1302 Å, and the rotational and vibrational excitation of the product OH 2Σ+ has been determined from its emission spectrum. Most of the energy beyond that necessary to produce electronically excited OH goes into rotation of that molecule. Roughly one-third of the OH molecules have one quantum of vibrational energy, and in these molecules too, the highest energetically allowed rotational levels are strongly populated.
Knowledge of the energy and rotational angular momentum of the OH allows estimation of the kinetic energy and orbital angular momentum of the H as it flies away from the center of mass. This is interpreted in terms of two-body forces at large distances, with the most probable dissociation corresponding to an orbiting interaction.
Spin—Echo NMR Studies of Chemical Exchange. I. Some General Aspects
Authors: Allerhand Adam , Gutowsky H. S. 
Published: January 2005

The applicability to chemical-exchange studies of the Carr—Purcell nuclear magnetic resonance spin-echo method has been investigated for the case of two exchanging sites with equal T20, the transverse relaxation time ``in the absence of exchange.'' Theoretical calculations indicate that the decay of the echo amplitudes should be exponential, or very nearly exponential in all cases, the apparent decay constant T2 being a function of T20, of δω the chemical shift between the sites, of τ the lifetime between exchanges, and also of tcp the rf pulse separation. Values of the apparent T2 for different values of these parameters were obtained by numerical methods with a high-speed computer. These values agree with an approximate equation derived by Meiboom, except at slow exchange and large pulse separation.
A method is described for calculating the exchange rate from the observed dependence upon tcp of the apparent T2. This method has several advantages over the high-resolution NMR methods. A knowledge of δω and T20 is not required; these quantities are also determined from the spin-echo data. Larger values of exchange rate (shorter lifetimes) can be determined accurately. The spin-echo method does have the serious drawback that it lacks ``resolution.'' The method was applied to the hindered internal rotation of N,N-dimethyltrichloroacetamide (DMTCA) and dimethylcarbamyl chloride (DMCC) as a function of temperature. The resultant activation energies of 14.6 and 14.0 kcal/mole and frequency factors of 3.5×1012 and 7.1×1010, respectively, are appreciably higher than previously reported values. Comparative determinations were carried out using the high-resolution NMR methods. The relatively large differences in the results from the various methods and from different laboratories indicate that systematic errors are present, several possibilities for which are discussed.
A simple arrangement is described for generating the Carr—Purcell pulse sequence with three waveform generators and two pulse generators.
Reinterpretation of the Electron Spin Resonance Spectrum of the o-Xylene Negative Ion
Authors: Bolton J. R. 
Published: January 2005

The electron spin resonance spectrum of the o-xylene negative ion has been re-examined in view of a discrepancy between one of the previously reported splitting constants and the predictions of molecular orbital theory. This splitting constant has been found to be 1.81 G instead of ∼0.2 G.
The new values of the hyperfine splittings reported here are in excellent agreement with the predictions of both molecular orbital and valence bond theory.
A technique is described by which molecules such as o-xylene can be reduced.
Range of Validity of Born Approximation for Molecular Fragmentation Following High-Energy Proton and Electron Impact
Authors: Wexler S. 
Published: January 2005

Arguments based on the Born approximation lead to the expectation that the ionic fragmentation pattern of a polyatomic molecule is independent of the nature of the ionizing and exciting charged projectile provided the velocity is the same and is sufficiently high. An experimental assessment of this expectation has been made. The patterns of positively charged fragments of methane, acetylene, ethylene, ethane, propane, and n-butane from bombardment of these molecules with 2.25-MeV protons have been compared with the mass spectra resulting from impact of 1225-eV electrons. At these energies the velocities of the two particles are 2×109 cm/sec, 9.5 times the Bohr velocity. The relative abundances of the more prominent ionic species were observed to be generally in good agreement, but large differences were found for ions of low yield. Almost invariably, the fragments were produced in higher abundances relative to the parent ion in electron impact than in proton bombardment.
The apparent failure of the Born approximation for describing molecular dissociation in high-energy-transfer collisions was expressed for each fragment quantitatively as the deviation from unity of the ratio of relative abundances from the electron and proton bombardments. Correlations of these deviations with several other characteristics of inelastic collision processes have been made. At the velocity employed the Born approximation is found to be valid for a large fraction of the ionizing and exciting collisions of almost all the target molecules. The apparent failure of the approximation appears to be related to the amount of energy transferred to the struck molecule by the projectile and to the kinetic energy of the fragment.
Vapor Pressures of the Rare-Earth Metals
Authors: Habermann C. E. , Daane A. H. 
Published: January 2005

Vapor-pressure measurements on the rare-earth metals were made by the Knudsen effusion technique using a quartz-fiber microbalance over a pressure range of 10—1 to 10—4 mm of Hg. The material used was specially prepared in order to minimize impurity effects. Ytterbium is the most volatile of the rare-earth metals, while lanthanum and cerium are the least volatile.
The data were fitted to a straight line by the least-squares method and the heats of vaporization or sublimation were calculated from the slope of the line. The heats of sublimation at 298°K were then calculated using the best available data for the enthalpies of the condensed and vapor states. For nine of the elements, measured heat content and entropy data for the condensed state as well as calculated free energy functions for the gaseous state were available, permitting a third law calculation of ΔH298°. The second- and third-law methods were generally in good agreement, but a comparison of the present work and previous investigations revealed several differences, amounting to as much as 15 kcal/mole in the case of gadolinium.
A possible explanation for the variations in the room temperature heats of sublimation of the different rare-earth metals, based on the differences in the electronic structures of the gaseous atoms and the number of d electrons present in the condensed phase is presented.
Decomposition and Oxidation of C2F4 Behind Shock Waves
Authors: Modica Anthony P. , LaGraff John E. 
Published: January 2005

Ultraviolet absorption and mass-spectrometric observations of shocked C2F4–Ar gas mixtures have indicated that the C2F4 monomer exists in thermal equilibrium with CF2 radicals and that the initial C2F4 oxidation mechanism involves two steps C2F4→ lim Ar2CF2CF2+O2→CO+2F+O.Dissociation and oxidation rates were determined from uv absorption measurements of CF2 at 2536 Å behind incident shock waves.
The C2F4 dissociation reaction appeared to be second order, 12d[CF2]/dt=kAr[C2F4][Ar], with kAr=7.82×1015T12 exp(−55 690/RT) cc/mole·secover the temperature interval from 1200° to 1800°K at total concentrations between 0.9×10−5 and 1.7×10−5. A least-squares fit to the experimental equilibrium constants for the reaction C2F4=2CF2, using the integrated form of the van't Hoff equation, yielded logKc=−69 432/2.303RT+4.62 (Kc in mole/cc).From the measured heat of reaction, the heat of formation of CF2 at 298°K was calculated to be −39.7±3.0 kcal/mole.
Mixtures of C2F4 and O2 in varying mole ratios were allowed to react at temperatures between 1500° to 2500°K with molar concentrations of reactants ranging from 4×10−8 to 6×10−7 mole/cc. The oxidation reaction was observed to be first order in both CF2 and O2, d[CF2]/dt=−kox[CF2][O2], with kox=2.92×1010T12 exp(−13 280/RT) cc/mole·sec.