bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure of Oriented Sodium Metaphosphate Glass Fibers
Authors: Milberg M. E. , Daly M. C. 
Published: January 2005

The structure of oriented sodium metaphosphate glass fibers has been investigated employing cylindrical distribution functions obtained from the x-ray scattering pattern. Although this method has rarely been used, it is the only sound one available. The difficulties in interpreting the functions were eased somewhat by the use of difference, rather than complete, cylindrical distribution functions. The former are usually less cluttered with spurious peaks than are the latter.
The results indicate that the NaPO3 fibers are made up of long chains of PO4 tetrahedra, and that the axes of these chains have a strong preference for lying along the fiber axis direction. Both the general appearance of the distribution functions and the results of normal distribution function calculations agree with the existence of a very high degree of orientation in the fibers. The locations of sharp peaks on the functions suggest that the individual PO4 tetrahedra have shapes similar to that found in crystalline RbPO3. In the latter material the average in-chain P–O distance is 1.62 Å and the average out-of-chain distance is 1.46 Å. Best agreement with the experimental distribution functions is obtained with a puckered version of a planar chain, in which each tetrahedron is tilted relative to the chain axis through two mutually perpendicular angles of 20° to 30° and the intratetrahedral angles are near 110°.
The high effective radial resolution obtained in the difference cylindrical distribution functions, as a result of the angular resolution, suggests that the simplified cylindrical distribution function will be a useful way to study the structures of orientated amorphous polymer fibers.
Electron Diffraction Study of the Molecular Structures of Sulfur Tetrafluoride (SF4) and Thionyl Tetrafluoride (SOF4)
Authors: Kimura K. , Bauer S. H. 
Published: January 2005

The molecular structures of SF4 and SOF4 in the gaseous state were determined by electron diffraction using sector-microphotometer data. Both molecules were confirmed to have trigonal bipyramidal structures (C2v symmetry), with two nonequivalent sets of F–S bond distances. The bond lengths, in terms of the center of gravity parameter, rg, and the bond angles are as follows: For SF4:rg(equatorial S–F)=1.542±0.005 Å,rg(polar S–F)=1.643±0.005 Å,∠(equatorial F–S–F)=103.8∘±0.6∘,∠(polar F–S–F)=176.8∘±2.5∘.For SOF4:rg(equatorial S–F)=1.539±0.005 Å,rg(polar S–F)=1.602±0.005 Å,rg(S–O)=1.422±0.008 Å,∠(equatorial F–S–F)=122.8∘±1.8∘,∠(polar F–S–F)=182.8∘±0.7∘.
The polar F–S–F angles are measured along an arc which bisects the equatorial FSF angle.
Investigation of Early Ionization Processes in Shocked Xenon
Authors: Hacker D. S. , Bloomberg H. 
Published: January 2005

Measurements of ionization rates in noble gases have been of considerable interest, with much of the recent experimental work performed at very high temperatures with shock-tube techniques. As a result, there have been several conflicting theories formulated to trace the history of ionization phenomena. A major difficulty has been the problem of precisely identifying the earliest stage of the ionization process. Since the probability of atom—atom collisions leading to ionization is small, another source of energy sufficient to promote the necessary early stage of the process must be provided. It appears that under conditions of relatively low temperatures, as in weak shock waves, the assumption of a photoexcitation mechanism of the gas is plausible. Biberman and Veklenko have suggested such a mechanism for the production of excited states of rare gases in shock waves. This mechanism has been used to explain the initial shock-front ionization. The nature of the processes responsible for visible emission at the shock front, which has been designated as impurity radiation, appears to be a result of the transfer of energy from the excited rare-gas atoms to the impurity molecule.
Spectral observations of the shock zone in xenon have been made in a carefully outgassed shock tube (10—6 mm Hg). The absorption spectrum is typical of molecular fragments of carbon (C2) which has been shown earlier to be localized in the region of 4500 to 4960 Å. Calcium or sodium, usual alkali impurities, were not observed in any measurement. The emission appeared to be predominantly from the xenon and possible carbon impurities.
Microwave absorption measurements were made normal to the shock front. By use of a plasma model which assumes a linear varying electron density, microwave attenuation in the region of cutoff was measured to determine the rate of ionization and the plasma collision frequency. The observed ionization rate was of second order with respect to xenon pressure for the temperature range of 4000° to 9000°K. The observed activation energy was 1.60 eV±0.2. This was the approximate activation energy for the following reactions in xenon:  Xe*+Xe⇒Xe2++e−or Xe*+C2⇒XeC2++e−}collision of the second kind.The experimentally determined rate expression for ionization is given as ki=3.58×1014T12exp[−1.6±0.2/kT]cm3moles−1sec−1.Radiation at the shock front appears to be best described by the excitation of impurity or by the dissociation of Xe2 as suggested by Tanaka: Xe*+C2 ⇒Xe+C2*,collision of second kind,C2*(A3π) ⇒C2(X3π)+hν,radiative transition,XeC2++e−⇒XeC2*⇒XeC2+hνXe2++e− ⇒Xe2* ⇒Xe2+hν}dissociated recombination (visible emission).
Polyhedral Clathrate Hydrates. V. Structure of the Tetra-n-butyl Ammonium Fluoride Hydrate
Authors: McMullan R. K. , Bonamico M. , Jeffrey G. A. 
Published: January 2005

The structure of (n-C4H9)4N+F—·32.8 H2O is tetragonal, of space group P42/m with the unit-cell dimensions a=23.52 Å and c=12.30 Å. The clathrate host structure is similar to that of the (n−C4H9)4N+C6H5−COO−·39.5 H2O and consists of a tetragonal pseudo body-centered arrangement of groups of five face-sharing pentagonal dodecahedra interlinked by tetrakaidecahedra and pentakaidecahedra. Whereas in the benzoate there are four salt molecules per unit cell, in the fluoride there are five. This difference in the number of guests accommodated in essentially the same host structure is possible because the four tetrakaidecahedra occupied by the benzoate groups are available for the four alkyl groups of the additional cation. In the fluoride hydrate, four of the cations have the central N+ atom at the fourfold positions (j) and that of the fifth is disordered over the twofold position (f). Thus the structure has lower symmetry than the benzoate hydrate, which is P42/mnm by reason of the disorder of the four cations over eightfold positions.
The fluoride ions replace water molecules in the host lattice, with F—···O distances of 2.80 to 2.87 Å forming an anionic host lattice. As in the other clathrate hydrate structures of this type, some of the pentagonal dodecahedra which are distorted by the presence of the cations are occupied by a guest species presumed to be additional water molecules.
Photoconduction in Charge-Transfer Complexes
Authors: Akamatu H. , Kuroda H. 
Published: January 2005

The photoconduction in the solid molecular complexes of pyrene with tetracyanoethylene, bromanil, and 1,3,5-trinitrobenzene has been observed. In each case, the intrinsic photoconduction arises with photon energy a little higher than the energy gap for the excitation to the conduction state, while its spectral region does not coincide with the charge-transfer band in the electronic spectrum. It has been suggested that in these ``weak'' charge-transfer solid complexes, the excited state associated with the charge-transfer band cannot contribute to conduction, and an energy diagram for the electronic state in these crystals has been proposed.
A structure-sensitive secondary photoconduction has been observed in the spectral region around the threshold of the charge-transfer band, which is likely due to the interaction between charge-transfer excitons and imperfections in the crystal.
Gaseous Metaborates. I. Mass-Spectrometric Study of the Vaporization of Lithium and Sodium Metaborates
Authors: Büchler Alfred , Berkowitz-Mattuck Joan B. 
Published: January 2005

The vaporization of lithium and sodium metaborate has been studied mass spectrometrically. The vapors of these compounds consist principally of the monomers LiBO2 and NaBO2, with some dimer and a very small amount of trimer also present. Heats of vaporization of the two metaborates and of boron oxide were determined with an effusion cell designed to give reliable second-law heats. The values obtained are: B2O3(l)=B2O3(g)ΔHv,1300=93.6±3 kcal mole−1LiBO2(c)=LiBO2(g)ΔHs,1060=79±3 kcal mole−1LiBO2(l)=LiBO2(g)ΔHv,1160=70±3 kcal mole−12 LiBO2(g)=Li2(BO2)2(g)ΔH1120=−67±3 kcal mole−1NaBO2(c)=NaBO2(g)ΔHs,1070=73±3 kcal mole−12 NaBO2(g)=Na2(BO2)2(g)ΔH1070=−53±3 kcal mole−1.
The composition and the dimerization energies of the metaborate vapors thus resemble those of the alkali halides, hydroxides, and cyanides.
Interactions in Polar Media. II. Continua
Authors: Marcus R. A. 
Published: January 2005

It is shown that the electronically polarizable continuum model of a particle satisfies the equations of part I, after suitable choice of operator Ai appearing there. The proof is given for the case where the system is regarded as composed of particles and treated statistically mechanically. It is also given for the case where several particles receive special attention and the remainder of the system (the ``medium'') is treated as an orientationally and electronically polarizable continuum. For the second case it was necessary to extend the results of Part I, so as to include several particles in the presence of the above ``medium'' and to compute the free energy of such systems. Calculations are given for media possessing equilibrium and nonequilibrium dielectric polarization.
It follows from the foregoing proofs that a wide variety of models assumed in the literature for treating polar interactions are special cases of the model in Part I and of the extension to particle-medium systems in this paper. Electrode systems, for example, are included, even when the electrode is treated in the usual dielectric continuum manner.
The relation and relative merits of the two models for the induced charge distribution that are standard in the literature, both special cases of Part I, are discussed. These models are the induced dipole and the electronically polarizable continuum. Possible direct experimental investigation of the second of these by scattering experiments is examined.
NMR in Hydrate Crystals: Structural Information from Second Moments
Authors: Pedersen Bjo/rn 
Published: January 2005

The effects of fast 180° flip motion of the water molecules in hydrate crystals on the first and second moment of the proton magnetic resonance spectrum are explored theoretically. When the spectrum consists of two well-separated line components, it is proved that the first moment of the spectrum about the midpoint is the correct measure of the interaction responsible for the main splitting. Earlier this has been proved for a system of water molecules rigidly bound in the lattice.
A formula for the second moment, consisting of an intramolecular term, an intermolecular term, and a term due to unlike spins, is derived. The first and the last of these terms are shown to be independent of the shape of the spectrum. The intermolecular term, however, is proportional to a factor which is 5/6 when the spectrum consists of two well-separated line components and 1 when the spectrum shows no sign of a fine structure. This shape dependence of the intermolecular term is due to the fact that some of the intermolecular spin exchange transitions are forbidden to first order when the spectrum consists of two well-split lines. It is pointed out that the partial quenching of some transitions when the spectrum shows signs of a fine structure will in general lead to an uncertainty in the theoretical second moment. It is concluded that to get accurate structural information from second moments, the fine structure has to be completely resolved or the spectrum should show no signs of a fine structure.
The obtained formula for the second moment has been used to calculate the second moments for a particular set of orientations of a single crystal of gypsum. The experimentally measured second moments show fair agreement with the calculated values.
Intramolecular Electron Transfer in Bis(p-Nitrophenyl) Anions and Its Effect on Electron Spin Resonance Hyperfine Structure
Authors: Harriman John E. , Maki August H. 
Published: January 2005

The hyperfine structure of electrochemically generated mononegative ion radicals of the type[Complex chemical formula]has been observed, where X=CH2, S, O, CH2CH2, and where X is absent. The hyperfine structure is found to be especially sensitive to the intramolecular electron transfer rate when the latter is the same order of magnitude as the hyperfine intervals when expressed as frequencies. The transfer rate is found to be sensitive to the solvent, and a model is presented that expresses the trapping of the electronic charge by the orientation of solvent dipoles. The mechanism for electron transfer then proceeds through the random motions of the solvent molecules.
Hyperfine structures are calculated for a series of transfer rates on the basis of the Anderson—Weiss model for motional narrowing. Good agreement is found between the unusual hyperfine structure observed experimetally and the calculated spectra for certain values of the transfer rate.
The shape of the composite two-electron polarographic reduction wave is related to the equilibrium constant for the reaction, S+S==2S—, assuming reversibility of all electron-transfer reactions at the electrodes. Equilibrium constants are reported.
Deuteron Magnetic Resonance Study of Barium Chlorate Monohydrate
Authors: Chiba Takehiko 
Published: January 2005

Quadrupole splitting of deuteron magnetic resonance was measured for a single crystal of Ba(ClO3)2·D2O. Quadrupole coupling, asymmetry parameter, and principal axis directions of the field gradient tensor were determined at 20° and at —130°C. eqQ/h=121.5±0.4 kc/sec, η=0.976±0.007 at 20°C, and eqQ/h=243.5±1.5 kc/sec, η=0.074±0.002 at —130°C. The field gradient at room temperature shows a rapid reorientation of the water molecule in a crystal. At room temperature, the spectral line exhibits fine structure due to coupling of two spins, which was utilized to determine the sign of eqQ in the present case.
The line broadening effect in the intermediate temperature region (—45°∼—121°C) was measured and was used to obtain the reorientation rate at various temperatures. The barrier to reorientation of 6.6 kcal/mole was obtained from the comparison of the experimentally determined reorientation rate with that calculated from a tunneling process through a hindering barrier, or that of 6.5 kcal/mole from classical process. The temperature dependence of quadrupole splitting was also measured and the oscillation frequencies were derived for the torsional motion of D2O. It was found that the quadrupole coupling for a vibrationless molecule is about 12% less than that of a free molecule.
The observed eqQ, principal axis directions of field-gradient tensor are discussed in connection with the disposition of atoms in the crystal. A qualitative explanation is given for the change of eqQ from a free molecule to that in the crystal as due to the effect of the hydrogen-bonded oxygen atom.
Yield of ``Free Ions'' in Gamma-Irradiated Liquid Saturated Hydrocarbons
Authors: Freeman G. R. 
Published: January 2005

When a hydrocarbon is subjected to ionizing radiation, some of the electrons that are ejected from the molecules escape the electric field of their parent ions. An ``escaped electron'' and its parent ion can diffuse independently of each other, so they may be considered as free ions. The number of electrons that escape their parents per hundred electron volts of energy absorbed by the system, G(esc e—), is approximately 0.2. This value was determined by conductance measurements and is probably accurate to within a factor of 50%.
From numerical analysis of delta-ray energy spectra, it appears that secondary electrons with energy greater than 30 or 40 eV can escape from their parent ions.
Molecular Rotation and Ortho—Para Nuclear Spin Conversion of Water Suspended in Solid Ar, Kr, and Xe
Authors: Redington Richard L. , Milligan Dolphus E. 
Published: January 2005

Additional data supporting the nearly free rotation of the water molecule trapped in a rare-gas lattice are presented. Ortho—para spin conversion is strongly induced by adding O2 to the matrix. A simple model is suggested which correlates the intensities observed for H2O, HDO, and D2O suspended in Ar, and which estimates the rate of nuclear spin conversion to within a factor of 5 or 10. The majority of the water molecules occupy substitutional sites in the lattice obtained by removing a single rare-gas atom.
Several sharp, intense lines are tentatively assigned to the H bonded OD stretch of HDO and D2O dimers in Ar. They contrast markedly with the corresponding broad band of the OH stretch.
Chemistry of Positive Ions. III. The Radiation Chemistry of Solid n-Hexane at 77°K
Authors: Kevan Larry , Libby W. F. 
Published: January 2005

The mechanism of the chemical effects of ionizing radiation on solid straight-chain saturated aliphatic hydrocarbons such as polyethylene was studied by use of n-hexane. This hydrocarbon was short enough to allow analysis of the cross-link C12 products and of the hexenes formed. It was thought to be long enough to serve as a legitimate substitute for polyethylene. In any case, the yields of H2, olefines, and cross linkages were very similar in the two systems and we believe the mechanistic implications found here for solid n-hexane at 77°K should apply even to polyethylene.
The results indicate: (a) the active species is the original ion radical produced by the ionizing radiation (Co60 gammas); (b) the ion radical reacts before relaxing to redistribute the positive charge or to isomerize in any way, and the products show that there are three primary ions formed corresponding to the first, second, and third carbon atoms in the chain; (c) the ion radical reacts with nearest neighboring groups to bond and release H2, thus forming olefines by reaction with neighboring C atoms in the same molecule four times out of five, but reacting with neighboring chains to form C12 dimers one time out of five; the dimers being only the five hydrocarbons possible by close-neighbor interaction: the 1,1 interaction being n-dodecane; the 1,2 being 5-methylundecane; the 2,2 being 5,6-dimethyldecane; the 2,3 being 4-ethyl-5-methylnonane; the 3,3 being 4,5-diethyloctane and no others; (d) the principal mechanism of the fast interaction of the primary ion is the direct elimination of H2 and formation of a bond due to charge exchange attraction between the primary ion and the neutral group with which it interacts; (e) the second most important mechanism is the abstraction of H to form the electronically saturated analog of CH5+ which when neutralized eliminates H2 and leaves a free radical to combine with the neighboring free radical left by the H abstraction; (f) free radicals seem to play a minor role in the solid hydrocarbon, n-hexane.
Cyclotron Resonance in Slightly Ionized Gases
Authors: Fehsenfeld Fred C. 
Published: January 2005

The conductivity of a slightly ionized gas in a uniform magnetic field has been obtained from the solution of the Boltzmann equation for cases in which the collision frequency between electrons and neutral particles are dependent on the electron velocity. The line shapes of the cyclotron resonance absorption of energy from a high-frequency electric field and the derivative with respect to the magnetic field of the resonance absorption have been computed. Also the relationship between the linewidth of the above curves and the collision frequency was obtained.
The absorption of 9 kMc/sec microwave energy by the weakly ionized thermalized afterglows of helium, argon, oxygen, and carbon dioxide near cyclotron resonance has been measured experimentally. From these measurements the collision frequencies for thermal electrons with He, Ar, O2, and CO2 have been obtained. These collision frequencies are 2.0+0.2×108, 1.6±0.5×108, 1.7±0.2×108, and 24+2×108, respectively, for the above gases at 300°K and 1 mm Hg pressure.
Diffraction Studies of Photochemical Decomposition of Azides. I. X-Ray and uv-Induced Lattice Constant Changes in TlN3
Authors: Krause Brigitte H. 
Published: January 2005

Diffraction methods were applied to study irradiation and annealing effects on TlN3. Crystallographic lattice constant and cell volume changes upon x-ray irradiation were determined as function of irradiation time and radiation intensity. From the character of these curves some conclusions were drawn about the physical processes causing the effects. The reversibility of these processes was studied by annealing experiments at various temperatures and in both air and helium atmospheres.
Preliminary studies of radiation damage on uv-irradiated samples were carried out in order to relate the diffraction results to the TlN3 absorption spectrum and photoconductivity data.
Proton Chemical Shifts in Polysubstituted Benzenes
Authors: Martin John S. , Dailey B. P. 
Published: January 2005

The ring proton chemical shifts of an extensive series of polysubstituted benzenes may be represented, with an accuracy of about 0.1 part per million, as simple sums of substituent shielding constants, except in the case of ring protons next to substituents which are ortho to one another.
The small, uniform deviations from additivity of the 46 shifts measured in a series of para disubstituted benzenes are well represented by a linear variation, so that the chemical shift of proton 2 in a 1,4-substituted benzene may be expressed as δ2=d0(R1)+γ(R1)dm(R4).The polarizability γ decreases as d0 increases.
The values of the shielding parameters d are consistent with a mechanism dominated by the pi-electron charge distribution, although other effects are present, especially at the meta position, which cannot be accounted for in a consistent manner. It can be shown that the molecular-orbital theory of substituent interaction with the pi-electron system can yield a variation of polarizability with charge density of the order of magnitude of that observed; however, the symmetry of this variation is inconsistent with a single-parameter interaction mechanism.
Structure of Molten Oxides. I. Viscosity of GeO2, and Binary Germanates Containing Li2O, Na2O, K2O, and Rb2O
Authors: Riebling E. F. 
Published: January 2005

An improved counterbalanced sphere viscometer was used to determine the viscosity of pure molten GeO2 at temperatures from 1470° to 1720°C. This data agrees with the Kurkjian and Douglas data obtained below 1500°C. Activation energy and entropy calculations suggest a gradual thermal breakdown of molten GeO2 compared to SiO2.
Viscosity information was obtained at temperatures between 1000° and 1500°C for binary alkali germanate melts containing up to 32 mole % Li2O, Na2O, K2O, and Rb2O. Viscosity isotherms, activation energies, and activation entropies suggest gross similarities between the viscous flow mechanisms of binary alkali germanate and silicate melts. However, differences of detail imply divergent modes of network alteration with the addition of a given amount of alkali oxide.