bluuebunny/crossref_metadata_2025_split huggingface dataset:
11B Quadrupole Coupling Tensors in the Hydrated Borates. I. The Tunellite Polyanion
Authors: Cuthbert J. D. , MacFarlane W. T. , Petch H. E. 
Published: January 2005

The quadrupolar splitting of the 11B nuclear magnetic resonance signals has been investigated in a single crystal of tunellite, SrO·3B2O3·4H2O. The electric quadrupole coupling constants, eqQ/h, and asymmetry parameters, η, of the electric field gradient tensors at the six unique boron sites were determined to be eqQ/h (kc/sec)ηTetrahedral sites673±20.386±0.004612±20.157±0.006705±20.090±0.007Triangular sites2509±50.093±0.0052503±40.156±0.0032505±40.123±0.004The orientations of the principal axes of the electric field gradient tensors at all boron sites have also been determined.
The NMR results are in agreement with the crystal structure as to numbers and coordinations of the boron atoms and orientation of the planes of the triangularly coordinated boron atoms. The values found for eqQ/h and η at the triangular sites are quite typical, but the eqQ/h values for the tetrahedral sites are significantly higher than normal. This may be due to the fact that the three tetrahedrally coordinated boron atoms are bonded to one oxygen atom in common, a situation which, among the hydrated borates whose structures are known, is unique to the tunellite-type polyanion.
High-Pressure Effects on Organic Liquids. II. Infrared Spectra and P—V—T Relationships of Rotational Isomers of Some Halogenated Ethanes
Authors: Brasch J. W. 
Published: January 2005

Infrared spectra were obtained of single crystals of various rotamers of a series of halogenated ethanes. The spectrum of the trans rotamer of 1,1,2,2-tetrachloroethane is reported for the first time. P—V—T relationships of rotamers are more complex than was expected, with both polymorphism and solid—solid phase transitions involved.
A new technique for measuring compressibilities at high pressure is described. This technique is used to demonstrate a solidification at constant volume and a solid—liquid equilibrium over a considerable range of pressure.
Second Differential Ionization-Efficiency Curves for Fragment Ions by Electron Impact
Authors: Dorman F. H. 
Published: January 2005

A study has been made of the information obtainable from second-differential ionization-efficiency curves for fragment ions produced by electron impact. To aid in the interpretation of the appearance-potential data, measurements were made of the kinetic energy of the fragment ions.
From the second-differential electron-impact curves, it is shown that accurate appearance potentials of many fragment ions cannot be obtained by orthodox methods, e.g., CH3+(C2H6). For a few fragment ions such as CH3+(CH4), it is possible to obtain a valid appearance potential.
The main result of the kinetic-energy retardation studies is that few fragment ions appear to have kinetic energy for electron ionizing energies near to the fragment-ion appearance potential.
On the Orientation of Nonspherical Particles in an Alternating Electrical Field
Authors: Schwarz Gerhard , Saito Masao , Schwan Herman P. 
Published: January 2005

It is shown in general that any nonspherical particle imbedded in a medium with a different complex dielectric constant will experience orienting forces from an impressed alternating electrical field. The direction of stable orientation is determined by the geometry of the particle, by the dielectric properties of the material involved, and also by the frequency of the field. A continuous change of frequency may result in a continuous rotation of the particle as well as in a sudden ``turnover'' covering an angle of 90 deg.
The case of an ellipsoid suspended in an isotropic medium is discussed in more detail. If the complex dielectric constant of the ellipsoid can be represented by a tensor with principal axes coinciding with the geometrical axes, the direction of stable orientation always is given by one of these axes. However, the choice of ``stable axis'' may be frequency dependent, so that turnover effects may occur as the frequency is changed. Such behavior is possible even if the dielectric properties of the ellipsoid are isotropic. Similar effects are displayed by a system approximating the passive electrical properties of biological cells in an electrolyte solution, thus accounting for some unusual experimental observations of this kind.
Proton Magnetic Resonance Shifts in Aqueous Solutions of Paramagnetic Metal Ions
Authors: Luz Z. , Shulman R. G. 
Published: January 2005

The nuclear magnetic resonance of the water proton in aqueous solutions of paramagnetic metal ions is shifted by the isotropic hyperfine interaction AI·S with the electron spin of the metal. These shifts have been measured for solutions of Cr3+, Fe3+, Mn2+, Co2+, Ni2+, and Cu2+ between 0° and 100°C. Complete averaging of the shift due to rapid exchange of H2O in and out of the solvation shell occurred for Co2+, Cu2+, and Mn2+. However, the averaging of the shift was not complete for Cr3+, Fe3+ (and possibly Ni2+) and the kinetic parameters for the exchange process had to be considered in order to evaluate A.
From the temperature dependence of the proton shifts in Cr3+ and Fe3+ solutions, we determined the pseudo first-order rate constants k and the activation energies ΔE for the proton exchange between solvation shell and bulk. These values are: 8.7×104 sec−1 and 7.5 kcal mole−1 for Cr3+, 2.8×106 sec−1 and 12.1 kcal mole−1 for Fe3+. The proton exchange reaction proceeds via the acid dissociation of the hydrated ions.
From the measured values of A which are all positive, it is shown that the interaction arises from d electrons in dxy, dxz, and dyz, which can only form π bonds with the oxygen of the water. The π bonding is able to proceed via two orbitals on the water, one in the H2O plane and one perpendicular to it. These two orbitals transfer spin to the hydrogen 1s orbitals with similar efficiency but opposite sign, the dominant path being through the orbital in the plane. Following McDonald and Phillips, it is shown how the water proton shifts can be used to measure the number of sites in the first hydration shell of Co2+ which are occupied by H2O. For Co2+ bound to inorganic phosphates or to RNA, this number is five, indicating that Co2+ in these complexes makes only one bond at a time to RNA or to inorganic phosphates.
Theory of Chemical Exchange Effects in Magnetic Resonance
Authors: Gutowsky H. S. , Vold R. L. , Wells E. J. 
Published: January 2005

The Anderson—Weiss formalism is used to develop a general theory for calculating the effects of chemical exchange and spin coupling on echo amplitudes in Carr—Purcell pulse sequences on spin systems in the liquid phase. The theory is shown to involve the matrix integral solution of the Hahn—Maxwell—McConnell equations, generalized to include spin coupling, and of Alexander's equations for the relevant density matrix elements, subject to the boundary conditions imposed by the pulses. Some specific systems are treated in detail, and closed formulas are given for the decay of the echo train in several situations, including the coupled and uncoupled AB systems, and the coupled ABX and ABXq systems.
We show that if the natural relaxation rates of nuclei in exchanging sites are identical, then in general effects of both exchange and spin coupling can be removed by pulsing sufficiently rapidly. Modulation of the echo train by spin coupling is removed by rapid exchange between the coupled sites. The Carr—Purcell experiment on an equivalent set of spins affords effective decoupling from another equivalent set unaffected by the pulses, in the absence of exchange between the sets. An analogy is drawn between chemical exchange and quadrupolar relaxation, and a method is outlined which in principle should provide an indirect determination of quadrupolar or other fast relaxation rates.
We illustrate the applicability of the theory to the calculation of line shapes in steady-state spectra by treating the exchanging coupled AB system in detail, and show that in the fast exchange limit the theory predicts weak broad resonances not previously described.
Deuteron Magnetic Resonance of Ferroelectric Potassium Ferrocyanide Trihydrate
Authors: Tsang Tung , O'Reilly D. E. 
Published: January 2005

The quadrupolar splittings and linewidths of the deuteron magnetic resonance of single crystals of ferroelectric K4Fe(CN)6·3D2O(KFCT) have been measured from −100° to 58°C. At low temperatures eight pairs of resonance lines are observed corresponding to four types of water molecules A, B, C, D, and their ac plane enantiomorphs A+, B+, C+, D+. The molecules are undergoing a fast 180° flip motion about the bisectrix of the DOD bond angle. At temperatures above the Curie temperature (−20°C) only two pairs of lines are observed which are shown to result from fast molecular reorientations within the sets A, C, A+, C+ and B, D, B+, D+. Molecular orientations are determined at low temperatures from rotation patterns and these become shifted for the C- and D-type molecules in the transition to the paraelectric phase.
A structure for ferroelectric KFCT is proposed based on the deuteron resonance data. Activation energies and frequency factors for the 180° flip, AC, and AA+ averaging motions are derived and discussed. The temperature dependence of proton resonance second-moment data and the single-crystal spectra at 25°C are interpreted in terms of the motions deduced from the deuteron resonance experiments and compared with the results of inelastic neuteron scattering experiments.
Mass-Spectrometric Study of the Yttrium—Carbon System
Authors: De Maria G. , Guido M. , Malaspina L. , Pesce B. 
Published: January 2005

A high-temperature investigation of the vapor in thermodynamic equilibrium with Y–C condensed system was carried out in the temperature range 2075°—2340°K. Y and YC2 are shown to be important species in the vapor phase. Utilizing the pressure-independent reaction Y(g)+2C(s)→YC2(g), second- and third-law methods yielded D00=155±6 kcal mole−1 and D00=156±5 kcal mole−1, respectively, for the Y–C2 bond energy. An estimated heat of formation ΔH°f298=−27±6 kcal mole−1 for solid dicarbide is also obtained.
Comparison between Me—C2 and Me—O bond strengths is made for Group IIIA elements and for the first two elements of the lanthanide series.
Approach to Simple Exponential Decay in Vibrational Relaxation
Authors: Carrington Tucker 
Published: January 2005

When diatomic oscillators are dilutely dispersed in an inert heat bath, populations of the various vibrational levels in an initial nonequilibrium distribution relax toward thermal equilibrium with a time dependence that is a sum of terms like exp (λmt), where λ0=0, all other λm&lt;0, and λm+1&lt;λm. −1/λ1 ordinarily corresponds to the experimental relaxation time τ, since this term will dominate at long times. This work investigates cases in which the coefficient of the λ1 term, depending on the initial vibrational distribution and the heat-bath temperature, may vanish or be so small that the final simple exponential decay corresponding to λ1 is never reached under experimental conditions.
For harmonic oscillators, if the initial distribution has its first n moments equal to the corresponding moments of the equilibrium distribution, then the first n coefficients in the sum of exponentials will be zero. Furthermore, there will be one or more values of the heat-bath temperature, independent of the initial distribution, for which the normally dominant exponential decay will be missing in the expression for the time dependence of population in any particular level. Some of these results can be extended qualitatively to anharmonic oscillators and more general systems.
Infrared Detection of Diimide, N2H2, and Imidogen, NH, by the Matrix Isolation Method
Authors: Rosengren Kjell , Pimentel George C. 
Published: January 2005

Hydrazoic acid labeled with deuterium and 15N was photolyzed in solid nitrogen at 20°K. The 15N multiplet splitting positively identifies absorptions of photolysis products as those of trans-N2H2 (at 1286 cm−1), trans-HNND (at 1481 and 1058 cm−1), trans-N2D2 (at 946 cm−1), and cis-N2H2 (at 3074 and 1279 cm−1). The spectrum of trans-N2H2 is in agreement with a planar symmetric structure and the vibrational frequencies are quite close to corresponding vibrations of ethylene.
Imidogen, NH, was also observed in both solid argon and in solid nitrogen as another photolysis product. The 15N splitting in the ammonia absorptions shows that the ammonia dimer in solid nitrogen has a cyclic structure.
Intensity Distribution in the Electron-Impact Spectrum of Carbon Monoxide at High-Resolution and Small Scattering Angles
Authors: Meyer Vincent D. , Skerbele Ausma , Lassettre Edwin N. 
Published: January 2005

An electron spectrometer, which provides velocity selection before scattering, is described; and the results of a study of relative intensities in the carbon monoxide spectrum are reported. The vibrational levels of the fourth positive band system have been resolved and relative intensities determined for the first nine. The relative intensities are compared with calculated Franck—Condon factors. The agreement is good at low vibrational quantum numbers but noticeable discrepancies are found for high-vibrational levels.
The problem of calculating relative oscillator strengths from a fully resolved spectrum is considered and applied to data obtained in the present research. Relative oscillator strengths are compared with those obtained previously from unresolved spectra.
If the Born approximation is valid, then the electron-impact and ultraviolet absorption spectra should be closely similar. This is actually observed for most of the spectrum but the transition at 12.79 V is an outstanding exception. The relative oscillator strength obtained from the electron-impact spectrum exceeds that from the ultraviolet absorption spectrum by almost a factor of 3. The reason for this anomaly is not known.
Conduction in Paraffinic Polymers
Authors: McCubbin W. L. , Gurney I. D. C. 
Published: January 2005

A band scheme is developed for the linear paraffinic polymer. It is found that the valence band is 10 eV wide and that the hole effective mass is 0.1 m. Consistency with experiments on dc conductivity is invoked to decide the identity of the thermal and optical transitions which generate holes. The results are at best semiquantitative and are intended as a preliminary to more rigorous calculations. The proposed band structure is shown to be capable of explaining the thermoluminescence emission spectrum, although more data would be required for a detailed analysis.
Since there is evidence that certain types of substitution may be treated as a perturbation of the paraffinic system, the band model is extended to polymers of type (—CH2—CHR—)n. It is concluded that the resistivity may be lowered by the substitution, but that no choice of R will yield a greater resistivity than that of the paraffinic polymer.
Pyrolysis of Ethyl Iodide by the Toluene-Carrier Flow Technique
Authors: Yang Jae-Hyun , Conway D. C. 
Published: January 2005

The pyrolysis of tagged ethyl iodide has been studied in the presence of the radical scavenger toluene in a flow system. The rate constants for the formation of C2H4(kD), C2H6(kS), and bibenzyl have been determined as a function of the contact time, toluene pressure (2–18 mm Hg), and C2H5I pressure PE(0.6–40×10−3 mm Hg) at 774°K. It is concluded that kD≈k1 and kS≈k2 at low kiPE, where C2H5I→ lim k1C2H4+HI,C2H5I→ lim k2C2H5+I.The first reaction appears to be first order at 14 mm Hg of toluene pressure with a high-pressure Arrhenius rate constant k1∞ of 1.27×1014 exp (−52.8×103/RT) sec−1. The second reaction is not first order at any pressure, but by extrapolation k2∞ was estimated to be 4.5×1013 exp (−50×103/RT) sec−1.
The RRKM theory was used to fit the pressure dependence of k1 and k2 in the approximation that the same degrees of freedom are active in the energized molecule A* for both reactions. The disagreement between theory and experiment could be the result of fewer of the rotational degrees of freedom of A* being active in the second reaction than in the first.
Pressure—Volume—Temperature Relations in Solid Parahydrogen
Authors: Cook Gerhard A. , Dwyer Robert F. , Berwaldt Oren E. , Nevins Hugh E. 
Published: January 2005

Experimental data are presented for the molar volume of solid parahydrogen at five different temperatures over the range 11.49° to 19.97°K and at pressures from 0 to 350 atm. In making the density measurements, it was found that there is a fairly well-defined region of temperature and pressure in which solid hydrogen is viscoelastic. At higher pressures the solid is rather hard and rigid.
A diagram is included which gives an idea of the PVT relations for solid parahydrogen up to a pressure of about 400 atm. The accuracy with which the points on this diagram are known ranges from ±0.2% along the melting line to ±5% at points far from the melting line. A striking feature is the shape of the isobars in the neighborhood of the melting line; at pressures above about 150 atm, each isobar passes through a maximum at a molar volume which is greater than the corresponding molar volume along the melting line. It appears that the thermal coefficient of expansion of solid parahydrogen is negative in a narrow range of temperature and pressure.
Investigations of Hexanol-1 Multimers and Complexes by the Method of Dielectric Polarization in Weak and Strong Electric Fields
Authors: Mal/ecki J. 
Published: January 2005

Results on dielectric polarization and its variations in strong electric fields are presented for solutions of hexanol-1 in hexane, benzene, 1,4-dioxane, and triethylamine. A method for calculating the dipole moments of multimers and complexes on the basis of experimental results is proposed. Also, the concentrations of molecular clusters versus that of the investigated compound in solution and their dipole moments in an ionized (when proton shifted) form of the hydrogen bridge are given.
The determined dipole moments of complexes are used for establishing the arrangement of the hydrogen-bond chain. The concentrations of cyclic structures of multimers and the changes in free energy involved by a transition from cyclic to open structure are estimated.
Isotopic Thermal-Diffusion Factor for Xenon
Authors: Paul R. , Howard A. J. , Watson W. W. 
Published: January 2005

The isotopic thermal-diffusion factor α0 for xenon has been determined over a mean temperature range of 245° to 543°K. An artificial mixture of xenon isotopes containing approximately 18% 129Xe and 15% 136Xe was subjected to thermal diffusion in a 10-tube swing separator; the isotopic thermal-diffusion factor was obtained from the change of concentrations of these two isotopes only. A best-fitting procedure yields potential parameters α=16 and ε/k=257°K for the exponential-six interaction-potential model, whereas the Lennard-Jones (12:6) model fails to reproduce the experimental results. This exp-6 potential was then used to calculate the values of diffusion, viscosity, thermal conductivity, and second virial coefficient, and a reasonably good agreement was obtained with rm=4.41 Å.
An intercomparison of the observed and the theoretically calculated isotopic thermal-diffusion factors for all the inert gases from T*=0.6 to 60 is also presented.
Thermodynamic Properties of Thionyl Fluoride from 13°K to Its Boiling Point. Entropy from Molecular and Spectroscopic Data
Authors: Pace E. L. , Turnbull B. F. 
Published: January 2005

The heat capacity of thionyl fluoride has been measured from 12° to 230°K for a sample of 99.976 mole% purity as determined by the melting-point method. The heat of fusion was 1505.9 cal/mole at the solid—liquid—vapor equilibrium temperature of 143.25°K. The heat of vaporization at the normal boiling point of 228.84°K was 5091 cal/mole. The vapor pressure of the liquid to the normal boiling point has been measured, and the data are represented by log10Pmm=24.41879–1719.074/T−5.94452 log10Twhich was obtained by minimizing the square of the residuals of the pressure.
The density of the liquid is represented by d(g/cc)=2.389–0.003398T.
The entropy of thionyl fluoride gas in the standard state at the normal boiling point calculated from the experimental data is 63.56 cal/(mole·°K). A spectroscopic entropy of 63.28 cal/(mole·°K) is calculated from the product of the moments of inertia, IAIBIC=1.6562×10−114 g3·cm6 from microwave data and the following frequency assignment: v1(a′)=1336 cm−1; v2(a′)=808 cm−1; v3(a′)=530 cm−1; v4(a′)=378 cm−1; v5(a″)=748 cm−1; and v6(a″)=396 cm−1. The discrepancy between the two entropies is accountable in terms of the experimental uncertainty and therefore, the molecular parameters and frequency assignment are confirmed.
Kinetics of the Thermal Decomposition of Tetrafluoroethylene Oxide
Authors: Lenzi M. , Mele A. 
Published: January 2005

The thermal stability of gaseous tetrafluoroethylene oxide has been examined between 40° and 140°C. In this range of temperatures two distinct modes of decomposition have been observed. At higher temperature a unimolecular process takes place with the formation of carbonyl fluoride, tetrafluoroethylene, and perfluorocyclopropane. Isomerization occurs through a heterogeneous reaction on the wall in the low-temperature range leading to trifluoroacetyl fluoride.
The unimolecular behavior is treated according to the Rice—Ramsperger—Kassel theory. A kinetic scheme, which is in agreement with the experimental results, is proposed for the formation of the products.
Diffusion Theory of Nonequilibrium Dissociation and Recombination
Authors: Keck James , Carrier George 
Published: January 2005

The coupled vibration—dissociation—recombination process for molecules and atoms has been examined. Techniques for solving the appropriate master equations for both quantum (discrete) and classical (continuous) models are given. It is shown that the process is most easily treated classically and that in this case the master equation can be reduced to an equivalent diffusion equation. It is assumed that, after an initial vibration transient, during which reactions are negligible, the process may be treated using the steady-state approximation. During the steady-state phase, the usual phenomenological rate equations are valid and the ratio of the forward and reverse rate constants is the equilibrium constant, though the individual rate constants are depressed below their equilibrium values.
Comparison of the results with other theoretical work shows general agreement for similar models; comparison with shock-tube experiments on molecular dissociation and stellarator experiments on ionic recombination is encouraging.