bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonstationary stochastic analysis in well capture zone design using first‐order Taylor's series approximation
Authors: Bakr Mahmoud I. , Butler Adrian P.
Published: January 2005

Nonstationarity of flow fields due to pumping wells and its impact on advective transport is of particular interest in well capture zone design and wellhead protection. However, techniques based on Monte Carlo methods to characterize the associated capture zone uncertainty are time consuming and cumbersome. This paper introduces an alternative approach. The mean and covariance of system state variables (i.e., head, pore water velocity, and particle trajectory) are approximated using a first‐order Taylor's series with sensitivity coefficients estimated from the adjoint operator for a system of discrete equations. The approach allows nonstationarity due to several sources (e.g., transmissivity, pumping, boundary conditions) to be treated. By employing numerical solution methods, it is able to handle irregular geometry, varying boundary conditions, complicated sink/source terms, and different covariance functions, all of which are important factors for real‐world applications. A comparison of results for the Taylor's series approximation with those from Monte Carlo analysis showed, in general, good agreement for most of the tested particles. Particle trajectory variance calculated using Taylor's series approximation is then used to predict well capture zone probabilities under the assumption of normality of the mass transport's state variables. Verification of this assumption showed that not all particle trajectories (depending on their starting location) are normally or log‐normally distributed. However, the risk of using the first‐order method to delineate the confidence interval of a well capture zone is minimal since it marginally overestimates the 2.5% probability contour. Furthermore, this should be balanced against its greater computation efficiency over the Monte Carlo approach.
Postsynaptic scaffold proteins at non‐synaptic sites
Authors: Kneussel Matthias
Published: January 2005

Synapse‐associated proteins that are located at the postsynaptic density (PSD) have recently been shown to have a structural role at non‐synaptic locations. Here, they act as adaptor proteins between neurotransmitter receptors and the microtubule‐ or microfilament‐based motor‐protein complexes that are responsible for transport to the PSD. The use of a common set of proteins that contain multiple domains for protein–protein interactions as both intracellular transport adaptors and synaptic scaffold proteins might contribute to the transport specificity and postsynaptic integration of receptors that underlie synapse formation and plasticity.
RNA sequence‐ and shape‐dependent recognition by proteins in the ribonucleoprotein particle
Authors: Stefl Richard , Skrisovska Lenka , Allain Frédéric H.‐T.
Published: January 2005

At all stages of its life (from transcription to translation), an RNA transcript interacts with many different RNA‐binding proteins. The composition of this supramolecular assembly, known as a ribonucleoprotein particle, is diverse and highly dynamic. RNA‐binding proteins control the generation, maturation and lifespan of the RNA transcript and thus regulate and influence the cellular function of the encoded gene. Here, we review our current understanding of protein–RNA recognition mediated by the two most abundant RNA‐binding domains (the RNA‐recognition motif and the double‐stranded RNA‐binding motif) plus the zinc‐finger motif, the most abundant nucleic‐acid‐binding domain. In addition, we discuss how not only the sequence but also the shape of the RNA are recognized by these three classes of RNA‐binding protein.
Argon—Nitrogen Phase Diagram
Authors: Barrett C. S. , Meyer Lothar
Published: January 2005

The phases and phase transformations in the argon—nitrogen system have been determined by x-ray diffraction with results very different from previous published phase diagrams. The solid phase in equilibrium with the liquid between 1% and 100% N2 is close-packed hexagonal in spite of the fact that pure argon is face-centered cubic. The argon-rich solid solutions with 1% to 55% N2 undergo a strain-induced martensitic transformation from cph (stable at high temperatures) to fcc at low temperatures. The highest temperatures at which this transition becomes possible are those at which the combination of thermal expansion plus solid solution expansion gives a lattice constant for the fcc phase of a0=5.486 Å, which corresponds to that obtained by extrapolating the curve of a0 for pure argon to a point 5° above the melting point. The c/a value for the cph argon-rich phase is 1.633 within experimental uncertainty at all compositions and temperatures.

Stacking faults are infrequent in the as-frozen samples but are very numerous in the deformed samples. At temperatures and compositions where fcc and cph have nearly equal free energies it is possible to destroy the crystalline diffraction pattern by cold work, leaving only an amorphous pattern.

The α-N2 solid solution forms spontaneously and isothermally from the β-N2 solid solution at N2 contents above 77.5% N2. The transformation appears to be that known in metallic systems as a ``massive'' type, and presumably involves only short-range diffusion in the phase interface. The curve of distance between nearest molecular centers in the β phase is not an extension of the curve for the argon-rich phase. The α phase, which is cubic, is not continuous with the cubic argon-rich solid solution; samples with 55%—75% N2 do not transform from the hexagonal form even when cold worked at 4.2°K.
Influence of Paramagnetic Resonance on the Static Susceptibility. Spin—Lattice Relaxation Time of Cupric Sulfate Pentahydrate
Authors: Candela George A.
Published: January 2005

The static direct-current susceptibility of cupric sulfate pentahydrate was measured as a function of microwave power absorbed at electron spin resonance. This technique was used to study the spin relaxation process of cupric sulfate pentahydrate as a function of temperature, microwave power level, and crystal size. Up to less than one-half saturation, the relaxation time τ1 was found to be independent of the degree of saturation and inversely proportional to the temperature τ1T=0.2 sec·°K, showing that the predominant mechanism at liquid-helium temperatures is the direct spin—lattice process. At high saturation levels there is evidence of crystal heating. These results are compared with those obtained by the cw saturation method on cupric sulfate pentahydrate, and the discrepancy in the magnitude of the relaxation time and its temperature and power dependencies are explained. This new technique is shown to be especially useful for studying power-transfer mechanisms in concentrated spin systems.
Solid Solution of Argon and Krypton; Refined Measurements
Authors: Fender B. E. F. , Halsey G. D.
Published: January 2005

Vapor pressures of argon—krypton mixtures at vanishingly small solid accumulation have been analyzed to give values of the interaction energy parameter wAB for a number of Ar–Kr solid solutions at temperatures between 85° and 101°K and in the argon mole-fraction range 4% to 18%. Vapor pressures and triple points of pure argon and krypton are also reported. The mole-fraction dependence of wAB is negligible, and compatible with that predicted by an exact form of the regular solution or Ising lattice problem.
Spin—Orbit Interactions and Their Effect on the Zero-Field Splitting of the Methylene Radical
Authors: Fogel Sidney J. , Hameka Hendrik F.
Published: January 2005

It is proposed that certain matrix elements of the spin—orbit interactions may combine with the spin—spin interactions to cause zero-field splittings. The calculation is performed for the linear CH2 radical, where it is found that the contribution from spin—orbit coupling to the parameter D=0.1128 cm−1. This should be added to the spin—spin contribution of 0.9055 cm−1 to give a total value D=1.0173 cm−1. We conclude that the general belief that spin—orbit contributions to zero-field splitting are always negligible is questionable.
Electron Coupling of Nuclear Spins. VIII. Temperature Dependence of JFF in 2-Fluorobenzotrifluorides
Authors: Jonás̆ J. , Gutowsky H. S.
Published: January 2005

The F–F coupling constant between the CF3 group and the fluorine atom at the 2 position was measured and found to have an appreciable temperature dependence in several 2-F, 6-X-benzotrifluorides. The magnitude of JoFF (F–CF3) and the direction of its change with temperature is consistent with the existence of two different rotational conformations of the CF3 group, whose relative stability depends upon the balance of repulsive steric interactions between the CF3 group and the 2 and 6 substituents. These results were supported and extended by measurements of the fluorine chemical shifts for the CF3 and 2-F, both of which move downfield with increasing temperature. For a particular compound, the ΔE between the two conformations is the potential barrier to internal rotation of the CF3 group, and the temperature dependences of JoFF (F–CF3) and of the fluorine chemical shifts are attributed to thermally excited torsional oscillations and reorientations of the CF3 group in the potential well. An approximate analysis of the temperature dependence of JoFF (F–CF3) indicates that ΔE is about 1 kcal for X = H, Cl, and I; however, the stable orientation of the CF3 group is rotated by 60° in the 6 Cl and 6 I derivatives from that in the 6 H. Similar conformational isomers should exist for 2,6-asymmetrically disubstituted toluenes, and more complex isomers are possible when the threefold symmetry of the CF3 and CH3 groups is reduced by substitution to CF2X and CH2X or to CFXY and CHXY. Values are reported for the long-range F–F and F–H coupling between the CF3 group and fluorines and protons at the meta and para positions in several benzotrifluorides.
Rate-of-Growth Technique for the Measurement of Molecular Dipole Moments from Microwave Spectra at Weak Modulation Fields
Authors: Lindfors Karl R. , Cornwell C. D.
Published: January 2005

Under suitable conditions, commonly met in practice, rotational lines observed with low amplitude zero-based square-wave Stark modulation have the shapes of the first or second derivatives of the zero-field absorption lines. From the rate of growth of the peak-to-peak spectrometer deflection as a function of the modulation amplitude, the molecular electric dipole moment may be calculated. As this procedure does not require the resolution of individual Stark components, it should prove useful when the analysis of Stark splittings is not feasible, as in the case of cluttered spectra, spectra complicated by nuclear quadrupole hyperfine splittings, and spectra for which no low-J transitions are accessible. Working equations are given for the case where the Stark shifts, when smaller than the linewidths, are linear or quadratic in the field.

The method has been tried with OCS, CH3Br, and SO2. It appears that an accuracy of the order of several percent in the dipole moment can be achieved. Several experimental precautions and techniques are described, including a null method for measurement of the square wave voltage amplitude.
Gaseous Diffusion. The Systems He–Ar, Ar–Xe, and He–Xe
Authors: Malinauskas A. P.
Published: January 2005

Relative values of the diffusion coefficients of the systems He–Ar, Ar–Xe, and He–Xe have been determined over the temperature range 0° to 120°C by a two-bulb method. The experimental diffusion coefficients, at 1 atm pressure, can be described by the following equations: He–Ar: log10D=1.684log10T−4.2902,Ar–Xe: log10D=1.955log10T−5.7807,He–Xe: log10D=1.720log10T−4.5251.

The apparatus was calibrated with the He–Ar diffusion data; the results for the system Ar–Xe are in essential agreement with the data reported by other workers, but the He–Xe diffusion coefficients are about 9% lower than previously published values. The present He–Xe coefficients are in good agreement, however, with results which have been determined from a consideration of the composition dependence of the viscosities of He–Xe mixtures.
Hydrazine—Water System. I. Phase-Equilibria Diagram
Authors: McMillan J. A. , Los S. C.
Published: January 2005

The phase equilibria diagram of the solid system H2O–N2H4 has been completed by differential thermal analysis. A univariant equilibrium peritectic reaction involving a new hydrate N2H4·4H2O that melts incongruently at 193°K has been identified.
Energy Levels of U4+ in an Octahedral Crystalline Field
Authors: Satten R. A. , Schreiber C. L. , Wong E. Y.
Published: January 2005

The electronic energy levels determined from absorption spectra of U4+ in crystals containing UCl62— complexes are identified as to irreducible representation and the resulting set of levels used to determine the least-squares best values of Slater Fk integrals, spin—orbit ζ5f, and fourth- and sixth-degree crystalline potential parameters A 〈r4〉 and B 〈r6〉. It was necessary to diagonalize within the 5f2 configuration all these interactions simultaneously. The values are F2=191.4,F4=33.83,F6=3.98,ζ5f=1796,A〈r4〉=912,B〈r6〉=56.5. New data on the spectra of the UBr62— complex are presented.
Intra- and Intermolecular Contributions to the Proton Spin—Lattice Relaxation in Liquids
Authors: Bonera G. , Rigamonti A.
Published: January 2005

By measuring proton spin—lattice relaxation in mixtures of benzene and acetone with their respective perdeuterated analogs the intra- and intermolecular contributions to the relaxation have been separated. The correlation time for the molecular motion responsible for the intramolecular relaxation is obtained and discussed. With regards to the intermolecular contribution to the relaxation, it is pointed out that in some cases the fluctuations in the local field arising from the neighboring molecules are mainly due to the reorientational motions.
Electric-Field Gradients in Liquids by Deuteron Quadrupole Relaxation
Authors: Bonera G. , Rigamonti A.
Published: January 2005

The deuteron quadrupolar relaxation is studied for some liquids. As the spin—lattice quadrupole relaxation depends on the electric-field gradients (efg) at the nucleus the experimental values of T1 have been used in order to obtain the field gradients at the hydrogen site in the benzene and acetone molecules. For this purpose, the correlation times for the molecular motions responsible for the quadrupolar relaxation have been estimated from proton magnetic relaxation measurements in mixtures of the liquid with its perdeuterated analog. A theoretical evaluation of the efg tensor has also been performed by using MO's in the LCAO approximation with Slater's orthogonalized AO's. The agreement between the theoretical evaluation and the experimental results is more than satisfactory and it seems to confirm a certain validity of the wavefunctions and the method of calculation used. For chloroform a calculated efg tensor has been used to obtain a value for the reorientational correlation time from the deuteron spin—lattice relaxation time. This work shows the possibility of using proton and deuteron relaxation measurements to obtain reliable values for the quadrupole coupling constants in liquids.
Spin Resonance of SnO2:V and the Vanadium 3d Electron Orbital
Authors: Kikuchi Chihiro , Chen Inan , From William H. , Dorain Paul B.
Published: January 2005

The ESR spectrum of SnO2 containing about 0.5% vanadium observed in K band at liquid-nitrogen temperature shows two sets of shfs. Relative intensity measurements show that the large shfs (168 G) is due to the two tins located along the c axis and the small shfs (28 G) due to the four tins lying in a diagonal plane of the unit cell containing four oxygens. The large shfs is largely isotropic, with an axial maximum along the c axis. This suggests that the ground electron level is 3d(x2−y2). The next level is 3d(xz). This is deduced from the g values (gxx=1.939,gyy=1.903,and gzz=1.943).
Mechanism of Superhyperfine Structure in SnO2:V4+
Authors: Chen I. , Kikuchi C. , Watanabe H.
Published: January 2005

Molecular orbital theory has been applied to SnO2:V4+ to account for the large and small superhyperfine structure observed by From et al. The unpaired spin density at the next-nearest ligand tin nucleus is formulated. The result can be intepreted as due to two electron-transfer processes. The first comes from the formation of antibonding molecular orbital. The second arises from the configuration mixing. The first process is found to be dominant and is proportional to the square of overlap integral between vanadium 3d and tin 5s orbitals. Calculated ratio of the large and small superhyperfine structure is in good agreement with experiment.
Superhyperfine Structures in ESR and ENDOR of Cubic CdTe:Mn2+
Authors: Chen I. , Kikuchi C. , Watanabe H.
Published: January 2005

Superhyperfine structure tensors for the 12 next-nearest ligands in CdTe:Mn2+ have been expressed in terms of molecular orbital and geometry parameters. ESR and ENDOR transition frequencies are related to the superhyperfine tensor components. An attempt is made to obtain the amount of d-electron delocalization from such relations.
Sound Absorption in Gases in the Critical Region
Authors: Botch W. , Fixman M.
Published: January 2005

A theory is based on a dynamic heat capacity associated with long-wavelength density fluctuations in the critical region. Evaluation of the dynamic heat capacity requires the time-dependent response of the long-range radial distribution function to a uniform harmonic variation of temperature with time. This response is calculated on the assumption that the motion of matter in the neighborhood of a fixed molecule is determined by macroscopic laws of momentum and energy transport, except for the addition of a familiar critical contribution to the pressure. Relaxation of the important Fourier space components of the radial distribution function is not hindered appreciably by fluid inertia or viscous resistance. Rather the relaxation follows a generalized heat diffusion law. The calculations are applied to data on Xe and HCl, and satisfactory agreement between theory and experiment is found.
Magnetothermodynamic Properties of MnCl2 from 1.3° to 4.4°K at 90 kG. A Zero Entropy Reference. The Magnetomechanical Process at Absolute Zero
Authors: Giauque W. F. , Brodale G. E. , Fisher R. A. , Hornung E. W.
Published: January 2005

The heat capacity of single-crystal manganous chloride has been measured in a constant magnetic field, accurately stabilized at 90 000 G and parallel to the b magnetic axis (a crystallographic axis), over the range 1.4° to 4.35°K. The heat capacity approaches zero and magnetic saturation occurs near 1°K, thus providing a reference for the zero of electronic entropy which might otherwise be difficult to obtain due to possible irreversible behavior of this antiferromagnetic system below 1°K. It has been established that loss of magnetic moment from the saturated magnetic domain of the crystal occurs with increasing temperature through the loss of individual Bohr units of angular momentum. By extrapolating reversibly measured values of the magnetic moment, on isoerstedic paths to 0°K, the magnetomechanical process of magnetization at the absolute zero has been described in fairly complete detail. The magnetization curve at 0°K consists of two nearly straight lines joined by a small deviation near 10 kG and approximating saturation at about 32 kG. The value of the quantity (Esat−EH=0)0∘K=10.80 cal/mole. It has been shown that (∂E/∂T)H for MnCl2 at 90 kG is a negative quantity, as would be expected for an antiferromagnetic substance near magnetic saturation. Magnetic work is by far the dominant effect in determining the size of the quanta absorbed near magnetic saturation. The initial increments of demagnetization, with increasing temperature, are assisted by withdrawal of stored internal energy. Thus, the quanta with the smaller energies are those connected with the loss of angular momentum from individual atomic centers, rather than proportionally from the entire cooperative system of electron spins. The limiting heat content at 90 kG is given by HH–Hlattice=20.3exp(−20.3/RT) cal/mole, and the limiting magnetic moment is represented by M=Msat−Ngβ/[exp(20.3/RT)−1]G·cm3/mole, where Msat=27 988 and Ngβ=11 194 G·cm3/mole, with g taken as 2.004. The abuse of the word ``point'' in thermodynamics is discussed and the word ``pernt'' is defined.
Range of Electron Correlation in the Helium Atom
Authors: Gimarc B. M. , Cooney W. A. , Parr Robert G.
Published: January 2005

For the helium atom, a new type of correlation factor is tested which has the form 1+ch(r12) where h(r12) is a cutoff correlation variable such that h(r12) = r12 for 0≤r12≤D, and h(r12) = D for D≤r12≤∞, with c and D adjustable parameters. In a series of energy calculations using wavefunctions which contain both configuration interaction and cutoff r12 terms, it is found that, as far as the energy is concerned: (1) The correlation cusp is unimportant, and (2) The range of the Coulomb correlation effect is of the order of the atomic diameter. For very small D, the correlation energy per unit volume is calculated to be 0.048 hartree/bohr3.
Dependence of Some Ethylenic Jgem Values on Solvent and Concentration
Authors: Watts V. S. , Goldstein J. H.
Published: January 2005

Measurements of Jgem for α-chloroacrylonitrile (α-CAN) over wide concentration ranges in a number of nonaromatic solvents reveal a marked dependence on medium and concentration, and more limited studies on α-bromoacrylonitrile (α-BAN) give similar results. In addition, Jgem for five vinylic compounds appear to vary with solvent to a smaller, but statistically significant extent. The variation for a given solute with solvent follows the dielectric constant and is roughly proportional to the reaction field of the medium. In α-CAN it has also been established that the variation of Jgem and of the two chemical shifts, as concentration changes, are rather parallel. The practical and theoretical significance of these observations are discussed, and some of the possible factors involved are broached in qualitative terms.
Vibrational Spectra of Isotopic Nitric Acids
Authors: McGraw G. E. , Bernitt D. L. , Hisatsune I. C.
Published: January 2005

The vibrational spectra of four isotopic nitric acid molecules including the 15N and D species have been obtained in the vapor and solid phases. The Raman spectra of anhydrous and wet normal nitric acid were also studied. Previous assignment of the fundamental modes has been revised, and the spectra in the three phases have been correlated. The potential barrier against internal rotation of the hydroxyl group has been calculated to be 7.8±0.1 kcal/mole in both the H and D acids. A set of least-squares fitted valence force constants which reproduce the observed fundamentals with an average error of 0.6% has been derived.
On the Relative Roles of Free Volume and Activation Energy in the Viscosity of Liquids
Authors: Macedo P. B. , Litovitz T. A.
Published: January 2005

The rate-theory approach of Eyring and the free-volume theory of Cohen and Turnbull for liquid viscosities have been reconsidered. The rate theory has been reformulated using the Cohen and Turnbull expression for the probability of finding a vacant site and yields an equation of the form η=A0exp[Ev*/RT+γV0/Vf].This result has been applied to many liquids ranging from fused silica to liquid argon and including polyatomic van der Waals as well as hydrogen-bonded liquids.

Consistent fits to both temperature and pressure dependence of viscosity were obtained. A significant conclusion is that the free volume of liquids is considerably higher than that suggested by the WLF and Cohen and Turnbull equations.
Determination of the Atomic Kinetics of the Freezing Process. II. Experimental
Authors: Kramer J. J. , Tiller W. A.
Published: January 2005

The applicability of the ``thermal wave'' technique for determining the mechanism and kinetics of atomic exchange across the liquid—solid interface during melting and freezing has been tested for several different orientations of tin crystals. The experimental conditions produced low driving forces for melting and freezing. The results are consistent with atomic attachment at layer edges generated by screw dislocations. A ``diffuse interface'' model fits the kinetic data.
Viscosity of Moderately Dense Gases
Authors: Kim Shoon Kyung , Ross John
Published: January 2005

At moderate densities the viscosity of a gas may be represented by a virial expansion in density η=η0+bρ+···, and we present a calculation of the contribution of triple collisions to the coefficient b. We approximate three-body encounters by two-body collisions between a single molecule and a dimer. We derive the equilibrium constant for dimers, according to classical statistical mechanics for spherically symmetric short-range potentials, which include bound, metastable, and orbiting pairs. Numerical results are obtained for the Lennard-Jones (6–12) potential and the equilibrium constant is found to be approximately proportional to T−32. We then apply the Chapman—Enskog theory of the viscosity of a binary mixture of dilute gases, one component being the monomer, the other the dimers. Collisional transfer in binary collisions is not taken into account.

The analysis based on this simple model yields substantial agreement with experiment, in particular the temperature dependence of b∼T−1 at high reduced temperature, and the near invariance of b with T at moderate reduced temperatures. In comparison, Enskog's theory of hard spheres predicts b∼T½ and the anomalous behavior at high reduced temperature is not removed by ad hoc variation of the hard-sphere diameter with temperature. For given parameters (σ, ε) of the Lennard-Jones intermolecular potential, good agreement with experiment is obtained, if the monomer—dimer interaction is represented by a similar potential with parameters 1.02σ, 1.23ε. The results are essentially independent of the use of other potential parameters which maintain the magnitude of the attractive potential. We conclude that the physical origin of the initial density dependence of viscosity requires consideration of not only repulsive but also attractive forces between molecules.
Degree of Dissociation of Aqueous Perchloric Acid Determined by Raman Spectrophotometry
Authors: Heinzinger Karl , Weston Ralph E.
Published: January 2005

The degree of dissociation (α) of HClO4 in 2–12M aqueous solutions has been determined by measuring the Raman intensity of the 931-cm−1 ClO4— band. These measurements indicate that the acid is completely dissociated at concentrations up to 8M. Throughout the range of these experiments, α is found to be significantly higher than the values in the literature which were obtained by the use of proton magnetic resonance spectroscopy. The temperature dependence of α was found to be very small.
Inhibited Dissolution of {100} Surfaces of Single Crystals of Lithium Fluoride
Authors: Ives M. B. , Plewes J. T.
Published: January 2005

A technique is described for the determination of the dissolution rates of {100} lithium fluoride surfaces in dilute aqueous solutions of ferric fluoride. The effect of ferric ion content of the etchant on the rate is found to be constant for ion concentrations substantially in excess of the optimum for the production of smooth-faced square etch pits at dislocations. The results correlate well with recent theories concerning the adsorption of ferric ions during etching.

The effect of lithium fluoride undersaturation varies greatly from specimen to specimen and demonstrates the heterogeneous nature of hole nucleation in the close-packed surfaces.
Method of Adjusting Force Constants and Its Application to H2O, H2CO, CH2Cl, and Their Deuterated Molecules
Authors: Shimanouchi Takehiko , Suzuki Isao
Published: January 2005

A new method for the adjustment of vibrational force constants is presented. It avoids some of the divergence difficulties which may be encountered in perturbation and least-squares procedures. The new method employs an efficient computer program to adjust an initial set of force constants in accordance with the requirement that each successive adjustment leads to a smaller sum of squared deviations between calculated and observed eigenvalues. Several variants of the procedure are given, and their application to a number of actual cases is discussed in detail.
Effect of Electrical Fields and Density in the Radiolysis of Ethane
Authors: Carmichael Halbert H. , Gorden R. , Ausloos P.
Published: January 2005

The gamma-ray radiolysis of C2H6–C2D6–NO and CH3CD3−NO mixtures has been investigated as a function of applied electrical field. In the saturation current region, a number of products resulting from the decomposition of neutral excited molecules increase about fivefold before the onset of secondary ionization while several other products, which can be ascribed to ion molecule reactions, remain essentially unchanged. The modes of decomposition of the excited ethane molecules formed by electron impact, as derived from the applied field experiments, are the same as those observed in the vacuum ultraviolet photolysis at 1470 and at 1236 Å. From the isotopic composition of the products it could be deduced that the average energy transferred to ethane by electron impact is greater than 10 eV. A value of 0.5 was derived for the number of neutral excited molecule decompositions per ion pair.

A change in density has a pronounced effect on the product distribution, both in the photolysis at 1236 Å and the radiolysis. In the radiolysis, several of the changes can be ascribed to the diminishing fragmentation of the parent ion with an increase in density. However, products resulting from the fragmentation of the neutral excited ethane molecules formed in the radiolysis also show a strong dependence on density because of collisional stabilization of the primary fragments and of the products formed in secondary reactions. For instance, the propane which could be entirely ascribed to the insertion reaction CH2+C2H6+M→C3H8+M increases with an increase in density in the photolysis as well as in the radiolysis.
Phonon Spectrum of Graphite
Authors: Young James A. , Koppel Juan U.
Published: January 2005

The phonon spectrum of reactor grade graphite is computed by means of the essentially exact root sampling technique for a sampling 47 788 points in an irreducible segment of the Brillouin zone.

Measurements of the specific heat (over the range 100°—1000°K) are used to determine the force constants, resulting in good agreement of the calculated phonon spectrum, and neutron scattering measurements.
On the Theoretical Calculation of Vibrational Frequencies and Intensities of Polyatomic Molecules; H3+, H2D+, HD2+, and D3+
Authors: Huff Norman T. , Ellison Frank O.
Published: January 2005

A straightforward method is described for calculating the fundamental vibrational frequencies and intensities for a polyatomic molecule starting with a theoretically obtained potential energy surface and associated electronic state wavefunction. Given the latter two quantities, this method is much easier to carry out than the common reverse problem of predicting force constants from observed frequencies and molecular dipole moment derivatives from absolute intensities. The proposed method can be programmed easily and generally to handle any polyatomic system for which a theoretical energy surface and electronic-state wave-function are available. An application to H3+ and its isotopic counterparts is described.
Analysis of the Eigenstates of Pr3+ in LaCl3 Using the Zeeman Effect in High Fields
Authors: Sarup R. , Crozier M. H.
Published: January 2005

The Zeeman effect of the absorption and fluorescence spectra of Pr3+ in LaCl3 has been studied at liquid nitrogen and liquid helium temperatures in magnetic fields up to 69 kG. Both linear and quadratic effects have been observed, and these are used to establish unequivocally the crystal quantum numbers of the observed energy levels. Crystal-field theory is used to calculate the magnetic behavior of the energy levels, and good agreement is found with experiment, but some systematic deviations are also noted. The second-order effect has been found useful in understanding the nature of these deviations, and it appears that a crystal-field calculation fitted to the energy levels does not yield the eigenstates giving the best agreement with the observed behavior in high magnetic fields.
Crystal Fields at Rare-Earth Ions
Authors: Burns Gerald
Published: January 2005

The object of this paper is to find out why the calculated rare-earth crystal-field parameters do not agree with those determined experimentally. As is well known, in explaining the 4f spectra in the rare-earth compounds, one needs relatively few crystal-field constants, Vnm's. These Vnm's have been measured for many rare-earth ions in LaCl3, ethylsulfates and other lattices. One can study the Vnm's in a given lattice as the nuclear charge is varied (starting from Ce, Z=58 to Yb, Z=70). For a given n and m one finds that the Vnm's vs Z vary fairly smoothly. However, when the crystal fields are calculated using an ionic model one cannot get good agreement with the Vnm's. In general, neither the magnitude nor the Z dependence of the Vnm's can be reproduced. The calculated crystal-field parameters are written as: (1−αn)〈rn〉Anm, where αn is the shielding factor (the outer 5s2p6 electrons to some extent shield the inner 4f electrons from the crystal field), 〈rn〉 is the expectation value of rn over the 4f electrons, and Anm is a lattice sum over the charges in the lattice that produce the crystal field. To try to determine why the agreement is bad, the effect of the lattice in altering the values of αn and 〈rn〉 was calculated. However, the principle trouble appears to come from the Anm values. Anm∝̃1/Rn+1, where R is the distance between the rare-earth ion and the charges in the lattice that produce the crystal fields. For the important n=4 and 6 lattice sums one gets very rapid convergence. The Anm sums are usually calculated assuming the lattice can be replaced by point charges, point dipoles, etc., at the nucleus of the ions surrounding the rare-earth ions. Thus, R is taken as the various internuclear distances. However, for lattice sums that depend on such high powers of R, one must consider the extended nature of the charge distribution of the ions surrounding the rare earths. Another way of stating the trouble is: Since the distance between the observer (rare-earth ion) and the charge distribution is not large compared to the extent of the charge distribution it is not a good approximation to replace the charge distribution by point moments. From numerical examples it is easy to see, for n=4 and 6, that most of the contribution to the Anm sums comes from the parts of the surrounding ions that are closest to the rare-earth ions. Thus it becomes difficult to calculate the Anm's accurately. However, using this idea, agreement is obtained with the dependence of the Vnm's on Z and some of the interrelationships between the different n terms.

For the lattices usually used as hosts one cannot calculate the A20 sum because of its sensitivity to the x-ray data and charge distribution parameters. However, by using nuclear quadrupole resonance data to eliminate calculating the actual lattice sum, one gets good agreement between the measured V20's and (1−α2)〈r2〉A20.
Electron-Impact Spectra
Authors: Skerbele Ausma , Lassettre Edwin N.
Published: January 2005

Electron-impact spectra at zero scattering angle have been obtained for nitrogen, carbon monoxide, water, ammonia, and benzene. Vibrational structure has been resolved for the a 1πg state in nitrogen and two Rydberg transitions in water spectra. The results have been compared with ultraviolet absorption data.
Temperature Dependence of the Total Integrated Intensity of Vibrational—Rotational Band Systems
Authors: Breeze J. C. , Ferriso C. C. , Ludwig C. B. , Malkmus W.
Published: January 2005

The temperature dependencies of the total integrated intensities of vibrational—rotational band systems are discussed and general expressions are given for the temperature dependencies for the harmonic oscillator approximation. The derived dependencies indicate that while the total integrated intensity of a fundamental is independent of temperature, the integrated intensity of an overtone or combination band system increases with increasing temperature. The theoretically derived temperature dependencies are compared with available experimental data and good agreement is found where self absorption within the test gas does not influence the experimental results.
Crystal-Field Splitting in Yb3+ Chelates
Authors: Perkins W. G. , Crosby G. A.
Published: January 2005

Optical absorption and emission spectra of trivalent ytterbium in various chelates are reported. The experimental energy levels of Yb3+ are compared with predictions of electrostatic crystal-field theory and of a contact model of ligand-field theory. Good agreement is found between theory and experiment for the electrostatic crystal-field calculation. Poorer agreement is obtained using the ligand-field contact model calculation. The crystal-field calculation uses a single geometrical parameter θ. By using the calculations, x-ray results for other compounds, and the observed spectra, it is possible to obtain a reasonable estimate of the molecular geometry, which appears to be that of an octahedron distorted by shortening a threefold axis.
Optical Properties of Small Silver Particles
Authors: Doremus R. H.
Published: January 2005

The optical absorption of very small silver particles in glass was measured as a function of particle size and temperature. The shape of the measured absorption band was Lorentzian, as required by the simple free-electron theory, and the position of the band was close to that calculated from the optical properties of bulk silver. The width of the absorption band was inversely proportional to the particle radius, showing that the mean free path of the electrons was determined by the particle size. The absorption band for particles much smaller than the mean free path of the electrons was little changed from room temperature to 500°C; however, for larger particles the band broadened somewhat with increasing temperature.
Magnetic and Other Studies of a Reversible Phase Change in CoSiF6·6H2O
Authors: Majumdar Manju , Datta Sunil K.
Published: January 2005

Magnetic, optical, and thermal expansion studies reveal a reversible phase transition in CoSiF6·6H2O at a temperature, Tc, which was found to be 246°±2°K during cooling and 259°±1°K during heating. This thermal hysteresis appears to be real as Tc is independent of the heating or cooling rate. The magnetic symmetry of the crystal is uniaxial above Tc but orthorhombic below it. The sharp change in color from pink to orange-yellow at Tc is accompanied by spectral changes with the appearance of a new band, presumably indicating the effect of changes in the closed-packed structure on the symmetry and shape of the Co(H2O)6 clusters. Crystals diluted with the similar zinc salt have an approximately uniaxial magnetic ellipsoid, a feeble anisotropy appearing in the ``symmetry'' plane at low temperatures. From these and the available resonance data the g values for the undiluted crystal have been estimated which resemble more closely those for a typical orthorhombic case than for a trigonal.
X-Ray Study of Critical Opalescence of Polystyrene in Cyclohexane
Authors: Chu B.
Published: January 2005

The small-angle x-ray scattering of polystyrene (M̄n=14 700;M̄w/M̄n=1.04) in cyclohexane has been investigated at the critical concentration over a range of temperatures near the phase-separation temperature in the one-phase region. A composite light and x-ray scattering curve was constructed by extending small-angle x-ray measurements down to a scattering angle of 5×10−4 rad with CuKα radiation. The angular distribution of the scattering was analyzed in terms of the Debye theory of critical opalescence and was found to be consistent with the results obtained from visible-light scattering studies.
Absorption Spectrum of Solid Anthracene—TNB Complex under Pressure
Authors: Offen Henry W.
Published: January 2005

The intermolecular charge transfer (CT) and intramolecular absorption spectrum of the crystalline anthracene—TNB complex as well as (for comparison) the crystalline anthracene La band have been studied in KBr pellets as a function of pressure to 27 kbar. It is observed that the magnitude of the red shift in the band maxima is ∼1450 cm−1 at 27 kbar for both the CT band and the La band, but is only ∼300 cm−1 for the intramolecular donor (anthracene) absorption at 16 kbar. Broadening of the CT band appears absent, but the molar extinction coefficient at the band maximum increases by ∼50% at 16-kbar applied pressure. The La band of anthracene broadens but shows only small changes in band height. Plausible explanations of the observed results are discussed.
ESR Spectra of γ-Irradiated Polycrystalline Powders of Some Fluorine-Containing Compounds
Authors: Iwasaki Machio , Toriyama Kazumi , Eda Bunzo
Published: January 2005

The powder spectra of γ-irradiated salts and amides of some fluorinated acids were interpreted based on the spectral shapes of the α-fluorine hyperfine-coupling line. Because of the large anisotropy of α-fluorine coupling tensor, it was possible to observe the shoulders corresponding to the maximum principal value of the coupling tensor. The separation between the wing patterns and the wing hyperfine structures made it possible to identify the radical species produced. The probable radicals were the ones formed by the removal of the atoms attached to the α carbon.
Fragment Ions from CH3CHO and (CH3)2CO by Electron Impact
Authors: Dorman F. H.
Published: January 2005

The ionization-efficiency curves for the parent and fragment ions from CH3CHO and (CH3)2CO have been examined by the second differential method. The appearance potentials for CH3CO+, namely, 10.2±0.1 eV [(CH3)2CO] and 10.5±0.2 eV (CH3CHO), are much lower than previously accepted electron-impact values. Apart from CO+(CH3CHO) no appearance potentials can be easily obtained for any of the other fragment ions. No kinetic energy was found for the light ion CH3+, nor the heavier ions CO+, HCO+(CH3CHO), and CH3CO+[(CH3)2CO].
On the Motion of Hydrogen in the Tantalum—Hydrogen System
Authors: Pedersen Bjo/rn , Krogdahl Tore , Stokkeland Odd E.
Published: January 2005

The proton spin—lattice relaxation time T1 has been measured by a pulse technique as a function of temperature in a series of tantalum-hydrogen samples with hydrogen content from H/Ta=0.1 to 0.66. The spin—lattice relaxation is determined by the rapid translational diffusion of the hydrogen atoms in the tantalum lattice. Discontinuities in the T1 curves indicate two phase transitions in the temperature range investigated, 200° to 400°K. The transition temperatures depend on the composition of the sample in a way which is in conflict with the present view of the phase relations in the Ta/H system. The activation energy in the low-temperature phase (β1 phase) is found to decrease linearly with increasing hydrogen content from 3.7±0.5 kcal/mole in TaH0.10 to 2.6±0.3 kcal/mole in TaH0.66. In the high-temperature phase (α phase) the activation energy is 1.6±0.4 kcal/mole, and in the intermediate-temperature phase (β2 phase) the activation energy is 6.3±0.6 kcal/mole. Neither of the latter values changes significantly with the composition of the sample.
Effect of Solvents on 19F Spin—Spin Coupling Constants
Authors: Ng Soon , Tang Jane , Sederholm C. H.
Published: January 2005

The effects of solvents on the coupling constants of the compounds CF2=CFBr,  CF3CFCl2,  and  CF2BrCFBrClhave been studied. The coupling constants are found to vary with the solvents. This implies that intermolecular interactions affect coupling constants to a degree that is not negligible. The variations in the coupling constants are to some extent correlated with the size, electronic character, and dipolar nature of the solvent molecules. The temperature dependence of fluorine coupling constants that has been reported previously may be due to this temperature-dependent molecular interaction as well as the population of excited vibrational states.
Equilibrium Polymerization. Polyfunctional Initiators
Authors: Baur M. E. , Eisenberg A.
Published: January 2005

The equilibrium polymerization theory of Tobolsky and Eisenberg is extended to the case of initiation by polyfunctional species, under the assumption that only a single monomer is involved and no ring or loop formation occurs. A general indexing scheme is given which permits derivation of the relation between degree of polymerization and equilibrium constants for initiation and propagation steps for any functionality of initiator. An explicit derivation for the case of trifunctional initiator is given, and the result for general functionality is provided.
Self-Consistent Group Calculations on Polyatomic Molecules. I. Basic Theory with an Application to Methane
Authors: Klessinger M. , McWeeny R.
Published: January 2005

In polyatomic molecules it is usual to recognize physically distinct groups of electrons (e.g., inner shells, σ bonds, π electrons). The π electrons of conjugated molecules have received most attention, other groups of electrons being recognized only as a ``framework'' with empirically determined characteristics. In this series of papers, all groups of electrons are admitted, each group (localized or nonlocalized) being made self-consistent in the field of the others. In this way bond properties, π-electron parameters, etc., may be determined from first principles, taking into account the whole molecular environment. Excited states may be determined by admitting ``excitons'' (i.e., localized excitations) within the various groups.

The theory is illustrated by means of a completely nonempirical calculation on the methane molecule. The ground state is somewhat better than that given by approximate SCF theory, the excited states are somewhat worse. One advantage of the approach is that it lends itself admirably to semiempirical development.
Diffusion Coefficients of the Systems He—T2 and He–TH
Authors: Amdur I. , Malinauskas A. P.
Published: January 2005

Binary mutual diffusion coefficients have been measured for the systems He—T2 and He–TH by a radioactive tracer method at four temperatures in the range 195° to 374°K. The results, reduced to one atmosphere and normalized to the system He–H2, can be expressed within an average deviation of slightly less than 1% by the empirical relations He−T2:  log10D=1.6599log10T−3.9230,He–TH:  log10D=1.6960log10T−4.0140.

The ratio of the normalized coefficients for He—T2 and He–TH show a small departure from unity, starting at 1.02 at the lowest temperature and decreasing smoothly to 0.996 at the highest. On the assumption that deviations from classical mechanics, contributions from internal degrees of freedom, and the effects of asymmetric force fields are the same, or negligibly small, for both systems, different sets of Lennard-Jones (12–6) potential parameters have been obtained which correlate the experimental results as well as the empirical equations.
Diffusion Coefficients of Hydrogen Isotopes
Authors: Amdur I. , Beatty J. W.
Published: January 2005

Binary mutual diffusion coefficients have been measured by a radioactive tracer method for the following systems: H2−T2 and D2−T2 at 195°, 273°, and 353°K; H2–TH and D2−TH, at 195° and 273°K.

The ratios of the normalized coefficients for H2−T2 relative to H2–TH and for D2−T2 relative to D2−TH show the same trend as that previously reported for He–T2 relative to He–TH. In the present case both ratios are slightly greater than unity at 195° and slightly less than unity at 273°K. A larger isotope effect, produced by the substitution of D2 for H2, is reflected in the normalized coefficients for D2−T2 relative to H2−T2 and for D2−TH relative to H2–TH. The average values of these ratios are about 2% greater than unity at the lowest temperature and about 5% greater than unity at the higher temperatures.