bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-Crystal Magnetic-Susceptibility Study of Linear Antiferromagnetic Interactions in CsCuCl3
Authors: Rioux F. J. , Gerstein B. C.
Published: February 2004

The single-crystal magnetic susceptibilities of CsCuCl3 were measured along the a and c axes in the temperature range 2–140°K. Graphs of XMT vs T indicate that deviations from Curie law behavior commence at approximately 55°K. Least-squares analysis of the data above 70°K yielded values of the Curie constants of 0.464 and 0.445 for a and c axes, respectively. Structural evidence indicates the existence of linear chains of Cu ions in CsCuCl3. Comparisons of the experimental magnetic susceptibilities with the calculations of Bonner and Fisher indicate that the one-dimensional intrachain interactions between nearest-neighbor copper ions predominate down to approximately 30°K, whereupon, three-dimensional interactions of copper ions on neighboring chains become important. The exchange integral in the linear region has the value of J = − 4°K. This explanation is not in disagreement with the powder susceptibility and the heat capacity of CsCuCl3 measured previously. The single-crystal susceptibilities exhibit cusps at 10°K, near the heat capacity λ-type anomaly at 10.4°K.
Magnetic Resonance Spectroscopy of Triplet-State Organic Molecules in Zero External Magnetic Field
Authors: Hutchison Clyde A. , Nicholas John V. , Scott Gary W.
Published: February 2004

Some derivations are given for approximations to the energy levels and eigenstates of triplet-state organic molecules in external magnetic fields of such a magnitude that the electron Zeeman interaction is small relative to the intramolecular electron–electron interaction. An exact calculation of the exactly zero external field magnetic resonance spectrum of photoexcited naphthalene is given. Experimental measurements of the zero-field spectrum of naphthalene are presented. The results of the approximate and exact treatments are compared with these results and with other available experimental information.
Variational Approach to the Equilibrium Thermodynamic Properties of Simple Fluid Mixtures. III
Authors: Mansoori G. Ali , Leland Thomas W.
Published: February 2004

The variational technique proposed earlier for the calculation of the equilibrium thermodynamic properties of simple pure fluids, melting transitions, and simple pure solids is extended to binary mixtures of simple fluids. The working inequality is introduced and the variational parameters are characterized. For a case study, the present variational approach is applied in predicting the thermodynamic properties of the liquid mixture of argon and krypton at zero pressure and 115.77°K. The thermodynamic and excess properties of this mixture over that of the pure systems (at zero pressure and in liquid state) are calculated and compared with the results of the available Monte Carlo calculations, experimental measurements, and several theories of solutions. Preliminary investigation indicates good agreement between the result of the present variational technique with the experimental and machine-calculated data. Variations of the thermodynamic properties of the binary mixture, with the variation of the ratios of the force constants of the potential functions of the two components, are calculated at 97°K, zero pressure, and equal mole fractions. These values are compared with the existing values of the Monte Carlo calculations.
Analytical Approach to Semiclassical Inelastic Collision Theory for General Impact Parameters
Authors: Roberts R. E.
Published: February 2004

A simple method is described for the evaluation of classical trajectory integrals which play an important role in semiclassical collision theory. The results for a Lennard-Jones potential are compared with the exact results of Bernstein and Kramer and then are applied to an optical analysis of glory quenching for low energy Li–HBr collisions. Calculations and comparison with exact results are also presented for an exponential interaction.
Semiclassical Theory of Atom–Diatom Collisions: Path Integrals and the Classical S Matrix
Authors: Miller William H.
Published: February 2004

The aim of this work is to show how one can use exact solutions of the classical equations of motion (numerically obtained trajectories) to construct the corresponding classical approximation to the time-independent S-matrix elements for use in quantum mechanical expressions for cross sections; it is argued that this should accurately describe many quantum effects in heavy particle collisions. The expression for the S matrix in terms of the classical trajectory is given for systems of any number of degrees of freedom, and the matter is pursued in detail for the A + BC collision system. It is shown that within this classical limit the magnitude of an S-matrix element is explicitly determined by its phase. Constancy of total angular momentum is used throughout to reduce the 12 first-order differential equations of the A + BC system in its center of mass to eight equations. A practical method is also given (in Appendix B) for further reducing the number of coupled equations to six, the minimum number possible.
Possible New Type of Molecular Bound State
Authors: Rosenfield Joan , Voigt Bjo/rn , Mead C. Alden
Published: February 2004

It is shown that the corrections to the Born–Oppenheimer approximation may lead to the appearance of a new type of bound state, the theory of which is mathematically analogous to that of Cooper pair states in superconductivity theory. Some of the properties of these states, and the conditions for their existence, are studied for the special case of diatomic molecules. In all cases of interest, one such state at most can appear below the continuum threshold belonging to the ground electronic state of the molecule, i.e., they have no rotational or vibrational structure. In the case most likely to arise, the binding energy, considered as a function of the Born–Oppenheimer expansion parameter κ, has an essential singularity at zero, so the state could never have been discovered by the power-series expansion method. Experimental observation of these states is expected to be difficult since their wavefunctions do not differ importantly from those for ordinary bound states of the same energy. However, the theory predicts that an accurate Born–Oppenheimer calculation of the number of bound states should sometimes be too low by one, and the isotope effect on the binding energy is different from that of ordinary bound states.
Adiabatic Theory of Chemical Reactions
Authors: Truhlar Donald G.
Published: February 2004

The recent results of Morokuma, Eu, and Karplus on what collision cross sections and reaction probabilities are implied by the usual transition state theory of reactions are examined in terms of the adiabatic justification of transition state theory. Eliason and Hirschfelder's and Marcus's definition of a generalized activated complex and the theory of adiabatic reactions are used to remove the inconsistencies and divergences Morokuma et al. found in the transition state theory. It is found that the usual transition state theory is not exactly equivalent to the adiabatic theory of reactions. The corrected transition state theory is equivalent to the adiabatic theory at low temperatures for the simple barrier-potential type of reactions, e.g., H+H2.
Intermediate Operators and the Kinetic Theory of Gases
Authors: Monchick L.
Published: February 2004

A decreasing set of intermediate operators, L(N), are defined that are greater than the linearized Boltzmann operator in the sense that they correspond to collision models with a lower rate of entropy production. With these operators upper bounds for transport properties may be calculated to supplement the lower bounds calculated by the usual variation method. Two examples are given, both for the rigid-sphere model. One is the thermal conductivity, and the other, the perturbation to the reaction rate by the depletion of the faster moving molecules. In the second instance, new lower bounds are calculated as well. The extension to other collision models is indicated. We also find that a measured transport property determines a mean relaxation frequency that must lie within the spectrum of relaxation frequencies of the fluctuation variable corresponding to the flux.
Interactions of Hyperthermal Gas Particles with Contaminated Surfaces
Authors: Chiang K. C. , Knuth E. L.
Published: February 2004

Interactions of hyperthermal molecules with contaminated surfaces are studied analytically for a simple classical model in which the surface is covered by a monolayer of physisorbed contaminant and the gas particle energy is much greater than that corresponding to the temperature of the solid. Calculations indicate that if the adsorption potential varies periodically along the surface, then the adsorbed particles are sputtered into a multilobular distribution. The positions of the peaks depend on the velocity of the incident particles, the heat of adsorption, the amplitude of the adsorption-potential variation, and the equilibrium adatom–surface distance. Predictions for argon beams impinging on mica and silver surfaces contaminated with water vapor agree qualitatively with pertinent experimental results. Hence the present model provides a possible explanation for the observed multilobular scattering distributions.
Optical Properties of Amorphous Polypeptides. I. One State Solutions
Authors: Aebersold Dennis , Pysh E. S.
Published: February 2004

A model for the optical properties of disordered polymers is presented to describe both flexible polypeptides in solution and disordered regions of films or proteins. The model links current optical theory with configurational statistics. The partition function determining population averaged rotational and dipole strength is constructed with current approximate potential-energy functions. Oligopeptides are randomly generated and the circular dichroism and optical absorption for the π–π* amide transition are reported. This one state calculation can account for both the large negative and small positive circular-dichroism bands observed experimentally, as well as the unusual noncoincidence of the circular-dichroism and absorption extrema.
Corrections to the Fuoss–Onsager Theory of Electrolytes
Authors: Murphy T. J. , Cohen E. G. D.
Published: February 2004

Mathematical corrections are made to the theory of Fuoss and Onsager for the conductivity of ionic solutions to first order in the concentration. The theory is extended to cover the case of asymmetric binary electrolytes; it is found that in this case the results are strongly affected by deviations of the equilibrium ion pair distribution function from that predicted by the Debye–Hückel theory. The results of the conductivity theory are compared to corresponding results of the equilibrium theory.
Ionic Conductivity of NaCl: SrCl2 Crystals
Authors: Laredo E. , Dartyge E.
Published: February 2004

The ionic conductivity of NaCl crystals highly doped with SrCl2(10−5 ≤ c ≤ 2 × 10−2, expressed in molar fraction) has been measured from room temperature to the melting point. In this wide range of concentration a unique value for the migration energy for the cation vacancy has been found: 0.75 ± 0.02 eV. With this value all the parameters for the creation and motion of lattice defects have been determined. Simple association theory could not explain the observed results. The Debye–Hückel approach was used to account for the observed absence of association at high temperature. Quenching experiments from high temperatures were performed on these doped crystals and a saturation limit of 8 × 10−4 was found for the dilution of dipoles in the matrix. The effect of clustering of these dipoles was followed by quenching from different annealing temperatures.
Exclusion Problem for Mobile Atoms of Any Size in One Dimension
Authors: Verhagen A. M. W.
Published: February 2004

Successive random desorption and random readsorption of atoms of any size leads to Fermi–Dirac statistics, in which all possible nonoverlapping patterns become equally probable. This equivalent characterization of the adsorption process of individual mobile atoms, discussed in greater detail in previous papers, lends itself to a stochastic pattern generating process, yielding the required Fermi–Dirac statistics, at any required adsorption density and atom size. For the discrete case where all potential adsorption sites are equally spaced, the process reduces asymptotically to the continuous case where all sites of the continuum are potential adsorption sites, by letting the diameter of the atom become large relative to the spacings. The parameters of the process are readily expressible in terms of the adsorption density and atom size. The proportion of “excluded sites,” usually obtainable only by simulation, is here derived exactly as a function of the adsorption density, for both the discrete and the continuous case.
Radio-Frequency Spectrum of Metastable N2(A 3Σu+). I. Magnetic Hyperfine and Electric Quadrupole Constants
Authors: Freund R. S. , Miller T. A. , De Santis D. , Lurio A.
Published: February 2004

Measurements have been made of the rf spectrum of metastable N2(A 3Σu+) by the molecular beam magnetic resonance method. Transitions obeying selection rules δF = 0, δMF = ± 1, were observed in states with quantum numbers (N, J, F) equal to (0, 1, 2), (0, 1, 1), (1, 2, 1), (1, 2, 2), (1, 2, 3), (2, 1, 1), and (2, 3, 2). The theoretical basis of this spectrum is presented in detail and used to derive hyperfine constants and the following molecular averages: Fermi contact: ∑ i′12〈δ(rai)〉Φ = (2.7 ± 0.4) × 1023cm−3, Electron–nuclear dipolar: ∑ i′12〈rai−3(3 cos2ωai − 1)〉Φ = (− 4.3 ± 0.4) × 1024cm−3, Quadrupole coupling: e2q0Q / h = − 1.8 ± 1.0 MHz (primes indicate that the summations are to be carried out over only the unpaired electrons).
Pure Thermal Diffusion. I. Time-Dependent Phenomenological Theory for Binary Liquids
Authors: Horne Frederick H. , Anderson Terry G.
Published: February 2004

Solutions to the partial differential equations which describe pure thermal diffusion in a binary liquid are obtained by means of perturbation and Fourier transform methods which retain explicitly the temperature and composition dependences of density, heat capacity, and the coefficients of diffusion, thermal diffusion, and thermal conductivity. Inclusion of the effects of time-dependent temperature and center-of-mass velocity gradients during the warming-up period yields unambiguous identification of zero time. Inclusion of the variability of the coefficients makes it possible to evaluate the effects of such variability. The theory provides clear criteria for experimental design. Practical formulas are given for both demixing and remixing experiments.
Yield of Ions and Excited States Produced in the Radiolysis of Polar Organic Liquids
Authors: Hayon E.
Published: February 2004

The yield of ions and triplet excited states produced in the radiolysis of polar protic and aprotic organic liquids was studied using the technique of pulse radiolysis. Anthracene and naphthalene were used to determine the yield of electrons and triplet excited states, respectively. Taking εmax = 9.9 × 103 M−1·cm−1 for (anthracene)−, the yields of anthracene anions, considered to represent the yield of free ions produced, were found to vary from G values 0.1 to ∼ 2.6 for the 20 organic liquids examined. The yields of triplet states were found to depend, in a number of cases, upon the presence of electron scavengers in the liquids. The liquids studied include p-dioxane, MTHF, pyridine, aliphatic alcohols, acetone, benzonitrile,acetonitrile, dimethylsulfoxide, 1,2-propanediol carbonate, dimethylformamide, dimethylacetamide, and N-methylpropionamide. The static dielectric constant values of these liquids ranged from ∼ 2.0 to 165.0. These results are evaluated and discussed, and the potential interest of some of these liquids is indicated.
Properties of Fluorine along the Vapor–Liquid Coexistence Boundary
Authors: Prydz Rolf , Straty G. C. , Timmerhaus K. D.
Published: February 2004

Saturated liquid and vapor densities from the triple point to the critical points are reported. These data were derived from experimental PVT isochores and an accurate vapor pressure equation. The critical point parameters were estimated by fitting an equation to all experimental data within 20% of the critical temperature. Separate equations, each constrained to the new critical point parameters, were fitted to the saturated liquid and vapor densities. Latent heats of vaporization were calculated from the Clapeyron equation and compared to other published values. A vapor pressure equation based on the IPTS 1968 temperature scale is reported.
SCF Relativistic Hartree–Fock Calculations on the Superheavy Elements 118–131
Authors: Mann Joseph B. , Waber James T.
Published: February 2004

The energies of a number of configurations of the elements with atomic numbers 118–131 were computed by means of the relativistic Hartree–Fock method to establish the probable ground states. The series of elements beginning at 121 differs markedly from the lanthanide and actinide series because spinp–orbit and direct relativistic effects cause the 8p1/2 electron states to be partially filled before the 7d3/2 states. The inner shell of 5g electrons begins to fill at element 125. The Breit magnetic interaction energy is calculated by a perturbation method; an approximate correlation energy correction is included. Isotopic mass effects on the atom total energy and on the electron eigenvalues are discussed.
Pair Association in Matrix Isolated Pyridine
Authors: Taddei G. , Castellucci E. , Verderame F. D.
Published: February 2004

Absorption spectra of pyridine-H5 in frozen nitrogen exhibit concentration dependent sidebands due to pairwise interactions in the Λ10 region at 606 and 607.5 cm−1, in the Λ26 region at 706 and 709 cm−1, and in the Λ14 region at 1442 and 1443 cm−1. For pyridine-D5 pair absorption bands were observed at 584.5, 586(Λ10), 533, 535(Λ26). Calculations of exciton splittings and shifts for various pair configurations using nonbonded atom–atom potentials including short-range repulsive, dispersion, and electrostatic terms were performed. The results of the calculations predict that pairs of pyridine molecules face each other with the nitrogen atom opposite to the hydrogen atom of the partner, the distance separating them being 3.4 Å.
Infrared Spectra and Geometry of Matrix-Isolated Diboron Tetrachloride and Tetrafluoride; Raman Spectra of the Liquids
Authors: Nimon L. A. , Seshadri K. S. , Taylor R. C. , White David
Published: February 2004

The infrared spectra of diborontetrachloride and diboron tetrafluoride molecules, isolated in a matrix of solid argon at liquid-hydrogen temperatures, along with the Raman spectra of the two compounds in the liquid phase are presented. Also reported are the 11B–10B isotopic shifts of the fundamental vibrations which have been used to establish the Vd molecular symmetry in the solid argon matrix. The Raman data also support a staggered configuration for B2Cl4 and B2F4 in the liquid phase. These data combined with the matrix infrared results are used to obtain a force constant analysis of both molecules using a Urey–Bradley force field.
Harmonic Forces Linear Model for Reactions of Cs Atoms with Alkyl Iodides
Authors: Parrish David D. , Herm Ronald R.
Published: February 2004

The Cs plus alkyl iodide reaction dynamics are investigated by means of a classical, linear, four-particle model, Cs–I–CH2–R, where R is H, CH3, C2H5, or C3H7, with linear harmonic restoring forces between adjacent particles. The full reaction exothermicity is initially partitioned between potential energy of Cs–I extension and I–CH2 compression, and the trajectories of the four particles are followed until the I–CH2 distance reaches a critical extension, at which point the reaction is assumed to be complete. The model is examined as a function of two parameters, the I–CH2 force constant, k2, and the initial repulsive energy in I–CH2 compression, P. By varying k2, the model spans the spectrum of possible direct interaction reaction dynamics from the limit of the adiabatic, very slow CsI–CH2R separation (low k2 limit) to the limit of impulsive release of the I–CH2 compression (high k2 limit). In contrast to previous calculations, we obtain a good qualitative fit to the experimentally reported product recoil energies if: (1) a relatively high value of k2, near the impulsive limit, is used; (2) the potential surface is largely repulsive, with P = 19.0 kcal/mole out of a total 28.7-kcal/mole reaction exothermicity; and (3) both the CsI and the CH2–R alkyl radical carry off substantial internal excitations.
Vibronic Interactions between nπ* and ππ* States and Radiative and Nonradiative T1 → S Transitions in Aromatic Carbonyl Compounds
Authors: Lim E. C. , Li Y. H. , Li R.
Published: February 2004

Out-of-plane vibrations which may be effective in vibronic coupling between nπ* and ππ* states of aromatic carbonyl compounds are investigated, and the probable importance of these vibrations in radiationless transitions is demonstrated through the dependence of vibrational features, quantum yields, and lifetimes of π* → π phosphorescence upon deuteration of the COR (R is H or an alkyl) group, nature of solvents, and molecular structure (e.g., ketones versus aldehydes).
Paramagnetic Resonance Study of Liquids during Photolysis. X. Hyperfine Interactions from 13C
Authors: Livingston Ralph , Dohrmann Jürgen K. , Zeldes Henry
Published: February 2004

Hyperfine splittings due to 13C in natural abundance have been observed in several short-lived radicals produced photolytically in liquids. Signal averaging was used for the weaker spectra. A radical made from acetate ion, ĊH2COO−, has carbon couplings of 32.09 and 13.85 G assigned to the ĊH2 and COO− carbons, respectively. Linewidth effects were seen. These results are discussed, and it is concluded that the species is a planar π radical. The coupling for the methyl carbons of (CH3)2ĊOH is 5.35 G, and that for the central carbon is 65.05 G. It is concluded that the radical skeleton is not planar; the species is not a pure π radical. A coupling of 11.05 G found in CH3COCH2NO2·− is assigned to the carbonyl carbon, and the results are described in terms of a β-coupling model. The acetoin radical, CH3̇COHCOCH3, in strongly acid media undergoes rapid dynamic exchange. The two central carbons become equivalent and the 13C coupling is 5.12 G. In the absence of acid, all carbons of the radical are inequivalent. Satellites due to 13C were seen, and one coupling of 7.8 G was evaluated. A provisional coupling for another carbon was assigned.
EPR Study of the Hindered Motion of NO2 and ClO2 Adsorbed in Synthetic Zeolites
Authors: Pietrzak Theodore M. , Wood David E.
Published: February 2004

The temperature-dependent EPR spectra of NO2 and ClO2 adsorbed in sodium (NaX) and calcium (CaX) cation type-X zeolite were investigated. Motional narrowing occurs above 77°K in each case. The time-dependent spectra of NO2 in CaX zeolite were simulated by linear combinations of stationary-state solutions of the spin Hamiltonian. The model used to produce these linear combinations required that there be no preferred axis of rotation for NO2 in this system and that rotation greater than ∼ 35° from the equilibrium position be strongly hindered. Although no comparably detailed study has been made for the other systems, it appears that NO2 in NaX also has a high barrier to rotation but that ClO2 in both NaX and CaX zeolite has a greater degree of rotational freedom.
Oxygen Monofluoride (OF, 2π): Hartree–Fock Wavefunction, Binding Energy, Ionization Potential, Electron Affinity, Dipole and Quadrupole Moments, and Spectroscopic Constants. A Comparison of Theoretical and Experimental Results
Authors: O'Hare P. A. G. , Wahl Arnold C.
Published: February 2004

Self-consistent-field wavefunctions near the Hartree–Fock limit have been calculated by the Roothaan expansion method for OF(2π) at several internuclear separations; the total energy at the Hartree–Fock minimum (1.321 Å) was found to be − 174.19502 hartree. Based on the assumption that the correlation energy was approximately the same as for O2−, and also by interpolating the correlation energy of OF across the CF, NF, OF, and F2 sequence, the binding energy D(OF) was deduced to be 3.0+0.3−0.8 eV. A Dunham analysis of the potential-energy curve gave values for the various spectroscopic constants. In addition, the ionization potential and electron affinity for the vertical processes, and the dipole and quadrupole moments of OF+(3Σ), OF(2π), and OF−(1Σ) were also calculated.
Scattering of Lithium by a Series of Molecules. IV. Miscellaneous Molecules
Authors: Rothe Erhard W. , Helbing Reinhard K. B.
Published: February 2004

This is the final paper in a series which describes measurements of the velocity dependence of the total cross section for the scattering of lithium-7 by a series of molecules. The experiments are similar to the previous measurements of the scattering from 52 molecules. The molecules here consist of seven triatomics, five tetra-atomics, and nine miscellaneous organics. Potential parameters are obtained. Some qualitative correlations of the quenching of the glory amplitudes are made, but no real theoretical explanation is attempted.
Raman and Infrared Spectra of Dimethylnitrosamine
Authors: Levin Ira W. , Milne G. W. A. , Axenrod T.
Published: February 2004

The Raman and infrared spectra of (CH3)2NNO, (CH3)2N15NO, and (CD3)2NNO were recorded in the liquid state. For (CH3)2NNO, gas-phase infrared spectra, Raman depolarization measurements, and the Raman spectra of solid polycrystalline samples were also obtained. A vibrational assignment for the 27 fundamental modes is proposed on the basis of Cs symmetry.
Steric Effects in the Translation-Vibration Energy Transfer in Cyclopropane-Inert Encounters
Authors: Welsh Alan G. , Taylor Jay E.
Published: February 2004

The data for a study of steric effects in the exchange of translational and vibrational energies are provided by the velocity dispersions in cyclopropane-inert mixtures at 307.0°K. With helium, neon, and argon as projectiles and cyclopropane as the target, a comparison of the experimental results with results from the theoretical equation of Herzfeld and Litovitz is used to determine the dependence of the probability of energy transfer on the size of these atoms. The apparent variation of the interchange of translational and vibrational energy between molecules as a function of molecular size is explained by the assumption of active sites on the cyclopropane molecule.
Microwave Spectrum and Rotational Constants for the Ground State of D2O
Authors: Benedict W. S. , Clough S. A. , Frenkel L. , Sullivan T. E.
Published: February 2004

The rotational levels of the ground vibrational state of D2O have been studied utilizing 29 observed microwave transitions and 259 rotational energy differences obtained from infrared measurements. Seventeen of the microwave lines in the region 70–310 GHz have been observed in the course of this work. Eighteen linearly independent rotational constants are required to fit the observations: three constants of the second power of the angular momentum, five constants of the fourth power, seven constants of the sixth power, and the coefficients of the operators Pz8, Pz6P2, Pz10. Values of these constants and the calculated microwave transition frequencies up to 1000 GHz are reported. The coefficients of Pz2, Px2, Py2 are, respectively, A = 462 292.37 ± 0.43, B = 217 979.95 ± 0.27, and C = 145 303.34 ± 0.14 MHz.
Self-Consistent-Field Study of the Cluster Model in Ionic Salts. I. NiF64−
Authors: Moskowitz Jules W. , Hollister C. , Hornback C. J. , Basch Harold
Published: February 2004

Self-consistent-field calculations have been carried out on the NiF64− cluster in a near-Hartree–Fock basis (for the valence electrons) of Gaussian functions to test the validity of the model for describing the localized properties of ionic salts. Both the spin-restricted and spin-polarized treatments are compared for ground and excited states of the complex ion. From comparison with experimentally obtained results it is concluded that a Hartree–Fock description of the cluster gives reasonably good wavefunctions and energies. Surprisingly, the crystal-field splitting parameter obtained using just the ground-state wavefunction is too large by a factor of 3.
Expansion Techniques for Multicenter Integrals over Slater-Type Orbitals
Authors: Mehler Ernest L.
Published: February 2004

A method is developed for analytically continuing power series expansions of the plane wave for use in evaluation of multicenter integrals over Slater-type orbitals. The method is applied to the three-center nuclear attraction integral, for which analytic formulas and recurrence relations are developed. Convergence of the expansion is discussed and a numerical example is presented.
Molecular Motion and Spatial Order in Liquids: The Aniline/Cyclohexane System
Authors: Anderson J. E. , Gerritz W. H.
Published: February 2004

This work probes the relationship between molecular motion and spatial order in binary solutions. We deal with the aniline–cyclohexane system, in which the components are completely miscible above a critical solution temperature, Tc, of 29.5°C and separate into aniline-rich and cyclohexane-rich layers at lower temperatures. Previous light-scattering measurements indicate spatially ordered regions with dimensions of roughly 50 Å some 10° above Tc; the size of these regions increases to 1000–2000 Å at 0.1° above Tc. Spatial correlations between the positions of the aniline and cyclohexane molecules were examined through studies of: (1) the PMR solvent shift; (2) the intermolecular contribution to spin–lattice relaxation. The results indicate a statistical preference for aniline–aniline and cyclohexane–cyclohexane neighbors rather than aniline–cyclohexane pairings. The self-diffusion coefficients of both aniline and cyclohexane were determined by pulsed NMR methods over a wide range of temperature and concentration. We employed a sinusoidal time-dependent field gradient, locating the rf pulses at field-gradient nodes one cycle apart. Owing to the refocusing effect of the periodic gradient, multiple spin echoes can be generated from a simple 90–180 pulse sequence. The self-diffusion measurements indicate that the basic translational process involves the motion of individual aniline and cyclohexane molecules. We found no evidence for the translation of polymolecular aggregates. This is clearly a system of uncomplexed aniline and cyclohexane molecules that happen to translate in spatially ordered surroundings. We examined self-diffusion in the cloudy solutions characteristic of the phase-separation temperature. The experimental diffusion coefficients were indistinguishable from those determined at a temperature 1° higher. Evidently, the self-diffusion coefficients, Da, do not exhibit anomalous behavior near Tc, as does the mutual diffusion coefficient, Dm. These two quantities are related by the expression Dm = Da(∂ lna / ∂ lnc) and the experimental results are consistent since (∂ lna / ∂ lnc) becomes vanishingly small near Tc.
Effect of Impurities on Electron Emission in Liquid Hexane
Authors: Hughes J. F.
Published: February 2004

Electron injection characteristics for different grades of liquid hexane are compared with impurity content for each particular sample; the impurities identified by chromatographic techniques. Hexane isomers and other impurities in low concentration (∼ 0.5%) do not appreciably affect the emission and conduction properties. For high current injection the charge carriers are believed to be predominantly formed by electron attachment to molecules of water; a concentration of as low as ∼ 100 ppm having a marked effect on the magnitude of emission.
Curvature Dependence of the Surface Tension and the Theory of Solubility
Authors: Choi Dong Sik , Jhon Mu Shik , Eyring Henry
Published: February 2004

While the theory of the dependence of surface tension on curvature was well formulated in 1950, experimental support for the surface tension of molecular-sized spherical interfaces is extremely sparse. Here, a correlation between the solubility of a solute gas and the surface tension of the solvent liquid is discussed theoretically and the curvature dependence of the surface tension is calculated for C6H6, C6H12, and CCl4. The determined dividing thickness, Z, for CCl4, C6H6, and C6H12 is 4.7, 4.2 and 4.9 Å, respectively. The calculated values of the solubility and the molar heat of solution for various gases He, Ne, H2, O2, N2, Ar, CH4, and Kr shows good agreement with experimental data. The equilibrium radius and the surface tension at that radius are evaluated and tabulated.
Interdiffusion Measurements in Fused Alkali Nitrates by Wave-Front-Shearing Interferometry
Authors: Arvidsson Torkel E. G. , Afsenius Sven-Åke , Gustafsson Silas E.
Published: February 2004

Interdiffusion coefficients in molten alkali nitrate systems have been measured by recording the phase variations introduced on an initially plane wave front when passing through a diffusion vessel. The recording of the path differences is performed with a wave-front-shearing interferometer giving a high degree of accuracy. Two different methods have been used to initiate bottom layer diffusion experiments, one of which has been developed in the course of this work. The interdiffusion studied here has been that of rubidium and cesium ions and in some cases that of sodium and potassium ions diffusing into the pure melts of lithium nitrate, sodium nitrate, and potassium nitrate. The diffusion coefficients have been measured over a temperature range of some 100°C above the melting point.
Paramagnetic Resonance of Eu2+ in BaF2
Authors: Miller James R. , Watson Robert L.
Published: February 2004

The EPR spectrum of Eu2+ in cubic sites of BaF2 has been observed at various temperatures between 2 and 360°K. The spin Hamiltonian constants b4, A, b6, and g have been measured for 151Eu in this temperature range. Certain qualitative analysis is reported on the “forbidden” lines that appear as the temperature is lowered.
Neutron-Diffraction Study of CoCl2·6H2O
Authors: Kleinberg Robert
Published: February 2004

Neutron diffraction data on the (h0l) zone of CoCl2·6H2O have been taken at temperatures above and below the Néel temperature. Measurements at 77°K confirm that the hydrogen parameters are essentially the same as for NiCl2·6H2O. Below the measured Néel temperature of 2.25°K, the magnetic structure consists of antiferromagnetic (001) planes with an antiferromagnetic coupling between planes, and has the magnetic space group Cc2 / c. Magnetic intensities taken at 1.5°K indicate that the spin direction is along the c axis. This is in agreement with reported susceptibility data.
Liquid Surface Tension near the Triple Point
Authors: Egelstaff P. A. , Widom B.
Published: February 2004

It is shown that the product of the isothermal compressibility ξ and surface tension Σ of a liquid near its triple point may be expected to be a fundamental length characteristic of the liquid. From experimental data on 30 liquids (including liquid metals) it is observed that while ξ and Σ separately vary by a factor of 150, the product ξΣ varies by a factor of less than 3 and is equal always to a few tenths of an angstrom unit.
Optical and Magnetic Field Studies of the Lowest Triplet State of the Pyrazine Crystal
Authors: Hochstrasser Robin M. , Lin Tien-Sung
Published: February 2004

The electronic absorption spectrum of pyrazine crystals has been studied using single crystals at 4.2°K and polarized light. The origin shows three lines that are interpreted as (i) a B3u+, k = 0, factor group state at 26247.6 cm−1, (ii) two lines at 26254.7 and 26253.4 cm−1 corresponding to a split B2u−, k = 0, factor group state. These interpretations are made on the basis of high-field Zeeman effect studies. A low-field Zeeman study has revealed the ordering of magnetic substates in each factor group level at Tc < Tb < Ta. This yields the order Ty < Tz < Tx for the free molecule. The zero-field splitting is approximately + 0.3 cm−1 (D = − 32Y). A discussion of the relationship between such spin-state ordering and the electronic structure of pyrazine in a n3+π4*(nπbb) state is also presented.
Molecular Arrangement, Exciton Splittings, and Lattice Vibrations of Crystalline Ethylene
Authors: Taddei G. , Giglio E.
Published: February 2004

Molecular arrangement, vibrational splittings, and lattice frequencies have been calculated for two possible monoclinic P21 / n structures of solid ethylene and deuteroethylene, using several sets of pairwise potentials of the Lennard-Jones and Buckingham type. The results show that the calculated frequencies depend strongly upon the number of the intermolecular interactions taken into account and that the attractive dispersion forces, usually neglected in previous calculations, play an important role. For very strong bands electrostatic (dipole) interactions are also of importance in the exciton splitting calculations.
Reactive Scattering. A Simple Three-Body Model
Authors: Locker David J. , Wilson David J.
Published: February 2004

A simple model is created which can be solved for the change in population probabilities of reactive and nonreactive channels due to molecular collision. The system consists of an atom collinearly colliding with a diatomic molecule. Both the reactant molecule and the product molecule are chosen to be square well oscillators. The possibility of the formation of three free particles is forbidden. Matching wavefunctions at the various boundaries in an orthogonal function sense permits the calculation of a scattering matrix. The effects of varying the parameters of the model are then examined: relative translational energy, atomic masses, molecular orientation, potential energy barrier height, and passage widths.
Molal Volumes of the Isotopic Homologs of Ethylene
Authors: Menes Francis , Dorfmüller Thomas , Bigeleisen Jacob
Published: February 2004

The molal volumes of ethylene (C2H4), trans-dideuteroethylene (C2H2D2), and tetradeuteroethylene (C2D4) have been measured over the temperature range 105–175°K with a precision 10−2% (± 0.005cm3). The order of the molal volumes is VC2H4 > VC2H2D2 > VC2D4. The difference in molal volume between ethylene and each of its deutero derivatives is approximately 0.05 cm3 mol−1 per deuterium atom and decreases with temperature. The difference in molal volumes is compared with two limiting models. The “size effect” model, which is a consequence of the difference in lengths of the C–H and C–D bonds leads to the correct magnitude of the difference in molal volume, but predicts δV / V to be temperature independent for ethylene, contrary to the experimental findings. Calculations based on an anharmonic intermolecular potential show that the hindered rotation in liquid ethylene makes a significant contribution to the molal volume difference. Finally a correlation is made between the observed molal volume differences and the measured vapor-pressure differences of the deuteroethylenes.
Effusion. VI. Velocity Distributions of Gaseous CsCl from Near-Ideal and Right-Circular Cylindrical Orifices
Authors: Wang K. C. , Wahlbeck P. G.
Published: February 2004

Velocity distributions have been measured for CsCl(g) effusing from double-oven effusion cells equipped with a near-ideal and nonideal right-circular cylindrical orifices. The back oven contained CsCl(s or l), and the front oven possessed an orifice. A multiple slotted-disk velocity selector was used to determine velocity distributions. The disks had slots cut at an angle (with respect to the selector axis) to provide improved transmission. Detectors utilized surface ionization. Data were acquired for states of CsCl(g) (as determined by temperatures of the back and front ovens) ranging from the molecular flow region into the transition region and for several effusion angles. The velocity distribution data may be summarized as follows: near-ideal orifice—data are in accord with the Maxwellian theoretical velocity distribution, and data show no dependence on Knudsen number (ratio of mean free path to orifice diameter) or effusion angle; nonideal cylindrical orifices—deviations from the Maxwellian distribution (with too many high-speed molecules or too few slow molecules) occurred at low pressures under molecular flow conditions, were largest at effusion angles near the axis of the orifice, and were enhanced by increasing pressure in the transition region. These data and previously published angular number distributions may be explained by introducing some specular reflection on the orifice wall for the nonideal orifices. Both sets of data were combined to yield angular momentum distributions.
Viscous Relaxation above the Liquid–Liquid Phase Transition of Some Oxide Mixtures
Authors: Simmons J. H. , Macedo P. B.
Published: February 2004

The viscosity anomaly observed above the critical points of a series of sodium borosilicate melts is investigated by ultrasonic shear relaxation spectroscopy. The measurements were conducted at frequencies between 3 and 25 MHz and temperatures between 800 and 1300°C. The samples tested have different critical temperatures as a result of small doping additions to the critical composition of the immiscibility surface in the phase diagram of the sodium borosilicate system. This permitted measurements over a wide range of reduced temperatures. Analysis of the data yields three structural relaxation parameters which are: the instantaneous shear modulus, the most probable relaxation time, and the width of the distribution of shear relaxation times. These parameters are related to the viscosity. It is found that while the instantaneous modulus and the most probable relaxation time appear unaffected by the presence of super-critical composition fluctuations, the width of the spectrum of shear relaxation times broadens drastically as the critical temperature is approached from above. Similar and parallel curves are formed from the widths of the distributions of relaxation times of all four samples when the temperature is properly normalized by the critical temperature. The general behavior of these curves exhibits the three reduced temperature regions predicted in a previously published relaxation model. The supercritical broadening of the width of the distribution of relaxation times accounts for the observed viscosity anomaly.
Low-Energy Electron Diffraction Study of Tungsten (100) Surface
Authors: Wei P. S. P.
Published: February 2004

The diffraction of electrons by a tungsten (100) surface was studied in a display-type LEED apparatus. The sample surface was cleaned by repeatedly heating to 2300°K in high vacuum. Instrumental factors and the effect of adsorption of ambient gases on intensities were checked. The 00 beam intensity profile was measured in the energy range 100–300 eV for sequences of primary-beam orientations. Special effects associated with the simultaneous occurrence of different Bragg conditions were found. A tabulation of energies and orientations at which simultaneous Bragg conditions occur is presented.
Temperature-Dependent Optical Phonons in Lead Titanate
Authors: Tornberg N. E. , Perry C. H.
Published: February 2004

Ceramic platelets and oriented single crystals of PbTiO3 have been investigated by Raman and infrared spectroscopy. The symmetries of the zone-center optical phonons are described and their temperature dependences from 20–760°K are studied, demonstrating that the doubly degenerate modes are relatively the “softest.” It is shown that their behavior accounts for the variation of the static dielectric constant in the ceramic between those temperatures if singly and doubly degenerate modes coexist as pairs of a two-mode type of behavior. It is found that the short-range crystal anisotropy predominates over the long-range electrostatic force in determining phonon frequencies. Above the 760°K Curie temperature the Raman spectrum is entirely second order and quite indistinct. No low-temperature phase transition is found.
Matrix Infrared Spectrum and Bonding in the Monochloromethyl Radical
Authors: Andrews Lester , Smith David W.
Published: February 2004

Simultaneous deposition of CH2ClX (X = F, Cl, Br, I) with atomic lithium (6Li or 7Li) on a CsI window maintained at 15°K produces new infrared absorptions attributable to LiX and the monochloromethyl radical. The identity of the radical is confirmed by comparing the spectra of the reactions of CHDCl2 and CD2Cl2 with lithium and CH2ClBr with sodium. Absorptions assigned to the symmetric C–Cl stretch, the symmetric H–C–H bend, and the out-of-plane hydrogen bend of the monochloromethyl radical are supported by normal coordinate calculations. The high C–Cl force constant (4.09 ± 0.03 mdyn/Å) suggests (p–p)π bonding in CH2Cl. The large positive quartic term in the out-of-plane bending potential function is consistent with a planar radical.
Photochemistry of Aromatic Olefins. II. Intramolecular Energy Transfer in 5-Phenyl-2-pentene
Authors: Nakagawa C. S. , Sigal P.
Published: February 2004

Intramolecular energy transfer in 5-phenyl-2-pentene has been studied monitoring cis–trans isomerization of solutions of the compound in cyclohexane. The intersystem crossover yield of the phenyl moiety is calculated to be 0.66 or less. The rate of intramolecular energy transfer is found to be much faster than that of intermolecular energy transfer in the concentration range studied.
ESR Studies of Deuterated dl-Tartaric Acid X Irradiated at 195°K
Authors: Moulton Grace C. , Cernansky Barbara
Published: February 2004

Using electron spin resonance techniques, the free radical produced when single crystals of deuterated dl-tartaric acid are irradiated at 195°K with either 50 kV x rays or 3 meV x rays was shown to be ·CHODCHODCOOD·D2O. The C–C bond to the carboxyl group is broken and the unpaired electron is primarily in a 2pπ orbital on the carbon atom with the p orbital close to the normal to the carbon plane. This results in a hyperfine coupling to two H atoms with eigenvalues of − 33.4, − 23.0, − 10.7 G for the α-H hydrogen, and 37.2, 35.8, 30.5 G for the β − H. This radical is the same radical that is observed if deuterated dl-tartaric acid is irradiated at 77°K and allowed to warm to 195°K. This radical follows the decay of the cation radical produced at 77°K and subsequently decays to the stable room temperature radical. The anion radical which was observed at 77°K is still present at 195°K.
Anisotropic Chemical Shifts in Trigonal Cobalt Carbonyls Containing Metal–Metal Bonds
Authors: Spiess H. W. , Sheline R. K.
Published: February 2004

The 59Co NMR was studied in a number of single crystals and solutions of cobalt carbonyl complexes X3MCo(CO)4 (M=Si, Ge, Sn, Pb; X=Cl, Br, I, C6H5) containing metal–metal bonds. The z component of the chemical shift as determined by single crystal measurements in I3GeCo(CO)4, Br3SnCo(CO)4, and (C6H5)3SnCo(CO)4 was found to be constant within the series and showed a paramagnetic contribution of at least 3.6‰. As ligand field theory predicts no paramagnetic shift in this case, the data showed that for low oxidation state complexes the chemical shift can only be explained using MO theory. Good agreement with experiment was obtained using MO coefficients for the isoelectronic Fe(CO)5. The paramagnetic contributions to the x and y components of the shift vary considerably within the series (3.3‰–5.0‰). These variations were attributed to differences in the metal–metal bonds. It was found that for a given X the shifts do not vary linearly as the atomic weight of M is changed. This was attributed to differences in the importance of π-bonding effects for the metal–metal bonds. The data suggest that in this series π-bonding effects are strongest for the Co–Sn bond.