bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous Transport Properties of a van der Waals Gas
Authors: Mountain Raymond D. , Zwanzig Robert
Published: February 2004

The contribution of the long-range potential to the transport coefficients of a van der Waals gas in the critical region are calculated using the time-correlation-function method. The microscopic currents are expanded in terms of wave-vector-dependent density fluctuations (found previously by van Kampen) whose time dependence is assumed to be described by the linearized hydrodynamic equations. Self-consistent solutions for the thermal conductivity and volume viscosity are found to diverge near the critical point. The fluctuation correction to the specific heat at constant volume is found to diverge as | T − Tc | −1 / 2. The fluctuation correction to the equation of state yields a critical point for the system which differs from the critical point of the van der Waals equation of state. In as much as the divergence in the specific heat occurs at the van der Waals critical temperature rather than at the true critical temperature, these calculations are to be viewed as indicative of the qualitative behavior of a gas in the critical region, not too near the critical point.
SCF Minimal Basis Set Calculations and Exclusive Orbitals for CN−, HCN, N3−, HN3, NCO−, and HNCO
Authors: Bonaccorsi Rosanna , Petrongolo Carlo , Scrocco Eolo , Tomasi Jacopo
Published: February 2004

The ground-state SCF wavefunctions for HCN, HN3, HNCO, and related anions were computed, using the minimal basis set of STO's (best-atom zetas). The differences in the molecular properties of the anion and the acid are discussed, also using the results of a population analysis. By means of unitary transformations the Boys' exclusive orbitals were obtained and an analysis was made of their transferability.
Ion-Molecule Reactions of NH3+ by Photoionization
Authors: Chupka W. A. , Russell M. E.
Published: February 2004

Photoionization-efficiency curves were measured for NH3+, and NH4+, and H3O+ ions in NH3 gas and in gaseous mixtures of NH3 and H2O. The results are interpreted to determine how the relative reaction cross section depends on the vibrational energy of the NH3+ ion for the reactions NH3+ + NH3→NH3+ + NH2, NH3+ + H2O→NH4 + OH. The cross section for Reaction (1) decreases with increasing vibrational energy while that for Reaction (2) is nearly independent of vibrational energy. The results are discussed in terms of the formation of an intermediate complex and in terms of stripping models. The upper limit of the proton affinity was determined to be ≥ 8.54 eV for NH3 and ≥ 7.0 eV for H2O.
Diffusion of Lead Ions in Purified NaCl Crystals
Authors: Mannion W. A. , Allen C. A. , Fredericks W. J.
Published: February 2004

The diffusion of Pb2+ in purified NaCl has been studied over the temperature range from 348° to 553°C by a radiotracer technique. Measurement of the concentration-dependent diffusion coefficient provides an estimate of the free energy of association for the Pb2+-cation vacancy complex. It was found to be 0.35 eV at 553°C and increase to 0.48 eV at 348°C. As expected the free energy of association was lower in these purified crystals than that previously measured in commercial crystals. The saturation diffusion coefficient, Dδ, is given by Ds = 0.0175 exp ( − 22 800 cal / RT) over this temperature range. The results of these experiments agree with the previous work on the NaCl-PbCl2 system and support the idea that lead ion impurities are more stably bound to a substitutional cation site in KCl than NaCl.
Valence-Bond Theory for Simple Hydrocarbon Molecules, Radicals, and Ions
Authors: Simonetta Massimo , Gianinetti Ermanno , Vandoni Ida
Published: February 2004

Valence-bond (VB) theory is formulated in a general form, to be applied to states of any multiplicity, with inclusion of both spin and orbital degeneracy. Structures are related to products of spin functions, the leading terms, and a one-to-one correspondence is established between these products and extended Rumer diagrams. A relationship is also found with genealogical spin functions. The leading terms can be directly used in the calculation of energy eigenvalues and eigenvectors. Applications to simple hydrocarbon systems are shown, and the results are compared with experimental data.
Relative Interaction Radii for Quenching of Triplet-State Molecules
Authors: Siegel Seymour , Judeikis Henry S.
Published: February 2004

The relative efficiencies with which O2, NO, and Xe enhance the transition from the excited triplet state to the ground state in naphthalene have been determined from static experiments. Essentially, the experiments consisted of the observation of the steady-state phosphorescent emission intensity and the intensity of the electron spin resonance (ESR) signal of the triplet-state moelcules as functions of added quencher. All measurements were made in 3-methylpentane (3-MeP) glass solutions at 77°K, where material diffusion is minimized. The data were analyzed in terms of the expression N / N0 = exp{ − [0.0025(Rq)3Cq]}, where N and N0 are the steady-state naphthalene triplet-state concentrations in the presence and absence of added quencher, respectively, Rq is an effective interaction distance for the quenching process, and Cq is the concentration of added quencher. This equation has previously been shown to be an adequate approximation for interaction mechanisms that are controlled by electron exchange overlap integrals. The values of Rq derived from the experimental data are 10.5 ± 0.3, 13.1 ± 0.2, and 5.8 ± 0.4 Å for O2, NO, and Xe, respectively. Corresponding values for quenching of phenanthrene triplet-state molecules by naphthalene and for naphthalene-naphthalene energy transfer are 13.6 ± 0.1 and 12 ± 1 Å, respectively. Analysis of the emission and ESR data shows that the mechanisms of quenching by NO and O2 are essentially radiationless while the Xe perturbation affects mainly the radiative transition probability. The derived results are discussed in terms of triplet-state quenching by energy transfer to the quencher and by the enhancement of intramolecular triplet-singlet intersystem crossing. Since NO does not have the necessary energy levels for energy transfer from naphthalene to proceed, the result that the value for Rq for NO is larger than that for O2 indicates that energy transfer probably does not occur in the O2 case either.
Symmetry Breaking Instabilities in Dissipative Systems. II
Authors: Prigogine I. , Lefever R.
Published: February 2004

The thermodynamic theory of symmetry breaking instabilities in dissipative systems is presented. Several kinetic schemes which lead to an unstable behavior are indicated. The role of diffusion is studied in a more detailed way. Moreover we devote some attention to the problem of occurrence of time order in dissipative systems. It is concluded that there exists now a firm theoretical basis for the understanding of chemical dissipative structures. It may therefore be stated that a theoretical basis also exists for the understanding of structural and functional order in chemical open systems.
Molecular Collisions. VI. Diagrammatic Methods
Authors: Curtiss C. F.
Published: February 2004

The expressions, developed in previous papers of this series, for the coefficients in spherical harmonic expansions of the degeneracy-averaged cross sections for collisions between diatomic molecules are reformulated. The reformulation is based on the introduction of a new basis set of functions in the expansion of the wavefunctions. In the new basis set, the three basic angular momenta of the problem (the angular momenta of each of the molecules and that associated with the relative motion) are treated symmetrically. The manipulation of the vector coupling coefficients is facilitated by the use of diagrammatic methods.
Reconsideration of the Internal Tetramethylsilane Reference for Proton Magnetic Resonance Studies
Authors: Laszlo Pierre , Speert Arnold , Ottinger Robert , Reisse Jacques
Published: February 2004

The hypotheses implicit in the choice of tetramethylsilane (TMS) as an internal reference for liquid-phase proton magnetic resonance spectra are examined. Experiments are designed to test the postulated chemical inertness, and the equality of van der Waals shifts for TMS and the solute. It is found that TMS, as well as GeMe4, or PbMe4, gives rise to interactions with aromatic solvents such as pyridine, nitrobenzene, benzaldehyde, benzonitrile, or aniline. The apparent heat of formation for these complexes are in the 1-2-kcal/mole range, while the observed chemical shifts are of the order of 0.10-0.15 ppm. Caution is therefore urged in the use of TMS, and suitable molecules, not presenting these effects, are suggested for internal referencing.
Nature of the Two-Electron Chemical Bond. VII. Multicenter Bonds and H3+
Authors: Christoffersen Ralph E. , Shull Harrison
Published: February 2004

The nature of the chemical bonding in H3+ has been studied by means of a natural spin–orbital analysis of a previously calculated wavefunction. H3+ is shown to resemble closely its united-atom analog, Li+, and the Hartree–Fock energy of H3+ is estimated to be −1.301 hartrees. Also, electron-density plots are presented in order to clarify the physical picture of the bonding in H3+, and suggestions are made as to how further calculations might proceed most efficiently.
Influence of Preferential Diffusion on the Stability of a Laminar Flame
Authors: Parlange Jean-Yves
Published: February 2004

The stability of a laminar flame subjected to a small perturbation is examined. The case of a reaction involving one species much lighter than the others is considered. An analysis of the basic equations governing a reactive mixture gives the dependence of the flame speed on the flame curvature. Stability criteria are then deduced. The analysis also confirms in quantitative terms the theory that preferential diffusion tends to stabilize (or destabilize) a flame whenever the deficient component of the mixture is also the less (or more) mobile component, i.e., with higher molecular weight. The analysis also predicts that preferential diffusion will tend to stabilize the flame if the more mobile species is a product of the reaction.
Concentration of Clusters in Nucleation and the Classical Phase Integral
Authors: Lothe Jens , Pound G. M.
Published: February 2004

A classical phase integral treatment of the equilibrium concentration of clusters in homogeneous nucleation from the vapor is discussed. It is concluded that the motions of a stationary cluster, i.e., a cluster in a bulk liquid, are more nearly those of translational and torsional vibration than free translation and rotation in a large free volume. In this case one returns to the original Lothe-Pound equation. Accordingly, the 1017 factor of correction to classical homogeneous nucleation theory in condensation still remains.
Effect of Side-Group Interactions on the Mean Dimensions of Vinyl Polymers
Authors: Naghizadeh Jamshid , Bruns Wolfgang
Published: February 2004

Mean-square end-to-end distances for stereoregular vinyl polymers with interacting side groups are calculated. It is found that the steric interaction of the side groups always results in a shrinkage of the molecule as a whole, the effect being more pronounced for the syndiotactic conformation. As the side-group diameter increases, both isotactic and syndiotactic polymers tend to a limiting configuration which is probably helical. It is proposed that the difference in the degree of shrinkage between isotactic and syndiotactic polymers may be used as a criterion for measuring tacticity of partially tactic polymers.
Symmetry Coordinates and Factorization of Vibrational Problems for Crystals with Symmorphic Space Groups
Authors: Oehler O. , Günthard Hs. H.
Published: February 2004

In this paper a method is presented for construction of symmetry coordinates for crystals with symmorphic space groups. By using projection operators for both the translation group and the rotational part of the space group, formulas for symmetry coordinates are given, which reduce the vibrational problem into irreducible blocks under both the translational group and the little group Ĝk Further, a short discussion is given for selection rules for infrared and Raman transitions and the importance of the dispersion surface in analyzing empirical spectra is pointed out.
Electrical Conductivity of AgI to 100 kbar
Authors: Schock Robert N. , Katz Samuel
Published: February 2004

The electrical conductivity of AgI has been determined to 100 kbar at room temperature, using a 1-kc/sec 20-V pulse as source. Conductivity increases with pressure in the low-pressure phase, stable to 2.5 kbar, and then decreases in the two high-pressure phases. The increase in the low-pressure phase is in agreement with its negative thermal expansion. A reversal of slope above 45 kbar in the cubic (NaCl-type) phase is explained in terms of the formation of I3−, recently reported from spectroscopic studies, in amounts decreasing with pressure to 70 ± 5 kbar, where I3− is no longer present.
Relaxation Times for the Volume Viscosity of Simple Fluids
Authors: Mountain Raymond D.
Published: February 2004

Effective relaxation times for the volume viscosity of a corresponding-states fluid in the dense-gas region are calculated using low-frequency volume viscosity data and previously developed estimates of high-frequency elastic moduli. The times are found to be on the order of 10−13 sec.
Magnetic Susceptibilities of Metallic V2O3 Single Crystals
Authors: Arnold Donald J. , Mires Raymond W.
Published: February 2004

The magnetic susceptibilities of single-crystal V2O3 have been measured by the Faraday method along and perpendicular to the trigonal axis between 300° and 700°K. Both χ‖ and χ⊥ have a high-temperature transition, as was expected, which occurs over a range of temperature from 450° to 550°K. An approximate fit of the data can be obtained with a Curie-Weiss law including a temperature-independent term with one set of parameters below 400°K and a different set above 550°K. It is found that the reciprocal susceptibility curve over the entire temperature range is at least cubic in T, indicating a rather complicated temperature dependence for the density of states function in the band approximation.
Soluble Model for Fibrous Structures with Steric Constraints
Authors: Gennes P.-G. de
Published: February 2004

We consider a set of thin, long, flexible chains in two dimensions. The chains are in thermal equilibrium under a strong unidirectional stretching force. Configurations where different chains intersect each other are excluded. The chain configurations yn(x) are interpreted as the trajectories of an assembly of quantum mechanical particles, x playing the role of the time. The model is thus brought into correspondence with a one-dimensional gas of free fermions, and can be solved exactly. The system of chains has no long-range order, but a remarkably strong short-range order: the x-ray form factor, for a wave vector q normal to the stretching direction, shows a sharp peak at q = 2kF, where kF is the Fermi wave vector of the associated set of particles.
Matrix-Isolation Study of the Reaction of Atomic and Molecular Fluorine with Carbon Atoms. The Infrared Spectra of Normal and 13C-Substituted CF2 and CF3
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

Carbon atoms, resulting from the photolysis of cyanogen azide, are found to react with molecular fluorine in an argon matrix at 14°K to produce CF2. The use of carbon-13 has led to confirmation of the previous assignment of features at 1073 and 1191 cm−1 to 13CF2 present in natural abundance. Using recent structural data on CF2 and the 12CF2 and 13CF2 frequencies, it has been possible to calculate the complete valence force potential of CF2. Values of the potential constants are compared with those of the related species NF2 and OF2. When the sample is subjected to radiation of wavelengths effective in photolyzing F2, CF3 is also produced. Sufficient yields of both 12CF3 and 13CF3 have been obtained for observation of all four vibrational fundamentals. Data have been fitted to a four-constant valence force potential. Agreement is most satisfactory for a C3v structure with a deviation of 13° from planarity. Using this structure, the thermodynamic properties of CF3 have been estimated.
Ionization of Strong Electrolytes. X. Proton Magnetic Resonance of the Ternary System HClO4-DClO4-H2O-D2O
Authors: Duerst Richard W.
Published: February 2004

New measurements of the nuclear magnetic resonance (NMR) of perchloric acid solutions furnish results of higher accuracy (about 0.002 ppm in the chemical shift) between 0° and 65°C. Discrepancies in the degrees of dissociation derived from older NMR data and Raman intensities are ascribed to short-comings in the earlier interpretation. Extension of the measurements to deuterium solutions furnishes information to be used in the discussion of the molecular state of the acid and of the hydrogen ion.
Neutron Diffraction from Liquid Carbon Tetrachloride
Authors: Rao K. R.
Published: February 2004

The structure of liquid carbon tetrachloride has been studied by neutron diffraction. The theoretical basis of neutron diffraction from multiatomic liquids is discussed in terms of polyatomic and molecular assemblages. The data is analyzed using these models. The parameters obtained in this study agree with those obtained from x-ray and electron diffraction.
Heat Capacity of Silver Iodide. II. Theory
Authors: Perrott C. M. , Fletcher N. H.
Published: February 2004

Experiment has shown that the specific heat of stoichiometric α-AgI is abnormally large, Cυ ranging from 18 cal/mole·°C at 150°C to 26 cal/mole·°C at 400°C. This result is explained as an order–disorder transition among silver ions and silver ion vacancies on six sublattices in the structure. Because of the complex nature of the lattice sites, each of which consists of a cluster of seven nonequivalent potential wells, there is also a major anomalous contribution to the specific heat from the vibrational partition function. In addition there may be a small contribution from a coupled disordering of iodide ions. The behavior of nonstoichiometric α-AgI, which has Cυ ≈ 12 cal / mole·°C, is attributed to essentially complete disordering above the phase transition at 150°C together with a modification of the vibrational potentials.
Oxygen-17 NMR and Copper EPR Linewidths in Aqueous Solutions of Copper(II) Ion and 2,2′-Dipyridine
Authors: Noack Manfred , Gordon Gilbert
Published: February 2004

Between 0° and 60°C the transverse relaxation rate of oxygen-17 nuclei in water is increased in proportion to the concentration of diaquobis (2,2′-dipyridine) copper(II) which exists in equilibrium with the tris(chelate) species in solutions of tris(2,2′-dipyridine) copper(II) nitrate. The excess relaxation rate 1 / T2p due to the presence of the paramagnetic ions is controlled by the rate of relaxation of oxygen-17 nuclei in the coordination sphere of the [Cu(dipy)2(OH2)2]+ + species where the paramagnetic electron–oxygen-17 hyperfine interaction AL / h is of the order of 1.0 × 107 Hz. This value is large in comparison with the one previously reported for diaquobis (ethylenediamine) copper(II), where the two water molecules occupy positions trans with respect to each other on the long axis of the Jahn–Teller distorted complex. The X-band EPR spectrum of an ethanol–water glass where 2,2′-dipyridine/copper(II) ratio is 2.00 indicates that the cis and the trans isomers of the diaquobis (2,2′-dipyridine) copper(II) species are present in the glass. In aqueous solutions at 24°C only one disubstituted species can be observed in the EPR spectrum. It is assumed that this spectrum is predominantly due to the cis-diaquo isomer which may exist in equilibrium with small amounts of the trans isomer. Lower limits of the electron spin–lattice relaxation times and the apparent tumbling correlation times at 25°C were obtained from the X-band EPR spectra for the tetraaquo (2,2′-dipyridine), the diaquobis (2,2′-dipyridine), and the tris-(2,2′-dipyride) copper(II) species. The tumbling correlation time for the latter species is unusually low. It is proposed that the phenomenon can be explained by applying the previously discussed concept of the dynamical Jahn–Teller effect to complex ions in aqueous solutions.
Stability Criterion for the Localization of an Excess Electron in a Nonpolar Fluid
Authors: Springett B. E. , Jortner Joshua , Cohen Morrel H.
Published: February 2004

In this paper we consider the properties of an excess electron in the nonpolar dense fluids 3He, 4He, Ne, Ar, and H2. The energy of the quasifree electron state was estimated through the use of an approximate polarization potential and of pseudopotential theory, together with average Wigner–Seitz boundary conditions. The Wigner–Seitz approximation was also applied to the study of the localized state. A stability criterion was derived for the localization of an excess electron in a dense fluid of nonpolar molecules. The stability criterion is expressed in terms of a relation between the energy of the quasifree electron state and the bubble surface energy. Three cases of physical interest which can be distinguished are those of the existence of a quasifree state, the existence of a metastable bubble, and the formation of an energetically stable bubble. The stability criterion predicts that excess electron states in liquid He and in liquid He, should be localized, the excess electron state in liquid Ar should be quasifree, while liquid neon provides a borderline case between the stable and the metastable bubble. The available experimental data concerning the energy barrier for adiabatic electron injection and electron mobilities in liquid He, liquid H2, and liquid Ar are consistent with the results of the present treatment.
Integral Equation Methods in the Computation of Equilibrium Properties of Ionic Solutions
Authors: Rasaiah Jayendran C. , Friedman Harold L.
Published: February 2004

Computations have been made for a system of charged hard spheres with parameters chosen to correspond to an aqueous solution of a 1 − 1 electrolyte in the range from 0.001 to 1M. Correlation functions were computed by the analogues of the HNC and PY integral equations due to Allnatt in which the integral equations are constructed after the Mayer resummation has been performed on the expansion of g(r). Activity and osmotic coefficients are computed both by the compressibility and pressure equations and tested for consistency. Based on this test and others, including a comparison with computations published by Carley, it is concluded that the HNC equation gives very accurate results for this primitive model at least up to 1M. The accurate results show that the effect of the excluded volume of the hard-sphere cores has been considerably underestimated in earlier treatments of the primitive model.
Spin Degeneracy in the AMO Method. Excited States of the Benzene Molecule
Authors: Lunell Sten , Lindner Peter
Published: February 2004

The spin-degeneracy problem in the alternant molecular-orbital (AMO) method, as applied to excited states of the benzene molecule, is investigated. The results obtained using the full nine-dimensional triplet spin space and the five-dimensional quintet space show in the one-parameter method an energy improvement over the ones obtained by a conventional AMO treatment of 0.659 eV for the B31u state and 0.975 eV for the A31g state. When two mixing parameters are used the corresponding improvements are much smaller, 0.029 eV and 0.032 eV, respectively. Results are also presented for some additional states, not occurring in the ordinary AMO method.
Energy Distribution of Energetic Atoms in a Gaseous Medium. II. Elastic Scattering by a Spherical Two-Term Potential Composed of a Hard and a Soft Term
Authors: Baer M.
Published: February 2004

The energy distribution function n(E) for energetic particles in a gaseous medium is treated (classically), assuming the particles to be scattered by a potential of the form V(r) = ∞;0 ≤ r ≤ R = A / rs;R < r ≤∞. The function n(E) is computed using the Boltzmann integral equation with the probability function g(E, E′) as the kernel. A method is described for the computation of g(E, E′) for a potential V(r) + ΔV(r) if it is known for the potential V(r). This method is used to represent g(E, E′) in an analytic explicit form for the above potential. Substituting g(E, E′) in the Boltzmann equation, the function n(E) is computed following some approximations.
Pressure Dependence of the Elastic Moduli of Liquid Glycerol
Authors: Slie W. M. , Madigosky W. M.
Published: February 2004

Ultrasonic measurements were made of the longitudinal sound velocity, the absorption coefficient, and the shear impedance of liquid glycerol at constant temperatures over the pressure range 1 − 4000 kg/cm2. Low- and high-frequency limiting compressional moduli and the high-frequency shear modulus were obtained from the measurements. The relaxational moduli were found to increase linearly with pressure. A reduction of the data showed that the width of the distribution of acoustic relaxation times, shear and compressional, is independent of pressure and temperature over the region studied. Low-frequency absorption measurements made at 26°C as a function of pressure showed the ratio of the bulk to the shear viscosity to be pressure independent. It was observed that the ratio of the acoustic compressional relaxation time to the dielectric relaxation time was independent of pressure. However, it is noted that the width of the distribution of relaxation times for the two processes behaved differently as a function of pressure.
Adsorption of Flexible Macromolecules. IV. Effect of Solvent–Solute Interactions, Solute Concentration, and Molecular Weight
Authors: Silberberg A.
Published: February 2004

The adsorption of a linear flexible macromolecule to a plane interface brings about a change in its conformational topology. Instead of an isotropic random coil (single three-dimensional random walk) the molecule becomes a cooperative structure of adsorbed segment trains (two-dimensional random walks; average length PS) alternating with free standing loops (barrier restricted three-dimensional random walks; average length PB). These adsorbed macromolecules generate a surface-attached phase of a thickness proportional to PB in which the segment concentration φB is considerably different from the concentration φ* in the bulk equilibrium phase and from the concentration θ in the surface proper. An approach is developed for deriving the configurational factor and the configurational energy in the partition function of such a composite system in the Bragg–Williams approximation using a lattice model. The parameters of the adsorbed phase (θ, φB) and the adsorbed macromolecules [PB, PS, p = PS / (PB+ PS)] are determined as functions of the bulk equilibrium phase concentration (φ*), the molecular weight (P), the polymer flexibility (adaptibility to the surface) parameter (γBγS), and the polymer–solvent (χ) and the polymer–surface energy interaction parameter (χS). Two cases are discussed, an athermal polymer solvent mixture (χ = 0) and a θ-solvent mixture (χ = 0.5). It is shown that concentration and solvent effects considerably alter the results obtained for the isolated macromolecule. Whereas in the case of the isolated macromolecule, a molecular-weight dependence of the conformation arose only as a result of end effects at the point of desorption, considerable changes in configuration are introduced due to the concentration, solvent, and molecular-weight dependence of the segment activity parameter α. The experimentally observed concentration and molecular-weight dependence of the amount adsorbed (θ / p) and the loop size (PB) are found to be qualitatively and quantitatively predicted by the model. It turns out that the concentration θ in the surface phase in immediate contact with the adsorbent is (for given P and χ) primarily determined by χS, while the concentration φB and the loop size PB, characterizing the diffuse surface-attached bulk phase, are primarily a function of φ*. The change in surface tension Δσ in the case of a free-solvent-air interface, i.e., the equation of state of the surface layer, is also computed.
Dissociation Energies of Group VIa Gaseous Homonuclear Diatomic Molecules. I. Sulfur
Authors: Budininkas P. , Edwards R. K. , Wahlbeck P. G.
Published: February 2004

A simultaneous Knudsen-torsion effusion experiment has been performed to establish equilibrium constants for the equilibrium S2(g)⇌2S(g). The gas was supplied from elemental sulfur vaporized from one-half of an alumina double oven to the other half from which effusion took place. Thrid-law values for the dissociation energy of S2(g) average to 101.7 ± 2.9 kcal/mole. As a test of the method, the dissociation energy of I2(g) was determined as 36.17 ± 0.77 kcal/mole in comparison with an accepted value of 35.538 kcal/mole.
Kinetic-Theory Deviations from Blanc's Law of Ion Mobilities
Authors: Sandler Stanley I. , Mason E. A.
Published: February 2004

Ion mobilities in gas mixtures are investigated by rigorous kinetic theory. It is shown that the Einstein relation between mobility and diffusion coefficient is exact in higher approximations, contrary to previous conjectures, and an explicit expression for the deviations from Blanc's law for ions in a binary gas mixture is obtained in second Chapman–Enskog approximation. Numerical calculations show that deviations from Blanc's law are usually small, as expected, but that systems with large deviations are possible. The results apply generally to any tracer diffusion, and are not limited to ions.
Analysis of Fluorescence Spectra of Rare-Earth Chelates. II. Dipyridyl Complexes of Europic Chloride
Authors: Filipescu Nicolae , Bjorklund Sven , McAvoy Nelson , Degnan John
Published: February 2004

The emission spectra of two dipyridyl complexes of EuCl3 were analyzed in detail treating the ligand field as a perturbation on the free-ion levels. The ligand-field parameters were calculated from the splitting in the F71 and F72 levels of the Eu3 + ion without assuming a known molecular geometry and the model suggested by these parameters is discussed. In addition, the ligand-field parameters are used to calculate interatomic distances and to compare the coordinative properties of water and dipyridyl ligands. The method developed for deriving and verifying the geometrical arrangement and interatomic distances from fluorescence spectra proves to be a powerful tool.
Nernst-Planck Equations and the Electroneutrality and Donnan Equilibrium Assumptions
Authors: MacGillivray A. D.
Published: February 2004

The Nernst-Planck flux equations and Poisson's equation are used to describe the transport of ions across a membrane carrying a fixed charge. The resulting problem is studied using a perturbation theory in order to derive the so-called “electroneutrality” condition as a certain limiting case. It is found that the electroneutrality condition is a consequence of Poisson's equation when a certain dimensionless parameter is small. It is also shown that a Donnan equilibrium at the membrane boundaries is a consequence of the Nernst-Planck equations when this dimensionless parameter is small, and a separate assumption of such an equilibrium is redundant. The small parameter can be interpreted as the ratio of a Debye length and the membrane thickness.
Separation of Isotopic Mixtures of Polyatomic Gases by Thermal-Diffusion Columns: Interpretation of Data on Oxygen
Authors: Raman S. , Saxena S. C. , Watson W. W.
Published: February 2004

The extension of Furry and Jones theory of thermal-diffusion columns (or more appropriately its generalized version given by Saxena and Raman) to pure polyatomic gases by Youssef and Hanna is used to interpret the experimental results of Narten and Landau on oxygen. It is found that the results obtained on the basis of extended theory are in better agreement with the experimental values by a few percent than the predictions of the simpler theory of Furry and Jones which is applicable only to pure monatomic gases. The disagreement between the theory and experiment is still relatively larger than the difference between the results of simple and extended theories.
Evidence for Slow Rotation Around the sec-Alkyl-to-Nitrogen Bond in Some N ,N-Di-sec-alkyl Amides
Authors: Siddall T. H. , Stewart W. E.
Published: February 2004

The methine proton signals (\–CH/) of certain N,N-di-2-propyl amides were shown to broaden selectively as the temperature is lowered. For N,N-di-2-propyl isobutyramide, the high-field methine signal broadened around room temperature, but sharpened again between −50° and −60°C. For other related amides, the low-field methine signals broke up into subsets of signals at low temperature. This broadening and multiplicity is interpreted as evidence for slow rotation around the 2-propyl-to-nitrogen bonds. This sort of behavior is viewed as potentially a serious complication in determining rotation rates by PMR-signal-shape analysis for rotors to which the 2-propyl and related groups are attached.
Quantum-Mechanical Treatment of Inelastic Collisions. II. Exchange Reactions
Authors: Diestler Dennis J. , McKoy Vincent
Published: February 2004

The theory for the quantum-mechanical treatment of inelastic collisions developed in the first paper of this series is extended to treat collinear, electronically adiabatic exchange reactions. The formalism is applied to three model potential energy surfaces for the exchange of identical particles. The calculated reaction probabilities are reasonable and two independent checks indicate that they are reliable.
Vibration Spectra of Polyglycine
Authors: Gupta V. D. , Trevino S. , Boutin H.
Published: February 2004

Dispersion curves for the polyglycine I chain are calculated for both the in-plane and out-of-plane modes of vibration, and the force constants are fitted by comparison with observed infrared frequencies. Frequency distributions for polyglycine I and polyglycine II are calculated from inelastic neutron scattering. The intensity difference of the C–N torsional band between polyglycine I and polyglycine II suggests the presence of additional C–H···O-type hydrogen bonding between chains in the helical (II) form. An estimate of the sum of conformational and lattice energy difference in the two forms is made.
Radiative Lifetimes of BBr and of Ultraviolet Emissions in Electron-Beam Excited BBr3 Gas
Authors: Lutz Barry L. , Hesser James E.
Published: February 2004

The radiative lifetime of BBr in the A 1Π state is determined by the phase-shift method to be τ = 25.6 ± 5.0 nsec. Comparison of the experimentally determined electronic transition moments for the A 1Π→X 1Σ+ transitions in BF, BCl, and BBr is made. Phase measurements made in an unidentified emission system, excited in BBr3 gas and extending from about 2200 to 3700 Å, are also briefly described.
Electron Production by Associative Detachment of O– Ions with NO, CO, and H2
Authors: Moruzzi J. L. , Ekin J. W. , Phelps A. V.
Published: February 2004

Electron currents resulting from associative-detachment processes involving O– ions have been observed in a drift tube containing mixtures of oxygen and either hydrogen, carbon monoxide, or nitric oxide. The associative-detachment rate coefficients are obtained from analyses of the electron current waveforms. The results indicate that the associative detachment proceeds by a two-body process. The observed rate coefficients are consistent with results obtained from studies of O– destruction using mass spectrometric techniques. Associative detachment rate coefficients of 2.2, 6.5, and 7.5 × 10− 10 cm3 sec− 1 have been measured at near-thermal ion energies for the O– + NO, O– + CO, and the O– + H2 reactions, respectively. The average energy of the O– ions ranged from thermal up to 0.16 eV. A search for a reaction between O2– and CO was unsuccessful indicating that the rate coefficient of this reaction is less than 10− 14 cm3 sec− 1.
Magnetic-Dependent Frequency Shift Arising from Interaction of Two Paramagnetic Spin Types
Authors: Kaplan J. I.
Published: February 2004

It is shown that in a rigid lattice the previously discarded part of the spin–spin interaction a12(S1+ S2− + S1− S2+), where S1 and S2 are two types of nonequivalent spins, leads to a shift of the resonant frequencies by a term of the form Δ2ν / (ν01 −ν02), where Δ2ν is the order of the second moment of the absorption line about either resonant frequency.
Calculation of Natural Orbitals and Wavefunctions by Perturbation Theory
Authors: Davidson Ernest R.
Published: February 2004

A computationally convenient formulation of perturbation theory is developed. In this formulation either the SCF wavefunction or the SCF function plus important corrections may be used as a trial function. Corrections to the trial function are expanded in powers of the residual error. The reduced density matrices may be expanded in a series in this error. If the SCF function is used as the trial function, parts of the density matrix are needed to second order in the error to determine the natural orbitals and geminals to zeroth order.
Evaporation of Submicron Platinum Particles in a Shock Tube
Authors: Falk T. J.
Published: February 2004

A series of shock-tube experiments was carried out to determine the evaporation rate of submicron platinum particles suspended in xenon-argon and pure xenon carrier gases. The particle suspensions were produced by electrically exploding platinum wire in the carrier gases in a chamber attached to the end of the shock tube. Visible radiation from the shock-heated aerosols was recorded by a drum camera viewing a strip along the centerline of the shock tube and by a photomultiplier viewing a point near the shock-tube end wall. The duration of the short pulse, ∼100 μsec, of intense continuum radiation behind the reflected shock was used to determine approximately the evaporation time of the particles and, more precisely, the temperature dependence of the particle-evaporation time. The experimental results confirmed an analytical prediction that the platinum particles could be vaporized readily in the short high-temperature residence time available in a shock tube. Furthermore, since the experimental temperature dependence of the evaporation time agreed with theory and since this agreement is sensitive to the saturation vapor pressure assumed for platinum, the results appear to confirm the accuracy of the tabulated (by Hultgren et al.) vapor pressure of platinum at high temperatures ( ≈ 3700°K). The technique described provides a useful method for introducing metallic test samples into shock tubes, and it further suggests an experimental approach to the determination of metallic vapor pressures at high temperatures.
Zeeman Effect in the (0, 0) Band of OD
Authors: Thakur S. N. , Rai D. K. , Singh N. L.
Published: February 2004

The rotational structure of the (0, 0) band of the 2Σ+−2Πinv system of OD has been photographed with and without magnetic field. The Zeeman splittings are clearly resolved in some of the lines whereas in the other cases only a shift in the intensity maxima is observed. These splittings and shifts have been measured and correlated with the predictions of Hill and Van Vleck. The polarization characteristics have also been studied.
NMR Study of Ferroelectric LiNbO3 and LiTaO3. II
Authors: Peterson G. E. , Bridenbaugh P. M.
Published: February 2004

A study of the 7Li nuclear magnetic resonance in a LiTaO3 single crystal is made and the electric field gradient at the lithium site is determined. Electric-field-gradient calculations indicate that the net charge on the tantalum is +1.21 while that on the oxygen is −0.74. This shows that the tantalate ion is predominantly convalently bonded. The 93Nb resonance in a LiNbO3 single crystal is also studied and the quadrupole coupling constant is found to be 22.02 Mc/sec.
Photoionization Cross Sections for N and O+
Authors: Henry Ronald J. W.
Published: February 2004

Photoionization cross sections for atomic nitrogen are presented for wavelengths longer than 150 Å. Multichannel expressions, in the dipole approximation, are used to calculate cross sections for ejection of an outer subshell electron. The effect of coupling between final state channels is to bring the dipole velocity and length forms of the cross sections into slightly better agreement with each other. Single channel expressions, in the dipole approximation, are used to calculate cross sections for the ejection of an inner subshell electron. Cross sections, calculated in the dipole velocity approximation, are in good agreement with experimental results of Comes and Elzer, except for wavelengths where autoionization occurs. Photoionization cross sections for singly ionized oxygen are presented for wavelengths longer than 100 Å.
Exchange Effects in the Degenerate Perturbation Theory of Intermolecular Potentials
Authors: Micha David A.
Published: February 2004

The contribution of electron exchange to intermolecular potentials is studied using the operator form of perturbation theory, when the noninteracting system of atoms or molecules is degenerate. A symmetry-adapted, degenerate perturbation theory is developed, including the almost-degeneracy case. Perturbation expansions are given up to second order in the energy. Differential equations for the perturbed wave-functions are obtained, as well as their associated variational principles.
Microwave-Optical Double Resonance Using Circularly Polarized Light: Spectrum of Yb3 + in CaWO4
Authors: Kiel A. , Crane G. R.
Published: February 2004

A double-resonance technique using circularly polarized light and microwave paramagnetic resonance is described. The use of the circular polarization will, in many cases, allow one to uniquely determine the representations of the states being probed. Satisfactory signal levels are obtained in most cases where Kramers doublets are being investigated. This technique is applied to CaWO4: Yb3+. Several interesting results are obtained including definite proof that there is considerable magnetic-dipole character in one of the optical transitions and very little in the others. The satellite structure of the lines is discussed but the nature of these extra lines is still an open question.
PVT Properties of Water. II. Virial Coefficients in the Range 150°–450°C without Independent Measurement of Vapor Volumes
Authors: Kell G. S. , McLaurin G. E. , Whalley E.
Published: February 2004

The equation of state of steam has been determined at 25° intervals from 150° to 450°C by measuring the mass of water injected into a high-temperature vessel as a function of pressure. The observations have been analyzed by a new method that does not require an independent volume of the vessel and are reported as the second and third virial coefficients and as empirical equations for them. The standard error of the second virial coefficient, taking account of the effects of experimental scatter and of truncation of the virial equation, which are comparable at 450°C, is 3% at 150° and 1% at 450°C. The Stockmayer potential fits the second virial coefficient fairly well, but predicts the wrong form for the third.
NMR and EPR Line-Broadening Effects of Vanadyl Ion in N,N-Dimethylformamide
Authors: Jordan Robert B. , Angerman Neil S.
Published: February 2004

The temperature dependence of the NMR linewidths of the formyl proton in solutions of VO2+ in N,N-dimethylformamide (DMF) indicates that proton relaxation is controlled by outer-sphere dipole–dipole interactions, chemical exchange, and inner-sphere dipole–dipole interactions, in the temperature ranges −55°–+6°, +7°–107°, and 108°–150°, respectively. At 25°C the rate constant for chemical exchange is (2.3 / n) × 103sec−1, ΔH† = 7.25 kcal / mole, and ΔS† = (−18.2 − 4.58 logn) eu, where n is the number of exchanging DMF molecules. The linewidths of the EPR spectrum of VO2+ in DMF solutions have been interpreted in terms of the theory developed by Kivelson. The rotational correlation time, τc = 1.2 × 10−10sec, calculated from this theory is shown to be consistent with the observed EPR linewidths and adequately explains the dipole–dipole line broadening observed in the NMR spectra.
Electron-Diffraction Investigation of the Hexafluorides of Tungsten, Osmium, Iridium, Uranium, Neptunium, and Plutonium
Authors: Kimura Masao , Schomaker Verner , Smith Darwin W. , Weinstock Bernard
Published: February 2004

An electron-diffraction investigation has been made by the sector–microphotometer method on WF6, OsF6, IrF6, UF6, NpF6, and PuF6. The photographs of all these compounds reflect a phase shift which if not accounted for leads to asymmetric structures for the molecules. It sets in at smaller values of s = 4πλ−1sin(θ / 2) the heavier the molecule and the greater the electron wavelength. There is good evidence for the symmetrical octahedral structure of all the compounds. The metal–fluorine distances were found to be 1.833 Å (W–F), 1.831 Å (Os–F), 1.830 Å(Ir–F), 1.996 Å (U–F), 1.981 Å (Np–F), and 1.971 Å (Pu–F), with estimated limits of error of ±0.008 Å except for ±0.010 Å for Pu–F.
Excitation Energy Transfer Chromium–Chromium from the Cation to the Anion in [Cr urea6][Cr(CN)6]·3H2O
Authors: Gausmann Hans , Schläfer Hans L.
Published: February 2004

Luminescence measurements with crystalline [Cr urea6][Cr(CN)6]·3H2O using light of 580 mμ and 435 mμ for excitation clearly indicate an excitation energy transfer from chromium(III) in the cation to chromium(III) in the anion.
Nature of Isomeric-Transition-Induced Bromine-82 Reactions with CH4 and CD4
Authors: Nicholas J. Blair , Rack Edward P.
Published: February 2004

The role of excess kinetic energy and thermal processes in the 82Br reaction in gaseous CH4 and CD4 activated by 82mBr isomeric transition (IT) was determined using rare-gas and bromine additives. Possible isotope effects were investigated between (n, γ-induced 80Br and 80mBr and between CH4 and CD4 target molecules. The “freeze–thaw” technique and (n, γ) “in-reactor” technique were employed in determining the 82Br organic yields. The effects of He, Kr, Xe, and Br2 additives on the reaction of CH4 and CD4 with 82Br activated by the (IT) process are presented. The data appear to extrapolate, at zero mole fraction CH4, to 3.7% ± 0.5% for the He, Kr, and Xe additives and to 0% for Br2. This would indicate that 7.4% minus 3.7% is formed via excess kinetic-energy processes and that 3.7% of the organic 82Br is formed via thermal (kinetic-energy-independent) processes, probably involving Br+ ions in their first two excited states, P13 and P03. The data suggest the absence of a target molecule isotope effect between CH4 and CD4 in the 82Br(IT)-activated process, but does suggest a target molecule isotope effect for (n, γ-activated bromine reactions. The data for bromine reactions involving excess kinetic energy were analyzed using the kinetic theory of hot reactions. The reactivity integral values I were found to be very low. The kinetic theory showed good internal consistency for (IT)-activated bromine reactions. Experimental data showed the absence of any isotope effect between (n, γ)-induced 80mBr and 80Br reaction in CH4. The use of HBr as a source molecule was reinvestigated in the CD4 system and found to give organic yields higher than those of Br2 systems at low mole fractions. This difference diminished at higher HBr concentrations.
Spectral Distribution of Light Scattered by Monodisperse Rigid Rods
Authors: Pecora R.
Published: February 2004

The spectral distribution of light scattered from an infinitely dilute solution of monodisperse, optically isotropic, rigid rods is investigated. The contributions to the total scattered intensity of terms dependent on the rotational diffusion coefficient are calculated as a function of the product of lengths of the rod and the scattering vector. It is found that rotational diffusion contributions become important in scattering from long rods at large scattering angles.