bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a Finite-Contact-Angle Meniscus on Kinetics in Porous Electrode Systems
Authors: Bockris J. O'M. , Cahan B. D.
Published: February 2004

The behavior of the meniscus in a static gas-electrode–gas-electrolyte system has been studied to clarify the mechanism(s) involved in the electrochemical dissolution of gaseous reactants in porous electrodes. Concurrent optical and electrochemical measurements in a specially designed cell, constructed from Teflon and fused quartz, demonstrated conclusively that although metastable thin films could be produced on the electrode by immersion followed by slow draining under high potentials (i.e., > 0.8 V with respect to the normal hydrogen electrode), these films broke down irreversibly at lower potentials, and were never observed to form spontaneously. The most stable configuration was a meniscus with a finite contact angle which was between 1° and 3°. On the basis of the observed geometry of the meniscus and a finite contact angle, a detailed second-order nonlinear nonhomogeneous differential equation of the form d2ηdx2 + F(x) dηdx + A[exp(kη) − exp(k2η)]G(x)[1 + B G(x) exp(k1η)] = 0, where F(x), G(x), A, B, k1, and k2 include only the pertinent experimental conditions (meniscus shape, exchange current, diffusion coefficient, etc.), was derived involving both concentration and activation polarization and the IR drop in the meniscus. This equation was solved numerically in complete form on a digital computer. The computed relations of current to potential were within 10% of the experimentally obtained ones for both H2 and O2 in 1N H2SO4 on Pt electrodes, without the inclusion of “calibrating” factors. The results of the computations show that the meniscus is effectively divided into three regions. In the first, near the tip, the reaction kinetics on the electrode surface is the primary limiting factor. The second region has mixed diffusion and activation limitation up to the zone where the meniscus is so thick that negligible additional currents can be drawn. This zone starts the third (inactive) region which extends down into the bulk of the solution. The experimental conditions (potential, gas pressures, etc.) determine the location of the boundaries of these regions and thus the over-all behavior of the meniscus. At moderate polarizations, over 90% of the current is produced within a very small (10−4–10−5 cm) distance from the meniscus tip.
Interpretation of the Infrared Absorption Spectra of Stannic Oxide and Titanium Dioxide (Rutile) Powders
Authors: Luxon James T. , Summitt Robert
Published: February 2004

Correlation of the absorption frequencies of powders of noncubic crystals has been achieved with the substantially different bulk-mode lattice frequencies. A general Fröhlich equation is derived which relates the ir-absorption frequencies of a powder (consisting of “small” spherical particles embedded in a matrix), to the bulk-mode lattice frequencies obtained from single-crystal reflection spectra. This equation is applied to stannic oxide and titanium dioxide (rutile). By means of electromagnetic scattering theory, the transmittance of powdered stannic oxide and rutile is computed with use of the complex refractive index obtained from bulk crystals. The absorption peaks obtained in the scattering calculations compare well with experimental results and are consistent with the generalized Fröhlich equation.
Photoionization of HCN: The Electron Affinity and Heat of Formation of CN
Authors: Berkowitz J. , Chupka W. A. , Walter T. A.
Published: February 2004

A re-examination of the photoionization of HCN has revealed two processes, HCN + hν→H + +CN−, and HCN + hν→H + +CN+e, not previously reported. The difference in threshold values for the two processes leads directly to the electron affinity for CN, 3.82 ± 0.02 eV. The threshold for the second process leads to ΔHf0°(CN) = 105.5 ± 2 kcal/mole, but ΔHf°(HCN) remains a major source of uncertainty.
Intramolecular Triplet Energy Transfer in Poly(1-vinylnaphthalene)
Authors: Cozzens Robert F. , Fox Robert B.
Published: February 2004

Poly(1-vinylnaphthalene) in a rigid glass at 77°K exhibits a delayed fluorescence due to triplet–triplet annihilation following intramolecular triplet energy transfer through the naphthalene chromophores. Delayed fluorescence does not appear in the spectrum of 1-ethylnaphthalene at equivalent concentrations, about 10−3M. Delayed emission from the polymer but not from 1-ethylnaphthalene is quenched by piperylene. End groups are more important than chain length in the control of triplet migration in the homopolymer; experiments with 1-vinylnaphthalene-methyl methacrylate copolymers, however, indicate that some minimum chain length is required for efficient annihilation.
Equation of State of Gaussian Molecules
Authors: Watts R. O. , Henderson D.
Published: February 2004

The equation of state of Gaussian molecules is calculated by three methods: Padé extrapolation based on the known virial coefficients; solution of the Percus–Yevick (PY) theory and a self-consistent generalization of the PY theory; and a perturbation treatment based on hard spheres. With the exception of the PY compressibility isotherm, the results of these methods are in close agreement and should provide very good approximations to the, as yet unknown, exact results for this system at high densities.
Role of Potential Curve Crossing in Subexcitation Molecular Collisions: Exact (Two-State) Computations vs Decoupling Approximations for Resonance Positions
Authors: Levine R. D. , Johnson B. R. , Bernstein R. B.
Published: February 2004

Exact numerical solutions for two-state curve-crossing problems in the subexcitation region are presented and discussed in terms of various decoupling schemes. These provide an approximate, single-channel description of the problem. The energies of the bound states in the (decoupled) closed channel are used as approximations for the resonance positions. The transition from a weak to a strong coupling regime is discussed and a treatment of the resonances in the intermediate coupling region using a diabatic basis is provided.
Vibrational Intensity Progression in the V ← N Transition of Ethylene
Authors: McDiarmid Ruth
Published: February 2004

The relative intensities of the vibrational subbands of the V ← N transitions of C2H4 and C2D4 have been measured and compared with the squares of the vibrational overlap integrals of two choices of one-dimensional oscillators—one hindered by a harmonic barrier and one hindered by a sinusoidal barrier. The harmonic oscillator is found to more adequately describe the experimental data. The value of the upper-state A′ rotational constant deduced from the experimental data, 5.45 cm−1, precludes structures of the V state in which the carbon atoms lie off the minimum axis of inertia. The difference between A and A′ can be explained by reducing the distance between the geminal hydrogens 5%. The electronic transition moment is shown to be independent of torsional quantum number from υ′ = 5–12 (C2H4 or υ′ = 12–18 (C2D4). In this range of υ′ for C2H4 the oscillator strength is estimated to be 0.1.
Studies in Molecular Dynamics. VII. Hard-Sphere Distribution Functions and an Augmented van der Waals Theory
Authors: Alder B. J. , Hecht C. E.
Published: February 2004

Hard-sphere radial distribution functions are evaluated in the dense fluid phase and compared to the predictions from various integral equations. Perturbation theory is then used to add various attractive potentials to the hard core in order to demonstrate the near constancy of the van der Waals energy density parameter a. The augmented van der Waals theory which replaces the parameter b by the hard-sphere equation of state and “a” by its theoretical value is then used to predict the dependence of the critical point on the shape of the intermolecular potential. The critical volume and temperature are found to be sensitively dependent on the range and depth of the intermolecular forces.
Configuration Analysis in the LCAO Molecular Orbital Theory
Authors: Baba Hiroaki , Suzuki Satoshi , Takemura Takeshi
Published: February 2004

A procedure is described which makes it possible to analyze and interpret the results of calculations performed by means of the LCAO–SCF molecular orbital method including configuration interaction (the Pariser–Parr–Pople method) in the language of the isoconjugate-hydrocarbon model, localized-orbital model, or other appropriate models. A general process is shown for expressing the wavefunctions of any electronic configurations or states based on the SCF orbitals by the corresponding wavefunctions based on “reference” orbitals. Specific formulas are given for expanding the wavefunctions of lower singlet and triplet configurations of the former type in terms of the configuration wavefunctions of the latter type. The π-electronic states of the phenol molecule are dealt with to illustrate the present analysis.
Tracer Study of Photochemically Excited Cyclobutanone-2-t and Cyclobutanone. II. Detailed Mechanism, Energetics, Unimolecular Decomposition Rates, and Intermolecular Vibrational Energy Transfer
Authors: Lee Norman E. , Lee Edward K. C.
Published: February 2004

A detailed photochemical transformation mechanism for the electronically excited cyclobutanones is proposed. It is inferred that the quantum yield of the radiationless, internal conversion process (S ↝ S0) is significantly large and varies from 0.7 at 3130-Å to 0.5 at 2480-Å excitation, while the remaining quantum yield is being attributed to the competing intersystem crossing process (S1 ↝ T1). Energetic and mechanistic differences of two nondegenerate photochemical decomposition pathways are discussed and compared to the singular thermal decomposition pathway. The rates of internal conversion, intersystem crossing (S1 ↝ T1), and the decomposition of CB*(T1) could be greater than 1 × 1011 sec−1 since no observable perturbations of these rate processes by various gases appear at a gas kinetic collision frequency of 1 × 1010 sec−1. The highly vibrationally excited CB**(S0) produced by an internal conversion process following the monochromatic photoactivation of the ground state CB(S0) decomposes unimolecularly. The observed specific rate constant k(E) of CB**(S0) for its decomposition varies from 0.7 × 1010 sec−1 at E = 93 kcal/mole to 5 × 1010 sec−1 at E = 114 kcal/mole, within the limitations of the strong collision assumption, and these experimental values of k(E)'s are in good agreement with the values of k(E) obtained with an approximate RRKM calculation. Efficiencies per collision of deactivating CB**(S0) with E = 93 kcal/mole have been determined for monatomic gases (He, Ne, Ar, Kr, and Xe), diatomic gases (H2, D2, and O2), and organic molecules (C3H6 and C3H8), and they vary from 0.06 for He to 1.00 for C3H6.
Percus–Yevick Type of Integral Equation for the Excluded Volume Problem
Authors: Curro John G. , Blatz Paul J. , Pings C. J.
Published: February 2004

A cluster expansion is written for the partition function of a polymer chain. An exact expression relating “nodal” and “elementary” graphs is presented. An analog of the Percus–Yevick approximation is made which leads to an integro-difference equation. This equation is solved exactly using a hard-core potential for the special case of the hard-core diameter equal to the polymer segment length (the “pearl-necklace” model). Results of numerical calculations are given for other values of this diameter ranging from zero to the segment length. This leads to values of γ ranging correspondingly from 1.0 to 2.0, where 〈ρ1N2〉Mγ with 〈ρ1N2〉 the mean-square end-to-end distance and M the molecular weight. The numerical results for 〈ρ1N2〉 as a function of chain length are in good agreement with the second-order perturbation theory of Fixman for small hard-core diameters.
Small Gaussian Expansions of Atomic Orbitals
Authors: Stewart Robert F.
Published: February 2004

Expansions of Clementi STO SCF AO's for some first-row atoms with GTO's have been obtained by the method of least squares. Expansion lengths vary from two to five Gaussians for each AO. In addition, Gaussian sets with constraints that the exponential parameters be shared for 1s and 2s and 2s and 2p orbital expansions are reported. For all cases a full matrix least-squares procedure was employed whereby the expansion coefficients and exponential parameters were simultaneously varied. All orbital expansions were constrained to a normalization condition. These expansions are useful for computing x-ray scattering factors and can be used in quantum-chemical studies.
Rotation–Translation Levels of a Tetrahedral Molecule in an Octahedral Cell
Authors: Friedmann H. , Shalom A. , Kimel S.
Published: February 2004

The theory of King and Hornig dealing with the rotation of a tetrahedron in an octahedral cell is extended to include the translational motion of the molecular center of mass (c.m.) with respect to the center of the cell (c.c.). Use is made of a representation diagonalizing the total angular momentum, composed of the angular momenta associated with the rotation of the molecule about its c.m. and that of the molecular c.m. relative to the c.c. Moreover, the particular symmetry of the system has been fully exploited. Closed-form expressions for the second-order energy corrections are given and used to interpret experimental data on the spectra of matrix-isolated methane.
Dispersion of the Electrically Induced Refractive-Index Anisotropy in Nonpolar Fluids
Authors: Pecora R.
Published: February 2004

A Kubo-type theory of the dispersion of the refractive-index anisotropy induced in nonpolar fluids is given to second order in the external electric field strength. The results are expressed in terms of moments of the space–time singlet and pair angular correlation functions of the fluid. This general theory is then applied to a system of nonpolar molecules with negligible angular pair correlations undergoing anisotropic rotational diffusion.
Vibrational Analysis of Polytetrafluoroethylene
Authors: Hannon M. J. , Boerio F. J. , Koenig J. L.
Published: February 2004

With the aid of newly obtained Raman data, a normal coordinate analysis has been performed on the polytetrafluoroethylene (PTFE) molecule. Calculations were made for three different helix models including the 13/6, 15/7, and planar zigzag. The frequencies corresponding to the 15/7 helix were fitted by adjusting the force field. The conformation was changed, and the changes in the frequencies for the 13/6 helix and the planar zigzag were calculated using the same force field. Changes predicted for the 13/6 helix from the normal coordinate calculations are not in agreement with those actually observed at the 19°C transition. It was therefore hypothesized that the changes in the infrared and Raman spectra at this transition were due to Raman thermal defects as suggested by Brown. The potential-energy distribution was obtained for the optically active modes of the 15/7 helix, and the eigenvectors were presented for the motions of the A modes. The dispersion curve for the 15/7 helix is presented, and the coupling which occurs between the chain stretch and the CF stretching modes is discussed.
Radiative Decay of Polyatomic Molecules
Authors: Freed Karl F. , Jortner Joshua
Published: February 2004

In this paper we present a quantum-mechanical treatment of the radiative decay of polyatomic molecules. The decay of a manifold of closely spaced coupled levels is handled by applying the Green's function formalism for the transition probability, where the matrix elements are displayed in an energy representation which involves either the Born–Oppenheimer or the molecular eigenstate basis set. General criteria are obtained for the occurrence of an irreversible intramolecular electronic relaxation process. The features of radiationless transitions in large, medium-sized, and small molecules are elucidated, deriving general expressions for the radiative decay times and for the fluorescence quantum yields. Some possibilities for studying radiative interference effects in intersystem crossing are explored. A general theoretical demonstration of the occurrence of long radiative lifetimes of small molecules is presented.
Absorption Spectrum of Ni2+ Ions in Spinel
Authors: Sakurai Takemaro , Ishigame Mareo , Arashi Haruo
Published: February 2004

Single crystals of Ni2+-doped spinel were made by using a large solar furnace in our laboratory, and their absorption spectra were measured in near-infrared, visible, and ultraviolet regions. The observed bands were analyzed according to the crystal-field theory in which the spin–orbit coupling was taken into account, and all of them were identified with the bands of Ni2+ ions not only in octahedral but also in tetrahedral site symmetry. The crystalline-field parameter Dq in both symmetries are − 1015 and 452 cm−1, respectively. Their ratio Dq(tetra) / Dq(octa) amounts to − 4.008 / 9 which shows an excellent accordance with the theoretical value − 4 / 9. By adjusting the MgO concentration, the crystals with slightly different Ni–O distance r could be obtained. From the measurement of r and Dq of these crystals, it was found that Dq varies linearly as r−5. These results are considered to show the validity of applying a point-charge model in the treatment of the problem of this kind.
Lower Bounds to Energy Eigenvalues
Authors: Mazziotti Alexander
Published: February 2004

Recently, Schwartz has considered the application of the lower-bound formulas of Temple, Weinstein, and Stevenson to molecular systems whose wavefunctions are built up from a Gaussian basis set. To test the convergence of the lower-bound formulas, he applied them to the ground state of the hydrogen atom. The results, using variationally optimized upper-bound Gaussian wavefunctions, were poor. It is demonstrated here that the convergence rate of these lower bounds can be accelerated by optimization of both linear and nonlinear parameters in the wavefunction with respect to the maximization of the lower bound. These improved results are then analyzed from the spectral-impurity and local-energy viewpoints, and it is shown that the lower-bound wavefunctions obtained are particularly suited for reproducing the slope of the wavefunction at regions very close and very far away from the nucleus. Finally, the previous lower-bound calculations of Wilets and Cherry are considered in the light of these results.
Oxidation of Propylene by Photolysis in the Presence of NO2
Authors: Jaffe S. , Grant R. C. S.
Published: February 2004

Mixtures of propylene and NO2 were photolyzed at 3660 Å, and quantum yields of NO2 consumption were determined as a function of propylene pressure, NO2 pressure, total pressure (using N2), and temperature. The quantum yields increased as a function of (C3H6) and approached a value of about 6. The rates of production of the principal products of the reaction were measured, and a mechanism is presented to explain the quantum yield behavior and the products found. The essential features of the mechanism are that O atoms produced by the photolysis of NO2 add to propylene, producing intermediates that are either stabilized by collisions or dissociate into free radicals. Nitrogen dioxide reacts rapidly with the free radicals producing stable products.
Carrier Mobility in Poly(N-Vinylcarbazole)
Authors: Szymanski A. , Labes M. M.
Published: February 2004

Transient photoconductivity experiments in poly(N-vinylcarbazole) have yielded data on the drift mobility of holes and its temperature dependence. Hole mobility is thermally activated with Ea = 0.12 eV, and the room-temperature mobility is ∼ 10−3 cm2 V−1·sec−1. An intermolecular hopping mechanism appears to be the most appropriate model for carrier transport.
Green's Function for Noninteracting Particles
Authors: Laurenzi Bernard J.
Published: February 2004

The Green's function for N identical noninteracting particles has been obtained. Some calculations in perturbation theory are explored.
Nitrogen Quadrupole Coupling Constants in Ethyl Cyanide; Coupling Constant of the Cyano Group
Authors: Li Ying Sing , Harmony Marlin D.
Published: February 2004

An investigation of the hyperfine structure of the microwave transitions of ethyl cyanide has led to the following values of the nitrogen quadrupole coupling constants: χaa = − 3.309 ± 0.033, χbb = 1.265 ± 0.013, and χcc = 2.044 ± 0.020 MHz. These results indicate the existence of cylindrical symmetry about the CN bond with a quadrupole coupling constant along the bond axis of χCN = − 4.14 ± 0.04 MHz. The coupling constants in ethyl cyanide and several other cyano compounds have been described by an extended Hückel scheme.
Diffuse Interface in a Critical Fluid Mixture
Authors: Huang J. S. , Webb W. W.
Published: February 2004

The interface between the two fluids in equilibrium at temperature T below the critical (consolute) temperature Tc of a binary mixture in a gravitational field has been observed to expand into a transition layer that thickens, while the coexisting phases become more similar and the interfacial energy vanishes as T→Tc. The effective thickness L of the transition layer has been deduced from reflectivity measurements as a function of light wavelength λ and temperature. The shape of the interface concentration distribution function has been found from the λ dependence of the reflectivity to be close to an error functon and to a function recently proposed by Fisk and Widom and distinguishable from the classical hyperbolic tangent distribution. In the range 0.02 < Δ T < 3.0°C, L∝(ΔT)−ν where ν = 0.67 ± 0.02 and ξ the appropriately defined thickness L′ = 2(Δ T / Tc)−0.67 is comparable with the correlation length of the bulk fluids for corresponding ΔT. The critical index ν, together with the critical index β for the coexistence curve, and μ for the surface tension, can be combined to test various theoretical relations amongst the critical exponents and theories of the critical interface.
Cluster Distributions on a One-Dimensional Lattice
Authors: Rawlings P. K. , Schneider F. W.
Published: February 2004

An exact and comprehensive calculation of monomer distributions on a one-dimensional Ising lattice is presented using the matrix method. The monomer sequence probabilities are expressed in terms of three parameters: the first nearest-neighbor interaction energy between bound monomers, the lattice length, and the intrinsic binding constant of a monomer to a lattice site. Graphical illustrations are given as fractional quantities which can be directly converted to concentrations for experimental systems. An expression of the average length of monomer sequences and their standard deviation is presented.
Molecular Correlation Functions and Dielectric Relaxation
Authors: Klug D. D. , Kranbuehl D. E. , Vaughan W. E.
Published: February 2004

A relation between the molecular dipolar autocorrelation function and the complex dielectric permittivity is derived using the Kubo–Kirkwood method.
Photoionization with Atomic Beams. I. Zinc Atoms between 247 and 1242Å
Authors: Harrison Halstead , Schoen Richard I. , Cairns R. B. , Schubert Keith E.
Published: February 2004

The wavelength dependences of the photoionization cross sections of zinc atoms have been measured with a modulated atomic beam and pulsed, dispersed vacuum-ultraviolet radiation. The photoions were mass analyzed, counted, and digitally demodulated. Apparatus and technique are described, and results are presented for singly charged ions at wavelengths between 247 and 1243 Å.
Thermal-Diffusion Columns and Intermolecular Potential. I. The Noble Gases Ne, Ar, Kr, and Xe
Authors: Alvarez D. González , Savirón J. M. , Yarza J. C.
Published: February 2004

A glass concentric-tube-type thermal-diffusion column is used to study column operation for inert gases. The formal criteria of how to introduce column construction faults in the formulation is investigated. It seems that the relation lnQ̄0*exp = m̄ lnQ̄0*theoret holds for all inert gases, m̄ being a geometric constant, independent of temperatures and gases in the column. Therefore, this relation provides us with a method of testing the gas interaction parameters which appear in literature.
Light-Scattering Studies of Critical Opalescence in Binary Liquid Mixtures. IV Paraffins in β,β′-Dichlorodiethyl Ether
Authors: Kao W. P. , Chu B.
Published: February 2004

A specially designed light-scattering photometer with a measurable angular range of 15°–140° and with a temperature control of better than 0.001°C was used to study the angular dependence of the scattered intensity from binary critical liquid mixtures, consisting of a homologous series of alkanes as one of the two components, and β,β′-dichlorodiethyl ether (or chlorex) as the other component. Both components were purified by preparative gas chromatography and subsequent vacuum distillation. Special care was taken to prevent contamination of the systems from moisture. Scattering data were obtained by means of cylindrical light-scattering cells of different diameters (6 and 8 mm i.d.), detectors of different slit-widths (one set consisting of two slits: 1 × 10 mm each and 20 mm apart, and the other set: 0.5 × 10 mm each and 20 mm apart) and incident light of different wavelengths (λ0 = 365, 436, and 578 mμ). Phase diagrams for n-decane–chlorex and n-dodecane–chlorex were carefully determined in order to properly locate their critical mixing points. From our studies we have observed that (1) the classical theory of Ornstein–Zernicke and Debye provides a very good representation of experimental facts in the intermediate-temperature distances over large ranges of s / λ; (2) deviations seem to exist at small temperature distances (say ΔT < 0.03°C) for the n-dodecane–chlorex system. Estimates on the exponent η show qualitative agreement with Fisher's theoretical prediction of 0.059; and (3) the reciprocal scattered intensity extrapolated to zero angle has the form lim K → 0 Ic− 1 = f[T − Tc]γ, where f and γ are constants with respect to temperature. We estimate the true value of γ to be between 1.1 and 1.3 for our systems.
Brownian Motion of Lattice-Model Polymer Chains
Authors: Iwata Kazuyoshi , Kurata Michio
Published: February 2004

The dynamical behavior of lattice-model polymer chains is studied by assuming the Markoff nature of the motion of chain elements. In accord with the Monte Carlo calculations of Verdier, the autocorrelation function obtained for the square of the end-to-end distance of a simple-cubic-lattice-model chain is in close agreement with that for a spring-bead-model chain. The diffusion equation for the lattice-model chain is also exactly similar to that for the spring-bead-model chain. The diffusion constant for a lattice element is found to be pl2 / 3 and the equivalent spring constant to be 3kT / l2. Here, l is the lattice constant, p is the probability that a given chain element moves to its adjacent lattice points in unit time, and kT has the usual meaning.
Hall Coefficient of Metal–Ammonia Solutions
Authors: Vanderhoff J. A. , Thompson J. C.
Published: February 2004

The Hall coefficient and electrical conductivity of Li–NH3, K–NH3, and Ca–NH3 solutions were measured as a function of concentration and temperature. The temperature range extended from 203–243°K and the concentration extended from metal saturation down to ≈ 4 MPM. The Hall coefficient was temperature independent for all solutions studied, but upon dilution, increased to values above the free-electron value at different electron concentrations for the monovalent and divalent solutions. The conductivity values ranged from 100–5000 Ω−1·cm−1, and dσ / dT was positive. Using an ionized impurity scattering model and an adjustable effective mass for the metal–ammonia solutions, a qualitative fit for the conductivity, Hall coefficient, and thermopower can be made in the region 4–8 MPM. The loss of degeneracy upon dilution seems to be responsible for anomalies in this region, and hence the metal–nonmetal transition can be narrowed down to the 1–4 MPM region.
Fusion Curve and Electrical Conductivity of Molten HgCl2 and HgI2 at Elevated Pressure
Authors: Darnell A. J. , McCollum W. A.
Published: February 2004

The fusion curves of HgCl2 and HgI2 were measured to a pressure of 22 kbar. The melting temperature can be represented as a function of pressure by tP = t0 + b1P + b2P2, where tP is the melting temperature in degrees Centigrade at a pressure P in kilobars; b1 and b2 are constants. Values for t0 (deg), b1 (deg kbar−1), and b2 (deg kbar−2) are 276, 259; 19.8, 17.1, and − 0.26, − 0.41, respectively. The electrical conductivities (K) of molten HgCl2 and HgI2 were measured to 805 and 620°C, respectively, at a pressure of 5.4 kbar. The electrical conductivity of HgCl2(l) was also measured from 557 to 634°C at P = 20.5 kbar. At these elevated pressures K varies exponentially with 1 / T, i.e., K ≅ A exp −  (Ek / RT). At 5.4 kbar, A = 2.13 and 0.36 (ν·cm)−1; Ek = 8.46 ± 0.14 and 2.53 ± 0.12 kcal/mole, respectively, for molten HgCl2 and HgI2. The behavior of HgCl2(l) and HgI2(l) at this elevated pressure is now typical for a strong electrolyte. This is in contrast to their behavior at ordinary pressures where HgCl2 shows a maximum in its K vs T curve and HgI2 has a negative temperature coefficient of K from the onset of melting. The conductivities of molten HgCl2 and HgI2 were also examined from 3 to 20 kbar at constant T. At 600°K, KP=20 kbar / KP=3 kbar for HgCl2 = 12.4; at 555°K this ratio for HgI2 is 1.66. Thus pressure increases the conductivity of these salts. This is attributed to a greater degree of ionic dissociation at elevated pressures.
Electronic Spectrum of Cyclobutanone
Authors: Whitlock Rodger F. , Duncan A. B. F.
Published: February 2004

The electronic spectrum of cyclobutanone is examined to 78 100 cm−1. Nine electronic transitions are found, of which five form an ns Rydberg series leading to an ionization potential of 75 444 cm−1 (9.354 eV). The remaining four transitions are assigned in order of increasing energy as π* ← n, π* ← n′, Σco* ← n, and π* ← π. Earlier vibrational analyses of the first two of these are extended and corrected, and the excitation of the carbonyl stretch mode in the π* ← n′ transition is demonstrated. Vibrational analyses are also given for the structure observed in the π* ← π and Rydberg transitions. An analysis of existing data on the electronic and photoelectron spectra of acetone is used to support the general assignment of the second electronic transition of ketones as π* ← n′. Second and third ionization potentials of cyclobutanone are predicted to be about 11.70 and 13.34 eV.
Experimental Core Polarization of Transition Ions from Electron Paramagnetic Resonance Data
Authors: McMillan J. A. , Halpern T.
Published: February 2004

Treatment of available electron paramagnetic resonance data of 2D ions of the 3d and 4d transition series taking into account the transfer of unpaired electronic density to the ligand molecules leads to experimental values of the core polarization within 20% of the theoretical estimates. Experimental values are given for Nb3+, Mo5+, Ag2+, VO2+, and Cu2+. Tentative values are also given for two 5d ions: Pt3+ and Re6+.
Core-Electron Binding Energies and Slater Atomic Shielding Constants
Authors: Snyder Lawrence C.
Published: February 2004

The Slater–Zener expression for the energy of an atom is generalized to include hypothetical states for which the Slater atomic shielding constants do not minimize the energy. The generalized energy expression is used with Slater's rules for atomic shielding constants to study the Koopmans' theorem ionization potential for core electrons and its dependence on nuclear charge and the number of valence electrons on an atom. An electronic relaxation energy for x-ray states is defined and is shown to be proportional to the number of electrons in shells outside the core hole, independent of nuclear charge, and quadratic in the change of shielding constant for each shell upon core-hole formation. Finally, arguments are given to show that the core hole should be thought of as localized, even when there are several equivalent atomic sites over which it may be delocalized.
Location of Energy Barriers. IV. Effect of Rotation and Mass on the Dynamics of Reactions A + BC
Authors: Hodgson B. A. , Polanyi J. C.
Published: February 2004

In Paper I of the present series a study was made of the effect of barrier location on the dynamics of thermoneutral reaction A + BC → AB + C, for which the atomic masses were mA=mB=mC. Two contrasting potential-energy hypersurfaces were used; on ``surface I'' the crest of the 7 kcal mole−1 energy barrier was slightly displaced (∼ 0.3 Å) into the entry valley of the collinear energy surface, whereas on ``surface II'' the crest of the barrier was displaced by the same amount into the exit valley. Precisely the same potential-energy hypersurfaces have been used in the present work as were used in Paper I. The present work was undertaken to examine the effect (a) of the inclusion of a small but significant amount of rotational energy in the reagents, and (b) of a change in reagent masses from the extreme case L+ HH ( L ≡ 1 amu, H ≡ 80 amu) to the opposite extreme H + HL. [These mass combinations were identified as extreme cases, the former giving rise to the ``light-atom anomaly'' and the latter to a maximum of ``mixed energy release,'' in earlier work, see J. Chem. Phys. 44, 1168 (1966)]. The qualitative generalizations introduced in Paper I are found to remain valid despite the introduction of variables (a) and (b), above. Of these generalizations the most important is that reagent translational energy favors reaction on surface I, whereas reagent vibration is the most favorable to reaction on surface II. If barrier location on the ``diagnostic'' collinear potential-energy surface is to be used as an approximate quantitative guide to reaction dynamics, then the diagnostic surface should be the scaled collinear surface appropriate to the particular mass combination.
Pressure-Consistent Integral Equations
Authors: Mandel Frederick , Bearman Richard J.
Published: February 2004

The behavior of the Hurst and Rowlinson—Carley—Lado pressure-consistent equations for the Lennard-Jones (6–12), hard-sphere, and Gaussian potentials and their dependence on the adjustable parameters m and φ are discussed. Numerical solutions of the Hurst and Rowlinson—Carley—Lado equations are compared with the Percus—Yevick, PY2, hypernetted chain, and Monte-Carlo results. It is shown that the pressure-consistent equations are more satisfactory for the hard-sphere potential than the Lennard-Jones potential.
Electronic Splitting between the 2B1 and 2A1 States of the NH2 Radical
Authors: Bender Charles F. , Schaefer Henry F.
Published: February 2004

Theoretical calculations are reported for the ground and first excited states of NH2. A contracted Gaussian basis of four s, two p, and one d functions is centered on the nitrogen atom, while for hydrogen two s and one p functions are used. Both self-consistent-field (SCF) and multiconfiguration first-order wave-functions have been computed, the latter using the iterative natural-orbital method. Two new theoretical ideas were tested and found useful: (a) Bunge's partitioning of degenerate spaces and (b) a procedure for generating uniform sets of starting orbitals for multiconfiguration calculations. For the 2B1 state the SCF, CI, and experimental geometries are θ=105.4°, r=1.019 Å; θ=102.7°, r=1.055 Å; θ = 103.3± 0.5, r=1.024± 0.005 Å. The analogous results for the 2A1 state are θ=141.9°, r=0.997 Å; θ144.7°, r=1.010 Å; θ = 144± 5, r=0.97–1.00 Å. For the upper 2A1 state the barrier to linearity is 1370 cm−1 in the SCF approximation, 1030 cm−1 from the correlated wavefunctions, and 770± 100 cm−1 experimentally. The 2B1—2A1 splitting Te is predicted to be 12 800 cm−1 (SCF) and 14 500 cm−1 (CI), whereas the experimental value is thought to be ∼ 11 000 cm−1. Potential curves are shown and electronic structure considerations discussed.
Pulsed Nitrogen—Proton Double Resonance Study of the Ferroelectric Transition in Triglycine Sulfate
Authors: Blinc R. , Mali M. , Osredkar R. , Prelesnik A. , Zupančič I. , Ehrenberg L.
Published: February 2004

The technique of nuclear magnetic pulsed double resonance in the rotating frame has been used to study the changes in the 14N quadrupole interactions in a triglycine sulfate (TGS) single crystal on going from the paraelectric to the ferroelectric phase. The 14N electric field gradient tensors have been determined above as well as below Tc. The most significant effect of the ferroelectric transition is a large change in the time averaged value of the C–N bond direction of glycine I and the onset of chemical nonequivalence of glycines II and III due to an ordering of the protons in the short O–H ··· O bond. The results show that the phase transition in TGS is of the order—disorder type as far as the glycine groups are concerned.
On the Constant Volume Viscous Properties of Molten Alkali Nitrates
Authors: Copeland James L. , Christie James R.
Published: February 2004

The viscosities of molten NaNO3 and KNO3 have been determined by a rolling ball technique over a pressure range from 1 to 414 bar and over temperature ranges from 328 to 444°C for NaNO3 and from 355 to 467°C for KNO3. Constant pressure activation energies, Ep = − R[d ln φ/d (1/T)]p, are fairly constant for a given salt at different pressures and are about 16.3 to 17.5 kJ for NaNO3 and about 18.2 to 19.0 kJ for KNO3, with the larger values occurring at higher pressures. There appears to be a tendency towards temperature dependent Ep values at the highest pressures employed, which could be traceable to compression forcing the melts towards a glassylike state, especially at lower temperatures. Activation volumes, Δ V* = − RT (d ln φ/d P)T, are typically from about 14 to 17 cm3 mole−1 for each melt, which are quite large values in contrast to those obtained by other workers for equivalent electrical conductance. These large ΔV* values lead to very small constant volume activation energies, Ev = − R[d ln φ/d (1/T)]v = Ep − (α/β) T Δ V*, of only about 2% to 6% of Ep. These are much smaller Ev values than those obtained in conductance work, and even in comparison to those obtained for the viscosities of ordinary nonpolar liquids. A modified Batchinski free volume model: φ = V sp, 0 (1−β P) / B − b/B, even with crude approximations for isothermal compressibility, β, and with assumed pressure independence of excluded volume, b, and the flow unit size parameter, B, gives fairly good agreement with experiment. It may be that viscous properties of fused NaNO3 and KNO3 are, then, more exactly describable by a hard-sphere free volume type of model and that the average size of a neutral flow unit is greater than that of the average charged unit involved in conductance.
Optical Bleaching and Deviations from Beer—Lambert's Law of Solutions Illuminated by a Ruby Laser. II. Sodium—Propylenediamine Solutions
Authors: Andorn M. , Bar-Eli K. H.
Published: February 2004

The bleaching of sodium solutions in propylenediamine by illumination with Q-switched ruby laser pulse was studied. The transmission-intensity curves were interpreted in terms of two absorptions, the first from the sodium anion, and the second from a metastable state whose existence was shown earlier. The results are compared with previous study on cryptocyanine.
Linear Canonical Transformations in the Theory of Vibrational-Rotational Interactions in Molecules. A Practical Closed Form N-Dimensional Procedure
Authors: Witriol Norman M.
Published: February 2004

A general N-dimensional linear transformation is written, wherein each original variable xi, pi (i=1, ···, N) is expressed in closed form as a linear function of the 2N transformed variables xi′, pi′ A set of 2N2-N relationships between the linear coefficients is then derived for the transformation to be canonical. This procedure provides one with the most general form of N-dimensional linear canonical quantum mechanical transformation, while giving the operators in closed form. The procedure is compared with the alternate method of using unitary generators, and its advantages over that method are discussed.
Ledge Dynamics in Crystal Evaporation
Authors: Surek T. , Pound G. M. , Hirth J. P.
Published: February 2004

Crystal evaporation proceeding by the terrace-ledge-kink mechanism is treated by a computer simulation technique in which ledge creation at some source is treated simultaneously with the motions and interactions of the ledges. Time dependences of the surface topography and rate of vaporization are obtained. Conditions for observing low evaporation coefficients are described.
Paramagnetic Resonance of Fe(II) Ions in Single Crystal CdCl2
Authors: Trapp Charles , Smith David , Johnson Richard
Published: February 2004

The paramagnetic resonance of Fe(II) ions in single crystal CdCl2 has been studied in order to determine the strength of the trigonal crystal field, δ, relative to that of the spin-orbit coupling parameter, λ′. The ratio δ/λ′ determines the nature of the magnetic properties of FeCl2. Kanamori originally proposed |δ/λ′|≫ 1 which leads to an effective Ising model of spin 12. We find for Fe(II) in CdCl2, however, that δ/λ′=−0.4, in qualitative agreement with the value −0.85 calculated from the magnetic susceptibility data on pure FeCl2. Thus we confirm that the magnetic properties of FeCl2 should be treated in terms of an effective spin S̃ = 1.
ESR Line Shapes for Triplets Undergoing Slow Rotational Reorientation
Authors: Freed Jack H. , Bruno Gerald V. , Polnaszek Carl
Published: February 2004

The stochastic Liouville method is applied to analyze the general problem of unsaturated ESR line shapes for triplets undergoing rotational diffusion. Detailed line shape simulations are obtained for the cases of high-, low-, and zero-field resonance, large or small values of an axially symmetric zero-field splitting, and slow through fast rotational diffusion. It is shown how all these parameters can have profound effects on the observed ESR spectra.
Proton Relaxation Times and Bromine Nuclear Quadrupole Resonance Frequencies in Bromine–Benzene 1:1 Complex
Authors: Kadaba P. K. , O'Reilly D. E. , Peterson E. M. , Scheie C. E.
Published: February 2004

Proton relaxation times (T1) were measured in Br2 · C6H6 complex from the melting point (259°K) to 130°K. T1 data exhibit a minimum which corresponds to the reorientation of the benzene ring about the sixfold axis. The mean activation energy for this process is 5.0 ± 0.3 kcal mole−1 and the correlation time for the motion is 8 × 10−11sec just below the melting point. The bromine-81 nuclear quadrupole resonance (NQR) frequency extrapolated to 0°K is 319.75 MHz. The 81Br signal is very weak and asymmetric, but appears to correspond to the Br2 · C6H6 complex. Evidence for a phase transition near 60°K is presented. As pointed out earlier by Hooper, the proximity of the bromine NQR frequency in the complex to that for the Br2 molecule in solid Br2 demonstrates that the complex is not a ``charge-transfer'' complex in the usual sense but rather is bound by van der Waals and classical electrostatic forces.
Molecular Collisions. XVI. Comparison of GPS with Classical Trajectory Calculations of Rotational Inelasticity for the Ar–N2 System
Authors: Pattengill M. D. , La Budde R. A. , Bernstein R. B. , Curtiss C. F.
Published: February 2004

The classical limit of the ``infinite order'' generalized phase shift (GPS) treatment of rotationally inelastic atom-molecule collisions was put into computationally feasible form in Paper XV of this series. It is now applied to a model problem intended to approximate thermal scattering of the Ar–N2 system (collisional energy of 32kT at 300°K), at the same time comparing its predictions with exact classical trajectory (CT) results. This comparison indicates that the present version of the GPS method over-estimates the rotational excitation and underestimates the de-excitation, while maintaining the total inelasticity at approximately the correct (CT) value. An approximate ``quantization'' of the classical results leads to an estimate of the quantal cross sections corresponding to changes by ±2, ±4, and ±6 from an initial rotor quantum state l¯=10. It is found that most of the total inelastic crosssection (of some 32 Å2) arises from the first-order-allowed transitions (Δ l=± 2).
Dielectric Behavior of Some Binary Mixtures of Polar Liquids, One Being an Alcohol
Authors: Daumezon Pierre , Heitz Roger
Published: February 2004

Dielectric constants and losses in the 50 Hz—5 MHz range are reported for some binary mixtures of an alkyl halide and an alcohol at low temperatures. The dielectric spectrum presents two absorption ranges: the low frequency region seems of the Debye type, like for the structural relaxation of alcohols; the high frequency region has two contributions, attributed to the alkyl halide molecules and the alcohol free molecules. This last region cannot be experimentally separated into two dispersion regions and in this respect is like the dielectric spectrum of mixtures between two alkyl halides in a nonpolar solvent or not. It is concluded that the high frequency region in the alkyl halide—alcohol mixture has to be linked to a cooperative process between two species of molecules.
Hydrogen Dibromide Radical: Infrared Detection through the Matrix Isolation Technique
Authors: Bondybey Vladimir , Pimentel George C. , Noble Paul N.
Published: February 2004

When hydrogen bromide–bromine–argon mixtures are passed through a glow discharge and the products are condensed at 20°K, prominent absorptions appear at 727.4, 892.1, and 1053.0 cm−1. With deuterium, these features shift to 496.1, 666, and 833 cm−1. Both deuterium and bromine isotope shifts show that these features can be assigned to the BrHBr (BrDBr) free radical in a linear, symmetric (D∞h) structure with ν3 = 727.4 (496.1) cm−1 and ν1 = 164.7 (170) cm−1. The evidence that these bands are not due to HBr2− is reviewed. The vibrational potential function for ν3 includes a large quartic term and it suggests that the hydrogen bond in HBr2 is comparable in strength to that in HBr2−.
Vapor Phase Homogeneous Nucleation and the Thermodynamic Properties of Small Clusters of Argon Atoms
Authors: McGinty David J.
Published: February 2004

The steady state rate of homogeneous nucleation in a vapor of Lennard-Jones spheres has been calculated using statistical mechanical techniques to compute the equilibrium concentrations of clusters in the vapor. All degrees of freedom of the clusters are explicitly considered. The harmonic approximation is used in the calculation of vibrational contributions to the cluster partition functions and the rigid body approximation is used in the calculation of rotational contributions. The Gibbs free energy of cluster formation as a function of cluster size is calculated and its dependence on temperature is examined. Size effects on the vibrational free energy are found to be mainly energetic rather than entropic. The rate of nucleation as a function of pressure is calculated at four temperatures and found to have a behavior similar to what would be expected from “liquid drop” model calculations.
Ab Initio Calculations of Harmonic Force Constants. V. Application to Natural Expansions
Authors: Bishop David M. , Macias A.
Published: February 2004

The analytic method of calculating force constants is extended to handle wavefunctions built from the natural orbitals obtained from a configuration interaction wavefunction. The method is applied to a series of wavefunctions for H2. No correlation between the force constant and the degree of truncation of the natural expansion is detected. In a study of some rank 1 functions for H2 (considered to be close to the SCF wavefunctions) it is found that the contribution to the force constant (k) from allowance for flexibility in the nonlinear parameters is important and that the k's for the rank 1 functions and CI wavefunctions (from which they are derived) are very similar.