bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic Arrangement of Au(100) and Related Metal Overlayer Surface Structures. I
Authors: Palmberg P. W. , Rhodin T. N.
Published: February 2004

It has been shown, through analysis of simple overlayer structures consisting of a monolayer of Au or Ag on Cu(100) and Pd(100) surfaces, that Au atoms have an abnormal tendency to contract when positioned in a surface environment. This strong tendency for reduced interatomic spacing of Au surface layers is related to the atomically rearranged Au(100) surface, which consists of a hexagonal layer of Au atoms superimposed on a square array of substrate atoms. The driving force for rearrangement is interpreted in terms of the extreme sensitivity of the effective valency of Au to its atomistic environment. It is concluded that this interpretation of surface rearrangement is consistent with other unique properties of gold reported for binding energies of molecules in the vapor, and features of the band structure. In addition to providing information regarding the Au(100) surface structure, examination of metal overlayer structures has shown that pseudomorphism occurs during early growth stages of Ag and Au on the Pd(100) surface. Surface alloying of Au and Cu on the Cu(100) and on the Au (100) surfaces are also discussed.
Analysis of Low-Energy Electron-Diffraction Patterns from Simple Overlayer Surface Structures. II
Authors: Palmberg P. W. , Rhodin T. N.
Published: February 2004

The role of multiple diffraction and overlayer distortion in low-energy electron diffraction from simple overlayer structures is discussed. In a development of the multiple-diffraction approach from scattering theory, the contribution of evanescent waves, scattered from the substrate or overlayer, to the intensity of multiple-diffraction beams is included. This generalized multiple-diffraction treatment is applied to a simple Ag-covered Cu(100) surface structure and shown to be adequate for explaining salient features of the observed pattern. The contribution of overlayer distortion to the pattern from the same structure is also considered and shown to be significant at high energy. It is concluded that in the very low energy range, multiple-diffraction effects are very likely dominant in determining pattern intensity.
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Conduction in Organic Polymers
Authors: Klöpffer W. , Rabenhorst H.
Published: February 2004

A polyurethane was synthesized from bi- and tri-functional isocyanates and N,Ns-bis(β-hydroxyethyl)-p-dimethylaminoaniline (BHDA) as hydroxy compound. In this polyurethane BHDA acts as electron donor and can be doped with bromine such that its conductivity increases as a function of the concentration by several orders of magnitude, compared with the undoped polymer. On the basis of spectroscopic measurements, of measurements of the Seebeck coefficient, and of the found concentration dependence, conductivity is shown to be due to holes.
Mössbauer Effect and the Dynamics of the Molecular Solid SnI4
Authors: Hazony Y.
Published: February 2004

The available Mössbauer data on 119Sn and 129I in solid SnI4 are analyzed in terms of a detailed molecular-dynamical model to give characteristic Einstein temperatures for the intermolecular translational and rotational vibrations: θl = 44°K and θrot = 66°K. θl is very close to the observed (ir) antitranslational vibrational frequency (48°K) of the eight molecules in the unit cell. The calculated specific heat, based on the present analysis, is consistent with the experimental results for Cp.
Kinetic Energy of Molecules That Traverse an Excess-Energy Barrier During Sublimation
Authors: Mar Raymond W. , Searcy Alan W.
Published: February 2004

The flux of molecules that evaporate from a free surface of gallium nitride in vacuo and the corresponding force imposed on the surface were independently measured by the Langmuir and torsion–Langmuir methods. Comparison of the results shows that the kinetic energy of the escaping vapor molecules is that expected for equilibrium with the surface. For gallium nitride, therefore, it is proved that vapor molecules that evaporate by crossing an energy barrier higher than the equilibrium energy of sublimation are not at a higher average temperature than the surface from which they evaporate.
Gaseous Metal Nitrides. III. On the Dissociation Energy of Thorium Mononitride and Predicted Dissociation Energies of Diatomic Group III–VI Transition-Metal Nitrides
Authors: Gingerich Karl A.
Published: February 2004

Mass-spectrometric evidence for the existence of gaseous thorium mononitride over a nitrogen-containing thorium–boron–phosphorus alloy has been obtained. The enthalpies ΔH°298 of the reactions ThN(g) = Th(g) + 0.5N2(g) and ThP(g) + 0.5N2(g) = ThN(g) + 0.5P2(g) have been calculated from the experimentally determined partial pressures of the reactants as 23.1 ± 6.0 and 7.0 ± 5.0 kcal/mole. Combined with published thermodynamic data these reaction enthalpies yield the respective dissociation energy D°298, the heat of formation, ΔH°f,298, and the heat of sublimation, ΔH°s,298 of 138.0 ± 8, 112.5 ± 7.5, and 203.1 ± 10 kcal/mole for gaseous ThN. The dissociation energies of the diatomic nitrides of the Group III–VI transition metals have been estimated on the basis of empirical correlations by Colin and Goldfinger and by Pauling. The values, which range from 96 kcal/mole for CrN to 145 kcal/mole for TaN, are explained in terms of a strong ionic contribution to the bonding. On the basis of the calculated dissociation energies and published thermodynamic data, the corresponding heats of formation and heats of sublimation have also been estimated.
Pseudonatural Orbitals as a Basis for the Superposition of Configurations. II. Energy Surface for Linear H3
Authors: Edmiston C. , Krauss M.
Published: February 2004

A superposition of configurations (SOC) trial function is applied to the calculation of the H3 energy surface. The convergence of the SOC trial function is improved by constructing the configurations with approximate or pseudonatural orbitals (PNO). For a given atomic-function basis the PNO exhaust the accuracy of that basis in relatively few configurations compared to the total of all possible configurations. Gaussian-type functions (GTF) are then practicable as a basis for a SOC trial function. Results are presented for the linear H3 energy surface. The error when one hydrogen is removed to infinity is 0.1 eV, and an extrapolation of this error yields a “probable” barrier energy of 0.53 eV or 12 kcal.
Determination of Eucken Factor from Relative Change in Thermal Conductivity of Gas Mixtures. Ortho–Parahydrogen Mixtures at 77°K
Authors: Harris Lee B.
Published: February 2004

At 77°K the measured change in thermal conductivity of hydrogen caused by a change in the relative proportions of ortho- and parahydrogen can be used to determine the dimensionless parameter δ (introduced by Hirschfelder in his formula for the “modified Eucken correction”) which is a measure of the contribution of rotational energy to the thermal conductivity of a polyatomic gas. The present method, which is very reproducible and is not sensitive to systematic errors in the measurement of absolute thermal conductivity, yields δ = 0.73 ± 0.04. An analogous method, using the variation of thermal conductivity at 311°K of a H2–Ar mixture as the proportion of H2 is increased, yields δ = 0.76, which is in excellent agreement with values previously obtained by other investigators from absolute measurements of thermal conductivity and Prandtl number. These experimental values of δ are lower than Hirschfelder's theoretical values. Possible reasons for this discrepancy are discussed.
Vibrational–Vibrational–Translational Energy Transfer between Two Diatomic Molecules
Authors: Zelechow Ann , Rapp Donald , Sharp Terry E.
Published: February 2004

A semiclassical calculation of transition probabilities for vibrational–vibrational–translational energy transfer in a collision of two diatomic molecules is presented. The collision model is approximate, utilizing a collinear collision of harmonic oscillators with an exponential repulsion between center atoms. The method of Kerner and Treanor is used to solve the Schrödinger equation with linearized potential in the oscillator coordinates. Our procedure is a logical extension of the Treanor method to diatomic–diatomic collisions. Closed form analytical results are obtained for this model. The general magnitudes and trends of the probabilities are expected to be indicative of the behavior of real molecules. General formulas for the probabilities of processes of the type AB(n1) + BA(n2) → AB(n1′) + BA(n2′) as a function of collision velocity are presented. Special attention is given to “resonant” energy transfer where n1′ + n2′ = n1 + n2.
Further Study of Umbrella vs Bridged Geometries: SCF–MO and CI Calculations for C2H6++ and Ammonia Borane
Authors: Peyerimhoff Sigrid D. , Buenker Robert J.
Published: February 2004

The potential surfaces and molecular properties of ammonia borane BNH6 and certain positive ions of ethane are investigated by means of SCF–MO and CI calculations for these systems. The role a single molecular orbital plays in determining whether the equilibrium configuration of A2H6 and related molecules possess umbrella or bridged arrangements of their hydrogen atoms is re-emphasized by the work. The calculations also indicate that differences in the effectiveness of boron and carbon p AO's restrict the class of molecules with bound states in umbrella conformations to those containing carbon (or nitrogen) atoms; at the same time it appears that only boron compounds can have bound states for bridged hydrogen arrangements. Even though BHN6 has less symmetry than A2H6 systems its geometry is also found to be easily interpretable in terms of the behavior of one of its MO's, the 2b1→2e, and because of the basic similarity between the latter and its C2H6 counterpart, the molecule as a whole is also observed to favor an umbrella geometry; further comparison finds ammonia borane to possess a smaller total binding energy, major force constant, and minimum ionization potential than does ethane. Charge-density contour diagrams clearly show that BNH6 is characterized by a weak pσ dative bond, originating from an N→B charge transfer which, in turn, produces a rather large experimental dipole moment of 4.9 D; the calculated result from the best wavefunction obtained (total energy estimated to be 0.1 hartree above Hartree–Fock limit) is 5.71 D. Finally a large CI calculation is found to produce only a small effect on the single determinantal representation of the ground state; only far-uv electronic transitions are found, with the lowest singlet–singlet (1E←1A1) occurring at 74 000 cm−1.
Question of Energy Migration in Liquid Benzene and Some of Its Derivatives. II. Studies of Foreign Quenching of Luminescence
Authors: Ludwig P. K. , Amata C. D.
Published: February 2004

Quenching of luminescence of benzene, toluene, p-xylene, and mesitylene and of their solutions in n-nonane by CCl4 is studied under conditions of steady-state and nonsteady-state uv excitation. An increase of the specific rates of quenching with concentration of aromatic is observed when the data are treated by a simple Stern–Volmer reaction mechanism. Consideration of the presence of excimers in these systems shows, however, that the specific rate of quenching of excited monomers of the aromatics is invariant with concentration. The specific rate of excimer quenching, on the other hand, is found to be concentration dependent. A simple model is suggested to explain the observations, and the validity of the hypothesis regarding energy migration in these systems is discussed.
Rayleigh Scattering: Orientational Relaxation in Liquids
Authors: Pinnow D. A. , Candau S. J. , Litovitz T. A.
Published: February 2004

A systematic investigation of orientational relaxation in liquids has been initiated employing the technique of Rayleigh scattering. The experimental results are interpreted based on an approximate theory which is developed and justified. Scattering spectra from 15 different liquids, including the homologous alkyl bromides and polyethylene glycols as well as glycerol, 1,3-butanediol, and n-octyl alcohol, were obtained as a function of temperature using a 6328-Å Ne–He laser source and a Fabry–Perot interferometer. All spectra were found to have approximately Lorentzian form symmetric about the source frequency, which implies molecular reorientation is a relaxational process. Also, the width of these Lorentzian lines (which is reciprocally related to the orientational relaxation time) increased with increasing temperature in such a way that an effective orientational activation enthalpy was determined. In both the alkyl bromide and polyethylene glycol series, increased molecular size resulted in increased relaxation time, which is explained using both activation-enthalpy and free-volume approaches. The measured orientational relaxation times which reflect motion of the induced dipole moments are compared with dielectric relaxation times associated with the permanent moments and mechanical relaxation times determined ultrasonically. This comparison provides additional information about the detailed nature of the reorientation mechanism. For example since orientational relaxation is shown to be governed by rotation of ellipsoidal-shaped molecules about their minor axes, it is concluded that mechanical motions are more nearly about major axes. In addition, it is possible to determine whether reorientation is a diffusion, jump, or an intermediate process. Experimental results indicate molecules in n-octyl alcohol and probably in the alkyl bromides reorient by a diffusional process and that glycerol molecules reorient by rather large jumps, while 1,3-butanediol is an intermediate case. These results are in excellent agreement with predictions based upon the McCuffie–Litovitz explanation for the distribution of dielectric relaxation times.
One-Dimensional Model for Exchange Forces
Authors: Certain Phillip R.
Published: February 2004

Four different types of perturbation theories for the exchange forces between two atoms are applied to the lowest gerade and ungerade state of a simple one-dimensional model. It is shown that the second-order energy in one of the expansions (the Eisenschitz–London, van der Avoird, or Hirschfelder HAV expansion) exhibits undesirable behavior in the limit corresponding to large internuclear distances.
Phase Transitions in Two-Dimensional Lattice Gases of Hard-Core Molecules. The Triangular Lattice
Authors: Orban J. , Bellemans A.
Published: February 2004

The thermodynamic properties of assemblies of molecules with a hard core on a triangular lattice have been investigated by the matrix method and by series expansions. Three particular cases have been considered (denoted as B, C, D), corresponding, respectively, to exclusion ranges extending up to second-, third-, and fourth-neighboring sites. Case A (i.e., exclusion on first-neighboring sites only) has been studied previously by other authors, who concluded to the existence of a second-order continuous transition at high density. For all three cases B, C, and D, there is a good evidence for a first-order phase change of the fluid–solid type, similar to the transition observed for hard disks and hard spheres.
Interrelation of the Virial Coefficients
Authors: Holleran Eugene M.
Published: February 2004

An equation of the form F(T, B, C, D, ···) = 0, in which the temperature T is the only independent variable, is presented to interrelate the virial coefficients, B, C, D, ···, which are functions of temperature only. The equation is derived from the experimental observation that temperature and density are linearly related at unit compressibility factor. Further relations are presented according to which the value of any virial coefficient at the Boyle temperature can be found from the temperature derivatives of the previous coefficients at that point. It is shown that the theoretical virial coefficients of the Lennard-Jones potential, which are known through the fifth coefficient E, obey the interrelation closely, and an estimate of the sixth coefficient is made at two temperatures. The coefficients of the Stockmayer potential for polar molecules also appear to conform. These results tend to confirm the validity of the unit compressibility law. Experimental coefficients are considered briefly, and the interrelation is suggested as a guide for estimating and eliminating the errors usually inherent in the determination of experimental virial coefficients from PVT data.
Fourth-Order Vibration–Rotation Hamiltonian of the Nonlinear XYX Molecule
Authors: Yallabandi Krishna K. , Parker Paul M.
Published: February 2004

Detailed expressions in terms of fundamental molecular parameters are given for the fourth-order centrifugal distortion constants of the nonlinear XYX molecule. It is shown how these expressions can be used for the determination of the cubic potential constants of the XYX molecule if they are considered in conjunction with the reduced-Hamiltonian theory of Watson. Three reduced Hamiltonians are treated in detail, and a generalization of Watson's theory is presented, and its need is justified.
Atom-Formation Rates behind Shock Waves in Hydrogen and the Effect of Added Oxygen
Authors: Myerson A. L. , Watt W. S.
Published: February 2004

A direct isothermal measurement has been made of the rate of formation of atomic hydrogen behind shock waves in hydrogen–argon mixtures. This has been accomplished by using atomic resonance absorption spectrophotometry at the Lyman-α line of both 1H and 2H. The observations were made in an ultrahighpurity shock tube. Absorption coefficients for the atoms were determined experimentally. The hydrogen–argon dissociation rate is given by the expression kH2−Ar = 2.23 × 1012T1 / 2exp(−92 600 / RT) cm3mole−1·sec−1 over the temperature range 2290°–3790°K. The hydrogen molecule was found to be five times more effective than argon as a collision partner. Because of the sensitivity of the technique, it was also possible to determine quantitatively the catalytic effect of the addition of small amounts of oxygen. From these observations an expression kH−O2 = 6.0 × 1012T1 / 2exp(−17 750/RT) cm3mole−1·sec−1 was obtained for the reaction H + O2 = OH + O over the temperature range 1700°–2700°K.
Dynamics of Free Liquid Films
Authors: Felderhof B. U.
Published: February 2004

The dynamics of free liquid films is studied from an electrohydrodynamic point of view for the case where stability of the film is determined by the attractive van der Waals force and by the repulsive force arising from the overlap of diffuse electric double layers. There are two modes, a squeezing mode and a stretching mode, and the dispersion equations for these modes are obtained. The long wavelength limit is studied in detail and is related to results obtained from the thermodynamic theory of fluctuations.
Adiabatic Approximation for Nonreactive, Subexcitation, Molecular Collisions
Authors: Levine R. D.
Published: February 2004

The decoupling approximation, which neglects the interaction between open and closed channels, is discussed and derived from the Lippmann–Schwinger variational principle. The adiabatic approximation is shown to be the “best local” decoupling approximation in that the adiabatic phase shift is the highest lower bound to the exact phase shift obtainable from a local potential.
Computational Investigation of Internal Excitation in Nonreactive Molecular Collisions: Resonances in Rotational Excitation
Authors: Levine R. D. , Johnson B. R. , Muckerman J. T. , Bernstein R. B.
Published: February 2004

Resonances in subexcitation molecular collisions are demonstrated by exact numerical solution of the close-coupled integral equations for rotational excitation including closed channels in the total-angular-momentum representation. These results serve as a reference for comparing various approximate theoretical predictions. In particular, the limitations of the adiabatic approximation are exhibited. The resonance energies can be essentially predicted by a “best local” potential approximation. The resonance line shapes are fitted by a simple Breit–Wigner form.
Spin-Extended Hartree–Fock Functions for Atomic Boron
Authors: Kaldor Uzi
Published: February 2004

A recently described method for calculating extended Hartree–Fock functions was applied to the ground state of atomic boron. The total energy was −24.5297 hartree. The calculated spin density has the correct sign, but is in poor agreement with experiment.
Inelastic Molecular Collisions: Exponential Solution of Coupled Equations for Vibration–Translation Energy Transfer
Authors: Chan Sai-Kit , Light J. C. , Lin Jeong-long
Published: February 2004

A new numerical method is used to solve the quantum-mechanical problem of energy transfer between vibrational and translational degrees of freedom in collisions between an oscillator and an atom. The dependence of the probability of vibrational excitation on the energy of the collision and the size of the truncated basis set is examined. The oscillatory dependence of this transition probability on the energy is is shown to be an artifact due to the truncation of the basis set. The new numerical method is the stepwise solution of the coupled first-order differential equations by exponentiation of the integrated coupling matrices, an application of the general method investigated by Magnus. It is shown to be fast and accurate.
Spectroscopy of K2 Using Laser-Induced Fluorescence
Authors: Tango William J. , Link John K. , Zare Richard N.
Published: February 2004

When potassium vapor contained in a cell of aluminosilicate glass at 300°C is irradiated with the 6328-Å line of the He–Ne laser, several fluorescence series are excited which originate from the B 1Πu state of the 39K2 molecule. Analysis of the fluorescence allows the spectroscopic constants (cm−1) of the X 1Σg+ ground state as measured by Loomis and Nusbaum to be corrected, giving ωe = 92.021, Be = 0.056743, ωexe = 2.829 × 10−1, αe = 1.65 × 10−4, ωeye = −2.055 × 10−3, γe = − 7.2 × 10−6, De = 8.63 × 10−8, δe = +1.5 × 10−7. The laser line is found to coincide with several molecular transitions. Three of these were determined from analysis of the spectrum to be (v″ = 0, J″ = 82) → (v′ = 7, J′ = 81), (v″ = 0, J″ = 18) → (v′ = 6, J′ = 17), and (v″ = 1, J″ = 72) → (v′ = 8, J′ = 72). Radiation from K atoms accompanying K2 excitation is also observed. It is proposed that the mechanism primarily responsible for the atomic potassium emission is the excitation transfer reaction K2*+K → K2 + K*, leaving the K2 molecule vibrationally excited.
Matrix-Isolation Study of the Vacuum-Ultraviolet Photolysis of Difluorosilane. The Infrared and Ultraviolet Spectra of the Free Radical SiF2
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

The vacuum-ultraviolet photolysis of difluorosilane in inert matrices at cryogenic temperatures has been found to lead to the stabilization of an appreciable concentration of SiF2. A system of ultraviolet absorption bands observed in a neon matrix corresponds very well with the 0v2′0–000 bands recently reported for gas-phase SiF2 produced by another technique. In an argon matrix, the bending fundamental of SiF2 appears at 343 cm−1, and the two stretching fundamentals at 843 and at 855 cm−1. Evidence is presented supporting a previous assignment of these two fundamentals to the symmetric and antisymmetric stretching modes, respectively. Carbon monoxide matrix observations indicate that H-atom detachment plays an important role in the photolysis of difluorosilane. There is no evidence for the occurrence of processes involving F-atom detachment. It appears likely that an appreciable concentration of HSiF2 is also stabilized in the present experiments.
Lattice Vibrations of Solid Cyanogen
Authors: Richardson Phillip M. , Nixon Eugene R.
Published: February 2004

The infrared and Raman spectra of the lattice vibration region of solid cyanogen are reported. All six of the pseudotranslational modes permitted by symmetry are observed in the infrared. In the Raman, seven distinct bands are observed, compared with the eight symmetry-allowed pseudorotational modes. A Lennard-Jones, quadrupole–quadrupole intermolecular potential of the type suggested by Walmsley and Pople leads to calculated lattice-mode frequencies which are in only moderately good agreement with the observed. On the other hand, a quite satisfactory fit of all of the observed frequencies is obtained by arbitrary adjustment of a single parameter ε in a crystal potential consisting of 6–12 interactions between pairs of nitrogen atoms. Infrared intensities calculated from a quadrupole-induced intensity model and Raman intensities derived from radiation field induced moments agree reasonably well with observed intensities. The atom–atom potential is also applied to solid CO2 and satisfactorily predicts the lattice mode frequencies.
Hybrid Integrals over Slater-Type Atomic Orbitals
Authors: Christoffersen Ralph E. , Ruedenberg Klaus
Published: February 2004

General formulas for the evaluation of two-center hybrid integrals over Slater-type orbitals of arbitrary integral quantum numbers (nlm) are developed. The development leads to a single numerical integration over quantities f(r) and F(r), which are required for several integrals, and require only small tables of auxiliary functions for their evaluation. Formulas that are appropriate for use on an electronic computer have been given for all auxiliary functions, in which numerical differencing has been found to be negligible. Use of this approach results in a significant lowering of the time necessary for the evaluation of hybrid integrals, without loss of accuracy.
New Aspects of the Bipolar Expansion and Molecular Multicenter Integrals
Authors: Salmon Lydia S. , Birss Fraser W. , Ruedenberg Klaus
Published: February 2004

Standard bipolar expansions contain radial functions Jl1l2 L(r1, r2, R) which depend on three variables, r1, r2, R. Using representations of Bessel functions as series of Laguerre polynomials, the J's are expanded in terms of functions of the individual variables. As a result, the inverse distance between two points is brought into the form r12−1 =  ∑ nlllml ∑ n2l2m2 Fn1l1m1, n2l2m2(R, θ, Ψ) Yl1m1(θ1, φ1)fn1l1(r1)Yl2m2(θ2, θ2)fn2l2(r2). This modified bipolar expansion is used to derive expressions for multicenter electron repulsion and nuclear attraction integrals. The method is particularly suitable for Gaussian orbitals expressed with spherical harmonics and yields compact expressions directly. For Slater-type orbitals, the multicenter energy integrals appear as series involving only integrals of the two-center overlap type. The one-center and multipole limits of the bipolar expansion are examined.
Overlap Integrals over Slater-Type Atomic Orbitals
Authors: Silver David M. , Ruedenberg Klaus
Published: February 2004

A general formula is derived for the overlap integral between two Slater-type atomic orbitals of arbitrary integer quantum numbers. The integral is expressed as a finite sum involving powers and confluent hypergeometric functions. The expressions differ substantially from previously given formulas and are particularly suitable for use with an electronic computer of large storage capacity. Computing times are quoted.
Excluded-Volume Effects in Dilute Polymer Solutions. I. Equilibrium Properties
Authors: Norisuye T. , Kawahara K. , Teramoto A. , Fujita H.
Published: February 2004

Data of the statistical radius 〈 S2 〉1 / 2 and the second virial coefficient A2 were obtained for sharp fractions of polychloroprene (PCP) in methyl ethyl ketone (MEK), n-butyl acetate, and carbon tetrachloride at 25°C and in trans-decalin at temperatures ranging from 1° to 50°C. MEK at 25°C and trans-decalin at 2°C were found to be theta solvents for PCP. From these data two dimensionless quantities defined by αs2 = 〈 S2 〉 / 〈 S2〉0and Ψ = A2M1/2[4π3/2NA( 〈 S2 〉 / M3 / 2]−1 were calculated for all combinations of molecular weight M, solvent species, and temperature, where 〈 S2 〉0 is the value of 〈 S2 〉 under θ conditions and NA is Avogadro's number. These two quantities should be functions of a single parameter z, usually known as the interaction parameter, which is proportional to M1/2. With the data for these quantities from the present experiments on PCP as well as from Berry's experiments on polystyrene, comparative tests of typical theories for the excluded-volume effects on dilute polymer solutions were attempted. The criteria used for this purpose were (a) linearity between M1/2 and z calculated from αs determined under fixed solvent conditions and (b) agreement between calculated and observed curves for Ψ against αs. It was found that, though not perfectly, the modified Flory equation for αs(z) combined with the modified Flory–Krigbaum–Orofino equation for Ψ(z) or Yamakawa's recent theories for these quantities were best consistent with the experimental data chosen. The Fixman equation and the Ptitysn equation failed to obey criterion (a).
Excluded-Volume Effects in Dilute Polymer Solutions. II. Limiting Viscosity Number
Authors: Kawahara K. , Norisuye T. , Fujita H.
Published: February 2004

Measurements of [η] were made for seven fractions of polychloroprene (PCP) in methyl ethyl ketone, n-butyl acetate, and carbon tetrachloride at 25°C and for three fractions of PCP in trans-decalin at a number of temperatures ranging from 0.05° to 65°C. On a log–log graph paper, the values of αη3( = [η]/[η]θ) calculated from these data formed a composite curve when plotted against αs3( = 〈S2〉3/2/〈S2〉03/2) obtained from light-scattering experiments under the same conditions. This curve is characterized by a relatively marked upward curvature in the vicinity of the origin, followed by a linear portion of unit slope. Its initial tangent has a slope of 0.65, which is much smaller than 0.81 predicted theoretically by Kurata and Yamakawa. Plots of αη3 vs the interaction parameter z were prepared by evaluating z for each αs by use of the Yamakawa equation. They were fitted by a single curve having a slight downward curvature, suggesting that no drainage effect manifests itself in the viscosity behavior of the systems studied. This curve explains why the familiar Stockmayer–Fixman method to treat [η] in non-θ solvent systems works, despite the fact that, as shown previously, data for αs as a function of molecular weight, solvent species, and temperature can be reasonably well described by the modified Flory or by the Yamakawa equation. Recent viscosity data of Berry on polystyrene were re-examined in terms of the present method, and it was found that his demonstration of the drainage effect on [η] is not yet conclusive.
Cooperative Excitons in a Crystal with Two Molecules per Unit Cell
Authors: Chock David P. , Rice Stuart A.
Published: February 2004

The cooperative exciton formalism of Jortner and Rice is extended to crystals with two molecules per unit cell. Both degenerate and nondegenerate crystal states are considered. A numerical estimate is made of the double-to-single-excitation-probability ratio in a specific energy level of crystalline naphthalene. The previously unassigned 32122-cm−1 level observed at low temperatures by many spectroscopists may be interpreted as a double excitation.
Vibrational Spectra of Molten Salts. V. Infrared and Raman Spectra of Some Molten Sulfates
Authors: Hester R. E. , Krishnan K.
Published: February 2004

Infrared spectra of thin films of pure alkali-metal sulfates at temperatures just above their melting points have been obtained. These indicate retention of Td symmetry by the SO42− ion, though the ν1(a1) and ν3(f2) bands move to lower frequencies as the alkali metal is changed from Li to Rb, and the formally forbidden ν2(e) mode gives rise to a very weak band, indicating some interionic interactions. Much more striking changes in the spectra are produced by addition of divalent metal or silver sulfate to a K2SO4 melt. Spectra from 40 mole % solutions of Ag(I), Mg(II), Ca(II), Sr(II), Ba(II), Zn(II), Cd(II), Pb(II), Cu(II), Co(II), and Ni(II) sulfates have been obtained. These indicate the presence of perturbed SO42− ions with C3V symmetry, and full assignments of the fundamental modes of these C3V species have been made for the Zn, Cu, Co, and Ni solutions. The Raman spectra of ZnSO4 at two different concentrations in molten K2SO4 further showed small but definite frequency differences from the corresponding infrared spectra. These differences are analyzed in terms of possible metal-complex formation and the quasilattice structure of these melts.
Dependence of Radiation-Induced Conductance of Liquid Hydrocarbons on Molecular Structure
Authors: Tewari P. H. , Freeman G. R.
Published: February 2004

The radiolytic ion mobilities u, ion-neutralization rate constant k, steady-state radiation-induced conductance κ, and free-ion yield Gfi have been measured for a number of saturated hydrocarbon liquids of different molecular shape. The values of G>fi in the following liquids at 20° were; cyclohexane, 0.11; n-hexane, 0.11; n-pentane, 0.12; 2,2-dimethylbutane, 0.40; 2,2-dimethylpropane, 0.81. The unusually high values for the last two compounds were partly associated with a current “overshoot” that occurred at the beginning of current-vs-time oscillograms that were obtained for the evaluation of k / u. The overshoot was not present in oscillograms obtained from the first three liquids. The causes of the overshoot and the high Gfi values are not known, but their magnitudes correlate with the closeness to spherical shape of the molecules. The facility of electron trapping and of electron energy loss in the subvibrational-excitation energy region are probably dependent on molecular shape and on liquid structure, in addition to electron affinities and dipole moments. The overshoot was eliminated and Gfi was reduced by adding an electron scavenger to 2,2-dimethylbutane or 2,2-dimethylpropane. Electron scavengers had little or no effect on the other liquids.
Analysis of Distortion Effects of the H2O Molecule
Authors: Bruscato Dianne Garrett , Genusa Vincent A.
Published: February 2004

The method of moments is used to determine the centrifugal-distortion constants of the water molecule. However, to obviate the inclusion of sixth-power terms of the angular-momentum operators in the Hamiltonian, an expression obtained from a second-order transformed Hamiltonian is included to determine the independent centrifugal-distortion constants. By application of the method to infrared spectral data, nine distortion constants were obtained, as were the rotational constants.
Determination of the Li–Hg Intermolecular Potential from Molecular-Beam Scattering Measurements
Authors: Olson R. E.
Published: February 2004

The experimental differential-cross-section extrema data of Groblicki and Bernstein have been analyzed and yield a family of potential parameters. These results were combined with the inferences obtainable from the glory extrema in the total cross sections of Rothe and Veneklasen to deduce a potential compatible with both experiments. The resulting potential is found to have a well depth ε = 1.70 × 10−13erg ± 3% with a size parameter rm = 3.02 Å ± 3%. The long-range coefficient is C6 = 4.4 × 10−58erg·cm6 ± 60%.
Measurement and Analysis of Mössbauer Data for Compounds Containing 125Te
Authors: Unland Mark L.
Published: February 2004

Mössbauer isomer shifts and quadrupole splittings are reported for a number of tellurium compounds. The isomer-shift data are analyzed by setting up localized orbitals and converting to their equivalent delocalized orbitals in order to calculate the electron density at the 125Te nucleus. Similarities between data for tellurium and tin compounds are noted. The theoretical calculations confirm the expectation that hydrogenic orbitals are more appropriate for calculations of electron density at a nucleus than the Slater-type orbitals generally used in molecular-orbital calculations.
Charge-Transfer Spectra of Matrix-Isolated 3d Transition-Metal Dichlorides
Authors: DeKock C. W. , Gruen D. M.
Published: February 2004

The charge-transfer spectra of MnCl2, FeCl2, CoCl2, and NiCl2 molecules isolated in argon matrices near 4.2°K have been measured. The results are consistent with the d-configuration ground states Σ6, Δ5, Φ4, and π3 deduced in earlier work from gas-phase Laporte-forbidden absorption spectra of these molecules.
Light Scattering by Spheroidal Particles Oriented by Streaming
Authors: Stevenson A. F.
Published: February 2004

Formulas are given for the intensity of light scattered by spheroidal particles which are partially oriented by streaming, as in a concentric cylinder apparatus. The calculation uses a general theory of scattering which is based on an expansion in inverse powers of the wavelength and the theory of streaming alignment developed by Peterlin and Stuart and numerically evaluated by Scheraga, Edsall, and Gadd. Different polarizations of the incident wave are taken into account. Numerical calculations have been made for a number of values of the relevant parameters, the results of which are illustrated by a series of graphs. The results should be accurate to within at least 5% if the ratio [(π × longest dimension)/wavelength] does not exceed 0.8 and the relative refractive index does not exceed 1.20.
Hydrogen Formation in the Radiolysis of Liquid n-Butane
Authors: Shida Shoji , Fujisaki Noboru , Hatano Yoshihiko
Published: February 2004

The effects of a radical scavenger (C2H4) and electron scavengers (N2O or SF6) on hydrogen formation in the radiolysis of liquid n-butane at room temperature have been studied. Further, the isotopic composition of the hydrogen from n-C4H10–n-C4D10, n-C4H10–n-C4D10—0.3M N2O, and n-C4H10–n-C4D10—0.15M C2H4 mixtures has been measured, and the ratios of unimolecular to bimolecular hydrogen formation determined for each mixture. Combining these results, the yields of six primary processes by which hydrogen is formed have been determined separately with the results that G (thermal hydrogen atom), G (hot hydrogen atom), and G(molecular hydrogen) are, respectively, 0.7, 1.4, and 0.6 by direct excitation and ionization and 0.5, 0.6, and 1.0 by neutralization, with probable errors ± 0.2. It is noticeable that the largest contribution is from hot hydrogen atoms produced by direct excitation and ionization.
Analysis of the High-Resolution Zeeman Spectra of Nitrogen Dioxide in the Near Infrared
Authors: Olman M. D. , Hause C. D.
Published: February 2004

High-resolution (∼0.03 cm−1) longitudinal Zeeman spectra in absorption and magnetic rotation spectra have been obtained for the (1, 0, 1) and (2, 0, 1) vibration–rotation bands of 14NO2 and 15NO2. Equations are derived which predict the Zeeman splittings of the molecular energy levels (neglecting nuclear spin) as a function of field and the rotational transition probabilities for the longitudinal Zeeman spectra. Computer-generated plots of the predicted Zeeman spectra show quantitative agreement with the experimental spectra at all available magnetic fields (up to 6800 G). The dependence of the observed magnetic-rotation spectra on the magnetic field strength can be understood qualitatively from the predicted Zeeman patterns.
Raman and Infrared Studies of Coupled PO4−3 Vibrations
Authors: Kravitz L. C. , Kingsley J. D. , Elkin E. L.
Published: February 2004

The vibrations of PO4−3 ions in single crystals of hexagonal Ca10(PO4)6F2 have been observed by means of polarized Raman scattering and polarized infrared reflectance. The T2(ν3) and T2(ν4) Raman vibration frequencies are each observed to split in accord with the predictions of the factor group of the unit cell. The optically active vibrational modes are also observed, and the anisotropy of the extraordinary ray frequencies have been measured. The observations are analyzed in terms of dipole–dipole interionic forces using Ewald dipole summation techniques to account for the entire phosphate lattice. Qualitative agreement between the dipole model and experiment is achieved. The roles of short-range forces and background dielectric shielding are discussed.
Background Polarization Corrections to the Davydov Splittings of Phosphate Vibrations
Authors: Kingsley J. D. , Mahan G. D. , Kravitz L. C.
Published: February 2004

The effects of the host dielectric properties on the magnitudes of the Davydov splittings and infrared oscillator strengths of the phosphate T2 vibrations in Ca10(PO4)6F2 have been calculated. The splittings and oscillator strengths are shown to depend on the magnitude of the background polarizability, which is the polarizability due to the electronic transitions and the other vibrations of the host as evaluated at each T2 frequency. The dependence of each vibrational frequency on the host dielectric properties is a function of the symmetry of the vibrational mode. The numerical values of the frequencies of the Raman-active and infrared-active modes, including the dependence of the latter on propagation direction, computed using the experimental oscillator strengths and polarizabilities, agree well with the experimentally determined frequencies.
Fluorescence of Benzene. The Effects of Solvent and Temperature on the Quantum Yield
Authors: Eastman J. W.
Published: February 2004

To investigate the mechanism of the solvent and thermal quenching of fluorescence, the absolute quantum yield of benzene excited at 254 mμ has been determined in four deaerated solvents as a function of concentration (10−4–10−2 M) and temperature (77°–330°K). In the limit of low temperature, the yield in the four solvents was found to be within experimental error (± 20%) of the yield 0.18 determined at 298°K for the vapor by Noyes, Mulac, and Harter. In the limit of high temperature, the yield approached zero in all the solvents at all concentrations. Similarities between the fluorescence properties of benzene in solution and vapor suggest that the thermal quenching may be related to an intramolecular process, not intersystem crossing, with an activation energy about 2000 cm−1, and which is induced by solute–solvent interactions.
Hydrogen Ions in the Positive Column of a Hydrogen Glow Discharge
Authors: Yamane Mikiya
Published: February 2004

A mass-spectrometric technique has been applied to the investigation of the positive column of a hydrogen glow discharge. Ions emerging out of the tube are found to be composed of major components of H+ and H3+ ions and minor component of H2+ ion over a range of E / p (the ratio of electric field strength to pressure) from about 30 to 100 V/cm·mm Hg and in a pressure range from 0.2–1.6 mm Hg. The relative density of H+ ions decreases monotonically with increasing pressure from 57% at p = 0.2 mm Hg (E / p ≑ 100) to 36% at p = 1.6 mm Hg (E / p ≑ 30), while that of H3+ ions increases from 38% at p = 0.2 mm Hg (E / p ≑ 100) to 62% at p = 1.6 mm Hg (E / p ≑ 30). The H2+ ion density decreases with increasing pressure or with decreasing E / p and is less than 10% of the total ion over the pressure range investigated. It is then found possible to obtain collision frequencies of the reactions H2++H2→H3++H and H2++H2→H++H+H2 as a function of E / p, assuming that these collision processes predominate in the plasma.
Effusion from Knudsen Cells with Conical Channels
Authors: Dunham T. E. , Hirth J. P.
Published: February 2004

Effusion from conical channels in Knudsen cells, including both vapor-transport and surface-diffusion contributions, is analyzed. A computer solution is obtained for the resulting integro-differential equations describing flow. The effects on effusion of various combinations of channel geometries and surface properties are examined. The results indicate that the relative contribution of surface diffusion increases with increasing conical angle, with decreasing channel radius, with decreasing channel-length-to-radius ratio, and with increasing surface diffusivity.
Bonding in Sandwich Compounds
Authors: Prins R. , Voorst J. D. W. van
Published: February 2004

A study is made of the bonding in sandwich compounds by means of ESR and susceptibility measurements. Data obtained for vanadocene and nickelocene are discussed in terms of various calculated MO schemes. The experimental results are compatible with the level order e2g ≲ a1g < e1g* for the highest-bonding and lowest-antibonding orbitals, all orbitals having a strong metal 3d character. The assignments given for the ground-state configurations are quantitatively checked by comparison of calculated and experimental D and g values. Both spin–orbit and spin–spin coupling are shown to give a substantial contribution to the value of D. The excitation energies used in the perturbation calculation of the DLS and g values are obtained from a ligand-field treatment of the low-energy bands in the optical absorption spectra.
Electronic Spectra of Weak-Field Fluoride Complexes of Tetravalent Neodymium
Authors: Varga Louis P. , Asprey Larned B.
Published: February 2004

Elevated temperature and pressure fluorination of Cs3NdF6, mixtures of neodymium oxide and cesium chloride containing 3:1 cesium:neodymium molar ratios, or Nd(III) dissolved in borax glass beads yielded products with absorption and fluorescence spectra characteristic of the 4f2 configuration, confirming the presence of Nd(IV). The observed levels were fitted satisfactorily using the Slater Coulomb integrals F2, F4, F6, and the spin–orbit interaction ζ as adjustable parameters in an iterative least-squares free-ion energy-level calculation. Comparison of the free-ion f2 levels of Nd4+ in intermediate coupling with literature data for Pr3+ ,Th2+, and U4+ gave excellent agreement with expected behavior.
Theoretical Calculation of the Electronic States of C2+
Authors: Verhaegen G.
Published: February 2004

Results of ab initio calculations are presented for a series of valence levels of C2+ and for the two lowest states of C2 (x 1Σg+and X′ 3Πu). Correlation energies of all the levels are estimated by a new scheme taking into account near-degeneracy effects in the molecule and in the constituent ion pairs. Results for C2 are in close agreement with experiment for equilibrium internuclear distances, vibration frequencies, term energies and dissociation energies. For C2+ the calculations show the ground state to be Σg−4 with relatively low-lying (∼ 0.6 eV) Δg2 and Πu2 levels. The electron-impact measurement for the appearance potential of C2+ is interpreted as C2(3Πu, υ = 1) → C2+(4Σg−, υ = 0). The quartet transition Σg−4 → Σu−4 is predicted to lie at 6000 Å. The major doublet transitions all lie in the infrared.
Effect of Overlap on Dispersion Energies near the van der Waals Minimum
Authors: Murrell J. N. , Shaw G.
Published: February 2004

It is shown that a single excited configuration with optimized ζ can give accurate values of the dispersion-energy coefficients of H2 and He2. The resulting wavefunctions are then used to obtain the effect of overlap on dispersion energies. It appears that this correction is small in the region of the van der Waals minimum.
EPR Study of Irradiated Zinc Acetate Dihydrate Single Crystals
Authors: Tolles W. M. , Crawford L. P. , Valenti J. L.
Published: February 2004

X-ray irradiation of zinc acetate single crystals at 77°K with subsequent examination at 133°K reveals initially an intense EPR signal due to methyl radicals. Decay of the methyl radicals is accompanied by a corresponding increase in another species shown to be the ·CH2CO2− radical. The proposed mechanism is a simple abstraction of a hydrogen atom by the methyl radical from a neighboring acetate ion. In support of this mechanism, observation of the reaction using Zn(CH2DCO2)2·2H2O indicates an isotope effect. The ·CH2CO2− radicals are produced in two magnetically distinct sites. Spectra taken over a range of temperatures reveal both the slow and rapid exchange of the hydrogen atoms. The barrier to internal rotation is 5.0 ± 1.0 kcal/mole, with less than two entropy units of activation. Parameters characterizing the ·CH2CO2− radical are determined with a 12-parameter least-squares calculation utilizing spectra taken at 55 different crystal orientations. The radical is planar with an HCH bond angle of 116.9°. The coupling constants are compared with other radicals using molecular-orbital calculations.