bluuebunny/crossref_metadata_2025 huggingface dataset:
Second-Order Perturbation Calculation of the Hindered Rotator Model for Adsorbed Hydrogen
Authors: Evett Arthur A.
Published: January 2005

A refinement of the previously reported models for adsorbed hydrogen is presented, based on the assumption that each hydrogen atom interacts with the adsorbent by a van der Waals force of the Lennard-Jones type. The calculation is accomplished by using the previous model based on a parabolic potential well interaction, for which exact wave functions are obtained, as the zeroth-order approximation and then carrying out a second-order perturbation calculation to obtain accurate results for the Lennard-Jones type interaction. The results lead to the conclusion that agreement with data on ortho-para hydrogen separation coefficients can be obtained only by assuming a magnitude for the rotational barrier which is inconsistent with data on adsorption energies. To eliminate this discrepancy a perturbing term involving a hindrance to rotation in the plane parallel to the surface is introduced and a second-order perturbation analysis shows that such a term can lead to agreement with both separation coefficient and adsorption energy data.
Orbital Radii and the Dependence of Bond Length Upon Ionicity, Hybridization, and Bond Order
Authors: Wilmshurst J. K.
Published: January 2005

Expressions for the dependence of hybrid orbital radii upon the constituent atomic orbitals and the ionicity of the bond to be formed are given. Using accurate bond-length data (±0.005 A) and a suitable expression for bond ionicity, atomic orbital radii have been obtained for the elements of the first four periods (other than transition metals). These radii can be used to calculate bond lengths in lone molecules, ionic crystals or metals or, alternatively, the experimental internuclear distance can be used in the same manner as the nuclear quadrupole coupling constant to describe the bond parameters in some detail.
Electron Coupling of Nuclear Spins. IV. Temperature Dependence in Substituted Ethanes
Authors: Schug John C. , McMahon Paul E. , Gutowsky H. S.
Published: January 2005

The proton-proton coupling constant, AHH′, in H–C–C′–H′ groups is known to depend upon the dihedral angle, φ. Previous valence-bond calculations by Karplus have given the result that AHH′≅A0cos2φ+B.This relation is used to estimate the effects upon the average coupling constant of torsional vibrations and reorientations about the C–C′ bond. For substituted ethanes, it is found that torsional vibrations produce a modest temperature dependence, of opposite sign for the trans and gauche coupling. However, for molecules in which the potential function, V(φ), has threefold symmetry, rotational averaging leads to a cancellation of the vibrational effects, giving a temperature independent value, 〈AHH′〉, for the average coupling. This prediction has been verified in experiments on ethyl nitrate for which 〈AHH′〉 was found to have a constant value of 6.92 cps over a 100° temperature range.

When there is an energy difference, ΔE, between trans and gauche forms, ΔE determines the sign and magnitude of the temperature dependence of 〈AHH′〉; however, corrections for the vibrational effects appear desirable if accurate values of ΔE are to be obtained from such experiments. The temperature dependence of 〈AHH′〉 could not be calculated analytically for any but the simplest potential functions and simplest approximations to the torsional motions. However, it was found that the detailed form of V(φ) has but a slight effect on the results. 〈AHH′〉 is, of course, more sensitive to the functional form of A(φ).
Electronic Spectra of Dimers: Derivation of the Fundamental Vibronic Equation
Authors: Witkowski Andrzej , Moffitt William
Published: January 2005

The Hamiltonian describing the vibronic states of a dimer formed by two identical molecules is derived. The monomeric units are assumed to couple by resonance forces only and to have different equilibrium positions in the ground and excited states. The competition of these two effects is formulated mathematically. The strong coupling case occurs when the resonance forces dominate; the weak coupling case arises when the effect of the change of equilibrium positions dominates.
Mean Square Length of a Hindered Alkane Chain
Authors: Smith Richard P.
Published: January 2005

An exact formula, valid for any number of links and any constant angle between links, is derived for the mean square end-end length of a chain, subject to the following conditions. Any three successive bonds must be in a trans configuration or one of two gauche configurations. The energy of a trans configuration is lower by E (per mole) than the energy of a gauche configuration. The excluded volume problem is ignored.
Oxygen Diffusion in Periclase Crystals
Authors: Oishi Y. , Kingery W. D.
Published: January 2005

Oxygen self-diffusion coefficients have been determined for MgO crystals over the temperature range 1300–1750°C. Results can be represented by the equation D=2.5×10—6 exp (—62 400/RT). By comparison with data for alkali halides and previous measurements for aluminum oxide, diffusion is probably extrinsic in nature. The diffusion coefficient for oxygen in this material is about two orders of magnitude less than that reported in the literature for magnesium.
Microwave Spectrum, Structure, Dipole Moment, and Internal Rotation of Trimethyl Silane
Authors: Pierce Louis , Petersen D. H.
Published: January 2005

The microwave spectra of eleven isotopic species of trimethyl silane have been measured and assigned. From the observed ground state rotational constants the structural parameters of trimethyl silane are calculated to be CH  1.095 ASiH  1.489 AHCH 107∘56′SiC  1.868 ACSiC 110∘10′The equilibrium conformation is found to be the one in which each methyl group staggers the SiH and adjacent SiC bond axes. Stark effect measurements yield a dipole moment of 0.525 debye. Relative intensities of torsional satellites of (CD3)2CH3SiH have been measured and analyzed to provide information about the barrier to internal rotation in trimethyl silane. Structural changes which accompany methylation and fluorination of methyl silane are discussed.
Sublimation of Small Sodium Chloride Spheres into Argon
Authors: Whitmore D. H. , Moser J. B.
Published: January 2005

The rate of vaporization of sodium chloride into an argon atmosphere was investigated over the temperature range 726° to 770°C using a hot-stage method to follow the change of radius of a small, subliming sodium chloride sphere. In general, the pressure and temperature behavior of the empirical rate data is consistent with the kinetic law derived by Langmuir on the basis of a model which assumes that the vaporization rate is controlled by molecular diffusion of sodium chloride vapor away from the surface of the sphere undergoing sublimation.
Far Infrared Spectrum and Structure of Disiloxane
Authors: Aronson J. R. , Lord R. C. , Robinson D. W.
Published: January 2005

Study of the infrared absorption of gaseous disiloxane in the range 50–150 cm—1 shows that significant absorption is confined to the lower part of the range. A broad band with five rather flat maxima at about 56.4, 69.2, 80.1, 90.5, and 100 cm—1 is interpreted as the spectrum of the mixed vibrational and rotational transitions of a quasilinear triatomic molecule. The consequences of this model of disiloxane for the vibrational spectra of the molecule at higher frequencies are discussed and various unusual features of the spectra explained on the basis of the model.
Line Shapes of Electron Paramagnetic Resonance Signals Produced by Powders, Glasses, and Viscous Liquids
Authors: Kneubühl Fritz Kurt
Published: January 2005

The line shapes arising from randomly oriented particles in a fixed position have been calculated. It has been found that it is possible to determine the three principal g factors with relatively high accuracy and without investigating single crystals. Measurements on powders of CuCl2·2H2O and CuSO4·5H2O are used as examples. In addition, the influence of Brownian rotation in viscous liquids on line shapes has been studied. Equations have been derived for the case of high viscosities, supplementing the well-known ones given by McConnell [J. Chem. Phys. 25, 709 (1956)]. To a first approximation, the effect of decreasing viscosity can be described by an over-all diminishing line width and an unchanged line shape function. The hyperfine splittings are neglected, but can be taken into account.
Partition Function Ratios for Molecules Containing Nitrogen Isotopes
Authors: Begun G. M. , Fletcher W. H.
Published: January 2005

Nitrogen isotopic partition function ratios have been calculated for the following molecules and ions: N2, N2O, NO, NOCl, NO2, NO2—, NO3—, and N2O4. All available isotopic and anharmonic data have been used, and values of Q15/Q14 are tabulated for temperatures at intervals from 100°K to 600°K. Isotopic equilibrium constants calculated from the partition function ratios are compared with those that have been observed experimentally.
Pressure Dependence of Some Infrared and Vacuum Ultraviolet Bands Occurring in Active Nitrogen
Authors: Young Robert A.
Published: January 2005

By comparing the infrared (7000 to 11 000 A) and vacuum ultraviolet (1050 to 1350 A) nitrogen afterglow emission to the visible (5300 to 6500 A) afterglow it has been determined that: (1) all these portions of the afterglow spectrum decay identically with time; (2) the predominant emission in the vacuum ultraviolet between 1050 and 1350 A may be attributed to the Lyman-Birge-Hopfield bands from the 6, 5, 4 vibration levels and that the population of these levels is collisionally deactivated by molecular nitrogen with a probaability of 1×10—2/collision; and (3) that apparently half the intensity of the first positive infrared bands with ν′<6 are excited through an intermediate state or complex whose lifetime is no shorter than 10—7 sec and which, in the absence of collisions, does not contribute to the emission in the regions between 1050 and 11 000 A that have been monitored.
Magnetic Rotation Spectra of Nitric Oxide in the Near Infrared
Authors: Mann Glen A. , Hause C. D.
Published: January 2005

Magnetic rotation spectra of the 3–0 band at 1.8 μ and a portion of the 2–0 band at 2.7 μ of nitric oxide have been observed and recorded. Rotations in excess of 10° in fields of 2400 gauss have been observed in some cases. The P and R branch lines arising from the 2II½ states show negative rotation (counter clockwise when looking against the incident light) while the P and R branches from the II322 states show positive rotation. The Q branch signals are more complex and both positive and negative rotations are observed. Certain anomalies in the magnetic rotation spectrum of the 3–0 band are noted.
Efficiency of Energy Transfer in a Solution of PPO in Xylene
Authors: Berlman Isadore B.
Published: January 2005

The nonradiative energy transfer of an organic scintillating solution as a function of the solute concentration has been determined by three independent methods: namely, direct measurements of the fluorescent lifetime, the light output of the solvent, and the light output of the solute. The efficiency of energy transfer ranges from 12% at 0.02 g/l, to 92% at 2 g/l of PPO in xylene. The results from the three methods agree within a few percent.
Structure of Potassium Hydroxide: An X-Ray and Infrared Study
Authors: Ibers James A. , Kumamoto Junji , Snyder Robert G.
Published: January 2005

Infrared evidence has been obtained which indicates that the crystal structure of KOH reported in the literature is incorrect. A subsequent x-ray examination has shown that this is the case and has led to a structure compatible with the infrared spectrum. KOH crystallizes in the monoclinic space group C22–P21 (chosen over P21/m on the basis of the infrared evidence), with two molecules in a cell of dimensions a=3.95, b=4.00, c=5.73 A, β=103.6°. Each potassium atom is surrounded by a distorted octahedron of oxygen atoms. There is an oxygen-oxygen zigzag chain parallel to the b axis. Stereochemical arguments are advanced to suggest that the hydrogen atoms are near to or lie in the plane of the zigzag oxygen chain; infrared data obtained at —180°C for KOH and KOD are interpreted as supporting the placement of the hydrogen atoms in ordered positions along the chain with the O–H···O bonds (of length 3.35 A) nearly or exactly linear. It is argued that breaking of these hydrogen bonds will lead to the high-temperature cubic structure of KOH reported in the literature.
Charge Transfer and Fluorescence Quenching
Authors: Majumdar Dilip Kuman , Basu Sadhan
Published: January 2005

A charge-transfer-interaction mechanism has been proposed for the quenching of fluorescence of a number of polynuclear aromatic hydrocarbons by aromatic solvents, especially methylated benzenes. The quenching efficiency has been found to be in the order benzene<toluene<xylene<mesitylene, which is also the order in which ionization energy of the solvents diminishes.
Three-Body Recombination of Oxygen Atoms
Authors: Bauer Ernest , Salkoff Morris
Published: January 2005

We have made a quantum mechanical perturbed stationary state calculation of the rate of three-body recombination of oxygen atoms in the presence of an oxygen molecule as third body. The recombination is considered to take place into highly vibrationally excited states (ν=9, 10) of the A 3Σu+ state of O2. There are no adjustable parameters in the calculation. For the interaction potential we have used the results obtained in a previous calculation, which were obtained by comparison with experimental measurements of vibrational relaxation times in oxygen. At temperatures of the order 300–3000°K, the calculated recombination coefficient into these two states is of the order 1–10×10—33 cm6/sec, and agrees to within better than a factor of three with recent experimental measurements.
Charge Transfer between Atomic Hydrogen and N+ and O+
Authors: Stebbings R. F. , Fite Wade L. , Hummer David G.
Published: January 2005

The cross sections for charge transfer in collisions between atomic hydrogen and singly charged atomic ions of nitrogen and oxygen have been measured within the energy range from 400 to 10 000 ev, using modulated-beam techniques. The results are compared with recent calculations.
Photolysis of Carbon Dioxide
Authors: Mahan Bruce H.
Published: January 2005

The vacuum ultraviolet photolysis of carbon dioxide has been investigated. Kinetic data and quantum yield measurements indicate that electronically excited (1D) oxygen atoms are produced in the primary process at 1470 A and 1236 A. Such a primary process is consistent with the tentative spectral assignments which have been made for carbon dioxide.
Quantitative Considerations Concerning Catalysis at a Semiconductor Surface
Authors: Garrett C. G. B.
Published: January 2005

The theory of charge-transfer catalysis, originally proposed by Wagner and Hauffe, is set up in quantitative form. The objects of the treatment are to write down quantitative expressions for the absolute reaction rate, to show what are the consequences of the Wagner-Hauffe mechanism insofar as they concern the adsorption properties of the individual reacting materials, and to outline an experimental program for determining, by means of experiments on the semiconductor, alone and in association with each of the reacting substances in turn, the values prevailing in a practical case for the various parameters occurring in the theory.
Evidence for Internal Rotation in the Fine Structure of the Infrared Absorption of Oxygen in Silicon
Authors: Hrostowski H. J. , Alder B. J.
Published: January 2005

Interpretation of the spectra of silicon saturated with oxygen highly enriched with O18 confirms that oxygen is located in an interstitial site. The over-all features of the absorption indicate that the oxygen is in a nonlinear Si2O configuration. The fine structure in the asymmetric Si–O stretching vibration and its temperature dependence can be largely explained by motion of the oxygen in a potential barrier with six-fold symmetry. A symmetry analysis of this process predicts additional structure some of which has now been observed under higher resolution. The spectra of oxygen contaminated silicon containing 2% germanium corroborate our explanation of the fine structure.

The potential barrier hindering rotation of the oxygen about the axis joining its two bonded silicons has been ascribed to the surrounding silicon lattice. Calculation of the potential shows that as the oxygen rotates it can also wobble. Since the fine structure indicates that the ground-state splitting due to rotation is near 2 cm—1, the barrier hindering rotation is about 200 cal/mole. Calculation of this barrier then indicates that the maximum wobble angle is 0.2° and the Si–O–Si angle near 150°.
Diffusion of Weak Electrolytes
Authors: Stockmayer W. H.
Published: January 2005

An expression is obtained by standard irreversible thermodynamics for the diffusion coefficient of a weak electrolyte in rapid equilibrium with an arbitrary number of species. The general result reduces to a simple form if all mobilities are independent of concentration.
New Type of Freezing-Point Apparatus. Freezing Points of Dilute Lanthanum Chloride Solutions
Authors: Scatchard G. , Vonnegut B. , Beaumont D. W.
Published: January 2005

A new type of freezing-point apparatus is described that reduces the errors of previous types. The freezing-point depressions of aqueous lanthanum chloride solutions up to 0.04 m are adequately expressed by the Debye-Hückel approximation for ions with a=6.15 A plus a very small linear term. The ``higher terms'' are computed by combining the equations of Mayer and Kirkwood, using the tables of Poirier, and are found to be very small in this case.

The parameters for the calculation of the activity of water from freezing point depressions, for the Debye-Hückel theory, and for the Kirkwood parameter Bik are redetermined, and the more general use of Bik is discussed.
Optical and Other Electronic Properties of Polymers
Authors: Tinoco Ignacio
Published: January 2005

The properties of a polymer are related to the properties of its constituent groups and to its geometry. That is, relations between polymer wave functions and group wave functions are obtained. The equations generalize a result of Kirkwood to include the effect of time-average fields. The main assumption in the derivation is that no exchange of electrons between groups occurs. The usefulness of these wave functions is illustrated by expressions for the absorption coefficient, polarizability, optical rotation, dipole moment, and stability of a polymer.
Ultrasonic Attenuation in the Critical Region
Authors: Fixman Marshall
Published: January 2005

The interaction of forced sound waves with critical density fluctuations is discussed quantitatively. The nonlinear equations of motion are analyzed to distinguish three contributions to the instantaneous density and temperature variation: (1) the spontaneous fluctuations that are defined as the solution to an initial value problem, (2) the macroscopically observed sound wave which oscillates with harmonic time dependence, and (3) the result of an interaction between (1) and (2). The three contributions satisfy three equations, which are discussed separately. A completely general combination of these equations to compute ultrasonic absorption and attenuation is avoided, as the requisite thermodynamic and transport coefficients are inadequately known. Because, however, a thermal relaxation mechanism has previously been treated on the basis of an oversimplified multiphase picture of spontaneous fluctuations, the present calculations are carried to completion on the assumption that only the local heat capacity is affected by the density fluctuations. The sound wave together with the fluctuating heat capacity produce temperature fluctuations, whose relaxation is the source of the absorption.
Scaled Particle Theory of Fluids
Authors: Helfand E. , Reiss H. , Frisch H. L. , Lebowitz J. L.
Published: January 2005

A statistical thermodynamic theory has been developed employing distance scaling as a coupling procedure. This is an extension to real fluids of the technique applied by Reiss, Frisch, and Lebowitz to rigid-sphere systems. One considers molecules interacting with pair potential u(r), except for one particle which interacts with potential u(r/λ). This single particle, essentially a scaled version of a normal molecule, is termed a λ-cule. It is convenient to restrict discussion to potentials with rigid cores at r=a and cutoffs at γa. Attention is focused on a function, θ(λ, ρ, T), which reduces to G of footnote reference 1 in the case of rigid spheres. The pressure, chemical potential, and work of expanding a λ-cule are simply related to θ. One can write θ exactly for λ<1/2γ and simple connection conditions hold at λ=1/2γ. An integral condition and λ=∞ condition on θ also exist. While θ is not completely specified, the foregoing conditions determine much of its behavior.
Some Tests of the Superposition Approximation in the Liquid Phase
Authors: Buff Frank P. , Brout R.
Published: January 2005

The statistical mechanical theory of the concentration dependence of the pair correlation function provides a delicate test of the superposition approximation in the liquid phase. The numerical assessment is carried out directly with use of the experimental x-ray scattering function for liquid argon. It is found that the utilization of superposition in the theoretical expression produces too high a concentration dependence of the first coordination sphere of the radial distribution function. Although the superposition approximation fails for integrals possessing a pure density fluctuation origin, it becomes progressively more useful in applications in which the superposition error is damped by short-range force contributions.
Statistical Mechanics of the Nonuniform Gas
Authors: Auer P. L. , Tamor S.
Published: January 2005

The method of the previous paper is applied to the derivation of a transport equation for the nonuniform dense gas. The required short time propagator is computed by an approximation scheme based upon the assumption that the duration of a binary collision is small compared to the mean free time between collisions. A transport equation for the phase space distribution function is obtained in which the ``collision operator'' satisfies a simple integral equation. The collision operator is nonlocal in the coordinate space and hence contains interference effects between collisions and the streaming motion. The limit of infinite dilution is examined by means of a moment expansion in which case the collision operator reduces to the Boltzmann collision integral. In this limit one obtains the master equation for the nonuniform gas.
Statistical Mechanical Theory of the Viscosity Coefficients of Binary Liquid Solutions
Authors: Bearman Richard J. , Jones Peter F.
Published: January 2005

The method of the pair space linear relations is used to develop a formula for the coefficient of viscosity of a binary liquid solution from statistical mechanics. When the solution is regular a statistical-mechanical analog of the Stokes-Einstein equation is obtained in which the product of the self-diffusion coefficient and the viscosity is expressed as a composition independent average over the radial distribution function for unlike pairs. The relationship between the present theory and the results of experimental measurements of viscosity and diffusion coefficients is discussed at some length, and the Gordon equation for the mutual diffusion coefficient is derived.
Boltzmann Equation and Inverse Collisions
Authors: O'Toole J. T. , Dahler J. S.
Published: January 2005

The equations of change for the statistical distribution functions involved in the kinetic theory are examined for molecular species which interact with arbitrary central forces. It is shown that the notion of inverse encounters follows in a straightforward fashion from the fundamental Liouville equation. The analysis also establishes that it is not the usual singlet distribution function, but a particular modification thereof, which should satisfy an equation of the Boltzmann variety. Three body collision processes are briefly examined and the extension of the method to the domain of chemical kinetics discussed.
Infrared Spectra of Lithium Halide Monomers
Authors: Klemperer William , Norris W. G. , Büchler Alfred , Emslie Alfred G.
Published: January 2005

The infrared spectra of the lithium halides have been re-examined. The vibrational constants of the diatomic molecules are LiClωe=641±3ωexe=4.2±0.3LiBrωe=563.2±0.2ωexe=3.53±0.15ωeye=0.02±0.03LiIωe=498.2±0.2ωexe=3.39±0.15ωeye=0.08±0.03.The first five coefficients of the Dunham expansion of the potential energy have been obtained for lithium bromide and iodide. Rittner's ionic model has been found to give a good representation of the potential energy. The ionic-model treatment of the lithium halides has been extended to take account of the higher multipole polarizabilities of the halide ions. The introduction of quadrupole and higher polarizabilities destroys the agreement between observed and calculated spectroscopic constants which is found when only dipole polarizabilities are used.
Dissociation Energies of Diatomic Molecules
Authors: Somayajulu G. R.
Published: January 2005

Force constant, dissociation energy, and equilibrium internuclear distance in a sequence of similar diatomic molecules have been found to be related by the expression kere/D0=const. The applicability of this relationship has been shown for eighteen sequences of similar molecules. With the help of this relationship, the dissociation energies of several important diatomic molecules have been determined. Evidence has been adduced in favor of the value 170 kcal for the heat of sublimation of graphite.
Derivation of Thermodynamic Relations for Three-Dimensional Systems
Authors: Manning Francis S. , Manning William P.
Published: January 2005

The relations between the first-order derivatives of the thermodynamic properties of three-dimensional systems have been evaluated. The method of Jacobians which was used previously for simple or two-dimensional systems has been extended, and the results presented in tabular form.
Molecular Size Distribution and Gelation of Irradiated Copolymers
Authors: Inokuti Mitio
Published: January 2005

A theory is developed about the molecular size distribution in a system of copolymers which are composed of two different kinds of monomer units and undergo random crosslinking when exposed to high-energy radiations. The radiation-induced change in the molecular size distribution is described by an integro-differential equation, which we solve exactly by means of Laplace transform for an arbitrary initial distribution to obtain the number-average as well as the weight-average degree of polymerization as a function of radiation dose. Further, the gel point, or the dose required for incipient gelation, is given as a function of concentrations of the monomer units constituting the copolymeric system. The present theory, which also involves the problem of crosslinking in a mixture of two kinds of polymers as a special case, leads to a condition for gelation of such a mixture due to irradiation when crosslinking competes with main-chain scission. This condition proves to be completely independent of the initial distribution.
Potential Energy Curves for CO
Authors: Tobias Irwin , Fallon Robert J. , Vanderslice Joseph T.
Published: January 2005

Potential energy curves for the X 1Σ+, a 3πr, a′ 3Σ+, d 3Δ, e 3Σ—, A 1π, and B 1Σ+ electronic states of the CO molecule have been calculated by the Rydberg-Klein-Rees method. The curve for the A 1π state will have to bend sharply in the range between 1.9 and 2.1 A or it will have to pass through a maximum to reach the proper dissociation limit.
Halogen Bond Character in the Alkyl Halides
Authors: Dailey B. P.
Published: January 2005

The quantity (I+s2), the sum of the ionicity and s hybridization, has been calculated from nuclear quadrupole coupling data for 24 alkyl halides. The ionicity has been estimated independently from calculated values of εx, the effective charge on the halogen. The average derived values of s2, the amount of s character in the hybrid halogen bonding orbital, are 13.6% for carbon-chlorine bonds, 8.6% for carbon-bromine bonds, and 1.8% for carbon-iodine bonds.
Small Angle X-ray Scattering Study of Sodium Montmorillonite Clay Suspensions
Authors: Hight Robert , Higdon William T. , Schmidt Paul W.
Published: January 2005

Suspensions of montmorillonite clay with concentrations of ½ and 2% have been investigated by small angle x-ray scattering, with two different centrifuge fractions being studied for each concentration. At a given concentration the scattering was observed to be the same for both centrifuge fractions. The scattered intensity was always proportional to the concentration. These results are what would be expected from dilute suspensions of thin platelets of identical thickness but different surface areas. When corrections for the finite height of the collimating slits are applied to the scattering curves, good agreement with the theoretical curves for thin platelets is obtained. From the deviation between the experimental and the theoretical curves at the largest observed scattering angles, the thickness of the platelets was calculated to be 9 A. An independent determination of the thickness can be made from a measurement of the zero angle scattered intensity from some material for which the ratio of the scattered intensity to the scattering from a single electron can be calculated. Two heavy gases, SF6 and C2Cl2F4 (Freon 114), were used for this purpose. The feasibility of using Ludox colloidal silica as a third standard was investigated. Within experimental accuracy, the thickness values calculated from these data agree with the values obtained from the shape of the scattering curves. Both values agree with the thickness determined from the light scattering experiments of M. B. M'Ewen and M. I. Pratt [Trans. Faraday Soc. 53, 535 (1957)]. Since the scattering curve for the clay is proportional to the inverse square of the angle at the smallest observed angles, the large dimensions of the particle must be at least 500 A.
Transferability of Urey-Bradley Force Constants. V. Bromoethylenes
Authors: Scherer James R. , Overend John
Published: January 2005

Urey-Bradley force constants (UBFC's), calculated by a least-squares method, were obtained for ethylene, vinyl bromide, vinylidene bromide, trans-dibromoethylene, cis-dibromoethylene, tribromoethylene, and tetra bromoethylene. Even with complete isotopic data it was found impossible to determine all the force constants for an individual bromoethylene; moreover, from the viewpoint of giving stability to the calculation, values have been supplied by transfer from other molecules within this series and these force constants have been constrained in the least-squares refinement. By inspection of the correlation matrix, the uncertainties in the various force constants were, in many cases, found to be intimately related, and, it was usually found unnecessary to constrain both force constants of an indeterminate pair; in this manner we have kept the number of transferred force constants to a minimum. A comparison of the remaining UBFC's shows that they are moderately transferable. Although the flexible bond parameter SHH was found to be significant (but not transferable) in those molecules containing hydrogen atoms trans to one another, i.e., ethylene, vinyl bromide, and trans-dibromoethylene, its value in cis-dibromoethylene was small and made no significant contribution in explaining the observed frequencies. A potential function which includes a quadratic cross term between trans-hydrogen bending coordinates was found to be adequate throughout the series and moderately transferable.
Dielectric Study of Some Liquid Alkyl Nitrites
Authors: Grant R. F. , Davidson D. W. , Gray Peter
Published: January 2005

The dielectric constants of liquid methyl, n-propyl and isopropyl nitrite have been measured over an extensive range of temperature and the results used to estimate the relative abundances of the trans and cis isomers. It is concluded that the trans form predominates in all three liquids, in contradiction, in the case of the propyl nitrites, to the conclusions from recent NMR studies. It is suggested that the assignments to the appropriate NMR peaks should be reversed for the higher alkyl nitrites. Dielectric relaxation in n-propyl nitrite was found to be of the asymmetrical Cole-Davidson type.
Mass Spectrometric Determination of the Dissociation Energies of the Molecules AgAu, AgCu, and AuCu
Authors: Ackerman Marcel , Stafford Fred E. , Drowart Jean
Published: January 2005

The vapors issuing from mullite and graphite Knudsen cells containing pure metals and alloys of the triad Cu–Ag–Au have been analyzed mass spectrometrically. From the experimental ratios of diatomic to monoatomic species and the vapor pressures of the elements, the following dissociation energies are obtained: D00(Cu2)=45.5±2.2 kcalD00(AgAu)=47.6±2.2 kcalD00(Ag2)=37.6±2.2 kcalD00(AgCu)=40.7±2.2 kcalD00(Au2)=51.5±2.2 kcalD00(AuCu)=54.5±2.2 kcalThese are based on ΔH298vap=81.1, 68.4, and 87.5 kcal/g-atom for Cu, Ag, and Au where D00 of AgCu depends on the value for Cu, and D00 of AgAu and AuCu on Au. The uncertainties quoted do not include the uncertainty in ΔHvap.
Gradient Dependence of Intrinsic Viscosity of Freely Flexible Linear Macromolecules
Authors: Peterlin Anton
Published: January 2005

In laminar flow the randomly coiled macromolecule expands nonuniformly. The averaged distances between close-by chain elements increase much slower than those between elements situated far away on the molecular chain. Because the latter move in opposite direction and the former in the same one, yielding a negative and positive contribution respectively to hydradynamic interaction, the nonuniform expansion results in a much faster decrease of negative terms. As a consequence hydrodynamic interaction first increases with the gradient yielding an initial drop in intrinsic viscosity proportional to the square of the gradient. With persisting coil expansion, however, the positive terms too decrease so far that the viscosity, after reaching a minimum, rises again and eventually surpasses the initial value at zero gradient. The increase is coming to an end when the rms end-to-end distance approaches the extended length of the molecule.
Variational Calculation of Magnetic Hyperfine Interaction. Nitrogen Atom
Authors: Das T. P. , Mukherjee A.
Published: January 2005

A variational method, employing the unrestricted Hartree-Fock approximation, is proposed for the calculation of isotropic magnetic hyperfine constants in paramagnetic atoms and ions with unpaired electrons in non-S states and in free radicals. The method is applied to the ground state of the nitrogen atom. The N14 hyperfine constant in the ground state is calculated to be +7.3 Mc as compared to the recent experimental value of +10.4509±0.0003 Mc. Reasons for the discrepancy are discussed.
Critical Solution Phenomenon in Two-Component Liquid Systems. The System Water-Ethylene Glycol Mono-Isobutyl Ether
Authors: Rudd De F. P. , Widom B.
Published: January 2005

The system water-ethylene glycol mono-isobutyl ether is studied in the neighborhood of its lower critical mixing point, and it is found that the two lines in a Cox-Herington plot have slopes which, to within a small experimental error, are of exactly equal magnitude. The lower critical solution point is found to be at 25.8°C and 30.4 weight percent ether. It is shown that in an earlier study of this system by Cox and Cretcher there were probably significant impurities in the ether. A theorem derived by Rice for a one-component fluid is extended to binary systems, and it allows one to conclude from the symmetry of the Cox-Herington plot that at the critical solution temperature the chemical potential of either component, as a function of composition, has a discontinuous fourth derivative at the critical composition, the discontinuity being a simple reversal of sign.
Vibrational Spectra of Orthorhombic Metaboric Acid
Authors: Parsons J. L.
Published: January 2005

Infrared absorption spectra have been obtained in the 430 to 4000 cm—1 region for B3O3(OH)3, B310O3(OH)3, and B3O3(OD)3, as polycrystalline mulls and, in the case of B3O3(OH)3, as a single crystal section. A partial Raman spectrum has been obtained for B3O3(OH)3 in the polycrystalline form. The spectral data have been interpreted in terms of the vibrations of the B3O3(O—)3 unit, with the D3h symmetry of the unit perturbed by the crystal's potential field, plus the motions of the hydrogen atoms. The latter are regarded as those of an infinite chain which has a factor group isomorphic with the point group D2h.
Electron Spin Resonance and Optical Absorption of K3[Cr(CN)5 NO]· H2O
Authors: Bernal Ivan , Harrison S. E.
Published: January 2005

Electron spin resonance of a water solution and of the pure powder of K3[Cr(CN)5NO]·H2O reveal a single sharp resonance line at room temperature. The water solution resonance gives a Cr53 hyperfine structure which is further split by a ``superhyperfine'' structure due to the nitrogen in the NO ligand. From the electron spin resonance the Cr1+ ion appears to be in a spin quenched (dε5) orbital singlet ground state. The optical absorption data allows the determination of the splittings of the d levels in concordance with the ESR spectrum.
Free-Volume Model of the Amorphous Phase: Glass Transition
Authors: Turnbull David , Cohen Morrel H.
Published: January 2005

Free volume vf is defined as that part of the thermal expansion, or excess volume Δv̄ which can be redistributed without energy change. Assuming a Lennard-Jones potential function for a molecule within its cage in the condensed phase, it can be shown that at small Δv̄ considerable energy is required to redistribute the excess volume; however, at Δv̄ considerably greater than some value δv̄g (corresponding to potentials within the linear region), most of the volume added can be redistributed freely. The transition from glass to liquid may be associated with the introduction of appreciable free volume into the system. Free volume will be distributed at random within the amorphous phase and there is a contribution to the entropy from this randomness which is not present in the entropy of the crystalline phase. According to our model all liquids would become glasses at sufficiently low temperature if crystallization did not intervene. Therefore whether or not a glass forms is determined by the crystallization kinetic constants and the cooling rate of the liquid. The experience on the glass formation is consistent with the generalization: at a given level of cohesive energy the glass-forming tendency of a substance in a particular class is greater the less is the ratio of the energy to the entropy of crystallization.
Densities of Solutions of Potassium in Liquid Ammonia and Deutero-Ammonia
Authors: Hutchison Clyde A. , O'Reilly Donald E.
Published: January 2005

The densities of solutions of K in liquid NH3 have been measured at —33.7°, 0.0°, and 20.0°C over a concentration range from 0 to 1.2 mole liter—1. The correlation of these results with paramagnetic resonance measurements is discussed in terms of a cavity trapping model.
Reflection Spectra and Absolute Infrared Intensities in Pure Liquids: Benzene, Chloroform, Bromoform, Carbon Disulfide, and Carbon Tetrachloride
Authors: Schatz P. N. , Maeda Shiro , Hollenberg J. L. , Dows David A.
Published: January 2005

Reflection spectra of liquid benzene, chloroform, bromoform, carbon disulfide, and carbon tetrachloride have been studied in the infrared region. On using a method developed in this work, absolute intensities of the vibrational transitions involved have been obtained from the experimental data. The results are in reasonable agreement with intensities obtained from dispersion studies except for the case of carbon disulfide. The benzene intensity obtained is in disagreement with the value from absorption measurements on the pure liquid.
Condensation Coefficients in the Growth of Cadmium and Zinc from the Vapor
Authors: Rapp R. A. , Hirth J. P. , Pound G. M.
Published: January 2005

Condensation coefficients of essentially unity have been determined for the growth of zinc and cadmium from the vapor phase at high supersaturations in ultra-high vacua. These data indicate that no impingent atoms are reflected, and that all adsorbed atoms are incorporated into the growing crystal by Volmer's disk nucleation and growth mechanism. The adsorption of gaseous impurities at a residual gas pressure of 10—4 mm Hg did not affect the condensation coefficient for condensation at high fluxes.
High-Energy Radiation Damage to Fluorescent Organic Solids
Authors: Sharn Charles F.
Published: January 2005

Radiation damage to organic solids exposed to Co60 gamma rays has been studied through the analysis of the induced fluorescent changes. From the fluorescence degradation for two series of aromatic hydrocarbons, correlations between chemical structure and radiation damage have been established. In addition, modifications in a conventional model used to describe the fluorescent degradation mechanism in organic materials are suggested by the data. Some of the organic materials studies have potential application in a dosimetry system based on fluorescence degradation.
Paramagnetic Resonance Study of Irradiated Single Crystals of Calcium Tungstate
Authors: Zeldes Henry , Livingston Ralph
Published: January 2005

Gamma irradiation of calcium tungstate at 77°K produces two paramagnetic species in high yield. Measurements of yields and of rates of disappearance upon warming indicate the two species are formed and disappear upon warming in one to one correspondence. The principal axis directions and g tensors have been measured and indicate that one species contains a surplus electron while the other is electron-deficient (hole). Hyperfine effects of W183 have been observed. The electron-deficient species contains two tungsten atoms with small isotropic hyperfine interactions. Its unpaired electron must be highly localized in orbitals of atoms other than tungsten. The electron-surplus species contains one tungsten atom with an anisotropic hyperfine interaction. This center could be WO43—, but from the lack of symmetry of the measured g values it must be formed near a lattice defect. Experiments with heat-treated crystals indicate lattice defects to be important in the radiation effect.
Study of the Wurtzite-Type Compounds. V. Structure of Aluminum Oxycarbide, Al2CO; A Short-Range Wurtzite-Type Superstructure
Authors: Amma E. L. , Jeffrey G. A.
Published: January 2005

Al2CO has a long-range disordered structure based on the wurtzite lattice and a short-range √3a, 2c superstructure. The long-range atomic parameters were determined from the single crystal sharp diffraction data with Mo K radiation. The diffuse spectra, although very apparent on the single-crystal x-ray photographs, were inadequate to completely define the short-range structure; however, the general features of this structure could be inferred and some analogies made to known structures which are wholly or in part wurtzite-lattice superstructures.
Composition Dependence of the Thermal Conductivity of Regular Solutions
Authors: Bearman Richard J. , Vaidhyanathan V. S.
Published: January 2005

It is demonstrated from the statistical mechanics of transport processes that the product κη of the coefficients of thermal conductivity and viscosity may be expected to be independent of composition in regular solutions. This conclusion is verified for the system benzene-carbon tetrachloride.
Emission Spectra of Trivalent Thulium
Authors: Van Uitert L. G. , Soden R. R.
Published: January 2005

Trivalent thulium can be caused to fluoresce selectively from different levels by choice of the wavelength of exciting radiation. This has made it possible to correct the assignments of emission transitions occurring in the visible range. As a consequence, the detailed data of Gobrecht have been found to be in much closer agreement to the theoretical predictions than formerly realized.
Electron Spin Resonance in a Gamma-Irradiated Single Crystal of L-Cystine Dihydrochloride
Authors: Kurita Yukio , Gordy Walter
Published: January 2005

The electron spin resonance of a gamma-irradiated single crystal of L-cystine dihydrochloride, HOOC–CH–CH2–S–S–CH2–CH–COOH·2HCl,         –                             –        NH2                      NH2has been measured at 9 kMc/sec and at 24 kMc/sec for various orientations of the crystal in the magnetic field. The resonance pattern was found to be a doublet, the spacing between the components of which is independent of the crystal orientation as well as of the strength of the static magnetic field. The spectroscopic splitting factor was found to be anisotropic with the principal values: gu=2.003, gv=2.025, and gw=2.053. A model of the free radical, HOOC–CH–CH2–S·,          –        NH2in which the electron spin density is mainly concentrated in a nonbonding 3 p orbital of the sulfur atom, is proposed. The model accounts very well for the principal values of the g tensor as well as their directions relative to the atomic configuration. It also can give rise to the observed proton hyperfine structure.
Bonding in Icosahedral Complexes
Authors: Macek Joseph H. , Duffey George H.
Published: January 2005

Results of a group theoretical investigation of icosahedral AB12 are presented. These are used in setting up twelve equivalent, orthogonal bond orbitals. Each of the orbitals exhibits a Pauling strength of 3.921. Crystal-field splitting of valence levels of A is also discussed.
Low-Temperature Chemisorption. I. Flash Desorption of Nitrogen
Authors: Ehrlich Gert
Published: January 2005

Flash desorption (desorption by continuous temperature displacement) is applied to a study of the low-temperature interactions of N2 with an initially clean tungsten surface. Molecular nitrogen is found to dissociate into atoms on adsorption even at 115°K, at a rate which diminishes with increasing temperature, but is initially independent of surface concentration. Formation of this atomically bound β nitrogen is hindered at low temperatures (T∼115°K) by competitive growth of an additional state γ, in which nitrogen, at ∼2½ times the concentration in the β state, is bound as molecules with an energy of 9 kcal mole—1, resulting in a total surface concentration of 600×1012 molecules cm—2. The population in this γ state depends sensitively upon the arrangement of atoms in the β state. Preadsorption at T∼300°K equalizes the populations in β and γ; annealing at T∼1000°K at impingement rates of 7×1015 molecules cm—2 min—1, further lowers nγ/nβ and brings about rearrangement of the tungsten surface as well, without appreciable change in the adatom concentration. A third state α is formed at temperatures up to 400°K, with a binding energy of ∼20 kcal mole—1. Initially its rate of formation, just as that of γ at low temperatures, is dictated by the concentration of the atomically held β state. At 300°K and above the α concentration passes through a maximum, then diminishes; at low temperatures, it remains constant, achieving a maximum value 1/30 that of the γ state.
Strong Coupling in Nuclear Resonance Spectra. IV. Exact Analysis of Three-Spin Spectra
Authors: Castellano S. , Waugh J. S.
Published: January 2005

A method is developed for calculating the chemical shifts and spin-spin coupling constants for a system of three spin-½ nuclei (ABC) directly from the nuclear resonance spectrum. Trial-and-error adjustment of these parameters is avoided entirely, and the values obtained are exactly consistent with the input information. The use of experimental intensities is kept separate from that of experimental frequencies, and the former may be omitted entirely when experimental values of sufficient accuracy are not available. It is shown that previously unknown ambiguities in the assignment of parameters sometimes arise, and that conventional iterative analyses may occasionally lead to the wrong answer. The proton resonance spectra of four compounds containing vinyl groups are discussed as illustrations of the method.