bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Orbital Theory of Diamagnetic Polarization. III. Anisotropic Properties of the Carbonate and Nitrate Ions
Authors: Pople J. A.
Published: January 2005

Many conjugated molecules have anisotropic diamagnetic susceptibilities (with the axis of high diamagnetism perpendicular to the molecular plane) which cannot be explained in terms of interatomic ring currents as for aromatic hydrocarbons. The carbonate and nitrate ions are well-known examples. In this paper, the approximate molecular orbital theory developed in Part I is applied to these systems and predicts considerable anisotropy of the correct sign for both, mainly on the central atom. A corresponding calculation of the C13 chemical shift of CO32— provides an interpretation of the NMR anisotropy observed by Lauterbur [Phys. Rev. Letters 1, 343 (1958)].
Triplet—Triplet Annihilation and Delayed Fluorescence in Molecular Aggregates
Authors: Sternlicht H. , Nieman G. C. , Robinson G. W.
Published: January 2005

This paper deals with triplet—triplet annihilation in pure and mixed organic crystals. In crystals containing a small concentration of impurity traps, triplet excitation migration may proceed from trap to trap on a time scale which is short compared with the long triplet state lifetime but which is long compared with the normal fluorescence lifetime. Nearest-neighbor and long-range mutual annihilation of two triplets may then take place giving rise to delayed fluorescence. The rates of long-range triplet excitation migration and annihilation show a concentration dependence, a temperature dependence, and a solvent dependence. Providing the triplet—triplet annihilation rate is not too fast, the intensity of the delayed fluorescence can be shown to depend upon the square of the intensity of the exciting light. This expectation is borne out by experiments, briefly reported here, on delayed fluorescence in dilute isotopic mixed crystals. In crystals containing high concentrations of such impurity traps, or in pure crystals, the annihilation rate becomes extremely rapid and this mechanism effectively quenches phosphorescence in many, but not all, classes of pure organic crystals. The kinetics of the over-all process are discussed in both the limits of fast and slow annihilation rates. A theoretical investigation of the origin of the annihilation matrix element is carried out, and it is shown that exchange interactions play the largest role in determining annihilation rates. Past work [H. Sponer, Y. Kanda, and L. A. Blackwell, J. Chem. Phys. 29, 721 (1958); N. W. Blake and D. S. McClure, ibid., p. 722] on delayed fluorescence of assumed pure naphthalene crystals containing very small amounts of β-methyl naphthalene (traps) can be understood within the framework of this paper. The need in organic crystals for the major delayed fluorescence mechanism to be based upon ionization and electron trapping seems now to be considerably lessened.
Ring Currents in Pentacyclic Hydrocarbons
Authors: Memory J. D.
Published: January 2005

McWeeny's modification of London's molecular orbital theory of π-electron ring currents has been used to calculate the individual currents in the 15 pentacyclic hydrocarbons. The results, useful in themselves for the calculation of NMR chemical shifts, are also significant in the light of what they shed on the question of the range of validity of the assumption that the current in each ring is approximately equal to the benzene ring current.
Effect of Purification on the Semiconduction of Imidazole
Authors: Brown G. P. , Aftergut S.
Published: January 2005

The technique of measuring the temperature dependence of the electrical resistance of organic compounds directly in a zone-refining tube has been explored with imidazole. The temperature dependence, determined as a function of the number of zone-refining passes, became constant after 39 passes. The results were compared with those of imidazole purified by successive sublimations. The contribution of hydrogen bonding to the semiconduction of imidazole is discussed.
Self-Diffusion of Lead 210 in Single Crystals of Lead Sulfide as a Function of Stoichiometry and Doping Additions
Authors: Simkovich George , Wagner J. Bruce
Published: January 2005

Self-diffusion of lead 210 in single crystals of lead sulfide has been studied in the temperature range of 500° to 800°C. Measurements were made on undoped crystals and on crystals doped with Bi2S3 or Ag2S under well-defined sulfur pressures and under an inert gas. Results show that increasing the cation vacancy concentration by means of excess sulfur or by bismuth additions increases the diffusion coefficient, whereas decreasing the concentration of cation vacancies by means of excess lead or by silver additions also increases the diffusion coefficient over those of stoichiometric PbS. In all cases the electron concentration is accounted for according to: [interstitial lead atoms]∝pPb/[excess electrons],and [cation vacancies]∝[excess electrons]/pPb,assuming singly ionized interstitial lead atoms and singly ionized cation vacancies. The activation energies decrease in the order, stoichiometric PbS, lead excess PbS and sulfur excess PbS.

Results support a Frenkel disorder of the cation type.
Statistics of Random Placement, Subject to Restrictions, on a Linear Lattice
Authors: Gordon M. , Hillier I. H.
Published: January 2005

By iterative methods of solving difference equations (or by a Monte Carlo method), statistical parameters are calculated for a number of models concerned with linear lattices. These contain sites which may be in one or two states (empty or occupied), and the progressive occupation of the sites is arranged to occur at random, but subject to specified restrictions. Examples of applications are cited from the field of crystallization or chemical reactions of chain polymers, sorption in graphite, and the close packing of hard spheres in one dimension. Special interest attaches to limiting cases in which the lattice is made to go over into a continuous, infinite straight line. It is shown that when such a line is covered with straight-line segments of constant length by placing these segments on the line at random (but avoiding overlap), the asymptotic packing density approached is approximately 0.748.
Identification of Color Centers in Lithium Fluoride
Authors: Kaufman J. V. R. , Clark C. D.
Published: January 2005

The optical absorption spectra induced in LiF by 2.0-MeV electron irradiation at a number of doses and at temperatures of 120° and 293°K have been measured. The effects resulting from thermal and optical bleaching experiments on such specimens are described.

A determined effort to color LiF additively was made. No induced absorption was observed between 1.0 and 6.0 eV.

Anisotropic absorption was induced in the 4500-Å (2.76-eV) band by plane polarized 4047- and 4358-Å (3.06- and 2.84-eV) light at 293°K. The anisotropy was not affected by standing in the dark at 293°K. Results indicate that at least two absorption bands constitute the 4500-Å band, and it is suggested that one of these is the M band.

It seems to have been generally accepted that the 2500-Å (4.948-eV) band in LiF is the F band, by analogy with the other alkali halides. However, the present results show that analogies between results on LiF and the other alkali halides cannot be carried very far.
C13 Nuclear Magnetic Resonance Spectroscopy. IV. Aniline, N,N-Dimethylaniline, and Their Methyl Derivatives: Steric Inhibition of Conjugation
Authors: Lauterbur Paul C.
Published: January 2005

The C13 nuclear magnetic resonance spectra of aniline, nine methylanilines, N,N-dimethylaniline and eight methyl-N,N-dimethylanilines have been obtained and analyzed. A detailed study of the influence of methyl substituents on ring carbon shieldings has been made, and estimates of the changes in charge distributions resulting from steric inhibition of conjugation derived from the results. Reasonably good agreement with other theoretical and experimental investigations of these effects has been found. The N-methyl carbon shieldings appear to be correlated with the base strengths of the amines.
C13 Nuclear Magnetic Resonance Spectroscopy. V. Nitrobenzene and Methylnitrobenzenes: Steric Inhibition of Conjugation
Authors: Lauterbur Paul C.
Published: January 2005

The C13 nuclear magnetic resonance spectra of nitrobenzene and nine methylnitrobenzenes have been obtained and analyzed. Steric inhibition of conjugation leads to marked increases in para carbon shieldings in the ortho methyl compounds. The observed shielding changes are in good agreement with those calculated from earlier theoretical and experimental studies of such inhibition and the dependence of para shieldings on π-electron densities established previously.
Linear Velocity-Gradient Term in Time-Dependent Pair Distribution Function
Authors: Nettleton R. E.
Published: January 2005

A Chapman—Enskog-type perturbation solution, in gradients of energy, velocity, and density, is proposed for the hierarchy of integro-differential equations obeyed by the time-dependent Ursell—Mayer functions. The hierarchy is then terminated by an ansatz relating the three-particle Ursell functions to those of lower order, which yields a closed system for the perturbations to the singlet and pair distribution functions (it is assumed the equilibrium functions are known). Attention is focused on the equation for the two-particle functions, and on the term therein proportional to the divergence of fluid velocity, from which the bulk viscosity may be calculated. An expansion for this term is assumed in powers of scalar products of particle separations and velocities, in which the coefficients in turn are expanded in Sonine polynomials in the velocities. The functions which multiply these polynomials satisfy a system of integral equations, for which a first approximation is written down and the solution discussed. Finally, it is shown that substitution of the solution for the pair distribution function into the hierarchy equation for the singlet distribution yields an infinite number of conditions which may be used to evaluate a corresponding number of parameters in the ansatz employed to close the hierarchy.
Dependence of Surface Tension on Temperature
Authors: Mayer S. W.
Published: January 2005

It is shown that the equation of Reiss et al. for the surface tension of liquids composed of hard-core molecules does not usually provide the proper dependence of surface tension on temperature for typical non-ionic liquids. Because of this, an empirical computation procedure is adopted, whereby the hard-core diameter is given a temperature dependence similar to that of the collision cross section for gas viscosity. When Lennard-Jones 6–12 or Sutherland intermolecular-potential data are then used to calculate a hard-core diameter, the agreement between computed and measured dependence of surface tension on temperature is usually very good, even for liquids composed of such polar, aspherical molecules as water, ethanol, and ammonia. As an illustration of the potential value of the empirical use of gas-viscosity data for improving computations of the dependence on temperature of physical properties and thermodynamic values for liquids, the Lennard-Jones 6–12 and Sutherland data are applied to two rigid-sphere relationships for liquid compressibility.
Free Energy of Nonequilibrium Polarization Systems. II. Homogeneous and Electrode Systems
Authors: Marcus R. A.
Published: January 2005

The polar contribution to the free energy is calculated for a system containing ``particles'' imbedded in a continuum having nonequilibrium dielectric polarization. Each particle may either be a single molecule or a whole collection of molecules (such as an electrode) at specified nuclear configuration and may possess a general permanent and induced charge distribution. Thereby, the results of Part I of this series are extended to a variety of systems. It is also shown that the polar contribution to the free energy can be written as the sum of free energies of equilibrium polarization systems, thereby permitting the immediate application of literature expressions for the latter to calculating the former. This expression is also derived for systems possessing partial dielectric unsaturation under a certain typical condition. Applications are made to the theory of electron-transfer reactions in solution and at electrodes and to the theory of the shift of electronic spectra of polar solutes by polar solvents.
Evaluation of Vapor-Pressure Data for Mercury, Lithium, Sodium, and Potassium
Authors: Hicks W. T.
Published: January 2005

Vapor-pressure data for the elements mercury, lithium, sodium, and potassium were correlated using an equation of state, PV = RT+BP, where B was evaluated empirically with the relationship B = b/Tm. Values of B thus obtained are compared with values of the second virial coefficient calculated from a Lennard-Jones 6–9 potential curve. Calculated values for vapor pressures and fugacity-to-pressure ratios are presented for these elements as a function of temperature.
Relation between the Chemical Composition and the Electronic Properties of the Charge-Transfer Complex, p-Chloranil: p-Phenylenediamine
Authors: Ottenberg A. , Hoffman C. J. , Osiecki Jeanne
Published: January 2005

The charge-transfer complex p-chloranil:p-phenylenediamine has been prepared by three methods: (a) precipitation from benzene, (b) precipitation from methylene chloride, (c) direct reaction between the dry solid constituents. A 1:1 complex was found in all cases, with entrapped solvent present in the cases of samples precipitated from solution. It has been shown that the concentration of unpaired electron spins and the conductivity are characteristic of the complex and do not depend upon the method of preparation. The thermal activation energy for conductivity has been found to be 0.43 eV, and for spin concentration it has been found to be 0.13 eV. Theoretical difficulties involved in the consideration of activation energies are discussed. A mechanism is considered in the light of the thermal activation energies and the Seebeck coefficient, which was found to be +1.4 mV/°C.
Fluorescence and Pre-Ionization in Nitrogen Excited by Vacuum Ultraviolet Radiation
Authors: Huffman R. E. , Tanaka Y. , Larrabee J. C.
Published: January 2005

Fluorescence in nitrogen following absorption of vacuum ultraviolet radiation has been found to begin at a wavelength of 661.3 Å and to extend to at least 580 Å, the shortest wavelength available in this experiment. The energy of the longest wavelength at which the fluorescence appears is almost exactly equal to the energy required to excite the N2 molecule from the ground state, X1Σg+, to the B2Σu+ state of the N2+ ion. It is thought that the first negative bands of N2+, B2Σu+→X2Σ g+, are responsible for the observed fluorescence. The fluorescence is excited by dispersed radiation from a stabilized helium gas discharge which produces the Hopfield continuum in the region 580–1100 Å. Fluorescence is also detected in carbon monoxide and in oxygen, but it is too weak for accurate measurements of the appearance wavelength. Experiments with a quartz cell window, in the presence of the electric field from the end window of the photomultiplier, enabled the pre-ionized bands of nitrogen to be observed.
Comparison of the Classical Theories of Unimolecular Reactions. II. A Model Calculation
Authors: Thiele Everett
Published: January 2005

A formulation due to Slater is used to determine the first-order rate constant at all pressures for the dissociation of a linear, symmetric, triatomic molecule with Morse bond-stretching potentials. The gap distribution is examined with the aid of numerical calculations carried out on a digital computer. It is found that the gap distribution is adequately represented by a gamma distribution, which approaches a random distribution as the energy approaches E0. The Giddings—Eyring theory is in excellent agreement with the ``exact'' result. Harmonic approximation theories are in poor agreement.
Heat Conduction in Metal—Ammonia Solutions
Authors: Varlashkin P. G. , Thompson J. C.
Published: January 2005

The thermal conductivity of solutions of lithium, sodium, or potassium in liquid ammonia has been measured as a function of temperature and concentration. The conductivity shows a strong dependence on concentration and rises with increasing concentration to values of 30–60 mW/cm deg at saturation. Pure ammonia has a conductivity of 5 mW/cm deg. Two modes of heat transport, molecular and electronic, may be invoked to interpret the data. The molecular term follows a semiempirical equation often used for insulating liquids. The electronic heat conductivity obeys a Wiedemann—Franz law, with a Lorenz number about 75% of the free-electron value.
Radiation Decomposition of Aqueous Azide Solution Containing Mercuric Salts
Authors: Shinohara Kenichi , Shida Tadamasa , Saito Nobufusa
Published: January 2005

The addition of mercuric salts causes a marked change in the radiolytic reactions of aqueous azide ion solution. Hydroxyl radicals and hydrogen atoms are scavenged by the azide ion and mercuric salt, respectively.

In order to explain the high yields of nitrogen and mercurous azide in terms of the current theory of water radiolysis, it is suggested that the excited water molecule which might be formed by primary recombination between the H2O+ ion and the ejected electron, and by slow electron collision in spur, may be involved. The excited water molecule is assumed tentatively to be a triplet and to behave like a diradical, which with an azide ion gives a comparatively long-lived complex (N3–H2O)(triplet)*.

The previous results of the radiolysis of pure azide ion solution have been rediscussed in terms of this new assumption.
Model for the Electronic Structure of Metal Tungsten Bronzes
Authors: Mackintosh A. R.
Published: January 2005

The electronic properties of the metal tungsten bronzes of high x value are interpreted in terms of a model in which the conduction electron wavefunctions are derived principally from the metal atomic p functions. It is shown that the physical properties of the bronzes are consistent with this model, which is compared, in this respect, with others. The transition to metallic conductivity at low x values is discussed, using the theory of Mott, and a number of experiments are suggested for clarifying some features of the electronic structure of the tungsten bronzes, and also of the related vanadium bronzes.
ESR Study of Rotational Isomerism in Substituted Benzaldehyde Anions
Authors: Stone Ellery W. , Maki August H.
Published: January 2005

The ESR spectra of terephthalaldehyde-2,5-d2, phthalaldehyde, phthalaldehyde-4-d, o-nitrobenzaldehyde, and p-nitrobenzaldehyde anions have been obtained and analyzed. It is shown experimentally that the trans rotamer of the terephthalaldehyde anion is more stable and has a higher ratio of ring proton coupling constants than the cis rotamer. In each rotamer the largest coupling constant is due to the aldehyde protons. All detectable phthalaldehyde anions exist in the unsymmetrical meso conformation, in which one pair of coupling constants has been assigned experimentally to a pair of ring protons. The other two pairs are assigned theoretically. The values of all coupling constants in both terephthalaldehyde anion rotamers can be calculated very accurately by either of two crude extensions of simple MO theory, designated the β- and α-effects. These two effects predict opposite assignments of ring proton coupling constants within each rotamer, and the detailed assignment cannot be established by deuteration experiments. When the β and α effects are applied to phthalaldehyde anion, the results explain the observed coupling constants only qualitatively. Spin densities are predicted by MO calculations for benzaldehyde anion, which was not detected experimentally. The application of the superposition model to terephthalaldehyde anion is discussed. The large relative stability of the meso rotamer of the phthalaldehyde anion is attributed to an intramolecular hydrogen bond.
One-Dimensional Fermion Density Formula
Authors: Payne Herbert
Published: January 2005

An expression for the sum of the position-probability densities for a one-dimensional system of fermions in the ground state is derived from wave mechanics. Its accuracy in application to three different potential-energy functions is shown. For the square well of infinite height it preserves the sinusoidal contributions which disappear in the corresponding Fermi—Thomas treatment. Where the potential energy exceeds the Fermi level, it is properly characterized.
Studies with a Single-Pulse Shock Tube. I. The Cis—Trans Isomerization of Butene-2
Authors: Lifshitz Assa , Bauer S. H. , Resler E. L.
Published: January 2005

The cis—trans isomerization of butene-2 was investigated behind reflected shocks in a single-pulse shock tube of a novel design. The temperature range covered was 1000°—1250°K, and concentrations of 1% and 6% of the butene in argon were used. Analyses were made by vapor-phase chromatography. The first-order rate constants obtained in this work fall slightly above the extrapolated Arrhenius curves of two recent low-temperature studies. An activation energy of 65, rather than 62.8 kcal/mole, is obtained when a straight line is drawn between the high and the low temperature data. |The rate constant obtained is kcis∞=3.5×1014exp(−65×103/RT).Possible sources of errors in evaluating reaction times in the single-pulse shock tube are discussed.
Heat Content of Uranium Dicarbide from 1484° to 2581°K
Authors: Levinson L. S.
Published: January 2005

The heat content of uranium dicarbide was measured from 1484° to 2581°K using a drop calorimeter.
Fe57 Mössbauer Effect in Ferrocene Derivatives
Authors: Wertheim G. K. , Herber R. H.
Published: January 2005

The hyperfine structure in the Mössbauer spectrum of Fe57 in ferrocene and in related compounds shows that the bonding of the iron atom is not affected by ring substitution. The temperature dependence of the fraction of recoil-free absorption events in these compounds indicates that the Debye temperature is low (∼150°K) and that the optical modes make only a minor contribution to the reduction of the recoil-free fraction at low temperature.
Iterative Method for Solution of the One-Dimensional Wave Equation: Eigenvalues and Eigenfunctions for L-J (12, 6) and Exponential (α, 6) Interatomic Potentials
Authors: Harrison Halstead , Bernstein Richard B.
Published: January 2005

A method of direct numerical integration of the one-dimensional wave equation is described and illustrated by calculations of the radial wavefunctions, vibrational energy levels, and numbers of bound states for diatomic molecules. Within the validity of the Born—Oppenheimer approximation, the procedure yields arbitrarily accurate eigenvalues. Several potentials involving long-range, inverse-sixth-power attractions are examined. Results are compared with those from the first-order WKBJ integral and with the Dunham form of the second-order WKBJ approximation.
Energy Levels of Tb3+ in LaCl3 and Other Chlorides
Authors: Thomas K. S. , Singh S. , Dieke G. H.
Published: January 2005

The absorption and fluorescence spectra of Tb3+ in LaCl3 have been used to find the levels of Tb3+. All Stark components of 7F and 5D4 were unambiguously established. The classification of the higher levels is still doubtful.

The analysis was helped by Zeeman effects and particularly crystal field calculations. The latter gave as crystal field parameters: B20=92,B40=−40,B60=−30,B66=290 cm−1.

Tb3+ in YCl3 has a similar spectrum but, because of different crystal symmetry, with different fine structure. A third type of spectrum is obtained from pure TbCl3.
Contribution to the Statistical Geometric Basis of Radiation Scattering
Authors: Frisch H. L. , Stillinger F. H.
Published: January 2005

We describe a number of formal properties of the hierarchy of correlation functions describing the statistical geometry of a random porous medium consisting of homogeneous matter and void regions. Our principal result concerns the determination of the average number of interparticle contacts in a randomly packed aggregate of monodisperse hard spheres. We indicate how this number can be determined, in principle, from the analysis of large angle scattering of radiation. We discuss the bearing of our result on the Debye ``random scatterers'' and the study of models of random close packing of spheres. We give a brief list of possible applications and open problems suggested by this field.
Monte Carlo Study of Coiling-Type Molecules. I. Macromolecular Configurations
Authors: Wall Frederick T. , Windwer Stanley , Gans Paul J.
Published: January 2005

Monte Carlo methods have been employed on a high-speed digital computer to generate samples of random chains intended to simulate polymer molecules. The chains were generated on a tetrahedral lattice subject to the excluded-volume effect using both normal methods and procedures biased in favor of the more tightly coiled chains. Nonbonded nearest-neighbor interactions were counted and, by introducing an appropriate potential energy of interaction between such neighbors, a partition function was established. For N link chains, the mean-square end-to-end distances, 〈RN2〉, and the mean-square radii of gyration, 〈SN2〉, were calculated as functions of temperature. Using the ratio 〈RN2〉/N as a criterion, it is found that a Flory Θ temperature exists; it is also found that the observed ratio 〈SN2〉/〈RN2〉 is compatible with the Θ temperature concept. Finally, there are reported distribution functions for the end-to-end separations and for material densities of polymers subject to the excluded-volume effect but without other intramolecular interactions.
Kinetics of Thermal Ionization. II. Xenon and Krypton
Authors: Kornegay Wade M. , Johnston Harold S.
Published: January 2005

The rate and mechanism of the thermal ionization of xenon has been further studied by a microwave and shock-tube method. The negligible effect of impurities or background on the observed ionization rates was demonstrated. For a variety of added gases, the activation energy for the observed ionization was about 8 eV, not 12.1 eV, the ionization energy. Detailed time studies show an induction period for buildup of free electrons as a result of populating intermediate electronic states of xenon; however, the simple three-step mechanism proposed previously (Xe+M⇋Xe*+M,Xe*+M→Xe++e−+M) was shown to be insufficient to explain certain quantitative features of the data. At these high temperatures a large number of parallel paths are possible, and in general, entropy differences are more important than energy differences. On this basis it is argued that the final ionization process leads to Xe++e—+M and not MXe++e—. Limited data are presented on the ionization of krypton, and an activation energy of about 10 eV, not 14 eV (the ionization energy), is indicated. Reaction cross sections are given for xenon and krypton.
Far-Infrared Dielectric Measurements on Potassium Dihydrogen Phosphate, Triglycine Sulfate, and Rutile
Authors: Barker A. S. , Tinkham M.
Published: January 2005

Polarized reflection spectra have been made of single crystal KH2PO4, TGS, TiO2, and KD2PO4. KH2PO4 and TiO2 were studied in the range 2.5 to 1500 cm—1, TGS and KD2PO4 over a somewhat smaller range. The reflectivity data were analyzed using dispersion theory and classical-oscillator fits to obtain the optical constants. The hydrogen bonded ferroelectrics show a behavior quite different from the perovskite ferroelectrics studied earlier. A highly overdamped ferroelectric mode is found in KH2PO4 near 50 cm—1 at room temperature. The close similarities of certain modes in KH2PO4 and KD2PO4 do not support previous speculations on proton tunneling. An analysis of the mode strengths in TGS shows that the major dispersion which contributes to the low-frequency dielectric constant takes place below 14 cm—1. TiO2 exhibits strong modes near 190 cm—1 which are connected with its large value of low-frequency dielectric constant, and are quite similar to the low-frequency mode in SrTiO3.
On the Infrared Spectrum of Hydrogen Peroxide Matrix-Isolation Studies of the System H2O2:N2 (II)
Authors: Catalano Edward , Sanborn Russell H.
Published: January 2005

Matrix-isolation spectra of the system H2O2:N2 were obtained in the region 4000–300 cm—1 at 4.2°K. Spectra taken in this manner are free of complications due to association, over-all rotation, etc. The most unusual feature of these spectra is the band system at 385 and 350 cm—1 in the torsional region. This main band at 385 cm—1 is exceedingly broad for a matrix spectrum. These bands have been assigned to the n=0→1 and 1→2 torsional transitions.
Charge Transfer between Some Atmospheric Ions and Atomic Oxygen
Authors: Stebbings R. F. , Smith A. C. H. , Gilbody H. B.
Published: January 2005

Cross sections for charge transfer between oxygen atoms and N+, N2+, NO+, and O2+ ions have been measured within the energy range 50 to 10 000 eV, using modulated-crossed-beam techniques. The neutral beam effused from a Pyrex tube in which an electrodeless rf discharge could be established. It was determined, by use of a mass spectrometer, that about 40% of the molecules in the beam could be dissociated. The currents of slow ions which resulted from charge transfer between the primary ion beam and both the undissociated and partially dissociated oxygen beams were measured. The atomic cross sections were then evaluated from knowledge of these currents, the dissociation, and the previously determined molecular charge-transfer cross sections.
The Effect of Physical Adsorption on the Electrical Resistance of Activated Carbon
Authors: McIntosh R. , Haines R. S. , Benson G. C.
Published: January 2005

The change of electrical resistance of several rods of activated carbon on the adsorption of a variety of vapors has been determined. The direction and extent of the resistance change appear to depend upon the adsorbate. The hypothesis that the changes in resistance are due to the variations in contact resistance between the carbon granules does not appear to be adequate to explain the observations.
The Statistical Mechanical Theory of Transport Processes II. Transport in Gases
Authors: Kirkwood John G.
Published: January 2005

By means of the methods developed in the first paper of this series, SMTI, the Maxwell-Boltzmann integro-differential equation, underlying the well-developed Chapman-Enskog theory of transport phenomena in gases of low density, is derived from the principles of statistical mechanics. The derivation supplements and clarifies the usual physical argument employed to establish this important equation.
Kinetics of the Photolysis of Methyl Iodide and the Hydrogen Halides I. Photolysis of Hydrogen Iodide in the Presence of Iodine, Hydrogen Bromide and Hydrogen Chloride
Authors: Williams Russell R. , Ogg Richard A.
Published: January 2005

The photodissociation of hydrogen iodide by light of λ2537A has been utilized as a source of hydrogen atoms for a study of their subsequent reactions with iodine and the hydrogen halides. The observed rate of hydrogen formation has been used to evaluate the ratio of rate constants for the following reactions: H+HX→H2+XH+I2→HI+Iwhere X represents Cl, Br or I.
The Absorption Spectrum of Ozone in the Visible I. Examination for Fine Structure. II. The Effect of Temperature
Authors: Humphrey George L. , Badger Richard M.
Published: January 2005

The absorption spectrum of ozone in the visible spectral region has been investigated for fine structure and for changes in absorption with temperature. No fine structure was observed in spectrograms taken in the second order of a 21-ft. grating spectrograph. The absorption coefficients remained constant within experimental error in going from room to dry-ice temperature.
Ignition of Explosive Gas Mixtures by Electric Sparks. I. Minimum Ignition Energies and Quenching Distances of Mixtures of Methane, Oxygen, and Inert Gases
Authors: Blanc M. V. , Guest P. G. , von Elbe Guenther , Lewis Bernard
Published: January 2005

An apparatus and experimental procedure is described for measuring capacitances and gap voltages of condensed electric spark circuits for sparks just powerful enough to ignite explosive gas mixtures. Mixtures of methane, oxygen, and inert gases are investigated. From the measured capacitances and gap voltages the minimum ignition energies are calculated. These energies are found to be independent of gap voltage. With increasing gap length they attain a minimum at critical distances which mark the farthest penetration of the flame-quenching effect of the electrode material. Above the quenching distances the energies remain constant over some range which is governed by mixture composition and pressure. Energies measured in this range may be regarded as absolute minimum energies, as defined in a subsequent paper. Data of such minimum energies and of quenching distances are presented for mixtures at room temperature and pressures ranging from 0.2 to 1 atmosphere.
The Absorption Spectrum of Carbon Dioxide from 14 to 16 Microns
Authors: Kaplan Lewis D.
Published: January 2005

Absorption of a parallel beam of radiation from 14 to 16 microns by equivalent thicknesses of 0.004, 0.05, 1, 4, and 20 centimeters of carbon dioxide is calculated on the basis of quantum mechanics considerations for stratospheric conditions. The intensity values for the vibrationrotational lines in the P and R branches of the important vibrational transitions are computed and a method is suggested for correcting the absorption values when more accurate measurements of the matrix element of the electric dipole moments of transition are made. An empirical formula suggested by Sutherland and Callendar is found to give an inaccurate representation of the dependence of absorption on path length for conditions prevailing in the lower stratosphere.
The Asymmetric Rotor. VI. Calculation of Higher Energy Levels by Means of the Correspondence Principle
Authors: King Gilbert W.
Published: January 2005

The rotational levels of the rigid asymmetric rotor can be calculated by means of the correspondence principle. It is shown that the quantum-number ratio K/J(J+1) is the complete elliptic integral of the third kind tabulated by Heuman in the case of the energy levels of a hypothetical rotor with reciprocal moments of inertia −1, κ, and +1. The parameter of the integral is the reduced-energy ratio E(κ)/J(J+1), and its modulus is a function of both the reduced-energy ratio and asymmetry parameter. A double inverse interpolation has been made by Heuman's table to give the energy ratio directly in terms of quantum-number ratio and asymmetry. Power series expansions have been developed around limiting cases and around each point in the table, so that formulas for interpolation and estimating errors are available.
Foreign Ion Rejection in the Growth of Sodium Chloride Single Crystals from the Melt
Authors: McFee Raymond H.
Published: January 2005

A study is made of the process of purification that takes place when single crystals are grown from the melt. The rejection of potassium and copper ions from solid solution in sodium chloride crystals is measured quantitatively by analyzing by spectrochemical means sections of cylindrical crystals of sodium chloride to which has been added a known quantity of impurity. The theory of the distribution of impurity over the height of the crystal is derived in terms of the initial impurity concentration, height of completed crystal, and the fraction of the impurity concentration in the melt included in the crystal, which fraction is called the purification coefficient. Good agreement is obtained between theory and experiment for an initial concentration of 0.1 atomic percent potassium in sodium chloride. Purification coefficients for several crystals containing potassium and a few crystals containing copper are measured and correlated with rate of growth and temperature gradient conditions.
A Re-Evaluation of the Covalent Radii of Some of the Elements
Authors: Gordy Walter
Published: January 2005

The Schomaker-Stevenson correction for ionic character, —β|xA—xB|, of the covalent radii additivity rule, dAB = rA+rB, is extended to double bonds. The value of the parameter β found for these is 0.06. Several revisions in the table of covalent radii are proposed. The double-bond covalent radii of oxygen and nitrogen are chosen as 0.604A and 0.62A, respectively, or one-half the bond lengths of O2 and of the –N=N– length in azomethane. The single- and double-bond covalent radii of carbon are revised upward to 0.79A and 0.675A to make them in accord with the lengths predicted by Mulliken, Rieke, and Brown for ideal single and double CC bonds. The newly assigned values are shown to be consistent with double bonds formed between unlike atoms when the shortening caused by ionic character is taken into account. Some other covalent radii are determined by extrapolation of curves determined by the known radii and by application of the revised additivity rule.
The Asymmetric Rotor. V. An Analysis of the 3.7-μ Band of H2S by Punched-Card Techniques
Authors: Hainer R. M. , King Gilbert W.
Published: January 2005

The H2S band at 3.7μ described by Nielsen and Barker is interpreted as the R branch of band for which the induced moment is parallel to the least axis of inertia, between the ground state with moments of inertia determined by Cross and an upper state with moments 2.83, 3.10, and 6.02×10−40 gcm2 (reciprocal moments 9.90, 9.04, and 4.65 cm−1, respectively). The band center is 2625 cm−1. Punched-card methods were used to do the following calculations. The relative position and intensities of all the lines in the band are computed by the theory of the rigid rotor, their absorption coefficients α summed over an interval of 0.5 cm−1, or ⅕ of the slit width to give Σα. These are converted to transmissions, e−qΣα, where q is an adjustable parameter. The transmissions over a range of 5 intervals are combined with suitable weight factors (1, 2, 4, 2, 1) to give the transmission through a ``slit'' of finite resolution and half width of 1 cm−1. This computed transmission curve is compared directly with the actual experimental observations. These calculations were made for several estimates of the moments until a satisfactory fit was obtained.
The Crystal Structure of Hydrazinium Dichloride, N2H6Cl2
Authors: Donohue Jerry , Lipscomb William N.
Published: January 2005

Accurate values of the two parameters in the structure of crystalline hydrazinium dichloride have been determined by the x-ray diffraction method, with the use of one and two dimensional Fourier syntheses. The N–N separation in this crystal is 1.42A, and is equal to that in hydrazinium difluoride. This N–N distance is 0.05A shorter than in gaseous hydrazine. Each chloride ion forms hydrogen bonds with three nitrogen atoms, the structure consisting of a three dimensional network of N–H···Cl bonds. The angle N–N–H···Cl is 100°. The configuration of the N2H6++ ions is trans. The differences between this structure and that of hydrazinium difluoride probably arise from the greater coordinating ability of the chloride ion as compared with that of the fluoride ion. The shortening of the N–N distance may be caused in part by the formal charges on the nitrogen atoms, although it seems certain that this formal charge effect is not of general validity.
Infra-Red Absorption Spectra of Some C4 and C5 Dienes
Authors: Rasmussen R. S. , Brattain R. Robert
Published: January 2005

The infra-red absorption spectra from 2 to 15μ have been obtained of 1,3-butadiene, 1,2-butadiene, isoprene, and cis- and trans−1,3-pentadiene vapors. Salient features of the spectra are discussed.
On the Quantum Correction for Thermodynamic Equilibrium
Authors: Mayer Joseph E. , Band William
Published: January 2005

The behavior of any system at high enough temperatures approaches that of its classical counterpart. The probability of any configurational position is then proportional to exp—U/kT, with U the potential energy. Wigner has shown that quantum-mechanical deviations, as the temperature is lowered, may be approximated by multiplication of this with 1–f, where f is a function proportional to h2 and having terms in T−2 and terms in T−3. This type of approximation is unsatisfactory for a system of many degrees of freedom, that is, one of many dependent molecules. For such a system it is shown that instead of Wigner's approximation we may replace the classical potential U in the exponent by U—kTf, where f is the same as Wigner's function.
The Experimental Determination of the Intensities of Infra-Red Absorption Bands II. Measurements on Ethylene and Nitrous Oxide
Authors: Thorndike A. M. , Wells A. J. , Wilson E. Bright
Published: January 2005

The absolute intensities of the chief infra-red absorption bands of ethylene and nitrous oxide have been determined experimentally to be (in cycles per centimeter at N.T.P.): Ethylene            Nitrous oxide          950 cm−1 band: 1540×1010590 cm−1 band: 120×10101444 cm−1 band:  210×10101285 cm−1 band:1150×10103050 cm−1 band:  840×10102224 cm−1 band:5600×1010From these intensities it is possible to calculate the dipole moments, μ, of bonds between vibrating atoms and also the rates of change of dipole moment with inter-nuclear distances, ∂μ/∂r. The values of μ obtained are all of the order of magnitude of 0.5×10−18 c.g.s. unit, while values of ∂μ/∂r are of the order of 1×10−10 c.g.s. unit. The results are in agreement with available data on infra-red dispersion and on atomic polarization within the limits of experimental error, which are estimated to be approximately ±10 percent.
On the Theory of Accidental Predissociation
Authors: Kovács I. , Budó A.
Published: January 2005

Applying the results of quantum electrodynamics we investigate the case of perturbation between two discrete and one continuous term series. Even though no interaction between the first discrete and the continuous states exists, a considerable predissociation may arise for some spectrum lines in case of coincidence or close proximity between the levels of the two discrete terms belonging to the same rotational quantum number. The predissociation occurring in the first discrete term is caused by the second. This phenomenon is called accidental predissociation. Our results are in excellent agreement with the results obtained in the γ-bands of NO molecule by Schmid and Gerö.
Integral Equations between Distribution Functions of Molecules
Authors: Mayer Joseph E.
Published: January 2005

Integral equations are derived that relate variations in the potentials of average force between molecules of a system at two different densities or activities. These permit the calculation of the change in thermodynamic properties, or of the change in the distribution of molecules in space, in a liquid or crystalline phase, if either the temperature is varied, or if the the mutual potentials between the molecules is assumed to change. The equations are in a somewhat complex, but still distinguishable, matrix form. A matrix operates on the variations in potential occurring at one activity and transforms them into those occurring at a second activity. The matrix elements are combinations of the distribution functions at the second activity, to which the transformation is made, multiplied by powers of the difference of the two activities. The matrix approaches the unit matrix in value as this activity difference approaches zero. The product of the two matrices, one which transforms from activity α to activity β, with that which transforms from activity β to α, is the unit matrix. This leads to an integral (matrix) equation between the distribution functions at any two activities.

The calculation of one element of this matrix product leads to a cell type equation for the computation of the activity, or free energy, of a system in terms of the potential between a single molecule and the molecules that immediately surround it in the system.

The transformation matrices have solutions, at certain values of the activity difference y, corresponding to variations in the potentials of average force, which are transformed into zero variations at the new activity. The activities at which such variations can occur are those of the phase transitions in the systems. The solutions at these special values of the activity are differences of combinations of the distribution functions in the two pure phases that can coexist at these activities.
The Entropy of Solution of Molecules of Different Size
Authors: Hildebrand J. H.
Published: January 2005

The entropy of mixing two liquids whose molecules differ in size is expressed in terms which avoid the assumption of a lattice as an artificial frame of reference, and which is not limited to linear polymers. The equation obtained is ΔSR=N1lnV−N1b1−N2b2N1(v1−b1)+N2lnV−N1b1−N2b2N2(v2−b2),where N1 and N2 denote number of moles, V the volume of the solution, v1 and v2 the molal volumes of the pure components and b1 and b2 the sum of the actual geometrical volumes of 6×1023 molecules. With certain simplifying assumptions, equivalent to those used by authors who have analyzed the problem for linear polymers in a lattice frame of reference, the above equation reduces to the form obtained by the latter method. Various methods of obtaining experimental values for b are outlined.
Comments on the ``Hildebrand Rule''
Authors: Hildebrand J. H. , Gilman T. S.
Published: January 2005

According to the ``Hildebrand rule,'' normal liquids should have the same entropy of vaporization at temperatures at which their vapors have the same molal volume. Pitzer has shown that liquids which obey the theory of corresponding states should have equal entropies of vaporization at temperatures at which their ratio of vapor volume to liquid volume is the same. He pointed out, however, that this rests upon several assumptions, including, ``potential energy depending only on intermolecular distances and universal shape of potential energy curve.'' In this paper, two pairs of liquids with widely different liquid molal volumes but otherwise closely similar, are compared with the result that the former rule is more closely obeyed, supporting the suggestion that it is an oversimplification to regard the molecular fields of polyatomic molecules as radial from the center of the molecule. The entropy of vaporization of a van der Waals liquid, R[1n(V—b)−1n(v—b)], where V refers to vapor and v to liquid, indicates that equal V and equal v—b should give equal entropy of vaporization. In comparing ethane and diisopropyl, for example, the separation of the methyl groups is more significant than the separation of the molecular centers.
Infra-Red Spectra of Monomeric Formic Acid and Its Deuterated Forms. I. High Frequency Region
Authors: Williams Van Zandt
Published: January 2005

The hydrogen and deuterium stretching vibrations of the molecules HCOOH, HCOOD, DCOOH, and DCOOD have been studied with a high resolution echelette-grating infrared spectrometer. From the rotational structure of these bands parameters which are functions of the moments of inertia have been calculated. From these parameters, previous data, and assumptions of the hydrogen bond distances and molecular planarity, the following dimensions of the molecule have been derived: O–H, 0.96±0.01A; C–H, 1.08±0.01A; C=O, 1.225±0.02A; C–O, 1.41±0.02A; O–C=O, 125±1°; C–O–H, 107±5°; H–C=O, 122±5°.