bluuebunny/crossref_metadata_2025 huggingface dataset:
Consideration of ``Spherical Hot Spots'' Arising from Pion Capture in Explosives Using Thermal Initiation Theory
Authors: Cerny Joseph , Kaufman J. V. Richard
Published: January 2005

The process whereby relatively high energy density, ``spherical'' zones of radiation heating may arise from slow π—-meson irradiations is described, and the effects of such microscale hot spots on six explosives (lead azide, lead styphnate, mercury fulminate, RDX, TNT, and PETN) was investigated. No explosions or signs of thermal decomposition were observed with any of the explosives. Analysis of these results by the hot-spot model of explosive initiation and thermal growth was attempted. The conclusions were (1) that this model can not explain the experimental results observed for RDX, in that it predicts initiation, and (2) that the previous experiments attempting explosive initiation by the microscale thermal effects of ionizing radiation have not investigated those explosives most susceptible to initiation by this mechanism.
Role of Thermodynamic Activity in Rate Processes
Authors: Reiss H.
Published: January 2005

This paper contains an investigation of the relation between rates of diffusion and evaporation and thermodynamic activity. The method of proceeding involves the use of the one-dimensional Ising model for which an exact statistical treatment can be given. The actual system treated may be thought of as an edge dislocation with adsorbed impurity atoms. As a by product, some interesting results concerning the formation of cluster and pinning points along a dislocation are derived. However, the main purpose of this work remains the investigation of the connection between rate and activity.

For the one-dimensional model (for any degree of coupling between molecules) it can be shown exactly that the rate of evaporation is proportional to the thermodynamic activity with constant coefficient and that the rate of diffusion is similarly proportional to the gradient of the thermodynamic activity with constant coefficient. These results, which have been suggested before, therefore receive theoretical justification in terms of this simple model.

Certain not-too-restrictive conditions must be applied, however. The most important of these is the requirement that every subsystem of the system be at equilibrium with respect to all variations save the one which corresponds to the rate process.
Optical Absorption Spectrum of NiF2
Authors: Balkanski M. , Moch P. , Shulman R. G.
Published: January 2005

The optical absorption spectrum of NiF2 is reported for the paramagnetic and antiferromagnetic states. A prominent satellite appears in the 3A2→1E transition below the Néel temperature. This new line is explained in terms of the interaction of the excited Ni2+ ion with its six antiparallel Ni2+ neighbors.
Van der Waals Interaction Potential between Polar Molecules. Pair Potential and (Nonadditive) Triple Potential
Authors: Linder Bruno
Published: January 2005

A unified treatment, based on the method of the fluctuating reaction field, is presented for the van der Waals potential between polar molecules. Only dipolar interactions exclusive of retardation effects are considered. The general formulation is given in terms of frequency-dependent molecular susceptibilities and holds for any finite temperature. It is shown that, under certain restrictive conditions, the generalized potential can be decomposed into three parts representing the three constituents of the van der Waals attraction: dispersion, orientation, and induction. The general formalism is applied to the attraction between two bodies and between three bodies. The dispersive, orientative, and inductive parts of the pair potential are compared with the corresponding potentials of London, Keesom, and Falkenhagen and the (nonadditive) triple dispersive potential with the potential of Axilrod and Teller. Explicit expressions are also given for the (nonadditive) triple orientation and induction potentials. The significance of the results is discussed.
Absolute Correlation of Nuclear Spin—Spin Coupling Constants with Atomic Number. II. Couplings JX–C–H and JX—H
Authors: Reeves Leonard W.
Published: January 2005

A precise correlation of nuclear spin—spin coupling constants JX—Y is presented for molecules where X and Y are bonded or separated by a common atom in a series. If X is a central atom surrounded by equivalent Y atoms with no lone pair electrons and X varies down a group of the periodic table a relationship (JX−Y/γXγY)12=AZX+Bis obeyed where ZX is the atomic number of the element X. A and B are experimental constants to be determined. The constants A and B have been determined from literature values of coupling constants for the series JX—H and JX–C–H where X is a Group IV atom. In future work further series will be investigated. Unknown coupling constants in a symmetrical series can be predicted accurately by use of the equation.

Deviations from the correlation are expressed in terms of a deviation parameter ``D.'' The series (CH3)4Sn, (CH3)3SnH, (CH3)2SnH2, (CH3)SnH3, and SnH4 is investigated in terms of a defined deviation parameter. Positive deviations are shown to be regular in the series for JSn–C–H indicating increased ``s'' character in the Sn–C bond and corresponding negative deviations are noted for JSn–H in this series with decreasing s character in the Sn–H bond. A relative deviation parameter is suggested for a given set of molecules with slightly distorted symmetry which has not yet been investigated fully for a series of molecules.

The correlation fails when JX—H and JX–C–H are considered and X has a low atomic number. The interpretation on the basis of hyperfine splitting constants of the single s electron in the alkali metals suggests that such deviations are expected.
Multiple Equilibria in Macromolecular Systems
Authors: Deranleau David A.
Published: January 2005

The theory of multiple equilibria for binding of adsorbable molecules to macromolecules is extended to the case of polymerizing systems. The general result reduces to a simple form if no binding sites are excluded on polymerization. It is shown that nonlinear results may be obtained in a binding experiment, depending on the choice of variables, and a method of measuring macromolecular polymerization from a binding experiment is suggested.
Anharmonic Effects in Unimolecular Rate Theory. Vibrations and Collisions of Simple Polyatomic Systems
Authors: Harter Robert J. , Alterman Elliott B. , Wilson David J.
Published: January 2005

The equations of motion for the following systems were integrated numerically: (1) a four-atom linear molecule with Morse function bond stretching potentials; (2) a pair of Morse function diatomic molecules undergoing collisional interaction via a Lennard-Jones 6–12 potential; (3) a Morse function linear triatomic molecule interacting with an atom via a 6–12 potential; and (4) a Morse function diatomic molecule colliding with an atom via a 6–12 potential. A commonly used approximate method of solution is also used to analyze Case 4. In all cases the systems are constrained to colinear motion. Results are presented graphically. Our conclusions are as follows:

(1) The behavior of the four-atom anharmonic molecule shows features quite different from those shown by its harmonic counterpart.

(2) Collisional interaction via 6–12 potentials does not lead to efficient transfer of vibrational energy from one molecule to another or to efficient interconversion of translational and vibrational energies.

(3) A commonly used assumption in the calculation of the efficiency of collisional vibrational activation of diatomic molecules breaks down badly at high energies.
Helium Afterglow. I. Atomic Spectrum
Authors: Collins C. B. , Robertson W. W.
Published: January 2005

Spectroscopic investigation of a flowing helium afterglow revealed the presence of strong lines of neutral helium. An examination of the population distribution of the excited atomic states revealed the presence of a Saha equilibrium between the upper states and the free electrons indicating that the primary process of populating these states was the collisional—radiative recombination of He+. A comparison of the axial variation and pressure dependence of the intensity of the emission with the He2+ and He+ concentrations strengthened this conclusion.

Observations were made at times from 50–250 μsec into the afterglow (flow velocity ≈6×104 cm/sec) in a system having a diffusion half-life for He+ of the order of 100 μ sec, an ion density of 5×1012/cc and a maximum electron temperature corresponding to ≈0.15 eV.
Helium Afterglow. II. Molecular Spectrum
Authors: Collins C. B. , Robertson W. W.
Published: January 2005

Spectroscopic investigation of a flowing helium afterglow revealed the presence of strong bands of He2. An examination of the axial variation and pressure dependence of the intensity of the emission and He2+ concentration, as evidenced by titration, served to identify the dominant reaction populating the excited molecular states as being the collisional—radiative recombination of He2+.
Flows Through Charged Membranes. II. Oscillation Phenomena
Authors: Kobatake Yonosuke , Fujita Hiroshi
Published: January 2005

In connection with Teorell's finding on oscillation phenomena in his membrane model for nerves, flow processes of an electrolyte solution through a porous charged membrane are studied theoretically subject to the external conditions conforming to the experimental arrangements of Teorell, i.e., the total mass of the system is held constant, a constant electric current is passing through the membrane, and the pressure difference across the membrane is allowed to vary in accordance with the transport of fluid. The results of analysis show typical relaxation oscillations of the mass flow as well as the differences of potential and pressure across the membrane, and compare favorably with Teorell's observations in many aspects.
Electron Magnetic Perturbation in Diatomic Molecules of Hund's Case b
Authors: Chiu Lue-Yung Chow
Published: January 2005

The perturbation due to spin-orbit and spin-spin interactions has been studied for a Hund's Case b diatomic molecule with two outer electrons. The interactions are expressed as scalar products of two irreducible tensors and Racah's method is used to compute the off-diagonal matrix elements between states differing by ΔΛ=0, ±1, ±2; ΔS=0, ±1; ΔN=0, ±1, ±2. The matrix elements are used to study the ``forbidden predissociation'' of the metastable c 3Πu state of H2 via the repulsive b 3Σu+ state, which was the mechanism assumed by Lichten to account for the differences in the lifetimes of fs levels of c 3Πu state of H2. The relative lifetimes of fs levels thus calculated are in reasonable agreement with Lichten's measurements. The N dependence of the matrix element of spin-orbit interaction is shown to be similar to that of spin-spin interaction. The second-order perturbations via intermediate states are found to have N dependence similar to that of the first order when N is large. The interference among different transition processes between two states is discussed. The symmetric top wavefunction is used as the rotational wavefunction and its symmetry property under inversion which is necessary for this study is reviewed.
Calculation of Chemical Shifts. II. The Xenon Fluorides
Authors: Jameson Cynthia Juan , Gutowsky H. S.
Published: January 2005

Xenon chemical shifts in the xenon fluorides XeF2, XeF4, XeF6, and XeOF4 are calculated by means of the general methods presented in I. Comparisons with the experimental chemical shifts show that the change in σ(2), the paramagnetic contribution, is the dominant term and that a localized description using spd hybrid zenon orbitals gives better agreement with experiment than a delocalized MO description using no d hybridization. In addition, the indirect Xe–F and Xe–O coupling constants observed in XeF2, XeF4, and XeOF4 are more consistent with the localized models. The fluorine chemical shifts are used to estimate the ionicity of the Xe–F bonds. Also, a comparison of the anisotropy predicted for the fluorine shift in XeF4 with an experimental value shows that the fluorine shifts result almost entirely from differences in σ(2).
Infrared Spectra of Carbon Monoxide in an Argon Matrix
Authors: Leroi George E. , Ewing George E. , Pimentel George C.
Published: January 2005

The infrared absorption spectrum of carbon monoxide in an argon matrix shows prominent bands at 2148.8 and 2138.0 cm—1 with half-widths, respectively, 1.5 cm—1 and 3.5 cm—1. The relative intensities of these bands are extremely dependent upon a variety of experimental conditions, including sample concentration, window temperature, and deposition rates. The variability shows that CO isolated in argon absorbs at 2148.8 cm—1 and that it does not rotate. The lower frequency absorption is due to aggregates. The frequency shift of the argon-isolated CO absorption relative to that of gaseous CO shows that carbon monoxide fits tightly in the argon lattice. In contrast, the CO aggregates absorb at lower frequency than gaseous carbon monoxide. Isotopic studies using 13C16O reveal vibrational coupling of 1.1 cm—1 between isotopically identical molecules in an aggregate.

An increase in matrix cavity diameter would be needed if a stationary CO molecule begins to rotate in argon. This ``site expansion,'' which could be as much as 0.4 Å, may be an important factor inhibiting rotation.
Counter-Ion Penetration in Ionized Monolayers at a Dielectric Interface
Authors: Levine S. , Bell G. M. , Pethica B. A.
Published: January 2005

The equilibrium depth of immersion d in the aqueous phase of the head groups of long-chain molecules forming an ionized monolayer at an oil/water interface is considered. The free energy of formation of the monolayer is regarded as the sum of an electric double layer or ``collective'' term due to an average electric potential at the plane of head groups, a term due to the electrical images of the individual ions in the interface and a chemical term which includes the free energy of immersion of the CH2 chain groups in the aqueous phase. The balance of forces determining d is obtained by minimizing this free energy with respect to d. It is assumed that the diffuse layer ions penetrate behind the plane of head groups and the Poisson—Boltzmann equation is applied on both sides of this plane. The effects of this ion penetration have been emphasized by Haydon and Taylor but it is shown that both the electrostatic equations and the equilibrium conditions of these authors are incorrect. If, like Haydon and Taylor, one omits the image term then the correct equilibbrium relations with the remaining terms do not yield any solution for d with their values of the chain immersion free energy.
Chemical Shifts and Temperature Dependence of Spin—Spin Coupling Constants of Fluoropropenes
Authors: Ramey Kermit C. , Brey Wallace S.
Published: January 2005

NMR spectral parameters of the compounds CF2=CFY in which Y is CF3, CF2Cl, CF2Br, CF2I, or COF have been measured at room temperature and spin—spin coupling constants in four of these molecules have been investigated in the range of temperature from —100° to + 100°C. Some aspects of the temperature dependence of the coupling constants can be related to changing equilibria between cis—trans or rotational isomers, but there is an intrinsic temperature dependence, aside from these effects, which is attributed to excitation of molecular vibrations. Particular J values which change magnitude in one direction with increasing temperature are found to change magnitude in the opposite direction in regular fashion as one goes through the series of halogen-substituted compounds from fluorine to iodine. Chemical shifts observed at room temperature are discussed in terms of the effects of substituents.
Specialized Set of Molecular Distribution Functions
Authors: Squire David R. , Salsburg Zevi W.
Published: January 2005

A set of molecular distribution functions for molecules confined to a small volume is developed which makes explicit use of the short-range nature of most intermolecular forces. The excess chemical potential for systems of molecules with rigid impenetrable cores is expressed in terms of this specialized set or directly related probability functions. The general theory for rigid-sphere systems is formulated and is used in the analysis of the kernel appearing in the set of integral equations developed by Kirkwood and Salsburg.
Formation and Bleaching of Color Centers in NaN3
Authors: Miller Brian S.
Published: January 2005

Results of new experiments on low-temperature, photolytically colored sodium azide are presented. By use of a highly monochromatic light source, it has been found possible to bleach one component of the F2+ band and demonstrate the formation of F centers by the released electrons. Thermal bleaching experiments are described which illustrate the presence and lifetime of double anion vacancies. Decomposition of an excited azide ion at a vacancy is postulated as a necessary step in formation of double anion vacancies at low temperature.
Optical Properties of Small Gold Particles
Authors: Doremus Robert H.
Published: January 2005

The optical absorption of dispersions of gold particles is studied as a function of particle size, temperature, and method of preparation. The absorption spectra for gold sols in glass and water with small spread in particle size are compared to spectra calculated from Mie theory and the most reliable of recently measured optical constants of gold. The comparisons indicate that the real part of the dielectric constant ε1 for particles from 85 to 200 Å in diameter is the same as for bulk gold, and that the imaginary part ε2 is similar for particles and bulk, although some discrepancies exist. Gold sols in glass have optical properties closer to bulk gold than sols in water, probably because of defects and adsorbed material on the particles in water. Between wavelengths of about 0.40 and 0.45 μ the optical properties of the particles in glass are unchanged down to particles containing very few atoms. The optical absorption peak at 0.525 μ is unaffected by particle size down to a particle diameter of about 85 Å, showing that this absorption cannot be described by the simple free-electron model. This inadequacy of the model in this wavelength region was also deduced from the bulk optical constants. Below a diameter of about 85 Å the absorption peak is proportional to the particle diameter, as required by the free electron theory for particles much smaller than the mean free path of the electrons, but quantitative agreement with this theory is lacking. The absorption peak is shifted slightly with temperature because of the small change in electron concentration, and the peak is broadened as the temperature is increased for particles both larger and smaller than 85 Å in diameter.
Diffusion of Hydrogen, Deuterium, Nitrogen, Argon, Methane, and Carbon Tetrafluoride in Carbon Tetrachloride
Authors: Ross Marvin , Hildebrand Joel H.
Published: January 2005

The diffusion coefficients of gases in CCl4 have been determined by a steady-state method as follows: first figure in each case is for 0°C, the second for 25°C; 105D in cm2 sec—1: H2—6.28, 9.75; D2—···, 7.80; N2—2.44, 3.42; Ar—2.44, 3.63; CH4—2.05, 2.89; CF4—1.44, 2.04.

The product σ2D, where σ is the molecular diameter, is a constant within the limits of accuracy of the data, including the self-diffusion of CCl4, except in the cases of H2 and D2, where it is considerably larger.
Microwave Absorption and Molecular Structure in Liquids. LVII. Interpretation of the Parameters for the Dielectric Relaxations of 2,6-Dimethylanisole and 3,5-Dimethylanisole and Dipole Moments of 17 Aromatic Compounds
Authors: Fong Francis K. , Smyth Charles P.
Published: January 2005

The dielectric constants and losses at wavelengths of 1.25, 3.22, 10.02, 24.99 cm, and 575 m have been measured for 2,6-dimethylanisole and 3,5-dimethylanisole in benzene solutions at temperatures from 20° to 60°. Refractive indices were determined for the sodium D line at 34°. The data have been analyzed in terms of two relaxation times, the values of the short relaxation times for 3,5-dimethylanisole being consistent with the intramolecular mechanism involving the methoxy group rotation. The significance of the parameters for dielectric relaxation is discussed.

Dipole moments of seventeen compounds have been calculated for the temperature range 20°—60° from the static dielectric constants and indices of refraction in this and other papers of this series. The temperature dependence of the dipole moments of the 1,4-diacetobenzene molecule gives evidence of the hindered rotations of the acetyl groups. The presence of the two neighboring methyl groups appears to force the methoxy group out of the plane of the 2,6-dimethylanisole molecule, so that the dipole moment of 2,6-dimethylanisole is indistinguishable from that of 3,5-dimethylanisole.
Calculation of Electronic Spectra of Nonalternant Conjugated Hydrocarbons by the Semiempirical Method of Limited Configuration Interaction
Authors: Koutecký J. , Hochman P. , Michl J.
Published: January 2005

The semiempirical method of configuration interaction (the Pariser—Parr approximation) assuming equal bond lengths has been used to calculate the excitation energies of π-electron transitions for 45 nonalternant hydrocarbons (fluoranthene, azulene, the tropylium cation, the cyclopentadienide anion, fulvene, heptafulvene, their benzo derivatives, acenaphthylene, pleiadiene, and acepleiadylene). Oscillator strength has also been calculated for the most interesting of the compounds. A critical comparison with experimental data in presented and the agreement is found satisfactory. The extent to which the present results resemble those of other methods is discussed and some explanation of the successes of the simple Hückel method is obtained.
Extended Hückel Theory. IV. Carbonium Ions
Authors: Hoffmann Roald
Published: January 2005

The conformations, relative stabilities, and electronic distribution of a sample of the more important carbonium ions and positively charged hypothetical transition states are examined. The species studied include the methyl, ethyl, isopropyl, tertiary butyl, and higher alkyl carbonium ions; protonated ethylene, acetylene, benzene, cyclopropane; the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl carbinyl, allyl, and benzyl cations; the carbonium ions based on norbornane, norbornene, norbornadiene. Significant charge delocalization for a classical carbonium ion geometry is observed—the extent of this phenomenon is wider than anticipated. For the alkyl carbonium ions it is shown that the order of stabilities may be obtained from a calculation in which the polarity of the C–H bond is C—–H+. Protonated ethylene and acetylene show local minima for a symmetrical complex, but with rearrangement to an unsymmetrical cation favored. Protonated cyclopropane prefers an unsymmetrical three-center bonded structure, protonated benzene stabilizes in the familiar benzenium. The orientation of the empty carbonium p orbital with respect to other π-type orbitals determines the conformation in cyclopropyl carbinyl, benzyl, and allyl. The peculiar nature of the cyclopropane electron distribution is studied. The carbonium ions based on the bicyclo[2.2.1]-heptane structure show some nonclassical features; confirming experimental conclusions, the unusual 7-norbornadienyl cation is calculated to prefer an unsymmetrical geometry. Difficulties in applying the extended Hückel theory to charged species make some of the conclusions from the calculations less certain.
Electron Spin Resonance of Amine Solutions of Alkali Metals
Authors: Bar-Eli Kedma , Tuttle T. R.
Published: January 2005

Nuclear hyperfine structure has been observed in the electron spin resonance (ESR) absorption spectra of potassium and lithium dissolved in some alkylated amines. The four-line spectrum displayed by the potassium solutions is attributed to 39K-electron contact interaction. This interaction increases with increasing temperature. The spin density at the potassium nucleus in ethylamine solution is 3.37±0.05×1023 cm—3 at —40°C and 1.21±0.05×1024 cm—3 at 50°C. The contact interaction also decreases when methylamine is added to an ethylamine solution. This behavior is interpreted in terms of a modified view of the monomer of the theory of Becker, Lindquist, and Alder. The monomer changes its structure as its environment changes. A statistical model which relates the experimental observations to these changes is constructed.

The differences in the ESR absorption spectra observed for the three systems Na–NH3, K—EtNH2, and Li—EtNH2 are discussed, and in part, attributed to differences among the three systems in the rates of spin exchange, electron exchange, and solvent exchange. Order-of-magnitude calculations relating measured line breadths to the rates of these processes are carried out in certain limiting cases. The results of these calculations lend support to the idea that the monomer includes remote solvent molecules within its structure. The rate constant for spin exchange is shown to increase with decreasing temperature in some potassium—amine solutions.

No evidence for the solvated electron is found in the ESR spectra of K dissolved in ethylamine, or in a range of mixtures of ethylamine with methylamine. An upper limit of 10—4 is placed on the dissociation constant of the monomer. For Li in ethylamine a composite spectrum is observed under some conditions. It consists of a nine-line hyperfine pattern superimposed on a single relatively sharp line with the same g value. This sharp line is attributed to the solvated electron. The nine-line pattern is attributed to hyperfine interaction between the unpaired electron and four equivalent 14N nuclei in the Li monomer. The spin density at each 14N is 1.4±0.1×1023 cm—3, independent of temperature. Similar spectra are observed for Li dissolved in two mixed amine solvents.

The size of the monomer is discussed in terms of an expanded orbital approach. The K monomer is shown to vary between two and three times the size of atomic K. The trend toward lower percent atomic character with decreasing atomic number of the alkali metal is also discussed. Part of this trend may come about because the small atoms undergo a larger expansion in forming a monomer.
Scattering of Atomic Beams by Polycrystalline Nickel
Authors: Smith Joe N.
Published: January 2005

The results of recent experimental studies of the scattering of beams of Kr, Ar, Ne, He, and D2 from carbonized polycrystalline nickel targets are presented and compared with the findings of other investigations of the phenomenology of heavy particle scattering at a solid surface. In the present experiments, as in certain earlier experiments utilizing alkali—halide cleavage planes, large deviations from diffuse (cosine law) scattering are observed, which have not yet been satisfactorily interpreted. The present series of experiments tends to support a model for the scattering mechanism in which a fraction of the incident molecules are scattered diffusely and the remainder are scattered preferentially. From experimental observations, it is inferred that the slower particles in the incident beam contribute to the diffuse component while the faster particles are scattered preferentially. In addition, an angular variation in the degree of thermal accommodation of the incident particles is observed.
Laser Phenomena in Europium Chelates. I. Spectroscopic Properties of Europium Benzoylacetonate
Authors: Samelson H. , Lempicki A. , Brophy V. A. , Brecher C.
Published: January 2005

The absorption and fluorescence emission spectra of solutions of the chelate europium benzoylacetonate (EuB), the fluorescence decay times of these solutions, and the fluorescence emission spectrum of the solid chelate are described in detail. From this information an energy-level structure for the lower states of the ground multiplet is obtained for the solid and for the solutions and the room temperature radiative lifetime of the europium fluorescence in solutions of the chelate has been determined. The temperature dependence of the intensity and lifetimes of the fluorescence reveals that the efficiency of the intramolecular energy transfer must decrease as the temperature increases.
Elastic Constants of Single-Crystal Benzene
Authors: Heseltine James C. W. , Elliott Donal W. , Wilson O. B.
Published: January 2005

The elastic coefficients of benzene are determined from sound velocities measured with the use of an ultrasonic pulse technique over a temperature range of 170° to 250°K. At 250°K the results are (in units of 1010 dyn/cm2): c11 = 6.14; c22 = 6.56; c33 = 5.83; c44 = 1.97; c55 = 3.78; c66 = 1.53; c12 = 3.52; c13 = 4.01; c23 = 3.90. These elastic coefficients generally increase as the temperature is lowered. The observed absorption coefficients are relatively large, thus confirming data reported by L. N. Liebermann. However, it was found that the absorption is not isotropic and that the absorption for shear waves is comparable with that for longitudinal waves. Some of the experimental techniques used are described.
Energy Transfer from Carbon Dioxide in the Radiation Induced Synthesis of Water
Authors: Rudolph P. S. , Lind S. C.
Published: January 2005

Previous attempts to explain the sensitizing effect of CO2, on the basis of charge transfer, in the radiation-induced synthesis of water from its elements were not in agreement with the experimental data. Hence, this reaction was reinvestigated and compared to the nonsensitized synthesis of water. A series of reactions to explain the role of CO2 as a sensitizing agent is postulated herewith. The same scheme (omitting the reactions involving CO2) is applicable to the nonsensitized reaction. Rate equations are derived from these mechanisms. The rate constant for the sensitized reaction in a sphere of 2.43 cm diameter (K2.43) is 7.3±0.2 Ci—1. The constant for the unsensitized reaction is K2.43=7.3±0.3 Ci—1. Carbon dioxide appears to enter into the mechanism even though no CO2 is consumed in the over-all reaction. Evidence is also presented that there is no net reaction of CO2 with water vapor under alpha-particle irradiation.
Electron Spin Resonance of Irradiated Crystals of Sodium Perfluorosuccinate
Authors: Rogers M. T. , Whiffen D. H.
Published: January 2005

The electron spin resonance spectra of the radical CO2—CF2CFCO2— trapped in a single x-irradiated crystal of sodium perfluorosuccinate hexahydrate were examined at both 9000 Mc/sec and 35 000 Mc/sec. The principal values of the hyperfine coupling tensor for the α fluorine are +421, +165, and +11 Mc/sec; for one of the β fluorine +176, +64, and +52 Mc/sec, and for the other β fluorine +200, +75, and +64 Mc/sec. These are briefly discussed in terms of the electronic structure and the values in chemically related radicals.
Low-Frequency Motions of H2O Molecules in Crystals
Authors: Boutin Henri , Safford G. J. , Danner H. R.
Published: January 2005

A number of selected samples containing water of crystallization or adsorbed water have been systematically examined by neutron inelastic scattering using the Brookhaven slow chopper to study translational and librational motions of the H2O molecules in a region lying below 800 cm—1. To gain an understanding of these motions in various configurations, spectra were measured for polycrystalline samples of natrolite (isolated H2O molecules in a ``cavity''); chabazite (waterlike H2O molecules); analcime (two H2O molecules per ``cavity''); apophyllite (distorted H2O molecules); copper sulfate pentahydrate (H2O molecules forming hydrogen bonds of various lengths with the lattice); and beryl (adsorbed monomeric H2O molecules). Despite the large variety of lattice configurations and bonding forces, all these compounds, with the exception of beryl, show peaks corresponding to torsional motions of the H2O molecules in a narrow frequency region (480 to 600 cm—1). Beryl, however, shows only a broad spectrum centered approximately at kT, as expected for weakly bound H2O molecules. Besides indicating the frequencies of torsional motions and the degree of rotational freedom of the H2O molecules, these measurements provide information concerning: distribution of water molecules among various lattice sites, influence of the distortion of the H2O molecules on the observed frequencies, and the effects of its environment on the translational modes of the H2O molecules.
Proton Relaxation in Dilute Solutions of Cobalt(II) and Nickel(II) Ions in Methanol and the Rate of Methanol Exchange of the Solvation Sphere
Authors: Luz Z. , Meiboom S.
Published: January 2005

The nuclear relaxation of the hydroxyl and methyl protons in methanol containing low concentrations of Co++ and Ni++ ions has been investigated between —80°C and +80°C. This work complements previous studies of the NMR spectra of the solvation complexes in similar solutions. Over the temperature range studied, the relaxation due to the dissolved paramagnetic ions changes over two or three orders of magnitude. This dependence, as well as a corresponding temperature dependence of the chemical shift of the methanol peaks, can be quantitatively interpreted in terms of chemical exchange of methanol molecules between the coordination sphere of the paramagnetic ions and the bulk methanol. It is found that the dominant exchange process involves whole methanol molecules, i.e., proton transfer is relatively unimportant. The exchange rate is characterized by ΔH‡=13.8 kcal mole—1 and ΔS‡=+7.2 eu for Co++ ions; and ΔH‡=15.8 kcal per mole and ΔS‡=+8.0 eu for Ni++ ions. The hyperfine interaction between the paramagnetic ion and a methanol molecule in the coordination sphere is for Co++:+4.1×105 cps for the CH3 protons, and +80×105 cps for the OH proton; the corresponding numbers for Ni++ are: +5.7×105 cps and +6.8×105 cps. Proton relaxation times of the methanol in the coordination sphere are also obtained.
Trends in the Characteristic Phonon Frequencies of the NaCl-, Diamond-, Zinc-Blende-, and Wurtzite-Type Crystals
Authors: Mitra S. S. , Marshall R.
Published: January 2005

Several correlations are noted among the characteristic phonon frequencies of the I—VII, II—VI, III—V, and IV—IV compounds. In particular, the following linear relations are established: (1) between the Szigeti effective ionic charge q* and the zone center optical phonon separation (ν1—νt)/νt for the II—VI and III—V compounds; (2) between νt2 and ν12, and the reciprocal reduced mass 1/μ for the II—VI and III—V compounds, between νt2 and a/χμ, in the case of the alkali halides where a and χ are the lattice constant and compressibility, respectively; (3) between χ and an where n=4 for the zinc blende and n=3 for the alkali halides; and (4) between q* and α——α+, the difference between the atomic polarizability of the II—VI and III—V compounds. Comparison of observed and calculated compressibilities reveals that the Brout and Szigeti relations are more applicable to the IV—IV and III—V compounds, and to a lesser degree to the II—VI compounds, than to the alkali halides for which they were originally proposed.
Atomic Integrals Containing Functions of r12 and r13
Authors: Hinze Jürgen , Pitzer Kenneth S.
Published: January 2005

A method, not requiring infinite series expansions, for the evaluation of atomic integrals of type ∫ ψ1(x1)ψ2(x2)ψ3(x3)u(r12)w(r13)dτis given for the case where the ψi(Xi) are atomic Slater-type functions and the uij(rij) have the general form rijn exp (—arij).
Dependence of Lattice Gas Properties on Mesh Size
Authors: Hoover W. G. , Alder B. J. , Ree F. H.
Published: January 2005

The way in which the properties of a lattice gas converge to the properties of a real gas as the number of sites covered per particle is increased, till configuration space is a continuum, is investigated. Only for one-dimensional hard lines have the properties been worked out exactly for any mesh size, with the result that at any density the free volume per particle must span at least 50 lattice sites for the lattice gas pressure to approximate the real gas pressure within 1%. In the limit of close packing the lattice gas leads to an incorrect asymptotic form of the pressure for any finite mesh size. The virial coefficients for a lattice gas with a coarse spacing can be shown to differ in order of magnitude from the real gas coefficients. Inequalities between the real gas configurational integral and the lattice gas configurational sum can be established in any number of dimensions. Finally, by relating lattice and real gas results, an approximate way is found to predict properties of real gases in two and three dimensions from lattice results alone.
Polaron Band Structure and Carrier Mobility in Crystals of Diatomic Molecules and Aromatic Hydrocarbons
Authors: Siebrand W.
Published: January 2005

The theory developed in two previous papers is applied to crystals of hydrogen, oxygen, nitrogen, chlorine, iodine, helium, anthracene, naphthalene, and pyrene. The interaction of charge carriers with intramolecular vibrations is calculated and compared with electronic bandwidths. It is shown that the conventional band scheme, wherein electronic and nuclear wavefunctions are assumed separable for the crystal as a whole, is generally inadequate. For most of the systems studied vibronic interactions reduce the quasifree electron and hole bandwidths by a factor of 2 to 10, but in some cases the reduction is so large that the carriers can be considered localized for practical purposes. As a result halogen crystals will behave like p-type materials, whereas solid helium will be essentially n-type. The agreement between calculated band structures and measured mobilities in iodine, anthracene, and naphthalene is considerably improved by taking vibronic interactions into account. Without these interactions carrier mean free paths of the order of the lattice spacings are obtained, so that a conventional electronic band calculation produces inconsistent results.
On the Thermal Energy Transfer between Free Electrons and Molecular Vibration
Authors: Hurle I. R.
Published: January 2005

Thermally averaged probabilities for the electron de-excitation of the first vibrational level in N2 are calculated from the discrete velocity-dependent collision cross sections measured by other workers. The results are presented for the electron temperature range 1000° to 5000°K. Over this range the probability is found to have an empirical temperature dependence of the form AT—1.8 exp (T⅓), with A=1.58×10—3. The probability increases from 10—4 at 1000°K to 10—2 at 5000°K. By comparison, the corresponding experimental probabilities for the de-excitation of N2 vibration by nitrogen molecules are 10—8 at 1000°K and 3×10—4 at 5000°K. These figures imply that in some circumstances an electron concentration of only 1 in 3×106 could halve the normal nitrogen molecular relaxation time at 1000°K, and that a concentration of 1 in 6×103 could do so at 5000°K. Existing spectrum-line reversal measurements of N2 vibrational relaxation carried out in nozzle-expansion flows in the presence of small amounts of easily ionized Na and Cr atoms are reviewed in the light of these findings. It is shown that the electron concentrations in these experiments were too low to have significantly influenced the relaxation measurements.

The relative rates of degradation of electron kinetic energy to the translational, rotational, and vibrational modes of N2 are considered on the basis of the above calculations. From these considerations it is proposed that in many nonequilibrium molecular systems the kinetic electron temperature will be closely coupled to the vibrational temperature of the molecules. Some results of current expansion-flow experiments which support this proposed coupling process are briefly mentioned, and its possible importance in relation to the extent of chemical and ionization nonequilibrium in other expansion flows of shock-heated air in hypersonic nozzles and around re-entry vehicles is discussed. It is suggested that free electrons, although present perhaps in small quantities, could be important in energy-degradation processes in these systems. Other existing observations in N2 plasms which appear to support the proposed coupling mechanism are reviewed.
Collisional Deactivation of the Excited Singlet Oxygen Atoms and Their Insertion into the CH Bonds of Propane
Authors: Yamazaki Hideo , Cvetanović R. J.
Published: January 2005

Reaction of the excited singlet oxygen atoms with propane was studied at room temperature and at pressures from 400 to 6400 mm. Three main processes were observed: (1) insertion of the excited singlet atoms into CH bonds, (2) abstraction of hydrogen atoms, and (3) fragmentation of the paraffin. The yields of the insertion products increased approximately linearly with the pressure, the abstraction products remained almost constant and the fragmentation products decreased. The primary step is the insertion of the excited singlet oxygen atoms into the CH bonds of propane to form ``hot'' alcohol molecules. When gases capable of deactivating the excited atoms are added, the insertion and fragmentation decrease and the secondary hydrogen atoms are preferentially abstracted. From the increased discrimination in hydrogen abstraction the following relative rates (k2/k3) of the electronic deactivation of the excited singlet oxygen atoms by different gases have been obtained: Xe 0.47, N2 0.15, Kr 0.05, and He and SF6 close to zero.
Guest—Host Interactions: An Examination of the Solvent-Induced Spectral Shift in a Model System
Authors: Sun Huei-Ying , Rice Stuart A. , Jortner Joshua
Published: January 2005

In this paper we study the effect of a surrounding lattice of He atoms on the manifold of electronic states of the H2+ molecule-ion. One-center expansions of the molecular wavefunctions are employed, calculated by the Tibbs—Wannier method. The spherically averaged wavefunctions are in good agreement with the known exact solutions.

A detailed study of the environmental effect of the He lattice leads to the prediction of a blue shift of the first electronic transition, arising from a delicate balance between changes in the impurity excitation energy, Coulomb, exchange, van der Waals, and three-center interaction terms. The signs of the various energy changes are rationalized in terms of the overlap charge density. These results are compared with previous treatments of environmental spectral shifts based on continuum models.
Numerical Calculation of H2+ and H2 Wavefunctions
Authors: Goodisman Jerry
Published: January 2005

A numerical method of calculation, involving Gauss quadratures in four dimensions, is proposed for diatomic molecule calculations. It is applied to a linear variation function for H2+ and to James—Coolidge-type correlated functions for H2 with up to 15 basis functions. With a total of 1440 quadrature points, binding energies are reproduced to 0.1% and wavefunctions are reproduced to a few percent. Advantages and disadvantages of the method are discussed, and a comparison with the method of Frost is given.
Dependence of the Zero Shear Melt Viscosity and the Related Friction Coefficient and Critical Chain Length on Measurable Characteristics of Chain Polymers
Authors: Fox Thomas G , Allen Vernon R.
Published: January 2005

Available η—Z—T data for a wide variety of well defined linear and branched polymers and polymer—diluent mixtures are well represented by the single equation η=4.8×108(X/4.7×10—15)αζ , α=3.4 for X≥4.7×10—15, α=1.0 for X≤4.7×10—15. Here X=(〈s02〉Av/va)φ1, where 〈s02〉Av is the unperturbed mean-square radius of gyration of the macromolecule, va the volume per chain atom, and φ1 the volume fraction of polymer; values of the friction factor per chain atom ζ, computed from viscosity data by this equation, agree with independently determined values in the literature. This result confirms Bueche's theory for the viscosity of short chains and supports his theory for the viscosity of long chain macromolecules. An attempt to reduce ζ-T data for different systems to a single curve by introduction into the WLF equation of the term E/RT, where E may be related to the rotational barriers within the chain, is also presented.
Model for the Hydrodynamic Boundary Conditions at a Surface Vaporizing under High Temperatures and Pressures
Authors: Vulliet W. G.
Published: January 2005

The hydrodynamic theorems describing the conservation of energy, momentum, and mass flux are applied on each side of a vaporizing surface, and, further, the mass flux is assumed to be proportional to the difference of the chemical potentials of the vapor and condensed phases. Assuming that heat conduction is negligible, there is also conservation of the total energy (enthalpy and kinetic) of the vapor. From these theorems and assumptions, a simultaneous set of equations is derived which relates the thermodynamic properties of the vapor and condensed phases to the downstream hydrodynamic field and the heating rate of the condensed phase. For small vaporization rates, the set reduces to give the same dependence of the vapor pressure on the vaporization rate as that given by the kinetic calculation of Kucherov and Rikenglaz, but gives a different relationship between the temperature drop across the surface and the vaporization rate than the above authors have calculated.
Vibrational Interactions in Pariser—Parr Theory. I. Bandwidths and Transition Intensities
Authors: Donath W. E.
Published: January 2005

It is shown that bandwidths of some transitions can be calculated with good accuracy in the Pariser—Parr theory. For these calculations the critical point is a knowledge of the variation of the bond resonance integral β with respect to distance, which is given by κ=−dln(−β)/dR=2.0 Å−1. Calculations are carried out for the bandwidths of the N–V transition of ethylene and the 1A1g→1E1u, 1E2g transitions of benzene and the intensities of the 1A1g→1B2u, 1B1u transitions of benzene. Satisfactory agreement with experiment is obtained; the neglect of electronic repulsion terms is demonstrated to have a relatively small effect. Selection rules are established for the strength of vibrational coupling in alternant hydrocarbons.
Effect of Pressures (up to 4 kbar) on the Polymerization of Liquid Selenium from Measurements of Viscosity
Authors: Harrison D. E.
Published: January 2005

The viscosity of liquid selenium was measured between 220°—350°C and up to pressures of 4 kbar, using a rolling-ball viscometer. An extrapolation of the viscosity data to the freezing point at various pressures gave the viscosity along the melting curve of hexagonal selenium. This extrapolation showed that the viscosity along the melting curve decreased to 1/5 its initial value at 6.0 kbar, then rose with further increase in pressure. The data revealed that the slope of the log10 viscosity vs 1/T2 (°K) curve was independent of pressure up to at least 4.5 kbar. Analysis of the effect of pressure on the degree of polymerization in terms of the ring-chain equilibrium theory of Eisenberg and Tobolsky indicated that pressure has only a slight effect on the average chain length. Thus, the minimum in viscosity along the melting curve appears to be a balance between the effects of shorter chain length toward decreasing the viscosity and that of diminished free volume toward increasing the viscosity.