bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of Decomposition of HF in Shock Waves
Authors: Jacobs T. A. , Giedt R. R. , Cohen Norman
Published: January 2005

The decomposition of HF in HF–Ar and HF–H2–Ar mixtures was studied behind incident shock waves over the temperature range 3800° to 5300°K employing infrared emission techniques. For HF dissociation, a rate k1=1019.053T−1 exp (−134 100/RT) or, alternatively, k1=1022.710×T−2 exp (−134 100/RT) was found to best represent the experimental data; the exchange rate for H+HF was found to be k2=1013 exp (−35 000/RT); the recombination rate for H2 was best represented by k−3=1018.30T−1 (all rates are in cubic centimeter—mole units). Rates derived for H–F recombination were found to be in good numerical agreement with the theory of Benson and Fueno.
Single-Particle Theory for Systems at High Densities. III. Solid Neon and Some Considerations of the Second Virial Coefficient
Authors: Jenkins W. Ieuan , Walkley John
Published: January 2005

A quantal version of the Lennard-Jones and Devonshire cell model is used to predict the thermodynamic properties of solid neon. As was observed previously for solid argon, good agreement with experiment is obtained if the parameters of the assumed 12:6 pair-potential are calculated from zero-point crystal data. In view of the success of the application of this theory to the solid state, second virial coefficient data are interpreted using the zero-point reduction parameters. Again a satisfactory comparison of experiment and theory is observed.
Four-Proton System in Barium Bromide Dihydrate
Authors: McGrath J. W.
Published: January 2005

The PMR spectrum of BaBr2·2H2O shows resolved fine structure when the crystallographic b axis is perpendicular to the magnetic field. This fine structure can be explained upon assuming the existence of a four-proton system. Comparison between theoretically computed spectra and experimental spectra shows that the system is a parallelogram in the a—c plane. One side is perpendicular to the c axis while the longer side lies about 3° away from the c axis (toward the a axis). The intramolecular and intermolecular proton—proton distances are 1.57 and 2.60 Å, respectively. Neither value has been corrected for motional effects.
Growth of Large Sodium Chloride Crystals from Solution for Color-Center Studies
Authors: Gruzensky Paul M.
Published: January 2005

Sodium chloride single crystals with edge dimensions as large as 2.5 cm were grown from aqueous solutions. Solutions were purified by chemical precipitation of trace contaminants and filtration through membrane filters. Crystal defects were apparent in the initial stages of growth, but the outer portions of crystals were free of dislocations. F-band coloration by x rays at room temperature was not linear and the ``first stage'' was either absent or nearly so. Transition from extrinsic to intrinsic dc conductivity occurred at 350°C with the extrinsic conductivity two orders of magnitude lower than for ``pure'' melt-grown crystals.
Zero-Field Splitting Parameter of the Mn++ Ion in Glassy and in Polycrystalline Media
Authors: Allen B. T.
Published: January 2005

An attempt has been made to measure the zero-field splitting parameter of the manganous ion in glassy and polycrystalline media from the relative intensities of the allowed transitions of the EPR hyperfine spectrum. A value of this parameter D=96±5 G was determined for manganous ion in glassy 12N HCl for T≤140°K, and of D=145 G in glassy methnol for T≤118°K. In the crystalline phase, the D term in both cases approximately doubled. A value of D intermediate between that of the glassy phase and the final crystalline phase was found for methanol between temperatures of 120° and 135°K.
Pressures of Hg and Selenium over HgSe(c) from Optical Density Measurements
Authors: Brebrick R. F.
Published: January 2005

The optical density of the vapors at 860°C that are in equilibrium with Hg-saturated, Se-saturated, and congruently subliming HgSe(c) in the range 450° to 816°C has been measured between 2000 and 7000 Å. No indication of the species HgSe(g) is found. Assuming the optical density is the sum of those obtained with pure Se and pure Hg, the partial pressure of Hg(g), pHg, and the total selenium pressure, PΣ, are determined along a substantial portion of the HgSe(c) three-phase lines. Hg-saturated HgSe(c) is in equilibrium with essentially pure Hg(l) up to 659°C and is at least 48.5 at. % Se. The total selenium pressure attains a maximum value of 0.62 atm for Se-saturated HgSe near 722°C. The value of pHg for congruently subliming HgSe(c) is close to that required by the value of PΣ and the published thermodynamics of selenium vapor. Between about 450° and 600°C the standard Gibbs free energies of formation for both Se-saturated and congruently subliming HgSe(c) are obtained and are the same within experimental error. Taking an average, ΔGf°[Hg(g)+½Se2(g) = HgSe(c)] = −41.92+42.40(10−3)T kcal/mole. Extrapolating to 300°K, we obtain ΔHf° = −10.8 kcal/mole and ΔSf° = −4.99 eu/mole for the formation of HgSe(c) from Hg(l) and Se(c).
NMR Relaxation Times of Benzene Adsorbed on Charcoal: Molecular Rotation and Diffusion
Authors: Thompson J. K. , Krebs J. J. , Resing H. A.
Published: January 2005

NMR relaxation times have been determined as a function of temperature and composition for the protons of benzene adsorbed on charcoal. These relaxation times have been interpreted to give the following conclusions. The benzene molecule rotates more rapidly in a plane perpendicular to its sixfold axis than it does about other axes. The average enthalpy of activation for surface diffusion lies in the range 5–7 kcal/mole. At any composition, surface diffusion is characterized by a distribution of activation enthalpies with a standard deviation of about 1 kcal/mole. There are close to 1020 unpaired electronic spin/cm3. Some evidence for high-energy adsorption sites is presented.
Refractive Indices and Piezo-optic Coefficients of Deuterium Oxide, Methanol, and Other Pure Liquids
Authors: Reisler Emil , Eisenberg Henryk
Published: January 2005

The piezo-optic coefficients of deuterium oxide and of methanol and the refractive index of methanol have been determined over a range of temperatures up to 35°C. These results, and data available in the literature for benzene and a number of other pure liquids, have been examined in terms of an equation recently proposed for the dependence of refractive index of pure liquids on temperature and volume.
Influence of Electric and Magnetic Fields on the Molecular Alignment in the Liquid Crystal Anisal-p-aminoazobenzene
Authors: Carr E. F.
Published: January 2005

The molecular alignment has been studied for anisal-p-aminoazobenzene in the presence of external magnetic and ac electric fields. Measurements of the dielectric loss at a microwave frequency of 24 kMc/sec were used to indicate the extent of the molecular alignment. For the external fields parallel to each other, the degree of molecular alignment which could be obtained for a 370 kc/sec electric field was the same as that which could be produced by a magnetic field. For the magnetic and electric fields perpendicular to each other, the ratio of E/H corresponding to a random orientation of the molecules in the plane of E and H was obtained. As the magnetic field was changed from 500 to 3000 G the ratio of E/H remained constant within the limits of experimental error. The value obtained for E/H could not be explained by assuming that the processes responsible for the molecular alignment were associated with only the anisotropy in the dielectric constant and the permeability.
Theory of Shifts of Vibration—Rotation Lines of Diatomic Molecules in Noble-Gas Matrices. Intermolecular Forces in Crystals
Authors: Friedmann H. , Kimel S.
Published: January 2005

It is shown that the observed shift of infrared lines of diatomic molecules trapped in noble-gas crystals can be considered to be made up of a ``vibrational'' shift of the band center with a superimposed ``rotational'' shift dependent on the rotational quantum number J. These shifts were studied by means of a detailed analysis of the molecular motion. Application of the Born—Oppenheimer method shows that the intermolecular potential energy, which governs the rotational and translational motions of a system of electronically unexcited molecules, depends on v, the intramolecular vibrational state. This dependence is analyzed using an extension of the principle of corresponding states, thus introducing v-dependent Lennard-Jones force constants ε and σ. Explicit values of the variation with v of ε and σ have been calculated taking into account dispersion, induction, and repulsion forces. In this way vibrational shifts of HCl, DCl, HBr, and CO in Ar, Kr, and Xe matrices were obtained.

Rotational shifts are interpreted by assuming that the trapped molecule is free to rotate about a point which does not coincide with the molecular center of mass. The resulting coupling between the rotational motion of the molecule and its constrained translational motion in the lattice is treated as a perturbation. The relation between this theory and the crystal-field theory is discussed.
Ultraviolet Absorption Spectrum of Mercury in Low-Temperature Matrices
Authors: Brewer L. , Meyer B. , Brabson G. D.
Published: January 2005

The uv absorption spectrum of mercury (3P1←1S0) in Xe, Kr, and Ar matrices has been investigated previously by other workers. The present study verifies the previously published results, extends the investigation to include Ne, N2, and O2 matrices, and analyzes the effects of changing the temperature of the matrix and the concentration of mercury in the matrix. With respect to the gas-phase transition at 2537 Å, in Ne, Ar, Kr, Xe, and N2 the observed absorptions are shifted to shorter wavelength by 940, 1270, 775, 10, and 845 cm−1, respectively. The half-widths of the absorptions increase with increasing temperature and with increasing mercury concentration. Xe and Kr matrices show partially resolved triplets, while N2 yields a broad doublet. The separate components of the multiplets respond differently upon warming of the matrices. For matrices with a mercury concentration >1%, additional features, presumably due to dimers or other aggregates, are observed.
Some Aspects of the Energetics and Kinetics of Electrochemical Proton Transfer
Authors: Salomon M. , Enke C. G. , Conway B. E.
Published: January 2005

The mechanism of proton transfer in the discharge of H3O+ at metal cathodes is discussed. A kinetic method is presented in which the absolute metal—solution potential difference can be estimated for the half-cell reaction H3O++eM⇄½H2+H2O. The method is based on Johnston's BEBO method with a slightly modified triplet energy term. The results of the calculations indicate that the electrochemical discharge reaction can be treated as a simple proton transfer step as in acid—base-type reactions: the metal cathode is regarded as the base of variable strength dependent upon charge, or potential, and there is no neutralization (electron transfer) until the activated complex is formed by a classical activation process.
Interaction Potential of the Inert Gases. II
Authors: Munn R. J. , Smith Francis J.
Published: January 2005

The transport properties of the inert gases are used to define the interaction potential shape more precisely. It is found that nonadditivity contributes 10%—15% of the static lattice energy of the crystal at 0°K. The validity of the principle of corresponding states is also discussed.
Measurements of Catalytic Efficiency of Silver for Oxygen Atoms and the O–O2 Diffusion Coefficient
Authors: Hartunian R. A. , Thompson W. P. , Safron S.
Published: January 2005

Measurements have been made of the heat-transfer rate to the stagnation point of catalytic spheres and cylinders placed in the slow flow of dissociated oxygen produced in a glow-discharge tube. The use of a rapid-response thin-film heat-transfer gauge permitted operation in a transient mode; that is, a step function of atoms was produced by suddenly turning on the rf discharge. Use of this technique leads to small error in the measurement of heat transfer. Operating conditions, range of pertinent parameters, as well as flow tube and probe diameters were selected to conform with the results of the theoretical analysis for this flow. Specifically, the Reynolds number based on diffusion Ua/D, where U is the flow velocity, a is the probe radius, and D the diffusion coefficient, was varied from about 0.2–0.8, and the catalytic parameter K = kwa/D, where kw is the effective speed of the surface reaction, took on values from about 0.3–1.7. The freestream atom concentration was determined by the familiar NO titration technique. Comparison of the measurements with the theoretical results has led to the determination of surface catalytic efficiency of silver oxide and oxygen atoms and the O–O2 diffusion coefficient. These values are γ = 0.15±15% and Dp = 200 cm2/sec·mm Hg±30%. Preliminary measurements of catalytic efficiency of other metals are also presented.
On a Reduction of Liouville's Equation to Boltzmann's Equation
Authors: Hoffman David K. , Green H. S.
Published: January 2005

A solution to the Liouville equation is exhibited for an ensemble which is removed from its initial equilibrium state by the action of an arbitrary, time dependent external force. From this solution, an expression for the singlet distribution function is developed to first order in the perturbation. For rigid spheres, the singlet distribution function is shown to be a solution of the linearized Enskog equation; and for a general short-ranged interaction this function is shown to satisfy Boltzmann's equation in the appropriate approximation. The linearized Boltzmann equation is discussed and the manifestation of irreversibility is examined.
Vibrational Spectra and Potential Function for SnH4 and SnD4
Authors: Levin Ira W. , Ziffer Herman
Published: January 2005

The Coriolis zeta constants of the triply degenerate modes of normal and heavy stannane were obtained from rotational analyses and from band-contour considerations. These coupling data were then applied toward characterizing unique force constants for the F2 species.
Molecular Vibrations and Infrared Absorption of the Helical Form of Syndiotactic Polypropylene
Authors: Miyazawa Tatsuo
Published: January 2005

The molecular vibrations of the helical conformation (TTGG form) of syndiotactic polypropylene were treated on the basis of the intramolecular force field as transferred from that of isotactic polypropylene. The frequencies calculated for infrared-active vibrations (B1, B2, and B3 species) agreed closely with the observed values (rms deviation as small as 1.1%). The potential-energy distributions and atomic displacements (LX matrices) were also calculated for elucidating the nature of infrared bands. With reference to the calculated atomic displacements, the νa and νb vibrations of the TTGG form were also identified.
Influence of Rare-Gas-Configuration Cations on the Absorption Spectra of Nickel(II) Centers in Liquid Chloride and Bromide Salts
Authors: Smith G. Pedro , Boston Charles R.
Published: January 2005

Absorption spectra of dilute Ni2+ centers in melts of CsCl, RbCl, KCl, NaCl, LiCl, MgCl2, CsBr, KBr, and LiBr were measured in the near-infrared, visible, and, in a few instances, ultraviolet regions. Substantial differences were found in these spectra which correlated with the size of the cations in the solvent salts. The coordination geometry of halides about nickel in CsCl, CsBr, RbCl, KCl, and KBr melts was identified from the spectra as distorted tetrahedral. Coordination geometry in the remaining melts was uncertain. The spectrum for MgCl2 as solvent was very similar to that for LiCl as solvent.
Nuclear Quadrupole Spectra in Very Asymmetric Field Gradients
Authors: Alexander S. , Ganiel U.
Published: January 2005

Pure nuclear quadrupole resonance spectra in asymmetric field gradients are discussed. Contrary to the usual approach, the fully asymmetric case (η=1) is taken as a starting point. It is shown that in this case the Hamiltonian has an important symmetry property, which gives information on the energy-level spectrum and relations between the eigenfunctions. Closed solutions in terms of quadratic equations can be obtained for spins up to 92. A perturbation expansion around η=1, which seems to converge very well, is also described.
Some Comparisons of the Classical RRK and the RRKM Theoretical Rate Formulations
Authors: Placzek D. W. , Rabinovitch B. S. , Whitten G. Z. , Tschuikow-Roux E.
Published: January 2005

It is shown by comparison with RRKM (Rice—Ramsperger—Kassel—Marcus) calculations for unimolecular reactions that the classical Kassel empirical fit parameter s is a complex function of temperature, the critical energy ε0, and of the vibrational pattern of the molecule and activated complex considered. The comparisons have afforded a delineation of quantal molecular behavior and of the empirical classical interpretation. Some detailed application is made to the methane and fluoroform decomposition reactions. Possible discrepancies in shock-tube measurements are discussed.
On the Magnetic Susceptibility of Aromatic Hydrocarbons and ``Ring Currents''
Authors: Musher Jeremy I.
Published: January 2005

It is shown that the anisotropic magnetic susceptibility (and chemical shift) of aromatic hydrocarbons generally attributed to π-electron ``ring currents'' can be correctly represented as the sum of contributions from localized electrons of both π and σ character. The ``delocalization'' of the electronic distribution plays no part whatever is the effect and is only an artifact of London's approximate calculation. Anisotropic Pascal's constants for aromatic carbon atoms are determined empirically and excellent agreement with the experimental anisotropic susceptibilities is obtained.
Theory of Hyper-Raman Effects (Nonlinear Inelastic Light Scattering): Selection Rules and Depolarization Ratios for the Second-Order Polarizability
Authors: Cyvin S. J. , Rauch J. E. , Decius J. C.
Published: January 2005

The symmetry properties of the third-rank tensor β which comprises the set of coefficients of quadratic terms in the expansion of the induced-dipole moment in the electric field are investigated, and the various linear combinations belonging to the irreducible representations are tabulated for the important molecular symmetry groups. Depolarization ratios are calculated for a sample composed of randomly oriented molecules (liquid phase). Examples of the selection rules in both liquid and crystalline phases are discussed, and these selection rules are contrasted with the ones appropriate for infrared absorption and the ordinary Raman effect.

Molecular modes allowed in the infrared are always allowed in the hyper-Raman effect and have a depolarization ratio (for linearly polarized incident radiation) ≤⅔, while allowed hyper-Raman transitions forbidden in the infrared have a depolarization ratio of ⅔.
Shock-Tube Experiments on Inhibition of the Hydrogen—Oxygen Reaction
Authors: Skinner Gordon B. , Ringrose Gordon H.
Published: January 2005

The ignition of hydrogen—oxygen—argon mixtures containing small amounts of CH4, C2H4, CF3Br, and 1,2-C2F4Br2 was studied in a shock tube at 970°—1300°K. All four additives inhibited ignition of the gas mixture, higher temperatures being required to give ignition in a given time than when no inhibitor was present. The additives are consumed during the ignition, CH4 and C2H4 being converted mainly to CO, CF3Br to CF3H, and C2F4Br2 to C2F4 in the relatively rich mixture studied. The data have been correlated in terms of elementary chemical reactions. Pyrolysis of CF3Br and C2F4Br2 was studied to aid in the interpretation of the inhibition process.
Force Constants of N2O4 and NO2 and the Viscosity of the Dissociating System N2O4⇌2NO2
Authors: Barua A. K. , Dastidar T. K. Rai
Published: January 2005

By analyzing the experimental viscosity of the dissociating system N2O4⇌2NO2, the force constants of N2O4 and NO2 have been obtained for the Lennard-Jones (12:6) potential. The calculations made with the force constants thus obtained suggest that, in agreement with theory, chemical reaction has no significant effect on the viscosity of a chemically reacting gas mixture.
Concurrent Ion—Molecule Reactions. I. Reactions in X—CD4 Mixtures
Authors: Shannon T. W. , Harrison A. G.
Published: January 2005

A ratio-plot method, whereby the contribution of concurrent ion—molecule reactions to the same product ion may be estimated, has been applied to the study of the formation of the XD+ ion in X—CD4 mixtures for X=CO, N2, and CO2. It is shown that XD+ is formed by both deuteron transfer from CD4+ and by deuterium atom abstraction by X+. The cross sections for the individual reactions have been determined and compared with theory.
Concurrent Ion—Molecule Reactions. II. Reactions in X—D2 Mixtures
Authors: Shannon T. W. , Harrison A. G.
Published: January 2005

The formation of XD+ in X—D2 mixtures where X is CO, A, CO2, and CH3CN is shown to be the result of the two concurrent ion—molecule reactionsX++D2→XD++D,D2++X→XD++D.The cross sections for the individual reactions have been measured and compared to theoretical predictions.
Statistical Thermodynamics of Bolaform and Dipolar Ionic Solutions by the Mayer Method
Authors: Manning Gerald S.
Published: January 2005

We have applied the ring-diagram approximation of the Mayer ionic solution theory to solutions containing bolaform ions and to solutions containing dipolar ions. For the former case we derive a simple expression for the activity coefficient of the counterion to the bolaform ion. This expression has the property of increasing with the length of the bolaform ion from the Debye—Hückel limiting value for a uni-divalent salt (zero length) to the limiting value for a uni-univalent salt (infinite length). For dipolar ions we recover as a limiting case an expression derived by Kirkwood by classical means. We also derive a term accounting for dipolar ion—dipolar ion interactions, which is comparable to one obtained by Fuoss for a different model.
Quantum Statistical Theory of Atoms in Hydroquinone Clathrates
Authors: Neece George A. , Poirier Jacques C.
Published: January 2005

A quantum statistical mechanical theory of clathrates is presented. This theory, like the van der Waals theory, idealizes a clathrate as (1) a lattice having properties unaffected by the extent of occupancy of its cavities by guest atoms, and (2) a system of independent cavities randomly occupied by guest atoms. Within a cavity, the guest atom is assumed to move in the cell potential Φ(x, y, z)= ∑ q=x,y,zVq[ρqtan2(πq/2γq)−1],rather than in the sphericalized Lennard-Jones—Devonshire cell potential used in the van der Waals theory. The corresponding Schrödinger equation is exactly soluble and the energy eigenvalues are easily incorporated into a convenient quantum statistical mechanical formalism, valid at both low and high temperature, for the ``guest'' contribution to thermodynamic functions. With an assumed cubical cell symmetry, shown to be not unreasonable, one of the three parameters can be approximately determined by structural data on the β-hydroquinone lattice. After adjusting the remaining two parameters to fit some data, the thermodynamic predictions are found to be in satisfactory agreement with all other thermodynamic data on rare-gas hydroquinone clathrates. The energy of the transition from ground to first excited state for the motion of guest atoms is in very good agreement with experimental data.
Classical Unimolecular Rate Theory. III. Effect of Initial Conditions on Lifetime Distributions
Authors: Baetzold Roger C. , Wilson David J.
Published: January 2005

The distribution of lifetimes of classical anharmonic and harmonic triatomic molecules capable of dissociation is found to depend upon the distribution of initial conditions immediately after collisional activation. Two types of collisional-activation mechanisms are treated: one in which the density of initial points in phase space depends only upon the energy (the random mechanism), and the second in which the vibrational energy of the molecule is initially entirely kinetic (the impulsive mechanism). The random mechanism leads to a roughly exponential distribution of lifetimes for both harmonic and anharmonic molecules, in agreement with earlier work. The impulsive mechanism leads to lifetime distributions showing very marked peaks and minima for the harmonic model; this effect is much smaller for the anharmonic model.
Proton Magnetic Resonance Studies of Solid Triethylenediamine—Molecular Structure and Motions
Authors: Smith George W.
Published: January 2005

Proton magnetic resonance (PMR) studies of solid triethylenediamine (TEDA) were made between 77° and 420°K. Measurements of linewidth, second moment, and spin—lattice relaxation time were determined. Rigid-lattice second moments yielded a C–H distance of 1.09±0.02 Å but could not distinguish between the D3h and D3 molecular configurations. A line narrowing at about 190°K was explained in terms of a restricted molecular reorientation about the N–N axis plus a wobbling of the axis, the activation energy being about 7 kcal/mole. At the temperature of transition to a plastic crystal (351°K) the second moment dropped discontinuously to a value characteristic of general molecular reorientation. Simultaneously, molecular self-diffusion became effective as a line-narrowing agent. The activation energy for diffusion was found to be 16.2 kcal/mole, in good agreement with the lattice energy of 14.8 kcal/mole, as estimated from the heat of sublimation. A high-resolution experiment failed to reveal any interconversion between the D3 and D3h molecular configurations. Theoretical expressions for the second moment for isotropic molecular reorientation are given in terms of the density, the molecular mass, and the number of protons per molecule for simple cubic, fcc, bcc, and hcp structures. Within 0.5% the expressions are the same for the last three lattices, and the simple cubic lattice expression is only 13% larger.
Linewidths of the Microwave Inversion Spectrum of Ammonia
Authors: Legan Robert L. , Roberts James A. , Rinehart Edgar A. , Lin Chun C.
Published: January 2005

The linewidths of some 25 inversion spectral lines of ammonia in the frequency region of 18–29 kMc/sec have been measured. Corrections due to various effects such as source modulation, cell-length broadening, and Doppler shift were applied to the experimental data to evaluate the linewidth parameters. Self-broadening and foreign-gas broadening by some 15 different gases have been studied. In the case of self-broadening of the series of lines with J=K for which the effect of rotational resonance is negligible, the width parameters determined experimentally agree well with those calculated by Anderson's theory from (2, 2) to (5, 5), but appreciable deviations are found at higher J. For the lines with J≠K, the discrepancy becomes larger and increases with increasing difference between J and K. The quantum number dependence of the foreign-gas broadening by methyl chloride and by carbon dioxide has been investigated in detail. For methyl chloride broadening the theoretical and measured widths agree with each other to about the same extent as in self-broadening, whereas the agreement is somewhat less satisfactory in the case of carbon dioxide. An alternative formulation of the collision theory of line broadening is presented. Here the theory of radiation interruption is treated as a problem of multichannel collision. The essential feature of this formulation is that it includes the higher-order effects of the collision process rather than just the usual first-order terms. This analysis leads to suggestions as to possible directions of improving the calculations.
Vibrational—Rotational Spectrum of Difluoroborane and Difluoroborane-d
Authors: Lynds L. , Bass C. D.
Published: January 2005

Four HBF2 and two DBF2 fundamentals have been resolved into their fine structure under medium dispersion. The three A1 modes, v1, v2, and v3 are characterized by a series of evenly spaced lines having the general appearance of a ⊥ band of a symmetric-top molecule. The B2 modes, v6, have a strong Q branch in addition to a well-defined subband system and have the appearance of Type-C bands near the prolate limit. Using a symmetric-top approximation, an analysis of the spectra provided six independent measurements for the smallest moment of inertia from which the average apex angle F–B–F was calculated to be 117.4±2° assuming the BH(BD) bond distance to be 1.20 Å. In HBF2, interband agreement of the rotational constant A, associated with the smallest moment of inertia, was quite good. It was possible to assign K values to the individual lines and to determine the position of the band centers for the resolvable fundamentals v1, v2, v3, and v6.
Fluorescence and Defect Fluorescence of Anthracene at 4.2°K
Authors: Helfrich W. , Lipsett F. R.
Published: January 2005

Previous measurements of space-charge-limited hole currents have shown that anthracene crystals, even if very pure, contain large numbers of hole traps distributed exponentially in depth. Arguments are presented that these defects, if structural, should also act as singlet excitation states below the singlet exciton band. In order to detect such excitation states, the following experiments were carried out at 4.2°K: (1) observation of fluorescence with ordinary excitation within the singlet absorption band (vexc>v0–0) to check the purity of the anthracene crystals, (2) observation of fluorescence with defect excitation (vexc<v0–0), (3) observation of both kinds of fluorescence after the crystals were annealed at 130°C.

Some of the ordinary fluorescence spectra showed sharper lines than spectra previously reported. These lines appeared as doublets. Three kinds of defect fluorescence, which depended on the crystal used and on vexc, were observed: (a) fluorescence without structure in its excitation and emission spectra, (b) fluorescence with structured emission spectrum, (c) strong background emission in the ordinary fluorescence. No indications of chemical impurities were found. The results indicate that disordered regions, point defects, and dislocations play a significant role in the fluorescence process.
Monte Carlo Equation of State for a Mixture of Hard Spheres
Authors: Rotenberg A.
Published: January 2005

The equation of state for an equimolar binary mixture of hard spheres has been calculated by the Monte Carlo method for the case where the ratio of diameters is 1.1 to 1. The contact values of the three radial distribution functions are compared with those obtained from the solution of the Percus—Yevick equation as well as with an approximation obtained from scaled particle theory and are found to be in good agreement for densities below the phase transition. The density at which the phase transition occurs is about the same as the corresponding density for the one-component system. At higher densities the contact value of the radial distribution function between pairs of small spheres remains essentially constant.
Dissociation of Molecular Hydrogen by Electron Impact
Authors: Corrigan S. J. B.
Published: January 2005

The dissociation of molecular hydrogen by electron impact was studied by observing the rate of pressure decrease in a closed system when the dissociation fragments were trapped on molybdenum trioxide. An onset potential of 8.8 (±0.2) eV was obtained, indicating that a large part of the dissociation must proceed through direct excitation of the repulsive b 3Σu+ state of the molecule. From the onset potential to 95 eV, the upper energy limit of our observations, the dissociation rate increased rapidly at first, then more slowly above 14 eV passing through a flat maximum at 40 eV and then slowly decreasing up to the highest energy investigated.

Reasons are given for supposing that the observed cleanup of hydrogen at high electron energies contains an effect due to dissociative neutralization of molecular ions. With this assumption the cross section for excitation of the molecule to triplet states is derived by subtracting the molecular ionization cross section from the observed total dissociation cross section. In this way we obtain a cross section for dissociation into neutral atoms which has a maximum of 9×10−17 cm2 at an energy of 16.5 eV, followed by a rapid decrease with increasing electron energy.
Adiabatic Demagnetization of MnCl2 with the Magnetic Field Parallel to the b Magnetic Axis
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: January 2005

Adiabatic measurements on single-crystal MnCl2 as a function of magnetic field have been tested as isentropics for use with isoerstedic heat capacity data in a ``saw-tooth'' method of establishing entropy values as a function of field and temperature in the region above 1°K where absolute temperatures are readily available. All measurements were made with the field parallel to the b magnetic axis. Adiabatics with an entropy less than about 0.6 gibbs/mole became irreversible at some unknown temperature below 1°K. However, determinations of the differential magnetic susceptibility on these adiabatics disclosed three high peaks at low temperatures and fields of about 4, 13, and 15 kG. The peaks are evidence of substantial but gradual magnetic structural changes which are much more complex than previously realized. The correction of data obtained during demagnetization for minor heat leak to give true entropy values is discussed.
Remarks on the Calculation of the van der Waals Energy
Authors: Epstein Saul T.
Published: January 2005

We look for conditions under which the van der Waals energy calculated by means of variationally determined polarizabilities according to the formula of Mavroyannis and Stephens, is an upper bound to the true energy. The conditions we find are quite restrictive.
Vibrational Relaxation in Methane—Oxygen Mixtures
Authors: Parker J. G. , Swope R. H.
Published: January 2005

Measurements have been made of the relaxation frequency and vibrational specific heat of mixtures of oxygen and methane, with the methane concentration varying from 0.05% to 1.6%. The temperature in all cases was 23°C and the total pressure of the mixture atmospheric. Results of these measurements show that the relaxation frequency does not vary linearly with methane concentration and that the vibrational specific heat is concentration dependent. Theoretical interpretation of these results indicates that there is a strong coupling of the vibration of oxygen to that of methane and that losses due to radiation from the methane are significant. It is further determined that methane is approximately as effective in exciting vibration in oxygen as in itself and that oxygen is considerably less efficient in exciting vibration in methane.

Supplementary measurements were also made on pure methane and methane dilute in gases characterized by their vibrational inertness — N2, Ne, Ar, and Kr. The relaxation time of pure methane was found to be in excellent agreement with values determined by previous investigators. Nitrogen was found to have a measurable effect in shortening the relaxation time of methane; surprisingly, Ne, Ar, and Kr were all found to be more effective than nitrogen.
Spectrum-Line Reversal Measurements of Free-Electron and Coupled N2 Vibrational Temperatures in Expansion Flows
Authors: Hurle I. R. , Russo A. L.
Published: January 2005

Spectrum-line reversal measurements of the excitation temperature of Na atoms in expansion flows of shock-heated Ar and 1% N2+Ar mixtures are described. The measurements were made in a conical nozzle attached to the end of a conventional shock tube. For expansion flows of pure Ar from reservoir temperatures of 3200° to 4200°K and a reservoir pressure of about 37 atm, the measured Na temperatures (≈2200°K) were considerably in excess of the local-translational temperature (≈400°K). These high excitation temperatures are interpreted in terms of the excitation of Na by free electrons produced from ionization of the Na in the reservoir. On this basis, free-electron temperatures are deduced which indicate freezing of the electron thermal energy at values corresponding to those expected at the nozzle throat. This result suggests a slow rate of transfer of electron thermal energy to the Ar translational mode.

The addition of 1% N2 to the Ar expansions produced large reductions in the measured Na temperatures. The reduced temperatures are shown to correspond to the frozen N2 vibrational temperatures expected on the basis of previous results. These reductions are explained in terms of an efficient transfer of the excess-electron thermal energy to the N2 vibrational mode, the free-electron and N2 vibrational temperatures being thereby coupled and equilibrated during the expansion.

The present results also substantiate the faster vibrational relaxation rates inferred previously from similar expansion-flow studies of pure N2; they further suggest that the simple Landau—Teller rate equation, when used with relaxation times measured in shock-wave flows, is not adequate to describe the vibrational relaxation process under the extreme nonequilibrium conditions associated with nozzle-expansion flows.
Differences in the Spherical Intermolecular Potentials of Hydrogen and Deuterium
Authors: Mason E. A. , Amdur I. , Oppenheim I.
Published: January 2005

The differences in the Lennard-Jones parameters of hydrogen and deuterium are determined from a reanalysis of the second-virial-coefficient data of Michels et al. and an analysis of the diffusion data of Amdur and Beatty and of Mason, Annis, and Islam. The effects of higher Chapman—Enskog approximations, spherical quantum corrections, inelastic collisions, and the anisotropy of the intermolecular potentials on the transport coefficients are found to be very small, and the experimental differences can be ascribed unambiguously to differences in the isotropic intermolecular potentials. The reanalysis of the second-virial-coefficient data yields the results that (εH2—εD2)/εH2=0.06 and (σH2—σD2)/σH2=0.00 8; these results are consistent with the transport-coefficient data.
Bond Energies and the Interactions between Next-Nearest Neighbors. II. Theoretical Calculations of Next-Nearest-Neighbor Interaction Energies in Saturated Hydrocarbons
Authors: Cignitti Maurizio , Allen Thomas L.
Published: January 2005

Next-nearest-neighbor interactions in saturated hydrocarbons have been considered from a number of different points of view, including van der Waals radii, previous theoretical calculations of various types, nonbonded potential-energy functions, magic-formula calculations, and evidence from bond-dissociation energies. Most methods indicate that the interactions are repulsions of several kcal/mole each. Two sets of potential functions give results in fairly good agreement with thermodynamic data. In each set the C···C function rises most steeply with decreasing distance and the H···H function least, a condition related to the thermodynamic data and the geometric mean used to obtain the H···C function. Magic-formula calculations with invariant SCF orbitals lead to additivity of bond energies. Calculations on alkyl-hydrogen bond-dissociation energies indicate that methyl, ethyl, s-propyl, and t-butyl radicals have about the same reorganization energy, the decrease in bond dissociation energy on methyl substitution being predominantly a third-neighbor effect.
Power Series Representation of Generalized Oscillator Strengths
Authors: Lassettre Edwin N.
Published: January 2005

Expansion of generalized oscillator strengths in powers of the momentum change K (of the colliding electron) generally leads to series with finite radii of convergence. From a study of singularities of the function for complex values of K it is possible to transform the series into one which converges for all physically attainable values of K. The transformation depends on the ionization potential and the excitation energy, both of which can be determined experimentally. The transformed series should be useful in fitting experimental data and in the extrapolation of oscillator strengths. It is especially useful, however, when applied to transitions for which a few terms of the series in inverse powers of K can be obtained. As an example the 11S→21S transition in helium is treated. The mere determination of the degree of the first nonvanishing term in the inverse power series is enough to severely restrict the form of series and, in fact, to sum the first six terms. These terms, which involve only one adjustable constant, fit the experimental data to within 3.5% and the deviation is mainly due to experimental error.
Effect of Surface Impurities on the Thermal Accommodation Coefficient
Authors: Allen R. T. , Feuer P.
Published: January 2005

The effect of surface impurities on the thermal accommodation coefficient, which is a measure of the energy exchange between a beam of gas atoms and a solid, is studied with a one-dimensional model. Quantum theory is used to obtain an expression for this coefficient as a function of temperature, mass of the lattice atoms, mass of the impurity atom, force constant associated with the coupling of the lattice atoms to each other, and force constant associated with the coupling of the impurity to the lattice. The conditions under which a localized mode, due to the presence of the impurity, can contribute strongly to the energy exchange are examined. Results are considered in connection with the accommodation coefficient of helium on metals with surface impurities.
Internal Rotation and Kerr Effect in Polymer Molecules
Authors: Nagai Kazuo , Ishikawa Toshihide
Published: January 2005

A theory of the Kerr effect (the electro-optical birefringence) of dilute polymer solutions is developed. If interactions between polymer molecules are neglected, the molar Kerr constant of polymer molecules is expressed as Km=(2πNA/45kT){(3〈utrγu〉−Tr〈u2γ〉)(kT)−1+[3Tr〈γγ′〉−〈(Trγ)(Trγ′)〉]},where NA is the Avogadro number; k is the Boltzmann constant; T is the absolute temperature; u, γ, and γ′ are the dipole-moment vector and the optical and static polarizability tensors of a polymer molecule, respectively; utr is the transpose of u; Tr denotes the trace of a matrix; and the averages refer to those about a free polymer molecule. In addition to Km, the two quantities 〈r2〉F/〈r2〉 and 〈x2〉F/〈y2〉F are calculated, which, respectively, are considered to be measures of the degrees of deformation and orientation of a polymer molecule by an electric field of strength F. Here r is the absolute value of the end-to-end vector r = (x y z)tr, the field being assumed along the x axis; the averages with and without subscripts refer to those in the presence and in the absence of the field, respectively. Alternative expressions for Km, etc., are derived by assuming the additivity of bond dipole moments and bond polarizabilities.

An application is made to the polyethylene molecule, by using geometrical models proposed by Hoeve and by Nagai and Ishikawa, and also using Denbigh's and Bunn and Daubeny's values for bond polarizabilities. It is found, for example, that the elimination of the GG′ conformation for neighboring bonds, which has been known to increase markedly 〈r2〉, increases only slightly Km.

It is pointed out that the molecular-weight dependence of specific Kerr constants, found by Le Fèvre and his collaborators for a variety of polymer—solvent pairs, should be ascribed to the excluded volume. Thus need for a theory of the effect of the excluded volume on Kerr constants, and for experimental data obtained at the so-called Θ condition, is emphasized.
Vibration—Rotation Spectra and Structures of Germyl Halides
Authors: Rhee Kee H. , Wilson M. Kent
Published: January 2005

The rotational constants A″ and ζ values have been determined by the analysis of the rotational structure of the perpendicular bands of GeH3F, GeH3Cl, GeH3Br, and GeH3I. By combining the microwave and the infrared data, the structural parameters of some of the germyl halide molecules have been refined. A strong rotational perturbation was observed in the GeH3 deformation fundamental v5 of GeH3Br which has been interpreted as a second-order Coriolis interaction between two fundamental vibrations (v2 and v5) of different symmetry.
Probability Tables for Clusters of Foreign Atoms in Simple Lattices Assuming Next-Nearest-Neighbor Interactions
Authors: Kreitman Marshall M. , Barnett Donald L.
Published: January 2005

Concentration dependent probabilities for clusters of impurities of one kind in simple cubic, body-centered cubic, face-centered cubic, and hexagonal close-packed lattice structures are given. Polynomials which give the probabilities of singles, pairs, and different configurations of triads are tabulated for concentration values ranging from 10.0% to 0.01%. The existence of the next-nearest-neighbor and nearest-neighbor interactions between impurities randomly distributed throughout the lattice is assumed. Results obtained by considering only nearest-neighbor interactions are graphically compared with those of the present paper, and a significant reduction in the probability of singles, pairs, and triads is claimed in the present work. The inclusion of next-nearest-neighbor interactions produces a change in the number of single, pair, or triad clusters similar to that caused by increasing the concentration. Among other conclusions, it is noted that, for impurity concentrations below 3%, changes in the cluster probabilities are influenced by the consideration of interactions with more distant neighbors, while for higher concentrations it is wise to consider, in addition, clusters of four or more.
Bounds on the Configurational Integral for Hard Parallel Squares and Cubes
Authors: Hoover William G.
Published: January 2005

Upper and lower bounds on the configurational integral for hard parallel squares and cubes are obtained. These bounds are valid over the entire density range and apply to infinite (thermodynamic) systems. Both the upper bound and the lower bound approach the free-volume form at high density.

This strong result proves rigorously that the free-volume form is correct for these systems in the thermodynamic limit.
Calculation of Virial Coefficients. Squares and Cubes with Attractive Forces
Authors: Hoover William G. , Ree Francis H.
Published: January 2005

A general combinatorial formulation of the star integrals occurring in calculations of virial coefficients is presented. The usefulness of the formulation is demonstrated by the exact calculation of the first five virial coefficients for gases of hard parallel squares and cubes with attractive forces.

For these gases the three-, four-, and five-term virial series are examined, and each series is found to have a critical point. Most of the critical properties of these truncated virial series are sensitive to the number of terms included, but the product PcVc remains nearly constant as more terms are added.

It is shown that any two- or three-dimensional square-well virial coefficient is negative at low temperature. Despite this, the low-temperature contribution of the complete star integral can be either positive or negative.
Thermodynamics of the Rigid Rotor at High Temperature
Authors: Kilpatrick John E. , Fukuda Yoshiichi , Larsen Sigurd Yves
Published: January 2005

It is shown that Qe, the partition function for a rigid rotor summed over even levels and Qo, summed over odd levels, have exactly the same asymptotic (power series in σ=ℏ2/2IkT) expansion. No information as to differences in thermodynamic properties due to spin and statistics can be obtained from this expansion. The exchange partition function, Qe—Qo, is calculated directly and used to give simple expressions for the differences in thermodynamic properties between the para, ortho, and equilibrium cases.