bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Decomposition of Hexamethylethane, 2,2,3-Trimethylbutane, and Neopentane in a Single-Pulse Shock Tube
Authors: Tsang Wing
Published: January 2005

Hexamethylethane, 2,2,3-trimethylbutane, and neopentane have been pyrolyzed in a single-pulse shock tube. The initial steps of the main reactions involve the breaking of carbon—carbon bonds. The rate parameters of the following reactions: C4H9–C4H9→ lim kI2 t−C4H9·,C4H9–C3H7→ lim kIIt−C4H9·+i−C3H7·,and C4H9–CH3→ lim kIIIt−C4H9·+CH3·have been found to be kI=1016.3exp(−68 500/RT) sec−1,kII=1016.2 exp(−73 000/RT) sec−1(1100∘K and 4 at m),and kIII=1016.1exp(−78 200/RT) sec−1.The pre-exponential factors are several orders of magnitude lower than what would have been expected on the basis of previous measurements of radical combination reactions.
Electric Polarization of Solutions of Rodlike Polyelectrolytes
Authors: McTague John P. , Gibbs Julian H.
Published: January 2005

A statistical-mechanical model for electrical polarizability of solutions of rodlike polyelectrolytes has been developed. The polyion is treated as a linear array of sites for adsorption of counterions. It is essentially the Rice—Harris model with an applied electric field. Calculation of the partition function of this system is performed by the matrix method and predictions are made for the effect on the low-frequency dielectric constant of added salt, degree of polymerization, and degree of neutralization. The results are in approximate agreement with measurements of solutions of polymethacrylic acid and deoxyribonucleic acid.
Generalized Sternheimer Potential
Authors: Epstein Saul T. , Karl John H.
Published: January 2005

The definition of the Sternheimer potential is generalized to include wavefunctions which involve spin in a nonfactorable way.
General Solution for One-Center Zero-Field-Splitting Integrals
Authors: Lounsbury John B. , Barry George W.
Published: January 2005

By use of Fourier integral transforms, a general and exact solution is derived for all possible one-center zero-field-splitting (zfs) integrals using Slater-type orbitals. This solution may be used for development of tables of functions or programmed directly for computer calculations. Direct computer calculation of one-center zfs integrals using the analysis developed is discussed.
Kinetics of Ionic Processes in the Radiolysis of Liquids. II. Proton Transfer from Cyclohexane Ions to Ethanol
Authors: Buchanan James W. , Williams Ffrancon
Published: January 2005

The extent to which positive ions produced by the radiolysis of cyclohexane undergo proton transfer to a dissolved scavenger before geminate recombination has been studied by an isotopic method. Ethanol-d (C2H5OD) has been used, and the yield of HD is related to the yield of scavengable ions. The yield is strongly dependent on ethanol concentration over most of the range but at high concentration (>1M) a limiting value is reached corresponding to an estimated total yield of 2.6 ion/100 eV. The dependence of the yield on scavenger concentration suggests that the distribution of recombination times for ion pairs lies in the range between 10−7 and 3×10−11 sec corresponding to initial separation distances between 280 and 19 Å, respectively. A median separation distance of 50 Å is indicated. The results are consistent with the earlier supposition that the electron is trapped as a negative entity with molecular dimensions. Some implications of this model are examined.
K-Absorption Fine Structures of Sulfur in Gaseous SF6
Authors: LaVilla Robert E. , Deslattes Richard D.
Published: January 2005

Measurements are reported on the K-absorption fine structure of sulfur in gaseous SF6. The results differ qualitatively from previous measurements on molecular gases of lower coordination. Comparison is also made with preliminary results on H2S.
Classification of Rotational Energy Levels for Linear Molecules
Authors: Dalton B. J.
Published: January 2005

The classification of the rovibronic energy levels according to the symmetry species of the molecular point group, previously presented only for nonlinear molecules, is extended to linear molecules, within the approximation that the interaction between rotational and vibronic motions can be neglected. Selection rules in terms of these species are obtained for the rovibronic transitions. The effect of the rotation—vibronic interaction on the classification scheme and the selection rules is considered.
Formulation of Resonance Conditions
Authors: Coope J. A. R.
Published: January 2005

A resonance condition is a condition on the variables of a system (external field, orientation, etc.) such that two energy levels differ by a fixed energy δ. This paper discusses the formulation of exact theoretical resonance conditions by methods which do not require knowledge of the energy levels themselves. An exact resonance condition for an n-level system can be written as an algebraic equation of degree ½n(n−1) in δ2. The determination of this equation from the characteristic equation for the energies is an old algebraic problem discussed by Lagrange and by Cayley, the formulation of the equation of differences. Relevant properties are reviewed, and polynomial and determinantal formulas are given. Application is made to a particle of spin S≦52, with a second-order tensor zero-field term, in a uniform external magnetic field.

A second approach is to construct an operator F={(K1×12−11×K2)2}, in a ½n(n−1)-dimensional space of antisymmetric two-particle states, whose eigenvalues are the squares of the differences of the eigenvalues of the Hamiltonian K. The resonance condition is then det |F−δ2I|=0. A feature of this approach is that transition intensities can be calculated directly from the appropriate eigenvector of F, without knowledge of the individual eigenvectors of K.

For a system of many levels the exact resonance condition may be very complicated, and knowledge of the resonance condition is by no means equivalent to knowledge of the resonance fields.
ESR Linewidths in Solution. III. Experimental Study of the Solvent Dependence of Anisotropic and Spin—Rotational Effects
Authors: Wilson Raymond , Kivelson Daniel
Published: January 2005

The ESR linewidths of vanadyl acetylacetonate in diphenylmethane have been studied as a function of temperature. The results confirm the analysis made previously for the linewidths of vanadyl acetylacetonate in toluene. The major contributions arise from anisotropic g and hyperfine interactions and from spin—rotational effects. The parameter λ⅓=r/3.045 Å, where r, the hydrodynamic spherical radius of the radical, is introduced as an adjustable parameter. This one parameter is sufficient to enable the theory to explain the linewidth results in a number of solvents, but a slightly different value of λ is required for each solvent. This variation may be due to solvation effects.

Studies of deuterated vanadyl acetylacetonate in carbon disulfide indicate that neither intermolecular dipolar interactions nor unresolved proton extrahyperfine splittings contribute appreciably to the linewidth.
Transport Properties of Polyatomic Fluids. III. The Transport—Relaxation Equations for a Dilute Gas of Rough Spheres
Authors: McLaughlin Ian L. , Dahler John S.
Published: January 2005

The Boltzmann equation for a dilute gas of rough spheres is linearized and its solution expanded in irreducible tensors constructed from the linear and spin velocities of the spheres. This procedure is patterned closely after Waldmann's development of the kinetic theory for a Lorentz gas of rough spheres. Transport—relaxation equations are derived for the expansion coefficients, i.e., for the moments of the nonequilibrium distribution function. By examining selected subsets of these equations we are able to construct estimates for the transport coefficients and characteristic relaxation times. Relationships are established between these results and the transport coefficients generated by the method of Chapman and Enskog.
Studies of Zero-Field Splittings in Aromatic Molecules
Authors: Godfrey M. , Kern C. W. , Karplus M.
Published: January 2005

The zero-field splitting parameters corresponding to exponential-orbital wavefunctions for benzene and naphthalene have been evaluated by the Gaussian transform technique. Comparison of the results obtained with and without multicenter integrals shows significant differences; in particular, an erroneous value for E in naphthalene is found if only two-center integrals are included. For the lowest triplet in benzene, the use of accurate integrals with the wavefunction of van der Waals and de Groot for the quinoid structure improves the agreement with the experimental D* value. In naphthalene, Pariser's wavefunction and accurate integrals give a D that is close to the measured result; however, the E determined from the same wavefunction is considerably too small in magnitude.

A qualitative examination of the effect of D on substitution in benzene and naphthalene is made. For benzene it is found that most substituents should decrease D or D*; only if a weak mesomeric interaction is involved (e.g., CH3) is an increase in D* expected. In naphthalene, the effect of substituents is expected to be considerably smaller than in benzene. Comparisons with the limited available data show agreement with these conclusions.
Charge-Transfer Complexes of Carbonyl Cyanide in Gas and Condensed Phases
Authors: Prochorow J. , Tramer A.
Published: January 2005

Absorption spectra of carbonyl cyanide charge-transfer complexes with common donors were studied in gas phase and in solutions, their fluorescence spectra in n-hexane solutions at 77°K.

The general form of the absorption band is the same in the gas and liquid phases, but the gas-phase spectra show a blue shift of 2000–3500 cm−1, an intensity decrease, and a strong increase in the equilibrium constant of complex formation. The reasons of the frequency shift, the splitting of absorption bands, and the influence of complex formation on the electronic spectrum of carbonyl cyanide are discussed.
On the Melting of Copolymeric DNA
Authors: Reiss H. , McQuarrie D. A. , McTague J. P. , Cohen E. R.
Published: January 2005

A model for DNA molecules is introduced and treated by the methods of statistical mechanics. This model takes into account the difference in bonding free energy between adenine—thymine and guanine—cytosine base pairs.

The model used is an extension of the Zimm—Bragg model for polypeptides. The partition function for a certain class (which probably corresponds to most DNA sequences) of molecules is evaluated numerically and the linear dependence of the temperature of half-denaturation on base composition is obtained, in agreement with the experimental work of Marmur and Doty. A further, previously unnoted, result is that the breadth of the transition is a function of the base composition. Comparison of the predicted broadening with available experimental data is excellent for DNA from simple organisms which probably possess only one kind of DNA molecule each. However, for complex organisms, which are known to have compositionally heterogeneous DNA, the relationship is not obeyed. This suggests the possibility of using transition breadth as a simple and rapid test for compositional heterogeneity of DNA's.
Nuclear Quadrupole Effect on Rotational Levels of a Molecule with Two Nuclei Having Spins of 52
Authors: Rigden John S. , Nygaard Lise
Published: January 2005

The effect of two equivalent, symmetrically located quadrupolar nuclei of 52 spin on the rotational energy levels of a rigid asymmetric rotor is determined. Matrix elements are derived for the Hamiltonian which describes the quadrupole coupling in the molecule. First-order energy-level corrections for J≦12 have been calculated. Relative intensities for transitions involving J≦5 have likewise been calculated.
Intensity Distribution in the Energy-Loss Spectrum of Ethylene
Authors: Ross Kevin J. , Lassettre Edwin N.
Published: January 2005

The electron-impact spectrum of ethylene has been determined using a high-resolution electron spectrometer. The intensity distribution obtained at 200-V electron kinetic energies agrees well with previous measurements made with 33-kV electron kinetic energies, and ultraviolet-absorption measurements except in the region of the 7.45-V transition. This discrepancy is attributed to a quadrupole transition which occurs in this region.
ESR Spectrum of FOO
Authors: Fessenden Richard W. , Schuler Robert H.
Published: January 2005

The ESR spectrum obtained during the electron irradiation of liquid CF4 containing trace amounts of oxygen consists of a 12.83-G doublet at g=2.0038. Under the conditions of the experiments the radical producing this spectrum has a mean lifetime of ∼20 min. This observed spectrum is similar to the doublet which has been found in various oxides of fluorine. Addition of small amounts of oxygen enriched in 17O shows that the radical contains two nonequivalent oxygen atoms which have appreciable hyperfine constants. The 17O coupling constants, aO′=22.17 and aO″=14.50 G, are similar to those found in RO2·. The simplest radical which can be proposed to explain these results in FO2·. Upon prolonged irradiation the CF4 shows a second, transient spectrum which is tentatively assigned to CF3OCF2·.
Inelastic Electron Scattering from H2
Authors: Heideman H. G. M. , Kuyatt C. E. , Chamberlain G. E.
Published: January 2005

Energy-loss spectra have been measured for 13.7- to 50.7-eV electrons in H2. For incident energies below about 16 eV, energy-loss peaks are observed due to either or both of the a 3Σg+ and c 3Πu states of H2. The excitation cross section of the v=0 and v=1 vibrational levels of the B 1Σu+ state show sharp and large resonances, corresponding in energy with resonances in the total scattering. The absolute electron energy scale in H2 was recalibrated to an estimated accuracy of 0.1 eV.
Energy of Excimer Luminescence. V. Excimer Fluorescence of Naphthalene and Methylnaphthalenes
Authors: Smith F. J. , Armstrong A. T. , McGlynn S. P.
Published: January 2005

The interpretation of the energies of excimer luminescence of naphthalene and 12 of its alkyl derivatives is considered, and it is shown (i) that there is considerable configuration interaction between molecular-exciton and charge-resonance states and (ii) that the energy of excimer fluorescence may not be interpreted without invoking this configuration interaction. Excimer-fluorescence energies are calculated for the substituted naphthalenes using a four-electron MO treatment of the interaction and as a function of Z, the Slater orbital effective charge exponent, and of the interplanar distance D. Agreement with excimer-luminescence energies is obtained for values of Z=3.18 and values of D between 3.4 and 3.7 Å, with the largest intermolecular distance D being obtained for those compounds in which steric hindrance is expected to be largest.
Ionic Association in Molten AgNO3
Authors: Wait S. C. , Ward A. T.
Published: January 2005

An interpretation of the vibrational spectrum of molten silver nitrate based on normal coordinate analysis is presented. The results indicate that ion pairing may be responsible for the observed splitting of one degenerate fundamental and appearance of the infrared-active band in the Raman spectrum. A force constant of 0.5 mdyn/Å is estimated for the Ag–O interaction.
Isotope Effects on Molar Volume and Surface Tension: Simple Theoretical Model and Experimental Data for Hydrocarbons
Authors: Bartell L. S. , Roskos R. R.
Published: January 2005

Experimental measurements of molar volumes and surface tensions of benzene, toluene, cyclohexane, and methylcyclohexane and of their completely deuterated analogs are presented. The lighter species have a greater volume by about 0.3%. Surface tensions of the lighter species are greater, also, and increase from 0.2% to 1% as the number of hydrogens per carbon increases. Results are interpreted on the basis of the bond-stretching anharmonicity which makes C–H bonds longer and more polarizable than C—D bonds. The ``steric'' and polarizability effects are comparable in magnitude but opposite in sign in their influence on cohesive properties. It is shown by a simple theoretical model that the ``pure-mass effect'' on molar volume arising from zero-point translational motions of the molecules as a whole is negligible in comparison with the effects stemming from zero-point motions of the C–H and C—D bonds.
Photoionization by Argon Resonance Lines
Authors: Yoshida Masakazu , Tanaka Ikuzo
Published: January 2005

The direct and sensitized photoionization of ammonia and propane by argon resonance lines has been investigated. The ion current of direct photoionization approximately followed Beers law. The ratio of the absorption cross section of propane to that of ammonia was found to be 3.2. The ion current of sensitized photoionization generally increased with argon pressure. When the direct photoionization current was sufficiently large, however, the ion current decreased with increasing argon pressure, because the ionization induced by the energy transferred from the excited argon atoms is a competitive process of that induced by the photons absorbed by the sample molecules. From these results, it was concluded that the most important role of argon as a sensitizer is to increase the apparent absorption cross section of sample.
Reaction between Atomic Oxygen and Nitrous Oxide
Authors: Fishburne E. Stokes , Edse R.
Published: January 2005

A shock tube has been employed to study the reaction between atomic oxygen and nitrous oxide in an excess of molecular oxygen. The temperature was varied from 1700° to 2300°K. The total gas concentrations ranged from 0.085 to 1.42×10−5 moles/cc. The atomic oxygen was generated by the thermal decomposition of ozone. The rate constant for the reaction between atomic oxygen and nitrous oxide is shown to be k2′+k2″ = (2.3±0.4)×1013 exp(−25 000±800/RT) cc/mole sec.

It is shown that the best fit to the experimental data is obtained when the extrapolation of the low-temperature rate constant for the reactionO+NO+M⇌NO2+M,is employed rather than the rate constant obtained through the reverse reaction and the equilibrium constant. The former rate constant is a factor of 6 greater than the latter rate constant.
Proton Nuclear Magnetic Relaxation Studies on Water: The Rates of Acid- and Base-Catalyzed Proton Exchange
Authors: Glick R. E. , Tewari K. C.
Published: January 2005

The rates of acid- and base-catalyzed exchange of protons in water have been redetermined. Rather than employ 17O-enriched water, as in Meiboom's method, we have taken advantage of our observation that T2 is frequency dependent in order to simplify the analysis. The acid-catalyzed rate constant for proton exchange, k1, was found to be 7.9×109 liter mole−1·sec−1 and the base-catalyzed rate constant, k2, to be 4.5×109 liter mole−1·sec−1. The activation energy for k1 was 2.6 kcal, while that for k2 was 2.7 kcal. Our results are compared with those of others as well as with the related anomalous conductance of water. Further studies on the properties of water are suggested by the observation that T2 is frequency dependent.
Perturbation Theory of the Constrained Variational Method in Molecular Quantum Mechanics
Authors: Brown W. Byers
Published: January 2005

The variational problem of minimizing the energy of a trial wavefunction which is constrained to give the known theoretical or experimental expectation value of an operator is discussed. A perturbation approach is developed, which leads to simple equations for estimating the effect of the constraint on the expectation values of other operators, and the increase in energy due to the constraint. It is shown that for hypervirial operators the constraint procedure for satisfying the corresponding hypervirial theorem leads to equal and opposite results from the variational procedure. The equations are compared with those of a conventional perturbation treatment, which tends to support the constraint procedure. The theory is extended to cover the effect of constraints on second-order properties and multiple constraints. The perturbation equations are applied to Robinson's (1957) calculations on the lithium hydride molecule, previously discussed by Rasiel and Whitman (1965).
Relations Between Vibrational Spectroscopy and the Isotope Effect on Vapor Pressures
Authors: Gordon R. G.
Published: January 2005

The vapor-pressure difference between isotopes of diatomic molecules is calculated for systems in which the rotational and translational molecular motion show small quantum deviations from classical behavior. Four different terms contribute significantly to the isotope effect on vapor pressures. (1) The mean-squared force on a molecule in the condensed phase; (2) The mean-squared torque about the center of mass of a molecule; (3) The change in mean-squared torque when the position of the center of mass is changed by isotopic substitution; (4) The mean change in intermolecular potential due to isotopic substitution. The last three of these four terms are shown to be observable separately in the infrared or vibrational Raman spectrum of the system. Therefore by combining the thermodynamic and spectroscopic data, it is possible to derive experimental values of the mean-squared force on a molecule and the mean-squared torque as a function of the point on the molecular axis about which the torque is measured. Thus, the ``center of force,'' the point about which the mean-squared torque is a minimum, may be experimentally determined. The analysis is applied to liquid and solid carbon monoxide.
Nonequilibrium Effects in Recombination—Dissociation Kinetics
Authors: Kolker H. J.
Published: January 2005

It is well known that if a mixture of atoms and diatomic molecules are at thermodynamic equilibrium in a chemically inert, constant-temperature heat bath, the molecular internal degrees of freedom can be characterized by a Maxwell—Boltzmann or equilibrium distribution. If the temperature of this system is suddenly changed, atoms will start to recombine or molecules will start to dissociate in order to restore chemical equilibrium; however, the diatomic molecules will no longer have a Maxwell—Boltzmann distribution. The rate at which these internal energy levels approach equilibrium is influenced by the reaction velocity, the rate at which molecules are created or destroyed. Since it is relatively easy to dissociate highly excited molecules, the rate of reaction is coupled to the rate at which the internal degrees of freedom relax to an equilibrium or Maxwell—Boltzmann distribution.

It is very difficult to develop a theory of recombination—dissociation kinetics that explicitly accounts for the coupling of the rate of reaction to the rate of relaxation. Several theoretical techniques have been proposed for solving this problem; however there seem to be certain discrepancies in the theories that are based on these techniques. In the present study, an iterative perturbation procedure, which couples the rate of relaxation to the rate of reaction in a self-consistent manner, is used to derive a nonequilibrium theory of recombination—dissociation kinetics. One of the immediate advantages of this theory is that it includes many of the existing theories as special cases. This theory provides a way of predicting under what conditions it is possible to evaluate atomic recombination coefficients from a knowledge of the dissociation rate constant and the equilibrium constant for the reaction. For a nearest-neighbor transition model of a diatomic molecule, this theory also predicts that the atomic recombination coefficients should decrease as T−2 at sufficiently high temperatures.
Zeeman Studies of the 63Cu Nuclear Quadrupole Resonance in Potassium Dicyanocuprate (I)
Authors: McKown Gary L. , Graybeal Jack D.
Published: January 2005

A Zeeman study of the nuclear quadrupole resonance transition of 63Cu in KCu(CN)2 has determined the nuclear quadrupole coupling constant e2Qqzz to be 60.9±0.6 Mc/sec and the electric-field-gradient asymmetry parameter η to be 0.78±0.07. The crystal contains two physically inequivalent copper-atom sites giving rise to two zero-splitting loci. The direction of the principal electric-field-gradient z axis is nearly normal to the triangular plane formed by two carbon atoms and a nitrogen atom about each copper atom.
Excitation Studies on the N2(1+) and N2+(1—) Systems in Shock-Heated N–N2 Mixtures
Authors: Wray Kurt L.
Published: January 2005

The rate of excitation of the N2(1+) and N2+(1—) band systems was observed in shock-heated N–N2 mixtures in which the initial mixture ratio N/N2 ranged from 0 to 0.27. A pulsed discharge prior to diaphragm rupture produced the N atoms; their concentration was determined by monitoring the decay of the Lewis—Rayleigh afterglow for about 50 msec subsequent to the discharge and up to the arrival of the shock. The shock waves produced temperatures in the range 7000°—18 600°K close to the shock front, after rotational relaxation. The radiation intensities from the N2(1+) (6600 to 8000 Å) and N2+(1—) (0, 1) (4272 Å) bands were monitored as functions of time behind the shock front. The initial slopes of the radiation-time histories were compared with theoretical slopes. The rate-constant expression for exciting ground-state nitrogen X 1Σg+ to the A 3Σu+ state by collisions with N atoms was found to be kN = 1.9×10−6T−32 exp(—EXA/kT) cm3/particle·sec, where EXA = 6.168 eV. This yields an effective cross section of 2.7×10−18 cm2 at 12 000°K. The analogous rate constant for collisions with N2 was determined to be kN2≤0.01 kN. These rate constants were found consistent with unsuccessful attempts to obtain Vegard—Kaplan spectra in the discharged but unshocked gas. Attempts to fit the N2+(1—) data were not completely successful. It is most probable that the N2+ is formed by the associative ionization of a ground-state atom and an excited atom.
Transient Behavior of Domains in Liquid Crystals
Authors: Heilmeier George H.
Published: January 2005

Using an optical technique the formation and decay of domains in high applied electric fields has been studied for two nematic liquid crystals, p-azoxyanisole and p-butoxybenzoic acid. The decay time was found to be independent of the applied field but proportional to the sample thickness over the range studied. The rise time exhibited a d2/V type dependence on sample thickness (d) and applied voltage (V). This behavior is also found in solid ferroelectrics at high fields where domain propagation is the limiting switching factor. A phenomenological theory of domain kinetics was structed in the spirit of the Debye relaxation theory which accounts for the essential features of the experimental data. A justification for this approach was also found in its ability to account for the very low-frequency (<500 cps), large signal-dispersion data for these materials which featured a thickness dependence of the relaxation time.
Vibrational Relaxation of Deuterium by a Quantitative Schlieren Method
Authors: Kiefer John H. , Lutz Robert W.
Published: January 2005

A quantitative schlieren method is described which uses photomultiplier detection of the deflection of a narrow gas-laser beam to obtain a close approximation to a point measure of density gradient. This method is very sensitive to rapid density changes (a gradient of 5×10−5 g/liter·mm can be detected in argon) and laboratory relaxation times as short as 0.2 μsec can be measured in the shock tube. The application of this technique to studies of vibrational relaxation is discussed in detail, and the method is compared with the integrated schlieren of Resler and Scheibe for this application.

This technique has been applied to a shock-tube study of the vibrational relaxation of mixtures of D2 in Ar with the results, in atmosphere·seconds, Pτ = (2.7±0.3)×10−10 exp[(110.5±1.5)/T⅓], (1100°—3000°K) for pure D2, and Pτ = (1.0±0.7) × 10−9 exp[(118±10)/T⅓], (1600°—3000°K) for D2 dilute in Ar. The experimental results are in serious disagreement with both the correlation scheme of Millikan and White and the SSH theory.
Vibrational Energy of Ozone During Photolytic Explosion
Authors: Baiamonte Vernon D. , Snelling David R. , Bair Edward J.
Published: January 2005

Following a short photolysis flash of the proper energy the absorption spectrum in the region of the ozone ultraviolet system, a continuum centered at about 2550 Å, broadens and shifts toward longer wavelength as the reaction proceeds. Kinetic measurements of this shift over a period of 200 μsec following a mild photolysis flash of 12 μsec duration in 0.5 Torr pure ozone are interpreted in terms of population of ozone vibrational energy states by exchange of energy with vibrationally excited oxygen formed during the exothermic decomposition. Considerable O2†–O3† vibrational equilibration occurs within 50 μsec. A semiempirical model which correlates the ozone vibrational temperature and the observed data is discussed in relation to the over-all energetics of ozone decomposition.
Role of Free Volume in the Pressure Dependence of the Viscosity of Liquids
Authors: Matheson A. J.
Published: January 2005

The free-volume theory of liquid viscosities has been extended to account for the dependence of viscosity on pressure. The limiting specific volume of a liquid has an expansion coefficient and a compressibility similar to those of a solid.
Effects of Charge Compensation on the Absorption Spectrum of Yb3+ in Cadmium Fluoride
Authors: Banks E. , Wagner P.
Published: January 2005

The absorption spectrum of Yb3+ in CdF2 has been found to consist of two spectra which are distinguishable on the bases of differences in integrated absorption intensity, temperature dependence, and effects resulting from impurity compensation. One spectrum is similar to those observed for Yb3+ in yttrium gallium garnet and YbCl3·6H2O and is little affected by impurity compensation, nor does it exhibit any unusual temperature dependence. The other spectrum, which strongly resembles that for Yb3+ in aqueous solution, is markedly sensitive to both temperature and impurity compensation.

Optical correlations with the extent of impurity compensation and lattice parameter suggest that one of the spectra is due to an associative interaction between Yb3+ and interstitial F−, and that interstitial F− is removed in a quantitative manner by the impurity compensator Na+.
Ground States of Conjugated Molecules. VII. Compounds Containing Nitrogen and Oxygen
Authors: Dewar Michael J. S. , Gleicher Gerald Jay
Published: January 2005

The semiempirical SCF—MO procedures described in previous papers of this series have now been extended to compounds containing heteroatoms, in particular nitrogen and oxygen. This is a treatment based on the Hückel σ/π approximation, in which the total energy of the σ electrons is approximated by assuming additivity of bond energies (allowance being made for variations of these with length by using Morse functions) and in which the π energy is calculated by a Pople-type SCF—LCAO—MO treatment with neglect of differential overlap and penetration integrals. The problem of estimating the remaining integrals is discussed in detail; valence-state ionization potentials and one-center repulsion integrals are determined empirically by standard methods from spectroscopic data, but a new procedure is used for estimating effective nuclear charges. Two sets of values are used for the remaining repulsion integrals, one closely similar to that recommended by Pariser and Parr, the other corresponding to a modified SPO treatment. Calculations are reported for a wide range of conjugated and aromatic compounds of nitrogen and oxygen, including azines, azoles, furans, pyrylium, and quinones. Calculated heats of formation and bond lengths seem to be in satisfactory agreement with experiment in the cases where such data are available and the results seem in general to be much superior to those given by previous methods.
Calculation of the Dielectric Constant of a Fluid by Cluster Expansion Methods
Authors: Jepsen D. W.
Published: January 2005

Corrections are obtained to the Clausius—Mossotti—Debye formula for the dielectric constant of a fluid of polar but nonpolarizable molecules by a cluster method. The calculation shows the contributions to the moment of the sample which depend upon the size (and presumably also the shape) of the sample explicitly. A new term, not found in other treatments, is obtained in the third order of the expansion of the Clausius—Mossotti function in powers of μ2 which represents the effect of the exclusion of third molecules from between a pair which is close together.
Effect of Quenching of Polarizations in Polar Diatomic Molecules on Nuclear-Quadrupole Coupling, Its Vibrational Dependence, and Molecular Dipole Moments
Authors: de Wijn H. W.
Published: January 2005

A simple model is added to the theory of nuclear-quadrupole coupling, which together with the existing theories, viz., the Townes and Dailey theory and the theory of the antishielding effect, accounts for experimental data on nuclear-quadrupole coupling in the alkali halides. In the ionic configuration of the molecule the polarizations mainly of the halogen ions are assumed to be quenched by the repulsive forces between the ions, insofar as they involve expansion of electron density on the side adjacent to the core of the other ion. For halogen ions this results in a contribution to the electric-field gradient from dipolar polarization, while the antishielding effect is suppressed. This contribution is evaluated by use of experimental data of free halogens. For alkali ions the antishielding effect remains operative. Expressions are derived for the dependence of nuclear-quadrupole coupling on the vibrational state. Quenching of the polarization of halogen ions is also included in Rittner's theory of the electric dipole moment. It is shown that theoretical dipole moments of the alkali halides are consistent with experimental values.
Theoretical Interpretation of 31P NMR Chemical Shifts. I
Authors: Letcher John H. , Van Wazer John R.
Published: January 2005

An ASP—LCAO—MO quantum-mechanical calculation of 31P chemical shifts has been made using s, p, and d orbitals and allowing full latitude in the π bonding. This has been accomplished by use of an artfully chosen coordinate notation which allows the chemical-shift expression to be stated in a particularly simple functional form, using a minimum number of hybridization parameters. Numerical examples of the calculations are presented graphically, and they have been applied to experimental data for the symmetrically substituted 1 phosphines, 2 phosphoryl, 3 thiophosphoryl, and 4 selenophosphoryl derivatives, as well as to the 5 phosphonium salts. The calculations show that the 31P chemical shift is primarily sensitive to asymmetric electronic loading and affords a method for estimating the amount of pπ—dπ bonding to phosphorus.
Lattice Vibrations of Pyrazine Crystal
Authors: Ito Mitsuo , Shigeoka Tadayoshi
Published: January 2005

The Raman spectrum of crystalline pyrazine has been observed at several temperatures between 4.2° and 293°K. Five low-frequency Raman bands due to the lattice vibrations have been found. A normal coordinate calculation has led to definite assignments of these bands and to a reasonable set of intermolecular force constants. The Raman frequencies due to the intramolecular vibrations are also given.
Theory of the Low-Temperature Chromatographic Separation of the Hydrogen Isotopes
Authors: King James , Benson Sidney W.
Published: January 2005

A new electrostatic theory is presented which quantitatively explains the chromatographic separation of the hydrogen isotopes on an alumina column at low temperatures. The theory is based on the interaction of the surface electric fields of the alumina with the polarizable hydrogen isotopes. By calculating the electric fields over an adopted Al2O3 surface, it is found that there are two active adsorption sites at 77.4°K, one over a vacancy in the Al2O3 structure, and the other over an Al3+. The total interaction potential over either site is a function of the polarizabilities of the adsorbed molecules and the distance the molecules are from the surface. A 5–9 potential over a vacancy site gives results which favorably agree with experimental values. The rotational barrier, necessary to explain the separation of the ortho and para species, is shown to arise from the difference in the parallel and perpendicular components of the molecular polarizability of the hydrogen molecule.
Dielectric Relaxation in Liquid n-Octyl Iodide
Authors: Mopsik F. I. , Cole R. H.
Published: January 2005

Dielectric constant and loss were measured between −40° and +40°C at audio frequencies and at twelve frequencies from 10 Mc/sec to 9 Gc/sec. The frequency dependences deviate slightly from a Davidson—Cole skewed-arc function with β=0.67 by having slightly lower loss near the center of the dispersion. The dependence of relaxation frequency on temperature gives an average value 4.3 kcal/mole for the heat of activation, but the rate plot shows curvature. Previous measurements on alkyl halides believed to show symmetrical or ``left-skew'' complex dielectric constant loci are shown to be consistent with the present skewed arc dependence if certain data are systematically in error.
NMR Spectrum of a Nearly Linear Five-Spin System: Hydrogen Bonding in KH2F3
Authors: Blinc R. , Trontelj Z. , Volavšek B.
Published: January 2005

The nuclear magnetic resonance spectra of a rigid A—B—A—B—A system of spin-½ nuclei are calculated taking into account first- and second-nearest-neighboring dipole—dipole interactions. Both the cases of a linear and nonlinear nuclear arrangement are treated and are shown to yield a distinct fine structure. The results are applied to a study of the H2F3− ion in KH2F3 and NaH2F3, and comparisons with experiment are made for both proton and fluorine resonances. Though the F···F distances are very short and the hydrogen bonds in this crystal approach in stability those in the bifluoride ion, the obtained data show that the hydrogen atoms are unsymmetrically located.
Electronic Absorption Spectrum of Ni(II) in Cubic Perovskite Fluorides. II. Concentration and Exchange Effects
Authors: Ferguson J. , Guggenheim H. J.
Published: January 2005

Spectral absorption data from crystals of composition KMg1—xNixF3 and KZnF3 (1% Ni2+) are reported. It is deduced, from a comparison of the spin—orbit energies at 20°K, that the excited states are only weakly perturbed by exchange interactions. The effect on the ground state is relatively large and it is stabilized by about 170 cm−1. Absorption by ion pairs and larger clusters has been observed in the near-infrared magneticdipole transition. The mechanisms of the various electronic transitions have been studied and the vibrational structure of the electric-dipole bands interpreted. The four perturbing k = 0 phonon modes observed in the KNiF3 spectrum are split in the dilute crystal spectra and correspond to localized vibrations. The mechanism of the transition to the 1Eg state has been discussed and it is concluded that it can be described as a single-ion excitation which involves strong vibronic spin—orbit coupling with the nearby 3T1ga state.
Temperature and Pressure Dependence of the Elastic Constants of Ammonium Bromide
Authors: Garland C. W. , Yarnell C. F.
Published: January 2005

The adiabatic elastic constants of single-crystal ammonium bromide have been measured as functions of temperature and pressure by a pulse-superposition technique. The values at 1 atm and 300°K are: c11 = 3.414, C′ = (c11—c12)/2 = 1.316, and c44 = 0.722, in units of 1011 dyn cm−2. Measurements of c11 and C′ were not made below the lambda transition at 234.5°K because of a sudden increase in attenuation; c44 was not attenuated in this manner and was measured from 105° to 320°K. The elastic constants were measured as functions of pressure between 0 and 12 kbar at constant temperatures which ranged from 255° to 315°K. In this region, which is far from the lambda line, disordered ammonium bromide behaves like a normal CsCl-type crystal.
Order—Disorder Phenomena. I. Instability and Hysteresis in an Ising Model Near Its Critical Point
Authors: Garland Carl W. , Renard Rémi
Published: January 2005

The mechanical behavior of a system near a cooperative order—disorder transition point is discussed in terms of an Ising model for a set of spins located on mass particles which form a compressible lattice. With the assumption of weak coupling between the lattice and spin systems, it is shown that this Ising model is unstable in the immediate vicinity of its critical point and undergoes a first-order transition. In addition, many properties should show hysteresis in the critical region. These general conclusions are illustrated by several two-dimensional examples.
Monte Carlo Study of Flexible Branched Macromolecules
Authors: Gallacher Lawrence V. , Windwer Stanley
Published: January 2005

A Monte Carlo procedure was used to simulate flexible branched macromolecules on a high-speed digital computer. The molecules studied were of the regular-comb type. Configurational and statistical thermodynamic properties were evaluated according to prescriptions used for linear flexible chains. The effects of branching on these properties are discussed.
Alkali-Atom—Halogen-Molecule Reactions in Molecular Beams; The Spectator Stripping Model
Authors: Minturn Robert E. , Datz Sheldon , Becker Richard L.
Published: January 2005

Crossed-molecular-beam techniques have been used to study reactive collisions in some alkali-metal—halogen systems (Cs+Br2, K+I2, K+Br2, Rb+IBr). Both the absence of rainbow scattering in elastic-scattering distributions and the magnitude of the reactive collision yield suggest large reaction cross sections in the order of 100 Å2 for all the systems studied. The position and width of the angular distributions of alkali halide product molecules indicate forward scattering in the center-of-mass system with recoil energies close to zero.

These observations suggest a stripping mechanism for these reactions and a model, based upon the simplest possible stripping mechanism, has been proposed to explain the observations. This model, called spectator stripping, predicts the gross features of the distributions and leads to a prediction of the maximum intermolecular distance at which reaction can occur. This corresponds to a reaction cross section of approximately 100 Å2.

The effect of electron transfer from the alkali atom to the halogen molecule at large distances is shown to be almost equivalent to spectator stripping for these reactions if the vertical electron affinity of the halogen molecule is used. Even larger cross sections would be predicted if the adiabatic electron affinity were used; however, an evaluation of the probability of adiabatic adjustment of the halogen internuclear distances during the collision time appears to preclude this possibility.
Infrared-Reflection Spectra of Molten Fluoride Solutions: Nb (V) in KF:LiF
Authors: Fordyce J. Stuart , Baum Ruth L.
Published: January 2005

Infrared-absorption spectra derived from reflectivity measurements over the range 4000 to 200 cm−1 have been obtained for KF:LiF melts containing Nb (V). The results show two strong bands at 315 and 555 cm−1 and a very sharp medium band at 250 cm−1 superimposed on the former. Comparison of these spectra with well-characterized solid compounds such as K2NbF7 demonstrate that the NbF7−2 complex ion is the predominant species in these melts.

The NbOF63— anion is shown to be the predominant species in melts containing hydrolyzed Nb (V).
Transport Properties of Polyatomic Fluids. II. A Dilute Gas of Spherocylinders
Authors: Sandler Stanley I. , Dahler John S.
Published: January 2005

The Chapman—Enskog method is used to generate estimates for the transport coefficients of a dilute gas of rigid spherocylinders. Extensive tabulations are given of the coefficients of thermal conductivity and of shear and bulk viscosity. Our results clearly indicate that anisotropy of the molecular spin (angular momentum associated with molecular tumbling) field has little effect upon the numerical values of these coefficients.
Ionic Processes in γ-Irradiated Organic Solids: Electrons in 3-Methyl Pentane
Authors: Gallivan James B. , Hamill William H.
Published: January 2005

γ-irradiated 3-methylpentane (3MP) and solutions of biphenyl (φ) have been examined at −196° at doses of 1 to 26×1018 eV ml−1. The half-life for decay of the trapped electron (e−) in 3MP is independent of dose for t<1 h and the rate is approximately second order for t>1 h. This behavior, as well as very efficient formation of φ− at small % φ, requires electron track lengths of ∼10−4 cm. The 100 eV yield of (e−) shortly after γ irradiation is ∼0.9, in terms of the measured extinction coefficient ε(e−)≅3.0×104 liter mole−1·cm−1 at 2.3×1018 eV ml−1, but only 60% as great at 10-fold greater dose. At 0.04% φ, the rate of (e−) decay is much faster and approximates first order. The ratio of reaction cross sections of (e−) with positive holes and φ is ∼120. Addition of 2% 2-methylpentene−1 as positive hole trap increases the yield of (e−) and decreases the rate of decay, which becomes second order throughout. Recombination luminescence intensity from TMPD at t>1 h decays at the same rate following uv and γ excitation. The evidence for randomization of relatively large yields of ion pairs and very long track lengths, as well as trapping and escape, may require a new theoretical framework.
Studies of Lithium Hydride Systems. III. Solid—Liquid Equilibrium in the Lithium Bromide—Lithium Hydride and Lithium Iodide—Lithium Hydride Systems
Authors: Johnson Carl E. , Wood Scott E. , Crouthamel Carl E.
Published: January 2005

Thermal analysis has been used to determine the temperature—composition solid—liquid equilibrium diagrams for the two binary systems, LiBr–LiH and LiI–LiH. Both are simple eutectic systems with no experimental evidence for the formation of solid solutions. Eutectic compositions of 29.7 mole % lithium hydride, mp 453.3°C, and 23.5 mole % lithium hydride, mp 390.8°C, were observed for the bromide and iodide systems, respectively. The values of the chemical potential of each component have been calculated along the equilibrium curves where the solutions are saturated with respect to the pure solids.

The limiting slopes of the saturation curves are consistent with the interpretation that lithium bromide and lithium iodide both exist primarily as un-ionized dimers when dissolved in lithium hydride and that lithium hydride exists primarily as an un-ionized monomer when dissolved in either lithium halide.
Electronic Spectra and Structures of Tropone and Heptafulvene
Authors: Inuzuka Kōzō , Yokota Toshio
Published: January 2005

State energies, transition moments, and reactivity indices for tropone and heptafulvene are calculated by the semiempirical SCF—MO method including all singly excited configuration interactions. The results of the calculations are listed in Table II, III, and IV. In heptafulvene there are three absorption bands. The band of longest wavelength and the band of next-longest wavelength are transitions 1A1—1B1 and 1A1—1A1, respectively. In tropone these two transitions shift closely to each other and make one band. There are two absorption bands in tropone. Since π electrons of tropone and heptafulvene localize partially upon double bonds, the lowest triplet energy is lower than that of aromatic compounds which contain the same number of π electrons as tropone or heptafulvene.