bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heats of Combustion of Some Peroxides and the Heats of Formation of Acetate, Propionate, and Butyrate Radicals
Authors: Jaffe L. , Prosen E. J. , Szwarc M. 
Published: January 2005

Heats of combustion of acetyl, propionyl, and butyryl peroxide were measured using a bomb calorimeter. The heats of formation obtained are: ΔHf = — 127.9 for acetyl peroxide, — 148.2 for propionyl peroxide, and — 161.0 for butyryl peroxide (in kcal/mole for the liquid state at 25°C). The heats of formation of the acetate, propionate, and butyrate radicals have been computed and the relative stability of the acetate compared to the benzoate radical is discussed.
The RC(O)O–H bond dissociation energies in the respective acids and the sums of electron affinities plus solvation energies of the respective ions are computed.
These calculations seem to indicate that acidic properties of carboxylic acids are due to the high electron affinities+solvation energies of R·COO radicals, and not to the low R·CO·O–H bond dissociation energies, since the latter are comparatively high.
Pi Complexes between Organic Free Radicals
Authors: Hausser K. H. , Murrell J. N. 
Published: January 2005

The spectroscopic and magnetic properties of N-ethylphenazyl and Wurster's blue perchlorate show characteristic changes at low temperatures. Using Mulliken's charge-transfer theory, we have shown that the formation of π complexes can account for these changes.
The intense long wavelength absorption band which appears at low temperatures in both cases, is attributed to a transition to a state which is an antisymmetrical combination of two charge-transfer configurations, in which all the electrons are paired.
We have compared the properties of these π complexes with the properties of the biradicals related to 4,4′-bis-diphenylmethylenediphenyl (chichibabin hydrocarbon.)
Theory of Multi-Component Fluid Mixtures. II. A Corresponding States Treatment
Authors: Wojtowicz Peter J. , Salsburg Zevi W. , Kirkwood John G. 
Published: January 2005

The theoretical basis for a theorem of corresponding states for mixtures is examined in a rigorous manner by the use of statistical mechanics. With the aid of the general theory of mixtures presented in a previous paper, the theorem of corresponding states is found to be a consequence of the following assumptions: (a) the internal molecular partition functions depend only on the temperature, (b) the system is in a condition of random mixing, and (c) the several intermolecular interactions can be described by a set of pair-potentials of the same analytical form.
In addition to providing a firm theoretical foundation for the corresponding states treatments of Prigogine et al. and Scott, several new approaches to the use of corresponding states in the statistical thermodynamics of mixtures are also presented. In particular, the chemical potentials in binary mixtures of molecules of equal size, and of unequal sizes, are developed. The coefficients in the Margules expansion of the activity coefficients are found to be expressible as functions of the intermolecular interaction parameters and certain experimentally determined thermodynamic properties of the pure components.
The relationships of the Regular solution and Conformal solution theories to the present development are also demonstrated.
Estimates of Hammett's Sigma Values from Quadrupole Resonance Studies
Authors: Bray P. J. , Barnes R. G. 
Published: January 2005

A linear correlation exists between the Cl35 pure quadrupole resonance frequency in substituted chlorobenzenes and the Hammett parameter sigma for the substituent. The relation is expressed as f=1.024σ+34.826 Mcps.For the 52 frequencies used in determining this relation, the correlation coefficient is r = 0.96 and the root-mean-square deviation of the experimentally determined f values from those predicted by the equation is 360 kcps.
A proper ortho sigma parameter for use in the f vs σ correlation is apparently the value derived from the Hammett relation σ = lnK/K0 in which K and K0 are the equilibrium constants for ionization of the substituted and unsubstituted benzoic acid in water at 25°C. This parameter is linearly proportional to the polar substituent σ* of Taft for the ortho substituent.
In the many multiply substituted chlorobenzenes investigated, the proper total sigma value has been taken as the sum of the individual parameters. Few cases are apparent in which the linear relation of f to σ is seriously violated. Additivity of the electron displacement properties of substitution, suggested by Jaffe and indicated by studies of the magnetic shielding in fluorobenzenes, is apparently confirmed.
Sigma values for 29 substituents have been estimated from the Cl35 pure quadrupole resonance frequency measured in the substituted chlorobenzene.
Infrared Absorption Spectra of Nitric Acid and Its Solutions
Authors: Marcus R. A. , Fresco J. M. 
Published: January 2005

Infrared spectra of reactive liquids such as anhydrous nitric and sulfuric acids were determined using silver chloride windows and, in some cases, Teflon spacers. The absorption frequencies of nitric acid agree well with those found from Raman spectra.
A nitronium ion frequency was observed at 2360 cm—1. The intensity of this band is enhanced by the addition of nitronium fluoborate, sulfuric acid, phosphorous pentoxide, or small amounts of acetic anhydride. It is reduced by addition of sodium nitrate, potassium dihydrogen phosphate, water, or larger amounts of acetic anhydride. Its behavior in these media provides information about pertinent equilibria. A nitronium ion combination band was observed near 3745 cm—1 when the concentration of this ion was particularly large. Bands arising from unionized nitric acid are completely absent when a small amount of nitric acid is added to 100% H2SO4.
Various bands found in aqueous nitric acid solutions are attributed to hydrogen-bonded structures, both because of their behavior in different media and by analogy with effects observed in Raman studies.
Characteristics of Plastic Scintillators
Authors: Basile Louis J. 
Published: January 2005

Information on the light output of a group of organic solutes in polyvinyltoluene has been obtained. The primary solutes studied are p-terphenyl and 2-phenyl-5-(4-biphenylyl)-1,3,4 oxadiazole (PBD), the latter being the most efficient. Of the secondary solutes studied, 4,4′-diphenylstilbene and 2,5-dibiphenylyl oxazole (BBO) are the most efficient. The best plastic scintillator developed contains a combination of 2-phenyl-5-(4-biphenylyl)-1,3,4 oxadiazole (PBD) and 4,4′-diphenylstilbene.
The fluorescence spectra of these plastic scintillators were determined. When a secondary solute is added to a plastic scintillator the emitted light is mainly that of the secondary solute.
The effect on the light output of the plastic scintillator upon addition of diphenylmercury was also investigated. Regardless of which combination of solutes was used, the mercury compound proved to be a serious quencher of light output.
Adsorption and Diffusion of Oxygen on Tungsten
Authors: Gomer Robert , Hulm J. K. 
Published: January 2005

The surface diffusion and adsorption of oxygen on tungsten have been studied by a field emission technique, by utilizing the high sticking coefficient, and negligible vapor pressure of O2 at 4.2–20°K. Three types of migration were noted. At ∼27°K diffusion occurs with a sharp boundary and an activation energy Ed≈0.9 kcal. This is believed to be migration of physically adsorbed O2 over the chemisorbed layer, with precipitation on the bare surface. The distance traversed by the boundary was found to be limited by desorption above ∼40°K. A study of this effect yielded an estimate of 2.3 kcal for the heat of adsorption, Ha, in the physisorbed layer. At 400–500°K and high coverages, diffusion occurs within the monolayer with activation energies of 23–25 kcal. Boundaries moving radially outward from the close-packed faces are observed, and believed to result from precipitation of O atoms in trap sites on the rough regions of the surface. At low coverages boundary free diffusion with Ed≃30 kcal is observed and interpreted as migration from trap sites. The latter are believed to constitute ∼60% of all sites. Activation entropies for the various diffusion processes are estimated to vary from ∼7–13 eu.
It was found that 80% of the chemisorbed layer can be formed without appreciable activation at 27°K. The layer is stable up to 700°K, where desorption and oxidation start. The latter is markedly dependent on the amount of oxygen on the surface. At 300°K there is a slow oxygen uptake probably associated with incipient oxidation.
Stress-Enhanced Diffusion in Glass. I. Glass under Tension and Compression
Authors: McAfee Kenneth B. 
Published: January 2005

This paper describes a new technique for the determination of diffusion constants of gases in gas-solid systems. The method demands a careful analysis of the transient quantity of gas flowing after the gas pressure at the boundary is discontinuously changed. The exact quantity of gas flowing is recorded by a mass spectrometer. The method was used to study the effect of high tensile stress upon the diffusion constant of helium and other gases in glass.
The diffusion constant of helium was found to be a true constant with dilation of the glass until the stress became about one-half the breaking stress of the glass. Beyond this point the diffusion constant increased, and under very high stress was a factor of ten larger than its original value. No apparent change was produced in the glass, and reduced stress gave the same diffusion constant as previously, indicating reversibility of the effect with stress. It was further determined that equal and even larger compressional stresses on the same glass specimen had little or no effect upon the diffusion constant. The effect of shear stress upon the diffusion constant is dealt with in the following paper.
The magnitude of the observed increase in diffusion constant is larger by a considerable factor than can be explained by a straight-forward extension of prevalent theories of diffusion in glass. If it is assumed that the glass sample dilates on an atomic scale, i.e., each atom being isotropically displaced by the stress, then calculations show that the diffusion constant should not be strongly increased under stress. Observation of the large increase then points toward the opening of flaws or voids within the glass.
Diffusion of hydrogen, heavy water, oxygen, and nitrogen is discussed and upper limits for diffusion of the latter three under high stress are set.
Free Energy of a Nonuniform System. I. Interfacial Free Energy
Authors: Cahn John W. , Hilliard John E. 
Published: January 2005

It is shown that the free energy of a volume V of an isotropic system of nonuniform composition or density is given by : NV∫V [f0(c)+κ(▿c)2]dV, where NV is the number of molecules per unit volume, ▿c the composition or density gradient, f0 the free energy per molecule of a homogeneous system, and κ a parameter which, in general, may be dependent on c and temperature, but for a regular solution is a constant which can be evaluated. This expression is used to determine the properties of a flat interface between two coexisting phases. In particular, we find that the thickness of the interface increases with increasing temperature and becomes infinite at the critical temperature Tc, and that at a temperature T just below Tc the interfacial free energy σ is proportional to (Tc−T)32.
The predicted interfacial free energy and its temperature dependence are found to be in agreement with existing experimental data. The possibility of using optical measurements of the interface thickness to provide an additional check of our treatment is briefly discussed.
Theory of Separated Electron Pairs
Authors: Parks Joe M. , Parr Robert G. 
Published: January 2005

Electron pairs in a molecule are said to be separated if (i) the molecular electronic wave function is accurately expressible as an antisymmetrized product of individual pair wave functions, and (ii) the individual pair functions are mutually exclusive in the sense that if all pair functions are linearily expressed in terms of Slater determinants built from some orthogonal one-electron spin orbitals, no spin orbital enters the description of more than one pair function. It is shown that the electronic energy of a system of separated electron pairs may be written in a particularly simple form, and the problem of determining the best separated electron-pair description of a particular molecule is discussed.
The best orbital description of an electron-pair bond is defined to be the best wave function for the pair that can be built from two atomic orbitals, one on each of two atoms. Systematic adjustment of individual pair descriptions one at a time is shown to provide a rigorous yet practicable procedure for obtaining best orbital descriptions for several separated electron-pair bonds in a molecule.
The equations obtained are shown to simplify considerably when Mulliken approximations are introduced for certain electronic repulsion integrals. Under these approximations a single property of each bond is shown to dominate its effect on other bonds, the net charge transferred from one atom to the other in the bond. This charge is called the bond polarity parameter. The equations are rewritten in terms of polarity parameters, and a scheme is thereby obtained which is convenient for discussion of intrabond charge transfer effects in a molecule. Formulas are given for the terms to be added to the absolute electronegativity of an atom in a bond to correct for charge transfers in other bonds.
It is shown that the total molecular energy of a system of separated electron-pair bonds can be expressed quite rigorously as a sum of bond energies, and the approximate invariance of bond energy to molecular environment is verified.
Limitations of the assumption of separability and methods for transcending it are discussed.
Nature of the Glass Transition and the Glassy State
Authors: Gibbs Julian H. , DiMarzio Edmund A. 
Published: January 2005

The thermodynamic properties of amorphous phases of linear molecular chains are obtained from statistical mechanics by means of a form of the quasi-lattice theory which allows for chain stiffness and the variation of volume with temperature. A second-order transition is predicted for these systems.
This second-order transition has all the qualitative features of the glass transition observed experimentally. It occurs at a temperature which is an increasing function of both chain stiffness and chain length and a decreasing function of free volume.
The molecular ``relaxation times'' are shown to increase rapidly as the second-order transition temperature is approached from above.
To permit quantitative application of the theory and determine the relationship between the second-order transition and the glass transition observed in ``slow'' experiments these two transitions are tentatively identified. By this means quantitative predictions are made concerning the variations of (1) glass temperature with molecular weight, (2) volume with temperature, (3) volume with molecular weight, (4) volume at the glass temperature with the glass temperature for various molecular weights of the same polymer, (5) specific heat vs temperature, and (6) glass temperature with mole fraction of low-molecular weight solvent, since extensive experimental results are available for these properties. These and other theoretical predictions are found to be in excellent agreement with the experimental results.
Second-Order Sum Rule for the Vibrations of Isotopic Molecules and the Second Rule of the Mean
Authors: Bigeleisen Jacob 
Published: January 2005

A second-order sum rule for the vibrational frequencies of isotopic molecules is derived. The rule relates the second power of the λ's, Σλi2 and Σi≠j λiλj, for isotopic molecules of the type X′Yz—rYr′ and XYz—rYr′ with the second power of the λ's for the symmetrical molecules X′Yz′, XYz′, X′Yz, and XYz. Special consideration is given to the case where X′ and X are in fact Y′ and Y in positions structurally equivalent to the z Y atoms in XYz. In the latter case, if z is greater than 2, the rule may involve isotopic isomers. Just as in the case of the first-order sum rule, the second-order rule can be applied separately to the individual symmetry classes common to all of the molecules.
It is shown that the second-order sum rules for a homologous series of isotopic molecules can be found easily by a simple tabulation of the interactions between the equivalent isotopic atoms. Interaction tables are given for the deutero-ethylenes and the deutero-benzenes.
The second-order sum rule is used to derive the second rule of the mean for isotopic exchange equilibria. Examples of the latter are given involving the carbon dioxide, ethylene, and benzene molecules.
Chain Stiffness and the Lattice Theory of Polymer Phases
Authors: DiMarzio E. A. , Gibbs J. H. 
Published: January 2005

General formulas for the thermodynamic properties of amorphous polymer phases are obtained from statistical mechanics, with the aid of the lattice model, in a manner which avoids the use of restrictive assumptions concerning the nature of the individual polymer chains.
Certain results, such as prediction of a second-order transition for systems of semiflexible chains and the Flory-Huggins formula for the entropy of mixing with monomeric solvent, are thus shown to be independent of the precise nature of the model assumed for the polymer chains.
More complete information may be obtained by application of the general formulas to models descriptive of the molecular chains in question. As an example, the results of Flory for semiflexible linear chains whose stiffness arises exclusively from intramolecular nearest neighbors are obtained as a special case. (The conventional thermodynamic properties of polydisperse systems of chains of this type are shown to depend on the number average molecular weight.)
Reactions of Alkoxy Radicals. IV. Photolysis of Methyl-d3 Acetate at High Temperatures
Authors: Wijnen M. H. J. 
Published: January 2005

The photolysis of CH3COOCD3 has been investigated over the temperature range 145 to 350°C at varying initial pressures and light intensities.
The following reactions have been studied in detail: CD3O+CH3→CH3D+CD2O,CD3O+CH3→CH3OCD3,CD3O+CH3COOCD3→CD3OH+CH2COOCD3,CH3+CH3COOCD3→CH4+CH2COOCD3.A value of about 1.4 is obtained for k7/k6. The results indicate that the activation energy of reaction (7) is zero kcal. A value of 10±0.5 kcal is obtained for E12, while the data indicate a value of approximately 5 kcal for E16.
Spin Density Matrices for Paramagnetic Molecules
Authors: McConnell Harden M. 
Published: January 2005

The density of electron-spin angular momentum (erg-sec/cm3) at a point x, y, z in a paramagnetic molecule is ℏ Szρ(x, y, z), where Sz is the z component of the total electron spin angular momentum in units of ℏ. If the exact wave function for the molecule Ψ is built up from one-electron basis functions ψi, then the normalized spin density function ρ(x, y, z) can be expressed in terms of the ψi and the spin density matrix ρijρ(x,y,z)= ∑ ijρijψj*ψi.If the ψi are molecular orbitals, then ρij is the molecular orbital spin density matrix; if the ψi are atomic orbitals, then ρij is an atomic orbital spin density matrix. The equation of conservation of spin is Tr(Sρ)=1 where S is the non-orthogonality matrix, Sij=〈ψi|ψj〉.
The elements of the spin density matrices are sensitive to overlap and electron correlation effects. This is illustrated by calculations of the spin density matrices of the ethylene positive ion radical, and of the allyl radical. The spin density matrix for the latter molecule is calculated using (a) the simple molecular orbital approximation, (b) the simple valence bond approximation, and (c) the complete π-electron interaction configurational treatment given by Chalvet and Daudel.
It is shown that the general connection between σ-proton hyperfine splittings aN and the π-electron atomic orbital spin density matrix ρNN′, involves a (hyperfine interaction)-(exchange interaction) matrix QN′N″″N such that aN=Tr(QNρ).However, for practical calculations, observed hyperfine splittings may be used to estimate the diagonal elements of the spin density matrix, aN≈QρNN,where Q has the semiempirical value of —63 Mc or —23 gauss
Dispersion of the Electro-Optic Kerr Effect in the Infrared Region
Authors: Charney Elliot , Halford Ralph S. 
Published: January 2005

The infrared dispersion of electro-optic anisotropy has been investigated theoretically and experimentally. Anomalies of the refractive index in the neighborhood of resonant absorptions are accompanied by anomalous dispersion in the electro-optic Kerr effect. A theoretical analysis of the effect of molecular structure on the form of the anomalous behavior demonstrates that the relative orientation of the permanent molecular dipole and the radiation-induced dipole determines the sign of the deviation of the dispersive behavior from normal. The dependence on the applied electrostatic field strength is predicted to be the same in resonant and nonresonant regions.
Experimental examination of the electro-optic anisotropy of nitrobenzene at field strengths of 28 000 v/cm to 48 000 v/cm in the overtone region (1.5–5.6 μ) of the infrared spectrum confirms these theoretical conclusions.
Neighbor Interactions and Internal Rotations in Polymer Molecules. II. Polyelectrolytes
Authors: Lifson Shneior 
Published: January 2005

The influence of the interaction between neighboring ionizable groups of a polyelectrolyte molecule on the internal rotations around its skeletal bonds is considered. It is found that the repulsion between neighboring groups tends to contract the molecule by twisting the molecular chain, and acts therefore against other forces which tend to extend the molecular dimensions.
The quantitative analysis is based on calculating a grand partition function of the polyelectrolyte molecule, in which both the energy of interactions within each bond and the energy of interaction between neighboring ionizable groups are expressed as functions of the internal rotation angles. The grand partition function is used in obtaining the various averages of the trigonometric functions of the internal rotation angles which determine 〈h2〉 according to the results of the previous paper (Part I). These averages are given as functions of the degree of ionization of the macromolecule.
The effect of the internal rotation of the skeletal bonds on the potentiometric titration and buffering capacity of polyelectrolyte solutions is discussed.
Microwave Spectrum, Internal Barrier, Structure, Equilibrium Configuration, and Dipole Moment of Methyl Monofluorosilane
Authors: Pierce Louis 
Published: January 2005

The microwave spectrum of methyl monofluorosilane has been investigated in the region 18 to 38 kmc. Several transitions of the isotopic species CH3SiH2F and CH3SiD2F are split into doublets because of coupling of internal and over-all rotation. These splittings give a barrier to internal rotation of 1559±30 cal/mole. The form of the potential barrier was assumed to be V=12V3(1−cos3α). A few transitions belonging to the first excited torsional state were observed and assigned. The splittings in the excited state are consistent with the barrier as determined from ground state observations.
Rotational constants of CH3SiH2F, CH3SiD2F, C13H3SiH2F, CD3SiH2F, and CH3SiDHF have been determined and were used to calculate the structure of the molecule.
The structural parameters are: SiC1.848 ACSiF109∘ 13′SiF1.600HCH107∘ 52′SiH1.473CSiH109∘ 28′ (assumed)CH1.090HSiH109∘ 28′ (assumed).
A study of CH2DSiH2F proves conclusively that methyl monofluorosilane in its equilibrium configuration has the methyl group staggered with respect to the SiH2F group.
The dipole moment was found to be 1.71D.