bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of Binary Ion-Exchange Systems
Authors: Freeman David H.
Published: January 2005

From an algebraic expression for the total excess free energy of a two-component ion-exchange system, separate expressions are derived for the dependence of the logarithm of the activity coefficients of the two components upon the equivalent fraction of counterion in the exchanger. The numerical coefficients required by these expressions and the thermodynamic constant for the ion-exchange reaction are obtained from equilibrium measurements of species activities in the aqueous phase at varying exchanger compositions. This is illustrated with measurements on the distribution of chloride and perchlorate with anion-exchange resin.
Some Deductions from a Formal Statistical Mechanical Theory of Chemical Kinetics
Authors: Ross John , Mazur Peter
Published: January 2005

A perturbation solution of an assumed Boltzmann-type equation for bimolecular chemical reactions in a homogeneous gas phase consisting of molecules with or without internal degrees of freedom, leads to the conclusion that the law of mass action as well as the usually assumed phenomenological rate expressions for chemical reactions, is strictly valid only in lowest order of the perturbation. Higher order perturbations introduce an affinity and time dependence in the rate coefficient and the law of mass action becomes inadequate to the extent of the contribution of the effects of the perturbations.

A transition state formation of rate coefficients for bimolecular gas-phase reactions is presented under less restrictive sufficient conditions than reported previously.
Paramagnetic Resonance of X-Irradiated Single Crystals of Rochelle Salt
Authors: Moulton Grace C. , Moulton W. G.
Published: January 2005

The electron-spin resonances of single crystals of Rochelle salt and deuterated Rochelle salt irradiated with 40 kv x rays have been studied as a function of orientation of the crystal in the magnetic field. The spectra are time dependent, and by studies of the decay of the spectra it has been found that three kinds of centers are present. In Rochelle salt one of these gives rise to an intense doublet which decays rapidly, another to a doublet which grows and then decays, and the third is an eight-line spectrum which grows and is stable. It is shown that the waters of hydration play an important role in the kinetics of the growth and decay of the centers. The stable spectrum has been analyzed, and it is concluded that two of the lines arise from breaking one of the C–H bonds. This doublet is slightly anisotropic, and arises from hyperconjugation to the proton on the adjacent carbon, and dipolar coupling between it and the large spin density on the carbon. A second pair of lines arises from breaking the other C–H bond, and since the hydrogens are not equivalent, this pair has a different splitting. The other two pairs are shown to be couplings to either OH or water of hydration hydrogens.
On the Theory of Ion Pairs in Solutions
Authors: Poirier Jacques C. , DeLap James H.
Published: January 2005

Following the general lines of Fuoss' early analysis, two alternate definitions of ion partners (1) excluding and (2) including partners composed of ions having the same electrical sign are formulated. The resulting sets of coupled integral equations for the ion-partner radial distribution functions Gij(r), differ from Fuoss' by the inclusion of a factor for the probability that the orbital ion does not have a partner closer than the central ion and are valid for electrolytes of any symmetry type or any mixture of electrolytes at any concentration for which the ordinary pair correlation functions gij(r) for the various types of pairs of ions are known. By the presented iterative numerical method, the set of equations resulting from either definition (1) or (2) may be solved even for a general mixture. Explicit analytical solutions for Gij(r) in terms of an arbitrary (except for an easily relaxed restriction of a hard core) gij(r) are presented for the following electrolytes: definition (1) symmetrical and unsymmetrical binary; definition (2) symmetrical binary with equal ionic radii. For examples of these electrolytes, graphs of Gij(r) resulting from the use of the Debye-Hückel model and the infinite dilution form of gij(r) are presented (cations, 10—4M; D=20; T=25°C; interionic distance of closest approach, 4.6 A). Numerically obtained Gij(r) are also presented for a 1–1 electrolyte with unequal ionic radii [definition (2); conditions as above except ionic radii of 1.6 A and 3.0 A] and a mixture of two 1–1 electrolytes with a common anion [definition (1); interionic distance of closest approach of the second electrolyte, 7.0 A]. More extensive ion pair formation of the smaller cation shown in the latter case qualitatively explains anomalously low conductance in mixtures. The Gij(r), markedly smaller than the corresponding Fuoss curve at large separation, lead to the same association constant K—1 if the same critical distance is used to terminate the ion pair range; a constant critical distance, however, leads to a K—1 which is a continuous function of DT in qualitative agreement with some conductance data and is compatible with a ``contact ion pair'' concept. An equation for the activity coefficient ratio is presented and degrees of association are calculated in a variety of solutions. The formalism presented easily accepts more realistic gij(r) functions and can be extended to entirely different types of systems. The usefulness of the ion (or particle) pair approach is briefly discussed.
Relative Bond Strengths in Trigonal Bipyramid Molecules
Authors: Cotton F. A.
Published: January 2005

Calculations of the relative strengths of the axial and equatorial bonds in PF5 and PCl5 have been made using Pauling's criterion of bond strength and using overlap integrals for Slater orbitals as suggested by Mulliken. All calculations were for sp3d hybridization through the entire range of distribution of s and d character between the axial and equatorial orbitals. The overlap integrals correctly predict that axial bonds are weaker than equatorial ones whereas Pauling's criterion predicts the opposite for all reasonable hybridization conditions.
Shock Wave Studies by Mass Spectrometry. II. Polymerization and Oxidation of Acetylene
Authors: Bradley J. N. , Kistiakowsky G. B.
Published: January 2005

The polymerization and oxidation of acetylene have been investigated at temperatures from 1800°—2700°K and 950°—1100°K, respectively, by the technique of time-of-flight mass spectrometry in reflected shock waves. In the absence of oxygen, a simple bimolecular reaction produces a dimer, probably vinylacetylene, and higher polymers, which appear to reach ``equilibrium'' with the acetylene. A sharp drop in the concentration of these polymers is observed at a later time, which is correlated with the formation of carbon after an induction period. In the presence of oxygen, a dimer, probably diacetylene, is formed simultaneously with the formation of CO and H2O, after an induction period. This suggests that it is a product of the branching chain reaction, a specific mechanism for which is proposed.
Electrical Resistivity of Cubic Sodium Tungsten Bronze
Authors: Ellerbeck L. D. , Shanks H. R. , Sidles P. H. , Danielson G. C.
Published: January 2005

The electrical resistivities of the nonstoichiometric compounds NaxWO3 have been measured as a function of sodium concentration from x=0.48 to x=0.88, and as a function of temperature from T=4°K to T=873°K. The minimum in electrical resistivity near x=0.75, which had been reported by earlier investigators, was absent in single crystals which were selected to be electrically homogeneous. Above room temperature, the electrical conductivity increased approximately linearly with sodium concentration; at liquid-helium temperatures, the electrical conductivity increased approximately as the fourth power of sodium concentration.
Effect of Intermolecular Forces on Macromolecular Configurational Changes and on Other Isomeric Equilibria
Authors: Hill Terrell L.
Published: January 2005

The effect of intermolecular forces on isomeric equilibria (configurational changes in macromolecules are a special case) is investigated. The term corresponding to the second virial coefficient is derived but the method can easily be extended to higher terms. A significant and measurable effect is predicted for (a) isomeric equilibria involving atoms or small molecules or (b) configurational changes in macromolecules at a first-order phase transition or critical point. A negligible effect is predicted for configurational changes in macromolecules otherwise. These conclusions apply to ``proper'' thermodynamic variables only; the end-to-end length r of a random coil is excluded.
Electrostatic Energy Matrices of the f5 and f6 Configurations
Authors: Wybourne B. G.
Published: January 2005

The electrostatic energy matrices of f5 and f6 electron configurations are calculated by the Racah methods. Checking rules are used for all the diagonal matrix elements and certain of the nondiagonal matrix elements.
Use of Mass Spectral Data in Radiation Chemistry
Authors: Futrell Jean H.
Published: January 2005

The quasi-equilibrium theory of mass spectra of Wahrhaftig et al. is applied to the propane molecule ion to calculate the extent of unimolecular dissociation at 10—10 sec. This approximates the collision time for propane at moderate pressures and is therefore the ion distribution appropriate to irradiation studies. Two formulations of the theory are used, and it is concluded that the analytical mass spectrum of paraffin hydrocarbons is a good first approximation of the ion distribution in irradiated systems.
Effect of Pressure on the Charge Transfer Spectra of Heavy Transition Metal Hexahalide Complexes
Authors: Balchan A. S. , Drickamer H. G.
Published: January 2005

The effect of pressure has been measured on the charge transfer bands of seven hexahalide salts of heavy transition metal ions (with 4d and 5d configurations). The lowest energy peaks always exhibited a large red shift with increasing pressure. Higher energy peaks always showed less shift, and in one case actually shifted to the blue. While there are undoubtedly several factors involved, the data are consistent with the assumption of increased spin-orbit coupling at high pressure. The marked broadening of the bands can be discussed in terms of the effect of decreased lattice spacing on the molecular charge transfer.
Nuclear Transfer Effects in Nuclear Magnetic Resonance Pulse Experiments
Authors: Woessner D. E.
Published: January 2005

The Bloch equations for the nuclear magnetic resonance of a single nuclear species which is transferred between state environments having different relaxation times (T1 or T2) and different resonance frequencies have been solved for rf pulse experiments. Expressions have been obtained for the free precession signals in two-pulse experiments. A theoretical study of the signal envelopes has been made for several specific instances. In particular, the effect of the frequency difference between the two states on transverse (T2) relaxation has been investigated; the predicted effect is large in some cases. The longitudinal (T1) relaxation is independent of the frequency separation. A reduction of phase dispersion by the second pulse which is similar to that in molecular diffusion is also predicted.
Self-Diffusion and Velocity Correlation
Authors: Douglass Dean C.
Published: January 2005

Approximate expressions for the self-diffusion coefficients of spherical molecules in solid, liquid, and gas phases are obtained from the relation D=(kT/m) ∫ 0∞ρ(s)ds,where D is the diffusion coefficient and ρ(s) is the velocity correlation function of the spherical molecules. The correlation function is approximated by the function cosαδs/coshαs and the parameters α and δ are expressed in terms of molecular properties for liquids and gases. The approximate diffusion coefficient is found to obey an Arrhenius relation in the solid phase and a Sutherland equation for the gas phase. The results of a crude calculation of the self-diffusion coefficient for liquid neopentane are within a factor of two of the experimental diffusion coefficients. The temperature coefficient of the calculated diffusion coefficients is also within a factor of two of the observed temperature coefficient.
Magnetic Susceptibility of Mercuric Oxide at Various Temperatures
Authors: Mikhail H. , Hanafy Z. , Salem T. M.
Published: January 2005

Mercuric oxide exists in two forms, the red and the yellow oxides. Magnetic susceptibility determinations showed no appreciable difference between the two oxides; the red one has a mass susceptibility of (—0.2217±0.0002)·10—6 emu/g, while the yellow one has a slightly lower mass susceptibility of (—0.2165±0.0002)·10—6 emu/g at room temperature (25°C).

The temperature variation of their mass susceptibility between room temperature (25°C) and about 300°C was also investigated. The general shape of the curve for the two oxides is essentially the same, namely, an increase in diamagnetism with rise in temperature followed by a mild drop and subsequently a sharp rise. The position of the peak occurs at about 50°C for the red oxide and at about 114°C for the yellow oxide. A tentative explanation of their behavior was given, based on impurity ionization.
Spectrum of NBr Excited in Active Nitrogen
Authors: Milton Earl R. V. , Dunford H. B. , Douglas A. E.
Published: January 2005

The spectrum of NBr near 6000 A, excited by the action of active nitrogen on bromine, has been photographed at high dispersion and the rotational structure of the bands has been analyzed. The bands have been attributed to a Σ+1−Σ−3 transition in which the 3Σ— state is the ground state of the molecule. Only two of the five possible branches were observed, both of them belonging to the F1(J=N+1) component of the 3Σ— state. The unusual structure of the bands is attributed to the fact that the coupling in the 3Σ— state is intermediate between Hund's case b and case c. The equilibrium internuclear distances are re′=1.731 A and re″=1.79±0.02 A and the dissociation energy is estimated to be 67±5 kcal. The emission spectrum is believed to be caused by the combination of N(4S) and Br(2P32) atoms into some unknown excited state of NBr which is induced, by wall collisions, into the 1Σ+ state.
Mechanism of the Mercury Photosensitized Decomposition of n-Butane
Authors: Cvetanović R. J. , Falconer W. E. , Jennings K. R.
Published: January 2005

The results of further studies of the mercury photosensitized reactions at room temperature of n-butane and of its mixtures with nitrous oxide are reported. The importance of a self-scavenging process responsible for low quantum yields of hydrogen at finite conversions has been demonstrated by carrying out experiments at low conversions closely approaching initial conditions. The initial quantum yield of hydrogen has been determined relative to that of nitrogen from the mercury photosensitized decomposition of nitrous oxide. The mechanism of the self-scavenging process is discussed.
Relative Rates of Addition of Hydrogen Atoms to Olefines
Authors: Jennings K. R. , Cvetanović R. J.
Published: January 2005

Hydrogen atoms were produced by the mercury-photosensitized decomposition of n-butane at 435±5 mm pressure and at 23.5±1°C. By introducing known amounts of olefine, the rate of addition of hydrogen atoms to the olefine could be measured relative to the rate of abstraction from the n-butane by observing the fall in the rate of production of hydrogen. In this way, relative rates of addition to eight olefines were obtained, and the logarithms of the relative rate constants were found to correlate reasonably well with the atom localization energies of the olefines, but not with their maximum free valence.
Electron Density Distributions in ZnO Crystals
Authors: Mohanty Ganesh P. , Azároff Leonid V.
Published: January 2005

Electron density distributions have been determined for two ZnO crystals that had been heated in Zn vapor and for an undoped crystal by very accurate measurements of their x-ray diffraction intensities. An examination of the difference between the electron densities of doped and undoped crystals shows that the doped crystals contain 15–60×1019 atoms/cm3 in the octahedral interstices. The incorporation of this large number of interstitial Zn atoms increases the axial ratio of the hexagonal unit cell from 1.6019 to 1.6025. The density of interstitials is approximately 1000 times greater than that calculated from the electrical conductivity of these crystals so that it must be concluded that most of the interstitial Zn atoms are electrically neutral. The presence of these interstitials explains why the time required to reach saturation for electrical conductivity is much greater in virgin crystals than in previously doped ones.
Band Structure and Transport of Holes and Electrons in Anthracene
Authors: LeBlanc Oliver H.
Published: January 2005

Previous mobility measurements indicate that the band approximation can be used to describe the behavior of injected holes and electrons in anthracene, and the present theoretical investigation appears to confirm this. The structures of the bands appropriate to a hole or electron are calculated with the tight binding approximation. Hückel linear combinations of Slater-type atomic orbitals are used for the molecular basis functions. Both bands are highly anisotropic and each is found to be approximately 0.56 kT wide at room temperature. Mobility tensors are derived using a simplified treatment of scattering which assumes isotropic scattering parameters. The calculated mobilities exhibit roughly the anisotropy that has been observed experimentally. Magnitudes of the scattering parameters are estimated from the observed mobilities, and these are found to be reasonable (e.g., free path>lattice distances).
Molecular Orbitals in Some Boron Compounds
Authors: Moore Emmett B. , Lohr L. L. , Lipscomb William N.
Published: January 2005

An LCAO treatment of boron framework orbitals in B10H14 yields a charge distribution of +0.05e on atoms 1 and 3, of —0.25e on atoms 2 and 4, of —0.03e on atoms 5, 7, 8, and 10, and of +0.27e on atoms 6 and 9. When a charge of about —0.2e is assigned to each bridge H atom, the order of reactivity agrees with that expected from the chemical behavior (neg 2,4<1,3<5,7,8,10<6,9 pos).

An LCAO investigation of boron orbitals in the B5H5 molecule of D3h symmetry and with nine equal B–B distances indicates expected stability for the B5H5—2 ion, but not for the neutral molecule. A simplified method of accounting for the molecular orbitals in icosahedral B12H12—2 yields some conclusions concerning B11 hydrides and ions.
Ionization Cross Sections near Threshold by Electron Impact
Authors: Fox R. E.
Published: January 2005

Ionization curves near threshold have been taken with a mass spectrometer employing a monoenergetic electron beam. These curves have been fitted to previously published data from total ionization experiments in order to obtain absolute cross sections for the threshold energy region. Curves for helium, neon, argon, mercury, carbon monoxide, and nitrogen are given.
Molar Extinction Coefficients of Liquid O3F2, O2F2, and O3 in the Visible Range
Authors: Kirshenbaum A. D. , Streng A. G.
Published: January 2005

The absorption spectra for solutions of liquid O3F2, O2F2, and O3 in a Freon mixture of CClF3 and CCl2F2, and that of liquid O3 in liquid O2 were measured at 77°K and their molar extinction coefficients calculated. The effect of temperature on the molar extinction coefficient of liquid O2F2 in the Freon mix was studied.
Collision Mechanics in Crossed Maxwellian Molecular Beams
Authors: Datz Sheldon , Herschbach Dudley R. , Taylor Ellison H.
Published: January 2005

A general treatment of the mechanics of collision between two Maxwellian molecular beams is described. Expressions are obtained for the distribution in collision energy, for the elastic and reactive collision rates, and for the angular distribution of the center of mass vectors for beams colliding at any angle. The treatment can accommodate any reaction cross section which can be expressed as a step function multiplied by a linear combination of powers of the relative energy.

The recoil momentum which affects the product distribution in the laboratory system is discussed, and the treatment is applied to some experimental data on the reaction of K with HBr.
Motion of the Ammonium Ion in Lattices of the NaCl Type
Authors: Vedder W. , Hornig D. F.
Published: January 2005

The infrared spectrum of NH4I in the NaCl-type phase gives insufficient information about the motion of the ammonium ions in that phase. Dilute solutions of NH4+ in NaCl-type alkali halides provide considerably more detail in the form of a fine structure in most of the absorption bands which becomes visible on sufficient cooling. This fine structure is most certainly correlated with a rotational motion of the NH4+ ion. However, both models suggested in the literature—free rotation and rotation of the ion about a N–H···X— axis—deviate in many important respects from the experimental results.
Interfacial Solutions of the Poisson-Boltzmann Equation
Authors: Stillinger Frank H.
Published: January 2005

The linearized Poisson-Boltzmann equation is considered for boundary conditions corresponding to a fixed point-charge ion near the planar boundary between an electrolytic solution and a dielectric substrate. Use of the Fourier expansion for this fixed charge density allows the mean potential to be synthesized in the form of a simple quadrature. Subsequently, it is possible to compute the reversible work necessary to displace the ion atmosphere surrounding this charge into one hemisphere as the charge is brought up to the interface from the interior of the electrolyte phase. Implications for ionic adsorption processes are discussed. The result of a similar analysis for the mean potential surrounding a point dipole oriented normally to the boundary is also presented.
Heat Capacity of LiCuCl3·2H2O
Authors: Forstat H. , McNeely D. R.
Published: January 2005

The heat capacity of LiCuCl3·2H2O has been measured in the temperature range 2°—9°K. A λ-type anomaly in the heat capacity curve has been observed at 4.40±0.02°K. This has been identified as the Néel temperature for a paramagnetic-antiferromagnetic transition. The magnetic entropy associated with this transition is 1.35 cal/mole deg which agrees with the theoretical value to within 2% if the spin of the magnetic ion is taken as ½ in R log (2S+1). The fraction of the magnetic entropy above the Néel temperature is 0.48 which indicates a considerable amount of short-range ordering of the spins of the magnetic ions.
Quenching Effects and Negative Photoconductivity in Amorphous Selenium
Authors: Dresner J.
Published: January 2005

Negative photoconductivity and long wavelength quenching of photoconductivity have been observed in several evaporated layers of amorphous Se, with both effects showing a maximum for light of energy between 1.9 and 2.1 ev. From the position of the Fermi level, these effects have been identified with transitions from a set of sensitizing centers ranging from less than 0.58 to 0.65 ev above the valence band. Deep traps were investigated by thermally stimulated currents and by the analysis of space charge limited currents. Trapping states at 0.55 ev were detected which probably correspond to the same set of defect levels as the sensitizing centers. Several models which might account for the optical absorption, spectral response, quenching phenomena, and the exponential temperature dependence of the carrier mobilities, are discussed.
The Chemical Bond in Molecular Quantum Mechanics
Authors: Allen Thomas L. , Shull Harrison
Published: January 2005

It is postulated that a properly antisymmetrized product function over geminals (electron-pair wave functions) is adequate for discussion of the principal chemical properties of molecules. By application of the virial theorem it is shown that such a wave function has both of the properties essential to the bond-energy concept; namely (a) the energy of a molecule is the sum of the energies of its individual bonds and (b) the bond energies are invariant from one molecule to another. Within the framework of this approximation, bond energies become identified in magnitude with the kinetic energies associated with the respective geminals. The concepts are sufficiently general to include both localized and nonlocalized bonds, unshared electron pairs, odd electrons, and states of various multiplicities.
Cuboctahedral Bonding
Authors: Canon Jack R. , Duffey George H.
Published: January 2005

Molecular orbitals belonging to the different irreducible representations of a B12 cuboctahedron are set up and parametric expressions for the energy levels obtained. Terms neglected by Lipscomb and Britton are included. Directed orbitals for group Oh coordination of 12 ligands about a central atom are formulated and Pauling strengths calculated.
Low-Temperature Heat Capacities and Thermodynamic Functions of Some Palladium and Platinum Group Chalcogenides. II. Dichalcogenides; PtS2, PtTe2, and PdTe2
Authors: Westrum Edgar F. , Carlson H. Gary , Gr⊘nvold Fredrik , Kjekshus Arne
Published: January 2005

Heat capacities of platinum disulfide, platinum ditelluride, and palladium ditelluride were measured in the range 5° to 350°K. They show the normal sigmoidal temperature dependence with no evidence of transitions or other anomalies. The derived heat capacity equations were integrated. Values of Cp, S°—S0°, H°—H0°, and —(F°—H0°)/T are tabulated for selected temperatures. At 298.15°K the entropies are 17.85 cal gfw—1 °K—1 for PtS2, 28.92 cal gfw—1 °K—1 for PtTe2 and 30.25 cal gfw—1 °K—1 for PdTe2. Thermodynamic values have been estimated for other dichalcogenides and related chalcogenides of the platinum group metals.
Chemistry of Positive Ions. I. General Theory Particularly for the Radiation Induced Cross Linkage of Polymers and Polymerization of Saturated Hydrocarbons
Authors: Libby W. F.
Published: January 2005

The chemical properties of positive ions are considered to be analogous to those of the corresponding neutral atom or molecule. However, the charge strengthens bonds and provides the long-ranged attractive polarization force which causes the reaction cross sections to be very large. For organic ions dehydrogenation to form carbonium ions occurs frequently, so in addition to the parent ion radical with its great reactivity as a type of super fluorine atom, the carbonium ions with their extremely acidic (electrophilic) properties cause a wholly different set of reactions. These are analogous to those of carbene and may lead to the radiation-induced polymerization of saturated aliphatic hydrocarbons. Both ion radicals and carbonium ions can play important roles in the radiation induced cross linkage of polyethylene and other polymers. It is predicted that the effect of phase will be very important in radiation chemistry, because the cage effect of the surrounding close-packed molecules in the liquid and solid phase, as contrasted with the gas phase, will cause the fragmentation of the parent ions which is so marked in the gas phase to be reversed to a considerable extent and promote the formation of large molecules, particularly polymers.
Studies of Transient Species Formed During Catalytic Reactions of CO2 + D2 and of 1-Butene
Authors: Melton Charles E.
Published: January 2005

Transient species in a catalyzed reaction have been observed in the gas phase by placing the catalyst in a specially designed mass spectrometer ion source.

The reaction, D2+CO2→ lim PtD2O+CO,was studied over a pressure range 0.1–1 mm Hg and a temperature range 50–1100°C to demonstrate the applicability of the techniques. A free radical, of molecular formula CDO, was shown to be formed by and desorbed from the Pt catalyst during the reaction. In addition, DCOO— ions were observed suggesting the presence of an intermediate DCOOD on the catalyst.

The production of the products CO and D2O was not a monotonic function of catalyst temperature, but instead showed a maximum in the temperature range 400–500°C. The rate increased approximately as the first power of PCO2 and was nearly independent of the partial pressure of D2. The catalytic decomposition of butene-1 was studied in the same way. Free radicals produced by the catalytic decomposition of this compound are compared to those known to occur from thermal decomposition at the same temperature. In the catalytic decomposition, the radicals C4H7 and C3H5 were found to be most abundant; in contrast, CH3 and C3H5 are most abundant in the thermal decomposition.
Calculation of Interaction Matrix Elements for Asymmetric Rotors with Resultant Electronic Spin and Nuclear Spin
Authors: Curl R. F. , Kinsey James L.
Published: January 2005

The application of Racah or vector recoupling coefficients to the calculation of interaction matrix elements for asymmetric rotors with resultant electronic and nuclear spin is outlined. This approach is compared with Van Vleck's method of reversed angular momenta.
Primary Processes in Hg(3P1) Photosensitized Reaction of Cyclopropanes
Authors: Setser D. W. , Rabinovitch B. S. , Spittler E. G.
Published: January 2005

Cyclopropane-d2 and 1,2-dimethylcyclopropane have been studied at 25°C and above. Cis-trans isomerization is apparently of general occurrence in Hg(3P1) photosensitization of substituted cyclopropanes. The most important primary process in the quenching of Hg atoms by cyclopropane-d2 seems to be the formation of triplet cyclopropane diradicals through which isomerization proceeds. Some exchange occurs at higher temperature. The Hg(3P1) photosensitized polymerization and exchange of D2 mixtures with cyclopropane also proceeds readily at elevated temperature (135°C).
Paramagnetic Relaxation in Metal-Ammonia Solutions
Authors: O'Reilly D. E.
Published: January 2005

Relaxation processes for electrons in alkali metal-ammonia solutions are calculated to proceed via hyperfine interaction with nitrogen 14 nuclei in dilute solutions (<0.15M) and via spin-orbit interactions in concentrated solutions. Dipolar and exchange interactions are estimated to make only a small contribution to the observed relaxation times. Comparison of the mean square width due to the hyperfine interaction as obtained from relaxation time data and the observed N14 Knight shift allows a construction of an effective wave function for the electron in dilute solutions. In more concentrated solutions (0.60M) relaxation results from fluctuations in the electric potential at an unpaired electron with a correlation time of the order of 10—14 sec. Effects due to the substitution of D for H and Na for K are examined.
Theory of the Spin and Charge Distribution in Aromatic Ion Radicals; Application to the Naphthalene Negative Ion
Authors: Schug John C. , Brown Thomas H. , Karplus Martin
Published: January 2005

The valence-bond method is extended to positive- and negative-ion radicals. General formulas for the required energy, overlap, spin-density, and charge-density matrices are developed and specialized to pielectron systems. An application of the method to the pi electrons of the naphthalene negative ion is given. Included in the calculation are all unexcited structures with the negative charge in each of the ten possible positions. When approximate exchange and transfer integrals are used to determine the coefficients of valence-bond structures, the α to β position spin-density ratio is found to be equal to 2.60, in good agreement with the ``experimental'' value of 2.65. The magnitudes of the calculated spin densities are such that a Q of —26.3 gauss is required to obtain the measured hyperfine splittings.

To test the validity of these valence-bond results, their sensitivity to the molecular integral values is examined. Also, comparisons with a variety of molecular-orbital calculations are given. It is of considerable interest that the charge distributions obtained from the valence-bond theory and the molecular-orbital theory are very different in spite of the similarity of the spin distributions calculated by the two methods.
Diffusion of Kr and He in Liquid Hydrogen
Authors: Castagnoli G. Cini
Published: January 2005

Experimental results about diffusion of He and Kr in liquid H2 are given. Quantum deviations are analyzed with the principle of corresponding states.
Oscillator Models in Unimolecular Reactions
Authors: Vestal M. L. , Rosenstock H. M.
Published: January 2005

The absolute reaction-rate theory for the unimolecular decomposition of isolated excited molecules is applied to two models. The first considers the molecule as a set of harmonic oscillators in which only a finite amount of energy may be stored in a particular degree of freedom. In the second model the spacing between adjacent levels is assumed to decrease exponentially. The first leads to a decrease in the lifetime above that calculated for the conventional harmonic oscillator model for short-lived molecules. The second produces an increase depending directly on the rate of change of the level spacing.
Solvent Effects on Optical Rotation and Dipole Moment
Authors: Mukhedkar A. J.
Published: January 2005

It has been observed that the solvent effect on optical rotation goes hand in hand with the parallel effect on dipole moment, especially when the important dipoles are directly attached to the asymmetric center βλ=aμ+{βλ0−aμ0}.Here a is relative deformability constant and β and μ are the rotational parameter and the dipole moment, respectively; the superscript zero, indicates that property belongs to the molecule in the ideal state. The values of β5890 for a given substance in different solvents are comparable (∼1.1×10—32 for d-camphor and ∼3.65×10—32 for α-d-bromocamphor).
Microwave Spectrum and Internal Barrier of Methylphosphine
Authors: Kojima Takeshi , Breig Edward L. , Lin Chun C.
Published: January 2005

The microwave spectrum of methylphosphine has been investigated in the regions of 12–33 and 46–49 kMc. The rotational constants are found to be A = 71,869.5, B = 11,792.6, C = 11,677.7 Mc. Stark effect measurements yield a dipole moment of 1.100±0.010 D. The barrier to internal rotation of the methyl group, as determined from the A—E splittings of rotational lines in the ground torsional state and from the satellite frequency pattern of the 000—101 transition, is 685.2±5 cm—1. The structure of the molecule and the magnitude of the internal barrier in relation to other molecules are discussed.
Electron Spin Resonance Studies of Gamma-Irradiated Single Crystals of Sucrose
Authors: Ueda Hisashi , Kuri Zen'ichiro , Shida Shoji
Published: January 2005

The electron spin resonance of gamma-irradiated single crystals of sucrose has been measured at 9400 Mc/sec for various orientations in the magnetic field. The variations of the resonance with angle were greatest for rotation of the crystal about its b axis, which was kept perpendicular to the magnetic field. The anisotropic hyperfine structure was observed to vanish when the magnetic field is applied perpendicular to the (b, c) plane. It was ascertained that the radical formed is the type X—CH–Y, which had been proposed by Williams et al. from the data obtained from the polycrystalline samples.
Heat Capacities and the Residual Entropy of Ta2H
Authors: Saba W. G. , Wallace W. E. , Sandmo H. , Craig R. S.
Published: January 2005

Heat capacities of Ta2H have been determined over a range of temperature extending from 12° to 555°K. Three very sharp λ points were observed, at 306, 332, and 333.5°K, suggesting that Ta2H exists in four forms—β1 below 306°K, β2 between 306 and 332, β3 at about 333, and α above about 334°K. The heat capacity data for Ta2H are used together with similar data obtained earlier for elemental tantalum and the entropy of formation of Ta2H, evaluated from vapor pressure work by Kofstad, Wallace, and Hyvönen, to compute the residual entropy of β1—Ta2H. This is found to be —0.39±0.30 cal—1 deg—1 mole—1. The data also are used to estimate configurational entropies of the β2 and β3 forms. These are 0.70 and 3.3 cal—1 deg—1 mole—1, respectively. The corresponding quantity for the α form is 4.9.

The λ points are attributed to rearrangements of the hydrogens in the 12-fold more abundant tetrahedral sites. At low temperatures the solute hydrogen atoms are presumed to populate the sites in an orderly fashion. With increasing temperature the ordered arrangement is altered and finally, in the α phase, destroyed. It is inferred from entropy calculations, however, that local order, probably pairing, persists in the α form even to 555°K, the highest temperature studied.

Consideration is given to the possibility that the upper two λ points, which nearly coincide, should really be one, the splitting being due to concentration gradients or strains. Differential thermal analysis of samples containing from 27.5 to 44.0 atomic % hydrogen suggests that the splitting is a true property of Ta2H, but the results are not completely conclusive.
Electron Spin Resonance Study of Radiation Damage in Single Crystals of Urea Compounds
Authors: Jaseja Thadho S. , Anderson Roy S.
Published: January 2005

Single crystals of urea compounds were examined by 3-cm electron spin resonance techniques after x and γ irradiation. All experiments were conducted at room temperature. No resonances were observed in urea and thiourea. This is interpreted to indicate that the lifetimes of any resulting unstable species must be less than 30 min. at room temperature. However, methylurea and ethylurea showed strong, highly stable spectra centered at g≃2.00. Analyses of these spectra suggest that the trapped radicals[Complex chemical formula]are formed from methylurea and ethylurea, respectively, by the loss of a hydrogen atom.

In both cases all radicals in the unit cell were considered to be magnetically equivalent. Calculated hyperfine intervals agree favorably with those observed. The spin density of the unpaired electron at the adjacent N–H group is believed less than 0.002, since the only apparent effect of this group was a broadening of the hyperfine lines.

In methylurea the ·C–H2 group was found to have an H–C–H angle of 117°. The principal components of the diagonal electron-nuclear coupling dyadic were 10, 22, and 32 gauss. In ethylurea the ·C–H bond was observed to lie along a crystallographic axis. The principal components were 10, 21, and 24 gauss. In this case the isotropic coupling constant was 18 gauss.
Molecular-Orbital Model for Alkali Halide Phosphors Activated by Heavy Metals
Authors: Sugano Satoru
Published: January 2005

It is pointed out that the Seitz model may be interpreted as a molecular-orbital model. This enables us to avoid some difficulties encountered in the interpretation within a Heitler-London framework. It is demonstrated that the observed positions of the A, B, and C absorption bands and the observed ratio of the dipole strength of the C band to that of the A band are consistent with each other in the molecular orbital model for KCl:Tl, KI:Tl, and also for KCl:In with some reservation.
Solid-State Vibrational Spectra of Ethylene and Ethylene-d4
Authors: Jacox Marilyn E.
Published: January 2005

High-resolution infrared spectra have been obtained for polycrystalline C2H4 at 4° and 53°K and for C2D4 at 53°K. The observed multiplet structure of the fundamental vibrations is in good agreement with the group theoretical predictions. In C2H4 there is evidence for a gradual phase transition between 4° and 53°K, involving reorientation of the planes of the H atoms of C2H4 molecules in the crystal. The Raman-active fundamentals have been observed, weakly, in thick deposits of C2H4 at 4°K.
Molecular Diagrams of Some Nonbenzenoid Aromatic Hydrocarbons
Authors: Silvestri Anthony J. , Goodman Lionel , Dixon Joseph A.
Published: January 2005

The charge densities, π-bond orders, free valences, and vertical stabilization energies have been calculated by a semiempirical LCAO-MO-SCF method for pentalene, heptalene, fulvalene, sesquifulvalene, and heptafulvalene. The changes in the above quantities in going from the Hückel theory to the SCF method were found to be quite large for the fulvalenes. If one adopts the lack of chemical reactivity as a criterion for aromaticity then the results indicate that all five molecules and particularly the fulvalenes will have very little aromatic character.
Local Approximation Method in the Treatment of Anharmonic Crystals
Authors: Walnut Thomas H.
Published: January 2005

The exact wave functions of an anharmonic crystal are approximated by various locally derived approximate wave functions. The difference between the average of the square and the square of the average of the Hamiltonian operator of the entire crystal for these functions is used as a criterion to show the closeness with which they approximate true eigenfunctions. Three approximate wave functions are used. The first is a single product of local wave functions calculated in principle by neglecting the interactions between small local regions in the crystal and determining the exact wave functions for each uncoupled local region. The other two functions are different linear combinations of the product functions. The size of the criterion is found to depend on the size of the crystal for the first function but not for the other two. The size of the criterion is compared with the size of the same criterion determined for corresponding unperturbed eigenfunctions and linear combinations of unperturbed eigenfunctions derived from the harmonic part of the Hamiltonian operator. It is found that in a molecular crystal the local approximations should approximate exact eigenfunctions more closely than the other (nonlocal) approximations for all but the low-frequency acoustic modes. It is concluded that even the first type function can be used to give reasonable approximations to such quantities as vibrational absorption frequencies and intensities despite the fact that the wave function is a very poor approximation to any true eigenfunction in the sense that its projection on the true eigenfunction is extremely small.
PbSe Composition Stability Limits
Authors: Brebrick R. F. , Gubner E.
Published: January 2005

Pb-saturated and Se-saturated PbSe have been prepared by equilibrating small single crystals with two-phase ingots rich in either Pb or Se and quenching to room temperature. The Hall constant and conductivity were then measured. Pb-saturated PbSe is n-type with a room-temperature electron concentration that increases with increasing equilibration temperature from about 1.7×1018 cm—3 at 500°C to 1.4×1019 cm—3 at 800°C. The carrier concentrations are independent of quench rate in the range used and are proportional to exp (— E/kT) with E=0.49 ev. Se-saturated PbSe is p-type, the room temperature hole concentration definitely depending on the quench rates used at 600°C and above. The hole concentrations are between 3 and 6.5×1018 cm—3. Near 600°C, PbSe exists as a stable phase over a composition range whose limits are roughly symmetric about the stoichiometric composition and which is at least 0.012 atomic percent wide.
Absorption Spectrum and Zeeman Effect of Am3+ in LaCl3
Authors: Gruber John B. , Conway John G.
Published: January 2005

The polarized absorption spectrum and Zeeman effect of Am3+ in LaCl3 has been studied from 2000 to 8000 A. In almost every instance the peaks or lines observed are sharp, completely polarized, and appear in definite groupings. For the particular point symmetry C3h forced electric-dipole-transitions are observed from 7F0 to the excited crystal-field-spilt sublevels μ=±2 and 3 of J levels greater than one.
Copolymerization Mathematics and the Description of Stereoregular Polymers
Authors: Price Fraser P.
Published: January 2005

The mathematics of Markoffian processes has been applied to the description of the copolymerization of vinyl monomers and to the characterization of stereoregular polymers. Expressions for polymer compositions for copolymerization of two monomers are given for the cases where the terminal sequence of the growing chain contains one, two, or three units, including the terminal radical. Expressions for polymer compositions are also presented for the case of the copolymerization of three monomers.

The mathematics are extended to cover the characterization of stereoregular polymers formed either from monosubstituted or from α-β-disubstituted vinyl monomers. The mathematical requirements for the experimental characterization of such polymers are discussed.
Structure of Detonation Waves in Gases
Authors: Levitt B. , Hornig D. F.
Published: January 2005

The optical reflectivity technique has been used to study the structure of detonation waves in H2:3O2 at initial pressures of 20 to 40 psia. The detonation fronts were found to be comparable to those of normal shock waves in their thickness and planarity. The density change across the front appears to be less than the theoretical value, suggesting that rotational relaxation of oxygen (and hydrogen) in the front may not be complete. Experiments on shock waves in oxygen at M=3.0, where the final temperature is 872°K, confirm the rotational heat capacity lag and suggest that rotational relaxation is much slower at high temperatures than at room temperature.
Dissociation of the Hydroxyl Radical in an rf Discharge
Authors: Howgate David W.
Published: January 2005

The following information was obtained on by-product concentrations from the rf discharge of water vapor—molecular oxygen mixtures at H2O pressures from 50 to 200 μ and O2 pressures from 0 to 300 μ: the absence of the OH species below the region of 100 μ water vapor pressure, together with the absence of the O species above the region of 130-μ water vapor pressure, the independence of the OH and O cutoff points on the amount of oxygen added to the water vapor previous to the discharge, OH enhancements of as high as a factor of 5 to 1 upon addition of sufficient oxygen to the mixture, and total OH concentration throughout the recorded pressure range of less than 1%.
Activated Complexes of Fast Bimolecular Reactions
Authors: Ree Teresa S. , Ree Taikyue , Eyring Henry , Fueno Takayuki
Published: January 2005

The specific rates of radical association and ion-molecule reactions (e.g., CH3+CH3→C2H6, H2++H2→H3++H, etc.) were calculated with the use of the absolute reaction-rate theory and were compared with the observed values. Except for some special reactions, the observed rates agree with the theoretical values with a transmission coefficient, 1 to 1/10.

The over-all entropy change of the backward reactions ΔSb were calculated by the usual statistical thermodynamical method, and also the activation entropy of the backward reactions, ΔSb‡, were calculated. The two quantities agree fairly well.

From these results it was concluded that the activated complexes of the fast reactions have loose structures such that the reactant molecules (radicals or ions) rotate freely with the restriction that they cannot move independently in the translational degrees of freedom.
Hydrogen Formation in the γ Radiolysis of Ethylene
Authors: Ausloos P. , Gorden R.
Published: January 2005

The radiolysis of ethylene-d2 and C2H4–C2D4 mixtures has been investigated in the gas, liquid, and solid phases. The data indicate that hydrogen may be formed by two distinct molecular-elimination processes: CH2CH2→CH2C+H2 and CH2CH2→CH≡CH+H2. The effect of xenon and pressure on the yields of H2, HD, and D2 in the gas-phase radiolysis of CH2CD2 has been investigated. The results for the (2P1)Hg-sensitized and the 1237 A-photochemical decomposition have been compared with those for radiolysis.
Heat of Formation of the CN Radical
Authors: Berkowitz J.
Published: January 2005

The vapor in equilibrium with graphite and nitrogen in the temperature range 2200°—2500°K has been analyzed with a mass spectrometer. The partial pressure of CN radicals measured in this way has been used to calculate ΔHf°(CN) = 109 kcal/mole, equivalent to D0(CN) = 7.5±0.15 ev. The results of a variety of experiments are compared with this one, and in some cases, reinterpreted. The appearance potential of CN+ from CN is found to be 14.2±0.3 ev. Other possible azocarbon species up to C6N6 have been investigated and found to be much less abundant than CN.