bluuebunny/crossref_metadata_2025 huggingface dataset:
Annihilation of Positrons in Organic Liquids
Authors: Hatcher C. R. , Falconer T. W. , Millett W. E.
Published: January 2005

The mean life τ2 and fraction I2 of positrons which form 3S positronium have been measured for annihilation in 20 organic liquids—alcohols, glycols, acids, benzene derivatives, and others. By using the measured value of τ2, it is possible to calculate 〈σν〉Av where σ is the molecular cross section for annihilating 3S positronium on collision and ν is the velocity of the positronium atom. The results show that in general 〈σν〉Av is related to the ``size'' of the molecule although there are some consistent exceptions to this rule. There is also a rough correlation between τ2 and density, τ2 being shortest for the most dense liquids and longest for the least dense ones.
Study of the Wurtzite-Type Binary Compounds. IV. Theory of Double Refraction
Authors: Keffer Frederic
Published: January 2005

The Ewald-Born theory of double refraction is applied to wurtzite-type compounds. Except for the small distortion and polarization, these compounds have identical near-neighbor symmetry to zinc blende (cubic) structures, and hence the double refraction is caused primarily by the distant-neighbor interactions. The effects of anisotropy of the Lorentz-Lorenz force and of the Coulomb force are calculated. In the (ionic) approximation of zero cation polarizability the theory predicts a double refraction larger than the measured one by a factor ∼2 for all six compounds that have been measured. In the (covalent) approximation of zero effective ionic charge the theory underestimates the double refraction of AlN, but may be made to agree with the measured values of the other compounds by a suitable choice of atomic polarizabilities. In both approximations the theory predicts n0ne near the absorption edge of CdS.
Nucleation of Alumina at High Supersaturations and Subsequent Recrystallization
Authors: Sears G. W. , DeVries R. C.
Published: January 2005

Previous studies of the growth of alumina crystals have demonstrated the validity of current crystal growth theory for a high-temperature system involving a chemical reaction. The nucleation of alumina on a perfect alumina surface has been studied in the present report at very high supersaturations. The nucleation event is not consistent with the classical theory of nucleation, but rather is described by the Cahn-Hilliard theory of nucleation based on their treatment of the thermodynamics of nonuniform systems. In addition, the recrystallization of polycrystalline deposits to give near perfect crystal was observed.
Quantum Mechanical Cell Model of the Liquid State. I
Authors: Levelt J. M. H. , Hurst R. P.
Published: January 2005

In this paper the cell model for the liquid state, as proposed by Lennard-Jones and Devonshire, is recast in terms of quantum statistical mechanics. A method is developed by which the energy levels and wave functions in the liquid cell can be determined to any prescribed accuracy. Thus, in the present work, no additional approximations are introduced which are not inherent in the cell model. When a sufficient number of energy levels is obtained, the partition function and thus the thermodynamic properties are derived.

A method is devised by which from a knowledge of the wave function, the derivative of the corresponding energy with respect to the volume may be obtained. This derivative is required for the evaluation of the pressure.

The theory is applied to H2 and D2 at a density near that of the crystals at 0°K. The corresponding classical Lennard-Jones and Devonshire thermodynamic functions are obtained and compared with the results of the present theory. The calculations involved were performed on a Bendix G—15D computer.

The quantized cell theory predicts that for hydrogen and deuterium experimentally detectable differences in energy, entropy, and specific heat must persist at temperatures as high as − 150°C.
Nuclear Magnetic Resonance Study of the Proton Transfer in Water
Authors: Meiboom S.
Published: January 2005

Measurements of the nuclear relaxation in water are reported. The transverse relaxation rate (1/T2) of the proton resonance is pH dependent. The effect is shown to be due to a spin-spin splitting of the proton resonance by O17 (spin 5/2), which is only partially averaged out by proton exchange. The increase of relaxation rate is observable in natural water (0.037% O17), and becomes very appreciable in water enriched in O17. Additional information can be obtained by measuring relaxation rates in the presence of an rf field H1, using a method due to Solomon. A study of the width of the O17 resonance as a function of pH is in quantitative agreement with the results of the proton resonance. The observations provide a direct determination of the rate constants of the exchange reactions: H2O+H3O+→ lim k1H3O++H2O and H2O+HO−→ lim k2HO−+H2O.It is found that k1=(10.6±4)×109 liter mole−1 sec−1 and k2=(3.8±1.5)×109 liter mole−1 sec−1. The spin-spin interaction between H and O17 in water is determined as 92±15 cps. In the Appendices, theoretical equations for the exchange contribution to the relaxation rate are derived.
Interpretation of Viscosity Data for Concentrated Polymer Solutions
Authors: Fujita Hiroshi , Kishimoto Akira
Published: January 2005

An empirical viscosity vs concentration relation for concentrated polymer solutions is derived in terms of a simple free volume theory, and its applicability is tested with some available data for amorphous polymer+solvent systems. It is found that the derived relation fits well those data over the range of polymer concentrations so concentrated that interchain entanglements occur to form a weak network structure throughout the solution. In the region of relative low polymer concentrations, however, it shows deviation of a common feature from the experimental results. Two temperature-dependent parameters are contained in the viscosity equation derived; one is characteristic of the polymer species and the other is dependent upon the particular combination of polymer and diluent. These parameters are evaluated from comparisons with experimental data, and their variations with temperature are discussed.
Valence Bond Treatment on the B State of the Hydrogen Molecule
Authors: Tschudi Carmen S. , Cohan Norah V.
Published: January 2005

The potential energy of the lowest 1 Σu+ state of the hydrogen molecule is given as a function of the internuclear distance. Calculations were carried out by the valence bond method using Slater 1s and 2p atomic orbitals. Both ionic and covalent structures were considered. The 1s orbitals of the ionic and covalent functions included a variational parameter but the orbital exponent of the 2p orbital was kept constant. It is found that the introduction of the 2p orbital into the wave function results in a considerable improvement of the dissociation energy and that further the state is essentially covalent in character rather than ionic, as previously reported.
Approximate Theory of Transport in Simple Dense Fluid Mixtures
Authors: Rice Stuart A. , Allnatt Alan R.
Published: January 2005

The theory of transport proposed by Rice and Kirkwood is extended to the case of multicomponent systems. As in the previous case, the intermolecular force contributions to the shear and bulk viscosities and the thermal conductance are displayed as functions of the diffusion coefficient and the thermodynamic properties of the mixture. The self-diffusion coefficient is related to the intermolecular forces and molecular distribution function, thereby completing the molecular basis of the computation. Formulas are also given for the thermal diffusion factor and the heat of transport. The reader is referred to Eqs. (91), (104), (106), and (109). The theory presented predicts a form of volume fraction mixing. For example, the shear viscosity becomes η=(ν1*/ν)2η1*+(ν2*/ν)2η2*+2(ν1*ν2*/ν2)η12*,with v1* and v2* the volume of N1 molecules of component one and of N2 molecules of component two, respectively, at the same temperature and pressure as the mixture. The quantities η1*, η2*, η12* are composition dependent so that the predicted mixing law is not pure volume fraction mixing except in the case of an ideal solution. The theory is compared with experimental measurements of the viscosity of benzene—carbon tetrachloride mixtures, and good agreement is found. The agreement between theory and experiment is discussed with reference to the mechanism of irreversibility.
Spin Density in Pyrene Negative Ion
Authors: Hoijtink G. J. , Townsend J. , Weissman S. I.
Published: January 2005

Improved resolution has permitted assignment of all proton hyperfine coupling constants in pyrene negative ion. The results are accounted for by a simple calculation of configurational interaction.
Application of the Free-Electron Theory to Three-Dimensional Networks
Authors: Hoerni J. A.
Published: January 2005

The free-electron network theory is generalized to permit its application to covalent and metallic crystals. General expressions for the case where the various branches of the network have different lengths and potentials are derived. Delta function discontinuities of potential at the junctions of the branches are introduced to describe the effective field acting on valence electrons. The general equations can be applied to various special cases, such as the Kronig and Penney potential or the behavior of π electrons in planar organic molecules. The free-electron network theory is used to derive the energy band structure of diamond in the interpolation scheme proposed by Slater. Energy band features are in semiquantitative agreement with those obtained by other methods. Some discrepancies in the sequence of energy levels in different theories are pointed out. The discussion includes the possible application of the free-electron network theory to more complicated crystals.
Kinetics of the Reactions of Alkyl Iodides with HI
Authors: Benson Sidney W. , O'Neal Edward
Published: January 2005

A reexamination of Ogg's data on the kinetics of the reactions of RI+HI→RH+I2 where R=CH3, C2H5 or n—C3H7, shows that the mechanism is a simple I-atom catalyzed, radical reaction with the steps I+RI⇄ lim 21R+I2R+HI→ lim 3RH+I.The rate expression is d (I2)/dt=k1k3K12(RI) (HI)/[k2(I2)+k3(HI)],where K is the equilibrium constant for dissociation of I2. Values are obtained for k1, and the inhibition ratio k3/k2 at one temperature and for k1k3/k2 over a temperature range. Using some entropy estimates, values are deduced for A1, A2, A3, and A4 (reverse of step 3) all of which seem quite reasonable and self-consistent. The difference (E3—E2) appears to lie between 0 and 2 kcal/mole while E1 is in excess of the estimated endothermicity of reaction (1) by not more than 1.5 kcal mole. There seems to be good agreement with independent data on the kinetics of pyrolysis of alkyl and aryl iodides which also turn out to be I-atom catalyzed, radical reactions.
Electronic Structures and Spectra of Some Nitrogen-Oxygen Compounds
Authors: McEwen K. Lenore
Published: January 2005

The electronic structures and spectra of nitrite ion, nitrosomethane, nitrosamine, and nitrate ion have been calculated by a semiempirical method, which includes both the π-electron system and, in a more limited manner, the σ-electron system. The calculated transition energies and intensities for the first three compounds above agree fairly satisfactorily with experiment. For nitrate ion, however, it seems possible that the lowest observed transition may be a very low energy n→σ* transition, σ* being an antibonding σ orbital, rather than one of the n→π* transitions considered in the present work.
Electron Spin Resonance of Some Vanadyl Porphyrins
Authors: Roberts E. M. , Koski W. S. , Caughey W. S.
Published: January 2005

The electron spin resonance spectra of the vanadyl complexes of etioporphyrin II, vanadyl mesoporphyrin IX dimethyl ester, and deuteroporphyrin IX dimethyl ester have been studied and found to be identical to within experimental error. Unlike the corresponding copper complexes, the vanadyl complexes give no observable nitrogen hyperfine effects. An explanation is proposed for the lack of this hyperfine structure, and an approximate method is suggested for evaluating the bonding parameters.
Luminescence in a Scintillation Solution Excited by α and β Particles and Related Studies in Quenching
Authors: Berlman Isadore B.
Published: January 2005

The relative intensity of the light pulses produced by α and β particles in a scintillating solution of 2,5-diphenyloxazole (PPO) in xylene has been investigated as a function of the concentration of the solute. The α/β ratio is substantially smaller than that found in organic plastic scintillators. From the data the dynamic quenching parameter has been calculated. Several independent experiments, i.e., measurements pertaining to mean lifetime of fluorescence, uv excitation, and pulse heights, were undertaken to study the mechanisms of quenching by oxygen in a scintillating solution. The best interpretation of the oxygen effect is consistent with the existence of dynamic quenching of the solvent and of the solute.
Pauling's Model and the Thermodynamic Properties of Water
Authors: Frank Henry S. , Quist Arvin S.
Published: January 2005

A statistical-thermodynamic treatment is given of the model for liquid water recently proposed by Pauling, in terms of a variable distribution of water molecules between the two states—framework water and interstitial water—for which this model provides. This treatment shows that, with simple assumptions, the model can give a satisfactory representation of the P–V–T properties of water over limited ranges of temperature and pressure. The properties (enthalpies and entropies) which are derived for framework and interstitial water, respectively, also seem physically reasonable. The simple model is less successful in representing the heat capacity of water and the partial molal properties of nonpolar solutes. The fact that water is a liquid, however, requires that some molecules be in a ``third state,'' and it is suggested that if this third state is taken into consideration the shortcomings of the simple model can be remedied. Adoption of the Pauling model would seem to have as a corollary the likelihood that the structural ``transition,'' purportedly found in liquid water just above 30°C, may be real.
Step Formation during the Growth of BaTiO3 Crystals
Authors: DeVries R. C. , Sears G. W.
Published: January 2005

The growth behavior of barium titanate crystals from molten potassium fluoride at 1000°C may be described in some detail by the Frank growth mechanism. In particular the role of reentrant twin angles as growth step sources was examined. A finite supersaturation is required for the operation of this source and the event must occur by an easier nucleation process than homogeneous two-dimensional nucleation.
Thermodynamics of the Vaporization of Cr2O3: Dissociation Energies of CrO, CrO2, and CrO3
Authors: Grimley R. T. , Burns R. P. , Inghram Mark G.
Published: January 2005

The vaporization of Cr2O3 under neutral and oxidizing conditions has been studied using mass spectrometric methods. The vaporization proceeds with the formation of Cr, CrO, CrO2, O, and O2 as the principal gaseous species. Under oxidizing conditions CrO3 was also observed. Dissociation energies of the gaseous molecules are D00(CrO)=101.1±7 kcal/mole, D00(CrO2)=227.1±15 kcal/mole, and D00(CrO3)=341±20 kcal/mole.
Thermoluminescence in Dolomite
Authors: Medlin W. L.
Published: January 2005

The thermoluminescent properties of dolomite have been investigated by coprecipitating impurities which are likely to serve as activators with an otherwise pure sample. Only impurities which are likely to occur in natural samples were considered. The effects of cation and anion vacancies were also investigated and found to be unimportant. Divalent manganese was found to be the only activator of importance and its presence satisfactorily explains the important features of glow curves for natural samples. The results of luminescent efficiency as a function of activator concentration were determined. It was found that concentration quenching of the Mn++ luminescence is characteristic of an isolated activator site. Quenching of the manganese luminescence by Fe++, Co++, and Ni++ was also observed and quantitative results were compiled. All impurity ion concentrations were determined by colorimetric procedures. The presence of Co++ or Ni++ with Mn++ produces high-temperature glow peaks which roughly coincide with similar peaks observed in natural samples. However, it appears more likely that the peaks in natural samples are due to lattice defects resulting from deformation pressures. Isothermal decay curves were measured for all of the glow peaks due to Mn++ and found to have the form predicted for a second-order decay process. However, the behavior of one of the decay parameters as a function of activation time is different from the predicted behavior. The trap depth energies and frequency factors associated with most of the glow peaks due to Mn++ have also been determined.
On the Theory of Raman Intensities
Authors: Albrecht Andreas C.
Published: January 2005

The Herzberg-Teller development for vibronic transition moments is introduced into the Kramers-Heisenberg dispersion equation. It is shown how ``forbidden'' character (vibrationally induced intensity) in allowed electronic transitions is responsible for the Raman intensities of fundamentals. This suggests a direct link between certain vibronic spectroscopic observations and Raman intensities. The development is carried to the first order in nuclear displacements only—the higher terms give rise to Raman intensities of combinations and overtones. An equation for the polarizability components is obtained which leads directly to the Raman selection rules and in addition provides interesting predictions concerning the Raman and the resonance Raman effect in relation to excited electronic states. Rules are worked out governing the participation of excited electronic states in the Raman effect and these are employed to demonstrate a separability of σ and π contributions to the scattering of totally symmetric modes. The polarizability expression obtained here is compared with that of the semiclassical theory of Shorygin and an interesting resemblance is found. Finally it is shown how, depending on details of the electronic structure, the predicted form of the frequency dependence of scattered intensity ranges between the two expressions that have been commonly used to interpret observations.
Competitive Reaction Rates of Hydrogen Atoms with HCl and Cl2. Entropy Considerations of the HCl2 Transition State
Authors: Klein Fritz S. , Wolfsberg Max
Published: January 2005

The relative rates of the reactions H+HCl→ lim k3H2+Cland H+Cl2→ lim k6HCl+Cl,were determined in the temperature range of 0° to 62°C and found to be given by k3/k6=(0.143±0.033) exp−(1540±130/RT).The temperature-independent factor in the above expression is interpreted in terms of the structure and the vibrational frequencies of the HCl2 transition state. The doubly degenerate bending frequency of this transition state is found to have a value of about 105 cm−1.
Scattering of High-Velocity Neutral Particles. XI. Further Study of the He–He Potential
Authors: Amdur I. , Jordan J. E. , Colgate S. O.
Published: January 2005

Results are presented for two studies of the scattering by room-temperature helium of beams of helium atoms with controlled energies in the approximate range 150–1500 ev. The interaction potential derived from the two sets of measurements is represented by φ(r)=5.56×10−12/r5.03 erg  (0.97 A<r<1.48 A).Where there are common ranges of the interaction distance r this potential is in reasonable agreement with He–He potentials previously determined from scattering experiments. In its specified range of validity, it is somewhat lower than most of the corresponding values calculated quantum mechanically.
Probability of Initial Ring Closure in the Restricted Random-Walk Model of a Macromolecule
Authors: Hiley B. J. , Sykes M. F.
Published: January 2005

The probability of initial ring closure in the restricted random-walk model of a macromolecule is investigated. From a study of the known exact numbers of polygons on the simple quadratic lattice up to 18 sides and on the triangular lattice up to 16 sides, it is concluded that the probability of initial ring closure in two-dimensions of large ring size k varies inversely as k1.83—θ, where 0≤θ≤0.05, and this is significantly higher than the dependence on the inverse square of k found by Wall's statistical investigation. It is found that the mean area of initial ring closures in a plane varies as k32.
Statistical Mechanics of Monatomic Systems in an External Periodic Potential Field. II. Distribution Function Theory for Fluids
Authors: Hill Terrell L. , Saitô Nobuhiko
Published: January 2005

The theory of distribution functions for monatomic systems in an external periodic potential field is outlined. Particular attention is given to the equation of state, the second virial coefficient, and the Kirkwood and Born-Green-Yvon integral equations for the distribution functions. A brief discussion of a nonperiodic external field is given in an Appendix.
Infrared Spectra of Methanol and Deuterated Methanols in Gas, Liquid, and Solid Phases
Authors: Falk M. , Whalley E.
Published: January 2005

The infrared spectra of CH3OH, CH3OD, CD3OH, and CD3OD in the five phases gas, liquid, vitreous solid, α-crystal, and (except perhaps for CD3OH and CD3OD for which the solid-solid transitions have not been studied) β-crystal have been recorded in the range 4000 to 300 cm−1. The Raman spectrum of liquid CD3OH has been recorded. A complete assignment of the internal modes is given, which differs somewhat from previous assignments for the CH3 bending and rocking vibrations. No significant difference in spectrum occurred between the α-crystal and β-crystal phases. Under the full symmetry of the β-phase determined by x-ray diffraction only one OH out-of-plane bending band should occur. Two bands are observed, and it is concluded that the carbon and oxygen atoms in one chain are not coplanar, as is required by the symmetry determined by x-ray diffraction [K. J. Tauer and W. N. Lipscomb, Acta Cryst. 5, 606 (1952)], but that the chains are puckered and the x-ray symmetry arises because the puckered chains are irregularly distributed, a structure that had been previously suggested by Tauer and Lipscomb tentatively on the basis of high apparent thermal amplitudes. Bands occur in the crystal spectra near 500 cm−1 and 340 cm−1 at −180°C. These are interpreted as lattice modes, probably the two infrared-active modes that involve translations of the molecules.
Crystal Spectra of Metal Coordination Compounds. IV. Bis-Acetylacetonato-Copper (II)
Authors: Ferguson J.
Published: January 2005

The polarized crystal absorption spectrum of bis-acetylacetonato-copper (II) has been measured with light incident on three different crystal faces. Four absorption bands have been found and a consistent analysis made in terms of a strong rhombic (D2h) field from the ligands. The symmetries of the ground and excited states are not those predicted on the basis of simple crystal field theory and it has been suggested that strong metal-ligand π bonding will account for the observed order of states. The slight differences between the positions of the bands in the crystal and in chloroform are accounted for by weak intermolecular interactions between adjacent molecules in the crystal.
Infrared Spectra of Alkali Metal Azide Crystals
Authors: Papazian Harold A.
Published: January 2005

The infrared spectra of CsN3, RbN3, KN3, and NaN3 crystals have been recorded at room temperature and at liquid-nitrogen temperature. Considerable anharmonicity in the fundamentals of N3− and combinations with lattice modes has been observed. Splitting of the doubly degenerate ν2 has been observed. Discrepancies between the several reported values of ν3 are discussed.
Photolysis of Nitrous Oxide. I. 1236 A
Authors: Doering John P. , Mahan Bruce H.
Published: January 2005

The photolysis of nitrous oxide containing an N15 atom in the external position has been investigated using 1236-A light. The products include N229, N15O, N14O, and small amounts of N230. The appearance of N230 shows that there are two primary processes occurring at this wavelength, one of which is dissociation to a nitrogen atom and a nitric oxide molecule, the other dissociation to an oxygen atom and a nitrogen molecule. The latter process is approximately 10 times as important as the former. The quantum yield of nitrogen is 1.34±0.04.
Magnetic Properties and Optical Absorption Spectrum of K2ReCl6
Authors: Eisenstein J. C.
Published: January 2005

A phenomenological theory of certain physical properties of the (ReCl6)2− complex ion is presented here. The ion can be described in terms of a set of parameters which includes the strength of the octahedral ligand field, the Coulomb integrals, the spin-orbit coupling constant and the orbital reduction factors. The interaction matrices for the three-electron system are given in algebraic form. With an appropriate choice of the parameters the eigenvalues of these matrices are in fair agreement with the observed energy levels of the system. The effect of a departure from strict octahedral symmetry is discussed. The matrix elements of the magnetic moment operator are also given in algebraic form and then used in a calculation of the susceptibility. The discrepancy between theory and experiment is attributed to a superexchange interaction which leads, at sufficiently low temperatures, to antiferromagnetism of the compound. Finally, the results of paramagnetic resonance experiments on K2ReCl6 are considered.
Near-Infrared Absorption Spectrum of Solid Methane at the λ Point
Authors: Glasel Jay Arthur
Published: January 2005

Observations on the near-infrared absorption spectrum of solid methane in the region of ν1+ν4 and ν3+ν4 over a temperature range of 6° to 33°K are presented and discussed. There is no evidence of molecular rotation, and the observations are shown to lead to an interpretation involving an order-disorder transition. Approximate f numbers for the transitions are measured.
Application of Ligand Field Theory to the Electronic Spectra of Gaseous CuCl2, NiCl2, and CoCl2
Authors: Hougen Jon T. , Leroi George E. , James Thomas C.
Published: January 2005

The absorption spectra of CuCl2, NiCl2, and CoCl2 in the gas phase at 1000°C have been obtained under low resolution in the visible, near-infrared, and near-ultraviolet regions. The observed absorptions have extinction coefficients of the order of 100 liter/mole·cm, suggesting that they correspond to ``forbidden'' intraconfigurational dn←dn transitions analogous to those found in solutions and crystals containing these metal ions. The observed spectra are rather well described by the two ligand field parameters appropriate to a molecule of symmetry D∞h.
Theory of Localized Contributions to the Chemical Shift. Application to Fluorobenzenes
Authors: Karplus M. , Das T. P.
Published: January 2005

An expression for the magnetic shielding tensor is obtained by the use of single-determinant Hartree-Fock molecular wave functions. For nuclei of atoms in which the change in the second-order (paramagnetic) contribution is dominant, LCAO theory is employed to express the shielding in terms of localized bond parameters (ionic character, hybridization, and double bonding) and to compare it with the related treatments of the quadrupole coupling constant. Application of the formulation to the multifluorobenzenes provides an explanation of the available experimental chemical shift data and permits the prediction of shift values for other compounds. Of particular interest is the demonstration that double bonding in the C–F bond plays an important role in the fluorobenzenes. Also, the presence of an ``ortho'' effect in the shift is isolated by a comparison of experimental and theoretical results and tentatively explained in terms of charge repulsions.
Dissociation Processes in Electronically Excited Molecules. Linear Chain Model
Authors: Magee John L. , Funabashi Koichi
Published: January 2005

Dissociation mechanisms in a chain of coupled molecules have been considered. The attempt has been made to look at general features of the influence of electronic coupling on such processes. Actual calculations have only been made for the special case of a chain of H2+ ions. The weak-coupling and strong-coupling cases have been discussed explicitly, and various criteria for applicability of the special cases have been presented in terms of the physical constants of the system.
Inelastic Scattering of Atoms. I. Intermultiplet Transitions
Authors: Thorson Walter R.
Published: January 2005

Electronic-translational energy transfer processes have minute cross sections for atoms with thermally attainable kinetic energies, unless the amount of energy converted from electronic to translational form (or vice versa if the threshold permits) is rather less than 1 ev. The transfer processes of interest to chemical kinetics, therefore, involve highly restricted sets of energy levels. Two situations are commonly encountered: (1) The ``two-state'' case, in which two energy levels of the diatomic system cross or approach closely in energy, so that a respectable probability of resonance transfer is achieved; cases of this type almost always involve transfer of most of the excitation from one atom to the other. (2) Transitions among the multiplet levels of a given Russell-Saunders term of an atom, induced by collision with an ``inert'' atom. Spin-orbit coupling is the electronic interaction splitting the levels. The present work is concerned with the latter case. The ``high-energy approximation,'' a necessary modification of the Born approximation, and various ``modified adiabatic approximations,'' which take account of the details of angular momentum coupling during collision, are described, and practical methods of calculation considered.
Phase Transitions in the Ammonium Halides
Authors: Stevenson Richard
Published: January 2005

High-pressure experiments, using the piston displacement technique have been performed at temperatures down to that of liquid nitrogen on NH4I, NH4Br, ND4Br, and NH4Cl. For the iodide two new phase transitions under pressure and a new triple point were observed. A new transition and a new triple point were observed in both the bromides; the existence of another transition was confirmed. The role of multipole interactions in causing the transitions is discussed, and on the basis of structural data and the present experiments a generalized phase diagram is presented which describes the gross behavior of the transitions in these substances.
Irradiation Yields of Radicals in Gamma-Irradiated Ice at 4.2° and 77°K
Authors: Siegel Seymour , Flournoy John M. , Baum Lillian H.
Published: January 2005

The EPR spectra of both ice and deuterated ice which have been subjected to γ irradiation at 4.2°K are presented and discussed. Experimental radical irradiation yields at 4.2°K are reported for the H2O system as a function of sustained irradiation dosage. A comparison between the irradiation yields at 4.2° and 77°K is given and the resulting similarities discussed in terms of intra-spur reactions. Finally, preliminary evidence is presented for the existence of an appreciable isotope effect for the irradiation yields in a mixture of H2O and D2O.
Relaxation of Laminar Flow with Reference to Streaming Birefringence Decay
Authors: Hollingsworth C. A. , Granquist W. T.
Published: January 2005

Equations are obtained which express the decay of motion of fluids between concentric cylinders, parallel plates, and in tubes. Numerical examples are given which indicate that the time required for the flow to decay may not always be short compared to the streaming birefringence relaxation times.
Infrared and Raman Spectra of Fluorinated Ethanes. XIV. CF2Cl–CHF2 and CF2Br–CHF2
Authors: Klaboe Peter , Nielsen J. Rud
Published: January 2005

The infrared absorption spectra of gaseous CF2Cl–CHF2 and CF2Br–CHF2 at five temperatures between 30° and 180°C were obtained in the region 300–6000 cm−1 with a Perkin-Elmer double-pass spectrometer equipped with CsBr, NaCl, and LiF prisms. In addition, infrared spectra of the solids at −170°C were recorded in the region 350–5000 cm−1. The Raman spectra of the liquids at 30°, −30°, and −80°C were photographed with a three-prism glass spectrograph of reciprocal linear dispersion 15 A/mm at 4358 A, and polarization measurements were made. In all three states of aggregation both compounds exist as mixtures of rotational isomers. For each compound, the two isomeric forms (trans and gauche) are about equally stable, both in the gaseous and the liquid state. Tentative assignments have been made of the fundamentals of both compounds.
Ionized States in a One-Dimensional Molecular Crystal
Authors: Merrifield R. E.
Published: January 2005

Generalization of the theory of excitons in molecular crystals to include ionized states is carried out for an idealized one-dimensional model for which the exact wave functions and energy levels can be derived. The ionized states are found to form a progression of bands corresponding to bound states of the electron and hole. The bound levels converge to a band of free states in which the electron and hole move independently and can carry an electric current. The lowest-lying ionized states may interact significantly with the un-ionized molecular exciton states and give rise to weak charge-transfer absorption bands.
Estimation of Molecular Parameters of C/H Fragments
Authors: Cowperthwaite M. , Bauer S. H.
Published: January 2005

In this paper, we have assembled the molecular constants needed for the computation of the thermodynamic functions and the standard heats of formation for most of the low molecular-weight CmHn species which may be present in equilibrium at very high temperatures under a variety of external conditions. In the literature, the essential data are recorded for only 34 of the 73 species considered, and for those which are listed thermodynamic functions are given for the lower third of the temperature range included in our computations.

In order to arrive at an estimate for each of the 39 molecular fragments the following steps were used: (a) assign to each fragment a formal electronic configuration (this establishes the framework for the analogies to be sought and fixes its ground-state electronic degeneracy); (b) select several paths for dissociation which, when followed, generate the species under consideration in going from one molecule of known structure to another; and (c) estimate the bond dissociation energies from known simple dissociations, corrected for nonlocalized electron interactions. These corrections are relatively small and have been obtained by comparing similar reactions for known species. The success of this procedure is demonstrated by the good agreement found between a few predicted and experimental heats of formation. The self-consistency of the method is proven by the close check between estimates made for the heats of formation for many species following independent paths.
Equilibrium Composition of the C/H System at Elevated Temperatures
Authors: Duff Russell E. , Bauer S. H.
Published: January 2005

Thermodynamic functions for a large number of C–H molecules were computed from the molecular parameters presented in the preceding paper. These functions and others taken from the literature were used to calculate the equilibrium composition of the C/H gas phase system over the composition range C/H=1/10, ¼, ½, 1, 2, 3. The temperature range was 500–5000°K, and the pressures used were 0.1, 1.0, and 10 atm. In additional calculations solid carbon was assumed to be present. Representative graphs of the results are presented. They show that the familiar, stable hydrocarbons are not important in characterizing the equilibrium composition above 2000°K. Acetylenic molecules and their radicals dominate the composition at high temperatures.
Dissociation Energy and Rate of Decomposition of C2N2
Authors: Tsang Wing , Bauer S. H. , Cowperthwaite M.
Published: January 2005

The decomposition of cyanogen has been studied using shock wave heating. Kinetic and equilibrium concentrations of CN were obtained spectrophotometrically on 1, 5, and 10% solutions in Ar, in the incident and reflected shock regions. These data give C2N2=2 CN,    ΔH0∘=125±8 kcal.The dissociation reaction proceeds via a second-order process with a rate constant fitted by kdiss=[(3.3×1012)/5.5!]T12(E/RT)5.5e−E/RT, cm3 mole−1 sec−1.The three-body recombination-rate constant is given by krec=2.3×1012(E/RT)3, cm6 mole−2 sec−1;    E=125 000.Previous data on this reaction have been summarized and critically analyzed.
Effects of Rare-Earth Ion Substitution upon the Fluorescence of Terbium Hexa-Antipyrene Tri-Iodide and Sodium Europium Tungstate
Authors: Van Uitert L. G. , Soden R. R.
Published: January 2005

The directions and relative ease of transfer of energy between different rare-earth hexa-antipyrene aggregates are compared by examining the influences of rare-earth substitutions upon the fluorescence of terbium hexa-antipyrene tri-iodide. Data concerning much shorter range interactions between rare-earth ions are obtained employing the sodium rare-earth tungstates. Energy transfer and quenching effects show systematic relationships to the total orbital angular momentum of the 4f subshell electrons of the rare-earth ions.
Multicomponent Polyelectrolyte Solutions. Part II. Excluded Volume Study of Polyvinylsulfonate Alkali Halide Systems
Authors: Eisenberg Henryk , Woodside Daniel
Published: January 2005

Excluded volume theory of nonionic high-polymer solutions has been extended to mixed polyelectrolyte-added simple electrolyte systems. A systematic study has been undertaken of fractionated polyvinylsulfonate alkali halide systems. ``Ideal'' Θ temperatures, determined from phase separation experiments and from the vanishing of the second virial coefficient in light-scattering experiments, agree closely with each other. At the Θ temperature the intrinsic viscosity, for all systems investigated, is closely proportional to the square root of the degree of polymerization. Unperturbed dimensions (at the Θ temperature) in various systems are discussed. The entropy parameters ψ1* for various systems, derived from the temperature dependence of intrinsic viscosity and from phase separation, agree satisfactorily with each other. The value of ψ1* as a function of added electrolyte type and concentration is discussed. The relation between the intrinsic viscosity—sedimentation constant and intrinsic viscosity—second virial coefficient has been examined, for selected systems, as a function of the degree of polymerization.
Radial Distribution of Electrons in the Ammonia and Hydrogen Sulfide Molecules
Authors: Banyard K. E.
Published: January 2005

The model of ``floating'' hydrogen electron densities has been applied in detail to the molecules NH3 and H2S, both of the form XHn. In this way it has been shown that a reasonable radial distribution of electrons within these molecules may be obtained fairly easily from a knowledge of the molecular rotational magnetic moment which, in turn, is based on molecular beam or Zeeman effect microwave observations.

Some measure of the accuracy of these molecular electron densities has been obtained by calculating the coherent x-ray scattering factor and comparing it with the corresponding experimental values. Included in the present calculations for H2S is a determination of the paramagnetic contribution to the molar diamagnetic susceptibility. In addition, values of the molar diamagnetic susceptibility have been found for NH3 and H2S which are in good agreement with the experimental results.
Second Virial Coefficients of Argon, Krypton, and Argon-Krypton Mixtures at Low Temperatures
Authors: Fender B. E. F. , Halsey G. D.
Published: January 2005

Second virial coefficients of argon between 80–125°K, and krypton (105–140°K), have been measured. The experimental values are 5–15% larger in magnitude than those calculated from 12–6 or exp—6 potential functions by the substitution of parameters assigned to describe high-temperature virial coefficients. Second virial coefficients calculated from the potential-distance relationship proposed by Guggenheim and McGlashan are within 1% of the experimental values for argon, but are about 4% smaller in magnitude than the measured krypton coefficients.

Argon-krypton mixed virial coefficients have been determined between 105–125°K. These experimental results are best expressed by a 12–6 potential energy parameter combining rule ε12=2ε1ε2/ε1+ε2.
Heat Capacity of Diamond at High Temperatures
Authors: Victor Andrew C.
Published: January 2005

The enthalpy of gem diamonds has been measured from 273° to 1073°K using a ``drop'' method and a Bunsen ice calorimeter. The derived heat-capacity values, which are believed to be accurate to ±0.5%, are used to calculate the thermal functions of diamond above 298.15°K. Values of Cv0 (harmonic) derived from the present investigation and recent measurements of the thermal expansion and the elastic constants of diamond are compared with theoretical treatments. Reasonably good agreement in the temperature range of this study can be obtained with a single Debye function (ΘD=1860) obtained from the measured elastic constants. Extrapolation of the data gives Θ∞=1880±10.
Potential Function for the Inversion of Ammonia
Authors: Swalen J. D. , Ibers James A.
Published: January 2005

The data on the inversion of NH3 and ND3, summarized by Benedict and Plyler, have been fit in terms of the angular coordinate with a potential function of the form of a harmonic oscillator with a Gaussian barrier, with and without quartic anharmonicity. With the exception of one energy level of NH3, which seems obviously in error experimentally, the fit is to within a mean of 2 cm−1 for the first seven energy levels of NH3 and of ND3, far better than that previously achieved. The barrier height is found to be 2020±12 cm−1 and the distance of the nitrogen atom from the plane of the hydrogen atoms is found to be 0.382±0.004 A, in excellent agreement with the value of 0.3810 A derived by Benedict and Plyler experimentally. The improvement in agreement between observed and calculated energy levels upon addition to the potential function of a quartic anharmonicity term is not sufficient to support unequivocally such an addition. The derived value of the ratio of the reduced mass of NH3 to that of ND3 is consistent with an inversion motion involving an angular, rather than a distance, coordinate.
Quantum-Mechanical Integrals over Gaussian Atomic Orbitals
Authors: Browne J. C. , Poshusta R. D.
Published: January 2005

Formulas for the one-, two-, three-, and four-center energy integrals are derived using the general class of single-particle Gaussian atomic orbitals χ=xiyjzk exp[−(α1x2+α2y2+α3z2)].The overlap, kinetic energy, and dipole moment integrals are given in closed form. The potential energy integrals require a one-dimensional numerical quadrature. A technique due to Singer was used in obtaining these latter formulas.
ESR Detection of the Cyanogen and Methylene Imino Free Radicals
Authors: Cochran Edward L. , Adrian Frank J. , Bowers Vernon A.
Published: January 2005

The electron spin resonance (ESR) spectra of the cyanogen (CN) and methylene imino (H2CN) free radicals trapped in argon have been observed over the temperature range 4.2° to 37°K. The CN radical was produced by the vacuum uv photolysis of HCN in argon. The CN spectrum was a triplet whose outer lines varied with temperature from broad and weak at 4.2°K to narrow and strong at 37°K. This behavior was attributed to the broadening effects of an anisotropic nitrogen hyperfine interaction which was averaged out by the increased motional freedom of the radical at higher temperatures. The isotropic part of the nitrogen hyperfine splitting in CN was estimated to be 4.6 oe. The HCN photolysis also gave some weak ESR lines which were believed to be due to a radical formed by the addition of H atoms to HCN. This was confirmed when this weak spectrum was obtained with much greater intensity by photolyzing HI in the presence of HCN. From an analysis of the ESR spectrum it was shown that the addition of H atoms to HCN gave the H2C=N radical. The two protons each had an isotropic hyperfine splitting of 87.4 oe. The nitrogen hyperfine splitting was anisotropic, the isotropic and anisotropic hyperfine splitting constants being roughly equal and having the numerical value 32 Mc/sec.
Sum Rules for Vibrational—Rotational Energy Levels Including Centrifugal Distortion
Authors: Allen Harry C. , Olson W. Bruce
Published: January 2005

Sum rules are developed for the vibrational-rotational energy levels of an asymmetric rotor. These sum rules contain the corrections for centrifugal distortion correct for terms of the order P4 in the Hamiltonian. If the P4 terms of the Hamiltonian are neglected these sum rules reduce to those derived for a rigid asymmetric rotor by Mecke.
Note on the Theory of Singlet—Triplet Transitions
Authors: Hameka H. F.
Published: January 2005

A new mechanism for singlet—triplet transitions is developed by considering the direct interactions between the radiation field and the electron spins. It is concluded that this effect may in general be neglected with respect to contributions due to the perturbation of the wave functions by spin-orbit interactions, but that it might become important in some cases where the spin-orbit coupling is small.
Dielectric Constant of Ethanol in the Neighborhood of the Critical Temperature
Authors: Newton Peter , Copeland Charles S. , Benson Sidney W.
Published: January 2005

The dielectric constant of ethanol has been measured in the neighborhood of its critical temperature at different densities in the range 0.185 to 0.519 g/cc. Small amounts (2%—5%) of added water produce only a very small increase in the dielectric constant of ethanol at 245°C but a 10— to 20-fold increase in the specific conductance. There is a slow but unimportant decomposition of the ethanol into H2+CH3CHO which is catalyzed by the Pt metal of the conductance cell. Comparisons of the data for ethanol are made with the Clausius—Mosotti—Debye equation and also with the Kirkwood equation for the molar polarization as a function of density. Comparisons of the data are also made with that for NH3 and H2O where a comparable temperature and density range have been covered.
Monte Carlo Calculation of Triatomic Dissociation Rates. I. N2O and O3
Authors: Bunker Don L.
Published: January 2005

A very fast digital computer was used to simulate the motion of nonrotating triatomic molecules. Starting configurations were selected by a weighted random procedure which leads to correctly averaged dissociation rate constants vs energy. Trajectories were followed for 90 026 starting configurations representing various harmonic and anharmonic models of N2O and O3.

The conventional normal-mode description is very poor for all models studied; nevertheless, harmonic models give rise to large numbers of ``uninteresting'' molecules. The computations support a random gap assumption for anharmonic models only. It is concluded that calculations based on harmonic models give unrealistic rate constants below a pressure of about 100 atm for these molecules, and that the computed results are best described by a modified Rice—Kassel type of theory with a generalized postulate of limited molecular anharmonicity.