bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic Evidence for the Enhancement by Dissolved Salts of the Mole Ratio of the Gauche to the Trans Form of Ethylene Chloride
Authors: Inami Y. Harry , Ramsey J. B.
Published: January 2005

The infrared absorption spectra of two solutions of tetra-n-butylammonium perchlorate in ethylene chloride, 0.77 and 1.23 v.f., respectively, have been determined at ∼25°C. By comparison of these spectra with the spectrum of pure ethylene chloride it is shown that the mole ratio of the gauche to the trans form of ethylene chloride in each of these salt solutions (1.69 and 1.92, respectively) is significantly greater than it is in pure ethylene chloride (1.3).

The degree of dissociation of the salt in each of the two solutions is estimated from the measured values of their equivalent conductance-viscosity products. On this basis it is shown that in each of the solutions an appreciable fraction of ethylene chloride exists near enough to an ion to be appreciably influenced by its electric field.
Proton Nuclear Magnetic Shielding and the Diamagnetic Anisotropy of C–C and C–H Bonds in Propane
Authors: Narasimhan P. T. , Rogers Max T.
Published: January 2005

The nuclear magnetic resonance shielding σ of a proton in a molecule can be written as the sum of two contributions, namely, (a) the local or primary shielding σl due to the surrounding electron cloud, and (b) the distant or secondary shielding σd due to magnetically anisotropic charge distributions farther away from the nucleus. An internal chemical shift Δσ between two protons A and B may originate from differences in σl and/or σd (Δσl and Δσd, respectively). Using the hindered rotation model for propane (A6B2) an expression for Δσd between the methyl and methylene group protons has been derived in terms of the magnetic anisotropy (Δχ) of the C–H and C–C bonds in this molecule. If it is assumed that σl for both methyl and methylene group protons is the same, the internal chemical shift can be expressed solely in terms of the bond anisotropies. The value of the ratio ΔχCC/ΔχCH of the bond anisotropies thus obtained using the experimental value of Δσ is much larger than the theoretical value of ΔχCC/ΔχCH obtained by Tillieu. To the extent then that the theoretical studies of Tillieu on bond susceptibilities may be relied on, our calculations would indicate that there is a difference between the local shielding σl of the methyl and methylene group protons in propane. Since this difference in local shielding values may logically be related to an electronegativity difference between the CH3 and CH2 groups we have evaluated Δσl empirically from a modified form of the Dailey-Shoolery equation. Using this value along with the observed Δσ an estimate of Δσd was obtained which then led by our method to a value of ΔχCC/ΔχCH which is in reasonable agreement with the theoretical results of Tillieu. A semi-quantitative treatment for Δσl using theoretically calculated `atom charges' of methyl and methylene group protons also yields a value of ΔχCC/ΔχCH in satisfactory agreement with the theoretical value for this quantity. Our results may therefore be taken to indicate that both the local and distant shielding terms contribute to the total internal chemical shift in propane and that the former term is probably the more important.
Adsorption, Diffusion, and Evaporation of Carbon Monoxide on Tungsten
Authors: Klein Ralph
Published: January 2005

The surface migration, adsorption, and evaporation processes for carbon monoxide on tungsten have been examined with a field-emission microscope operating at liquid helium temperature. Carbon monoxide shows three distinct temperature regions of surface behavior. The first, a low temperature spreading from the Van der Waals layer, can be observed when several carbon monoxide layers are deposited on the ``shadowed'' portion of the tungsten point. After the low temperature spread, an emission pattern identical to that of clean tungsten is obtained, so that the lattice sites are completely occupied and the bonding is uniform. The second effect occurs above about 200°K and is characterized by development of graininess of the pattern. The third region can be observed when the point is shadowed with a monolayer or less. Surface migration from this chemisorbed layer takes place above about 625°K and has associated with it an activation energy of 36 kcal/mole. Desorption occurs in a temperature region commencing at about 1000°K with an activation energy of 52 kcal/mole. The pre-exponential factor of the Fowler-Nordheim expression was useful in following the desorption process, since it is essentially a measure of the low work function areas of the total emitting surface. In this way it was found that these areas follow first-order behavior for the desorption process.
Hückel Theory: An Effective Hamiltonian
Authors: Jones Walter D.
Published: January 2005

An effective one-electron Hamiltonian for molecules is presented that gives exactly the single-atom energies for its diagonal elements. An operator is used that selectively cancels the nuclear attraction for all nuclei except the one on which a particular AO is centered.
A Calculation of the Rates of the Ortho-Para Conversions and Isotope Exchanges in Hydrogen
Authors: Shavitt Isaiah
Published: January 2005

The rates of the various elementary reactions of the type H+H2→H2+H, involving ortho-para conversions or isotope exchanges, have been calculated by the absolute reaction rate theory, using new fundamental quantum-mechanical data for the shape of the H3 energy surface, but estimating the activation energy to fit experimental results. The transition complex is linear and symmetric, in contrast with the asymmetric complex of the semiempirical surface, resulting in some qualitative, as well as quantitative, differences in the calculation. The tunnel effect correction is computed exactly, on the assumption that the potential barrier is of the Eckart type. The disparity between the experimental results obtained by different authors and the probable inaccuracies in their data make it very difficult to assess the accuracy of the calculated rate constants.
Theory of Thermal Second-Order Decomposition of Molecules
Authors: Nikitin E. E. , Sokolov N. D.
Published: January 2005

A discussion is given of the rate of dissociation of diatomic molecules through collisions with a third body, taking into account the perturbation from the equilibrium Boltzmann distribution of the levels near the dissociation limit. An expression is derived for the rate of dissociation and it is compared with experimental results. Certain differences between association and dissociation are pointed out. Similar ideas are applied to the decomposition of polyatomic molecules, and a correction for quantization is introduced. After this correction, the results are shown to agree with the experimental data on several decompositions where the rate-determining step is the transfer of energy from some other molecule.
Use of the Self-Consistent Field in the Treatment of the Vibrations of Crystals
Authors: Walnut Thomas H.
Published: January 2005

It is shown that quantum-mechanical average equilibrium positions and average normal coordinates of ordered crystals are useful quantities. It is found that the wave functions calculated using these average quantities are more tractable approximations than those calculated from the true potential function with neglect of cubic and higher terms. A self-consistent field treatment is used to show how the average equilibrium positions and average normal coordinates could be obtained in principle. The wave functions derived from the self-consistent field coordinates are still very poor approximations to the exact wave functions in the sense that the projections of an approximate wave function on any exact wave function is extremely small.
Thermodynamics, Stationary States, and Steady-Rate Processes. I. Introduction and Migrational Equilibrium in Isothermal and Monothermal Fields
Authors: Tykodi R. J.
Published: January 2005

A method of obtaining thermodynamic relationships for systems in stationary states, for steady-flow processes, and for steady-rate processes in general is outlined. The method is shown to be applicable to equilibrium systems, and a monothermal concentration field is treated briefly.
Thermodynamics, Stationary States, and Steady-Rate Processes. III. The Thermocouple Revisited
Authors: Tykodi R. J.
Published: January 2005

The thermodynamic properties of the thermocouple are treated according to the principles developed in the first two papers of the series. The steps in the derivation of the Thomson relations seem to imply that a homogeneous thermoelectric effect does not exist.
Effect of Pressure on the Melting Points of Eight Alkali Halides
Authors: Clark Sydney P.
Published: January 2005

The melting curves of the alkali chlorides and the sodium halides have been determined at high pressures. The results can be represented within experimental error by Simon's equation. Comparison of the slope of the melting curve at low pressure with measurements of the changes of volume and entropy upon fusion suggests that the latter data are systematically in error.
Low-Temperature, Low-Pressure Transport Coefficients for Gaseous Oxygen and Sulfur Atoms
Authors: Konowalow Daniel D. , Hirschfelder J. O. , Linder Bruno
Published: January 2005

The transport properties of a gas at low temperature can be estimated in terms of the potential energy curves at very large separations. For this purpose it is only necessary to know the dispersion and multipole energies of interaction. Such calculations are carried out for the interaction of two oxygen or two sulfur atoms in their ground states. The atoms have an a priori probability pi of interacting in accordance with one of a set of potential energy functions Φi(R), where pi is proportional to the sum of the degeneracies of the states of the collision complex to which Φi(R) applies. For such collisional problems involving more than one potential energy function, the collision cross section Q for any process is rigorously additive in the sense that Q = ΣipiQi, where Qi is the collision cross section considering only the ith potential.
Effect of Adsorbed Water on the Optical Transmission Properties of Isotropic Powders
Authors: Debye P. , van Beek L. K. H.
Published: January 2005

An isotropic powder immersed in a liquid of the same refractive index in monochromatic light will scatter part of the light when an adsorbed layer of different index is present on its surface. A theory is developed that relates the apparent absorption coefficient to the thickness of the adsorbed layer. Data on water adsorption on glass powders show a good agreement between theory and experiment.
Infrared Spectrum and the Fundamental Frequency Assignments for Trifluoromethanethiol (CF3SH)
Authors: Dininny R. E. , Pace E. L.
Published: January 2005

Infrared spectral results for gaseous trifluoromethanethiol (CF3SH) in the 3–22 μ range are presented. By comparison with methyl mercaptan (CH3SH) and the isoelectronic molecule trifluoromethyl chloride (CF3Cl), the following assignment, (in cm—1 units), of the fundamentals has been made: v1 = 1136; v2 = 1179, 1167; v3 = 463; v4 = 521 (splitting not observed); v5 = 763; v6 = 342 (splitting not observed); v7 = 2618; and v9 = 540. The torsional mode v8 was not observed.
Substituted Methanes. XXIX. Vibrational Spectra, Potential Constants, and Calculated Thermodynamic Properties for Dibromochlorofluoromethane and Bromodichlorofluoromethane
Authors: Gilbert Robert L. , Piotrowski Edward A. , Dowling Jerome M. , Cleveland Forrest F.
Published: January 2005

Raman displacements, semiquantitative relative intensities, and quantitative depolarization factors for the Raman lines of the liquid, and wave numbers and estimated relative intensities for the infrared bands of the gas and liquid in the region 400 to 3000 c/cm (cycles/cm), were obtained for CBr2ClF and CBrCl2F. Assignments of the observed bands were made and reasonable sets of potential energy constants were determined by use of the Wilson FG matrix method and the procedure of Gold, Dowling, and Meister. Finally, the thermodynamic properties—heat content, free energy, entropy, and heat capacity—were calculated from the spectral and structural data for 12 temperatures from 100 to 1000°K.
Kinetic Theory of Nonspherical Molecules. IV. Angular Momentum Transport Coefficient
Authors: Livingston Peter M. , Curtiss C. F.
Published: January 2005

The kinetic theory of nonspherical molecules, as developed earlier, leads to an expression for the flux of angular momentum, involving several new transport coefficients. This paper is concerned with the evaluation of the first of these coefficients, L(0). The expression for this quantity as given earlier, is simplified by carrying out certain integrations explicitly. The resulting expression depends directly only upon the geometry of the molecular model. As an example, we consider the spherocylinder. The final integrations are then carried out analytically. The resulting expression for the dimensionless transport coefficient depends only upon three dimensionless groups of parameters characterizing the shape and mass distribution. The numerical results are illustrated graphically.
Molecular Partition Functions in Terms of Local Properties
Authors: Herschbach Dudley R. , Johnston Harold S. , Rapp Donald
Published: January 2005

The classical partition function for a polyatomic molecule is obtained in a form which has, for each atom, a factor that corresponds to free translational motion of the atom in an effective volume defined by the average vibrational amplitudes of the atom and the geometrical configuration of the neighboring atoms. A method is given for calculating the appropriate volume elements for any choice of internal coordinates. The treatment includes harmonic vibrations, internal rotations, and ``reaction coordinates.'' Quantum mechanical corrections introduce additional factors which shrink the volume elements for high-frequency vibrations.

Since the principal factors in this form of the partition function are determined by local properties largely characteristic of the bonds in the vicinity of each atom, many of these factors remain practically constant and can be omitted in calculations which compare the reactants in a chemical reaction with the products or with the ``activated complex.''
Studies of the Evaporation of Condensates Containing Nitrogen Atoms
Authors: Herron John T. , Dibeler Vernon H.
Published: January 2005

The products of an electrodeless discharge in nitrogen or mixtures of nitrogen in neon or argon were condensed at 4.2°K.

The products evolved from this condensate when it was allowed to warm up slowly were continuously analyzed by means of a mass spectrometer having a lower detection limit of 2×10—8 mm of nitrogen atoms. Experimental evidence is presented for the presence of nitrogen atoms in the warmup products. It was estimated that less than 10—3% of the nitrogen atoms originally condensed could be recovered.
Recombination and Disproportionation Reactions of Iodine Atoms and Ethyl Radicals
Authors: Guercione J. A. , Wijnen M. H. J.
Published: January 2005

In order to obtain information regarding disproportionation and recombination reactions of ethyl radicals and iodine atoms we have investigated the photolysis of various mixtures of diethyl ketone and methyl iodide.

Ethyl radicals, produced by photolysis of diethyl ketone, react with iodine atoms, produced by photolysis of methyl iodide, according to reactions (13) and (14) C2H5+I→C2H4+HI,C2H5+I→C2H5I.The results indicate k13/k14=0.33±0.03. The influence of added gas and the effect of temperature are discussed.
Electrical Conductivity of Near-Stoichiometric α-Nb2O5 in the Temperature Range 900° to 1400°C
Authors: Greener E. H. , Fehr G. A. , Hirthe W. M.
Published: January 2005

The electrical conductivity of near-stoichiometric α-Nb2O5 was measured in the temperature range 900° to 1400°C and at oxygen pressures between 1 and 0.005 atm. Over this entire range the change in conductivity with oxygen pressure is in accord with the relation σ∝Po2—¼. From the exponential temperature dependence of conductivity in the range 1400° to 700°C an activation energy of 1.65 eV can be calculated. These results are in excellent agreement with previous investigators who obtained the same relationships in the temperature range 600° to 900°C. Therefore, it is felt that the conduction process is controlled by a single mechanism over the temperature range 700° to 1400°C at oxygen pressures between 1 atm to 0.005. From mass-action considerations it is postulated that the mechanism responsible is probably the excitation of the first electron from an oxygen ion vacancy which has trapped two electrons.
Double-Resonance Parameters for Solutions of Fresh Asphaltene
Authors: Jeffries-Harris Michael J. , Poindexter Edward H.
Published: January 2005

The parameters describing electron—proton double-resonance phenomena in xylene solutions of fresh, washed asphaltene have been determined. The EPR line is found to be much more inhomogeneous than for air-blown asphalt. The values of T1e, T2e, and proton signal enhancement indicate that the particles of fresh asphaltene tumble faster than particles of air-blown asphalt. The surface electron—proton correlation frequency is found to be 30 Mc at 90°C.
Heats of Formation of Two Isomers of Difluorodiazine
Authors: Armstrong George T. , Marantz Sidney
Published: January 2005

The heats associated with the reactionN2F2(g)+83NH3(g)=2NH4F(c)43+N2(g),were observed for two mixtures containing the trans and the ``active'' isomeric forms of difluorodiazine (N2F2) in different proportions. From the observed heats of reaction of the two samples the heat of isomerization ΔH2980 of ``active'' to trans-N2F2 was found to be 3.0 kcal mole—1 with a calculated standard error of 0.3 kcal mole—1 based on four degrees of freedom. With the use of auxiliary data for NH3 and NH4F, the heats of formation ΔHf2980 were determined to be +19.4 and +16.4 kcal mole—1 for the trans and the ``active'' isomers, respectively. The bond energies in the two substances are discussed in terms of the possible molecular configurations.
Kinetic Isotope Effects in the Pyrolysis of Cyclopropane and Cyclobutane
Authors: Benson Sidney W. , Nangia Prakash S.
Published: January 2005

An analysis of the recent kinetic isotope effects in the pyrolysis of cyclopropane and cyclopropane-d6 is shown to be in excellent agreement with the diradical path for the reaction. This is true at the high-pressure limit and possibly near the low-pressure limit for the reaction.

Using the same transition state for the isomerization with a structure about half-way between trimethylene and propylene and containing a bridged H atom, leads to a frequency factor for the high-pressure rate constant in excellent agreement with the experimental data. It is also shown, from the examples of the C2H6 and H2O2 pyrolyses that ``secondary'' isotope effects may have temperature coefficients as large as or larger than those associated with ``primary'' isotope effects.

Extending the same type of analysis to cyclobutane pyrolysis leads to an excellent a priori calculation of the frequency factor for the high-pressure rate constant and of the kinetic isotope effects in cyclobutane-d8. It is further shown that the apparently discordant kinetic isotope effects reported for[Complex chemical formula]are actually in good agreement with those for cyclo-C4D8. Finally, the use of group additivity relations in kinetics is explored and shown to lead to excellent predictions in the reactions of isotopically labeled species with different isotopic content. Their application to other types of reactions cannot be evaluated at present because of insufficient data.
Some Stochastic Processes in Polymer Systems
Authors: Mazur Jacob
Published: January 2005

Certain distributional problems involving polymer configurations can be treated as special classes of stochastic processes known as regenerative processes. These processes have the property that the interval (of time or of length) between two consecutive events is a random variable. The method of regeneration point is applied to the problem of random crystallization of polymers and to the problem of force—length relationships in a one-dimensional simulation of a polymer network. By assuming that the events of randomly placing crystalline units on a polymer chain are statistically independent, and that the probability of the first event occurring in a given interval is a simple step function, the direct application of the method of regeneration point leads to a well-known equation from the theory of molecular distribution in one-dimensional hard-core fluids. In the second problem it is assumed that a single polymer chain consists of mesh points connected by flexible chains. A restriction is imposed that these mesh points cannot pass through each other. The molecular distribution functions for these mesh points are derived with the help of the regeneration-point process. By applying this method, the relationships of the network extension to the fixed force are derived. It is also found that the affine transformation rule for the force-biased distribution of chain lengths holds strictly only if the array represents a Poisson distribution of mesh points.
Shock-Tube Study of Vibrational Relaxation in Carbon Monoxide for the Fundamental and First Overtone
Authors: Hooker William J. , Millikan Roger C.
Published: January 2005

The rate of vibrational excitation in rapidly heated CO has been determined for the temperature range 1100°—2500°K by observation of infrared emission behind incident shocks. Great care was taken to eliminate impurity effects. The data agree to within 15% with those of Matthews. Separate observations of fundamental and overtone emission demonstrated that excitation occurs in a stepwise fashion. Collisional population of the v=2 level by successive single quantum transition is at least ten times faster than the direct 0→2 excitation process. Vibrational relaxation times of CO were determined for the pure gas and for the mixtures; 5% CO—95% Ar, 5% CO—95% N2, and 99% CO—1% H2. At 2000°K, τ(CO–CO) = 60 μsec, τ(CO–Ar) = 350 μsec, τ(CO–N2) = 640 μsec, τ(CO–H2) = 0.7 μsec, all for one atmosphere total pressure with the CO infinitely dilute in the second-named gas. The differences found between CO–CO collisions and CO–N2 collisions with respect to vibrational excitation are not explained by current theories.
Nucleation by Crystalline Particles
Authors: Fletcher N. H.
Published: January 2005

Classical nucleation theory is applied to the production of particles of a crystalline phase by growth upon small foreign particles. Various possible particle shapes are considered and general curves are derived which can be simply applied to a large variety of physical situations.
Thermodynamics of the Vaporization of Hf and HfO2: Dissociation Energy of HfO
Authors: Panish M. B. , Reif Liane
Published: January 2005

The vaporization of Hf and HfO2 have been studied using Langmuir vaporization and Knudsen effusion methods in combination with radioactive tracer and mass spectrometric techniques. The vapor pressure of hafnium over the temperature range from 2050° to 2300°K is represented by the equation: logpmm=9.765–31250/T. Third-law analysis of the data yields the heat of vaporization, ΔH2980=145.5±1.0 kcal/mole. The estimated boiling point of hafnium is 4575±150°K. The only hafnium containing species observed when HfO2 was vaporized was HfO. For the reaction HfO2(s)→HfO(g)+O(g)ΔH2980 was found to be 349±3 kcal/mole. The dissociation energy of HfO was estimated to be D00 (HfO)=182.6±6 kcal/mole.
Structural Interpretation of Asymmetrically Broadened NMR Fine-Structure Lines
Authors: Holcomb D. F. , Pedersen B.
Published: January 2005

The determination of precise structural information about solids by means of NMR fine-structure measurements is investigated theoretically. Attention is directed to the interpretation of broadening effects resulting from subsidiary dipolar interactions. Consideration is limited primarily to systems in which the fine structure is that produced by a strongly interacting pair of spin ½ nuclei, of which the water molecule in hydrate crystals is the prototype. It is shown that the fine-structure lines are expected to broaden asymmetrically and that the asymmetry is a measure of the anisotropy in the pair distribution. The nature of the asymmetry can often be interpreted in terms of the relative angular position of nearby interacting pairs in the crystal. It is further proved that, within the validity of a first-order perturbation theory approach, the center of gravity of a broadened fine-structure line is the correct measure of the interaction responsible for the main splitting. This result is independent of the number or relative positions of the interacting pairs.

The breakdown of the first-order theory with increasing interpair interaction strength is discussed. Using a simple two-pair model, calculations are made which show typical interpair distances at which one may expect a significant shift of the center-of-gravity position from that determined only by the intrapair interaction. Extension of the center-of-gravity theorem to other systems in which fine structure produced by a dominant interaction is asymmetrically broadened by subsidiary nuclear magnetic dipolar interactions is discussed briefly.
Asymmetric-Top Vibration—Rotation Hamiltonians
Authors: Chung K. T. , Parker Paul M.
Published: January 2005

From the general molecular vibration—rotation Hamiltonian in the Nielsen—Amat—Goldsmith formulation, Hamiltonians for asymmetric-top molecules of the orthorhombic, monoclinic, and triclinic point group symmetries are deduced. These Hamiltonians are appropriate for the calculation of vibration—rotation energies to the fourth order of approximation.
Application of Space-Group Theory to the Vibrational Problem of di-Tetramethyl Ammonium Uranium Hexachloride
Authors: Pollack S. A.
Published: January 2005

The absorption spectrum of [(CH3)4N]2UCl6 (abbr. TMA) is discussed. The spectrum is vibronic in nature, i.e., the electronic transitions between levels belonging to the 5f2 configuration of the U4+ ion are coupled with the vibrations of the TMA lattice. The number and symmetries of the normal modes of vibration of a unit cell are calculated in the factor group approximation. The Winston—Halford decomposition formula is used to reduce the representation of motions among the irreducible representations of the symmetry group of TMA.

Calculations are compared with the experimental results. The gross features of the spectrum are found to be in agreement with the theoretical predictions.

The method of obtaining the character tables for finite symmorphic space groups is presented in summary form. A general vibrational problem in crystals is discussed.
Stark Effect and Dipole Moment of Methyl Fluoride
Authors: Larkin Declan M. , Gordy Walter
Published: January 2005

High-precision Stark effect measurements have been made on the J=1→2 transition of methyl fluoride in the shorter millimeter wave region. A parallel-plate Stark cell employing silver-coated glass plates held apart by optically ground quartz spacers was employed. Millimeter wave power was fed between the plates by two sets of horns, one of which allowed for measurement of the ΔM=0 transitions and the other for measurement of the ΔM=±1 transitions. The dc voltage across the Stark plates was measured with a standard potentiometer. Both the first- and second-order effects were measured. The resulting value for the dipole moment of CH3F is μ=1.8555±0.0015 D for the ground vibrational state.
Semiempirical SCF-LCAO—MO Treatment of Furan
Authors: Orloff Malcolm K. , Fitts Donald D.
Published: January 2005

The self-consistent field—molecular orbital method including configuration interaction is utilized for the study of the π-electronic structure of the five-membered heterocyclic molecule furan. The calculation proceeds through the density matrix formalism of McWeeny. A judicious choice of the two empirical core parameters for oxygen, along with the semiempirical approximations of Pariser and Parr, leads to a satisfactory description of the ionization potential, electronic spectra, and chemical reactivity of furan.
Heat of Formation of Methylene
Authors: Prophet H.
Published: January 2005

Recent theoretical estimates of the heat of formation of methylene prompted the reanalysis of the electron impact data of Langer, Hipple, and Stevenson on CH4, CH3, and CH2. The analysis indicates that the potentials are not wholly self-consistent but consideration of only CH2+ and CH+ ions leads to self-consistent reactions. These yield a most probable value of 95±5 kcal mole—1 for the heat of formation of methylene, in excellent agreement with the theoretical estimates.
Molecular Orbitals for H2 Based on Central Potentials. Average Hamiltonian and Correlation Energy
Authors: Peek James M. , Lassettre Edwin N.
Published: January 2005

The exact Hamiltonian for H2 is averaged over trial functions composed of molecular orbitals which are defined by a model suggested by the authors [J. Chem. Phys. 33, 1803 (1960)]. The three trial functions studied are (a) the single configuration type, (b) a two-configuration type including the σu orbital defined by the model, and (c) a function composed of a product of the lowest σg orbitals multiplied by a correlation function including one term having σu symmetry. The results from the single configuration function indicate that the lowest σg molecular orbital is a good approximation to an SCF orbital. The configuration interaction (CI) calculation indicates that a CI expansion based on these orbitals will converge very slowly to an eigenfunction of H2. Adding a one-term correlation function gave significant improvement, and the construction of a more complicated correlation function, by means of the variation principle, would undoubtedly lead to a good approximation to the exact eigenfunction. Rather than proceed along these lines, analysis of the various average values contributing to the total energy and the corresponding values predicted by the model suggests a different approach. It is found that, at the equilibrium internuclear distance, potential energy terms computed from the model agree with the exact values much better than average values based on the three trial functions, while the kinetic energy is much more poorly represented. This indicates that calculation of the total energy from the potential energy by the virial theorem would give better results than using the less exact kinetic energy term to construct the total energy and, at the same time, provide a means of calculating the total energy without knowledge of the correlation function. A constraint on the average of the exact Hamiltonian is introduced to provide a rigorous foundation for the above observation, and an appropriately modified virial equation is derived. An approximate solution of this equation is investigated. It is found that a complete solution is not possible without knowledge of the exact energy at one point.
One-Electron Potential Function for H2
Authors: Lassettre Edwin N. , Peek James M.
Published: January 2005

A one-electron potential function is shown to exist such that the exact energy of the hydrogen molecule can be calculated with only a knowledge of the solution to the one-electron Schrödinger equation, its eigenvalue and an average, over this solution, of the potential energy of one electron in the mean field of the remaining electron. Hence, given this potential function in advance, the exact energy of H2 can be calculated from the solution of a one-electron problem. A formula for this potential function is obtained in terms of the exact eigenfunction for H2. The formula can only be applied to accurately calculate the potential function when the hydrogen eigenfunction is known, and hence the formula is useful primarily to demonstrate the existence of the potential. On the basis of the Heitler—London wavefunction, an approximate numerical comparison between this potential function and that suggested by Slater is given. An empirical formula for the potential function is suggested, and an undetermined parameter is obtained using an approximate eigenfunction.
Effect of Penetrating Radiation on the Production of Persistent Internal Polarization in Electret-Forming Materials
Authors: Murphy Preston V. , Ribeiro Sergio Costa , Milanez Fernando , de Moraes Rogerio J.
Published: January 2005

The electret state was produced in Teflon and carnauba wax by simultaneous action of penetrating radiation and an electric field. Polymethylmethacrylate, polyvinylacetate, polystyrene, polyethylene, and nylon did not form electrets under these conditions. The shapes of isothermal decay curves and thermal depolarization ``glow curves'' were used to calculate activation energies for the depolarization process in Teflon. The average activation energy as calculated from the ``initial rise'' of thermodepolarization curves was 0.93 eV. The persistent heterocharge of carnauba wax and of certain polymers may be caused by the orientation of dipolar units composed of a positive molecular ion and a partially solvated electron.
Nuclear Spin Relaxation in Liquids. Spheroidal Molecules
Authors: Moniz W. B. , Steele W. A. , Dixon J. A.
Published: January 2005

Nuclear spin—lattice relaxation times have been measured as a function of temperature for a number of liquid hydrocarbons. These data, together with other available measurements on rigid, spheroidal molecules, are compared with the Bloembergen, Purcell, and Pound (B.P.P.) theory of spin—lattice relaxation in liquids, and it is shown that the B.P.P. calculation of the rotational contribution to the relaxation time gives a value which are much shorter than the total experimental relaxation times. It is then assumed that the time dependence of the rotational angular autocorrelation functions of these molecules is dominated by dynamical coherence, rather than by frictional forces as assumed in the B.P.P. theory. If one calculates the net spin—lattice relaxation time T1 by summing the translational contribution calculated from the B.P.P. theory and the rotational contribution calculated from an approximate autocorrelation function valid for small but nonzero friction constants, one obtains values for T1 which are in quantitative agreement with the data for nonpolar, spheroidal molecules. Furthermore, when the two calculations are compared with the data for polar spheroidal molecules, it is seen that frictional forces are the predominant factor in the rotational motion of these systems, but the values obtained for the rotational friction constant from the Stokes—Einstein equation are in error by a considerable amount.
Infrared Spectrum of Chlorodifluoramine, ClNF2
Authors: Ettinger Raymond
Published: January 2005

The infrared spectrum of chlorodifluoramine, ClNF2, has been examined, and all but one fundamental frequency assigned. ClNF2 is readily identified by three intense absorptions at 930, 854, and 697 cm—1 corresponding to symmetric and asymmetric N–F stretching, and N–Cl stretching, respectively.
New Method for Determining Semiempirical One-Center Coulomb Repulsion Integrals
Authors: Ellison Frank O. , Huff Norman T.
Published: January 2005

Utilizing the ``core—peel'' approximation for atoms and assuming that correlation errors in orbital calculations of potential energy are independent of orbital exponents, a model is devised for assessing the ``true'' repulsion energy associated with a two-electron wavefunction (geminal). For two-electron atoms, results corresponding to the integral (1s1s:1s1s), but with correlation, conform to experiment within 0.01 eV. Values are also obtained for the integrals corresponding to (2p2p:2p2p) in boron to fluorine in various valence states.
Modification of the Born—Mayer Potential Function as Applied to the Crystalline Alkali Halides
Authors: Douglas Thomas B.
Published: January 2005

The repulsion constant ρ in the Born—Mayer potential function is assigned values which are different for like- and unlike-ion pairs in such a way that large deviations from the observed compressibilities of the lithium halides, attributable to marked anion—anion repulsion, are removed. Lattice parameters in excellent agreement with the experimental ones are than obtained using alternative sets of ``basic radii'' based on differently evaluated ionic radii, but an indeterminacy characteristic of the Born—Mayer equation is shown to affect markedly the calculated like-ion overlap-repulsive contributions. The possibility of considerable error in the calculated results through lack of correction for ion asymmetry is discussed. The calculated electron affinities, which are unaffected by these uncertainties, agree approximately with the most precise determinations by other methods.
Accurate and Facile Approximation for Vibrational Energy-Level Sums
Authors: Whitten G. Z. , Rabinovitch B. S.
Published: January 2005

Some exact sums of harmonic vibrational-energy-level densities for 45 molecules were obtained at various energies with a digital computer. An improved ``corresponding vibrational states'' type of approximation to these sums at low and moderate energies is described. The approximation has the great advantage or being very rapid, of requiring scarcely any calculational detail and of using the actual molecular frequencies. The agreement of the approximation with a smoothed true count is usually within a few percent at quite low energies, ε≳0.1 εz. It has the further advantage of being good also for the difficult case of a complex polyatomic molecule with noncommensurable frequencies.

The behavior of the sums for various vibrational patterns is considered. The importance of noncommensurability and number of frequency groups is displayed.
Nuclear Magnetic Resonance in Polycrystalline UF6
Authors: Blinc R. , Marinković V. , Pirkmajer E. , Zupančič I. , Maričič S.
Published: January 2005

An F19 magnetic resonance study of polycrystalline uranium hexafluoride as a function of temperature and magnetic field is presented. The low temperature spectra are resolvable into two symmetric components, demonstrating the existence of two nonequivalent sets of U–F bonds. At higher temperatures the two resonances coalesce in spite of the fact that the magnetic susceptibility of UF6 is temperature independent. The possible origin of this effect is discussed.
Atomic and Ionic Recoil from the (n, γ) Reaction
Authors: Thompson Joseph L. , Miller Warren W.
Published: January 2005

The occurrence of charge on the recoil atoms produced by the (n, γ) reaction has been examined for several elements and for different chemical states of the same element. The fraction of the recoil atoms leaving a substrate and crossing a potential gap that carries a positive charge was determined by observing the ratio of the atoms on charged and uncharged collector cylinders. The fractions of positively charged recoils are, for In, 0.46; In2S3, 0.50; In2O3, 0.55; InF3, 0.40; Mn, 0.52; KMnO4, 0.56; Dy2O3, 0.63. From considerations of the capture gamma-ray-decay schemes and lifetimes of states giving rise to transitions by conversion electron it appears that, in a condensed medium, the recoiling atom rarely develops a charge prior to the loss of its initial kinetic energy.
Symmetry Numbers and Reaction Rates
Authors: Schlag E. W.
Published: January 2005

It is shown here that absolute rate theory, in its use of symmetry numbers in the rotational partition functions, does not provide an infallible recipe for considering the possibility of multiple reaction paths. The conditions under which this recipe must fail are considered; and hence, in absolute rate theory calculations a correction factor must be included beyond that provided by the symmetry numbers. A general recipe is given for calculating the reaction path multiplicity; a direct count of all possibilities will, of course, always provide the correct answer.
FCC Elastic Constants for Arbitrary Central Forces by the Method of Long Waves
Authors: Overton William C.
Published: January 2005

Assuming a central-force pair potential of arbitrary form, the secular equation for the vibrations of a face-centered cubic lattice is derived for interactions through 23rd neighbors (the 682 nearest neighbors). An elementary treatment of all forces arising because of atom displacements shows that the first derivative of the potential inevitably enters as a force constant in the diagonal elements of the secular determinant in addition to the usual second derivative constants. The long-wave limiting case for [100] and [110] directions leads to sets of lattice sums, combinations of which give the elastic constants. We find the derived (c11+2c12)/3 to be the same as the bulk modulus derived independently from the static lattice potential energy, an internally consistent result not ordinarily obtained by the method of long waves. The lattice sums obtained are recast and evaluated for the —Ar—m+Br—n potential by averaging the sums through 23rd neighbors (corrected by integration to ∞) with those through 22nd neighbors (corrected by integration to ∞). Tests indicate high accuracy for the averaged results. The Cauchy relation c12=c44 is found not to be obeyed unless various known volume forces are assumed absent. In empirical application to copper at 0°K a 4–7 potential (with minimum closer than nearest neighbors) is found to give experimental c44 and C′=(c11—c12)/2, correctly, (∂c44/∂p) within 10%, but with (∂C′/∂p) off by a factor of 4. Other m—n potentials were also unable to give these experimental copper parameters properly. Applications to solid He3 and He4 are also considered.
Triplet State of Benzene
Authors: Dubois Jean T. , Wilkinson Francis
Published: January 2005

The sensitization of biacetyl fluorescence and phosphorescence using benzene as donor has been studied at 25°C in aerated and de-aerated hexane solutions. Electronic energy transfer from the lowest excited singlet state of benzene to biacetyl producing either the first or second excited singlet state of biacetyl proceeds with a rate constant (3.3×1010 liter moles—1 sec—1), which is consistent with a diffusion controlled process. No evidence for energy transfer from triplet benzene to biacetyl has been found in fluid solution. However, in rigid media, transfer from triplet benzene has been established with a transfer distance of ∼10 Å. The surprising lack of evidence for triplet benzene in fluid solution is discussed in the light of previous work.
Microwave Spectrum, Barrier to Internal Rotation, and Dipole Moment of Cis-Crotononitrile
Authors: Beaudet Robert A.
Published: January 2005

The microwave spectrum of cis-CH3CH=CHCN has been measured and assigned in the region 8–34 kMc/sec. The transitions were split by tunneling of the methyl group through the potential barrier to internal rotation. From these separations the barrier was determined as 1400 cal/mole. The total dipole moment is 4.08 D.
Self-Consistent-Field Theory. I. General Treatment
Authors: Birss Fraser W. , Fraga Serafin
Published: January 2005

A general method is described for obtaining SCF orbitals for electronic systems without restriction on the number or the symmetry of open-shell orbitals. A separation on the basis of symmetry designation is made at the beginning. The pseudo-eigenvalue equations are obtained from the SCF equations by the introduction of a new form of coupling operator. The new equations must be solved individually for orbitals of a separate symmetry designation. Some examples are given.
Interaction of Low-Energy Electrons with Water Vapor and with Other Polar Molecules
Authors: Hurst G. S. , Stockdale J. A. , O'Kelly L. B.
Published: January 2005

Electron attachment coefficients and drift velocities have been measured in mixtures of H2O vapor with N2, CH4, C2H4, and with CO2. Electron capture takes place only in the H2O–CO2 mixture, and even in this case the attachment coefficient is quite small. Thus, low-energy (less than 1 eV) electrons do not, in general, form stable negative ions with H2O.

Electron drift velocities are very sensitive to the addition of small quantities of H2O vapor in all the mixtures. When certain other polar molecules (acetone, heavy water, methyl alcohol, dimethyl ether, hydrogen sulfide, toluene and nitrous oxide) were mixed with C2H4, it was found that the decreases in drift velocity correlated well with the magnitude of the electrical dipole moments. The drift velocity data were analyzed to obtain the cross sections for momentum transfer. These cross sections are in fair agreement with the theory of Altshuler, except for H2O, D2O, and H2S, where the experimental values are a factor of 2 larger than theory. This discrepancy may be due to molecular rotational enhancement of the momentum transfer cross section, or it may be due to the temporary formation of negative ions, an effect which would decrease the observed drift velocity.
Low-Temperature Magnetic Susceptibilities of Some Hydrated Formates of Cu++ and Mn++
Authors: Flippen R. B. , Friedberg S. A.
Published: January 2005

The magnetic susceptibilities of powdered specimens of Cu(HCO2)2·4H2O, Cu(HCO2)2·2H2O, and Mn(HCO2)2·2H2O have been measured by an audio-frequency mutual-inductance method between 1.3° and 4.2°K, and from 14° to 20°K. At hydrogen temperatures Cu(HCO2)2·2H2O and Mn(HCO2)2·2H2O exhibit Curie—Weiss behavior which, however, breaks down significantly in the helium region. The susceptibility of Cu(HCO2)2·4H2O rises to a pronounced peak at 16.8°K and is essentially constant below 4.2°K. The susceptibilities of single-crystal Cu(HCO2)2·4H2O were measured along the three monoclinic axes in the same temperature intervals. χc and χb show sharp maxima at 16.8°, and are much larger in magnitude than χa. The possibility of this salt becoming weakly ferromagnetic below 16.8°K is considered, as is the unusual indirect-exchange coupling of Cu++ moments via formate groups.
On a Hole Theory of Fluids from Molecular Distributions
Authors: Baer Shalom
Published: January 2005

A previously developed method connecting the molecular distributions inside a cell with the molecular distribution in the surrounding fluid is applied to the case of a cell small enough to occupy at most one molecule. It is then possible to arrive at explicit expressions for the thermodynamic functions of the fluid. The method has the advantage over current hole theories in that it eliminates the problem of the dependence of the free volume on the occupation number of neighboring cells. General properties of the resulting formulas are discussed.
Atomic Screening Constants from SCF Functions
Authors: Clementi E. , Raimondi D. L.
Published: January 2005

The self-consistent-field function for atoms with 2 to 36 electrons are computed with a minimal basis set of Slater-type orbitals. The orbital exponent of the atomic orbitals are optimized as to ensure the energy minimum. The analysis of the optimized orbital exponents allows us to obtain simple and accurate rules for the 1s, 2s, 3s, 4s, 2p, 3p, 4p, and 3d electronic screening constants. These rules are compared with those proposed by Slater and reveal the need of accounting for the screening due to the outside electrons. The analysis of the screening constants (and orbital exponents) is extended to the excited states of the groundstate configuration and to the positive ions.