bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimized Minimum-Basis-Set SCF Calculations on BH3 and B2H6
Authors: Palke William E. , Lipscomb William N.
Published: January 2005

Wavefunctions and energies, optimized for BH3 and very nearly optimized for B2H6, have yielded a charge of −0.034 on H in BH3, and charges of −0.032 on H (terminal) and −0.001 on H (bridge) in B2H6 where the BB overlap population is 0.288.
Reaction Kinetics of Powdered Uranium and Deuteroammonia
Authors: Alire R. M. , McCrary J. H.
Published: January 2005

A rate law for the nitridation of pyrophoric uranium with deuteroammonia was established for the entire course of the reaction. The rate of reaction between powdered uranium and deuteroammonia was determined to be a linear function of the initial Brunauer, Emmett, and Teller (BET) surface area and the fraction of unreacted uranium. Sintering of powdered uranium to a stable surface area was found to be a prerequisite to reproducible experiments. The fractional composition of the products UN and U2N3–UN2 solid solution was found to be constant for the entire course of the reaction. An interpretation of the results was done in terms of a diffusion mechanism involving diffusion of uranium ions to the surface as the rate-determining step. The temperature coefficient in the range 265°—385°C was described by the Arrhenius law and the activation energy was measured to be 25±3 kcal/mole of uranium reacted.
Magnetic-Resonance Studies on Copper(II) Complex Ions in Solution. II. Oxygen−17 NMR and Copper(II) EPR in Aqueous Solutions of Cu(en)(H2O)42+ and Cu(en)2(H2O)22+
Authors: Lewis W. Burton , Alei Mohammed , Morgan L. O.
Published: January 2005

The temperature dependences of the 17O NMR and Cu(II) EPR spectra of solutions of the ethylenedi-amine complex ions Cu(en)(H2O)42+ and Cu(en)2(H2O)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17O NMR spectrum is broadened and shifted by Cu(en)(H2O)42+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H2O)22+ has no effect. The Cu(II) EPR spectra of both species have linewidth contributions from spin—rotational relaxation, from tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from 63Cu isotropic hyperfine and 14N isotropic extrahyperfine splitting. The results are discussed in terms of the antibonding molecular-orbital model for the B1g ground state of Cu(II) and compared with the previous study on Cu(H2O)62+.
Effect of Intra-atomic Correlation on London Dispersion Interactions: Use of Double-Perturbation Theory
Authors: Deal Walter J. , Kestner Neil R.
Published: January 2005

A simple double-perturbation-theory method is outlined for the calculation of the first-order effects of intra-atomic electron correlation on the dipole polarizability at imaginary frequencies, and on the London coefficient for interactions between two-electron systems. Both single-parameter Slater and Hartree—Fock orbitals are used as zero-order wavefunctions. The static polarizability of helium and the London coefficient for helium—helium interactions found with the Hartree—Fock wavefunction are (in atomic units) 1.3346 and 1.382, respectively; accepted values are 1.384 and 1.47. The extensions of this method to larger systems, higher multipole interactions, and more complicated zero-order wavefunctions are discussed.
Vibration Spectrum and Specific Heat of Lithium
Authors: Gupta Rajendra P.
Published: January 2005

The vibration spectrum and the specific heat of lithium have been calculated by using Sharma and Joshi's model of electron—lattice interaction. The calculated specific heats and the equivalent Debye temperatures are compared with experimental data. Except for temperatures below about 50°K, the theoretical Debye temperatures are in broad agreement with empirical data.
Theory of Fluids and the Fifth Virial Coefficient
Authors: Kim Sungwoon , Henderson Douglas , Oden Lynn
Published: January 2005

Expressions for the fifth coefficient are obtained for the Percus—Yevick (PY) theory, the convolution or hypernetted-chain (CHNC) theory, the self-consistent approximations of Rowlinson and Hurst (SCA), the PY2 theory and the CHNC2 theory. Numerical values for the fifth virial coefficient are computed using the 6:12 potential. Comparison with Barker's calculations of the exact fifth virial coefficient shows that the PY, CHNC, and SCA results are unsatisfactory. However, the PY2 and CHNC2 fifth virial coefficients are in good agreement with the exact results. The PY2 fifth compressibility virial coefficient is particularly accurate.
Ultrasonic-Absorption Measurements in Mixed Solvents: Water—Dioxane
Authors: Hammes Gordon G. , Knoche W.
Published: January 2005

Ultrasonic-absorption measurements in water—dioxane solutions have been carried out at 25° and 10° over the entire composition range in the frequency region 10 to 200 Mc/sec. The data can be described quantitatively in terms of two relaxation processes. A theory is presented for the absorption of ultrasonic energy in mixed solvents which can be approximated as ideal solutions. Deviations from ideality and excess absorption of ultrasonic energy are attributed to the formation of intermolecular complexes. If only a single relaxation process is observed, the composition at which the amplitude of the relaxational part of the absorption goes through a maximum and the concentration dependence of the relaxation time can be used to determine the stoichiometry of the aggregates, as well as associated kinetic and thermodynamic constants. For a system in which multiple relaxation processes occur, a normal-mode analysis must be used that yields a spectrum of relaxation times and normal thermodynamic variables. In the case of water—dioxane, all of the ultrasonic data are consistent with the formation of intermolecular hydrogen-bonded complexes according to the mechanism 2W+D⇌DW2, D+DW2⇌D2W2, where D represents dioxane and W water. Associated thermodynamic and kinetic constants have been evaluated. The standard volume and enthalpy changes for both reactions are quite small (about ±1 cc/mole and ±1 kcal/mole). The thermodynamic stability of the aggregates and their slow rate of breakdown relative to the rate of hydrogen bond breaking in pure water can be attributed to the formation of ``hydrophobic'' clusters of water around the hydrocarbon portion of dioxane.
Proton Nuclear Magnetic Resonance Solvent Shifts in Aqueous Solutions of Alkali Halides
Authors: Glick R. E. , Stewart W. E. , Tewari K. C.
Published: January 2005

Aqueous proton NMR chemical shifts induced by molal alkali halides have been re-examined and separated into two categories. The first, an upfield shift, has been quantitatively related to the change in hydrogen-bond fraction of the solvent as determined by others. The residue, a downfield shift, is anion dependent, cation independent, and directly proportional to effects induced in organic solutes present in the solvent in low concentration. For this latter effect, I−>Br−>Cl−>F− in inducing a downfield displacement; this order parallels certain Raman spectral changes reported for these solutions and is analogously attributed to charge-overlap effects.
Oxygen Loss in the Photolysis of CO2 at 1236 Å
Authors: Slanger Tom G.
Published: January 2005

The photolysis of CO2 has been carried out using a Kr resonance lamp, giving a light intensity of 1–2×1015 quanta/sec at 1236 Å. The O2/CO ratio in the products has been measured as a function of CO2 pressure, and it appears that the O2 loss reported by other investigators is due to a wall reaction. The active species in the system which causes the O2 loss is shown to be neither oxygen atoms nor ozone, and the contention that it is a CO3 molecule has been strengthened. The mechanism by which O2 is formed in CO2 photolysis at this wavelength seems to be by the reaction of two CO3 molecules, rather than by oxygen-atom recombination.
Mass-Spectrometric Study of the Vaporization of Cobalt Oxide
Authors: Grimley R. T. , Burns R. P. , Inghram Mark G.
Published: January 2005

A mass-spectrometric investigation of the vapor species in equilibrium with the Co–O system has shown the vapor phase to consist of Co, O2, and small amounts of CoO. The dissociation energy, D0°, of CoO(g) was found to be 86.4 kcal/mole and the heat of sublimation of CoO(s), ΔH0°sub, is 130.3 kcal/mole.
Magnetic Relaxation near a Second-Order Phase-Transition Point
Authors: Barry Jeremiah H.
Published: January 2005

A method combining statistical equilibrium theory and the thermodynamics of irreversible processes is used to study magnetic relaxation in the neighborhood of the Curie critical temperature Tc for an AB-type Ising model of ferromagnetism. Using a Bethe—Takagi statistical equilibrium expression, the magnetic Gibbs energy produced in the irreversible process is calculated, and the long-range and short-range order currents are treated as fluxes conjugate to their appropriate generalized forces in the sense of Onsager's theory of irreversible thermodynamics. Expressions (containing Onsager phenomenological coefficients) are found for the parallel isothermal magnetic dispersion and absorption factor near Tc, and the temperature and frequency dependencies of the expressions are analyzed.
Cell-Cluster Development for the Pair Distribution Function: Application to Rigid Disks at High Density
Authors: Larsen Russell D. , Salsburg Zevi W.
Published: January 2005

A technique, modeled after the cell-cluster theory for the partition function, is developed for estimating the molecular pair distribution function. This technique, while general, is thought to be particularly applicable to high-density crystalline systems. Attention is focused on Ω(ζ), the average number of pairs that have a distance between centers less than or equal to ζ. In the high-density crystalline limit, Ω(ζ) for a system of Nμ-dimensional rigid spheres has the following expansion, in the neighborhood of η=0, 2Ω/N=2μη+bη2+cη3+···,η=(ζ−σ)/(a−σ),where a is the distance between lattice sites and σ is the diameter of a sphere. The exact development for a one-dimensional system is given wherein the technique can be demonstrated to be convergent. For two-dimensional rigid disks all contributions from four-particle or fewer cell clusters to the constants b and c were calculated. The resulting series through fourth order is b=2−(192/217)−1.6069+0.3763+···=−0.1154+···,c=0−(216/217)+1.0986–0.6638+···=−0.5606+···.
Quantum Dynamics of Anharmonic Oscillators. II. Systems Having One and Two Degrees of Freedom
Authors: Baetzold Roger C. , Tahk Charlotte T. , Wilson David J.
Published: January 2005

Recent calculations on two simple anharmonic oscillators have indicated significant discrepancies between the evolution with time of the quantum and classical expectation values of the coordinate. These results cast some doubt on the propriety of classical-mechanical theories of unimolecular rates. The present paper extends the quantum calculations to two simple systems having two degrees of freedom and to the semi-infinite square-well oscillator.
Theory of the Hyperfine Structure of Molecules: Application to 3Π States of Diatomic Molecules Intermediate between Hund's Cases (a) and (b)
Authors: Freed Karl F.
Published: January 2005

In order to fully utilize the experimental accuracy of the high resolution afforded by radio-frequency spectroscopy, a fourth-order treatment of the energy is required. Especially, this fourth-order treatment is expected to be necessary in order to separate the quadrupolar interactions of light atoms in molecules from pseudoquadrupolar contributions to the energy due to magnetic hyperfine interactions which are off diagonal in the rotational state. The example of 3Π states intermediate between Hund's Cases (a) and (b), where J is still a good quantum number, is chosen to demonstrate the general techniques of such a fourth-order calculation. (Particular reference is made to the a 3Π state of isotopically substituted CO.) Van Vleck's method of reversed angular momentum is generalized to spherical tensor form in anticipation of future needs in the calculation of hyperfine structures of more complex systems. The spectroscopic parameters are explicitly written as matrix elements of the nonrelativistic wavefunctions in order that they be usable as checks on approximate molecular wavefunctions. Second-order Stark and Zeeman effects are also discussed.
Isotope Effects on Metastable Transitions: C3H8 and C3D8
Authors: Lifshitz Chava , Shapiro Moshe
Published: January 2005

Metastable transitions were studied in the mass spectra of propane and perdeuterated propane in a sector mass spectrometer. The relative abundances of the various metastable ions at 70 eV were determined. One parent-ion metastable transition was studied carefully: the methane loss at m/e=17.8 in C3H8 and at m/e=19.7 in C3D8. This transition shows a pronounced isotope effect on the yield. Appearance potentials were determined for the ions involved, by the RPD method and for the metastables themselves by conventional techniques. Reaction rate constants for the metastable transitions were determined by using a pulsed ion source. k=3.2×104 sec−1 for C3H8 and k=8.3×104 sec−1 for C3D8, at 13 eV. The results are discussed in terms of the quasiequilibrium theory of mass spectra.
Nonequilibrium Effects in Unimolecular Reaction Theory
Authors: Valance W. G. , Schlag E. W.
Published: January 2005

The rate constant for a unimolecular reaction is just the lowest eigenvalue of a relaxation matrix which describes all microscopic processes which may occur in the system undergoing reaction. A general solution to this eigenvalue problem has been given in a previous paper, including explicit corrections for non-steady-state behavior, but with one restriction, that the reactant energy distribution of states with insufficient energy to react (below the critical energy for reaction) is the equilibrium distribution. This is the so-called equilibrium assumption for reactant states. States above this critical energy barrier will always have less than their equilibrium population, approaching their equilibrium value in the high-pressure limit.

In this paper the eigenvalue problem is solved without this restriction, i.e., for the case that any or all reactant levels have nonequilibrium effects due to depletion of levels by reaction. This then completes a direct connection between the master equation and the theoretical unimolecular rate constant. The input for the problem is a table of microscopic transition probabilities for the master equation. The method suggested here produces a theoretically and computationally useful expression for the rate constant as a direct consequence of this input. The solution explicitly includes such effects as (a) inelastic scattering in the reactive gas, including many-shot effects, (b) nonequilibrium effects, and (c) non-steady-state effects. The expected relative importance of these effects is discussed.

As a guide in writing a master equation a generalized Lindemann mechanism was assumed operative since it affords some comparisons with RRKM theory. However, other mechanisms with strong time ordering between heat bath relaxation and reaction can be employed in this formulation. (When this ordering breaks down one can, in general, no longer discern first-order kinetics, and a different observable must be defined.)
Dilute-Solution Properties of Polystyrene in Θ-Solvent Media. II. An Analysis of Environmental Effects
Authors: Orofino T. A.
Published: January 2005

Intrinsic viscosity, light scattering, and associated dilute solution data for polystyrene in five Θ solvents are examined with the object of assessing the component contributions to unperturbed coil dimensions attributable to thermal and specific solvent effects. It is found that, if the latter environmental factors are treated as independently operative and if the temperature derivative of the second virial coefficient in the vicinity of Θ is taken as an index of the solvent effect, a basis for resolution of the perturbing contributions is provided. The same analysis applied to other published data for polystyrene:Θ-solvent pairs permits rational explanation of some heretofore anomolous variations of intrinsic viscosity [η]θ with temperature. Resolution of effects for a series of chemically related Θ solvents previously considered leads to a slightly larger value, +0.6×10−3, for the temperature coefficient of mean-square end-to-end distance d ln〈r02〉/dT. Equivalent chain parameters for the polymer in each of the five media are calculated and interpreted from the point of view of observed dilute-solution characteristics.
Electron Attachment and Detachment. II. Mixtures of O2 and CO2 and of O2 and H2O
Authors: Pack J. L. , Phelps A. V.
Published: January 2005

Electron-attachment coefficients in O2–CO2 and O2–H2O mixtures and electron-attachment—detachment equilibrium constants for O2–CO2 mixtures are obtained from drift-tube measurements similar to those used previously for O2. The three-body attachment coefficients involving O2 and CO2 are 3.1×10−30, 4.0×10−30, and 2.7×10−30 cm6/sec at 300°, 477°, and 525°K. The electron—negative-ion equilibrium constant data correspond to the formation of a CO4− with a large degree of freedom of internal motion and with an energy of dissociation into O2− and CO2 of 0.8 eV. The three-body attachment coefficient involving O2 and H2O is 1.4±0.2×10−29 cm6/sec at 300° and 395°K. In O2–H2O mixtures at temperatures of 500° and 555°K we observe the conversion of O2− to a more stable negative-ion form which shows no evidence of dissociation or detachment.
Collision-Induced Dissociation of D2+ Ions by Argon and Nitrogen
Authors: Champion R. L. , Doverspike L. D. , Bailey T. L.
Published: January 2005

The reactions D2++X→D++D+X, where X is Ar or N2, have been studied with an angular ion-scattering apparatus at ion laboratory energies in the range 5–120 eV. Kinetic-energy distributions as well as angular distributions of the product D+ ions have been determined. The experimental method consists of directing a well-collimated, mass-analyzed, and energy-selected ion beam into a scattering region and analyzing the product ions with a 127° electrostatic velocity selector and a radio-frequency mass filter. The product ion analysis and detection system rotates about the center of the scattering region. The results are discussed in terms of a simple two-step collision model, where the D2+ ion is first excited electronically to the antibonding 2Σu state, and then dissociates. The possibility of direct excitation of the D2+ ion into the vibrational continuum is also discussed. If either model is assumed for the reaction, the experimental results indicate that the most probable reaction channel for the collision-induced dissociation reaction is one in which primary D2+ ions with large vibrational energies give rise to D and D+ products which separate with small relative velocities. These results are consistent with some existing opinion that the collision-induced dissociation cross section increases rapidly as the vibrational excitation of the primary ion is increased.
Explicit Formulas for the Determination of the Exponents for Gaussian Atomic Orbitals
Authors: Lim T. K. , Whitehead M. A.
Published: January 2005

Explicit formulas of all the first- and second-order differentials of the energy of the atomic orbital with respect to the linear coefficients and/or the screening parameters of the ellipsoidal Gaussian functions, are given, so that all the exponents and linear coefficients of the atomic Gaussian orbital can be evaluated by the Newton—Raphson method. This method can be simplified to become the solution of several algebraic linear equations when αrxp≡αryp≡αrzp. The screening exponents are determined in such a way that the calculated Gaussian orbitals resemble Slater orbitals.
Transition-Moment Variation in the γ System of NO
Authors: Jeunehomme M.
Published: January 2005

The fluorescence lifetime of the v′=0 level of the A2Σ+ state of NO has been measured as 196.5±3.0 nsec. This figure is compared with the most recent literature results and conclusions are drawn for the variation of the transition moment on internuclear separation.
Critical Opalescence: The Rayleigh Linewidth
Authors: Cummins Herman Z. , Swinney H. L.
Published: January 2005

Debye's derivation of the Ornstein—Zernike modification of Einstein's theory of critical opalescence is reviewed. It is shown that Debye's free-energy function leads to a modification of the Landau theory for the width of the Rayleigh line which is equivalent to the results of Fixman, Botch, and Felderhof. This equivalence is utilized to predict the magnitude of the departure of Rayleigh linewidths from the Landau prediction by comparison with the results of angular-scattering intensity measurements. It is thus shown that in light-scattering experiments, pure fluids should obey the Landau theory quite accurately, whereas critical mixtures should show significant departures from the Landau prediction.
Kinetics of Growth of Multicomponent Chains
Authors: Lauritzen J. I. , DiMarzio E. A. , Passaglia E.
Published: January 2005

A theory is presented by which the rate of growth and composition (including all pair and higher distributions) of a chain growing in a multicomponent system may be calculated. Each position in the chain may be occupied by any of the components of the system. Only nearest-neighbor interactions are assumed and the rate constants αij for addition of Species j to a chain ending in Species i, and βij, for the removal of Species j from a chain ending in i, j are assumed known and independent of chain length, except for those referring to the first step of the chain, which are distinct. The full kinetic equations for the growth of such chains are formulated and a solution obtained for steady-state conditions. It is shown that when the matrix of αij/βij is indecomposable and primitive a solution of the equations which is independent of chain length always exists for sufficiently long chains and computational methods for obtaining this solution for a relatively large number of components (of the order of 10) are presented. In addition, the relationship of αij/βij to the energetics of the system is derived.
Chemistry of Positive Ions. VI. Positive-Ion Chemistry in Solid Methane
Authors: Davis Donald R. , Libby W. F. , Meinschein W. G.
Published: January 2005

The polymerization of solid methane at 77°K by γ rays was studied at two dose rates in the dose range 4 to 150 Mrad, corresponding to 0.04% to 1.4% conversion. The polymer contains an average of 20 carbon atoms per molecule and its empirical formula is C20H40, independent of the dose. The yield is 0.32 methane molecules converted to polymer per 100 eV absorbed and any induction dose must be less than 1 Mrad (0.01% conversion). We report a detailed characterization of the polymer based on physical and spectroscopic studies. Products up to heptane are identified. Preliminary studies of solid ethane and propane afforded polymer with lower yields and fewer numbers of monomer units than the methane polymer.

From an analysis of the dose and dose-rate dependence of the polymerization of solid methane, we conclude that only two types of mechanism are possible. The most useful mechanism is one in which a carbonium ion is transformed directly into a heavy hydrocarbon ion. This process would require about 6 eV of excitation energy. The other possible mechanism requires an efficient energy-transfer process leading to repetitive polymer-building and polymer-degrading reactions.
On the Analytical Mechanics of Chemical Reactions. Classical Mechanics of Linear Collisions
Authors: Marcus R. A.
Published: January 2005

The classical mechanics of chemically reactive linear collisions is investigated for vibrationally near-adiabatic reactions. A coordinate system which passes smoothly from one suited to the reactants to one suited to the products is used. The Hamilton—Jacobi equation is then solved in the adiabatic approximation by introduction of an ``adiabatic-separable'' method. Nonadiabatic corrections, which describe the probability of vibrational transitions, are also calculated. They involve the Fourier component of local internal centrifugal and vibration frequency-change terms. The reaction coordinate for the adiabatic system is shown to be that curve on which local vibrational and internal centrifugal forces balance pointwise. Applications can be made to the role of translational—vibrational energy interchange in reactions, reaction-cross-section theory, bobsled effect, and other topics. The results may be compared with electronic computer calculations as they become available.
Molecular Level-Crossing Spectroscopy
Authors: Zare Richard N.
Published: January 2005

Classical and quantum formulations are presented for the effects of level crossings on the angular distribution of molecular resonance fluorescence. It is shown that a study of the ``molecular Hanle effect,'' or its electric-field analog, may be used to determine the product of the radiative lifetime ρv′J′ with the magnetic moment μm, or the electric dipole moment μe, respectively, for the (v′, J′) excited state. The theory is developed for diatomic or polyatomic molecules characterized by symmetric-top wavefunctions. Order-of-magnitude estimates are performed, and the observation of zero-field molecular level crossings appears to be quite feasible.
Relativistic Interaction Energies between Atoms in Degenerate States
Authors: Meath William J.
Published: January 2005

The interaction of two like atoms in degenerate quantum states of the same energy and the interaction of two unlike atoms in arbitrary states is considered in the Breit—Pauli approximation. For these interactions the calculation of the relativistic long-range interaction energy, through O(α2), is discussed with specific allowance for degeneracy in the interacting atoms. Possible interactions where relativistic effects may be important are discussed. As a specific example the interaction of two spin-degenerate atoms (L=0, S≠0) is calculated through O(α2/R6) (where R is the interatomic separation). The nonrelativistic energy is given by the usual London dispersion energy which varies as 1/R6 while relativistic effects introduce an interaction energy which varies as α2/R3.
Vibronic Interactions in Vanadium Tetrachloride by Gas Electron Diffraction
Authors: Morino Yonezo , Uehara Hiromichi
Published: January 2005

The molecular structures of VCl4 and TiCl4 have been determined by gas electron diffraction. The mean square amplitude of the Cl–Cl distance in VCl4 is found to be abnormally large compared with that of TiCl4. This is attributed to the vibronic interactions in VCl4. The observed mean square amplitude has led to the evaluation of the first-order vibronic interaction constant |a′|. Other experimental results, such as bond lengths, the shrinkage effect, and vibrational spectra are discussed in relation to the theory of vibronic interactions.
Exact Quantum-Mechanical Calculation of a Collinear Collision of a Particle with a Harmonic Oscillator
Authors: Secrest Don , Johnson B. Robert
Published: January 2005

Exact quantum-mechanical calculations of the transition probabilities for the collinear collision of an atom with a diatomic molecule are performed. The diatomic molecule is treated as a harmonic oscillator. A range of interaction potentials from very hard to very soft are considered. It is found that for ``realistic'' interaction potentials the approximate calculations of Jackson and Mott are consistently high, even when the transition probabilities are low and good approximate results are expected. In some cases double and even triple quantum jumps are more important than single quantum jumps. Comparisons are made with exact classical calculations. A semiempirical formula is given for computing quantum-mechanical transition probabilities from classical calculations.
Vibrational Spectroscopic Study of Contact Ion Pairing between Zn++ and NO3− in Water
Authors: Hester Ronald E. , Plane Robert A.
Published: January 2005

Raman and infrared spectra of zinc nitrate have been measured in the presence of various amounts of water. In the presence of NH4NO3, a liquid solution was studied which at room temperature contained but five H2O molecules per zinc ion. Spectral features characteristic of complexed nitrate and water were compared with those from various aqueous solutions of zinc nitrate, solid zinc nitrate hexahydrate, anhydrous zinc nitrate, ammonium nitrate, and pure water. The evidence obtained, both from spectral lines characteristic of complexed nitrate ions and those of hydrated zinc ions, shows the existence of contact ion pairs in the concentrated solutions. The symmetry of the complexed nitrate ion is lowered to C2v by association with a Zn++ ion through a single O atom, as shown by Raman line polarization data. Absence of Zn–O Raman frequencies indicates essentially ionic binding.
Nondissociative Electron Capture in Complex Molecules and Negative-Ion Lifetimes
Authors: Compton R. N. , Christophorou L. G. , Hurst G. S. , Reinhardt P. W.
Published: January 2005

The formation and decay of parent negative ions have been studied with electron-swarm and electron-beam techniques. The rate of attachment at thermal energies under electron-swarm conditions for SF6 and C6H5NO2 was determined to be 1.24×109 and 2.1×107 sec−1·torr−1, respectively. Autoionization lifetimes for SF6−, C6H5NO2−, and (CH3CO)2− are reported to be 25, 40, and 12 μsec, respectively. The absolute rate of electron attachment in SF6 was found to be independent of the temperature (298°≤T≤418°K), and is thus consistent with an electron capture cross section for SF6 which varies inversely with the speed of the electron. The attachment rates and lifetimes were combined through the principle of detailed balance to calculate the ratio of density of states of the negative ion to that of the neutral plus electron. A simple theoretical treatment of long-lived negative ions is presented, and the possibility of estimating electron affinities from measurements of attachment cross sections and negative-ion lifetimes is pointed out.
Theoretical Studies of Transannular Interactions. IV. The Electronic States of the Paracyclophane Anion
Authors: Hillier Ian H. , Rice Stuart A.
Published: January 2005

The π-electronic transition energies of the anion of the D6h benzene dimer have been computed at different interring separations. The transannular overlap is calculated using a carbon SCF atomic orbital. The numerical results are compared to the absorption spectra of the anion of [2,2] paracyclophane. Good agreement with the observed transition energies is found.
Study of the NMR Results in Some Crystalline Hydrates
Authors: El Saffar Z. M.
Published: January 2005

The NMR results have been studied in 12 crystalline hydrates whose neutron-diffraction structures are available. The purpose of this study is to examine the validity of the Pake technique which may appear questionable in view of recent studies, and to try to propose a general method for calculating hydrogen positions using the NMR data and the positions of the heavy atoms in the unit cell. Comparison of the NMR results with the neutron-diffraction structures shows that the Pake technique, when applied without considering the influence of thermal motion on the resonance spectrum, gives fairly accurate results. The method proposed for calculating hydrogen positions is described and the assumptions made are discussed in detail. It is found that in the general case, the positions calculated by this method are in close agreement with the corresponding positions obtained by neutron diffraction.
Electronic States of 9,10-Diazaphenanthrene
Authors: Hochstrasser Robin M. , Marzzacco Charles
Published: January 2005

The S1←S0 absorption spectrum of the diazaphenanthrene crystal has been measured at 4.2°K in polarized light. The strength of the transition and the coincidence of the (0, 0) band at 23 100 cm−1 in absorption and emission clearly indicates that the lowest singlet state is 1B1(nπ*). The T1←S0 spectrum has also been measured. It consists of weak sharp bands with an origin at 18 571 cm−1, and a broad continuum. The bands displayed Zeeman splitting in a magnetic field. The T1←S0 spectrum is polarized parallel to the S1←S0 transition. A comparison of the vibrations of the lowest singlet and triplet states with those of the ground state indicates that the state is 3ππ*. The spatial symmetry is assigned 3B2 by analogy with phenanthrene. The 3nπ*←S0 transition was not identified and some possible reasons for this are discussed. Some discussion of the efficiencies of radiationless transitions in o-diazines is also presented.
Barrier to Internal Rotation in Ethane Using the Hellman—Feynman Theorem
Authors: Goodisman Jerry
Published: January 2005

The Hellman—Feynman theorem permits the calculation of the barrier to internal rotation in ethane and related molecules from the electron density corresponding to a single rotational configuration. Previous results, using an extended Hückel calculation and a modification of the Pitzer—Lipscomb wavefunction to approximate the electron density, gave too low a barrier. It appears from the present work that this is characteristic of the method. We have used a MO LCAO function containing a single parameter α which may be fixed in several different ways unrelated to the barrier calculation. We also consider the effect of variation of the exponential parameter ζH for 1s orbitals centered on the protons. The result is that all calculations (corresponding to different choices of α and ζH) give a barrier of the proper sign, but much lower than the experimental value. Not considered in the preceding work was the effect of polarization of the charge density. Part of this effect is estimated here, but seems to lower the barrier further. It appears that the present method is not capable of giving good results unless the polarization and other corrections are considered carefully. Comparisons are made with the Integral Hellman—Feynman theorem.
Effects of Electron Correlation in X-Ray and Electron Diffraction. IV. Approximate Treatment for Many-Electron Atoms
Authors: Gavin R. M. , Bartell L. S.
Published: January 2005

A simple scheme is proposed for predicting effects of electron correlation on intra-atomic electron—electron radial distribution functions and on intensities of x rays scattered by gas atoms. It makes use of a relationship connecting the Coulomb hole function for an electron pair with the corresponding correlation energy. The method is applied to the beryllium atom in its ground state. Results compare favorably with results calculated directly from correlated and Hartree—Fock wavefunctions.
Three-Dimensional Morse-Potential Calculation of Vibrational Energy Transfer: Application to Diatomic Molecules
Authors: Calvert James B. , Amme Robert C.
Published: January 2005

A three-dimensional semiclassical analysis of the vibrational-energy-transfer problem is performed for the Morse potential. The resulting equation is compared with the Schwartz—Slawsky—Herzfeld formulation, and with experimental data for a number of diatomic molecules. The particular case of N2 gives a different Morse repulsive index than that obtained from the second virial coefficient. In contrast to the SSH formulation, a single value of the index suffices over a large range of temperature for N2, O2, and CO. Improvement in the theory is found for cases in which ε/kT becomes large.
C2F4 Dissociation in Nitrogen Shocks
Authors: Modica A. P. , LaGraff J. E.
Published: January 2005

A kinetic study of the tetrafluoroethylene—difluorocarbene radical reaction was conducted in excess nitrogen behind incident shock waves over the temperature range from 1200° to 1600°K at total gas concentration around 1.25×10−5 moles/cc. The rate of formation of CF2 was observed spectrophotometrically and is reproduced by the rate law 12d[CF2]/dt=kf[N2][C2F4]−kr[N2][CF2][CF2]with kfN2=(4.08±0.72)1040T−6.36±0.55exp[(−74 900±3000)/RT] cc/mole·secand krN2=(2.05±0.47)1038T−6.36±0.55exp[(−1840±263)/RT] cc2/mole2·sec.Comparisons between the tetrafluoroethylene—difluorocarbene thermal-equilibrium constants in N2 and Ar shocks indicate that N2 is vibrationally unrelaxed during chemical relaxation. The temperature determined from the chemical equilibrium constant and the time to reach 0.98 chemical equilibrium after shock compression are used to calculate the N2 relaxation time. The results show that N2 vibrational relaxation in the 1:100 tetrafluoroethylene—nitrogen mixture is about 10 to 50 times faster than in pure nitrogen.
Dielectric Studies. XIII. Relaxation Processes of Some Haloethanes in Cyclohexane Solution
Authors: Crossley J. , Walker S.
Published: January 2005

The dielectric absorption of several haloethanes in cyclohexane solution has been determined at microwave frequencies and the static dielectric constant at 2 Mc/sec. The dielectric data have been used to yield mean relaxation times and apparent dipole moments. Pentachloro-,1,1,2,2-tetrabromo-, and 1,1,1,2-tetrachloroethane which have a high potential-energy barrier to internal rotation are characterized by a single relaxation time and a distribution coefficient of zero, whereas those with low-energy barriers of about 3 kcal/mole all show a definite distribution coefficient which suggests a contribution from an intramolecular relaxation process.
Infrared Spectrum of Perfluoromethyldifluoramine
Authors: Atalla Rajai H. , Craig Alan D.
Published: January 2005

The infrared spectrum of gaseous CF3NF2 has been recorded in the region of 250 to 2000 cm−1 and has been interpreted in terms of Cs symmetry. Thirteen bands have been identified with fundamental vibrations. A 14th fundamental has been derived from combination bands and from its first overtone.
Isotope Exchange Rates. III. The Homogeneous Four-Center Reaction H2+D2
Authors: Bauer S. H. , Ossa Eugenio
Published: January 2005

The homogeneous isotopic exchange reaction between hydrogen and deuterium in an excess of argon was studied in a 1-in.-diam single-pulse shock tube. Reaction times behind the reflected shock were close to 1 msec and the temperature range was 1060°—1420°K. The hydrogen and deuterium were present in concentrations from 1%—10%, at total reaction densities of 1.18 to 5.31×10−2 mole/liter. Conversions were kept low in order to minimize the reverse reaction. From the average rates the reaction was found to be second order (total) and empirically represented by Δ[HD]/Δt=kp[Ar]0.98[D2]0.66[H2]0.38,kp=1012.84T12exp(−42 260/RT),cm3mole·sec−1.

This power-rate law, with the surprising asymmetry in the H2—D2 dependence, can be rationalized by assuming that exchange occurs with high probability only during encounters between H2—D2 pairs, one of which is vibrationally excited to approximately 30 kcal/mole; that the probability for metathesis is low between molecules in their low-lying vibrational states even when their relative kinetic energy along the line of centers plus vibrational excitation exceeds the activation energy. Support for this mechanism is provided by an approximate calculation of the pre-exponential term of the exchange rate constant from vibrational relaxation data.
Heat Capacities of Argon in the Two—Dimensional Critical Region
Authors: Barnes Mary W. , Steele William A.
Published: January 2005

Heat capacities of argon adsorbed on a layer of xenon which had been preadsorbed on a graphitized carbon black were measured from 50°—80°K. The surface was characterized by determining adsorption isotherms and heats of adsorption. It was found that these data were equivalent to those obtained by other workers. A maximum in the heat capacity of one-half monolayer of adsorbed argon was observed at 72°K. Since the analysis of the isotherm data indicates that this system should have a two-dimensional critical point at a temperature close to the temperature of the maximum, it is concluded that the experimental curve corresponds to that for a two-dimensional film at its critical density. The data are compared with theoretical calculations based on the lattice gas model and it is found that the experimental curve is not as sharply peaked as the theoretical. Possible reasons for this discrepancy are discussed.
Energy Levels of Single-Crystal Erbium Oxide
Authors: Gruber John B. , Henderson J. R. , Muramoto M. , Rajnak K. , Conway John G.
Published: January 2005

The absorption spectra of large single crystals of Er2O3 observed at 10°, 80°, and 290°K were analyzed in the 2200–10 000-Å wavelength region. Over 600 transitions from all eight crystalline Stark levels of the ground 4I15/2 state to over 30 excited J manifolds of the Er3+ ion in C2 sites were assigned. In thick crystals, evidence of vibronic spectra of ions in C2 and S6 sites was observed for seven J manifolds. The observed spectrum is compared with a calculation which includes configuration-interaction effects on all expected ``free-ion'' energy levels of Er3+ between the ground state and 44 000 cm−1. The parameters E1=6844, E2=32.04, E3=635, ζ=2354, α=12.2, β=−590, and Y(22, 1)=−4180 cm−1 yield an rms deviation of 73 cm−1 between observed and calculated energy levels. The significance of these parameters in comparison with those for Er3+ in other crystals is discussed.
Electronic Absorption Spectrum and Dissociation Energy of the Allyl Radical
Authors: Currie C. L. , Ramsay D. A.
Published: January 2005

A system of diffuse bands in the region 3700–4100 Å has been observed during the flash photolysis of allyl bromide and eight other allyl compounds. The bands are found to be shifted when a sample of allyl-d5 bromide is used. The new band system with the (0–0) band at 4083 Å is assigned to the allyl radical [Complex chemical formula]. The diffuseness of the bands is attributed to predissociation of the radical in the excited state and gives an upper limit of 70.0 kcal/mole (≡3.04 eV) for the dissociation energy of the radical.
Spectra and Structure of Perfluorocyclobutane
Authors: Bauman Robert P. , Bulkin Bernard J.
Published: January 2005

Perfluorocyclobutane has been re&examined in an attempt to determine more definitely the question of whether or not the ring is planar. The infrared spectrum of the gas has been obtained under higher resolution and has been extended to 33 cm−1. Two new fundamentals have been found, at 283 and 198 cm−1, and the observed fundamentals have been classified as perpendicular or parallel on the basis of band contours. Infrared and Raman spectra of the liquid have been obtained to facilitate identification of coincidences. The NMR spectrum has been measured from 25° to −102°C. An interpretation of the experimental results is given and the fundamental vibrational frequencies are tentatively reassigned, based on the convincing evidence for the nonplanar D2d structure.
Vibrational—Rotational Study of the Electronic Ground State of the Hydrogen Molecule
Authors: Wolniewicz L.
Published: January 2005

The Schrödinger equation for nuclear motion in H2, HD, and D2 has been integrated numerically with accurate internuclear potential for numerous vibrational and rotational states. The theoretical dissociation energies are larger than the experimental results by 3.9, 4.7, and 3.6 cm−1 for H2, HD, and D2, respectively. It is argued that this discrepancy exceeds the possible computational inaccuracies and is not due to the adiabatic approximation. The radiative corrections are also discussed and it is shown that the correction to the dissociation energy is definitely smaller in absolute value than 0.4 cm−1.

The computed vibrational quanta are larger than the observed ones by about 1 cm−1 while the theoretical rotational quanta are in a very good agreement with experiment.

The vibrational—rotational wavefunctions are used for averaging of some electronic expectation values. The computed quantities agree with experiment within the experimental errors.
Dissociative Electron Capture by Benzene Derivatives
Authors: Christophorou L. G. , Compton R. N. , Hurst G. S. , Reinhardt P. W.
Published: January 2005

We have studied dissociative electron capture in a series of benzene derivatives using the combined swarm—beam method. The benzene derivatives C6H5Cl, o-C6H4Cl2, o-C6H4CH3Cl, C6H5Br, C6D5Br, and o-C6H4CH3Br, capture low-energy (including thermal) electrons dissociatively in a capture process which peaks at about 1 eV and yields only Cl− or Br− ions. The energies (in electron volts) at which the capture cross sections σc(ε) for the ∼1-eV processes peak and the values of σc(ε) (in cm2×1017) at peak energy for the above compounds are 0.86, 1.4; 0.36, 43; 1.1, 2.2; 0.84, 9.6; 0.8, 10.4; 0.95, 6 for C6H5Cl through o-C6H4CH3Br, respectively. The rates of capture at thermal electron energies are also given for each compound (but because of impurities are in question). For comparison with the benzene derivatives, C2H5Cl was also studied with the swarm—beam method. Beam data are also presented for dissociative electron capture by C6H5I, C6H5NO2, and o- and m-C6H4CH3NO2.
Elastic Properties of Some Polycrystalline Transition-Metal Monocarbides
Authors: Brown Harry L. , Armstrong Philip E. , Kempter Charles P.
Published: January 2005

The elastic properties of polycrystalline HfC0.967, NbC0.964, TaC0.994, and WC1.007 were determined at 23°C, and the data were corrected to theoretical density. In units of 1012 dyn/cm2, the Young's moduli are 4.619, 4.884, 5.377, and 6.237; the shear moduli, 1.953, 1.987, 2.168, and 2.633; and the bulk moduli, 2.426, 3.008, 3.448, and 3.295, respectively. The Poisson's ratios are 0.183, 0.229, 0.240, and 0.185, respectively. The specific electrical resistivities (micro-ohm centimeters at 20°C, corrected to theoretical density) are 24.6, 49.1, 25.6, and 17.8, respectively.
Electronic Spectrum of the Benzene Negative Ion
Authors: Gardner C. L.
Published: January 2005

The electronic absorption spectrum of the benzene negative ion has been measured. It is found that the intensity distribution of the bands in this spectrum is not in agreement with calculations based on the ASMO treatment of Pariser and Parr. In an effort to resolve this difficulty the calculations have been extended to include the effects of Jahn—Teller distortion and electron correlation in the ground state.
Diffusion of Triplet Excitons in Anthracene Crystals
Authors: Williams D. F. , Adolph J. , Schneider W. G.
Published: January 2005

The diffusion coefficient for triplet excitons in anthracene is determined to be (1.0–0.2)×10−2 cm2sec−1, and the diffusion length 70–150 μ, in a direction perpendicular to the ab plane. The effect of surface quenching of triplet excitons is investigated, and a simple model describing the dependence of triplet lifetime on crystal thickness is proposed.
Study of Some Solutions of the One-Electron—Two-Center Problem for Heteronuclear Cases
Authors: Wilson L. Y. , Gallup G. A.
Published: January 2005

The Schrödinger equation for two nuclei and one electron has been solved for the first eight σ states of the system HeH2+, He23+, LiH3+, and LiHe4+. The resulting solutions are described and some of their properties are discussed.