bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Capacity of Plutonium Monocarbide from 400° to 1300°K
Authors: Kruger O. L. , Savage H.
Published: January 2005

The heat content of PuC above 298°K was measured with an isothermal drop calorimeter. No discontinuities were observed in the heat-content-vs-temperature curve, which is described by the equation HT−H298=−5035+13.08T+5.718×10−4T2+3.232×105T−1.The equation for the heat capacity CP=13.08+11.44×10−4T−3.232×105T−2was derived from the calculated enthalpy equation. Values of the change in enthalpy, heat capacity, and entropy increments are given up to the melting point of PuC. Corrections of the enthalpy data for the self-heating of plutonium and the defect structure of PuC are described.
Secondary Isotope Effects in the Chemically Activated sec-Butyl-d and -d8 Systems and sec-Butyl-d1 and -d9 Systems
Authors: Simons J. W. , Rabinovitch B. S. , Kubin R. F.
Published: January 2005

The decomposition of chemically activated sec-butyl-d8 and -d9 radicals, produced by H- and D-atom addition to cis-butene-2-d8, has been studied at 195° and 300°K over a range of pressures. These measurements, as well as internal comparison experiments with cis-butene-2-d0, reveal a large normal secondary intermolecular kinetic-isotope ratio which varies with the pressure and temperature, and whose minimum value is a factor of 4 and whose maximum value averages around 7. The absolute magnitude of the ratio, and its temperature, pressure, and energy dependence are in satisfactory agreement with the theory of these chemical-activation systems; some aspects of this dependence are discussed. Evidence against a significant mechanistic isotope effect on the energetics is presented. Calculated isotope effects for all of the possible sec-butyl radical systems, to be formed by H- and D-atom addition to butene-d0 and -d8 isomers, are given.
Carrier Trapping in Photoconducting Anthracene
Authors: Weisz S. Z. , Jarnagin R. C. , Silver M. , Simhony M. , Balberg J.
Published: January 2005

The techniques of transient space charge limited photocurrent have been employed to observe hole trapping in monocrystalline anthracene. Two trapping processes are clearly evident. One corresponding to fast traping with time about 102μsec and a relatively slow process with time about 104μsec. The fast process is shown to be associated with traps whose density is reducible by simple crystal annealing. Evidence is presented which suggest these traps to be molecules in distorted positions in the crystal lattice.
Small-Angle X-Ray Scattering from Hydrolyzed Aluminum Nitrate Solutions
Authors: Rausch William V. , Bale Harold D.
Published: January 2005

The solutions, which contained from 1 to 2.5 hydroxide ions added per aluminum ion, were studied immediately after preparation and also in the final equilibrium condition. Aggregates present in the freshly prepared solutions probably have a characteristic platelet shape. Mention is made of the possible importance of these platelet-shaped aggregates to the structure of freshly precipitated aluminum hydroxide gel. Estimates of the size of the clusters present in the aged solutions were obtained in terms of the radius-of-gyration parameter. For solutions with OH/Al ion ratios between 1.5 and 2.25, the parameter had a constant value of 4.3 Å. This value is in good agreement with the calculated radius of gyration for the complex [Al13O4(OH)24(H2O)12]7+.
NMR Studies of Phase Transitions. II. NaCN
Authors: Coogan C. K. , Gutowsky H. S.
Published: January 2005

The 23Na nuclear magnetic resonance absorption has been observed in the cubic phase of polycrystalline NaCN between about 15° and 170°C, but could not be detected in the orthorhombic phase which forms below 10.5°C. The observed lineshape and its second moment S are compatible with a model in which S=Sd+Sq0+Sq(T) , where Sd and Sq0 are temperature-independent terms, Sd≅0.39 G2 resulting from magnetic dipolar interactions of the ``rigid lattice'' of Na+ ions and Sq0≅0.16 G2 from first-order nuclear quadrupole interactions with field gradients produced by lattice defects. Sq(T) is a quadrupole broadening term which decreases exponentially from ∼13 G2 at 10.5°C to near zero at 170°C.

The electric-field gradients (EGF) involved in Sq(T) are attributed to the electric dipoles of the CN— ions, and the temperature dependence, to the averaging out of the gradients by thermally activated reorietations of the CN— ions. The reorientations are deemed responsible for the existence of a cubic phase. They are treated as a random-walk problem yielding algebraic expressions by means of which an activation energy of 6 kcal/mole is obtained from the experimental Sq(T), and 5×108 cps at 10°C and 1010 cps at 150°C are estimated for νi, the CN— reorientational jump frequency. A discussion is given of the relation between νi and the nucleation of the cubic to orthorhombic phase transition.
Molecular Structure of Dicyclopentadienylberyllium (C5H5) 2Be
Authors: Almenningen A. , Bastiansen O. , Haaland A.
Published: January 2005

The molecular structure of gaseous (C5H5) 2Be has been determined from electron-scattering data. The molecule consists of two planar, symmetrical C5H5 rings. C1–C2 = 1.424±0.002 Å and C1–H1 = 1.070±0.005 Å. The rings are parallel and staggered with a vertical ring—ring distance h = 3.37±0.03 Å. The CH skeleton thus has point group symmetry D5d. The beryllium atom may occupy two alternative positions on the fivefold rotation axis h = 1.485±0.005 Å from one ring and h2 = 1.980±0.010 Å from the other. The complete molecule thus has point group symmetry C5v.

It appears then that the potential energy curve of the beryllium atom has two minima. This is readily understood from an ionic binding model. The discrepancy between the values found for h and h1+h2 is believed to be due to intramolecular motion.
Combination Reactions of Imino Radicals in the Flash Photolysis of Isocyanic Acid
Authors: Back R. A.
Published: January 2005

The flash photolysis of HNCO vapor yielded CO, N2, and H2 in a ratio of 1/0.42/0.27, independent of HNCO pressure (7–40 mm) and flash energy (17–1150 J). From the mass balance, production of ammonia was implied; the stoichiometry was described approximately by 12 HNCO=12CO+5N2+3H2+2NH3. It was concluded that the reaction 2NH→N2H2 was much more important than 2NH→N2+H2, with the observed stoichiometry largely determined by the subsequent decomposition of N2H2.

The addition of ethylene or propane reduced the yield of CO (by competitive absorption of light), and reduced the value of N2/CO, apparently for the most part by interfering in the decomposition of N2H2 rather than by reacting with NH radicals. The effect on the hydrogen yield was complicated by the production of hydrogen by photolysis of ethylene and propane; in the HNCO—propane system, however, extra hydrogen definitely was produced, probably by the reaction of NH with propane.
Charge-Transfer Self-Complex Formed in Potassium Squarate Monohydrate
Authors: Macintyre Walter M. , Werkema Marilyn S.
Published: January 2005

The x-ray crystal structure analysis of the monohydrate of the potassium salt of squaric acid is reported. Squaric acid is the name given to 3,4-diketocyclobutenediol. The main feature of the structure lies in the packing of the squarate anions. These are arranged in stacks with the planes of the anions almost parallel. Two of the carbon atoms, on neighboring anions, approach one another very closely, their separation being 3.237 Å (σ=0.012 Å). It is concluded that the structure represents a charge-transfer self-complex. The anion was found to have the expected D4h symmetry with mean CO bond length of 1.259 Å (σ=0.007 Å) and mean CC bond length of 1.457 Å (σ=0.008 Å).
Maximum Overlap Orbital Treatment of 13C–H Substituent Effects in the Halomethanes
Authors: Goldstein J. H. , Hobgood R. T.
Published: January 2005

Substituent effects on 13C–H coupling constants in the halomethanes have been calculated by the method of maximum overlap orbitals. The simplest choice of halogen orbitals (npσ) produces good agreement with observed values. Introduction of s character (based upon microwave data) and adjustment of ionic content of the C—halogen bond to give agreement with experiment leads to an over-all structure of these bonds that is in quite good agreement with the conclusions of Townes and Dailey.
Vibrational Analysis of Substituted and Perturbed Molecules. II. Planar XY3 Molecules; Application to BCl3–HBCl2–DBCl2
Authors: Bass C. D. , Lynds L. , Wolfram T. , DeWames R. E.
Published: January 2005

The vibrational frequencies of isotopically substituted planar XY3 molecules have been obtained using the Green's function and partitioning techniques. Taking HBCl2 as an ``isotopic'' species of BCl3, we have calculated its spectrum, without invoking a force constant model. The excellent agreement between predicted and observed spectra indicates that even the force constant changes may be neglected as a first approximation. Using the information provided by the calculations, we have observed and identified five of the six HBCl2 fundamentals: ν1 = 762 and 740 cm—1, 10B— and 11B–Cl symmetric stretches; ν2 = 2617 cm—1, B–H stretch (no splitting); ν4 = 1100 and 1089 cm—1, 10B— and 11B–Cl asymmetric stretch; ν5 = 892 cm—1 (11B only), in-plane H deformation; and ν6 = 795 and 784 cm—1, out-of-plane deformation. Frequencies observed and identified for the deuterated compound are: ν2 = 1969 cm—1, B—D stretch; and ν6 = 661 and 645 cm—1, 10B–11B splitting. The calculations also indicate that the other frequencies we have not observed are hidden by BCl3 bands, and that ν3, a B–Cl bending mode is, at ≈285–290 cm—1, outside the range of our instrument.
Electronic Structure of N2, CO, and BF
Authors: Nesbet R. K.
Published: January 2005

Approximate Hartree—Fock calculations are reported for the 1Σ+ ground states of the isoelectronic 14-electron molecules N2, CO, and BF. In each case calculations have been carried out at five internuclear distances, chosen as the roots of an appropriately scaled Chebyshev polynomial, in order to facilitate interpolation. Electronic kinetic and potential energies, mean values of 1/r about each nucleus, and mean values of z, 3z2—r2, and r2 are obtained at each internuclear distance. The production runs used basis sets consisting of two exponential functions for each occupied atomic orbital plus dσ and dπ orbitals on each atom, combined to form molecular orbitals by the matrix Hartree—Fock (SCF—LCAO) method. It was found that 4fσ and 4fπ orbitals, with optimized exponents, contribute 0.3 eV to the dissociation energy of N2, but these orbitals were not included in the production runs. The effect on CO and BF of 4f orbitals is expected to be somewhat smaller. Various spectroscopic quantities (re, ωe, xeωe, Be) and electric dipole and quadrupole moments are computed and are in general qualitative agreement with experimental values. The polarity of the dipole moment of CO, while not definitely determined by present calculations, is indicated to be C+O—. The experimental determination of this polarity is discussed critically, and it is concluded that a definitive determination of the sign is not possible from microwave data, which had previously been interpreted to imply the polarity C—O+. Thus an independent redetermination of this sign is required. Dissociation energies are discussed in connection with an empirical estimate of the net correlation energy contribution to molecular binding.
Direct Determination of Natural Orbitals and Natural Expansion Coefficients of Many-Electron Wavefunctions. I. Natural Orbitals in the Geminal Product Approximation
Authors: Kutzelnigg Werner
Published: January 2005

The approximation of a many-particle wavefunction as an antisymmetrized product of strongly orthogonal geminals (APSG) (geminal means two-electron function) is analyzed in terms of its natural expansion. APSG wavefunctions have very simple and interesting properties. The ``generating spin geminals'' (GSG) are automatically natural spin geminals (NSG) of the system with Occupation Number 1 (in the Löwdin normalization); 1 is the upper bound for the eigenvalues of the two-particle density matrix for wavefunctions of this type. The natural spin orbitals (NSO) of the GSG are automatically NSO of the total wavefunction and of all the NSG.

A generalized ``paired orbital function'' is defined in terms of its natural expansion. It contains the APSG type as well as the Bardeen—Cooper—Schrieffer (BCS) functions as special cases.

Integrodifferential equations determining the NSO and their expansion coefficients for an APSG function are derived for the special case of a singlet state by minimizing the total electronic energy. An iterative resolution procedure is proposed. When the state under consideration can be regarded as a closed-shell state the first iteration step may already be a good approximation. In this case the equations become very simple and can be given a straightforward physical interpretation.

Finally possible refinements of the theory are discussed.
Viscosity of Neon—Helium and Neon—Argon Mixtures at 20° and 30°C
Authors: Kestin J. , Nagashima A.
Published: January 2005

The paper gives the results of the absolute determination of the viscosity of two binary systems of mixtures: neon—helium and neon—argon, together with those of the viscosity of the three pure components. The measurements were performed with the aid of our high-precision oscillating-disk viscometer at 20° and 30°C; they covered a range of pressures up to 35 atm (densities from 0 to 0.09 g/cm3).

The density effect can be expressed, essentially, in the form of a temperature-independent, linear correction in the case of the Ne–He mixtures, and in the form of a quadratic correction in the case of Ne–Ar mixtures, both applied to the excess viscosity Δμ = μ—μ0 in which μ0 is a function of temperature only.
Melting Curves of Pressure-Transmitting Fluids
Authors: Reeves Larry E. , Scott Gene J. , Babb Stanley E.
Published: January 2005

The melting curves of nine fluids which have been or could be used for pressure transmission have been measured to 10 000 bars. New forms are reported for isobutane and propylene. The substances showing the lowest melting temperatures at 10 000 bars are propane at —105° and propylene at —130.5°C. Most of the substances studied exhibit strong tendencies toward subcooling.
Microwave Spectrum of Vinyl Formate
Authors: Rao V. M. , Curl R. F.
Published: January 2005

The microwave spectrum of vinyl formate has been observed in the region 10–25 Gc/sec. Both ``a'' and ``b''-type transitions have been assigned for the ground and one of the excited vibrational states. The rotational constants obtained are consistent with a planar structure with the carboxyl oxygen cis with respect to vinyl group and the terminal vinyl carbon trans with respect to the acid group. The components of the dipole moment | μa | and | μb | were determined for the ground and excited vibrational state. The dipole moment μ is 1.48 D and | μa | and | μb | indicate it is probably oriented along the line between the oxygens.
Chemiluminescence and Radical Reactions in Diffusion Flames of Alkali Metals with Organic Halides
Authors: Miller William J. , Palmer Howard B.
Published: January 2005

Chemiluminescent reactions in diffusion flames of alkali metals with haloforms and carbon tetrahalides appear to provide examples of reactions in which essentially all of the exothermicity appears as vibration in a newly formed bond. A self-consistent account of the intensity distributions in the flame spectra requires that, in CX4—K flames, both excited and unexcited carbon atoms participate in the reactions, C+CX→C2*+X, and that the X atoms be produced both in the ground and first excited states. Excited C atoms appear not to be produced in CHX3—K flames in appreciable concentrations. The excited C2 intensity distributions in emission are compatible with the bond dissociation energies, C–Cl=77 kcal, C–Br=66 kcal, and C–I=50 kcal, with uncertainties of about 4 kcal in each.
Quenching and Temperature Dependence of Fluorescence in Rare-Earth Chelates
Authors: Bhaumik M. L.
Published: January 2005

Temperature dependence of the fluorescence quantum yield and decay time of several rare-earth chelates have been studied in an attempt to understand the quenching mechanisms in these compounds. It is observed that the quenching in either the ligand or the ion is reduced by lowering the amplitude of molecular vibrations. This indicates that a major part of the fluorescence quenching in rare-earth chelates occurs due to coupling of the electronic states to the environment through molecular vibrations. The results of the present measurement also indicate that the shielded 4f orbitals of the rare-earth atoms become more impervious to quenching when they are incorporated into a chelate. Importance of these results in connection with liquid laser research is discussed.
Vaporization Processes Involving Sulfur
Authors: Berkowitz J. , Chupka W. A.
Published: January 2005

Free evaporation of rhombic sulfur is shown to give rise solely to S8 vapor molecules, whereas the sublimation of an allotropic form (Engel's sulfur) produces only S6 vapor molecules. The vapor composition characteristic of equilibrium can be produced by mixing any allotropic form of sulfur with commercial Al2O3, which evidently catalyzes the transformation among sulfur species. The evaporation coefficients of S6 and S7 molecules from a rhombic sulfur surface have been measured. The behavior of other allotropes (Sμ, Sπ) is described as observed by mass spectrometry. Mass spectra of S6 and S8 molecules have been determined directly as a function of temperature and that of S7 deduced from a vapor mixture of S6, S7, and S8. Ionization efficiency curves and appearance potentials of the major ionic species are reported. Paramagnetic resonance measurements have been used to help elucidate the mechanism of catalysis.
Absorption Coefficients of Oxygen in the 1060–580-Å Wavelength Region
Authors: Huffman R. E. , Larrabee J. C. , Tanaka Y.
Published: January 2005

Absorption coefficients of oxygen have been measured in the 1060–580-Å wavelength region using a continuum background at a bandwidth of 0.5 Å. The background light source is a repetitive discharge through helium which produces the Hopfield continuum. Absorption bands and underlying dissociation and ionization continua are observed throughout this wavelength region. The continuum rises linearly from ≲20 cm—1 at the first ionization threshold (1026.7 Å), to about 300 cm—1 at 840 Å where the continuum begins to rise more sharply. Toward shorter wavelengths, there are three maxima in the continuum at about 800, 720, and 610 Å with approximate k values of 850, 850, and 1000 cm—1, respectively. The absorption bands appear diffuse, probably due to pre-ionization, and maximum k values of up to 1700 cm—1 are found. Dissociation and ionization processes responsible for the continua are discussed, and comparison is made with previous absorption coefficient measurements.
Gaseous Ion Recombination Rates
Authors: Mahan Bruce H. , Person James C.
Published: January 2005

The rate at which gaseous ions neutralize each other has been measured in a variety of gases over a relatively wide pressure range. The results indicate that neutralization occurs by parallel bimolecular and termolecular processes. The rate of the termolecular process is sensitive to the nature of the inert gas in which recombination occurs. Two mechanisms for the termolecular process are discussed.
Refinement of Peterson and Levy's Neutron Diffraction Data on KHF2
Authors: Ibers James A.
Published: January 2005

The neutron-diffraction data obtained by Peterson and Levy from a single crystal of KHF2 have been refined in an attempt to settle the question of the geometry of the bifluoride ion in KHF2. It turns out to be impossible from the neutron diffraction data alone to distinguish a linear symmetric F–H–F ion from a linear one in which the hydrogen occupies two equally probable positions on either side of the center, even when these positions are 0.16 Å from the center. However, the agreement between the differences in mean-square amplitudes of vibration of hydrogen and fluorine along the bond as obtained from an analysis of the diffraction data and as calculated from spectroscopic data lends support to a linear symmetric model of the bifluoride ion in KHF2. The F–H–F distance is 2.277±0.006 Å.
Simple Model for Some Dense Magnetic Exciton Systems
Authors: Chesnut D. B.
Published: January 2005

The (triplet-state) TCNQ ion radical salts and also Würster's blue perchlorate exhibit deviations from the normal behavior of typical molecular solids. These systems are believed to contain triplet excitons which are restricted to essentially a unidirectional propagation. A simple phenomenological model is presented which attempts to describe the gross aspects of the observed anomalous behavior in terms of the relatively high exciton concentrations indicated. The model derives its interesting features from a quadratic dependence of the free energy on the excitation density (exciton concentration); the presence of such a term is made plausible by considerations of exciton—exciton and exciton—lattice interactions. The model accounts for the occurrence of phase transitions similar to those observed in (φ3PCH3)+(TCNQ)2— and Würster's blue perchlorate and indicates that under appropriate conditions one may achieve unusual magnetic phenomena in molecular solids.
Raman Spectrophotometric Study of Complex Formation in Aqueous Solutions of Calcium Nitrate
Authors: Hester Ronald E. , Plane Robert A.
Published: January 2005

The Raman spectra of nitrate solutions of Ag I, Cu II, Zn II, Hg II, Ca II, Al III, In III, Ce III, and Th IV were measured. In every case there was evidence of specific association between the cation and nitrate with lowering of the nitrate symmetry from D3h to C28. The system Ca II–NO3— was studied in detail by making quantitative intensity measurements in solutions of various concentrations of Ca(NO3)2, some with added NH4NO3 and some with added Ca(ClO4)2. From these measurements it was found that the only associated species of importance was CaNO3+ for which the association constant in the ionic strength range of 10 to 40 was 0.12 to 0.17. This value was independent of temperature in the range 26° to 94°C.
Stability of the Ammonium Radical (NH4)
Authors: Bishop D. M.
Published: January 2005

The neutral ammonium molecule (NH4) is described by a wavefunction composed of Slater orbitals centered on the nucleus of the nitrogen atom. The molecule is predicted to be stable by approximately 0.007 a.u. in both a single- and a five-term treatment, and the ionization potential is found to be 3.94 eV.
Sedimentation in Chemically Reacting Systems. III. Slow and Fast Reaction Cases for Dimerization
Authors: Belford Geneva G. , Belford R. Linn
Published: January 2005

An approximate analytic formula, which is valid for small rate constants, is given for a simple model of sedimentation with concurrent dimerization. A graphical method for obtaining solutions for arbitrary initial concentration distributions in the fast-reaction-limit case is then described, and it is pointed out that large errors may arise from the oversimplified assumption of a step-function initial concentration distribution.
Quantum Yield of the Ferrioxalate Actinometer
Authors: Lee John , Seliger H. H.
Published: January 2005

The quantum yield of the potassium ferrioxalate actinometer at 365/6 mμ has been measured to be 1.26±0.03 relative to a calibrated thermopile. Comparisons of thermopiles were carried out at the Eppley Laboratory and at the National Bureau of Standards to ensure the flatness of thermopile response. Irradiations were made over the range 1012 to 3×1014 total absorbed photons.
Effects of Anharmonicity on Vibrational Energy Transfer
Authors: Mies Frederick H.
Published: January 2005

The diagonal matrix elements of the interaction potential which enter into the quantum theory of vibrational energy transfer generally have been assumed to be identical. Apparently the assumption is based on mathematic convenience rather than on any physical model. If Morse potentials are used to describe the intramolecular forces the elements are approximately but not identically equal. The transition probability is found to decrease markedly when the ratio of the diagonal elements of the initial and final oscillator states is allowed to deviate even slightly from one. Morse potentials were chosen to reproduce the observed anharmonicities of a variety of diatomic molecules and an anharmonic correction factor to the transition probability was calculated. It is found that the generally used calculated transition probabilities should be reduced by a factor of 10—1 to 10—2.
Absorption and Photoionization Coefficients of Acetylene, Propyne, and 1-Butyne
Authors: Nakayama Toshio , Watanabe K.
Published: January 2005

Absorption coefficients of acetylene, propyne and 1-butyne were measured by a photoelectric technique in the region 1050–2000 Å. Two or three Rydberg series accompanied by vibrational bands were observed in the spectrum of these molecules. The photoionization curves and the Rydberg series yielded the same ionization potential: 11.41, 10.36, and 10.18 eV for acetylene, propyne and 1-butyne, respectively.
Franck—Condon Factors and Electronic Oscillator Strengths for Nitric Oxide Ultraviolet Band Systems
Authors: Ory Horace A.
Published: January 2005

Franck—Condon factors have been calculated for the nitric oxide delta and epsilon band systems, based on Morse oscillator wavefunctions. Electronic oscillator strengths have been derived from data available in the literature for the beta, gamma, delta, and epsilon band systems; these are 0.00270, 0.00240, 0.0170, and 0.0137, respectively, exclusive of variations due to perturbations. The results have been discussed in terms of these perturbations, which cause enhancement of some beta bands and diminishment of some delta and epsilon bands. The results are in resonably good agreement with those obtained by other investigators for the beta and gamma bands. Aside from the effect of perturbations, no significant dependence of the electronic transition moments on internuclear separation is apparent.
Phonon-Coupled Interactions between Paramagnetic Excitons
Authors: McConnell Harden M. , Soos Zoltán
Published: January 2005

It is shown that exciton—phonon coupling in solid free radicals leads to a spin-independent repulsion between paramagnetic excitons. This repulsion may make a significant contribution to the activation energy for spin-exchange line broadening that is observed in the paramagnetic resonance of a number of solid free radicals.
Many—Body Aspects of Intermolecular Forces
Authors: Linder Bruno , Hoernschemeyer Donald
Published: January 2005

The many-body aspects of intermolecular forces are examined for the model based on a fluctuating reaction field. This is accomplished by expanding the reaction field in a series involving optical and translational parameters, and an expression is obtained for the cohesive free energy in terms of frequency-dependent polarizabilities and dipole-coupling tensors. When applied to a system of fixed translational parameters a series expansion is obtained for the configurational total potential energy, the leading term of which arises from pair interactions, the next higher term from triple interactions, etc. It is shown that the pair and triple potentials reduce to forms identical with the ones obtained by ordinary quantum-mechanical second- and third-order perturbation theory. The significance of the results is discussed.
Mass Spectrometric Measurement of Diffusion Coefficients
Authors: Mueller C. R. , Cahill R. W.
Published: January 2005

Binary diffusion coefficients of CH4–CO, CH4–N2, CH4–CF4, CH2CH2–N2, CH3CH3–CH2CH2, CH3CH3–CHCH, CH2CH2–CH3CH3 have been measured at 298.2°, 353.6°, and 382.6°K. By means of isotopic substitution, the self-diffusion coefficients of CH4, CH3CH3, CH2CH2, and CHCH have been determined at the same temperatures. In general, the depth of the potential minimum, ε, was less, when calculated from diffusion measurements, than when calculated from virial coefficients or viscosity measurements.
Quantum Calculation of the Sensitivity of Diffusion, Viscosity, and Scattering Experiments to the Intermolecular Potential
Authors: Mueller C. R. , Brackett J. W.
Published: January 2005

Correlations between the form of the intermolecular potential as a function of distance and the quantum mechanical phase shifts as functions of the angular momentum quantum number have served as the basis for estimates of the sensitivity of viscosity, diffusion, and low-energy scattering experiments to the attractive and repulsive portions of the intermolecular potential. The sensitivities of the experimental techniques are approximately as follows: repulsive portion of the potential, diffusion>viscosity>scattering; to the attractive region of the potential, scattering>viscosity=diffusion.

Quantum diffusion and viscosity cross sections for the Lennard-Jones potential have been calculated as functions of the reduced kinetic energy, K=μv2/2ε, and for decreasing values of the quantum parameter λ=h/σ(mε)½. The cross sections for systems with λ corresponding to T2, Ne, and CH4 are equal to the classical cross sections for K>1.2. At lower K's the deviations from classical behavior become larger as λ increases.
Model for the Lattice Dynamics of Metals. II. Application to Face-Centered Cubic Metal Copper
Authors: Sharma P. K. , Joshi S. K.
Published: January 2005

A model for the lattice dynamics of metals propounded by us earlier is applied to copper, a representative of face-centered cubic metals. The force constants appearing in the secular equation for the lattice frequencies are estimated from the knowledge of the elastic constants. The phonon dispersion curves for the three symmetry directions [100], [110], and [111] are presented and are found to be in fair agreement with the neutron spectroscopic measurements. The frequency distribution function has been calculated. The specific heat computed from the frequency distribution function is found to be in good agreement with the experimental measurements.
Metastable State of the Doubly Charged Carbon Dioxide Ion
Authors: Newton Amos S. , Sciamanna A. F.
Published: January 2005

A metastable state in CO2++ dissociating into CO++O+ with a half-life of 2.3±0.2 μsec has been observed. The corresponding metastable peaks are observed at (M1/q1)*=35.6 and (M2/q2)*=11.6, respectively. The widening of these peaks with accelerating voltage shows the repulsion energy to be 2.7 eV and the corresponding charge separation at fragmentation to be 5.3 Å. The appearance potential of CO2++ was found to be 38.0±0.2 eV, and this value is discussed in terms of the various repulsion energies and energy balances. The data is consistent with the hypothesis of an immediate fragmentation into CO+(2Σ) and O+ and the metastable fragmentation into CO+(2IIi) and O+. The fragmentation of CO2++ enriched in O18 has also been reinvestigated. It is shown that the unsymmetrical doubly charged molecule ion (CO16O18++) has a lower yield than the corresponding symmetrical molecule ions containing O16 and O18, respectively.
Nuclear Magnetic Resonance and Molecular Field Approximation in KCoF3
Authors: Tsang Tung
Published: January 2005

A molecular field calculation and a nuclear magnetic resonance study of F19 in paramagnetic KCoF3 are reported. The isotropic hyperfine interaction indicates presence of 0.57% unpaired 2s spins in F— orbitals from each Co++ neighbor; this result is consistent with the data of Hall et al. and the data of Shulman et al.. The calculations are shown to be in good agreement with the F19 resonance data and also the susceptibility data of Hirakawa and co-workers.
Crystal Spectrum and Magnetism of Tetrakis-Thiourea-Nickel Chloride
Authors: Hare C. R. , Ballhausen C. J.
Published: January 2005

The polarized crystal spectrum of tetrakis-thoiurea-nickel chloride has been determined. The molecular symmetry is C4v; however, the results indicate that the absorptions arise from a field of lower symmetry, since in C4v symmetry the observed ``parallel'' absorptions would be orbitally forbidden. The intensity of the parallel absorptions are explained by a vibronic mechanism in which vibrations of the proper symmetry give allowed character to forbidden transitions under the site symmetry C4 Factor group interaction may also, at least in part, be responsible for the parallel intensity. The agreement between the assigned transitions and theory for nickel complexes is good assuming a reduction of the Slater—Condon parameters. The magnetic susceptibility of the complex follows a Curie—Weiss law χ=1.14/(T+6°) between 77° and 370°K.
Polarized Crystal Spectra of Ni(NH3)4(NCS)2 and Ni(NH3)4(NO2)2
Authors: Hare C. R. , Ballhausen C. J.
Published: January 2005

The polarized crystal spectra of isostructural trans-Ni(NH3)4(NCS)2 and trans-Ni(NH3)4(NO2)2 have been determined at room temperature. In accordance with the spectrochemical series, the tetragonal splitting of the octahedral levels is virtually zero for the isothiocyanate and large for the nitrite. A vibronic intensity mechanism is invoked since the intensity is distributed in the polarization directions in the centro-symmetric crystals.
Electronic Absorption Spectrum of Ni II in Cubic Perovskite Fluorides. I
Authors: Ferguson J. , Guggenheim H. J. , Wood D. L.
Published: January 2005

The fine structure of the spectrum of Ni2+ in KNiF3 and KMgF3:Ni has been analyzed in terms of the spin—orbit splitting and vibrational intervals using a four-parameter crystal-field approach. The parameters obtained from the analysis differ from the free-ion values by relatively small amounts, but the differences are not interpretable physically because configuration interaction has been neglected. We find that Dq=698 cm—1, λ=—(305–320) cm—1, F2=1520 cm—1, F4=114 cm—1 (F4/F2=0.675). For the free ion we find that λ=—334 cm—1, F2=1622 cm—1, and F4=116 cm—1 by fitting the published values for the 3d8 energy levels in our analysis with Dq=0.

We find that the effects of exchange interaction on the excited state energy levels is small, and that no Jahn—Teller splitting is observed or expected for this crystal. An explanation is offered for temperature changes in the 3A2g→1Eg transition involving a breakdown of Born—Oppenheimer separability.
Thermodynamic Properties of Gaseous Yttrium Monoxide. Correlation of Bonding in Group III Transition-Metal Monoxides
Authors: Ackermann R. J. , Rauh E. G. , Thorn R. J.
Published: January 2005

The vapor from solid yttrium sesquioxide contained in a Knudsen cell made of tungsten has been investigated by measuring the absolute effusion rate and by studying the effusate in a mass spectrometer. The latter demonstrates that the gaseous species are yttrium monoxide, oxygen, and a small amount of yttrium. Measurements of the appearance potentials for the ions enable one to conclude that the ratio of monoxide-to-metal is at least 65 and that above 15 eV significant fragmentation of YO by the ionizing electrons to yield Y+ occurs. From the absolute effusion rates one derives the free energy of formation, ΔFf∘(YO,g)=−21 800–10.96 T,and the dissociation energy, 7.31±0.10 eV, for gaseous yttrium monoxide. A correlation of the dissociation energies and the molecular parameters of the monoxides of Group III transition metals indicates that the unexpected increase in bonding with increasing radii is accompanied by an increase in the electronic entropy of the metal atom. The correlation demonstrates the role of excited atomic states in chemical bonding.
Composition of Some Conducting Complexes of 1,6-Diaminopyrene
Authors: Kronick Paul L. , Scott Harvey , Labes Mortimer M.
Published: January 2005

The absorption spectra of solid complexes of 1,6-diaminopyrene with quinones exhibiting high electrical conductivity show them to be mostly radical-ion salts. The mole fractions of ionic component for complexes with bromanil, chloranil, and 2,3-dichloro-5,6-dicyano-benzoquinone are 0.65, 0.90, and 0.95, respectively. This is the order of the estimated electron affinities of the acceptors but not of the conductivity of the complexes. The iodanil complex, with much higher resistivity, shows little ionic component.
Molecular Structure of Cyclopropyl Chloride
Authors: Schwendeman R. H. , Jacobs G. D. , Krigas T. M.
Published: January 2005

The pure rotational microwave spectra of seven isotopic species of cyclopropyl chloride have been examined and rotational constants assigned. The data are sufficient for a complete structure determination by the substitution method. The bond distances and bond angles obtained are r(C1C2)=1.513 Å, r(C2C3)=1.515 Å, r(CCl)=1.740 Å, average r(CH)=1.08 Å, ∠CCCl=118.7°, ∠ClCH=115.8°, and ∠HCH=116.2°. The quadrupole coupling constants of C3H5Cl35 in the principal inertial axis system are χaa=—56.64 Mc/sec, χbb=36.72 Mc/sec, and χcc=19.92 Mc/sec. These values are consistent with χzz=—71.4 Mc/sec, and ηbond=0.029 if the z axis and the CCl internuclear line are assumed to coincide, and with χzz=—73.5 Mc/sec if the charge distribution near the chlorine nucleus is assumed to be cylindrically symmetric.
Reaction of O(1D) with CO
Authors: Raper O. F. , DeMore W. B.
Published: January 2005

The photolysis of O3 in liquid CO at 77°K has been studied with 2537-Å radiation. Carbon dioxide is formed with a quantum yield of 0.07 and in a 1:1 ratio with O3 disappearance. The CO2 quantum yield is reduced by addition of N2, O2, or Ar, but is increased by lowering the temperature of the solution.

Formation of CO2 is attributed to the reactionO(1D)+CO(+M)→CO2(+M),and the low quantum yield is believed to be caused by the reactionO(1D)+CO+M→CO+O(3P)+Mwhich leads to O3 reformation. The reaction of O(1D) with CO is an example of an association process in which the excited association complex may undergo unimolecular decomposition to products of lower electronic energy in the course of stepwise vibrational deactivation. Formation of the association product is of higher order than one with respect to M, the actual order depending on the number of vibrational states in which unimolecular dissociation competes with collisional deactivation. Because of the high-order dependence on M, the rate of product formation is very sensitive to the deactivation efficiency of the third body. The effect of added diluents is believed to arise partly from competition of the added diluents for O(1D) and partly from the resulting change in solvent deactivation efficiency. The effect of reduced temperature is attributed to an increased rate of deactivation resulting from an increased solvent density.
Ultraviolet Absorption of SO2: Dissociation Energies of SO2 and SO
Authors: Warneck P. , Marmo F. F. , Sullivan J. O.
Published: January 2005

The absorption intensities of SO2 were measured in the wavelength region 1849–3150 Å employing the hydrogen continuum as the source and at selected wavelengths utilizing the mercury line spectrum. The pressure dependence of the absorption intensity was investigated at 1849, 2537, and 3131 Å. The existence of an absorption continuum commencing at 2280 Å has been established and attributed to the dissociation of SO2 forming SO and a ground-state oxygen atom. The onset of the continuum provides an upper limit value to the dissociation energy of SO2. The implications upon the SO2 and SO dissociation energies are discussed.
Theory of Light Scattering from a Flexible Chain Molecule
Authors: Isihara A.
Published: January 2005

The standard Rayleigh—Gans theory is applied to evaluate the scattered intensity of light due to a perfectly flexible chain molecule in solutions. Depending on statistically different averaging processes, two different expressions for the intensity may be derived from the theory, one asymptotically reducing to the well-known Debye formula, and the other to the formula given previously by the present author. It is found that the scattered intensity is not only dependent on the variable x = (8π2Nb2 sin2½θ)/3λ2 but also on the molecular weight of the polymer molecule. Here, N is the number of repeated units in the polymer which are considered to be scattering centers, b the bond length, θ the scattering angle, and λ is the wavelength. The applicability of these asymptotic formulas is determined by the scattering angle and the molecular weight. Use of the asymptotic formulas for low-molecular-weight polymers at large scattering angles is not advisable. Instead, it is reommended to use the new formulas derived in this paper for arbitrary N and θ.
Fifth and Sixth Virial Coefficients for Hard Spheres and Hard Disks
Authors: Ree Francis H. , Hoover William G.
Published: January 2005

New expressions for the fourth, fifth, and sixth virial coefficients are obtained as sums of modified star integrals. The modified stars contain both Mayer f functions and f̃ functions (f̃≡f+1). It is shown that the number of topologically distinguishable graphs occurring in the new expressions is about half the number required in previous expressions. This reduction in the number of integrals makes numerical calculation of virial coefficients simpler and more nearly accurate. For particles interacting with a hard-core potential, values of the modified star integrals are shown to depend strongly on dimension; for example, several modified star integrals are identically zero for hard disks (two dimensions), but give nonzero values for hard spheres (three dimensions). Of all the modified star integrals contributing to the fourth, fifth, and sixth virial coefficients, the complete star integrals are shown to be the largest. Mayer's expressions for these coefficients made the complete star integrals the smallest contributing integrals.

The fifth (B5) and sixth (B6) virial coefficients of hard-sphere and hard-disk systems are obtained by Monte Carlo integration of the modified star integrals. The resulting values are spheres:B5/b4=0.1103±0.0003;B6/b5=0.0386±0.0004disks:B5/b4=0.3338±0.0005;B6/b5=0.1992±0.0008 where b is the second virial coefficient.

Estimated values of B7 obtained from a Padé approximation to PV2/(N2kT) — V/N are B7/b6=0.0127 for hard spheres and 0.115 for hard disks. For hard spheres virial series calculations including terms through the sixth virial coefficient give values of PV/(NkT) which agree closely, for densities less than half of closest-packing, with the molecular dynamics data of Alder and Wainwright. Furthermore the approximate Padé expression agrees within 2% with the molecular dynamics data for all densities on the fluid side of the solid-fluid transition. This agreement indicates convergence of the virial series along the entire fluid branch of the hard-sphere equation of state.
Configurations of Triarylborons
Authors: Weismann T. J. , Schug John C.
Published: January 2005

Potential energies were calculated for a series of methylated triarylborons considering interactions between all nonbonded atoms and pi-electron resonance energies. All nonbonded interactions were estimated using modified Buckingham (exp-six) potentials obtained from the literature; pi-electron energies were calculated using simple molecular-orbital theory. The resulting predictions of stable geometries were compared with those derived from proton magnetic-resonance chemical shift data. All calculations were performed using a rigid geometric framework permitting only rotation of aryl groups. Reasonable agreement was found for several of the molecules studied; however, a number of discrepancies indicate certain inadequacies in the present treatment. In particular, future refinements must include the possibility of bond bending.

For tri-1-(2-methylnaphthyl)boron, temperature dependence of the NMR spectra was indicative of rotational isomerism.
Heat Contents of Molten Zinc Chloride and Bromide and the Molecular Constants of the Gases
Authors: Cubicciotti Daniel , Eding Harold
Published: January 2005

The heat contents of zinc chloride and bromide were measured from room temperature to about 700°C. The heat capacities (cal/mole deg) of the solids were: 14.5+5.5×10—3T and 12.6+10.4×10—3T°K; those of the liquid were 24.1 and 27.2 cal/mole; and the heats of fusion were 2.45 and 3.74 kcal/mole. These thermal data, when combined with the entropies of evaporation of F. J. Keneshea and D. Cubicciotti [J. Chem. Phys. (to be published)], resulted in absolute gaseous entropies that were 5 eu larger than the values calculated from molecular constant data. The discrepancy can be resolved if the molecules are bent or have lower bending frequencies than the literature values.
Exchange Rates by Nuclear Magnetic Multiple Resonance. III. Exchange Reactions in Systems with Several Nonequivalent Sites
Authors: Forsén Sture , Hoffman Ragnar A.
Published: January 2005

The nuclear magnetic multiple resonance method for the study of chemical exchange rates has been applied to systems in which a nucleus X is reversibly exchanged between three nonequivalent sites. A procedure is outlined, which is applicable to systems with any number of sites and permits the determination of the lifetime τK at any one site K. In this procedure the effective ``relaxation time'' τ1K and the equilibrium z magnetization, M0K (τ1K/T1K), are determined in experiments (Type I) in which the X signals at all other sites are completely saturated. The rate constants λKL and λLK of the individual exchange reactions (K⇄L) may then be determined in Type II experiments in which the signals of all sites excluding K and L are saturated. In Type II experiments only the equilibrium signal intensities need be measured.

The method has been applied to the base-catalyzed proton exchange in the keto—enol system of acetylacetone and it was found that exchange between the olefinic =CH and hydroxylic —OH protons occurs merely as a consequence of the keto—enol transformation. Within the accuracy of the measurements no evidence was found for a proton exchange between the =CH and —OH protons which does not involve the CH2 group in the keto form as an intermediate.
Crystal Field Splitting in Potassium Perchromate
Authors: Anysas J. A. , Companion A. L.
Published: January 2005

Measurements of the diffuse reflectance spectrum of K3CrO8 and its dilutions in CaF2 essentially support the transmission results of Swalen and Ibers. Peaks observed at 2.00 and 2.53 eV are attributed to d—d transitions on the Cr5+ ion, others at 3.35 and 5.00 eV to charge transfer. A crystal field analysis yields a Dq value of 0.41 eV for the Cr5+ ion, a result consistent with that obtained from the spectrum of the hypochromate ion, 0.45 eV.
Nature of Metastable Peaks in Mass Spectra
Authors: Schug John C.
Published: January 2005

This paper discusses the possibilities of obtaining useful information from so-called ``metastable lifetime'' measurements. An approximate method is described for computing the ratios of parent-ion to metastable peak intensities via the statistical theory. The predictions of the statistical theory are compared with those of models employing a small number of discrete rate constants. It is shown that, in certain instances, it is possible to determine which model is correct by performing experiments as a function of ionizing voltage. Data for the 30.4 and 31.9 metastables of n-butane, and the 56.1 metastable of benzonitrile appear to substantiate the validity of the statistical theory.