bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Correlated Wavefunctions. III. Alternative Initial Approximations
Authors: Steiner Erich
Published: January 2005

The perturbation treatment of electron correlation is generalized to include an initial orbital approximation Ψ0 in which the orbitals are arbitrary within a unitary transformation which leaves Ψ0 unchanged. Various methods are considered for the partitioning of the total Hamiltonian into zeroth- and first-order parts consistent with a given zeroth-order Ψ0. One particular partitioning is discussed in detail which leads to simple and physically significant expressions for the second- and third-order energies, and for which the second-order energy gives a good estimate of the correlation energy when the orbitals are well localized and when no near-degeneracies are present. A calculation of the angular correlation in the ground state of the beryllium atom serves to investigate the validity of a number of concepts.
Some Calculations on the Hydrogen Bond
Authors: van Duijneveldt F. B. , Murrell J. N.
Published: January 2005

In this paper we present a perturbation approach to the calculation of the energies of weak to moderately strong H bonds. The method is based on an extension of London's theory of intermolecular forces to the region of nonnegligible intermolecular overlap. The H-bond energy is obtained as a sum of terms which are of first order (Coulomb, exchange) and of second order (induction, dispersion, charge transfer) in the intermolecular potential. The calculations have been performed for a linear model system A—H···B as a function of the orbital exponents of Atoms A and B, the ionicity parameter k of the A—H bond, and the H···B distance rHB. The results show that stable H bonds may be formed even when A—H is nonpolar and that the dipolar attraction due to A—H polarity is a good measure for comparing the stabilities of H bonds having a common acceptor B and equal rHB. The effect of H-bond formation on the A—H bond length is discussed briefly.
Spatial Correlation and Molecular Properties in Extended Hartree—Fock Calculations
Authors: Lyon William D. , Hirschfelder Joseph O.
Published: January 2005

Using the extended Hartree—Fock multiconfiguration wavefunctions of Das and Wahl, the first- and second-order density matrices are derived for the ground states of H2, Li2, and F2. The method of Weinhold and Wilson is used to obtain the natural orbitals and natural geminals. Expectation values of the following one-electron operators are calculated: (rai)−1, zai2, and rai2. Expectation values of the two-electron confocal elliptic coordinate operator, (ξi—ξj)2, (ηi—ηj)2 and cos (φi—φj), together with the Cartesian coordinate operator (zai—zaj)2, are also calculated. The two-electron expectation values provide a measure of in—out left—right, and angular correlation. The quadrupole moment and diamagnetic susceptibility of H2, Li2, and F2 are calculated as functions of R. Experimental values are lacking for Li2 and F2. Good agreement is obtained with experiments for H2 at its equilibrium separation.
NiSiF6·6H2O. Temperature and Other Thermodynamic Properties from Adiabatic Demagnetization without Low-Temperature Heat Introduction. H ∥ c Axis
Authors: Giauque W. F. , Hornung E. W. , Brodale G. E. , Fisher R. A.
Published: January 2005

Values of field and magnetic moment have been measured on 40 magnetic isentropes of NiSiF6·6H2O. The field was directed along the crystallographic c axis of the 3.5-cm-diam spherical single crystal. Typical derived values of the magnetic work, differential isentropic susceptibility, relative heat content (enthalpy), and relative internal energy have been tabulated. A principal purpose of the measurements has been to investigate the evaluation of temperature and other thermodynamic properties in the presence of any available magnetic fields without heat introduction below 0.3°K. This avoids the difficulty of distributing heat under small temperature heads in poor thermal conductors. Absolute temperatures from the thermodynamic equation T = (∂H/∂S)H, where H, S, and H are heat content, entropy, and field, respectively, and values of heat capacity CH = T (∂S/∂T)H have been derived at representative fields. At entropies below 1 gibbs/mole and within about ±200 G of zero field, the adiabatic magnetic susceptibility remains constant at 34.3 cm3/mole. At the same time the limiting temperatures of the adiabatics varied from about 0.05°—0.15°K. There was some evidence that the system was beginning to develop irreversibility near 0.05°K but it appeared to be reversible at higher temperatures.
Conformation and Reaction of Stereoisomeric Radicals Trapped in Irradiated cis- and trans-Cyclohexane−1,2-diol
Authors: Ohmae Tadayuki , Sakurai Hiroshi , Ohnishi Shun-ichi , Kuwata Keiji , Nitta Isamu
Published: January 2005

ESR measurements were carried out on the samples of electron-irradiated cyclohexanediols. In the case of 1,2-diols, the results are consistent with an interpretation of trapping of two conformationally isomeric radicals, cis- and trans-cyclohexane−1,2-diol−1, at −196°C and their intramolecular conversion to cyclohexanone−2 or 2-hydroxycyclohexanone−6 radicals upon warming to room temperature.
Magnetic and Crystal Structures of CeC2, PrC2, NdC2, TbC2, and HoC2 at Low Temperatures
Authors: Atoji M.
Published: January 2005

The light rare-earth dicarbides, CeC2, PrC2, and NdC2, having the tetragonal CaC2-type structure, have been shown by neutron diffraction to become a body-centered first-kind antiferromagnet with the Néel temperatures of 33°, 15°, and 29°K and with the ordered moments being 81%, 44%, and 90% of the free-ion values, respectively. The moment direction is parallel to the c axis in the above compounds. The isostructural heavy rare-earth dicarbides, TbC2 and HoC2, exhibit an antiferromagnetic, elliptic-helical spin alignment propagating along the a axis with the repetition quadrupole of the atomic spacing, where the Néel temperatures are 66° and 26°K, and the root-mean-square ordered moments are 5.1 and 6.9 Bohr magnetons, respectively. Here, the moments lie on the bc plane. A modulation of the above structure takes place below 40° and 16°K, with the maximum possible additional moments of 0.54 and 1.65 Bohr magnetons at 2°K in TbC2 and HoC2, respectively. In TbC2, another complex magnetic structure coexists below ∼33°K. Also presented are a discussion on the wavy diffuse backgrounds of TbC2 and HoC2 at temperatures down to 2°K, and the low-temperature crystallographic parameters.
Relativistic Corrections to the Electron Density at the Nuclear Surface and to the Alkali Halide Overlap Integrals
Authors: Hafemeister D. W.
Published: January 2005

The electron density at the nuclear surface and the alkali halide overlap integrals have been calculated with Hartree—Fock, Hartree—Fock—Slater, and the relativistic Dirac—Slater SCF wavefunctions. Both the full Slater exchange and ⅔ of it have been used.

The SCF relativistic enhancements of the electronic density at the nuclear surface are in good agreement with the enhancements predicted by Racah and by Rosenthal and Breit. The Slater exchange approximation slightly overestimates the density at small radii for valence electrons, but gives excellent results for core electrons.

The alkali halide overlap integrals are extremely dependent on the amount of Slater exchange used, thus implying that this approximation is less satisfactory for large radii. Our results indicate that the multiplicative factor modifying the Slater exchange should be between ⅔ and 1 for the calculation of overlap integrals. The overlap integrals for the heavier alkali halides are reduced by about 10% by relativistic effects.
Infrared-Absorption Spectra of Solid Solutions: The Rotatory Motions of Nitrate and Nitrite Ions in Alkali Halides
Authors: Bonn R. , Metselaar R. , van der Elsken J.
Published: January 2005

The infrared absorption spectra of nitrite and nitrate ions as impurities in potassium chloride single crystals show a fine structure that must be attributed to rotational motions of these ions. Evidence is found for the existence of different groups of nitrite ions that occupy different lattice sites and that are characterized by a varying degree of rotational freedom. No such evidence is found for the nitrate ion for which a librational type of motion is described.
Deactivation by Collision in the Photolysis of Azoethane
Authors: Worsham Walter C. , Rice O. K.
Published: January 2005

Though the excitation of azoethane by ultraviolet light is primarily an electronic process, a considerable fraction of the energy must go into the excitation of vibrations. As in unimolecular reactions, it is then possible for the vibrational energy to accumulate by chance in a weak bond, causing disruption of the molecule. On the other hand, deactivation may occur through collisions with other molecules. The greater the amount of energy put into the molecules, the more rapidly decomposition should occur and the less effective should be deactivation by collision. We have, therefore, investigated the photolysis at 3519, 3660, and 3776 Å, and, assuming deactivation at every collision, the average lifetimes of the activated molecules were determined to be roughly 1.6, 2.6, and 3.9×10−10 sec, respectively. The results have been compared with earlier results at 3660 Å at a series of different temperatures ranging up to about 120° above room temperature. They have been discussed in terms of the classical theory of unimolecular reactions. Though not all the parameters can be completely determined, and though some complications may be present, a reasonably good picture of the mechanism can be given on the basis of this theory.
Simple Model for Cohesion in Metals
Authors: Cutler Melvin
Published: January 2005

A simple model for the binding energy of metals has been examined. The electrostatic energy for the ion—electron interaction is calculated classically, assuming a uniform density of valence electrons within a Wigner—Seitz sphere but outside a spherical core of arbitrary radius rc. rc is determined by matching the equilibrium volume to the experimental value. Several expressions are examined for the kinetic energy and for the energy due to the electron—electron interaction, and the results are compared with experimental data for alkali metals. It is found that the best results are obtained if the presence of the core is ignored completely in computing the energy of the electron—electron interaction. One then obtains not only good agreement for the binding energy (ΔE≲0.01 Ry), but also values for the compressibility which are typically within 10% of experimental values. The empirical values of rc are comparable with the ionic radii. The pressure—volume curves agree with experiment to a degree comparable with the compressibility values. Modifications of the energy expressions from the optimum one yield moderately poorer agreement with experiment, except for a particular combination which has been used by Raich and Good. In that case, very poor values of rc and compressibility are obtained; this is apparently caused partly by a pecularity in the mathematical behavior of the energy expression. Application of the model to polyvalent metals was found to yield progressively poorer results with increasing valence for the binding energy and compressibility. The values of rc, however, generally remain comparable with the empirical ionic radii.
Evaporation Rate and Lifetimes of Clouds and Sprays in Air—The Cellular Model
Authors: Zung Joseph T.
Published: January 2005

A simple, yet effective, mathematical model based on the cellular method is proposed for the study of the evaporation rate of liquid droplets in assemblages in air. It has been found that the modified cellular model is adequate for the determination of the rate of evaporation, the saturation point, and the lifetime of a monodisperse system of droplets. All characteristic properties of the droplet system can be expressed in terms of known parameters in closed form. Correction for submicron droplets is also given. Numerical results obtained for various droplet systems of water and n-dibutylphthalate indicate that both the droplet radius and the degree of dilution have important effects on the evaporation rate of clouds and sprays. Several possibilities are suggested for further refinement of the theory and improvement on the model in order to account for the influence of dispersion and diffusion of droplets in air and the effect of polydispersity of the cloud itself.
Ground-State Molecular Constants of Hydrogen Sulfide
Authors: Edwards T. H. , Moncur N. K. , Snyder L. E.
Published: January 2005

A simultaneous analysis of 185 distinct ground-state combination differences taken from the (1, 1, 1) and (2, 1, 0) absorption bands of H232S together with the two microwave transitions reported by Burrus and Gordy, yielded the following values for the ground-state molecular constants (in cm−1): A0=10.3599±0.0004, B0=9.0156±0.0005, C0=4.7315±0.0004, τaaaa=—(8.06±0.13)×10−3, τbbbb=—(4.84±0.04)×10−3, τaabb=+(4.57±0.10)×10−3, τabab=—(1.31±0.06)×10−3, H0K=—(4.6±1.6)×10−8 (with simultaneous confidence intervals at the 95% level). Equilibrium structural parameters determined from the values of A and B in the (1, 1, 1) and ground states are: re=1.3356 and φ=92°07′.
Conductivity and Hall Effect in Cerium Dihydride
Authors: Heckman Richard C.
Published: January 2005

Results are given of measurements of the conductivity and Hall coefficient of cerium dihydride at 200°C as functions of composition. The conductivity, in agreement with earlier results, decreases with increasing hydrogen-to-cerium ratio. The Hall coefficient is positive and increases with hydrogen additions. The results are in agreement with a model in which hydrogen is assumed to be protonic. They are not compatible with the assumption of anionic hydrogen.
Electron Spin Resonance Study of the Photolytic Decomposition of HN3 in Inert Matrices at 4.2°K
Authors: Fischer P. H. H. , Charles S. W. , McDowell C. A.
Published: January 2005

The only paramagnetic species observed amongst the products of the photolytic decomposition of hydrazoic acid, HN3, in Ar, Kr, and Xe matrices at 4.2°K are NH2 and an unidentified species which contains one hydrogen atom and possesses a hydrogen hyperfine coupling constant aHiso=23.8 G and giso∼2.010. The NH2 is probably produced by photolytic decomposition of HN3 aggregates. Our experiments have shown that the production of paramagnetic species is critically temperature dependent as witnessed by the fact that if there is poor thermal contact between the matrix sample and the coolant, then in addition to the above-mentioned paramagnetic species, H and N atoms are also formed. The H and N atoms appear to be formed as a result of the diffusion of NH, the primary product of the photodecomposition of HN3, followed by unidentified secondary processes and not by direct photolytic decomposition of HN3 or NH.
Calculation of Zero-Field Splitting in NH. II. One-Center Representations of Triplet States
Authors: Lounsbury John B.
Published: January 2005

The zero-field-splitting (ZFS) parameters arising from electron spin—spin dipolar interactions in the known triplet states of NH are calculated. A variety of one-center expansion (OCE) representations are utilized, including an extended basis wavefunction for the ground state. Overlaps of limited basis OCE eigenvectors with extended basis OCE eigenvectors and with two-center eigenvectors are calculated for 3Σ−NH. In addition, electron-density distributions are calculated for the various 3Σ−NH representations. It is concluded that, at least for 3Σ−NH, OCE representations in general and limited basis OCE representations in particular describe the distributions of the innermost and outermost electron shells relatively better than distributions of the remaining electrons. Electron spin—spin dipolar interaction in 3Σ−NH is found to be much larger than for 3II0NH; D=1.5951 cm−1 for 3Σ−NH using a 24 basis representation and D=0.512 cm−1 for 3II0NH using a 12 basis representation. The electronic configurations of organic nitrenes are discussed qualitatively. Directions of future ZFS calculations for nitrenes are suggested.
Direct Measurements of Homogeneous Nucleation Rates in a Glass-Forming System
Authors: Hammel Joseph J.
Published: January 2005

A metastable liquid miscibility gap was shown to exist in the Na2O·CaO·SiO2 system. Nucleation rates were measured at a number of undercoolings for a composition at the edge of this gap. Accurate measurements were possible due to the extremely slow approach to equilibrium because of the high viscosities (>1010 P) of the liquid at the nucleation temperatures. The Lumsden-solution model and experimental miscibility-gap data were used to calculate volume free energies driving the separation at the various undercoolings. Measuring the variation of solubility temperature with particle size of the separating phase a value of 4.6 ergs cm−2 was obtained for the interfacial energy. An activation energy for diffusion of 94.5 kcal mole−1 was obtained from measured growth and miscibility-gap data. At most of the seven undercoolings the agreement between measured and calculated homogeneous nucleation rates when using the Lumsden model was excellent.
Vibronic Coupling. V. Several Theorems Concerning the Eigenfunctions and Spectra of the Vibronic Oscillator
Authors: Fulton Robert L.
Published: January 2005

Three theorems concerning the nature of vibronic coupling in a simple system are proven. These are that the eigenfunction of the lowest state of the negative system (a ``forbidden'' system in many dimers) is always of one sign, that the lowest eigenvalue of the negative system is lower than the lowest eigenvalue of the positive system (usually an allowed system in a dimer), and that the lowest eigenvalue of the negative system is lower than the lowest eigenvalue in the absence of coupling between the units comprising the dimer.

Some physical implications of these theorems concerning the radiative lifetimes of certain excited states are derived and discussed.
Origin of Rotational Barriers. I. Many-Electron Molecular Orbital Wavefunctions for Ethane, Methyl Alcohol, and Hydrogen Peroxide
Authors: Fink William H. , Allen Leland C.
Published: January 2005

An investigation into the origin of rotation barriers has been carried out with the aid of LC(Hartree—Fock) AO MO SCF calculations on CH3CH3, CH3OH, and H2O2. The general shape and magnitudes of the barriers are reasonably well represented by the wavefunctions and one may conclude that the origin of rotational barriers is to be found within the framework of the Hartree—Fock approximation. It is also found that study of several molecules, particularly ones of low symmetry, is required for a detailed understanding of barriers.

The electronic energy has been decomposed into one- and two-electron parts. The relative phase and relative amplitude of these two components provide the best invariants available for analyzing the barrier mechanism. On the other hand the nuclear—nuclear repulsion is shown not to be an appropriate invariant. A physical picture of the barrier mechanism constructed from the electronic-energy decomposition depicts the barrier origin as a balance between the interactions of lone pairs, bonds, and the protons.
Separation of Boron Isotopes. VIII. BF3 Addition Compounds of Dimethyl Ether, Dimethyl Sulfide, Dimethyl Selenide, Dimethyl Telluride, Dibutyl Ether, and Ethyl Formate
Authors: Palko A. A. , Drury J. S.
Published: January 2005

Studies were made of the physical and chemical properties of molecular addition compounds formed by BF3 and Group VIb donors. The dimethyl telluride complex was too unstable to exist at temperatures above −30°C. The freezing point of the 1:1 dimethyl selenide·BF3 compound was −43°C. From room temperature to its freezing point, the saturation pressure of the 1:1 dimethyl selenide complex was given by log10 P=9.945— (1824/T). The 1:1 butyl ether and ethyl formate complexes formed at 25°C but deteriorated slowly with the formation of noncondensible gases. The freezing points of these complexes were −30° and −8°C, respectively. Between room temperature and their freezing point, the saturation pressures of freshly prepared Bu2O·BF3 and HCOOEt·BF3 were given by logP=5.65— (1010/T) and logP=5.70— (1330/T), respectively. For the same temperature range, the equilibrium constant for the isotopic exchange reaction B10(g)+A·11BF3(l)=11BF3(g)+A·10BF3(l)was given by logKeq=(8.13/T) −0.0131, when A was dimethyl selenide and logKeq= (1.6/T)+0.0059, when A was dibutyl ether. Previously reported equilibrium constants for the Me2O and Me2S exchange reactions were redetermined: for Me2O, logKeq= (8.76/T) −0.0179, and for Me2S, logKeq= (10.7/T) − 0.0200. Related thermodynamic data were also computed.
Formula for Thermal Accommodation Coefficients
Authors: Goodman Frank O. , Wachman Harold Y.
Published: January 2005

A simple formula in closed form is proposed for the thermal accomodation coefficient from which the accommodation coefficient of a monatomic gas—solid system may be calculated from certain basic parameters of the system. The formula α(T)=1−exp(−T0/T)+α(∞) tanh{[(MT)1/2/α(∞)](a/λ)} exp(−T0/T)is obtained from consideration of certain aspects of Goodman's lattice theory of accommodation and from conclusions regarding certain properties of available experimental data. Adequate agreement is obtained of the formula with both the lattice theory and experimental data. Certain, corrections are applied to the lattice theory, and the gas—surface-potential interaction parameters relevant to the lattice theory are revised.
ESR Study of Manganese-Doped α-Zinc Silicate Crystals
Authors: Perkins Harolyn King , Sienko M. J.
Published: January 2005

Single crystals of dilute manganese-doped α-Zn2SiO4 have been grown hydrothermally and from the melt. ESR spectra have been examined at 9.5 and 35 Gc/sec. Results are interpreted in terms of Mn2+ at two environmentally different sites, having D parameters 729±8 and 413±4 G and E parameters 170±5 and 135±5 G, respectively. The relative population of the two sites appears to be independent of total manganese concentration or method of crystal growth. It is believed that the two sites correspond to substitution of Mn2+ for Zn2+ at two crystallographically nonequivalent zinc positions in the willemite structure.
High-Temperature Vaporization and Thermodynamics of the Titanium Oxides. I. Vaporization Characteristics of the Crystalline Phases
Authors: Gilles Paul W. , Carlson K. Douglas , Franzen Hugo F. , Wahlbeck Phillip G.
Published: January 2005

The vaporization behavior of the titanium—oxygen system has been established by experimental measurements of the change in composition of the solid residue accompanying vaporization as determined by x-ray diffraction, chemical analysis, and color of sample. The solid phases studied were Ti2O, TiO, Ti2O3, Ti3O5, Ti4O7, Ti5O9, Ti10O19, and TiO2. A congruently vaporizing composition was found in the Ti3O5 phase region. These results are compared with previous investigations and with thermochemical data available for solid and gaseous species.
Thermodynamics of C3. II. General Methods for Nonrigid Molecules at High Temperature
Authors: Strauss Herbert L. , Thiele Everett
Published: January 2005

A classical expression is developed for the partition function of the coupled bending and rotational degrees of freedom of a linear triatomic molecule. The usual rigid-rotator harmonic-oscillator partition function can be derived as an approximation to our result. Analytical approximations to both the bending-rotator and the rigid-rotator partition functions for a molecule with a quadratic—quartic potential are considered and the accuracy of these approximations is assessed by numerical calculations. Values for the thermodynamic functions for C3 are calculated using the best available spectroscopic data. It is shown that for the bending and rotational degrees of freedom, quantum corrections are negligible at temperatures above a few hundred degrees while anharmonicity and vibration—rotation coupling are quite important. For example, at 2400°K, a quartic term in the potential of C3 lowers the calculated value of S° by 2.8 eu, and the vibration—rotation coupling lowers it by another 1.1 eu to a computed value of 81.4 eu. A drastic steepening of the potential gives a lower limit, more or less consistent with the spectroscopic data, of 79.8 eu. The best experimental values for S°2400 are 76 or 77 eu.
Resolution of the Translation—Rotation Paradox in the Theory of Irreversible Condensation
Authors: Reiss H. , Katz J. L.
Published: January 2005

In this paper it is shown that the Lothe and Pound correction to nucleation theory based upon the introduction of translational and rotational partition functions for individual drops does not arise. The error originates in the improper assumption that the free energy assigned to a drop, in the conventional theory of nucleation, corresponds to that for a drop whose center of mass is stationary.
Reaction of O(1D) with Methane
Authors: DeMore W. B. , Raper O. F.
Published: January 2005

The reaction of O(1D) with CH4 has been studied by photolysis (2537 Å) of O3–CH4 mixtures dissolved in liquid argon at 87°K. The quantum yields of O3 decomposition and the product yields based on O3 decomposed were measured. The products found were CH3OH, CH2O, and H2. Added O2 was found to lower the quantum yields of O3 decomposition and to increase the product yields. Experiments with added 18O2 were carried out to trace the origin of the products. At 6000 Å, which can only give O (3P), no photo-reaction could be detected.

The results indicate that the O(1D)—CH4 reaction has essentially zero activation energy and proceeds by three paths: O(1D)+CH4+M→CH3OH+M,O(1D)+CH4→CH2O+H2,O(1D)+CH4→CH3+OH.

The effect of added O2 is attributed to scavenging of methyl radicals which otherwise react with O3. The reaction of CH3 with O3 has zero Ea and occurs at a rate approximately equal to the reaction of CH3 with O2. The magnitude of the scavenging effect shows that at least two O3 molecules are decomposed by each CH3. By contrast, OH radicals do not react with O3 in these experiments, indicating a nonzero activation energy for the reaction OH+O3→HO2+O2.
Complete Classification of the States of Three-Electron Atoms
Authors: Delves L. M.
Published: January 2005

A complete, finite expansion is given for an arbitrary state of a three-electron atom. This expansion separates the simple dependence of the wavefunction on the spin and Euler-angle variables from the complicated and in general unknown dependence on the relative positions of the particles.
Charge-Transfer Spectrum of the Tetrachlorocuprate Ion
Authors: Sharnoff Mark , Reimann Curt W.
Published: January 2005

The polarized ultraviolet absorption spectra of the tetrahedral CuCl4= ion oriented in single crystals of Cs2CuCl4 and Cs2ZnCl4 have been observed. The spectral bands are identified by means of an analysis which takes into account the observed variations with lattice of the band intensities and positions and which allows for the effects upon the spectra of terms of rhombic symmetry known to be present in the ionic Hamiltonian. The resulting band assignments differ from those proposed by Ferguson. Salient differences between the observed Cs2CuCl4 spectra and those reported by Ferguson are noted and tentatively explained.
Nuclear Quadrupole Resonance Zeeman Study of para-Chlorophenol
Authors: Peterson G. E. , Bridenbaugh P. M.
Published: January 2005

The major field gradient directions for Cl in para-chlorophenol as determined by NQR and x-ray diffraction are compared quantitatively, and found to agree. The minor field gradient directions are examined qualitatively, and are consistent with those predicted on the basis of Cl–C partial double bonding. From a measurement of the field gradient asymmetry parameter η, the degree of chlorine—carbon double bonding is calculated to be 0.038±0.004.
Hole-Theory Study of the Isochoric Behavior in the Liquid State
Authors: Fukuda Yoshichi , Kobayashi Riki
Published: January 2005

The hole theory of liquids is applied to study recent data on isochores of methane using the quasichemical approximation. The rather small deviations from linearity of the isochores have significant physical implications. Around the critical temperature the correlation between holes becomes important and the assumption of the random distribution of holes is quite unsatisfactory for explaining the observed behavior of the isochores. The detailed form of the free volume is required to study the over-all behavior of isochores.
Rings and Screws of Sulfur and Other Divalent Elements
Authors: Tuinstra F.
Published: January 2005

A conformational study of all a priori possible molecular forms of divalent elements with restricted rotation has been carried out using the matrix formalism introduced by Eyring. The calculations are confined to those forms which have a single value of the bond distance, a single value of the bond angle β, and a single value of the dihedral angle γ.

The way in which the regular conformations are built up by repetition of a ``module'' (i.e., a definite sequence of right and left turns) may be of two types: (i) the helical conformations, for which a relation between the pitch and the order of the helix and the angles β and γ is derived, for any finite module, the special case of pitch zero leading to ``improper rings,'' where the values of β and γ form a discrete set; (ii) the proper rings, characterized by a certain kind of sequence of the matrices in the module, making the pitch zero, independently of the value of β (or γ). The closure of the ring requires a relation between β and γ, which may be written down for any finite module of this kind.

For every module the correspondence between the symmetry of the sequence of matrices and the symmetry of the molecule is given. The study is applied to sulfur especially.
Reduced Density Matrices of Atoms and Molecules. I. The 2 Matrix of Double-Occupancy, Configuration-Interaction Wavefunctions for Singlet States
Authors: Weinhold Frank , Wilson E. Bright
Published: January 2005

Certain general features of the second-order reduced density matrix, or 2 matrix, for configuration-interaction (CI) wavefunctions are reviewed, with special reference to the simplifying features of spin singlet states. A restricted form of CI in which all spatial orbitals are doubly occupied (DOCI) is proposed for singlet states. The 2 matrix of the DOCI function is derived and shown to have an extremely simple (largely diagonal) structure in a spin symmetry basis of Heitler—London-like geminals constructed from the natural orbitals of the system. Of the three types, λi, Λij, λij, of nonvanishing 2-matrix elements, the λi are shown to be the occupation numbers of the 1 matrix, the Λij are occupation numbers of the 2 matrix, while the off-diagonal λij mix together the uncorrelated basis geminals to produce correlated natural geminals of singlet ``homogeminal'' type. The structural features of the DOCI 2 matrix are interpreted in terms of electronic correlation, and the physical applicability of the DOCI model is discussed.
On the Molecular Theories of Polymer Solutions
Authors: DeWames R. E. , Hall W. F. , Shen M. C.
Published: January 2005

This paper reports on a review of the basic molecular theories of polymer viscoelasticity and the proper extension of these theories to the continuum limit, including the effects of local changes in the submolecule friction factor. Our first concern is to show the equivalence of the hydrodynamic method of Kirkwood as exemplified by Zimm and the energetic method of Debye, Rouse, and Bueche. The discrepancy between the results of Zimm and Bueche is resolved by including the internal energy of the bead-and-spring model of the polymer molecule in Bueche's calculation. The dynamic viscosity and its Fourier transform, the elastic modulus, are obtained for the free-draining and non-free-draining cases and the appropriate continuum expressions for these functions are given. Finally, it is shown that a natural limit exists on the allowable strength of the hydrodynamic interaction, beyond which the molecule is unstable in solution. This is a result of the assumed additivity of the hydrodynamic perturbation in the present theories.
Quenching of Glory Undulations in Scattering of Na Atoms from Polyhalide Molecules
Authors: Gislason E. A. , Kwei G. H.
Published: January 2005

The velocity dependence of total cross sections has been measured for the scattering of Na atoms from CBr4, Br2, SnCl4, CCl4, CH3I, SF6, and SiCl4 (listed in order of decreasing chemical reactivity). All these systems show the ν−2/5 velocity dependence expected for the long-range r−6 dispersion force term in the intermolecular potential. However, the usual undulatory structure from ``glory scattering'' associated with the van der Waals potential well appears in only one case, Na+SF6. For the most reactive systems, Na+CBr4, Br2, SnCl4, this absence of undulations may be attributed to quenching by reactive scattering, which is important even at impact parameters outside the van der Waals radius. For CH3I, the quenching is probably due to the anisotropy of the intermolecular potential. For CCl4 and SiCl4, it seems plausible that the quenching may be due to the presence of low-frequency vibrations which distort the molecule appreciably during the collision.
Oxidation of Hydrogen Sulfide in Shock Waves. II. The Effect of Added Hydrogen on the Absorption of OH and SO2
Authors: Bradley J. N. , Dobson D. C.
Published: January 2005

The effect of added hydrogen on the appearance of OH and SO2 during the oxidation of hydrogen sulfide has been studied over the temperature range 1735°—2340°K. Although the hydrogen was present in concentrations comparable with the other reactants, the basic features of the hydrogen sulfide oxidation were preserved although the inductlon times for the appearance of SO2 and of OH were reduced and their temperature dependences altered. The hydrogen thus accelerates the H2S/O2 reaction but the oxidation of hydrogen is inhibited by the presence of H2S. These findings are discussed in terms of the competition between molecular species for the various radicals present, using as a basis the mechanisms for the oxidations of hydrogen and of hydrogen sulfide proposed previously.
Model for Melting-Curve Maxima at High Pressure
Authors: Rapoport Eliezer
Published: January 2005

A two-species model for the liquid proposed by Klement in order to account for the existence of high-pressure melting-curve maxima is further examined from the point of view of the theory of regular solutions. Equations for the concentration of the two species as a function of pressure and temperature are derived. A survey of structural data on liquids provides positive evidence for the existence of two species in the melts of some pure substances.
Semiempirical Potential and Bound State of the Helium−4 Diatom
Authors: Bruch Ludwig W. , McGee Ian J.
Published: January 2005

Hybrid potentials for the 4He–4He system composed of the theoretical short-range repulsion, an empirical potential at the minimum, and the theoretical long-range attraction have been constructed. Second virial coefficients calculated for these potentials are in poor agreement with experimental data. A semiempirical potential is constructed which fits the data well. This potential becomes the theoretical interaction at large separations; its gross features are a core radius of 2.645 Å and a potential minimum of −1.73×10−15 erg at 2.975 Å. There is one weakly bound state of the helium−4 diatom with a binding energy of roughly 0.01°K. An analysis of the effect of uncertainties in the experimental data upon these results is included; the bound state remains even with the allowed uncertainties.
Chemical Reactions in Molecular Sieves. I. NO3 Free Radical from Direct Reaction of NO2 and Atomic Oxygen
Authors: Wood David E. , Pietrzak Theodore M.
Published: January 2005

NO2 adsorbed in the cavities of 13-X molecular sieve reacts with oxygen atoms from a microwave discharge to form the NO3 free radical which remains trapped within the cavities. The EPR spectrum of the NO3 at 300°K is a single symmetrical line with g=2.019 and 11 G width between points of maximum slope. At 85°K a 5.9-G isotropic hyperfine coupling constant with the single 14N nucleus is resolved. The trapped NO3 free radical is apparently freely rotating even at 85°K. The odd-electron NO2 molecule is observed to exhibit free rotation in the 13-X sieve only down to ∼150°K.
Mechanisms of Excitation of Luminescence in Nitrogen Gas by Fast Electrons
Authors: Brocklehurst B. , Downing F. A.
Published: January 2005

The light emission from nitrogen excited by an electron beam (50 kV; 0–30 μA) has been studied at pressures between 1 and 770 mm Hg. Impurity emissions (from OH, O, NO, CN) are easily excited; their importance is exaggerated by their relatively low quenching rates. The intensities of the strong N2 emissions—N2+ first negative and N2 second positive—are (usually) proportional to current; collisional quenching of these systems has been studied, in the latter case, as a function of v′. These and other data are used to derive G values for the production of excited states of N2 and the impurities. The intensities of the weaker emissions from N2 and of the impurity bands are not proportional to current. The excitation mechanisms are discussed in the light of estimates of the equilibrium concentrations of ions, atoms, and other active species.
Electron-Spin-Resonance Study of Chlorine Atoms Adsorbed on a Silica-Gel Surface
Authors: Gardner C. L.
Published: January 2005

An electron-spin-resonance study has been made of chlorine atoms adsorbed on a silica-gel surface at 77°K. The experimental results indicate that the orbital degeneracy has been removed as a result of the electrostatic interaction with the surface and is, we believe, the first example of detection of trapped halogen atoms. From the experimental results an estimate of 2.7×1017 V/cm2 has been made for the electric-field gradient at the position of the chlorine atom.
Conformation and Internal Rotation of Nitroaromatic Amines in Solution as Detected by Proton Magnetic Resonance. II. Polynitro Acetanilides
Authors: Weil J. A. , Blum A. , Heiss A. H. , Kinnaird J. K.
Published: January 2005

The proton NMR spectra of several N-acetyl-N-methyl polynitroanilines reveal the presence of two conformers. The conformer ratio has been studied for the picrylaniline in various solvents, and the rate of conformer interchange for this substance was measured in 1,4-dioxane. Chemical-shift studies of these and various related molecules have given additional information about the configuration of these molecules. It is concluded that the acetamide group is normal to the plane of the aromatic ring for the N-acetyl-N-methyl-2,4,6-trinitro and 2,6-dinitro anilines.
Nonempirical Calculations of the Isotropic Hyperfine Splitting Constants of 13C, 14N, and 17O in Simple Radicals
Authors: Chung Alice L. H.
Published: January 2005

The isotropic hyperfine splitting constants in ESR spectra for simple radicals 13C1H3, 14N1H2, and 17O1H have been calculated nonempirically by using a configuration-interaction method correct to the second order in the energy matrix elements. Included in the treatment are all the singly excited configurations plus certain types of doubly excited configurations. Each configuration is expressed in terms of the self-consistent-field molecular orbitals and virtual orbitals derived for the ground state. The molecular orbitals are expanded about a single center with an extended basis set of Slater-type orbitals.

The calculated hyperfine splitting constants for 13C, 14N, and 17O are found to be 2.7, 0.9, and −0.5 G, respectively, when all the virtual orbitals with symmetry species A1′ or A1 are used; the values are improved to 40.6, 19.0, and −35.4 G, respectively, when certain virtual orbitals with undesirable characteristics are excluded. Though not to be given serious consideration because of the nature of the wavefunctions employed, calculations for 1H are carried out and the values are found to range from −4 to −7 G.

Attention is called to the possible danger in using virtual orbitals indiscriminately for calculations on ground-state properties other than energy. Based on the experience gained from this work we suggest that only the orbitals that are better approximations to the excited-state molecular orbitals be used.
ESR and Optical Spectroscopy of ScO, YO, and LaO in Neon and Argon Matrices; Establishment of Their Ground Electronic States
Authors: Weltner W. , McLeod D. , Kasai P. H.
Published: January 2005

ScO, YO, and LaO were vaporized from the solid oxides at temperatures near 2500°K and trapped in neon and argon matrices at 4° and 20°K. ESR spectra of these matrices show that the ground states of all of the molecules are 2Σ. The measured magnetic parameters for the three molecules are as follows: ScO, g=2.00±0.01, A=2.01±0.01 kMc/sec; YO, g=2.003±0.002, A=0.803±0.003 kMc/sec; LaO, g=2.01±0.01, A=3.89±0.01 kMc/sec. The A values then yield nuclear hyperfine-structure separations (Δν) of 0.27, 0.03, and 0.52 cm−1, respectively, and explain the large splittings observed in the optical spectra of ScO and LaO.

The optical spectra of the matrices exhibit the two transitions A2Π←X2Σ and B2Σ←X2Σ observed in the gas spectra of these molecules. The bands are exceptionally broad and shifted in the matrix relative to the gas, much more so than in the matrix spectra of other transition-metal diatomic oxides. Illumination of the matrices with tungsten light leads to a gradual disappearance of the absorption bands and loss of color. The ESR and infrared signals are similarly affected. An explanation of this bleaching phenomenon is offered which involves diffusion and reaction of excited M—O molecules in the matrix. New bands appear in the LaO—neon matrix during illumination and are tentatively attributed to LaO molecules in more ``gas-like'' sites.
Flow and Diffusion of Gases in Porous Media
Authors: Mason E. A. , Malinauskas A. P. , Evans R. B.
Published: January 2005

A generalized treatment of gas transport in porous media is presented as developed on the basis of the ``dusty-gas'' model, a model in which a porous medium is described as consisting of uniformly distributed, giant molecules (dust) held stationary in space. The problem is broken down into a series of special cases which involve the various combinations of gradients in composition, pressure, and temperature.

Equations are given for the description of several well-known phenomena. These include isobaric, isothermal diffusion; diffusion under the influence of a pressure gradient; Poiseuille's flow equation, including the Knudsen minimum; the Kramers—Kistemaker effect; thermal transpiration; and the effect of pressure on the thermal-diffusion factor. The results are likewise applicable to capillaries by a suitable substitution for geometric parameters.
On the Determination of Thermal Accommodation Coefficients in the Temperature-Jump Region
Authors: Harris Robert E.
Published: January 2005

The usual temperature jump relating the thermal accommodation coefficient, the heat flux, gas pressure, and temperature discontinuity between solid and gas is deduced on the basis of mean-free-path kinetic theory using explicit assumptions. A new method of analyzing temperature-jump heat conductivity data to yield the thermal accommodation coefficient is presented.
Nuclear Spin State Equilibration through Nonmagnetic Collisions
Authors: Curl R. F. , Kasper Jerome V. V. , Pitzer Kenneth S.
Published: January 2005

For nonlinear molecules with equivalent identical nuclei an important pathway leading to equilibration of nuclear spin statistics isomers is provided by wavefunction mixing induced by the spin—rotation interaction and in some cases the spin—spin interaction. For CH4 this mixing is very large and provides for very rapid equilibration of the three spin statistics isomers. For asymmetric rotor molecules such as H2O and CH2O the rapidity of the equilibration is sensitive to the exact rotational energy level pattern. The spin—rotation mixing may be very important if there is an accidental near degeneracy of the right sort. Then most of the isomerization ``funnels'' through the near-degenerate levels.
Electronic Structure of the B2 Molecule
Authors: Bender Charles F. , Davidson Ernest R.
Published: January 2005

The low-lying electronic states of the B2 molecule have been investigated using configuration interaction. Eighty-one states were considered and the lowest state was found to be the 5Σu− (−49.14567 hartrees at re=2.95 bohrs.
Electronic Population Analysis of Molecular Wavefunctions
Authors: Davidson Ernest R.
Published: January 2005

A general method for carrying out population analysis of wavefunctions calculated with arbitrary basis sets is presented. The difficulties in defining orbital populations is discussed. Results are presented for the sequence BF, CO, and N2 which indicate that back-transfer of charge in the π bond cancels the normal transfer of the charge in the σ bond. Contrary to popular belief, the more electronegative element has the larger degree of hybridization in each case. The amount of promotion of 2s electrons is greater on the less-electronegative element, as expected.
Nuclear Relaxation in CHFO
Authors: MacLean C. , Mackor E. L. , Hilbers C. W.
Published: January 2005

The present paper deals with experiments on the nuclear relaxation of CHFO from −142° to −20°C. The relaxation is analyzed in terms of intra- and intermolecular interactions that induce the relaxation. The deuterated compound has likewise been investigated as the pure liquid and in dilute solution in hexadeuteroacetone.

Spin—rotation interaction is found to be the dominant relaxation mechanism of fluorine in the high-temperature region. At the lowest temperatures the relaxation is practically exclusively dipolar in origin; intramolecular dipolar interactions are dominant.

Quadrupolar relaxation of the deuterium nuclei manifests itself in the transverse relaxation rates of the fluorine spins.
Alternating Linewidth Effect in the ESR Spectra of Anion Radicals of Dinitromesitylenes and -durenes
Authors: Allendoerfer Robert D. , Rieger Philip H.
Published: January 2005

Accurate measurements of line positions in the ESR spectra of the aminodinitromesitylene, dinitroisodurene, dinitromesitylene, and dinitrodurene anion radicals have permitted calculation of the dynamic frequency shifts arising from modulation of the isotropic nitrogen hyperfine splittings. The results are in good agreement with the predictions of the ``two-jump'' model proposed by Freed and Fraenkel to explain the phenomenon of alternating linewidths observed in the spectra of such radicals. The effects of solvent composition on the ESR splitting constants and linewidths of the dinitrodurene and dinitroisodurene anions were studied in DMF—water mixtures. The observed increase in nitrogen splittings and decrease in methyl-proton splittings with increased water concentration is in agreement with previous theories, and the data may be fitted to a simple model assuming equilibrium between 1:1 solvent—solute complexes. The MI=±1 lines for both the dinitrodurene and dinitroisodurene anions were found to rapidly increase in width with increasing water concentration. The two-jump model was combined with the assumption of 1:1 solvent—solute complexes to develop a four-jump model for dinitro radical anions in mixed solvents. The four-jump model was found, however, to be incapable of explaining the rapid increase in linewidth observed. Possible sources of difficulty are discussed.
Rotational Relaxation of Molecular Nitrogen
Authors: Miller David R. , Andres R. P.
Published: January 2005

A supersonic free jet was probed to obtain a direct measure of the rotational relaxation time (τr) of nitrogen. Definition of an effective collision cross section (πσr2) for translational—rotational energy exchange in terms of τr, yields a πσr2 for nitrogen that increases with decreasing temperature faster than the viscosity cross section. Comparison of the experimental πσr2 with values obtained using thermal-conductivity data and the theory of Mason and Monchick yields good agreement.