bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Dependence of the Infrared-Active Optical Phonon Modes in Alkaline-Earth Fluorides
Authors: Ferraro J. R. , Horan H. , Quattrochi A.
Published: February 2004

The pressure dependence of the infrared-active optical phonon mode (νTO1) in alkaline-earth fluorides has been determined up to 45 kbar. The dependence is found to be less than the Raman-active optical phonon mode. The pressure dependence of the νTO1 mode is observed to decrease in the order CaF2>SrF2>BaF2, while the Raman mode remains rather constant with pressure. Grüneisen parameters have been determined and are compared with those obtained for AB-type crystals.
19F Shielding Tensors from Coherently Narrowed NMR Powder Spectra
Authors: Mehring M. , Griffin R. G. , Waugh J. S.
Published: February 2004

Coherent line-narrowing methods are used to reduce the dipolar width of the 19F resonance in a number of powdered solids, disclosing the powder patterns arising from chemical shift anisotropy. The principal elements of the shielding tensors are reported and compared with previous experimental and theoretical results. In certain cases it has been possible to use the averaging induced by high-temperature restricted rotation to assign the principal elements of the shielding tensor to directions in the molecular framework. In C6F6 the shielding tensor is axially symmetric within experimental error; σ‖–σ⊥ = 155 ppm, with the unique (‖) axis parallel to the molecular sixfold symmetry axis. In CF3CO>2−Ag+ we find σXX = − 3 ppm, σYY = − 67 ppm, σZZ = + 70 ppm, and 〈σ〉 = − 96 ppm referred to liquid C6F6. Here the Z axis is approximately along the C–F bond and the Y axis lies in the CCF plane.
Phase Diagram of Benzene to 35 kbar
Authors: Akella Jagannadham , Kennedy George C.
Published: February 2004

The phase diagram of benzene has been determined to 35 kbar. Two triple points, liquid-benzene I–benzene II and liquid-benzene II–benzene III, have been located. These triple points are at 12 ± 0.5 kbar and 204 ± 5°C, and 22.5 ± 0.5 kbar and 335 ± 5°C, respectively. The benzene I–benzene II phase boundary is slightly convex towards the temperature axis. We were unable to locate the boundary separating the fields of benzene II and benzene III; thus the coordinates of the upper triple points were estimated entirely from the break in slope of the melting curve. Above 40 kbar and 580°C benzene disassociates.
Preparation and Structure of Thallium and Silver Germanate Glasses
Authors: Riebling E. F.
Published: February 2004

Binary thallium and silver germanate glasses containing up to 36 mole % Tl2O or 25 mole % Ag2O were prepared by carefully heating mixtures of GeO2 and TlNO3 or Ag2SO4. The measured densities and refractive indices of these highly colored glasses were converted to molar volumes and molar refractivities. Comparison of the partial molar volumes and refractivities with those of alkali germanate glasses suggests the Tl+ and Ag+ are about as effective in causing the transformation of GeO4 tetrahedra to GeO6 octahedra as are K+ and Na+. The presence of intense color with Tl+ and Ag+ is related to their stronger polarizabilities and polarizing power compared to the rare-gas-type alkali ions. The onset of color at 15 mole % Tl2O and 4 mole % Ag2O may be related to a change of bonding from ionic to covalent for Tl+. This conclusion agrees with recent NMR findings for thallium borate glasses.
Electronic Structure and Electronic Spectrum of Nitrogen Dioxide. III Spectral Interpretation
Authors: Gangi R. A. , Burnelle L.
Published: February 2004

The excitation energies, potential-energy surfaces, and oscillator strengths computed in the previous paper are discussed in light of experimentally reported spectroscopic data, namely absorption, fluorescence, chemiluminescence, predissociation, photolysis, and the absence of phosphorescence. It is found that the main components of the visible spectrum are due to the transitions B21 ← 2A1, and B22 ← 2A1, with the B22 state being responsible for the observed fluorescence emission. The anomalous fluorescence lifetime is also discussed.
Vibrational Energy Distribution through Chemical Laser Studies. II. Fluorine Atoms plus Chloroform
Authors: Parker John H. , Pimentel George C.
Published: February 2004

Laser emission by HF from the UF6–CCl3H chemical laser system and by DF from the UF6–CCl3D system has been studied, the latter by the equal-gain temperature technique. For HF, υ = 2 → 1 and 3 → 2 transitions were observed, with P2–1(3) reaching threshold first at room temperature. For DF, υ = 2 → 1, 3 → 2, and 4 → 3 transitions were observed, with P3–2(4) reaching threshold first at room temperature. The abstraction reaction F+CCl3H(CCl3D) is about 8 kcal more exothermic than the corresponding methane reaction, which accounts for the appearance of the higher υ transitions. The DF zero-pressure, equal-gain temperature of 386 ± 10°K establishes k3 / k2 = 1.54, the same, within experimental uncertainty, as that observed for the less exothermic F+CD4 reaction.
Thorium Monosulfide: Heat Capacity and Thermodynamic Properties from 1–350°K. Re-evaluation of the Magnetic Entropy of Uranium Monosulfide
Authors: Flotow Howard E. , Osborne Darrell W. , Walters Robert R.
Published: February 2004

The heat capacity of thorium monosulfide was determined between 1 and 22°K by an isoperibol method and between 8 and 350°K by an adiabatic method. Below 4.2°K the heat capacity is represented by CP = 3.70 × 10−3T + 3.98 × 10−4T3J °K−1·mole−1, where the first term is the conduction-electron contribution and the second term the lattice contribution to the heat capacity. Values for the thermodynamic quantities CP°, S°, (H° − H0°) / T, and (G° − H0°) / T at 298.15°K are 47.72 ± 0.24, 69.81 ± 0.35, 32.60 ± 0.16, and − 37.21 ± 0.19 J°K−1·mole−1, respectively. The entropy of formation at 298.15°K is − 15.46 ± 0.47 J°K−1·mole−1, and an estimated value for the Gibbs energy of formation at 298.15°K is − 430 kJ mole−1. The magnetic entropy of uranium monosulfide associated with the ferromagnetic transition at 180.1°K was previously estimated as 6.8 J°K−1·mole−1 but has been re-evaluated as 8.8 ± 0.4 J°K−1·mole−1. The re-evaluation was based upon a new estimate of the lattice heat capacity of uranium monosulfide from the heat capacity of thorium monosulfide and a corresponding-states calculation. These calculations also lead to the conclusion that the coefficient γ in the conduction-electron contribution to the heat capacity of uranium monosulfide above the ferromagnetic transition is only 59% of the value near 0°K.
Electron Paramagnetic Resonance Spectrum of O2(1Δg)—Its 17O Hyperfine Coupling and Electronic and Rotational g Values
Authors: Arrington C. Anthony , Falick Arnold M. , Myers Rollie J.
Published: February 2004

The 17O hyperfine coupling was measured for O2(1Δg) in its J = 2 angular momentum state. The coupling constant 2gIμNμB〈Σilzi / ri3〉 was measured to be − 424 ± 1 MHz. From this value we can follow Harvey's convention and determine 〈1 / rl3〉 = 39.6 × 10−24cm−3. The previous work by Miller et al. on O2(3Σg−) can be used to determine 〈1 / rs3〉 = 43.6 × 10−24cm−3. Even though these two values refer to different electronic states, they are in the same ratio that Harvey found for O(3P), but they are both appreciably larger than the values he found for O(3P). The gJ values were determined for both the J = 2 and J = 3 angular momentum states. From these values we obtain gL = 0.999860 and gr = − 1.70 × 10−4. The gL value is very close to the recent determination of Miller, but the gr value does not agree with Miller's work.
Effect of Orbital Transformations on Pair-Correlated Systems. I. General Formalism
Authors: Venanzi Thomas J. , Sanders William A.
Published: February 2004

The effects of small transformations of the occupied orbitals in pair-correlated systems are investigated formally for the special case of two doubly occupied molecular orbitals which belong to the same non-degenerate representation of the molecular symmetry group. General expressions are derived for the changes in the electronic energy and coefficients of the expanded wavefunction due to the transformation. The effects of the transformation on the pseudonatural orbitals of the correlated pair and their occupation numbers are also considered.
Transport Properties of a Gas of Diatomic Molecules. II
Authors: Curtiss C. F.
Published: February 2004

Explicit expressions, valid in the classical limit, are derived for certain sums and integrals of the cross sections which occur in the expressions for the transport coefficients of a low density gas of rotating, non-vibrating, diatomic molecules. The integration is over the angle of deflection and the sums are over the rotational quantum numbers of the molecules after the collision. The integrand is the product of the differential cross section and an arbitrary function of the angle of deflection and the inelasticities, i.e., the gain in the rotational energy of a molecule.
Infrared Spectrum and Structure of the SO2− Radical Ion
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

When a sample of SO2 in a large excess of argon is codeposited at 4 or at 14°K with an atomic beam of an alkali metal, prominent new absorptions appear near 500 cm−1 and between 975 and 1100 cm−1. The pattern of absorptions is somewhat dependent both upon the alkali metal and upon the temperature at which the sample is deposited. Product absorptions which appear at 495, 985, and 1042 cm−1 in samples containing a small concentration of cesium atoms have been demonstrated to be contributed by a single species, shown by isotopic substitution studies to contain one sulfur and two oxygen atoms. A slight splitting in the absorptions of the mixed oxygen isotopic species indicates that the two oxygen atoms are not symmetrically equivalent, either because of a site perturbation or because of a slight nonequivalence of the two S–O bonds. The absorptions have been assigned to the three SO2− vibrational fundamentals of a charge-transfer complex in which the residual interaction of the cation is sufficiently small that all of the vibrational data can be fitted within experimental error without considering the motion of the cation. The data are consistent with an O–S–O valence angle of 110° ± 5°. The S–O stretching force constant is significantly lower than that of SO2, consistent with the addition of an electron to an orbital which is antibonding between the sulfur and two oxygen atoms.
Crystal Structure Refinement of SrMoO4, SrWO4, CaMoO4, and BaWO4 by Neutron Diffraction
Authors: Gürmen Erdogan , Daniels Eugene , King J. S.
Published: February 2004

The crystal structures of CaMoO4, SrMoO4, SrWO4, and BaWO4 have been refined from neutron diffraction data taken in the (h0l) and (hhl) zones. Oxygen position refinement is started from the parameters proposed by Sillén and Nylander and results in an improvement of over an order of magnitude in the oxygen coordinates. A comparison of coordinates for the different compounds shows several systematic differences.
Polarization State of Light Scattered from Dense Fluids
Authors: Blum L. , Frisch H. L.
Published: February 2004

Using Racah algebra, we have extended our previous work on elastically scattered light to correlated systems and complex polarizabilities. The results show that rotation effects due to orientational correlations in some nonoptically active fluids are possible. For optically active fluids, the analysis could provide information about the first few (up to order R2) moments of the expansion of the two-body correlation function. An analysis of the order of magnitude of these effects is carried out.
Vacuum-Ultraviolet Photolysis of GeH3Cl; the Infrared Spectrum of Matrix-Isolated GeH2Cl
Authors: Isabel Roy J. , Guillory William A.
Published: February 2004

The vacuum-ultraviolet photolyses of GeH3Cl and GeD3Cl in argon and carbon monoxide matrices have been performed between 4 and 25°K. The major product of photolysis appears to be the free radical species GeH2Cl, and possibly some GeHCl as a result of secondary photolysis. Evidence that H atom detachment plays a major role in the photodissociation process is obtained by the formation of HCO in carbon monoxide matrix experiments. All six fundamental vibrational frequencies of GeH2Cl are observed and assignments are made for ν2 (GeH2valence bend), ν3(GeCl stretch), ν4(GeH2wag), and ν6(GeH2twist). Tentative assignments for the GeH stretching frequencies ν1(sym stretch) and ν5(antisym stretch) are made. A normal coordinate calculation using a six-constant valence potential function suggests that the molecule is pyramidal with approximate sp3 hybridization. The structure, bonding, and thermodynamlc properties of GeH2Cl are also discussed and compared with other Group IV species.
Chemical Oscillations around Steady States of Cooperative Linear Macromolecules
Authors: Schneider Friedemann W. , Rawlings Philip K.
Published: February 2004

This paper presents a theoretical investigation of the kinetic behavior of a system of linear macromolecules undergoing an irreversible quasiphase transition. A one-dimensional Ising lattice with nearest-neighbor dependent rate constants is used to represent the macromolecular system. A steady state of intermediate sequence concentrations is established by a constant flow of reactant from the outside. It is shown for the first time that damped chemical oscillations in this system may occur around the steady state only if the quasiphase change has a minimum cooperativity. The chemical oscillations arise as a consequence of both the quasiautocatalytic nature of the transition and the irreversibility of the kinetic processes. The effect of the degree of cooperativity on the period of oscillation, the damping factor per period, the rate of reactant in-flow, and the steady state concentrations are discussed.
Analysis of the 2973-Å Absorption System of Phosgene
Authors: Moule D. C. , Foo P. D.
Published: February 2004

The near-ultraviolet absorption of phosgene has been assigned to a π* ← n, 1A2 ← 1A1, electronic transition from vapor-phase spectra recorded under conditions of high resolution and low temperature. Progressions in ν1′, ν2′, ν3′, ν4′, and ν4″ have been identified in the spectrum and have been analyzed in terms of vibronic transitions between a planar ground and a nonplanar excited state. A barrier height of 3170 cm−1 and a nonplanar equilibrium angle of 32.5° were calculated for the upper state from a fit of the energy levels of a Lorentzian–quadratic potential function to the observed levels of ν4. The false origin, 401, of the spectrum has been assigned to the band at 33 631 cm−1. An oscillator strength of f = 1.04 × 10−3 has been obtained for the A21 ← A11 transition.
Cross Section for Double Ionization by Electron Impact: Li+, Na+, K+
Authors: Tripathi D. N. , Rai D. K.
Published: February 2004

The cross sections for double ionization by electronic impact on Li+, Na+, and K+ ions have been calculated using the Grysinski's semiclassical formula. Good agreement is obtained between calculated results and experiment in case of Li+, and it is expected that the results for Na+ and K+ would also be reliable. The ratio (σ+ / σ++) (single ionization/double ionization) is also calculated and compared with the experimental results and theoretical predictions.
Effect of Pressure on Molecular Motions of Bromobenzene and Toluene-d3 in the Liquid State
Authors: Parkhurst H. J. , Lee Y. , Jonas J.
Published: February 2004

The pressure dependences of the proton spin–lattice relaxation times have been measured at 30°C in liquid bromobenzene and its mixtures with bromobenzene-d5 up to 2.5 kbar, and in liquid toluene-d3 and its mixtures with toluene-d8 up to 4.5 kbar. The separation of the intramolecular and intermolecular contributions to proton dipolar relaxation allowed us to study the effect of pressure on reorientational and translational motions of the molecular liquids investigated. Activation volumes for the intramolecular and intermolecular T1; and the rotational and translational correlation times were calculated. The data obtained indicate that the molecular shape seems to play a decisive role on the degree of coupling between the rotational and translational motions of these two model liquids. The effect of the difference in the dipole moments on this coupling seems to be less important.
Transformation Properties of Hermite–Gaussian Functions
Authors: Živković T.
Published: February 2004

Transformation properties of Hermite–Gaussian functions against the rotation in the xy plane are considered. The formulas obtained can be used to make the basis set in a variational approach more flexible, and to improve the convergence.
Many-Body Theory of Autoionization
Authors: Yaris Robert , Boehm Richard
Published: February 2004

By regarding autoionization as the outgoing part of a resonant ion–electron scattering event, it is possible to employ a previously developed many-body theory of elastic and inelastic ion–electron scattering to develop a many-body theory of autoionization. This approach expresses the autoionization probability amplitudes in terms of the ion's one-particle Green's function and response function which are determined self-consistently.
Far-Ultraviolet Spectra of Fluoroethylenes
Authors: Bélanger G. , Sandorfy C.
Published: February 2004

The vacuum ultraviolet spectra of the complete series of fluoroethylenes were measured from 2000 to 1150 Å under moderate resolution. The π*←π transitions are easily identified in all the spectra. In most cases their maxima are only slightly displaced from their position in ethylene, but a very large hypsochromic shift is found in going from the tri- to the tetrasubstituted derivative. Three Rydberg series are observed in all the spectra, converging to the π ionization potential. They all exhibit vibrational fine structure dominated by C=C stretching and twisting vibrations. In the highly fluorine substituted ethylenes the first Rydberg band is well separated from the π*←π band (at about 1900 Å) as in the highly alkyl substituted derivatives. There is no evidence for transitions of σ electrons in this part of the spectrum except perhaps at the high frequency end of the range (1200 Å).
Thermal Electron Attachment to Nitrous Oxide
Authors: Wentworth W. E. , Chen E. , Freeman R.
Published: February 2004

Thermal electron attachment to nitrous oxide was investigated in the range −66 to 215°C. The attachment was found to be dissociative in nature with an activation energy of 10.4±0.4 kcal/mole. The activation energy is thought to arise from electron attachment to molecules thermally excited primarily in the bending mode. In an attempt to explain the activation energy a simple Morse function was employed. Potential energy as a function of internuclear distance for both N2O and N2O− was generated at different N2O bond angles. In this manner a three-dimensional surface for the reaction, N2O (linear)→N2O (bent)→ lim +e−N2+O−, was obtained. The potential surface has a minimum at a bond angle ∼160°. The electron affinity of N2O is estimated at 6.2±4 kcal from the calculated N2O− potential-energy surface. This is in general agreement with other reported values.
Spin-Orbit Contribution to the Zero-Field Splitting of the Oxygen Molecule
Authors: Zamani-Khamiri O. , Hameka H.F.
Published: February 2004

The spin-orbit contribution to the zero-field splitting of the oxygen molecule is calculated using the complete spin-orbit Hamiltonian. All calculations are performed at the equilibrium internuclear distance R=2.282 a.u. The spin-orbit contribution to D is found to be 0.3125 cm−1 which is about 7% of the total D value.
On Numerical Methods for the Improvement of Appearance Potential Measurements
Authors: Giessner B. G. , Meisels G. G.
Published: February 2004

The deconvolution of hypothetical and experimental ionization efficiency curves by the energy distribution difference (EDD) technique and by Fourier transforms was examined. The EDD method was found to be capable of removing the contribution from the high energy tail of the electron energy distribution, but did not lead to appreciable improvement in the resolution of fine structure for conventional electron guns which also suffer from energy broadening factors other than filament temperature. The Fourier transform approach was found to be relatively insensitive to the details of the electron energy distribution, but highly dependent on noise. A simple smoothing procedure based on a three-point least-squares polynomial was found to make possible the recovery of fine structure. Deconvolution of the experimental xenon ionization efficiency curve could be achieved with a nominal width at half-height of the quasielectron energy distribution of ≈ 0.17 eV as judged from the width of the line corresponding to the 6d autoionizing level.
uv Spectra of Mercuric Halides in Aromatic Solvents
Authors: Eliezer I. , Avinur P.
Published: February 2004

The absorption spectra of mercuric halides in a series of aromatic solvents, as well as in several other organic solvents, were measured. It is shown that a relationship exists between the frequency of the spectral bands obtained and the ionization potentials of the corresponding aromatic solvents. This, combined with other correlations presented in the paper is strong evidence for the existence of charge transfer interactions between mercuric halides and aromatic hydrocarbons, indicating π complexes.
Study of Collisions between Low-Energy N+ and N2: Reaction Cross Sections, Isotopic Compositions, and Kinetic Energies of the Products
Authors: Maier William B. , Murad Edmond
Published: February 2004

Reactive collisions between N+ and N2 have been studied, and cross sections for the production of N2+ have been measured for initial kinetic energies, Ec. m., in the center-of-mass system between 1 and 70 eV. The kinetic energies of the product N2+ have been determined. Isotopically labeled reactants were used, and the cross sections for producing N2+ containing different combinations of isotopes have been measured. The reaction N++N2→N2++N is found to proceed by both atom and electron transfer. For Ec. m. ≲ 11 eV, the cross sections for electron and atom transfer are roughly equal, but at higher Ec. m. the atom transfer cross section is considerably smaller than the electron transfer cross section. The kinetic energy −Q transferred into internal energy of the products is considerably larger than the minimum required for Reaction (1) to proceed. For the electron transfer process, the values determined for −Q are between 3 and 9.8 eV. The values of −Q found for the processes associated with atom transfer are between 3 and 50 eV. For Ec. m. ≳ 24 eV, it appears that a free electron may be produced by N++N2→N2++N++e. A model for the reactions occurring in collisions between N+ and N2 is developed and shown to be in qualitative agreement with the observations.
Intermolecular Potential and Ferroelectric Transitions in Hydrogen Halides
Authors: Tsang Tung , Shaw Elvira L.
Published: February 2004

A semiempirical molecular field approximation has been developed for the solid hydrogen halides. Including only the first- and second-order terms of the spherical harmonics expansion, the intermolecular potential may be characterized by two arbitrary parameters. The parameters were then evaluated from the infrared data. With this intermolecular potential, it is then possible to estimate the dielectric and NMR correlation times, the ferroelectric transition temperature, the heat of transition, etc. These calculations are in fair agreement with the experimental data. The correlation effects may be more important for ferroelectrics than for ferromagnets.
Electron Paramagnetic Resonance of Magnetically Dilute Cupric (3d9, 2D) Ion in Single Crystals of Zinc 3-Pyridine Sulfonate
Authors: Schatz George C. , McMillan J. A.
Published: February 2004

Single crystals of cupric 3-pyridine sulfonate diluted in the diamagnetic zinc compound were prepared and observed for paramagnetic resonance. The symmetry of the magnetic complex is orthorhombic, with two of the g values only slightly different. The ground state of the ion is dz2 which exhibits practically no orbital angular momentum along z. An analysis of the cupric hyperfine structure at room temperature has been performed, arriving at a value of the polarization of the core in very good agreement with the theoretical estimate. No nitrogen superhyperfine structure is resolved at room temperature, although experiments at 77°K show conclusively interaction with two equivalent nitrogens, which is interpreted in detail.
Infrared Absorption of Diatomic Polar Molecules in Liquid Solutions
Authors: Robert D. , Galatry L.
Published: February 2004

A theory of the infrared absorption spectrum of light dipolar diatomic molecules dissolved in simple liquid solvents is presented and discussed. This is done by keeping the quantum character of the orientational degrees of freedom of the absorbing molecules. Moreover, the low frequency part of the density fluctuations around this molecule is taken into account by introducing an almost static polarizing action which strongly disturbs the free rotation wavefunctions and therefore eliminates from the zeroth order of the calculation the usual selection rules of the diatomic rotator. The presence of this polarization is suggested by a study of the factorization of the density operator; the fluctuations of the true coupling of the active molecule with the liquid in respect to the quasistatic coupling considered above implies a broadening of all the possible transitions of the active molecule already polarized. Models are examined to represent the correlation of this fluctuation. An example of HCl molecule dissolved in liquid CCl4 is then studied, and this leads to a satisfactory comparison of the theoretical results with the experimental band profiles.
Neutron Scattering by Small Chainlike Molecules Dispersed in CS2
Authors: Deniz U. K. , Jannink G. , Taupin D.
Published: February 2004

The energy spectra of neutrons scattered by dilute solutions of chainlike molecules can throw light on the various types of molecular movements. Such a scattering experiment has been carried out using two low molecular weight (Z=3 and 9) polymers of the poly-oxy-ethylene type dissolved in CS2, as scattering samples. The quasielastic part of the energy spectra has been analyzed in terms of the motion of the center of mass and that of the chain segments. The variation with Z of the diffusion coefficient D (connected with the center of mass motion) indicates that the solvent—solute system interacts in the free draining limit. The constant a (related to the random motion of the chain segments) varies as qγ with the exponent γ increasing with Z. It is also found that in both the cases studied, the value of γ is smaller than 4, the value predicted by de Gennes' theory for the case of molecules for which Z tends to infinity. The inelastic part of the spectrum has been analyzed in terms of the Krieger—Nelkin approximation with a single effective mass. The effective mass obtained in the case of both scattering samples is much less than the real mass of the chain perhaps showing that the neutrons are sensitive to the rotation of the (CH2) groups. The agreement between the theory and experiment is not satisfactory in the inelastic case, indicating the need for a more sophisticated theory than the one used in our analysis.
Vibrational Spectra and Conformation of the Cyclopentyl Fluoride Ring
Authors: Wertz D. W. , Shasky W. E.
Published: February 2004

The infrared and Raman spectra of fluorocyclopentane in the wavenumber range 1300–30 cm−1 is reported. The skeletal vibrations are assigned. None of the skeletal modes were observed as doublets and the pseudorotational fundamental frequency is quite low, 59 cm−1. It was concluded, therefore, that the experimental results are consistent with only one stable conformer.
Structure and Symmetry Properties of Correlation Functions in the Sinanoğlu Nonclosed-Shell Many-Electron Theory
Authors: Westhaus Paul
Published: February 2004

The general nonclosed-shell many-electron theory of Sinanoğlu is analyzed to show the structure of the correlation functions which arise. A particular representation of these functions as projections from the exact many electron wavefunction is developed. The origin of the three distinct types of correlation effects—internal, semi-internal, and all external—present in open shell states is discussed. The representation of the correlation functions as projections is employed to examine their transformation properties under the operations of the symmetry group of the Hamiltonian.
Ion—Defect Pair Dissociation in Compensated Crystalline Lattices
Authors: Ford Robert L. , Fong Francis K.
Published: February 2004

A theory is presented to describe ionic distributions in compensated crystalline lattices in the intermediate temperature region in which dissociation of ion—defect pairs becomes significant. A conceptual model of an assembly of independent ion—defect pairs in equilibrium with unassociated ions and defects is introduced. The problem of volume exclusion evolves as a natural consequence in the interpretation of the model. Calculations for the KCl:Sr2+, and NaCl:Sr2+ systems are displayed and related to transport properties.
Infrared Spectrum of the BrHBr− Ion Isolated in an Argon Matrix
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

Infrared absorptions assigned to v3, (v3+v1), and (v3+2v1) of BrHBr− have been observed in samples of HBr in an argon matrix which have been subjected to 1216-Å photolysis or which have been co-deposited with an alkali metal atomic beam and then subjected to mercury-arc radiation. The corresponding experiments on deuterium-enriched samples support this identification. Mechanisms by which BrHBr− is produced in these experiments are considered in detail. An atomic mechanism leading to the stabilization of the uncharged species is shown to be inadequate. However, several ionic processes may contribute to the observed production of the anion. As previously postulated, dissociative electron attachment to (HBr)2 may occur. In addition, it is necessary to postulate the production of Br− by various charge-transfer processes, followed by the reaction of Br− with HBr. Analysis of the infrared spectra of BrHBr− and of BrDBr− indicates that the vibrational potential function must include significant contributions from both cubic and quartic terms.
ESR Study of the Alkyl Derivatives of DPPH
Authors: Erö-Gécs M. , Hegyháti M.-M.
Published: February 2004

The alkyl-substituted compounds of DPPH were investigated by ESR methods. Accurate values of the splitting constants were determined by calculating the experimental spectra. The activation energy of the hindered oscillation of the methylene group, as evaluated from the temperature dependence of the ethyl derivative, was found to be 910 cal/mole. Theoretical investigations, using the Hückel, McLachlan, and Löwdin method show an inversion in the spin density ratio at the two nitrogen nuclei.
Correlation of Pi-Electron Density with Vibrational Frequencies of Linear Polyenes
Authors: Gavin R. M. , Rice Stuart A.
Published: February 2004

Distributions of fundamental vibrational frequencies for linear polyenes are estimated from a transferable set of force constants. Particular attention is focused on reproducing observed experimental spectra in the carbon—carbon double-bond stretching region, 1400–1650 cm−1. Stretching force constants for carbon—carbon bonds are deduced from fractional pi-bond orders, whereas interaction constants for these stretching motions are inferred from the mutual polarizabilities of the bonds. Calculated distributions for vibrational frequencies are in agreement with experimental data only if long-range interaction constants are employed. The results obtained in the present study are compared to results obtained in previous studies where the long-range interaction constants were assumed to be zero. Predictions of the vibrational spectra of the first excited electronic states of linear polyenes are provided along with a discussion of the types of vibrational frequencies which are expected to undergo significant changes on electronic excitation.
Single Crystal Electron Spin Resonance Spectra of the 12-Tungstoferrate(III) Ion
Authors: So Hyunsoo , Pope Michael T.
Published: February 2004

Electron spin resonance spectra of 12-tungstoferrate (III) anion diluted into potassium 12-tungstoborate were measured and analyzed. ESR spectra are attributed to the ferric ion in a tetrahedral site. Parameters determined are g=2.00±0.01, a=86 G, D=− 103 G, F=− 18 G, and E=− 16 G.
Comparison of Shear and Conductivity Relaxation Times for Concentrated Lithium Chloride Solutions
Authors: Moynihan C. T. , Balitactac N. , Boone L. , Litovitz T. A.
Published: February 2004

Shear viscosity measurements over the temperature interval 23 –− 124 °C (5×10−2– 108 P) and shear impedance measurements at 88 MHz over the interval −75–−130°C have been performed for concentrated aqueous lithium chloride solutions in the concentration range R=4.49 – 5.77 where R is the mole ratio of water to salt. Average shear relaxation times, 〈 τs 〉, have been calculated from these results and compared with average conductivity relaxation times, 〈 τσ 〉, reported previously by Moynihan, Bressel, and Angell. 〈 τs 〉 and 〈 τσ 〉 are within 30% of one another at the low viscosity end ( ∼104 P) of the range of comparison, but at higher viscosities the 〈τs 〉/〈τσ 〉 ratio becomes significantly larger than unity (2–3 at the highest viscosities for which data are available). Estimated 〈τs 〉/〈τσ 〉 ratios for other ionic liquids suggest that the occurrence of 〈τs 〉/〈τσ 〉 ratios greater than unity at high visosities may be a common phenomenon. Description of the shear relaxation process for concentrated LiCl—H2O solutions is found to require a fairly broad, asymmetric (Cole—Davidson) distribution of relaxation times.
Nuclear Magnetic Relaxation in t-Butanol: Molecular and Internal Methyl Rotation
Authors: Margalit Y.
Published: February 2004

The correlation function of the randomly molecular reorientation, and internal (around some bond in the molecule) rotation, is calculated and discussed, assuming that both processes in the liquid are diffusional. The contribution of the internal rotation to the nuclear magnetic relaxation process is effective only when its rate is about the same order of magnitude as the molecular one. When the internal rotation is very much slower, or very much faster compared with the molecular rate of rotation (in the extreme narrowing limit), then its correlation time vanishes in the expression for the spectral density. Only when the ratio of the internal rotation correlation time τc′ to the molecular reorientation correlation time τc is between about 10 to 0.1, is it possible to obtain information about the internal rotation in the molecule from magnetic relaxation measurements. T1(D) of the two deuterated species of tert-butanol, (CH3)3–COD and (CD3)3–COH were measured, and by applying the formalism of the combined correlation function, it was possible to separate the correlation times for the molecular and the internal methyl rotation.
Emission Cross Sections of CO by Electron Impact in the Interval 1260–5000 Å. I
Authors: Ajello Joseph M.
Published: February 2004

Emission cross sections and band emission probabilities have been measured for the fourth positive system (A1Π→X1Σ+) and the Cameron system (a3Π→X1Σ+) of CO and the first negative system (B2Σ+→ X2Σ+) and the comet tail system (A2Π→X2Σ+) of CO+ by electron beam excitation of CO from threshold to 300 eV. Excitation cross sections have been measured for CI, CII, and OI multiplets produced by dissociative excitation of CO. A comparison of the measured emission probabilities with theoretical values based on Franck—Condon factors for direct excitation was made. Molecular branching ratios were used to extend the optical calibration from the blackbody region to the vacuum ultraviolet.
Molecular Dynamics Study of Liquid Water
Authors: Rahman Aneesur , Stillinger Frank H.
Published: February 2004

A sample of water, consisting of 216 rigid molecules at mass density 1 gm/cm3, has been simulated by computer using the molecular dynamics technique. The system evolves in time by the laws of classical dynamics, subject to an effective pair potential that incorporates the principal structural effects of many-body interactions in real water. Both static structural properties and the kinetic behavior have been examined in considerable detail for a dynamics ``run'' at nominal temperature 34.3°C. In those few cases where direct comparisons with experiment can be made, agreement is moderately good; a simple energy rescaling of the potential (using the factor 1.06) however improves the closeness of agreement considerably. A sequence of stereoscopic pictures of the system's intermediate configurations reinforces conclusions inferred from the various ``run'' averages: (a) The liquid structure consists of a highly strained random hydrogen-bond network which bears little structural resemblance to known aqueous crystals; (b) the diffusion process proceeds continuously by cooperative interaction of neighbors, rather than through a sequence of discrete hops between positions of temporary residence. A preliminary assessment of temperature variations confirms the ability of this dynamical model to represent liquid water realistically.
Excimer Delayed Fluorescence of Compressed Naphthalene Crystals
Authors: Beardslee R. A. , Offen H. W.
Published: February 2004

The compression of naphthalene crystals (to 30 kbar) at 77°K irreversibly, defects in the lattice. These defects capture singlet and triplet excitons, leading exclusively to excimer and delayer excimer fluorescence. Triplet trap depths of ∼600 cm−1 at 1 atm and ∼700 cm−1 at 30 kbar are estimated from the temperature dependence of the delayed excimer fluorescence. A wide distribution of singlet trap depths and excimer conformations is indicated by the pressure modifications of the excimer fluorescence band.
Optical Constants of Simple Molecular Crystals. II. Results for Kr and Xe
Authors: Scharber S. R. , Webber S. E.
Published: February 2004

The vacuum uv reflection and transmission spectra of unannealed films of Kr and Xe at 20.4°K have been obtained, and values of the optical constants (n and k) and the real and imaginary part of the dielectric constant (ε1 and ε2) determined. The total oscillator strength for the transition to the n=1 Γ (3/2), Γ(1/2) exciton states has been found to be less than than that of the analogous P13, P11←S01 transition in the gas phase. It has also been found that the ratio of the absorption strength due to the Γ(3/2) exciton to that of the Γ(1/2) exciton is larger than the comparable gas-phase value. These data are taken to show that the exciton excited orbital is more diffuse than the gas-phase atomic orbital.
Density Gradient Measurements of O2 Dissociation in Shock Waves
Authors: Breshears W. D. , Bird P. F. , Kiefer John H.
Published: February 2004

The dissociation of O2 in mixtures with He, Ar, Kr, and Xe has been studied behind incident shock waves in the temperature range 4000–8500°K. Using a laser-beam deflection technique, postshock density gradients were measured on a time scale such that vibrational relaxation and the onset of dissociation are resolvable. The density gradient profiles exhibit a highly characteristic local minimum immediately following the period of vibrational relaxation, at times which correlate well with the induction periods observed by others. The magnitude of the density gradient at this point is interpreted as a measure of the initial dissociation rate, i.e., the rate corresponding to conditions of complete vibrational equilibrium with no dissociation. Rate coefficients thus obtained exhibit a degree of precision unmatched in previous dissociation studies, and agree well in magnitude and temperature dependence with other reported results. Values of kO2 -M, the rate coefficient for O2 dissociation due to O2–M collisions, were determined for M=He, Ar, Kr, and Xe from measurements with mixtures containing 2.5%, 5%, and 10% initial O2. For O2- Kr collisions the value kO2- Kr=7.87×1013 exp (− 104 800/RT) cc/mole·sec, with R in calories per mole·degree, is obtained, with kO2- Xe≅1.6 kO2-Kr, kO2- Ar≅kO2-Kr and kO2-Xe〉kO2- He〉kO2-Kr. The value kO2-O2≅9 kO2-Kr was obtained independently from data for four different inert diluents, supporting the validity of the linear mixture formula for collision partners in O2 dissociation. The character of the density gradient profiles at later times suggests a higher rate coefficient for collisions with oxygen atoms.
Ising Chain with Several Phase Transitions
Authors: Theumann W. K. , Ho/ye J. S.
Published: February 2004

The one-dimensional spin-½ Ising model with very long-range ferromagnetic interaction and first and second neighbor antiferromagnetic interactions is solved exactly in a direct magnetic field. A study of the finite temperature behavior confirms the existence of up to four first-order phase transitions ending in classical critical points. We find a confluence of three critical lines at a ``tricritical'' point with exponents β=14 , δ=5, γ=γ′=1,α=0, and α′=12. We find also a confluence of four critical lines at a ``tetracritical'' point with exponents β=14, δ=7, γ=γ′=1, α=0, and α′=23. We show the existence of triple lines and ``quadruple'' lines, along which three or four phases are simultaneously in contact with each other, respectively. For some special values of the interaction strengths, five phases are in contact with each other at a ``quintuple'' point. We remark that our ``multiple'' lines and ``multicritical'' points are not ``true'' multiple lines and multicritical points but that they would be so in a somewhat extended model. This model satisfies a generalized form of the ordinary phase rule of Gibbs. In distinction to various models considered recently, our model does not exhibit a singular phase-boundary diameter.
Photoelectron Emission Spectroscopy of Solutions: An Interpretation
Authors: Delahay Paul
Published: February 2004

The process of photoelectron emission (PEE) by solutions is decomposed into two steps: generation of electrons in unbound states in solution by irradiation; escape of unbound electrons into the gas above the solution. The transition rate for the first step is expressed in terms of the photon energy and the energy for transition to the continuum. The complete absorption band for bound-unbound transitions in solution is calculated. Experimental PEE currents for different emitters (solvated electrons in liquid ammonia or hexamethyl phosphoric triamide, ferrocyanide in water) vary linearly with photon energy after normalization to a constant transition rate. This result is interpreted by assuming that unbound electrons undergo a random walk in solution and lose their kinetic energy at a rate inversely proportional to their speed. The Schottky effect on PEE is also interpreted.
Structure of Dielectric Fluids. I. The Two-Particle Distribution Function of Polar Fluids
Authors: Nienhuis Gerard , Deutch J. M.
Published: February 2004

A molecular fluid of identical molecules with a rigid dipole moment in an arbitrarily shaped volume is considered. The volume may or may not be embedded in a dielectric continuum. It is shown that when an arbitrary external field is applied, the constitutive relation P=(ε−1)/4 πE between the local polarization and the local macroscopic electric field is valid under some completely acceptable restrictions. In the establishment of this relation a crucial role is played by a long-range part of the two-particle correlation function, for which an explicit expression is obtained. One term in this long-range part is explicitly dependent on the shape of the sample volume and on the surroundings. The resulting dielectric constant of the molecular fluid can be formally expressed in only the local interactions of the molecules and is thus independent of the surroundings and the shape of the sample.
Viscous Liquids and the Glass Transition. III. Secondary Relaxations in Aliphatic Alcohols and Other Nonrigid Molecules
Authors: Johari Gyan P. , Goldstein Martin
Published: February 2004

The dielectric permittivity and the dielectric loss factor of 5-methyl-3, 4-methyl-3 and 3-methyl-3-heptanol, n- and iso-butanol, 1,2-propanediol, dimethyl and diethyl phthallate, and 3-methylpentane have been measured from 50 to 105 Hz and from −196 to about 20°C above their respective glass transition temperatures. The glass transition temperature Tg of these substances, several more isomeric octanols, and 1-phenyl-1-propanol have been measured by differential thermal analysis. All substances except for 3-methylpentane and iso-butanol show either a well-defined secondary relaxation peak in tanδ, or a clear indication of the presence of a secondary relaxation below their Tg's. Arrhenius plots for the α-relaxation process of the isomeric octanols are linear with an activation energy of 16–18 kcal/mole, while for other substances they are nonlinear with the activation energy changing from 30 to 70 kcal/mole. The Arrhenius plots for the secondary relaxations are linear and have an activation energy of 4–8 kcal/mole. It is pointed out that the presence of a spectrum of relaxation times in liquids near Tg is not necessarily concomitant with non-Arrhenius behavior. It is concluded that the presence of secondary relaxations should be considered as a characteristic property of the liquid in or near the glassy state, and do not require specific intramolecular mechanisms for their existance.
Viscoelastic Relaxation in Hydrated Melts
Authors: Darbari G. S. , Richelson M. R. , Petrucci S.
Published: February 2004

Measurements of longitudinal absorption for the system Ca(NO3)2·3.2H2O reveal the presence of a relaxation process. This relaxation is viscoelastic, i.e., the liquid is transformed into a pseudoglass. Shear velocity measurements conform the appearance of a viscoelastic relaxation with the condition τv≈τs in this system.
Mutual Orientations of the Principal Axes of the Electric-Field Gradient Tensors on 14N and 81Br by Combined Zeeman-Effect Measurements in a Single Crystal of p-Bromoaniline
Authors: Colligiani A. , Ambrosetti R. , Cecchi P.
Published: February 2004

The Zeeman effect of the nuclear quadrupole resonance of both 14N and 81Br nuclei in a single crystal of p-bromoaniline was studied. The precision of the technique used here is far greater than that of the few previous works in this field. Measurements were made by means of a newly designed spectrometer, working at both 14N and 81Br NQR frequencies, in which the radio-frequency assemblies could be interchanged without affecting the crystal position. The relative orientation of the electric-field gradient tensors at the sites of the nitrogen and bromine nuclei were directly determined. The results are interpreted in terms of known relations between the orientations of the field gradient tensor and the bond directions. The conclusion reached is that the amino group should be nearly coplanar with the benzene ring. Also observed was a large effect on line intensity as a function of the orientation and intensity of the static magnetic field H0 arising from nuclear dipole-dipole coupling between 14N and the 1H nuclei of the amino group.