bluuebunny/crossref_metadata_2025 huggingface dataset:
Configurational Excitations in Condensed Matter, and the ``Bond Lattice'' Model for the Liquid-Glass Transition
Authors: Angell C. A. , Rao K. J.
Published: February 2004

The characteristics of glasslike transitions in supercooled liquids and plastic crystals are discussed and a nearest neighbor interaction scheme, termed the ``bond lattice'' model, is proposed to account for the thermodynamic aspects of the phenomenon. Although the excitations of the bond lattice have features in common with those of the Ising lattice, the bond lattice has a zeroth order (noncooperative) case in which the thermodynamic properties are meaningful and readily evaluated. The zeroth order expressions appear adequate to account for the configurational heat capacity of the covalent bonded liquid ZnCl2, but are clearly incapable of explaining the transition behavior of most molecular and hydrogenbonded glasses. In these cases it is believed the configurational excitations have considerable cooperative character. While the complex cooperative problem is not properly treated in this paper, we show how an ad hoc introduction of temperature-dependent bond energies (a sort of Bragg-Williams approximation) modifies the bond lattice model properties in the direction demanded by experiment. A second order transition between supercooled liquid and glass is not required by the treatment. An expression for transport properties, based on a postulated exponential relationship between rearrangement probabilities and degree of configurational excitation, is evaluated. The VTF (Fulcher) equation, commonly used to describe transport properties of viscous liquids, results as a good approximation. The VTF T0 parameter is determined mainly by the bond strength parameter of the model, while the B parameter can be related to the change of heat capacity at Tg. It is implied that glasses with little or no thermal manifestation of Tg will have large and almost Arrhenius temperature dependences, as seems characteristic of the strong network glasses, BeF2, GeO2, and perhaps SiO2. The VTF transport parameters for the intermediate case of ZnCl2 are well predicted using the same molecular excitation parameters which account for the configurational heat capacity.
Dilute Solution Viscoelasticity of Simple Ionic Polymers—A Theory for Charged Bead-Spring Models
Authors: King M. , Eisenberg A.
Published: February 2004

As part of a comprehensive study of the viscoelastic properties of ionic polymers, a theoretical investigation of the dilute solution viscoelasticity of simple ionic polymers was undertaken. The bead-spring model of Rouse was modified to include electrostatic charges in the beads. For the two simplest cases of this model (the elastic dumbbell and the three bead-two spring assembly), the diffusion equation for the distribution function of bead separation in shearing flow was formulated. Numerical solutions were obtained for a range of values of the charge and spring parameters. The values were chosen to correspond to real polymers for which the charged bead-spring model would be appropriate, such as linear dicarboxylic acids and polymeric zwitterions for the dumbbell, and linear triacids for the three bead model. It was found that the effect of ions can be described by simple multiplicative shifts in the relaxation times of the uncharged material. For like-charged dumbbells, both the relaxation time and the intrinsic viscosity increase; for oppositely-charged dumbbells, both of these functions decrease in value. For the three bead model, the intrinsic viscosity and both of the relaxation times increase. In addition, the ratio of the two relaxation times increases, indicating a broadening in the distribution of relaxation times.
Nonlinear U(u) Hugoniots of Liquids at Low Pressures
Authors: Lysne P. C.
Published: February 2004

Low pressure (<15 kbar) shock compression experiments were performed on the liquids CS2, C6H14 (n-hexane), CH2I2, CHCl3, C6H6, and C6H12 (cyclohexane). In each case, the shock velocity-particle velocity, U(u), Hugoniot was nonlinear and the shock velocity smoothly approached the sonic velocity as the shock pressure approached zero. Enthalpy-pressure-volume equation of state parameters are given for CS2, C6H14, C6H6, and C6H12.
Positron Lifetimes in Pure and Doped Ice and in Water
Authors: Eldrup M. , Mogensen O. , Trumpy G.
Published: February 2004

Positron lifetime spectra were measured in mono- and polycrystalline light ice, polycrystalline heavy ice, doped light ice, as well as in light and heavy water. All spectra were resolved into three components. At temperatures between −196° and −100°C the lifetimes and relative intensities are virtually constant, being 0.12 nsec and 20%, 0.44 nsec and 28%, 0.68 nsec and 52%, and attributed to annihilation of para-Ps, free positrons, and ortho-Ps, respectively. Above −100°C the longest lifetime increases with temperature to 1.1 nsec at 0°C. Its relative intensity is unchanged, while the parameters for the other components show a complex behavior. The spectra for mono- and polycrystalline light ice and for polycrystalline heavy ice are identical. For water long lifetime components attributed to ortho-Ps are 1.86 nsec, 27% for H2O and 2.01 nsec, 22% for D2O. Theoretical explanations are suggested. Fast frozen solutions of HF with concentrations larger than approximately 10−5 mole fraction have a lifetime component at −160°C of 1.23 nsec, 52% attributed to trapping of ortho-Ps in amorphous regions. Very good agreement is found between the experiments and a trapping model. Irreversible changes of the spectra are found by heating above approximately −120°C. Measurements on a number of fast frozen aqueous solutions of acids, bases, and salts are reported, none of them showing as strong influence on the ortho-Ps lifetime as HF.
Vibrational Relaxation in Liquids
Authors: Davis Paul K. , Oppenheim Irwin
Published: February 2004

The binary collision model of vibrational relaxation in liquids is examined within the framework of statistical mechanics. The results apply to diatomic molecules with large vibrational spacings when very dilute in an effective thermal reservoir of structureless particles. It is demonstrated that a simple binary collision theory can be derived only if rather strong assumptions are made about the nature of the molecules. Even then, the theory which emerges differs significantly from those proposed by earlier workers.
Collision Frequencies in Liquids
Authors: Davis Paul K.
Published: February 2004

The collision frequency in liquids is computed with a cell model and with an exact formula. The results suggest that the cell model is qualitatively accurate in the region of high density if a particular definition of collision is used; it is not appropriate for estimating the frequency of high-energy collisions.
Low Temperature Infrared Study of Association in Dissolved N-Methylaniline
Authors: Bernard-Houplain Marie-Claude , Bélanger G. , Sandorfy C.
Published: February 2004

Self-association of N-methylaniline by hydrogen bonds has been examined. The fundamental of the NH stretching vibration and its first and second overtones were measured in solution down to −190°C. In addition to the band due to the free species, two bands due to oligomers and a polymer band are found. The anharmonicity of the oligomer NH vibrations is practically the same as that of the free NH vibration. The spectrum of the N-deuterated molecule yields similar results.
On the Evaluation of Kinetic Theory Collision Integrals: Diamagnetic Diatomic Molecules
Authors: Chen F. M. , Moraal H. , Snider R. F.
Published: February 2004

A partial evaluation of the collision integrals for the Waldmann-Snider collision superoperator is accomplished. This involves an exact integration over the center of mass coordinates and a distorted wave Born approximation treating the nonspherical part of the intermolecular potential as small. Certain exact relations between collision integrals are obtained after center of mass integration and further approximate relations are obtained within the DWB approximation. The general method of organizing the collision integrals has been considered according to their coupling (k ≠ 0) of angular momentum and velocity directions and uncoupling (k=0). In particular, for the latter, approximate formulas are obtained for the j dependence of the relaxation cross sections. For all this work, the collision cross sections are expressed in terms of averages of the nonspherical potential over the collision dynamics due to the spherical potential.
Optical Transition Probabilities for Trivalent Holmium in LaF3 and YAlO3
Authors: Weber M. J. , Matsinger B. H. , Donlan V. L. , Surratt G. T.
Published: February 2004

Optical absorption and emission intensities are investigated for trivalent holmium ions in crystals of LaF3 and YAlO3. Oscillator strengths of transitions to all levels up to 40 000 cm−1 were measured from absorption spectra recorded at 300°K. Corresponding oscillator strengths for transitions between J manifolds were calculated using the Judd-Ofelt approach and eigenstates for intermediate coupling. Phenomenological intensity parameters were derived from a least-squares fitting procedure. For both materials, the root-mean-square deviation of observed and calculated oscillator strengths was ±10%. The intensity parameters were also used to calculate the spontaneous emission probabilities and branching ratios from levels of Ho3+ which fluoresce in LaF3 and YAlO3. A table of reduced matrix elements used in the computations is included.
Structure Studies of Solutions of Large Organic Molecules. III. Liquid Crystallike Arrangement of Dissolved Long Chain Molecules
Authors: Brady George W.
Published: February 2004

An x-ray diffraction study has been made of the effect of chain length on the configuration of dissolved long chain molecules. In solutions of alkane monoiodides of nearly equal length, the molecules line up such that the interiodine distance is roughly equal to the sum of the chain lengths. When the lengths are quite disparate, the longer chains order preferentially, as manifested by a gross x-ray spacing of about twice the longest chain length. The morphology and concentration persistence of the solute aggregates are discussed and it is concluded that these latter are in quasiliquid crystal form.
HF Vibrational Relaxation Measurements Using the Combined Shock Tube-Laser-Induced Fluorescence Technique
Authors: Bott J. F.
Published: February 2004

Vibrational relaxation measurements in HF have been obtained at intermediate temperatures by combining the laser-induced fluorescence technique with shock compression heating in a shock tube. Usually, shock tube measurements of vibrational relaxation are limited to high temperatures, above about 1300°K in the case of HF. Laser-induced fluorescence measurements can be made in heated cells suitable for HF handling up to about 700–800°K. The combination of the two techniques offers several advantages including large range of temperatures, no wall reactions, and no leaky cells at high temperature. This method was used to obtain HF vibrational relaxation data at 460 to 1030°K and at 295°K. These data, together with shock tube data at high temperature (1350 to 3000°K), are compared with theoretical predictions. A measurement of the V-V rate for the reaction HF (1) + HF (1) ⇌ HF (0) + HF(2) gave a value of 2.2 × 1013 cc/mole · sec.
Asymptotic Behavior of Pair Correlations in One-Dimensional Systems
Authors: Perry P. , Fisk S.
Published: February 2004

Asymptotic decay of the pair correlation function G(r) is investigated for general square-well and triangle-well model intermolecular potentials. For all systems investigated loci are found in the (p, T) plane across which the asymptotic decay changes discontinuously from damped oscillatory to monotonic exponential behavior.
Thermal and Near-Thermal Electron Transport Coefficients in O2 Determined with a Time-of-Flight Swarm Experiment Using a Drift-Dwell-Drift Technique
Authors: Nelson D. R. , Davis F. J.
Published: February 2004

The drift-dwell-drift (DDD) or pulsing technique has been successfully applied to the study of low-energy electron transport coefficients in oxygen in spite of significant attachment at these energies. A thermal value of the electron diffusion coefficient times pressure DP=1.20± 0.11 cm2 μ sec−1 torr was determined. This DP value corresponds to a momentum-transfer cross section Qm=0.82× 10−16 cm2 at an energy ε=0.0258 eV if it is assumed that Qm ∞ ε1/2. This thermal value of Qm is ∼40% lower than the lowest values reported from other techniques.
Molten Mixtures of AgNO3 and TlNO3: Raman Spectra and Structure
Authors: Balasubrahmanyam K. , Janz G. J.
Published: February 2004

The laser-Raman spectra of the molten mixtures of AgNO3–TINO3 have been investigated from about 20°C above their respective melting temperatures to an upper limit of about 250°C. While the frequencies in the mixtures are nearly the same as in the pure molten AgNO3 and TlNO3, the shape of the bands in the 700–750-cm−1 region changes with the composition of the mixtures, and the relative molar intensities of the NO3− bands are markedly less than in the parent compounds. The results are understood if the ``backdonation'' of electrons to the NO3− from the cations is inhibited in the molten mixtures relative to this effect for the parent compounds as single-salt melts.
Velocity of Sound in Lithium–ND3 Solutions
Authors: Franceware L. B. , Priesand M. A. , Bowen D. E.
Published: February 2004

The velocity of 10 MHz compressional waves in solutions of lithium in liquid ND3 are reported. These data are quite similar to the earlier data in Li–NH3 solutions with the Li–ND3 sound velocity being lower than that in the Li–NH3 solutions. Data for pure liquid ND3 is also reported.
Ionization Cross Sections of F2 and Cl2 by Electron Impact
Authors: Center R. E. , Mandl A.
Published: February 2004

A measurement has been made of the electron impact ionization cross section of F2 and Cl2 over the energy range 15–100 V. Both species exhibit a maximum cross section at electron energies near 100 eV, the maximum values being approximately 1.5× 10−16 and 7.0× 10−16 cm2 for F2 and Cl2, respectively. The measurement in Cl2 fits an observed correlation between the maximum cross section and the square root of the polarizability. This correlation seems to apply to a wide variety of atomic and molecular species. Based on this correlation we estimate the polarizability of F2 to be approximately 8× 10−25 cm3
ESR and Optical Spectroscopy of the RhC Molecule at 4°K
Authors: Brom J. M. , Graham W. R. M. , Weltner W.
Published: February 2004

RhC molecules produced by the vaporization of a mixture of Rh and C powder from a graphite cell have been trapped in the 2Σ+ ground state in neon and argon matrices at 4°K. ESR spectra exhibit hyperfine structure arising from the electron interaction with the 103Rh (100% natural abundance) and 13C (by isotopic enrichment) nuclei, yielding the following parameters in a neon matrix: A∥(Rh)=1113(1) MHz, A⊥ (Rh)=1089(1) MHz, A∥ (C)=89(1) MHz, A⊥ (C)=55(1) MHz, g∥ =2.0039(6) and g⊥ =2.0541(6). The ground state configuration is determined to be largely ··· (4dσ)2 (4dπ)4 (4dδ)4 (5sσ) with some mixing of 4dσ with 5sσ. The relatively large positive value of Δ g⊥ is in agreement with the spin-doubling constant, γ =−0.062, determined earlier in the gas phase and indicates that there is strong coupling between the ground state and an unknown 2Πi state, possibly observed in the ultraviolet in the matrix spectra. Spectra of Rh atoms in a neon matrix observed between 2295 and 3540 Å are compared with known gas-phase transitions.
Relaxation of Excess Populations in the Lower Laser Level CO2(100)
Authors: Rosser W. A. , Hoag E. , Gerry E. T.
Published: February 2004

The rate of relaxation of excess population in the lower laser level, CO2 (100), has been measured by an electrical perturbation method. Gases studied included: CO2, CO2/Xe, CO2/H2O, CO2/He, and CO2/N2. In all cases, the measured rates of relaxation of CO2 (100) differ markedly from the accepted rates of relaxation of CO2 (010). The difference indicates that the levels (100) and (010) are not strongly coupled.
Monte Carlo Classical Trajectory Calculation of the Rates of H- and D-Atom Vibrational Relaxation of HF and DF
Authors: Thompson Donald L.
Published: February 2004

Monte Carlo classical trajectory methods have been used to investigate H- and D-atom vibrational relaxation of HF and DF. A semi-empirical valence-bond interaction surface was employed for the calculation of three-dimensional collision trajectories. Both vibration-rotation and vibration-translation are found to contribute to the vibration de-excitation. Multiple-quantum jumps contribute to the relaxation for initial excitation levels greater than v=1.
Measured Lifetimes of Some A 2Πu Vibrational Levels of N2+ Molecules
Authors: Gray D. D. , Roberts T. D. , Morack J. L.
Published: February 2004

A delayed coincidence technique has been used to measure the radiative lifetimes of the v′=2, 3, and 4 levels of the A 2Πu State of N2+. The data closely follows the simple theory for collisional deactivation. The lifetimes, extrapolated to zero pressure, are 9.4± 1, 9.5± 1, and 8.9± 1 μ sec for the v′=2, 3, and 4 levels, respectively.
Pair Potential in Liquids from the Exact Born-Green Equation. I. Model Testing
Authors: Wang Shein-shion , Krumhansl J. A.
Published: February 2004

Pair potentials which are derived from the experimental pair correlation functions by either the Born-Green, the Percus-Yevick or the hypernetted chain equation have built-in inaccuracies because of the approximate nature of these equations. In this paper we show that the results can be improved upon by using the exact Born-Green equation properly. This method is checked by several Monte Carlo models and seems to work well.
Reinterpretation of Molecular Beam Hyperfine Data for 14NH3 and 15NH3
Authors: Hougen Jon T.
Published: February 2004

Reassignments are presented for the hyperfine patterns of six 15NH3 inversion doublets. The new assignments alter the sign of the nitrogen-hydrogen spin-spin interaction constant. Previous disagreement between theory and experiment for the hyperfine pattern of the J = 3, K = 2 14NH3 inversion doublet is removed by including the effect of centrifugal distortion on the quadrupole splitting. An explanation is presented for a discrepancy remaining in the fit of the J = K = 6 hyperfine pattern of 15NH3.
Laser Raman Spectrum of Crystalline Cyclopentane-d and -d10
Authors: Schettino V. , Marzocchi M. P.
Published: February 2004

The laser Raman spectrum of the crystal form III of cyclopentane and cyclopentane-d10 has been measured at 85°K. The frequencies and splittings of the internal modes and the number of observed lattice modes are consistent with the crystal structure deduced from the analysis of the infrared spectrum. Some details of the vibrational assignment are discussed, and consistency with observed gas phase heat capacities is checked.
Density Effects on the Dynamic Structure of Liquid Deuterium Oxide
Authors: Lee Y. , Jonas J.
Published: February 2004

The temperature and pressure dependences of the deuteron spin-lattice relaxation time and of the density and viscosity of liquid deuterium oxide were measured in the range of 10–90°C and 1 bar-5 kbar. The experimental data enabled us to separate the effects of density and temperature on T1 and viscosity. We found that at constant density the quantity (ηT1/T) is independent of temperature within experimental error, while the change in density results in a significant increase in the quantity (ηT1/T). This experimental finding is qualitatively interpreted in terms of possible changes in the degree of coupling between rotational and translational motions and/or changes in the magnitude of the deuteron quadrupole coupling constant. Within the limited density range studied from 1.106 g/cm3 to 1.230 g/cm3, no extensive disruption of the random hydrogen bond network occurs. The data favor the tentative interpretation that an increase in pressure produces a decrease in the average O–O distance in the O–D···O hydrogen bonds resulting in a decrease in the magnitude of the deuteron quadrupole coupling constant.
Electron Paramagnetic Resonance Studies of X-Irradiated KH2AsO4, KD2AsO4, RbH2AsO4, RbD2AsO4, CsH2AsO4, NH4H2AsO4, and ND4D2AsO4 (Ferroelectrics and Antiferroelectrics)
Authors: Dalal N. S. , Dickinson J. R. , McDowell C. A.
Published: February 2004

Electron paramagnetic resonance (EPR) studies of defect centers produced by x or γ irradiation of the hydrogen-bonded ferroelectrics KH2AsO4, KD2AsO4, RbH2AsO4, RbD2AsO4, and CsH2AsO4 and of the antiferroelectrics NH4H2AsO4 and ND4D2AsO4, are presented. The spectra, observed over 300–4.2°K, are characterized by a very large hyperfine interaction of the unpaired electron with the 75As  (I=32) nucleus, and exhibit orthorhombic symmetry in general. The analysis thus required an exact diagonalization of the spin Hamiltonian. Such a procedure, coupled with the use of the method of least-squares adjustment, has resulted in accurate values for the hyperfine parameters describing the observed spectra, both for single crystal and powder samples. A comparison of the hyperfine parameters with those reported previously for the AsO44− in KH2AsO4 has enabled us to identify lines from this center in all the above crystals. The parameters are found to be sensitive to change of the cation and also to a variation of the sample temperature. This indicates that EPR can be used as a microscopic probe for studying hydrogen bonding and the proton-lattice motion in these compounds. An observed hydrogen-deuterium isotope effect on the hyperfine parameters has also been discussed. Absence of proton superhyperfine for AsO44− in RbH2AsO4, and CsH2AsO4 has been discussed in the light of preliminary ENDOR experiments on RbH2AsO4. Accurate values have also been obtained for the spin Hamiltonian parameters of several other centers which show fairly similar spectra, for both the high and low temperature phases. Here also the 75As hyperfine parameters show isotope effects, both for the change of the cation and for the substitution of D in place of H. All these centers are assigned to a family of AsO32− centers. A previously reported proton superhyperfine structure, which cast strong doubt on the identification of these centers, was not observed. This lends further support to our assignment. Possible mechanisms for the formation of these centers are discussed, but no definite answer could be obtained through these studies alone.
One-Electron Model for Charge Exchange in Ion-Atom Collisions
Authors: Storm David , Rapp Donald
Published: February 2004

In attempting to calculate cross sections for charge exchange in other than proton-hydrogen atom collisions, it has been common to simplify the system by assuming that only one active electron is moving in the field of two ions. With this one-electron approximation, the extensive formalism developed to treat proton-hydrogen atom collisions has then been applied. It is shown that the use of some common one-electron orbitals in such a formalism can destroy either the ability to interpret the expansion coefficients as transition amplitudes, or probability conservation. In this work, a one-electron model Hamiltonian and corresponding expansion functions are proposed by which the physical system is more accurately described. With this model it is shown that physically acceptable transition amplitudes can be calculated, probability is conserved, and the principle of microreversibility is satisfied.
Wavefunctions and Pseudopotential for Alkali Charge Transfer
Authors: Rapp Donald , Chang Chi-Ming
Published: February 2004

A set of wavefunctions and pseudopotential for alkali atoms is proposed, which should facilitate calculations of excitation and charge transfer in collisions of alkali ions and atoms. In this model, the inner core of electrons is replaced by an exponential charge cloud, and the Schrödinger equation for the outer electron in the combined field of the nucleus plus the inner cloud is numerically integrated. The resulting wavefunctions are fitted by analytical functions having the same general form as hydrogenic functions, and therefore the formalism readily available for H++H collisions can be directly applied to the one-electron model for alkali ion-alkali atom collisions. Since the functions proposed here are essentially exact for the Hamiltonian used, they do not lead to probability flow at ∞.
Paramagnetic Hyperfine Interactions in an eg2 Configuration of 57Fe
Authors: Oosterhuis W. T. , Barros F. de S.
Published: February 2004

Paramagnetic hyperfine structure (PHS) is observed in the Mössbauer spectrum of FeO4−2 diluted in concentrated NaOH in the presence of applied magnetic fields ranging from 0 to 2 kOe. The experimental results give an isotropic hyperfine interaction (A = − 1.17 mm/sec in the nuclear excited state), g=2.0 (isotropic) and no electric field gradient all of which are consistent with an eg2 configuration for the Fe6+ ion. Because of the dilution and low temperatures, the relaxation time among the electronic states is long enough for the 57Fe nucleus to couple to the magnetic moment in each state-when there is a moment induced by the applied field. The saturation value of the hyperfine field is somewhat smaller than expected (175 kOe).
Electron Scattering by Molecules with and without Vibrational Excitation. VI. Elastic Scattering by CO at 6–80 eV
Authors: Truhlar Donald G. , Williams Walter , Trajmar Sandor
Published: February 2004

Elastic scattering differential cross sections in relative units for electron scattering from CO have been measured in the scattering angle range 15°–85° and the impact energy range 10–80 eV. The experimental results are compared to the predictions of model polarized Born approximations using five different model interaction potentials. The model potential of Crawford and Dalgarno is in the best agreement with experiment, and agrees with experiment about as well as any local potential possibly can. Such a treatment is able to account for some of the features of the angle dependence of the differential cross sections. The largest discrepancies between theory and experiment are at 10 eV and at large scattering angles, and there are also smaller discrepancies at small scattering angles. Comparisons are also made to previous experimental studies by Ramsauer and Kollath and Arnot.
Light Scattering from Systems with Chemical Oscillations and Dissipative Structures
Authors: Deutch J. M. , Hudson S. , Ortoleva P. J. , Ross John
Published: February 2004

The spectrum of light scattered from a system of coupled nonlinear chemical reactions is considered for steady states far from equilibrium. Fluctuations from a steady state may exhibit oscillatory decay, marginally stable chemical oscillations, or dissipative structures. Qualitatively new features appear in the spectrum when compared to the light scattering spectrum from reacting systems at equilibrium. The principal new features found are splittings in the chemical lines and dispersive (non-Lorentzian) contributions. Two model reaction mechanisms, the Volterra-Lotka model and the Prigogine-Lefever model, are examined in detail.
Simplified Multiconfiguration Self-Consistent-Field Theory for Localized Orbitals. I Fixed Orbitals
Authors: Schlosser Herbert
Published: February 2004

We develop a simplified version of the fixed orbital multiconfiguration self-consistent-field theory (MC-SCF-FXO) for localized orbitals of Gilbert by analyzing the operators and matrix elements in powers of the overlap, neglecting terms quadratic and higher in overlap. This procedure eliminates many terms found in the complete theory. The matrix elements of the orbital operators are particularly simple since all strictly environmental terms and many of the subsystem-environment interaction terms vanish. The orbital and secular equations are then decomposed into equations for a subsystem coupled to its environment. A scheme for the self-consistent solution of these equations is discussed.
Simplified Multiconfiguration Self-Consistent-Field Theory for Localized Orbitals. II Fluctuating Orbitals
Authors: Schlosser Herbert
Published: February 2004

We develop a simplified version of the fluctuating orbital multiconfiguration self-consistent-field theory (MC-SCF-FLO) for localized orbitals of Gilbert. We proceed by analyzing the operators and matrix elements in powers of the overlap, neglecting terms quadratic and higher in overlap. This eliminates many of the terms found in the complete theory. The matrix elements of the orbital operators are particularly simple since all strictly environmental terms and many of the subsystem-environment interaction terms vanish. The orbital and secular equations are then decomposed into equations for a system coupled to its environment.
Lithium Niobate Coloration Caused by Hydrogen Ion Bombardment
Authors: Primak William
Published: February 2004

Bombardment with 140 keV protons or deuterons developed a broad absorption band extending from about 1 μ to the absorption edge at about 0.33 μ. The mean absorption coefficient increased quite linearly with ion dose until destruction of the surface occurred (∼0.05 C/cm2) and reached values ∼ 1.6 μ−1. Although the absorption band was similar to that developed by ionization (e.g., by electron bombardment), thermal annealing was quite different. The absorption band developed by ionization alone annealed by 140°C, while the proton one annealed mainly in the 100° above 220°C. The coloration was not observed following He+ or Ne+ bombardment. A specimen exposed in a nuclear reactor developed coloration, but the coloration was 70-fold less per hydrogen (isotope tritium, calculated from neutron fluence, concentration 3 orders of magnitude less than the proton or deuteron concentration above).
Hydrogen Bond Strength and Charge Distribution in the Bifluoride Ion, HF2−. Lattice Energies of LiHF2, NaHF2, KHF2, RbHF2, and CsHF2
Authors: Dixon H. P. , Jenkins H. D. B. , Waddington T. C.
Published: February 2004

Electrostatic energies and Madelung parameters for LiHF2, NaHF2, KHF2, RbHF2, and CsHF2 are reported together with a term-by-term calculation of the total cohesive lattice energy, all expressed as single-parameter quadratic functions of the charge Q(F) on the terminal fluorine atoms of the linear HF2− ion. An assessment of the charge distribution in this ion is made in conjunction with a calculation of the enthalpy change, Δ H1, of the reaction, HF2−(g)→ HF(g) + F−(g),thus measuring the strength of the hydrogen bond. The intersections of the curves for Δ H1 as a function of Q(F) are used to assign values of −0.73 e.u. to Q(F) and 252 kJ mol−1 to Δ H1 and the following values for the total potential lattice energies: Epot(LiHF2)=820.6  kJ mol−1; Epot(NaHF2)=755.3 kJ mol−1; Epot(KHF2)=648.2 kJ mol−1; Epot(RbHF2)=626.9 kJ mol−1, and Epot(CsHF2)=607.4 kJ mol−1.
Raman Spectra of Gases. IV. Methylenecyclobutane and Trimethylene Sulfide
Authors: Durig J. R. , Shing A. C. , Carreira L. A. , Li Y. S.
Published: February 2004

The low frequency Raman spectra of methylenecyclobutane and trimethylene sulfide in the gaseous state have been recorded. The observed Q branches for the ring puckering vibration have been assigned as Δ v=2 transitions from a double minimum potential function. The Q branches for trimethylene sulfide agreed with those predicted from far infrared and microwave data and confirm the predicted energy difference for the v = 2 to 3 transition. This is the first direct observation of the ring puckering vibration for methylenecyclobutane. The determined potential function, V=4.104 × 105χ4−1.519 × 104χ2, differs from those proposed from the microwave and midinfrared studies but is capable of explaining not only the Raman results but also the previous data. The barrier to inversion was found to be 141± 5 cm−1.
Nonsymmetric Perturbation Studies of One-Electron Diatomic Molecular Ions
Authors: Schulman Jerome M.
Published: February 2004

The interaction of a hydrogenic atom with a bare nucleus is studied perturbatively through infinite order in a model problem. Convergence of the energy and wavefunction expansions are discussed in Rayleigh-Schrödinger and Brillouin-Wigner nonsymmetric perturbation theories.
Microwave Spectrum of cis-Glyoxal
Authors: Durig J. R. , Tong C. C. , Li Y. S.
Published: February 2004

The rotational spectrum of glyoxal has been investigated in the region 18.0–40.0 GHz. Only B-type transitions were observed. Both Q-branch and R-branch assignments have been made for the ground state, and the Q-branch assignment has been made for the first excited state of the internal rotational mode. From relative intensity measurements of vibrational excited states, the torsional vibration is found to have a frequency of 114± 8 cm−1.. From a consideration of the rotational constants, it is concluded that the isomer giving rise to the microwave spectrum is the planar cis form and not the gauche isomer. The dipole moment was determined to be 4.8 ± 0.2 D.
Computed Bond Energies and Vibrational Frequencies for ClHCl, BrHBr, and IHI, Including Isotope Effects and Anharmonicity
Authors: Truhlar Donald G. , Olson Peter C. , Parr Christopher A.
Published: February 2004

The bond-energy-bond-order (BEBO) method of Johnston and Parr predicts ClHCl, BrHBr, and IHI are all bound and symmetric. When corrected for anharmonicity of the asymmetric stretch normal mode, it predicts the following vibrational frequencies in cm−1 (experimental results are in parentheses; s is the symmetric stretch and a is the asymmetric stretch): ClHCl, s: 371 (259); ClDCl, s: 370 (265), a: 318 (463); BrHBr, s: 222 (165), a: 533 (727); BrDBr, s: 222 (170), 442 (496); IHI, s: 165 (121), a: 862 (686); IDI, s: 165 (124), a: 677 (470). The predictions of the London-Eyring-Polanyi-Sato (LEPS) method for vibration frequencies are presented but are in much worse agreement with experiment. The BEBO method predicts the following depths of the potential energy minima (in kcal/mole) and equilibrium bond distances (in 10−8 cm), respectively: ClHCl, 1.56, 1.45; BrHBr, 3.02, 1.60; IHI, 6.77, 1.79.
Virial Expansions for a Binary Mixture Model and for a Related One-Component Model
Authors: Straley J. P. , Cotter M. A. , Lie Tae-Journ , Widom B.
Published: February 2004

We calculate the two- and three-dimensional virial coefficients for a binary mixture (with vAA=vBB=0; vAB→ oriented hard cubes), and for a related one-component system of the type proposed by Widom and Rowlinson. This information is used to study the coexistence curve.
Phosphorescence of Tetrahalomanganate Ions in Fused Salts
Authors: Sundheim Benson R. , Levy Ezra , Howard Brian
Published: February 2004

The phosphorescence of tetrabutylammonium tetrachloro-, tetrabromo-, and tetraiodomanganates was examined in the molten state. Absorption and emission spectra and phosphorescence lifetimes were obtained as functions of the temperature. For the tetrachloro- and tetrabromomanganates, the rates of radiationless transfer to the ground state, as evidenced by the falling off of the phosphorescence lifetimes, begin to be noticed in the solid state, increase abruptly at the melting points, and continue to increase slowly in the liquid state. For the tetraiodomanganate, no change in phosphorescence lifetime is seen on passing through the melting point. Self-quenching is absent for all three. The offsets in the absorption and phosphorescence spectra indicate that there is a considerable change in internuclear distance on passage to the excited state, which may be expected to display Jahn-Teller distortion. The form of the temperature dependence and symmetry considerations appear to rule out a vibronic mechanism for the radiationless process. It is proposed that a spin-rotation interaction mixes the ground and excited states and thus brings about the radiationless transfer.
Some Features of the CH3NC→CH3CN Potential Surface
Authors: Liskow Dean H. , Bender Charles F. , Schaefer Henry F.
Published: February 2004

Nonempirical self-consistent-field calculations are reported for about 75 points on the potential surface for the CH3NC→CH3CN isomerization. Due to interest in the possible non-RRKM behavior of CH3NC, the magnitude of the barrier to rotation of the methyl group is examined as a function of the reaction coordinate. The transition state or saddle point geometry is determined by minimizing the potential energy with respect to five geometrical parameters and maximizing with respect to a sixth. The geometries of CH3NC and CH3CN are also predicted and found to agree closely with experiment. Finally, it is established that, contrary to semiempirical results, the present theoretical approach does not predict the existence of a relative minimum in the reaction coordinate.
14N Quadrupole Resonance Study of a Hydrogen Bond: Hexamethylenetetramine Triphenol
Authors: Marino R. A.
Published: February 2004

The nuclear quadrupole resonance spectrum of hydrogen bonded hexamethylenetetramine triphenol was observed at 77°K and at room temperature. The absorption lines were assigned to two inequivalent nitrogen sites. N(1), which is not hydrogen bonded, gave e2qQ/h=4665.7 kHz and η=0 at 77°K. N(2), which takes part in an N···H–O hydrogen bond, has e2qQ/h=4208.1 kHz and η=0.05014 also at 77°K. By comparing these data with the spectrum of pure hexamethylenetetramine (HMT) the effects of the hydrogen bond on the HMT nitrogen sites could be obtained. It is concluded that the nitrogen site N(2) loses a few hundredths of an electron from its lone pair orbital as a result of the hydrogen bond interaction.
High Resolution Infrared Spectra of the Parallel Bands of Phosphorous Pentafluoride
Authors: Schatz Jan , Reichman Sandor
Published: February 2004

The v3 and v4 parallel bands of PF5 were recorded at a resolution of ∼0.06 cm−1. The J structure of the P and R lines was resolved, and we obtained a value of B0=0.10470. The lowest lying fundamental frequency v7 is estimated to be 166±15 cm−1.
Electron Excitation Cross Sections for Li (2s→ 2p, 2s→ 3p), Na (3s→ 4p), Mg (3p→ 4s), K (4s→ 4p), and Ca (4s→ 4p)
Authors: Simsic P. , Williamson W.
Published: February 2004

Electron excitation cross sections using the Born approximation are given. Two types of Slater wavefunctions have been used, and the results are compared with other theoretical calculations and experimental data where available.
Effects of Liquid Structure on dc Transport Coefficients in Brownian-Like Solutions
Authors: Harris S.
Published: February 2004

We determine the Ohmic and Hall conductivities for an infinitely dilute Brownian-like electrolyte by solving the generalized Fokker-Planck equation for the stationary value of the carrier particle distribution function. This is done by expanding at each field order in the natural parameter of smallness, γ = (solvent molecule mass/carrier mass)1/2. The corrections to the lowest order results (Brownian motion) are determined, and the Hall coefficient is then found. The value of unity obtained, identical to the Brownian motion value, indicates that liquid structure effects are not significant in this type of system.
Collisional Effects upon Rotational Correlations of Symmetric Top Molecules
Authors: Pierre Anthony G. St. , Steele William A.
Published: February 2004

Time-dependent conditional phase-space distribution functions are derived for classical ensembles of rigid molecules undergoing collision-interrupted free rotation. The J-diffusion and the M-diffusion models proposed by Gordon, [J. Chem. Phys. 44, 1830 (1966)] are explored in detail. The expressions for the conditional distribution functions are evaluated for these models in terms of multiple time integrals. It is then shown that Fourier transform techniques can be used to express the integrals as convolutions which are analogous to Fixman and Rider's expressions [J. Chem. Phys. 51, 2425 (1969)]. A number of numerical results are presented.
Photodetachment Cross Sections for CO3− and Its First Hydrate
Authors: Burt J. A.
Published: February 2004

The cross sections for the aeronomically important processes CO3−+hν→CO3+e− and CO3−·H2O+hν→CO3· H2O+e− are measured at a pressure of 2 torr. The ions are detected in a differentially pumped quadrupole mass spectrometer. The photodetachment threshold energy is 1.8 eV for CO3− and 2.1 eV for CO3− · H2O. Their solar photodetachment rates are, respectively, 1.4 and 1.1 sec−1 relative to the O− rate of 1.44 sec−1.
Calculation of Pressure-Broadened Linewidths of SO2 and NO2
Authors: Tejwani G. D. T.
Published: February 2004

Self-broadened and foreign-gas (N2 and O2) broadened linewidths of sulfur dioxide and nitrogen dioxide have been calculated using the Anderson-Tsao-Curnutte theory of line broadening. Computed values of linewidths are in good agreement with all the available experimental results and reported theoretical calculations by Murphy and Boggs on four self-broadened and one nitrogen-broadened line based upon the theory developed by them. Air-broadened linewidths have been calculated for SO2 at 200, 250, and 300°K. These results should be useful in predicting theoretical spectra of SO2 under atmospheric conditions. Such spectra are important in spectroscopic techniques for monitoring SO2.
Method for Measuring Relative Transition Probabilities of Cascading Molecular Bands: Application to CO Fundamental Bands
Authors: Djeu N. , Searles S. K.
Published: February 2004

A general method is presented to determine the relative transition probabilities for two molecular bands which have one vibrational level in common. It is based on optical gain (or loss) measurements on a number of vibration-rotation transitions in each of the two bands. The method has been applied to CO fundamental bands in the ground electronic state to yield |Rνν +1|2/|Rν −1ν|2 for v=6 through v=11, where Rν−1ν is the rotationless matrix element of the dipole moment connecting the v−1th and vth vibrational levels. The results were fitted by using the wavefunction approximation for Rν−1ν, and the ratio R04/R01=0.00021 was obtained.
Vapor Pressure and Heat of Vaporization of Cobalt
Authors: Wachi F. M. , Gilmartin D. E.
Published: February 2004

New vapor pressure data for cobalt have been obtained in the temperature range 1519–1926°K from Knudsen effusion experiments. The derived third-law heat of vaporization of cobalt is Δ H298°=101.0± 0.6 kcal/mole. Plausible explanations are presented that account for the widely differing vapor pressure data and heats of sublimation published in the literature. It is shown that the evaporation coefficient for cobalt is essentially unity rather than 3×10−4 and that the electron impact ionization cross section for cobalt is σ (Co=4.4± 1× 10−16 cm2 for 50 eV electrons.
Infrared and Raman Spectrum of KNCS Crystal. Mode Analysis and the Order-Disorder Phase Transition
Authors: Iqbal Zafar , Sarma L. H. , Möller K. D.
Published: February 2004

The laser excited polarized single crystal Raman spectrum between 30 and 2500 cm−1, the polarized single crystal transmission infrared spectrum between 400 and 4000 cm−1, and thin film transmission infrared spectrum between 70 and 250 cm−1 of potassium thiocyanate (KNCS), have been recorded. The NCS− ion internal mode frequencies were found to be in good agreement with previous observations and are collected together in this paper. The external motions of the KNCS lattice are assigned in terms of factor group selection rules. The infrared absorptions due to combinations of the internal N–C stretching (ν3) mode with the external modes, have been recorded at 90°K and the observed fine structure has been analyzed according to the selection rules for the entire Brillouin zone. The external modes, the infrared active bending mode and the ν3±external modes, have been studied as a function of temperature in the range 90°–450°K. Above the transition temperature (Tc=413°K), the resonant Raman spectrum due to the external modes is replaced by a broad band spectrum with singularities which correspond to those observed in the ν3±external mode spectrum above Tc. This has been related to the loss of local order and the emergence of dynamic disorder near the transition temperature. The temperature dependence of the Raman active external mode frequencies is discussed in the light of the lattice dynamics viewpoint of the phase transition problem.
Photoionization of Vibrationally Excited N2. II. Quenching by CO2 and N2O
Authors: McNeal R. J. , Whitson M. E. , Cook G. R.
Published: February 2004

The rate coefficients for quenching of vibrationally excited N2 in the ground electronic state (N2*) by CO2 and N2O have been measured using a photoionization mass spectrometer to detect the N2* in a flowing N2 afterglow. The reduction in the photoion count rate at amu 28 when CO2 or N2O is added to the afterglow is obtained at wavelengths longer than the photoionization threshold of ground state N2. The quenching data are analyzed with a kinetic model that includes nearly resonant transfer of vibrational energy from N2* to CO2 or N2O followed by radiative, wall, and gas-phase collisional quenching of the infrared-active gas. At low N2 partial pressures the measured quenching rate coefficient asymptotically approaches the rate coefficient (k1) for the V–V transfer reaction. From measurements at wavelengths where N2*(v″ =1) is efficiently photoionized, we find that k1 = 2±1×10−13 and 9±4×10−14 cm3 sec−1 for V–V transfer from N2*(v″ =1) to CO2 and N2O, respectively.
Close Coupled Calculations of Electron-Hydrogen Atom Scattering Using a Noniterative Integral Equation Technique
Authors: Knirk Dwayne L. , Hayes Edward F. , Kouri Donald J.
Published: February 2004

A noniterative integral equation approach to electron-hydrogen atom scattering, including exchange, has been developed for the case in which all available channels are open. The technique has been implemented on a computer for the calculation of cross sections in the 1s–2s strong coupling exchange approximation and the 1s–2s–2p close coupling exchange approximation. The results of these calculations were found to be in good agreement with those obtained by the iterative solution of the differential equations. The merits of the noniterative integral equation technique are compared with other computational schemes for obtaining scattering information.
Crystal Coulomb Energies. IV. A Rapid-Convergence Algorithm for Quantum-Mechanical Crystal Binding Energies
Authors: Metzger Robert Melville
Published: February 2004

Crystal electronic binding energies can be obtained from single-molecule wavefunctions by use of the tight-binding approximation and zero overlap between unit cells. Ewald's method yields a rapidly converging algorithm for performing part of the calculation in direct space and part in reciprocal space, with the help of fast-converging modified atomic wavefunctions. The reciprocal space part consists of summations of Silverstone's two-center Fourier transforms.