bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational deactivation rates of HF(ν = 1) by CH4, C2H6, C3H8, C4H10, C3H6, and ClF3
Authors: Hancock J. K. , Green W. H.
Published: February 2004

The rates at which vibrationally excited HF is deactivated by CH4, C2H6, C3H8, C4H10, C3H6, and ClF3 have been measured to be (5.3 ± 0.8) × 104; (1.10 ± 0.16) × 105; (1.35 ± 0.2) × 105; (1.7 ± 0.25) × 105; (3.2 ± 0.5) × 105 and (1.13 ± 0.17) × 105 sec−1 · torr−1, respectively, using the laser-excited vibrational fluorescence technique. It was found that the cross-section for HF deactivation by the lower alkanes, Cn H2n+2, varied linearly with n. The deactivation rate measured for HF–ClF3 is orders of magnitude greater than has been observed for HF deactivation by other fluorine sources. The importance of the above rate measurements in the understanding and analysis of pulsed HF lasers is discussed in detail.
Infrared spectra of matrix-isolated uranium oxide species. II. Spectral interpretation and structure of UO3
Authors: Gabelnick S. D. , Reedy G. T. , Chasanov M. G.
Published: February 2004

The midinfrared spectra of matrix-isolated UO3 and its oxygen-18 isotopes have been successfully interpreted in terms of a C2ν T-shaped structure. Values of the two bond-stretching and two bond-interaction force constants determined by a normal coordinate analysis using 13 observed frequencies reproduce all peaks in the observed spectrum to within ± 0.6 cm−1. The following assignments for U16O3 species trapped in argon matrices have been obtained: ν1(A1) = 843.50, ν2(A1) = 745.65, ν4(B1) = 852.60 cm−1. The structure and intensity distribution are discussed in terms of current bonding theory for uranyl compounds.
Determination of the proton affinity from the kinetics of proton transfer reactions. IV The equilibrium O2H++H2⇄ H3++O2 and the relative proton affinity of O2 and H2
Authors: Fennelly P. F. , Hemsworth R. S. , Schiff H. I. , Bohme D. K.
Published: February 2004

Equilibrium was established in both directions of the proton transfer reaction O2H++H2⇄ H3++O2 proceeding in a flowing afterglow system. The equilibrium constant K was measured from equilibrium concentrations to be 1.05 ± 0.12 at 297°K. Limits to the rate constants were determined to be kforward ≥ 1.4 × 10−10 cm3 molecule−1 · sec−1 and kreverse ≥ 1.3 × 10−10 cm3 molecule−1 · sec−1. The value of K corresponds to a standard free energy change, Δ G2970, of −0.03+0.07−0.06 kcalmole−1 and leads to a proton affinity difference P A (O2) − P A (H2) = + 0.002 ± 0.003 eV.
An efficient numerical multicenter basis set for molecular orbital calculations: Application to FeCl4
Authors: Averill F. W. , Ellis D. E.
Published: February 2004

The use of numerical solutions to atomlike single site potentials as a basis for molecular orbital calculations is investigated. The atomic Hamiltonian is modified by addition of a potential well to induce additional discrete levels with the desired spatial characteristics. The discrete variational method is employed, in the Hartree-Fock-Slater model, to compare levels obtained for FeCl4 using multiple-scattering, conventional Slater-orbital, and numerical basis sets. The numerical technique is shown to be an accurate and efficient method for treating general (non-muffin-tin) molecular potentials. The errors in energy levels due to the muffin-tin approximation are calculated.
Accurate analytic expectation values for an anharmonic oscillator using the hypervirial theorem
Authors: Tipping R. H.
Published: February 2004

An analytic recursion relation for the calculation of expectation values of any power of the internuclear displacement from equilibrium in an arbitrary vibration-rotation level of 1Σ-state diatomic molecules is derived via an iterative solution of the hypervirial theorem. Explicit results, more accurate than those previously published, are given for the first six powers of the displacement along with numerical results for H2 and HCl to illustrate the accuracy obtained.
Comparison of matrix methods applied to the radial Schrödinger eigenvalue equation: The Morse potential
Authors: Shore Bruce W.
Published: February 2004

This paper demonstrates the application of matrix methods based on finite differences and on variational (Rayleigh-Ritz-Galerkin) procedures to solution of the radial Schrödinger equation for bound states of the Morse potential. It demonstrates sources of numerical inaccuracy: truncation, termination, tolerance, and quadrature. Cubic splines, harmonic oscillators, floating Gaussians, and sines are used as basis functions.
Electronic spectroscopy of s-trans 1,3-butadiene by electron impact
Authors: Mosher Oren A. , Flicker Wayne M. , Kuppermann Aron
Published: February 2004

The electron impact excitation of 1,3-butadiene has been studied experimentally at impact energies of 20, 35, and 55 eV and scattering angles from 10° to 85°. The energy and angular dependences of the cross section ratios are used to identify the nature of the excited states. Two transitions with maxima at 3.22 and 4.91 eV are identified as singlet→triplet transitions. Comparison with theoretical calculations indicates that these are due to the 13Bu and 13Ag states, respectively. Their significance for the photochemistry of this molecule is discussed. The optically allowed X̃ 1Ag → 11Bu(N → V1) transition is observed with a maximum at 5.92 eV. An additional transition appears between 6.9 and 7.8 eV with vibrational features at 7.09, 7.28, and 7.46 eV. The optical absorption in this region was originally attributed to a 1A1 state of the s -cis molecule and subsequently to a Rydberg state or to a 1Ag state of the s -trans molecule. On the basis of intensity arguments and the angular dependence of the cross section ratios, we suggest that it may instead be due to the X̃ 1Ag → 21Bu transition of the s -trans molecule. Rydberg transitions are observed at 8.00 and 8.18 eV. Two broad transitions are also seen beyond the first ionization potential with maxima at 9.50 and 11.00 eV. The results of this study are in good agreement with recent ab initio configuration interaction (CI) calculations, and give support to the analysis of the valence excited states in terms of a ``molecules-in-molecules'' approach. This is consistent with recent interpretations of the resonance energy and reactivity of this molecule and differs from the older classic model of extensive delocalization in the π electron system.
Vibrational relaxation times in some hydrocarbons in the range 300–900°K
Authors: Wang James C. F. , Springer George S.
Published: February 2004

Vibrational relaxation times were determined in methane, ethylene, acetylene, and cyclopropane in the temperature range 300–900°K. The experiments were performed by measuring the absorption and dispersion of ultrasonic waves passing through the vapor. For all four vapors, the vibrational relaxation time τν (sec) was found to vary with temperature T(°K) according to the relationship log10(τν P) = aT−1/3 − b, where P is the pressure (atm) and a and b are constants. The results of the present measurements were also found to be in good agreement with existing data.
Low-lying valence states of the PO molecule according to configuration-interaction calculations
Authors: Tseng T. J. , Grein F.
Published: February 2004

Ab initio configuration-interaction (CI) calculations were carried out for low-lying 2Π, 4Π, 2Σ+, 2Σ−, 4Σ−, 2Δ, and 2Φ valence states of the PO molecule at 11 internuclear distances from 2.45 to 6.5 a.u. All configurations that can be formed from a minimal basis set of Slater-type orbitals, with the restriction of a frozen core, were included. Of the 57 states that dissociate up to 2P(P) + 1S(O), seven 2Π, two 4Π, three 2Σ+, three 2Σ−, one 4Σ−, two 2Δ, and two 2Φ states show a minimum in the potential energy curve. This is to be compared with seven observed valence states.
Solution of a new integral equation for pair correlation functions in molecular liquids
Authors: Lowden Lawrence J. , Chandler David
Published: February 2004

This paper discusses the first numerical solutions of the reference interaction site model (RISM) equation which was proposed by Chandler and Andersen [J. Chem. Phys. 57, 1930 (1972)] to provide a theory for the equilibrium pair correlations of molecular fluids in which the ``molecules'' are composed of fused hard spheres. The particular system studied herein is a one component fluid in which the molecules are symmetric ``diatomics'' (i.e., each is formed by two hard spheres of diameter σ with the centers of the spheres a distance L from each other). It is shown that the accuracy of the RISM equation for this molecular fluid is comparable to that of the Percus-Yevick equation for dense hard sphere fluids. Numerous calculations are presented which illustrate the usefulness of this theory in providing a detailed description of the intermolecular structure of complex fluids. One calculation provides a theory for the structure of liquid nitrogen.
Biaxial order in cholesteric liquid crystals: Phenomenological argument
Authors: Wulf A.
Published: February 2004

On the basis of a phenomenological Landau free energy for liquid crystals which includes the Frank (elastic) free energy, and allows for nonvanishing biaxialities, it is shown that cholesteric liquid crystals are biaxial. The biaxialities are very small, of order (q0a)2 (q0 = pitch wave vector, a = a molecular length), in agreement with recent molecular model calculations.
Flow-drift technique for ion mobility and ion-molecule reaction rate constant measurements. I. Apparatus and mobility measurements
Authors: McFarland M. , Albritton D. L. , Fehsenfeld F. C. , Ferguson E. E. , Schmeltekopf A. L.
Published: February 2004

The present paper describes the construction and operation of a new experimental device that combines the chemical versatility of a conventional flowing afterglow system with the energy variability of a drift tube. This allows the measurement of both positive and negative ion mobilities not previously measured. Ion mobility measurements offer a significant constraint upon the ion-neutral intermolecular potential and are therefore of value in testing either empirical or quantum mechanical theory. The mobilities of He+, He2+, H+, D+, O+, N+, Ar+, H2+, H3+, H2+, H−, O−, and OH− in helium and H3+ in H2 are presented in the present paper. The following papers describe positive ion-neutral and negative ion-neutral reaction rate constant measurements in the same device.
Flow-drift technique for ion mobility and ion-molecule reaction rate constant measurements. III. Negative ion reactions of O− with CO, NO, H2, and D2
Authors: McFarland M. , Albritton D. L. , Fehsenfeld F. C. , Ferguson E. E. , Schmeltekopf A. L.
Published: February 2004

A new combined flowing afterglow-drift tube experimental appartus has been used to measure the reaction rate constants as a function of ion kinetic energy for the following negative ion reactions: O−+CO→ CO2+e,O−+NO→ NO2+e,O−+H2→ H2O+e→ OH−H,O−+D2→ D2O+e→ OD−+D.Reaction (1) has been measured from thermal energy to ∼ 3 eV, (2) from thermal to ∼ 1.0 eV, (3) from thermal to ∼ 0.5 eV, and (4) from thermal to ∼ 0.8 eV. Reactions (1) and (2) are found to have rate constants that decrease by an order of magnitude with increasing ion kinetic energy, while Reactions (3) and (4) have total rate constants independent of energy. The channels (3b) and (4b) increase markedly with energy at the expense of the associative-detachment channels (3a) and (4a). The present results are compared with existing available data on these reactions.
Vibrational relaxation in HBr and HCl from 144°K to 584°K
Authors: Zittel Paul F. , Moore C. Bradley
Published: February 2004

A laser fluorescence technique was used to measure the vibrational relaxation rates of HBr(ν = 1) by HBr and HCl(ν = 1) by HCl between 144 and 584°K. A deep minimum in the relaxation probability was found near 300°K in both cases and is attributed to the effects of strong attractive interactions at low temperatures.
Wormlike chains near the rod limit: Path integral in the WKB approximation
Authors: Yamakawa Hiromi , Fujii Motoharu
Published: February 2004

The asymptotic forms of the distribution functions for two- and three-dimensional continuous wormlike chains near the rod limit are obtained by the path integral method with the use of the WKB approximation. The derived distributions give correctly the first-order corrections to the rod limiting values of all the moments.
Experimental determination of repulsive potentials between alkali ions (Li+, K+, and Cs+) and hydrogen molecules (H2 and D2)
Authors: Inouye H. , Kita S.
Published: February 2004

Integral elastic scattering cross sections of alkali ions (Li+, K+, and Cs+) in collision with room temperature hydrogen molecules (H2 and D2) were measured in the ion energy range 500–4000 eV. Some difference in the cross sections due to the replacement of the target gases were found in K+- and Cs+-hydrogen systems. Most of the difference can be explained by the difference of the target masses. The repulsive potentials deduced from the cross sections in a usual manner are represented by the following formulas independently of the isotopes: Li+: V(R) = 345 exp(−4.31 R), 0.88 < R < 1.43; K+: V(R) = 810 exp(−3.52 R), 1.33 < R < 1.98; and Cs+: V(R) = 1110 exp(− 3.26 R), 1.55 < R < 2.25; where V(R) is in units of electron volts and R in angstroms.
Low temperature heat capacities of one dimensional systems: Dimethylammonium trichlorocuprate (II) and tetramethylammonium trichloronickelate (II)
Authors: Hurley Michael , Gerstein B. C.
Published: February 2004

The heat capacity of DMACuCl3 has been measured from 1.156 to 28.608 K. The results indicate that three dimensional interactions are not negligible compared to those in one dimension. The one dimensional interactions may be interpreted in terms of the spin 1, antiferromagnetic Heisenberg model proposed by Weng and Griffiths, with an exchange parameter J of −4.92 K. Such a model is in agreement with a dimeric structure in which the Cu atoms are ferromagnetically coupled and in which the dimers within a chain order antiferromagnetically at low temperatures. The heat capacity of TMANiCl3 has been measured from 0.639 to 27.432 K. The results indicate that three dimensional interactions are not negligible compared to those in one dimension. The results were fit to the spin 1, antiferromagnetic Heisenberg model proposed by Weng and Griffiths, with an exchange parameter J of −2.73 K. Although such a model yielded a good fit, the sign of the interaction is in disagreement with that found by initial susceptibility measurements.
Phosphorescence emission and polarization of aminopyridines
Authors: Hotchandani S. , Testa A. C.
Published: February 2004

The phosphorescence quantum yield and lifetime of 2-, 3-, and 4-aminopyridine have been measured at 77°K in four solvent systems using 285 and 254 nm excitation. Luminescence polarization measurements in EPA at 77°K provide evidence that the lowest triplet in these molecules is π,π*. Of the three compounds studied only 4-aminopyridine exhibits vibronic activity in its phosphorescence spectrum and an out-of-plane and an in-plane vibration are readily discernible in its phosphorescence spectrum. No phosphorescence could be detected in methylcyclohexane for the three molecules, whereas it was measurable from EPA, acetonitrile and dichloromethane glasses. The observation suggests that intersystem crossing in these molecules may be strongly dependent upon the nature of the solvent. The O–O band in the phosphorescence spectrum is negatively polarized for all three molecules and the coupling scheme appears to be 1n,π*↔ s.o. 3π,π*. 4-Aminopyridine shows evidence for second order vibronic spin-orbit coupling and the mixing scheme appears to be 3π,π*↔vib 3n π*↔vib1π,π*.
Intermolecular potentials from crossed beam differential elastic scattering measurements VIII. He+Ne, He+Ar, He+Kr, and He+Xe
Authors: Chen C. H. , Siska P. E. , Lee Y. T.
Published: February 2004

Interatomic potentials for He-rare gas pairs have been obtained by fitting a multiparameter potential to low energy differential cross sections and second virial coefficients. There appears to be no single reduced potential which is valid for all He-rare gas systems; all asymmetric He-rare gas potentials have wider attractive wells than that of He2. rm and ε for He–Ne, He–Ar, He–Kr, and He–Xe are 3.21 Å, 14.3°K; 3.54 Å, 24.2°K; 3.75 Å, 24.7°K; and 4.15 Å, 25.2°K, respectively. Commonly used combining rules do not provide good estimates for well depths of these systems.
Investigation of the homogeneous nucleation of water vapor using a diffusion cloud chamber
Authors: Heist Richard H. , Reiss Howard
Published: February 2004

The temperature variation of the critical supersaturation for water vapor has been measured using a diffusion cloud chamber. By attaching a layer of glass wool to the upper plate of the chamber, the persistent refusal (in previous experiments) of water to wet this plate has been overcome. As a result, for the first time measurements without appreciable scatter have been achieved for water vapor. The resulting temperature dependence agrees reasonably well with that predicted by the classical Becker-Doering-Zeldovitch theory, while the experimental curve is shifted by approximately 8% from the classical prediction.
Nonequilibrium velocity distributions and reaction rates in fast highly exothermic reactions
Authors: Koura Katsuhisa
Published: February 2004

The nonequilibrium velocity distributions and reaction rates in fast highly exothermic reactions with a low activation energy ε*f/k T0 ≤slant 5, a high steric factor P ≥slant 0.1, and a large heat of reaction Q*/k T0 ∼ O (10), are investigated by solving the semiclassical Boltzmann equation with a Monte Carlo method. The explicit time-dependent velocity distribution functions and reaction rates from the initial equilibrium to the final chemical equilibrium are obtained for a model system, where the chemical species without internal degrees of freedom undergo a bimolecular single reversible reaction. The velocity distributions and the reaction rates indicate significant departures from equilibrium. The extent of departure of the reaction rate from the equilibrium rate increases with the heat of reaction and the activation energy and can be greater than 100%.
Equation of state for simple liquids from lattice theory
Authors: Laskin Saul , Weymann Helmut D.
Published: February 2004

The two-dimensional Kikuchi model for a lattice gas is adapted to describe real liquids. The resulting isochores for the liquid state predict that the pressure is a linear function of temperature in agreement with experimental results. It is shown that the equation of state of four simple liquids (argon, oxygen, nitrogen, and methane) can be described by the theory.
Vibrational relaxation by collisions of polyatomic molecules in excited states
Authors: von Weyssenhoff H. , Schlag E. W.
Published: February 2004

Inelastic collisions leading to a degradation of the internal vibronic energy of an electronically excited molecule (β-naphthylamine) have been observed by direct timing of the fluorescence from the excited state as a function of pressure of added gases. The zero-pressure lifetime spectrum as a function of excitation energy was employed as the energy scale calibration for the lengthening of the fluorescence lifetime. These experiments were performed also as a function of excitation energy and the results interpreted in terms of a collisional inefficiency when compared to a gas-kinetic cross section and a statistical model of energy transfer. Principally helium, argon, and propylene were studied, but preliminary experiments with propane revealed results similar to those for propylene. Helium, as expected, was less efficient than argon which, in turn, due to its lack of internal degrees of freedom was much less efficient than propylene. When the statistical complexions resulting from these added degrees of freedom were computed, it was found that the remaining ``one-dimensional'' efficiency of propylene was quite similar to that of argon. In view of their similar mass this would lend support to a previously advanced model in which simple collision mechanics determine energy transfer in one dimension.
Equilibrium properties of a one-dimensional kinetic system
Authors: Williams James H. , Joyce Glenn
Published: February 2004

One-dimensional systems of N = 500 and 250 particles in equilibrium are numerically simulated utilizing the method of molecular dynamics. Periodic boundary conditions are imposed. The classical two-body interaction potential is short range, repulsive and has a corresponding finite force. The equations of state are determined for densities both less and greater than one. Corresponding theoretical isochores are determined from models based on nearest-neighbor interactions and on a truncated virial expansion, and a comparison is made with the experimental isochores. Time independent radial distributions are constructed numerically and discussed. A change of state from a solidlike state to a fluid-gas state based on the penetrability of the particles is predicted. The transition temperatures are estimated from the radial distribution functions and the nearest-neighbor model. Self-diffusion is observed and the corresponding constants are determined from the velocity autocorrelation functions.
Vacuum ultraviolet absorption spectra of fluoromethanes
Authors: Sauvageau P. , Gilbert R. , Berlow P. P. , Sandorfy C.
Published: February 2004

The electronic absorption spectra of tetrafluoromethane, fluoroform, methylene fluoride, and methylfluoride were measured between 120 and 60 nm. Except for intenstities the spectra are found to be essentially the same as the electron impact spectra published previously by Harshbarger, Robin, and Lassettre. An experimental setup is described whereby absorption spectra can be measured in this part of the spectrum with relative ease.
Reaction of D3O+ with D2: Proton affinity of water
Authors: Cotter R. J. , Koski W. S.
Published: February 2004

The cross section for the endothermic ion-molecule reaction: D3O+(D2,D2O)D3O+ has been studied over the energy range 2–70 eV using a tandem mass spectrometer. The projectile beam was found to contain a significant fraction of the D3O+ in an excited electronic state which was relatively insensitive to collisional deactivation using high pressures but was readily deactivated using the paramagnetic gas NO in the primary ion source. Threshold measurements, using the ground state D3O+ beam, permitted a determination of the proton affinity of water and the conclusion that the reaction proceeded through a persistent intermediate complex at energies close to the threshold.
Zeeman nuclear quadrupole resonance study of antimony trichloride
Authors: Raman K. V. , Jagannathan R. , Narasimhan P. T.
Published: February 2004

The Zeeman effect of the nuclear quadrupole resonance (NQR) of 35Cl in crystalline power of SbCl3 has been studied at room temperature. The asymmetry parameters (η) of the electric field gradient (EFG) for the two inequivalent 35Cl sites have been obtained. For the 19.1749 MHz line the η value is 0.14 and for the 20.4074 MHz line the η value is 0.06. The present results on powder specimen agree with the earlier reported single crystal work. The experimental Zeeman spectra are compared with computer-simulated Zeeman spectra and good agreement is obtained between them. The validity of the point-charge model for EFG is also tested for the chlorine sites.
Determination of interatomic potentials by the inversion of elastic differential cross section data. III. Li–Ar7
Authors: Klingbeil Ralph
Published: February 2004

A set of phase shifts corresponding to the elastic scattering of lithium off of argon is extracted from a single set of differential cross section data. The phase shifts are inverted to a numerical Li–Ar7 interatomic potential.
Pyrene fluorescence in ethanol and cyclohexane under pressure
Authors: Johnson P. C. , Offen H. W.
Published: February 2004

The fluorescence of pyrene has been studied as a function of pressure, concentration and temperature in the solvents ethanol and cyclohexane. The spectra and lifetime of both monomeric pyrene and the excited state complex are characterized at different pressures. Compression of ethanol shifts the monomer-excimer equilibrium towards the monomer, while compression of cyclohexane leads to aggregation and pyrene excimer fluorescence over a large concentration range.
Pure rotational Raman scattering by symmetric top molecules
Authors: Patterson G. D.
Published: February 2004

The distribution of intensities between the branches of the pure rotational Raman spectrum of a symmetric top molecule is calculated according to the quantum mechanical method of Placzek and Teller. The total intensities are obtained by summing over the individual line intensities associated with transitions from rotational state J,K to state J′,K′. The exact distribution depends on the temperature of the system and the detailed geometry of the symmetric top molecule. In the classical (i.e., high temperature) limit, the fraction of intensity due to transitions for which Δ J=0 is found to be 0.25 for a linear molecule, to decrease to a minimum of approximately 0.167 for a prolate symmetric top, and to increase to a maximum of 0.254 for the limit of a disk. This fraction for an oblate symmetric top is in the range 0.20–0.254. Thus, measurements of the distribution of intensities of the branches of the pure rotational Raman spectrum can be used to obtain structural information for symmetric top molecules.
Study of H2++He → HeH++H at low energies
Authors: Neynaber R. H. , Magnuson G. D.
Published: February 2004

Laboratory-energy distributions of HeH+ were measured for the reaction H2++He → HeH++H (endothermic by 0.81 eV for ground-state reactants and products) with a merging-beams apparatus over a range of interaction energy W from 0.05 to 12 eV. The He was in the ground state; the H2+ was vibrationally excited. Absolute and relative cross sections were determined from these distributions. For W ≥ 5 eV, the distributions show that in the center-of-mass system the HeH+ peaks along both the incident direction of the H2+ and the incident direction of the He. The peak along the direction of the He is largest, and is the only one for W <5 eV. The role played by W and by the vibrational excitation of H2+ in the formation of the peaks is discussed. It is not clear what mechanism controls the reaction. The data cannot be satisfactorily explained with either the spectator-stripping or the Langevin model.
Analysis of the pressure virials and Clausius-Mossotti function for polyatomic gases
Authors: Ely James F. , Hanley H. J. M. , Straty G. C.
Published: February 2004

Statistical mechanical equations for the second pressure virial coefficient and the second and third dielectric virial coefficients for quadrupolar molecules are evaluated using the m -6–8 potential function. The results are compared with experimental data for nitrogen and fluorine. An approximate value for the quadrupole moment of fluorine is estimated. Agreement between theory and experiment is generally good.
Continuous absorption below the band convergence limit in the I2 B ← X transition
Authors: Tellinghuisen Joel
Published: February 2004

The I2 B(3Π0u+) ← X (1Σg+) transition displays both continuous and discrete spectral features. Because of absorption from thermally excited levels of the ground state, the continuum of such a system extends a considerable distance into the discrete spectrum below the spectroscopic dissociation limit D0. The extinction coefficient for B ← X absorption in I2 is resolved quantitatively into discrete and continuous contributions near D0, with application to several recent studies of this transition.
Kinetics of the uranium-hydrogen system
Authors: Condon J. B. , Larson E. A.
Published: February 2004

The reaction kinetics of U + 3/2 H2⇄UH3 was studied with fine powders on an ultrahigh-vacuum microbalance. The kinetics were found to be first order with respect to uranium for the hydriding reaction and nearly zero order with respect to uranium hydride for dehydriding. A new reaction mechanism is proposed to account for the experimental observations which involves diffusion in the reactant phase by hydrogen before nucleation to form the hydride phase. This reactant phase diffusion and phase transformation reaction with its associated solid state mathematics accounts for all the observations made to date on the kinetics of this system.
Cavity perturbation technique for determining the presence of molecular ions of helium in a dc discharge plasma
Authors: Congleton M. W. , Freeman R. H. , Roberts J. A.
Published: February 2004

A resonant cavity technique was employed as a probe to determine the presence of molecular ions of helium. The cavity resonance profile was displayed on an oscilloscope and the nature of the perturbation of this resonance observed to determine the nature of ions in a plasma filament placed coaxially within the cavity. The Slater perturbation technique for resonant cavities was employed to calculate relative ion abundances for each type of helium ion observed to be perturbing the resonant frequency of the cavity. The results of this work indicate that for specific currents, voltages and pressures, for a given geometry discharge tube, various molecular ions of helium can be produced and analyzed by the cavity perturbation technique.
Light scattering from dilute macromolecular solutions
Authors: Altenberger A. R. , Deutch J. M.
Published: February 2004

The polarized light scattering spectrum from a dilute solution of spherical macromolecules is customarily interpreted on the basis of independent particle diffusion. However, it is known that diffusion in such a system is governed by a many particle diffusion equation with cross-diffusion coefficients Dij that depend on the inverse distance between all pairs of particles (i, j). Here we prove that the spectrum from the system described by the N-particle diffusion equation is identical to the spectrum obtained from the simple, but incorrect, independent particle diffusion model. The physical reason for this suprising simplication is that the Dij are proportional to Oseen's tensor which holds for an incompressible fluid and hence has no longitudinal part. When short-range forces are taken into account as well as the long-range hydrodynamic interaction present in Dij, it is possible to obtain simple approximate expression for a k-dependent effective diffusion constant Deff(k). This expression is evaluated for the case where the macromolecules are treated as hard spheres and one obtains Deff(k) = D0[1 + 2.0φ] for low k where φ is the volume fraction of macromolecules in solution.
Effusion. X. Prediction of angular number distributions of chemically interacting species for cylindrical orifices
Authors: Liu Ming Biann , Wahlbeck P. G.
Published: February 2004

Angular number distributions of chemically interacting species have been calculated for cylindrical orifices. In these calculations, the assumption of chemical equilibrium among adsorbed species on the orifice wall and the basic assumptions of the Clausing theory including no surface diffusion were made. Numbers of molecules leaving the orifice wall and angular number distributions were calculated for the different species using equations originally developed for a single species by Edwards and Freeman. The calculated results are in good agreement with previous theoretical results by Voronin and are compared to those by Winterbottom. There is excellent agreement between the experimental angular number distributions measured and corrected by Grimley et al. and these calculated results.
Photoionization mass spectrometry of F2O
Authors: Berkowitz J. , Dehmer P. M. , Chupka W. A.
Published: February 2004

The photoionization efficiencies of the ions F2O+ and OF+ have been measured in a photoionization mass spectrometric study of F2O. The adiabatic first ionization potential of F2O is determined to be 13.11 ± 0.01 eV. The region near threshold (13.11–13.6 eV) has structure that is interpreted as vibrational autoionization. Additional peaks at 13.81, ∼ 15, and ∼ 15.5 eV are interpreted as Rydberg levels that decay by an electronic autoionization mechanism and which converge to the second ionization potential at 16.17 eV. An upper limit for the appearance potential of OF+(0°K) is found to be 14.438 eV, grossly different from the electron impact value of 15.8 ± 0.2 eV. The current result implies Δ H°f0(OF)=+26.1 ± 2.3 kcal/mole and I.P.(OF)=12.79 ± 0.10 eV.
Regional stationary principles and regional virial theorems
Authors: Mazziotti Alexander , Parr Robert G. , Simons Gary
Published: February 2004

If the Born-Oppenheimer Hamiltonian operator for a molecular system is averaged over all space for electrons 2,3, ··· , N, but for electron 1 is averaged only over the volume A, with surface S, it is shown that the regional expectation value so defined is stationary with respect to change of a parameter ζ in the exact wavefunction, provided that ∫S[(∂/∂ n1) Pζ(1,1′)]1=1′ dS1=0, where, for nodeless ψ, Pζ(1,1′)=∫ ··· ∫ψ*(1′,2,··· , N) ψ (1,2, ··· , N) × ∂ ln[ψ(1, 2, ··· , N)/ ψ*(1′, 2, ··· , N)]∂ ζ |ζ=1 dτ2 ··· dτN. Under this condition with ζ a scale parameter, a regional virial theorem is shown to hold for the volume A, in the sense previously described by Bader and co-workers [J. Am. Chem. Soc. 93, 3095 (1971): Chem. Phys. Lett. 8, 29 (1971), J. Chem. Phys. 56, 3320 (1972); 58, 557 (1973)]. This condition differs from the corresponding condition suggested by Bader (∂ / ∂ n1)ρ (r1)=0 on S, but in most cases the surfaces determined by it should be similar to those determined by Bader's condition. Corresponding conditions for approximate wavefunctions are discussed, and illustrations are given.
Rotationally inelastic scattering with effective potentials
Authors: Zarur George , Rabitz Herschel
Published: February 2004

Appropriate close-coupled equations and cross-section expressions are derived starting with a previously developed effective intermolecular potential between an atom and a diatomic molecule. A comparison is made between the effective equations and those arising from the use of conventional potentials in close coupling. The effective expressions are algebraically simpler, and fewer effective coupled equations must be solved. Rotationally inelastic cross-section calculations on the He–H2 system are carried out to illustrate the simplifications and also to present a more detailed study of this system. The effective total and differential cross sections agree quite well with previous conventional calculations. In addition, more extensive calculations are presented which include several transitions J → J′ not previously studied: 0 → 2, 0 → 4, 0 → 6, 2 → 4, 2 → 6, 4 → 6 for parahydrogen and 1 → 3, 1 → 5, 1 → 7 , 3 → 5, 3 → 7, 5 → 7 for orthohydrogen at total energies up to E = 0.86 eV. The important role of rotation-translation energy transfer is illustrated in these results. Finally, the expected region of validity and realm of usefulness of effective potentials is discussed.
Studies in molecular dynamics. XII. Band shape of the depolarized light scattered from atomic fluids
Authors: Alder B. J. , Strauss Herbert L. , Weis J. J.
Published: February 2004

The induced dipole-induced dipole autocorrelation functions for systems of atom interacting with Lennard-Jones, hard-sphere, and square-well potentials are presented. No evidence for long-time power-law tails on these functions is found. The band shapes calculated from the autocorrelation functions agree quantitatively with the available data on the band shapes of depolarized light scattering of atomic systems over an enormous range of temperature and density. The calculated results vary with the potential especially at high densities, and the agreement with experiment is within the uncertainty in the true atomic potential. This is true in spite of the earlier findings that the intensities calculated in this way are an order-of-magnitude too large at normal liquid densities because the calculations neglect the distortion of the polarizability of the individual atoms.
Simple classical model for the scattering of diatomic molecules from a solid surface
Authors: Doll Jimmie D.
Published: February 2004

The scattering of diatomic molecules from a solid surface is examined. The simple, classical hard-cube model of surfaces of Logan and Stickney is extended to include rigid rotor scattering. For simplicity the rotor's motion is confined to a single plane. As with the hard-cube model, energy transfer (as evidenced by maxima of scattering intensities) is overestimated, but the mass and temperature dependence are reproduced. Experimental agreement for widths is reasonable and is improved over the simple hard-cube model. Conditions are discussed under which qualitative differences between atom/hard-cube and rigid rotor/hard-cube scattering might be observed.
Energy transfer in monochromatically excited nitric oxide: A2Σ+ and B2Π
Authors: Melton L. A. , Klemperer William
Published: February 2004

Excitation of NO molecules into specific vibration-rotation levels of the A2Σ+ and B2Π electronic states by absorption of atomic lines has been studied under various experimental conditions by observing the steady-state fluorescence spectra of the (A 2Σ+−X 2Π) and (B 2Π−X 2Π) bands. Excitation of the A 2Σ+, v′=0–3 and B 2Π, v′=3, 4 levels was achieved. The fluorescence from NO A 2Σ+, v′=0–3 was found to be quenched by NO X2Π with an effective cross section of 25 Å2. The fluorescence from NO B 2Π, v′=0, 3, 4 was found to be quenched by NO X2Π with effective cross sections of 16, 21, and 20 Å2, respectively. The anomalously efficient vibrational relaxation of NO A 2Σ+, v′=1 by NO X2Π was found to be one aspect of an efficient electronic energy exchange process. The cross sections for exchange of electronic energy between N14O16 A Σ+2, v′=0 and 1 and N1615 OX 2Π, v″=0 were found to be 12 ± 3, 7 ± 4, and 1.7 ± 0.3 Å2 for the N14O16 A, v′=1→N15O16, A, v′=1,N14O16 A, v′=0→N15O16 A, v′=0, and N14O16 A, v′=1→N15O16 A, v′=0 processes, respectively. A transition dipole-transition dipole interaction is proposed for this transfer process. Rates of electronic energy transfer from NO A2Σ+ to NO B2Π, and vice versa, in collision with NO X2Π, were also measured.
Nonexponential spin lattice relaxation and its orientation dependence in a three-spin system
Authors: Mehring M. , Raber H.
Published: February 2004

Nonexponential spin lattice relaxation due to cross correlation of the intramolecular dipole interaction has been observed in a trifluoromethyl group. The orientation dependence of the spin lattice relaxation as described by the theory of Hilt and Hubbard has been confirmed experimentally. A value of τc=4.0× 10−11 sec for the correlation time at room temperature was obtained.
Variational theory of reaction rates: Application to F+H2⇄HF+H
Authors: Jaffe R. L. , Henry J. M. , Anderson J. B.
Published: February 2004

The classical variational theory of reaction rates is coupled with a Monte Carlo trajectory analysis to yield reaction rates and energy distributions of reactants and products for the forward and reverse reactions: F+H2⇄HF+H at 300°K. The results are compared with those of a standard quasiclassical trajectory analysis of the forward reaction using the same potential energy surface. Differences are attributed to the quantized distributions of reactants in the quasiclassical calculations. The combination of the two methods allows a substantial reduction in computation requirements for determining the characteristics of reactions in systems with reactants in thermal equilibrium.
Magnetic properties of concentrated metal-ammonia solutions. I. Magnetic susceptibility
Authors: Lelieur J. P. , Rigny P.
Published: February 2004

Magnetic susceptibility measurements of Na–NH3 and Cs–NH3 solutions have been performed in the concentrated range of solutions using the Gouy method. The paramagnetic susceptibility of metal in solution is very low for weakly concentrated solutions (about 1 MPM), and increases rapidly in the intermediate range of concentrations. For very concentrated solutions, the paramagnetic susceptibility of metal in solution is about that expected for an interacting free electron gas. The temperature coefficient of the magnetic susceptibility is always positive and is found to decrease when metal concentration increases. For concentrations of about 15 MPM, this temperature coefficient is of the same order of magnitude as for the corresponding liquid alkali metal.
Core excitation spectra of CH4 and SiH4
Authors: Deutsch P. W. , Kunz A. Barry
Published: February 2004

One-center Hartree-Fock calculations have been performed both on the ground and on some of the highly excited states of CH4 and SiH4. The calculations are in reasonable agreement with the salient features of recent soft x-ray absorption experiments on SiH4 [W. Hayes and F. C. Brown, Phys. Rev. A 6, 21 (1972)]; W. Hayes, F. C. Brown, and A. B. Kunz, [Phys. Rev. Lett. 27, 774(1971)] and on CH4 [H. U. Chun, Phys. Lett. A 30, 445 (1969)].
Conformational comparison of aromatic molecules and their ions. III N-(Diphenylmethylene)-aniline and benzil by NMR and EPR
Authors: Geraldes Carlos F. G. C. , Gil Victor M. S. , Eargle Dolan H.
Published: February 2004

Utilizing methods of conformational analysis developed from Johnson-Bovey tables and the Fraenkel electron density-chemical shift relation, the dihedral angle of the A ring of N-(diphenylmethylene)-aniline I is found to have its average position near that of benzalaniline, i.e., nearly vertical. Due to a complex spectrum, the geometries of the other rings are difficult to assess. The dianion I−2 shows a large chemical shift from I owing to the high negative charge. The average positions of the phenyl rings of benzil (II) are confirmed by NMR to be perpendicular to each other and those of II−2 to be nearly parallel to each other, but perpendicular to the plane of the cis chelate.
Ozone ultraviolet photolysis. VI. The ultraviolet spectrum
Authors: Simons John W. , Paur Richard J. , Webster Henry A. , Bair Edward J.
Published: February 2004

The ozone ultraviolet spectrum has been re-examined at low temperature to clarify features of photochemical interest. The origin of the system is a diffuse band at 28 450 cm−1, the long wavelength limit of band structure in the cold spectrum. The bands toward higher frequencies are identified as sequences of the upper state bending (333 cm−1) and symmetrical stretching (600 cm−1) modes. This band structure converges to a limit near 32 400 cm−1, consistent with the energy required to form O(1D) plus O2(1Δ). Both the shading of the bands and sequences which appear suggest that the Huggins bands are that part of the Hartley-Huggins system which lies below the dissociation limit, the system being a single transition B21← X A11. The component of the continuum due to excitation of the ν010″ bending mode is shown to be similar to that arising from the ν000″ ground state, except for a shift toward lower energy equal to the vibrational excitation energy. A rationale for predicting the effect of temperature on the shape of the continuum is presented.
Raman spectra and vibrational potential function of polycrystalline azomethane and azomethane-d6
Authors: Pearce Robert A. R. , Levin Ira W. , Harris W. C.
Published: February 2004

Raman spectra of polycrystalline azomethane (CH3N=NCH3) and azomethane-d6 were examined at liquid nitrogen temperatures using argon ion laser excitation. These data, in conjunction with a normal coordinate analysis, provide a basis for a modification of the vibrational assignments for the azomethane system. A 17 parameter molecular force field, based upon the solid state vibrational frequencies of azomethane and its deuterated analog, was determined by least-squares procedures. The unusual coupling characteristics between the X–N stretching and X–N=N bending coordinates are discussed for both azomethane and trans-1,2-difluorodiazine, FN=NF.
Calculation of van der Waals forces in systems with nonlocal conductivity
Authors: Chang David B. , Cooper Robert L. , Drummond James E. , Young Allan C.
Published: February 2004

A method is presented for calculating van der Waals forces in systems with nonlocal conductivity. The fluctuating fields in the electromagnetic stress tensor are obtained by applying the fluctuation-dissipation theorem to the response of the system to an external polarization. As an example, the method is used to calculate the contribution of conduction electrons to the interaction of two blocks of metal. When the electrons are described in a simple hydrodynamic approximation keeping only the lowest order nonlocal terms, the interaction force is the same as that obtained by Lifshitz assuming local conductivity. At separations large compared to the London penetration depth c /ωp the interaction is due to electromagnetic waveguide modes, while at distances small compared to c /ωp, the force is due to surface plasmons. As a second example, the method is applied to the interaction of two graphitelike blocks. With a quantum mechanically derived description of the electron motion, the resulting force differs from the Lifshitz expression both because of the anisotropy of the system and because of the nonlocal conductivity.
van der Waals forces between cylinders: Thin rods inclined at an angle
Authors: Mitchell D. J. , Ninham B. W.
Published: February 2004

The free energy of interaction of two long thin cylindrical anisotropic dielectric rods immersed in a medium at a finite temperature, and inclined at an arbitrary angle is calculated by the continuum theory of molecular forces.
Condensation in CO2 free jet expansions. I. Dimer formation
Authors: Dorfeld William G. , Hudson John B.
Published: February 2004

A theoretical and experimental investigation of the kinetics of CO2 dimer formation in the adiabatically expanding core of a free jet expansion has been carried out. The theoretical analysis is based on dimer formation by an efficient termolecular process and dimer destruction by bimolecular collisions. Account is taken of the expected variation of the specific heat ratio γ during the expansion and of the effective increase in the termolecular collision rate at low temperatures due to the presence of loosely bound orbiting pairs. Experimental dimer concentrations were measured mass spectrometrically by forming a molecular beam from the expanded gas mixture after the onset of molecular flow. Observed dimer concentrations, for a range of pre-expansion conditions of 400–900 torr pressure and room temperature, are in good agreement with the theoretical analysis, provided account is taken of the effect of loosely bound orbiting pairs at low temperatures.
Electron capture and excitation in alkali ion-atom collisions using an atomic eigenfunction expansion
Authors: Rapp Donald , Chang Chi-Ming
Published: February 2004

Previous calculations of (Li+, Li) scattering utilizing an expansion in traveling atomic orbitals have been extended to the collisions (Na+, Na), (Li+, Na), and (Na+, Li). While the over-all trends of the experimental energy dependences of the cross sections are reproduced by the theory, the detailed structure in the data is very poorly represented by our calculations. Since this structure is due to collisions at small impact parameter (less than ∼ 5 a 0) it appears that a variational technique is required to allow the atomic orbitals to contract at small separations. Unless this is done, the atomic expansion method fails badly at small impact parameter. We believe the calculations are reasonable at large impact parameters, however.