bluuebunny/crossref_metadata_2025 huggingface dataset:
A theoretical study of Li2H. I. Basis set and computational survey of excited states and possible reaction paths
Authors: England Walter B. , Sabelli Nora H. , Wahl Arnold C.
Published: February 2003

SCF potential curves for C2v (Li2+H) and C∞v (LiH+Li) symmetries have been calculated for the 26 lowest lying states of Li2H. The curves are estimated to be ≲0.1 eV above the Hartree–Fock–Roothaan limit. Correlated MCSCF/CI curves were computed for the lowest states of 2A1, 2B2, and 2Σ symmetries. All low-lying states of the complex Li2H involve substantial charge transfer. The most stable of these, 2A1, lies ∼20 kcal/mole below the ground state LiH+Li asymptote. The first excited state of the complex, 2B2, is but weakly bound relative to the same asymptote. Electron-jump geometries and vertical spectra were computed for all of these low-lying states. Possible low-energy paths for the reaction Li2+H→LiH+Li were determined, and all involve charge-transfer intermediates.
Density and temperature effects on motional dynamics of SF6 in the supercritical dense fluid region
Authors: DeZwaan J. , Jonas J.
Published: February 2003

The NMR 19F spin–lattice relaxation times and self-diffusion constants have been measured in the dense fluid of SF6 as a function of pressure and temperature over the density range 0.4⩽ ρ/ρc⩽2.6 and the temperature range 0.8⩽T/Tc⩽1.5. Densities have also been determined under the same experimental conditions. The relaxation mechanism for the fluorine nuclei is dominated by the spin–rotation interactions and therefore the analysis of the T1 data yields the angular momentum correlation time τJ. On the other hand, the self-diffusion data provide information about the behavior of the linear momentum correlation time τP, in SF6. Interpretation of the experimental data based on the hard sphere model of liquids allows us to draw several conclusions of general character about the molecular dynamics of the spherical molecule of SF6 in the dense fluid region: (a) The angular momentum relaxation can be approximated as occurring through a sequence of uncorrelated binary collisions; (b) the estimated hard sphere diameter is temperature dependent and in reasonable agreement with the theoretical prediction; (c) for fluid densities lower than twice the critical density one finds considerable deviation between experiment and theory; (d) due to many body correlations the linear momentum behavior differs from the Enskog theory predictions in agreement with the results of the molecular dynamics calculations.
Direct evidence of the natural predissociation of the I2 B state through systematic measurements of lifetimes
Authors: Broyer M. , Vigué J. , Lehmann J. C.
Published: February 2003

Lifetimes of individual rovibrational levels in the I2 B state have been systematically measured by the decay method. The J′ (J′+1) dependence of the inverse of the lifetime due to a gyroscopic predissociation, is clearly demonstrated. These predisssociation rates are in good agreement with those we obtained by another method based on the study of magnetic predissociation.
Generalized van der Waals equation of state
Authors: Hoover William G. , Stell G. , Goldmark E. , Degani G. D.
Published: February 2003

The quantitative thermodynamic effect of adding a weak, long-range attraction to inverse-power repulsive potentials is studied. The resulting phase diagrams exhibit two fluid phases and a solid phase, a critical point, a triple point, and, for sufficiently soft repulsions, an additional solid phase with an additional triple point. The effects of attractions other than van der Waals’ are studied too by using a simple analytic model for the canonical partition function. Although such models exhibit a wide variety of thermodynamic behavior, they are still not general enough to reproduce the results of high-temperature measurements on liquid metals.
Total cross section measurements for the scattering of argon by aliphatic hydrocarbons
Authors: Nenner T. , Tien H. , Fenn J. B.
Published: February 2003

Absolute values of total cross sections have been determined for the scattering of a monoenergetic molecular beam of argon by 30 aliphatic hydrocarbons. Included are the normal paraffins, cycloparaffins, olefins, and acetylenes with from one to eight carbon atoms. Also included are two diolefins and three butene isomers. Values are reported for the cross section at a relative velocity of 555 m/s. The van der Waals coefficients from the experimental data generally are within a few percent of those calculated by the Slater–Kirkwood approximation.
Dielectric relaxation and dynamic susceptibility of a one-dimensional model for perpendicular-dipole polymers
Authors: Shore John E. , Zwanzig Robert
Published: February 2003

The dielectric properties of a simple model are studied. The model consists of a one-dimensional lattice of interacting objects, called spins. Each spin is oriented in a plane perpendicular to the lattice axis and is free to rotate in that plane. The spins undergo harmonic interactions with each other and, if they are dipolar, a cosine interaction with external fields. At sufficiently low temperature and for sufficiently strong spin–spin coupling, the model is equivalent to one in which the spin–spin interactions are proportional to the cosine of the angular difference between spin positions. It is shown that solution of the rotational diffusion equation leads to an interaction-independent, nonexponential decay function that is quite similar to a decay function derived empirically from polymer data by Williams and his co-workers. Exact decay functions are derived for both strong and weak applied fields, for both periodic and open boundary conditions, and for both nearest-neighbor and longer-range spin–spin interactions. Results of numerical calculations of dynamic susceptibitlity are presented, and it is shown that the model’s qualitative behavior is consistent with much experimental data, especially polymer data.
ENDOR study of 171Yb3+ in Cs2NaYCl6 to determine Γ8–Γ6 energy splitting
Authors: Devaney P. , Stapleton H. J.
Published: February 2003

The ENDOR spectrum of trivalent 171Yb in Cs2NaYCl6 has been measured to determine the crystal field splitting of the 2F7/2 ground level. The pseudonuclear Zeeman correction to the spin Hamiltonian implies that the Γ8 quartet lies 225±10 cm−1 above the Γ6 ground doublet. A reasonable assumption concerning the ratio of fourth and sixth order crystal field terms then predicts the Γ7 doublet at 460 cm−1. Spin Hamiltonian parameters are found to be: g=−2.586±0.002, A=−(688.7±0.1) ×10−4 cm−1, and g′I=+(1.66±0.04) ×10−3, where the sign of the electronic g factor is inferred from theoretical considerations.
Collision dynamics of three interacting atoms: The multiple-collision expansion
Authors: Micha David A. , Yuan Jian-Min
Published: February 2003

Inelastic, atom–exchange, and dissociative atom–diatomic collisions are described by means of a multiple-collision expansion of the Faddeev equations for three atoms. Collision processes are described by a superposition of stripping, single-, double-, and so on, atom–atom encounters. The corresponding probability amplitude terms are expressed as integrals in momentum variables which require for their evaluation only two-body t matrices and the initial and final distributions of diatomic momenta. Analysis of these integrals leads to the spectator- and recoil-stripping models, and to kinematics rules that indicate whether a process may occur by single collisions or not. The kinematic rules are applied to (a) inelastic and reactive collisions of Ar++H2 and its isotopic variations; (b) inelastic collision of NO++He; and (c) inelastic collision of Li++H2, in order to illustrate their value in interpreting experimental results.
Fluorescence of nitric oxide excited by the 184.9 nm mercury resonance line
Authors: Hikida T. , Washida N. , Nakajima S. , Yagi S. , Ichimura T. , Mori Y.
Published: February 2003

The fluorescence of NO was obtained by excitation from the 184.9 nm resonance line of a low pressure mercury lamp. It was found that the β (v′=9) emission was induced by the absorption of the 184.9 nm line for [NO]=1.0 torr. Quenching of the β (v′=9) bands by He or N2 molecules was accompanied by an enhancement of the γ bands, v′=4 or 0 and 1, respectively. When CO was added to NO, intensities of the emission were weakened. These effects were explained by the following reaction scheme.
Resonance Raman scattering in molecular dimers
Authors: Gregory A. R. , Henneker W. H. , Siebrand W. , Zgierski M. Z.
Published: February 2003

A systematic study is initiated of resonance Raman scattering in molecular systems with overlapping electronic absorption bands. Resonance Raman spectra, excitation profiles, and depolarization ratios are calculated for a simple molecular dimer in which the two overlapping Franck–Condon progressions are related through the permutational symmetry of the dimer. The model used is highly idealized, but can be solved exactly for a complete range of intermolecular coupling strengths. In the weak and strong intermolecular coupling regions, the exact results are compared with the physically more transparent results obtained from a low-order perturbation treatment. The spectra and profiles show properties characteristic of both totally symmetric and nontotally symmetric modes. The profiles and polarization dispersion curves are subject to both electronic and vibronic interference effects. Anomalous extrema of the depolarization ratio are often found to coincide with minima rather than maxima in the excitation profile. A pairwise comparison of the excitation profiles of Rayleigh lines, Raman fundamentals, and Raman overtones shows characteristic resonance–antiresonance coincidences. It is shown that interference effects of this sort are a general feature of systems exhibiting strong vibronic coupling.
Two-dimensional carbon-13 NMR spectroscopy
Authors: Müller Luciano , Kumar Anil , Ernst R. R.
Published: February 2003

A method is developed for recording two dimensionally resolved undecoupled 13C NMR spectra. The technique, which is related to 2 D Fourier transform spectroscopy, permits analysis for inspection even for large molecules. (AIP)
Laser isotope separation using an intracavity absorption technique
Authors: Datta Saswati , Anderson Roger W. , Zare Richard N.
Published: February 2003

Selective adsorption of I 37Cl by a broad band dye laser is obtained by placing a cell containing I 35Cl in the cavity of the laser in order to create ’’holes’’ at the absorption frequencies of I 35Cl in the laser output. It is shown that this method can be used to obtain highly efficient photochemical isotope separation. (AIP)
Comment on ’’Semiclassical treatment of vibrational–translational energy transfer in the near-adiabatic approximation’’
Authors: Cady W. A. , Clark A. P. , Dickinson A. S.
Published: February 2003

Recently [W. A. Cady, J. Chem. Phys. 61, 1214 (1974)], a near-adiabatic (perturbed stationary states) approximation was used in an investigation the collinear vibrational excitation of a harmonic oscillator. This approximation reduced the problem to that of obtaining transition probabilities for a harmonic oscillator with time-dependent forcing function. Cady derived an apparently exact solution for this problem. It is shown that this solution is not exact but that the solution results from making a further adiabatic approximation and give a derivation that clearly shows the adiabatic character of this further approximation.
Ultrasonic investigation of viscosity coefficients in the nematic liquid crystal, EBBA
Authors: Monroe S. E. , Wetsel G. C. , Woodard M. R. , Lowry B. A.
Published: February 2003

The attenuation of ultrasonic compressional waves in the nematic liquid crystal, N- (p-ethoxybenzylidene) –p-butylaniline (EBBA), has been measured as a function of frequency, temperature, and the angle between an aligning magnetic field and the direction of wave propagation. The results are interpreted in terms of theories of nematic liquid crystals based on hydrodynamics and micropolar continuum mechanics. It is shown that the correct expression for the attenuation anisotropy can also be derived from Leslie’s theory of anisotropic fluids. It was found that shear viscosity coefficients had the usual exponential dependence on inverse temperature with an activation energy of 10 kcal/mole whereas volume viscosity coefficients had a more complex temperature dependence. The attenuation of compressional waves in the unoriented nematic phase is compared with that of the oriented crystal.
Use of percolation theory to estimate effective diffusion coefficients of particles migrating on various ordered lattices and in a random network structure
Authors: Brandt W. W.
Published: February 2003

Two computational strategies were developed to estimate from percolation theory the relative diffusion coefficients Dr of particles executing random walks on various ordered lattices of different coordination numbers z and in random networks, characterized by a uniform density of nearest-neighbor sites around a given site, beyond a certain minimum separation of the sites Rc. Relative solubilities sr also were estimated for these systems, using literature data. The way the computed Dr and sr depend on the probability that a given site is accessible to the migrating particle, and on z or on Rc, respectively, when compared to corresponding experimental results, may allow one to characterize the ordered or random network structure of the substrate used.
Reactions of germanium vapor with oxidizers: Photon yields and a new GeO band system
Authors: Capelle Gene A. , Brom J. M.
Published: February 2003

Germanium was reacted with N2O, O2, NO2, and NO in a flow system, which produced GeO. Chemiluminescence was observed from three electronic band systems of GeO: A 1Π→X 1Σ+ in the uv, a 3Σ+→X 1Σ+ in the blue, and b 3Π1→X 1Σ+ (a previously unreported system) in the near uv. Vibrational constants and Te values have been obtained for the a 3Σ+ and b 3Π1 states, and evidence is presented for a perturbation between the b 3Π (v=8) and A 1Π (v=0) states. Photon yields for each of the three GeO band systems were measured to be small (<0.1% in all cases) and to be strongly pressure dependent in the 0.5- to 20-Torr region. Reaction of Ge vapor with F2 produced GeF (A 2Σ+→X 2Π) chemiluminescence with a measured photon yield of 6.8×10−4; the flames from Ge+Br2 and Ge+Cl2 were too weak to measure.
The dimensionality and choice of effective Hamiltonians for molecular collisions
Authors: Rabitz Herschel
Published: February 2003

The flexibility in choice of effective Hamiltonians is illustrated by considering various different dimensionality reducing procedures. Only a few members of the entire family of effective Hamiltonians have thus far been employed in actual computations. All the effective Hamiltonians are presented for two colliding molecules, and the reduced atom–molecule situation is also considered. The two-molecule case in body-fixed coordinates is treated in more detail since it has not been extensively examined before. Exactly analogous space-fixed and body-fixed dimensionality reductions are shown to be possible by appropriate selection and coupling of states. The available ranges of computing expense are discussed and the various methods related in these terms. Computing time and accuracy requirements are examined in regard to choosing an effective Hamiltonian. Further avenues of pursuit and calculations are suggested by these considerations.
Enhancement by helium and argon of the formation rate of the 1720-Å-radiating states of Xe*2 excited by an E beam
Authors: Rice James K. , Johnson A. Wayne
Published: February 2003

Helium and argon added to xenon are shown to increase markedly the formation rate of e-beam excited Xe*2 (1720-Å radiator) without decreasing the 1720-Å fluorescence efficiency. The measured association rate is interpreted in terms of three-body collisions among excited xenon atoms, ground state xenon atoms, and the added gas atoms to give rate constants of 5.0×10−32, 1.4×10−32, and 2.3×10−32 cm6 sec−1 for undiluted xenon, added helium, and added argon, respectively.
Field induced charge-transfer exciton transitions
Authors: Haarer D. , Philpott M. R. , Morawitz H.
Published: February 2003

This paper reports the observation of a second zero-phonon line, induced by a static electric field, lying 10 cm−1 above the first singlet charge-transfer exciton state of crystalline anthracene-PMDA. The splitting of these charge-transfer exciton states is a quadratic function of the electric field strength for low fields and becomes linear for fields of order 104 V/cm. The origin of these features is discussed on the basis of a one-dimensional model of the charge-transfer exciton in the linear donor–acceptor stack. The effect of charge-transfer admixture to the neutral donor–acceptor ground state and the effect of creating a local charge-transfer (ionic) state by the absorption of light are considered by use of a second-quantized Hamiltonian for the charge-transfer exciton. The splitting of 10 cm−1 observed by use of the static electric field, which removes the inversion invariance of the one-dimensional donor–acceptor chain along the stack axis arises from the mixing of symmetric and antisymmetric exciton eigenstates by the field. Numerical estimates of the splitting, based on experimental data, are in order of magnitude agreement with observation. The charge-transfer exciton band structure is derived by considering both electron and hole hopping terms and tight binding (nearest unit cell) excitation transfer.
Thermal expansion near a critical solution point
Authors: Greer Sandra C. , Hocken R.
Published: February 2003

We report precise measurements of the density as a function of temperature in the one-phase region near the consolute point in nitroethane + 3-methylpentane. We find evidence of the critical anomaly in the thermal expansion, but are not able to determine a unique value for the critical exponent α. We have performed computer experiments to determine under what conditions α could be extracted from thermal expansion data.
Ion-pair states of O2
Authors: Krauss Morris , Neumann David
Published: February 2003

Valence states of O2 that correlate adiabatically to the ion pair asymptote, O+(4S)+O−(2P), have been calculated using the multiconfiguration description of the electronic structure. The production of the ion pair is attributed to valence–Rydberg mixing that predissociates Rydberg states of the excited O2+ ion such as those leading to the b 4Σ−g state. The electronic states required the calculation of excited states of a given symmetry. This is possible with the BISON-MC codes if the rigorous restriction on orthogonality to the lower states is relaxed. For homonuclear valence states, in particular, this should be a good approximation.
Merging beams study of the H+3(D2,H2)HD+2 reaction mechanism
Authors: Lees A. B. , Rol P. K.
Published: February 2003

Laboratory energy distributions of HD+2 product ions formed in the H+3(D2,H2)HD+2 reaction were measured for reactants with relative energy W in the range 0.1 eV?W⩽11.0 eV. The results show that most of the product ions appear as a single peak, asymmetric with respect to the c.m. zero energy, and suggest predominantly direct interactions over the entire energy range studied. The relative energy of products, calculated from the position of the peak in the measured distribution, follows the predictions of the spectator stripping (SS) model for W?8 eV. Above W=9 eV the SS peak disappears and a product peak found at lower laboratory energies becomes dominant.
Electron paramagnetic resonance of triplet diphenylmethylene in single crystal benzophenone: Evidence for a low temperature phase transition
Authors: Anderson Richard J. M. , Kohler Bryan E.
Published: February 2003

The angular variation of the field for resonance for diphenylmethylene in benzophenone at T?2 °K has been measured over the entire unit sphere. Both the values of the fine structure tensors T and g and the spatial relationships between the four substitutional sites in the unit cell change as the temperature is lowered from 77 °K to ∼2 °K. The geometrical changes are consistent with a benzophenone phase transition from P212121 to P21 symmetry.
Positronium spin conversion in Li–ammonia solution
Authors: Bisi A. , Bosi L. , Lazzarini E. , Zappa L.
Published: February 2003

The time spectrum of positrons annihilated in lithium–ammonia solutions of various concentrations was analyzed. It was found that the decay rate of the longest lived component increases at the same time as the Li concentration increases; likewise its intensity increases until it attains 100% at high concentration. The results are interpreted in terms of electron exchange collisions which convert triplet positronium to singlet and vice versa. The triplet to singlet conversion rate γ was found proportional to the number of Li atoms dissolved per unit volume.
Crystal Coulomb energies. VI. Madelung energies of simple TCNQ salts. What is the electron affinity of TCNQ (7,7,8,8-tetracyanoquinodimethan) ?
Authors: Metzger Robert Melville
Published: February 2003

The Madelung energy EC (classical interionic crystal Coulomb energy in the fractional point-charge approximation) has been calculated for Na+TCNQ−, Rb+TCNQ−(I), Rb+TCNQ−(II), and for NH4+TCNQ−. The values obtained are EC=−5.29, −4.71, −4.64, and −4.82 eV/molecule, respectively. When these values are coupled with available thermochemical data in a Born–Haber cycle, then the best recent experimental estimate of the electron affinity of TCNQ, 2.8 eV (obtained by Cs beam collisional ionization) is not verified, because apparently in these organic ionic crystals, as many as 2.5 eV of binding must be due to other interactions which our Madelung calculations ignore at present. It is likely that charge-induced dipole interactions may supply the several electron volts that are missing from the calculated crystal binding energy.
Crystal Coulomb energies. VII. The electrostatic binding energy defect in Tetrathiofulvalinium 7,7,8,8,-tetracyanoquinodimethanide
Authors: Melville Metzger Robert , Bloch Aaron N.
Published: February 2003

The Madelung energy EC of TTF TCNQ was computed by Ewald’s method using the 300 and 100 °K crystal structures and several charge models based on CNDO/2, PPP, and INDO atom charge densities, and as a function of charge transfer. In all cases EC compares unfavorably, by several electron volts, with the cost of ionizing the lattice. This had been noted previously for NMP TCNQ. This binding energy defect is too large to be explained by metallic binding or exchange forces, or by electron correlation, even in the Wigner crystal limit. We speculate that polarization forces, or covalent effects may play a large role in stabilizing the lattice. The Madelung site potentials in the TTF+1TCNQ−1 lattice are sufficient to explain the observed core level splittings in the photoelectron spectrum.
Pressure and temperature dependences of the Raman-active phonons in dichlorobis(pyridine)zinc(II) crystal
Authors: Wong P. T. T.
Published: February 2003

The effects of pressure and temperature upon the eight Raman-active phonons of the [ZnPy2Cl2] crystal were investigated. Two techniques were used to measure the presssure dependence of the phonon frequencies, which allowed us to determine the isothermal compressibility and the mode Grüneisen parameters. The isobaric temperature dependence of each frequency was separated into thermal strain and anharmonic ’’self-energy’’ contributions and discussed in terms of the cubic and quartic anharmonicities.
Derivation of stochastic equations for nonequilibrium Ising mean field model
Authors: Metiu Horia , Kitahara Kazuo , Ross John
Published: February 2003

Phenomenological master equations are useful for discussions of various aspects of the kinetics of phase transitions. The transition rate in such master equations is of a form proposed by Langer; the rate is an exponential of the change of the free energy of the system due to a change in a thermodynamic variable. We present a derivation of this form from a microscopic theory for an Ising model which exhibits first and second order phase transition. Using Zwanzig’s formalism we derive a master equation for a spin system which interacts with a phonon heat bath. Thus, we obtain the transition rate on a time scale of one microscopic event (one spin flip). This form differs from the phenomenological one in that it depends on details of the dynamics of the system, the heat bath, and the interaction between them. These details are removed by a further averaging (coarse-graining). If a Markoffian master equation is assumed to exist on a phenomenological time scale large compared to the microscopic time scale, yet small compared to the relaxation time of the system, then we show that the transition rate in that master equation has the form proposed by Langer.
Vacuum ultraviolet absorption spectra of solid OCS at 53 K
Authors: Monahan Kevin M. , Walker William C.
Published: February 2003

Photoabsorption spectra of thin films of solid OCS were obtained in the 110–300 nm wavelength region. The absorption intensities and excitation energies of the 1Δ←1Σ+ and 1Π←1Σ+ transitions were changed in the solid, and higher energy Rydberg absorption was reduced and diffuse. Three absorption continua not normally observed in the gas phase were found at 4.3, 4.7, and 6.9 eV and assigned to the 3Σ+←1Σ+, 1Δ←1Σ+, and 3Π←1Σ transitions, respectively.
Diffusion theory for crystal growth at arbitrary solute concentration
Authors: Müller-Krumbhaar H.
Published: February 2003

The influence of the solute concentration upon the kinetics of crystal growth is studied for various cases with equilibrium and nonequilibrium boundary conditions, constant cooling rate, and temperature-dependent diffusion coefficient. A perturbation expansion is used to calculate first-order corrections in the low concentration region. Complete numerical solutions for nonequilibrium crystal–liquid interface conditions are obtained by a finite difference method. The influence of the various parameters upon the time-dependent growth rates is discussed.
Radiative and predissociative lifetimes of the V ′=0, 1, and 2 levels of the A 2Σ+ state of OH and OD
Authors: German K. R.
Published: February 2003

A direct measurement of the fluorescent decay rates of the V ′=0, 1, 2 vibrational levels of the A 2Σ+ state of OH and OD has been performed using pulsed laser excitation and at total gas pressures of less than 1 mTorr. The present experiment is the first in which lifetime measurements have been performed for individual rotational levels (N ′) of each of the three lowest vibrational states of both OH and OD and at pressures where both quenching and excitation transfer should be minimal. The radiative lifetime was found to increase slightly for the higher vibrational levels in agreement with a model of linear decrease of the transition moment with increasing internuclear separation. The measured radiative lifetimes, τV ′± (3σ), for OH were τ0=693±30 nsec, τ1=736±33 nsec and for OD were τ0 =691±27 nsec, τ1=712±30 nsec, τ2=736±39 nsec. The V ′=2 level of OH was found to be strongly predissociated with a predissociation lifetime of about 270±25 nsec at N ′=1. An analysis of the energies at which predissociation occurs leads to the conclusion that the repulsive 4Σ− state is responsible for all the observed predissociations for V ′?2 in both OH and OD.
Numerical relativistic self-consistent field calculation of electron density and 〈r−3〉 for a number of electron configurations of iron and tin. Application to tin Mössbauer spectroscopy
Authors: de Vries J. L. K. F. , Trooster J. M. , Ros P.
Published: February 2003

Results of a relativistic self-consistent field calculation of ‖ψ (0) ‖2 and 〈r−3〉3d and 〈r−3〉5p of Fe and Sn, respectively, in different electron configurations are presented. A comparison is made with often used results of the Hartree–Fock calculations and significant differences are found, which are shown to have implications on the derivation of (ΔR)/R for 57Fe from measurements of an Fe in a rare gas matrix. The results on tin are used to reanalyze a number of determinations of (ΔR)/R and formulas are given expressing the Mössbauer isomer shift and quadrupole splitting of tin in occupation numbers of 5s and 5p shells. These are used in a simple MO model to explain some characteristic features of tin Mössbauer spectra.
The deactivation of HF(v=1) and DF(v=1) by O, Cl, and F atoms
Authors: Quigley G. P. , Wolga G. J.
Published: February 2003

The relaxation of vibrationally excited HF and DF by O, Cl, and F atoms at T=300 °K has been measured by the laser induced fluorescence method. The rate constants in units of cm3 molecule−1⋅sec−1 for HF(v=1) are kO–HF=3.1±0.6×10−12, kCl–HF=7.4±1.6×10−13, kF–HF=2.8±0.6×10−13; for DF(v=1) they are kO–DF=7.8±2.2×10−12, kCl–DF=2.0±0.3×10−12, kF–DF=6.5±1.2×10−13. The results provide further evidence for the validity of a vibronic to translational energy transfer mechanism. Atom transfer reactions are shown to be of no importance.
Spatial organization of chemical oscillators via an averaging operator
Authors: Pavlidis Theodosios
Published: February 2003

Spatial interaction of chemical oscillators is usually described in terms of diffusion. In this paper an alternative model is considered which is described by the following equations: dX/dt=G (X,ℱ[Y]), dY/dt=H (X,ℱ[Y]), where ℱ[Y] is an averaging operator of the values of Y (r,t) over a finite region. It is shown that in this case solutions corresponding to circular, spiral, and other waves are obtained. Thus simulation of phenomena observed in the Zhabotinsky reaction, fungi cultures, and circadian rhythms is obtained.
Determination of the torsional potential function for styrene
Authors: Carreira L. A. , Towns T. G.
Published: February 2003

A series of lines in the low frequency Raman spectrum of gaseous styrene has been observed and assigned to the torsional overtones (Δv=2) of the vinyl group. The spectroscopic data were fitted to a potential function of the form, V (φ) =Σi(Vi/2)(1−cosiφ), for even ’’i,’’ and the barrier to internal rotation calculated. The barrier height of 623 cm−1 and the frequency of the 2←0 torsional transition (127.7 cm−1) agree quite well with those values previously predicted from thermodynamic data.
Radiative lifetime of the B 2Σ− state of CH
Authors: Anderson Richard A. , Peacher Jerry , Wilcox David M.
Published: February 2003

The radiative lifetimes of the N′=3 to 15 rotational states of the v′=0 level of the B 2Σ− state of CH were measured. Emission lines were observed to N′=15, but no lines above this rotational state were observed. This result agrees with previous studies. The lifetimes of all rotational states were between 300 and 400 ns. Previous measurements have indicated that the N′=15 level might have a lifetime as short as 100 ns.
Charge-transfer energy in closed-shell ion–atom interactions
Authors: Alvarez-Rizzatti Milton , Mason E. A.
Published: February 2003

The importance of charge-transfer energy in the interactions between closed-shell ions and atoms is investigated. Ab initio calculations on H+–He and Li+–He are used as a guide for the construction of approximate methods for the estimation of the charge-transfer energy for more complicated systems. For many alkali ion–rare gas systems the charge-transfer energy is comparable to the induction energy in the region of the potential minimum, although for doubly charged alkaline-earth ions in rare gases the induction energy always dominates. Surprisingly, an empirical combination of repulsion energy plus asymptotic induction energy plus asymptotic dispersion energy seems to give a fair representation of the total interaction, especially if the repulsion energy is parameterized, despite the omission of any explicit charge-transfer contribution. More refined interaction models should consider the charge-transfer energy contribution.
A complete treatment of the electron propagator through third order
Authors: Jo/rgensen Poul , Simons Jack
Published: February 2003

Using the superoperator formalism we demonstrate how the electron propagator can be obtained consistent through third order in the electronic interaction and we establish the connection to the corresponding diagrammatic perturbation expansion of the self-energy. We further indicate some deficiencies in the third order theory of Simons and Smith for calculating ionization potentials and electron affinities.
Vibrational relaxation of the N2O ν1 mode
Authors: Kung R. T. V.
Published: February 2003

The vibrational relaxation of the ν1 symmetric stretch mode of N2O was studied at room temperature following an overtone excitation via a DF laser. The ν1 and ν3 (asymmetric stretch) fluorescence at 7.8 and 4.5 μ were, respectively, monitored as a function of time. A V–V equilibration time constant of 0.062 μsec⋅atm between the ν1 and ν2 (bending) modes was measured. The vibrational relaxations out of the ν2 and ν3 modes were measured to be 1.3 and 2.1 μsec⋅atm, respectively, with good agreement compared to previous measurements reported in the literature.
l-dominant study of rotationally inelastic Li+–H2 collisions
Authors: DePristo Andrew E. , Alexander Millard H.
Published: February 2003

For rotationally inelastic collisions at large total angular momentum J, the orbital angular momentum l exerts considerable dynamical importance. The inelastic T matrix is dominated by transitions between states characterized by small centrifugal barriers. Recognizing this fact, we have recently developed an ’’l-dominant’’ (LD) approximation to the space-fixed quantum-mechanical close-coupled (CC) equations, which consists in neglecting all channels with l≳J. In the present work we have applied the LD method to the determination of partial and total cross sections for the j=0→2,4,6 processes in Li+–H2 collisions at an energy of 0.5 eV. For the 0→2 and 0→4 transitions the LD results agree well with exact CC values, particularly at high J where the l dominance is most pronounced. By contrast, agreement is less satisfactory for the weak 0→6 transition, where high J values do not contribute significantly to the total cross section. Compared with the results of coupled-states (CS) calculations, the LD partial cross sections are considerably more accurate. In terms of computational expense, the LD method lies midway between CS and CC calculations.
Generalized mean spherical approximation for charged hard spheres: The electrolyte regime
Authors: Stell G. , Sun S. F.
Published: February 2003

A study of a generalized mean spherical approximation (GMSA) proposed by Ho/ye, Lebowitz, and Stell in J. Chem. Phys. 61, 3253 (1974) is made for a system of charged hard spheres. The complete solution of the GMSA is given explicitly. It yields a fully analytic theory—that is, both the thermodynamic properties of the GMSA and the structure factors associated with its distribution functions can be found in simple closed form. Moreover, the GMSA is constructed in such a way to insure that use of the virial theorem, fluctuation theory, and the expression for its internal energy all lead to identical thermodynamics, characterized by the same simple algebraic equations that appear in the mean spherical approximation (MSA). Quantitative results are given for the restricted primitive model electrolyte under conditions typical of 1–1 electrolytes. They demonstrate that the GMSA represents a significant improvement over the MSA, which is seriously lacking in thermodynamic self–consistency for charged spheres and is associated with negative pair distribution functions at low densities for spheres of like charge.
Approximate equilibrium pair correlation function for simple polar fluids
Authors: Ho/ye J. S. , Stell G.
Published: February 2003

A new approximation procedure to determine the pair correlation function of a dipolar fluid is given. A family of approximations for the pair correlation function is derived to yield a Padé approximant to the free energy that has already been shown to be highly accurate for dipolar spheres. The family is parameterized so that it can reproduce whatever prescribed dielectric constant is most appropriate to the particular application being comtemplated. It can also be made to yield thermodynamic self-consistency.
Comparison of classical, distorted wave, and straight path methods of evaluating the integrals over the intermolecular trajectory during molecular collisions
Authors: Sharma R. D. , Hart R. R.
Published: February 2003

The integrals over the intermolecular trajectory, relevant to pressure-broadening and energy transfer calculations, are evaluated for the classical path, straight path, and distorted wave approximations. The present work, coupled with previous published work, leads to the conclusion that the three approximations agree to within 25% for near-resonant collisions involving reduced energies E*≳1. For nonresonant collisions the classical calculation, which does not conserve energy, is in surprisingly good agreement with the distorted wave results even when the energy mismatch is one-half of the incident energy.
Potential constants of K2Zn(CN)4 in the crystal lattice
Authors: Jones Llewellyn H. , Swanson Basil I.
Published: February 2003

The vibrational spectra of the crystalline materials K2Zn(CN)4, K2Zn(13CN)4, K2Zn(C 15N)4, K2 64Zn(CN)4, and K2 68Zn(CN)4 have been observed using infrared and Raman spectroscopy. A number of the potential constants in this system have been calculated from the various isotopic frequencies. It was necessary to constrain several of the potential constants which are essentially indeterminate. An analysis of these constraints was made to show that they are justified. A comparison of the potential constants of Zn(CN)−24 with isoelectronic Ni(CO)4 shows that for the zinc complex there is negligible back-π bonding of the zinc d orbitals to the CN ligands. A number of interesting stretch–stretch and stretch–bend interactions are discussed.
Rate of the reaction O+SO2+M→SO3+M
Authors: Westenberg A. A. , deHaas N.
Published: February 2003

The rate of the reaction O+SO2+M→SO3+M has been measured under pseudo-first-order conditions in a discharge flow reactor with ESR detection. For M=He at room temperature, extensive measurements over a wide SO2 mole fraction range were used to evaluate the rate constant for both He (k1) and SO2 (k2) as third bodies. The results were k1=3.0±0.2×1014 cm6 mole−2⋅ sec−1 and k2/k1=9.5±2.7, the error limits being simply experimental mean deviations. Similar experiments for M=N2 (k4) at room temperature yielded k4=7.2±0.3×1014. Measurements of M=He over the temperature range 248–415 °K gave the Arrhenius result k1=3.9±0.9×1016 exp[−(1400±50)/T]. The positive Arrhenius activation energy is in good agreement with other published results, and some discussion of this unusual feature for termolecular reactions is presented.
Effective valence shell interactions in carbon, nitrogen, and oxygen atoms
Authors: Westhaus Paul , Bradford Edward G.
Published: February 2003

We present the first numerical results of the canonical tranformation formalism for generating the valence shell effective interactions. Considering the valence space to be formed as the antisymmetrized direct product of 2s and 2p type orbitals we have computed all the matrix elements of the two-body valence shell interactions for isolated carbon, nitrogen, and oxygen atoms. Explicit forms for the core, valence, and excited orbitals are the hydrogenlike functions defined by an effective nuclear charge. We compare our results with the semiempirical ’’electron–electron repulsion parameters’’ finding that for reasonable values of the effective charge—essentially a choice of the core and valence spaces—good agreement with the parameters deduced from atomic spectra data is obtained. Not only do the general features of semiempirical theory such as the reduction of the average strength of the two-body interaction appear, but also the somewhat more subtle effects such as the relative ordering of the diagonal matrix elements emerge. The nonlocal nature of the effective interactions is noted and its implications for the usual semiempirical schemes are discussed.
Thermodynamic perturbation theory for potentials of multipolar symmetry. I
Authors: Rasaiah J. C. , Larsen B. , Stell G.
Published: February 2003

Earlier work in simple polar fluids is extended to higher multipolar terms. Some general properties of multipolar expansions and of the three-body terms that appear in them are considered. Illustrative application is made to a system of quadrupolar spheres. A method of incorporating the effects of nonspherical molecular cores into our formalism is outlined, and some preliminary estimates are given for the relative size of such effects compared to that of the quadrupolar terms.
The kinetics of ionic/metallic ion-exchangers
Authors: Okongwu D. A. , Lu W. K.
Published: February 2003

A model for the kinetics of ionic/metallic ion-exchangers is developed from the Nernst–Planck equation for ionic diffusion and the chemical reaction rate equations assumed to be proportional to the electrochemical affinity of each species. The model is demonstrated for a number of hypothetical systems, and the uses and limitations of the model are discussed.
Temperature dependence of third order ion molecule reactions. The reaction H+3+2H2 = H+5+H2
Authors: Hiraoka K. , Kebarle P.
Published: February 2003

The rate constants k1 for Reaction (1): H+3+2H2 = H+5+H2 were measured in the temperature range 100–300 °K. The temperature dependence of k1 has the form k1∝T−n, where n=2.3. Pierce and Porter have reported a much stronger negative temperature dependence with n=4.6. The difference arises from a determination of k1 at 300 °K obtained by Arifov and used by Porter. The present k1 (300 °K) =9×10−30 (cm6 molecules−2⋅sec−1). This is more than an order of magnitude larger than the Arifov value. The temperature dependence of third body dependent association reactions like (1) is examined on the basis of the energy transfer theory and the recently proposed trimolecular complex transition state theory by Meot-Ner, Solomon, Field, and Gershinowitz. The temperature dependence of the rate constant for the reverse reaction (−1) is obtained from k1 and the previously determined temperature dependence of the equilibria (1). k−1 gives a good straight line Arrhenius plot leading to k−1 =8.7×10−6 exp(−8.4/RT) cm3 molecules−1⋅sec−1. The activation energy is in kcal/mole. The preexponential factor is much larger than the rate constant for Langevin collisions. This is typical for pyrolysis of ions involving second order activation.
On the ionic conduction in β-alumina: Potential energy curves and conduction mechanism
Authors: Wang J. C. , Gaffari M. , Choi Sang-il
Published: February 2003

Potential energy curves for various carrier ions in β-alumina have been calculated. All ions except the carrier ions (Li+, Na+, Ag+, K+, Rb+, Cs+) were assumed fixed in their equilibrium positions. These ionic positions were taken from Roth’s work. In our calculation the motion of carrier ions is restricted on lines of the two dimensional hexagonal network. We show that the site energy difference between the anti-Beevers–Ross site and the Beevers–Ross site is approximately 2 eV in stoichiometric crystals. In nonstoichiometric crystals the extra carrier ions may be paired to form interstitialcy pairs. The potential energy barriers for the in-phase motion of the interstitialcy pairs are found to be comparable to the experimental activation energies. Attempt frequencies have been calculated, and a simple random walk model is used for the electrical conductivities.
Interdependence of guest radiationless transitions and localized phonon structure: NH and ND(A 3Π) in rare gas lattices
Authors: Bondybey V. E. , Brus L. E.
Published: February 2003

Time and wavelength resolved fluorescence techniques are used to study vibrational relation of NH and ND(A 3Π) substitutional guests in rare gas lattices. Temperature dependent localized phonon spectral structure is analyzed to show that the ground X 3Σ− state undergoes near free rotation, while the excited A 3Π state librates. The barriers to free rotation in A 3Π reflect the anisotropy of the attractive, polarizability dependent NH–lattice interaction. The vibrational relaxation energy gap law is strongly violated, with NH rates 10–102 higher than ND rates. These rates are independent of temperature for T?25 °K in Ar, and T?37 °K in Kr; however, intersystem crossing by A 3Π (v′=0) in Kr shows a dramatic temperature dependence resulting from stimulated phonon emission. It is proposed that the localized near free rotation mode accepts energy during vibrational relaxation, while delocalized lattice phonon modes accept energy during intersystem crossing. The average accepting frequency in Kr is only ? (1/2) the host phonon maximum frequency, thus indicating that single accepting frequency theories are only semiquantitatively applicable.
A Raman spectrophotometric study of the effect of N,N-dimethylformamide and the electrolytes NaClO4, Zn(ClO4)2, NaNO3, and Zn(NO3)2 on the structure of liquid water
Authors: Rodgers Glen E. , Plane Robert A.
Published: February 2003

In order to facilitate an investigation of water structure, the Raman spectra of binary and ternary solutions involving H2O, N,N-dimethylformamide (DMF), NaClO4, NaNO3, Zn(ClO4)2, and Zn(NO3)2 have been studied. The resolution of the OH stretching region of these solutions has been attempted using both three and four band analyses. Only the four band resolutions (∼3623, 3542, 3430, and 3265 cm−1 for non-zinc-containing solutions) are successful for all six series of solutions. The four bands are interpreted in terms of hydrogen-bonded and non-hydrogen-bonded OH oscillators rather than (1) a mixture of water molecules with varying numbers of hydrogen bonds per molecule or (2) a continuum model for water structure. Evidence for hydrogen bonds among H2O molecules and between H2O molecules and the DMF, ClO4−, and NO3− species has been obtained through an analysis of the trends in the relative intensities of the four components of the OH stretching region of H2O as the concentrations of the above species vary. The trends observed in the vibrational modes of DMF, ClO4−, and NO3− are interpreted in terms of interactions of the above species with H2O molecules and zinc cations. In addition, interactions between zinc cations and H2O molecules are indicated by a general downward shift (15–20 cm−1) of the OH stretching frequencies.
Relativistic self-consistent-field (RSCF) theory for closed-shell molecules
Authors: Malli Gulzari , Oreg J
Published: February 2003

The relativistic Hartree–Fock–Roothaan (RHFR) formalism for closed-shell molecules is given. The wavefunction for such systems is taken as a single Slater determinant of 4-component molecular spinors (MS), where each MS is written as a linear combination of atomic spinors (LCAS/MS). The radial part of the atomic spinor (AS) is expanded in terms of Slater-type basis functions (STBF). The relativistic electronic Hamiltonian for the molecular system (in Born–Oppenheimer approximation) is the sum of Dirac Hamiltonians plus the interelectronic Coulomb repulsion and the magnetic part of the Breit interaction, but the retardation term is neglected at present. The reduction of the matrix elements of the relativistic Hamiltonian in terms of the nonrelativistic-type matrix elements is shown for any molecular system. Expressions for the matrix elements of the above-mentioned relativistic Hamiltonian are given for diatomics.