bluuebunny/crossref_metadata_2025 huggingface dataset:
An ab initio molecular orbital study of the unimolecular dissociation reactions of vinylchloride
Authors: Riehl Jean-Frédéric , Morokuma Keiji
Published: July 2002

The potential energy surface for the unimolecular ground state elimination/detachment reactions of vinylchloride (VCl) is studied with ab initio molecular orbital calculations. Using second order Mo/ller–Plesset perturbation (MP2) gradient optimizations and quadratic single and double configuration interaction including a triple contribution [QCISD(T)] single point calculations, many possible channels—three- and four-center elimination reactions of HCl and H2, H, and Cl migrations, single atom detachments—are systematically examined. The overall barrier for the HCl three-center elimination, 69.1 kcal/mol, and subsequent vinylidene rearrangement is lower than that for the four-center elimination, 77.4 kcal/mol, the result being consistent with the most recent experiments. The H2 elimination, with a barrier of 97.2 kcal/mol and more difficult than the HCl elimination, also proceeds via a three-center transition state, followed by an easy H migration from chlorovinylidene intermediate. The lowest energy path from VCl is the α-H migration with a barrier of 68.8 kcal/mol, which gives a stable intermediate, α-chloroethylidene, with an energy of 55 kcal/mol relative to VCl. This path cannot however proceed further because of a very high barrier for subsequent H2 and HCl elimination, but the return to VCl provides the easiest mechanism for H scrambling in VCl. The β-chloroethylidene species is only a marginally stable intermediate and would not contribute to the reaction.
Finite size effects in the simulation of crystallization
Authors: Visscher P. B.
Published: July 2002

We describe an algorithm for classifying and listing all possible hexagonal lattices into which a 2D system can crystallize, in the context of a simulation using periodic boundary conditions. The probability that a system will form one of these lattices depends on its strain energy, but also on the kinetics of nucleation—a crystal must become infinite in one direction before the others. The probability of a given lattice depends on the strain energy of this intermediate state, which we also calculate. The method is applied in an accompanying paper to the taxonomy of hexagonal string lattices that form in sheared colloids.
Variable-structure cell theory of liquids and glasses
Authors: Somer Frank L. , Kovac Jeffrey
Published: July 2002

A new kind of cell theory—one which formally accounts for the possibility of amorphous phases—is presented. The equilibrium partition function is transformed exactly by first classifying all particle configurations according to multidimensional potential-energy minima and then assigning to each minimum a system-spanning set of cells such that, for configurations near enough the minimum, each cell contains one particle. The theory is then extended to general amorphous systems, and approximate descriptions of supercooled liquids and glass transitions are given.
Laser flash photolysis studies of radical–radical reaction kinetics: The O(3P
J)+BrO reaction
Authors: Thorn R. P. , Cronkhite J. M. , Nicovich J. M. , Wine P. H.
Published: July 2002

A novel dual laser flash photolysis-long path absorption-resonance fluorescence technique has been employed to study the kinetics of the important stratospheric reaction O(3PJ)+BrO→k1Br(2PJ)+O2 as a function of temperature (231–328 K) and pressure (25–150 Torr) in N2 buffer gas. The experimental approach preserves the principal advantages of the flash photolysis method, i.e., complete absence of surface reactions and a wide range of accessible pressures, but also employs techniques which are characteristic of the discharge flow method, namely chemical titration as a means for deducing the absolute concentration of a radical reactant and use of multiple detection axes. We find that k1 is independent of pressure, and that the temperature dependence of k1 is adequately described by the Arrhenius expression k1(T)=1.91×10−11 exp(230/T) cm3 molecule−1 s−1; the absolute accuracy of measured values for k1 is estimated to vary from ±20% at T∼230 K to ±30% at T∼330 K. Our results demonstrate that the O(3PJ)+BrO rate coefficient is significantly faster than previously ‘‘guesstimated,’’ and suggest that the catalytic cycle with the O(3PJ)+BrO reaction as its rate-limiting step is the dominant stratospheric BrOx odd-oxygen destruction cycle at altitudes above 24 km.
Qualitative study of the symplectic Störmer–Verlet integrator
Authors: Hardy David J. , Okunbor Daniel I.
Published: July 2002

Symplectic numerical integrators, such as the Störmer–Verlet method, are useful in preserving properties that are not preserved by conventional numerical integrators. This paper analyzes the Störmer–Verlet method as applied to the simple harmonic model, whose generalization is an important model for molecular dynamics simulations. Restricting our attention to the one -dimensional case, both the exact solution and the Störmer–Verlet solution to this model are expressed as functions of the number of time steps taken, and then both of these functions are interpreted geometrically. The paper shows the existence of an upper bound on the error from the Störmer–Verlet method, and then an example is worked to demonstrate the closeness of this bound.
Solvation thermodynamic functions in the mean spherical approximation: Behavior near the solvent critical region
Authors: Wei Dongqing , Blum Lesser
Published: July 2002

Explicit expressions of the mean spherical approximation (MSA) solvation thermodynamic functions, the Gibbs free energy, energy, enthalpy, entropy, apparent molar heat capacities, and partial molar volume are derived starting from the Helmholtz free energy. The thermodynamic consistency of the MSA solvation thermodynamic functions are discussed. The limiting behavior of the MSA solvation thermodynamic functions is compared to the Born theory. The effect of the solvent structure on the Gibbs and the Helmholtz free energy in the MSA is discussed. The results for alkali and halide ions in water are compared with experimental data. The apparent molar heat capacities at constant volume and pressure, and the partial molar volume are calculated along an isobaric line to the critical region of a dipolar liquid. Some recent experiments on solvation thermodynamics in the critical region are discussed.
The ozonide anion: A theoretical study
Authors: Borowski Piotr , Roos Björn O. , Racine Stephen C. , Lee Timothy J. , Carter Stuart
Published: July 2002

Complete active space self-consistent field (CASSCF) and CASSCF second-order perturbation theory (CASPT2) methods have been used for the geometry optimization and calculation of harmonic and fundamental frequencies of the ozonide ion (O−3) and the ozonide lithium complex (Li+O−3). For O−3 harmonic frequencies have also been obtained using the coupled-cluster method, CCSD(T). Infrared intensities are computed from dipole moment derivatives at the CASSCF level. The predicted equilibrium geometry for O−3 is ROO=1.361 Å and ∠OOO=115.4°, and the fundamental frequencies are ν1=989 cm−1, ν2=556 cm−1, ν3=870 cm−1 [experimental values are ROO=1.36±0.02 Å, ∠OOO=111.8±2.0°, ν1=975(50) cm−1, ν2=550(50) cm−1, ν3=880(50) cm−1]. Corresponding data for the lithium ozonide complex have also been obtained. The presented data contradict the previous interpretation of the IR and Raman spectrum obtained after codeposition of ozone and alkali atoms in N2, argon, or neon matrices. The presence of the lithium cation raises the asymmetric stretch frequency to about 940 cm−1, which is contradictory to assumptions made in the assignments of the matrix spectra. Calculations made in a dielectric medium strongly suggest that the effect of the matrix on the IR spectrum is small for O−3 itself. The dissociation and atomization energies of O−3 are found to be in agreement with experiment.
Structure and spectroscopy of (HCN)n clusters: Cooperative and electronic delocalization effects in C–H⋅⋅⋅N hydrogen bonding
Authors: King Bretta F. , Weinhold Frank
Published: July 2002

We investigate ab initio energetic, structural, dielectric, and ir spectroscopic properties of linear (HCN)n clusters (extending the theoretical levels and cluster sizes previously considered) to quantitatively characterize cooperative effects in C–H...N hydrogen bonding that may be amenable to experimental detection. Our results indicate that large cooperative effects should be evident in H-bond energies (∼90% increase), intermolecular separations (∼0.10–0.15 Å shrinkage), average dipole moments (∼25% increase), and, particularly, in CH stretching frequencies (∼100 cm−1 shift) and intensities (∼300%–400% increase per monomer) as cluster size increases. Such non-pairwise-additive effects lie outside the scope of empirical potentials in common usage, and thus reflect fundamental inadequacies of these potentials and the underlying ‘‘electrostatic’’ picture of H bonding. We employ natural bond orbital (NBO) analysis to examine the detailed electronic origins of cooperative effects, particularly the dramatic ir intensity enhancements that may provide a unique spectroscopic signature of concerted intermolecular charge shifts. NBO analysis suggests how the nonlinear cooperativity effects can be rationalized in terms of the fundamental nN→σCH* ‘‘charge transfer’’ (‘‘resonance’’) nature of H bonding, manifested even in low-polarity H bonds involving CH groups.
A wave packet propagation study of inelastic and reactive F+D2 scattering
Authors: Billing G. D. , Rusin L. Yu. , Sevryuk M. B.
Published: July 2002

We compute the rotationally resolved differential cross sections for F(2P3/2)+D2(v=0,j) inelastic scattering as well as opacity functions for D2 rotational excitation and the reaction F+D2→D+DF. Two values of the collision energy (89.7 and 187 meV) and two initial D2 rotational states (j=0 and j=1) are probed. Four calculation techniques have been compared: the quasiclassical trajectory approach and the Wigner method on the ground state (12A′) surface, wave packet propagation (with the D2 vibrational degree of freedom treated quantum mechanically) on the 12A′ surface, and wave packet propagation on the two coupled surfaces 12A′ and 22A′. The effect of the nonadiabatic spin–orbit coupling on the nonreactive F+D2 scattering is almost negligible, whereas the reaction cross sections in the two-surface wave packet propagation treatment are considerably smaller than those in the calculations taking into account the ground state surface only.
Coexistence curve of perfluoromethylcyclohexane-isopropyl alcohol
Authors: Jacobs D. T. , Kuhl D. E. , Selby C. E.
Published: July 2002

The coexistence curve of the binary fluid mixture perfluoromethylcyclohexane-isopropyl alcohol was determined by precisely measuring the refractive index both above and below its upper critical consolute point. Sixty-seven two-phase data points were obtained over a wide range of reduced temperatures, 10−5<t<2.5×10−1, to determine the location of the critical point: critical temperature=89.901 °C, and critical composition=62.2% by volume perfluoromethylcyclohexane. These data were analyzed to determine the critical exponent β close to the critical point, the amplitude B, and the anomaly in the diameter. The volume-fraction coexistence curve is found to be as symmetric as any compositionlike variable. Correction to scaling is investigated as well as the need for a crossover theory. A model is proposed that describes the asymptotic approach to zero of the effective exponent β, which allows an estimation of the temperature regime free of crossover effects.
Homogeneous nucleation in a laminar flow diffusion chamber: The effect of temperature and carrier gas on dibutyl phthalate vapor nucleation rate at high supersaturations
Authors: Hämeri Kaarle , Kulmala Markku
Published: July 2002

The homogeneous nucleation rates of dibutyl phthalate vapor were investigated. The measurements using a laminar flow diffusion chamber technique were performed as a function of temperature in a wide range of supersaturations providing a large data set for future theoretical investigations. Tables of the homogeneous nucleation rates in the range from 101 cm−3 s−1 to 4.5×107 cm−3 s−1 as a function of saturation ratio in the temperature range from 246 K to 317 K are presented. The nucleation rates were compared to different theoretical predictions. The effect of carrier gas on nucleation rate was investigated and no significant dependence was found. From the slopes of the isothermal nucleation rate versus saturation ratio curves the number of molecules in the critical cluster were determined. Comparison to Gibbs–Thomson equation is presented.
Vacuum ultraviolet photoionization and dissociative photoionization of W(CO)6
Authors: Qi Fei , Yang Shihe , Sheng Liusi , Gao Hui , Zhang Yunwu , Yu Shuqin
Published: July 2002

Photoionization of W(CO)6 in the photon energy range of 8–40 eV produced a variety of intermediate ions of the form (WCm(CO)n)x+. Photoionization efficiency (PIE) curves of these ions have been measured for the first time by using a time-of-flight mass spectrometer (TOFMS) with vaccum ultraviolet (VUV) photons from a synchrotron radiation source. Appearance potentials (AP) of all the observed ions have been determined from their PIE curves. Based on these AP values, we obtained a series of bond dissociation energy (BDE) data for the intermediate ions produced by the dissociative photoionization.
Activation barriers for series of exothermic homologous reactions. V. Boron group diatomic species reactions
Authors: Blue Alan S. , Belyung David P. , Fontijn Arthur
Published: July 2002

Semiempirical configuration interaction (SECI) theory is used to predict activation barriers E, as defined by k(T)=ATn exp(−E/RT). Previously SECI has been applied to homologous series of oxidation reactions of s1, s2, and s2p1 metal atoms. Here it is extended to oxidation reactions of diatomic molecules containing one s2p1 atom. E values are calculated for the reactions of BH, BF, BCl, AlF, AlCl, AlBr, GaF, GaI, InCl, InBr, InI, TlF, TlCl, TlBr, and TlI with O2, CO2, SO2, or N2O. These values correlate with the sums of the ionization potentials and Σ–Π promotion energies of the former minus the electron affinities of the latter. In the earlier work n was chosen somewhat arbitrarily, which affected the absolute values of E. Here it is shown that examination of available experimental and theoretical results allows determination of the best values of n. Using this approach yields n=1.9 for the present series. For the seven reactions which have been studied experimentally, the average deviation of the SECI activation barrier prediction from experiment is 4.0 kJ mol−1. Energy barriers are calculated for another 52 reactions.
Comparison of aggregation of rodlike and spherical particles: A fractal analysis
Authors: Vincze Attila , Fata Rita , Zrı́nyi Miklós , Hórvölgyi Zoltán , Kertész János
Published: July 2002

Different structure-analyzing methods were applied to experimental and computer generated two-dimensional clusters. The real structures formed at water–air interfaces from polydisperse, cylindrical-shape carbon (thickness: 35 μm; average length: 140 μm) and close to monodisperse, spherical-shape glass (75 μm diam) microparticles. The clusters were characterized by the fractal dimension (Df) and the surface coverage (q) values in the case of individual clusters. For a series of different sized aggregates, the fractal dimension (Df) was also evaluated from the ln q versus ln Rg functions where Rg is the radius of gyration. The fractal dimensions for individual clusters determined by box counting, sand box, and by correlation function methods, were compared with each other and with those obtained for the series of clusters. Using the above methods, the aggregation of cylindrical carbon and spherical glass particles was studied from a structural point of view. The surface of glass beads was rendered hydrophobic chemically. Changing the extent of silylation, lower and higher hydrophobic samples were obtained (Θ/water/=68° and 89°, respectively). Conforming the earlier results, the ln q versus ln Rg functions revealed a crossover during the growth in every investigated case, which was an indication of cluster reorganization after the primary growth. At the first (quasi-non-equilibrium) stage of aggregation, the fractal dimensions obtained for the carbon particles (Df=1.44±0.07), for the lower (Df=1.53±0.05), and for the higher hydrophobic (Df=1.43±0.05) glass particles, indicated the universality of the growth.
Inversion of absorption spectral data for relaxation matrix determination. II. Application to Q-branch line mixing in HCN, C2H2, and N2O
Authors: Boyd Robert , Ho Tak-San , Rabitz Herschel
Published: July 2002

Experimental absorption spectral data from Q-branch line mixing in HCN, C2H2, and N2O are inverted to extract their respective relaxation W matrices. The formulation makes use of a general iterative inversion algorithm based upon first-order sensitivity analysis and Tikhonov regularization. The algorithm, previously applied to R-branch line mixing in HCN, is reformulated to explicitly require detailed balance for the real, off-diagonal W matrix elements. As with the HCN R-branch case, the W matrices recovered typically were found to describe line mixing much better than those derived from the fitting laws currently in use, and the inversion algorithm usually converged within just three iterations.
Transferable pair potentials for the description of liquid alkali metals
Authors: Boulahbak M. , Jakse N. , Wax J.-F. , Bretonnet J.-L.
Published: July 2002

The structural and thermodynamic properties of liquid alkali metals near the melting point are presented. For this purpose, we use the thermodynamically self-consistent integral equation of the liquid state theory, called the hybridized mean-spherical approximation (HMSA). The effective interionic potential is derived via the second-order pseudopotential-perturbation method, in which the very recent pseudopotential of Fiolhais et al. [Phys. Rev. B 51, 14001 (1995)], designed for the solid state, is combined with our semianalytical local-field function [J. L. Bretonnet and M. Boulahbak, Phys. Rev. B 53, 6859 (1996)]. We show that this pseudopotential is transferable to the disordered environment characteristic of the liquid state and, if used with our local-field function, predicts the structural and thermodynamic properties of the liquid alkali metals with a reasonable accuracy.
Induced orientational order in liquid layers
Authors: ten Bosch A.
Published: July 2002

A density functional approach has been used to study the effect of an orientation dependent substrate potential on a simple fluid of linear particles with weak anisotropy. Within a model potential, it can be shown that orientational order can be induced within the range of the substrate interaction near the freezing temperature. This is superimposed on the usual density variation at the surface and can cause an unusual negative temperature variation of the surface tension.
Electron impact overtone excitation via the Σu2 resonance in N2 films physisorbed on Ag(110) at 15 K
Authors: Bartolucci F. , Franchy R. , Silva J. A. M. C. , Moutinho A. M. C. , Teillet-Billy D. , Gauyacq J. P.
Published: July 2002

The growth and structure of solid nitrogen films on Ag(110) at 15 K was investigated by means of high resolution electron energy loss spectroscopy (EELS), thermal desorption spectroscopy (TDS), and low energy electron diffraction (LEED). The N2 film exhibits a parallelogram structure in the monolayer. For the bilayer and multilayers an incoherent hexagonal structure has been found. The dynamics of the resonant vibrational excitation of the N2 molecule via the Σu2 resonance is studied in detail both by the EELS method (as a function of the surface coverage) and theoretically. This allows a discussion of the effect of the adsorption on the vibrational excitation process and, in particular, on the overtone excitation. The Σu2 resonance excitation process is found to be almost not influenced by the adsorption in strong contrast with the case of the low energy (2Πg) N2 resonance. The differences between these two processes are discussed.
Evaluating and improving the cluster variation method entropy functional for Ising alloys
Authors: Ferreira Luiz G. , Wolverton C. , Zunger Alex
Published: July 2002

The success of the “cluster variation method” (CVM) in reproducing quite accurately the free energies of Monte Carlo (MC) calculations on Ising models is explained in terms of identifying a cancellation of errors: We show that the CVM produces correlation functions that are too close to zero, which leads to an overestimation of the exact energy, E, and at the same time, to an underestimation of −TS, so the free energy F=E−TS is more accurate than either of its parts. This insight explains a problem with “hybrid methods” using MC correlation functions in the CVM entropy expression: They give exact energies E and do not give significantly improved −TS relative to CVM, so they do not benefit from the above noted cancellation of errors. Additionally, hybrid methods suffer from the difficulty of adequately accounting for both ordered and disordered phases in a consistent way. A different technique, the “entropic Monte Carlo” (EMC), is shown here to provide a means for critically evaluating the CVM entropy. Inspired by EMC results, we find a universal and simple correlation to the CVM entropy which produces individual components of the free energy with MC accuracy, but is computationally much less expensive than either MC thermodynamic integration or EMC.
State-to-state differential cross sections for the reaction F+D2 at 90 meV: A crossed molecular beam experiment and a quantum mechanical study
Authors: Baer M. , Faubel M. , Martı́nez-Haya B. , Rusin L. Y. , Tappe U. , Toennies J. P.
Published: July 2002

The F+D2→DF+D reaction has been investigated in a high resolution crossed molecular beam scattering experiment at a collision energy of 90 meV (2.07 kcal/mol). Time-of-flight spectra of the DF products have been measured covering the backward hemisphere of center-of-mass scattering angles (θcm=90°–180°). The energy resolution achieved in the spectra, as good as 20 meV, together with a careful calibration of the beam source intensities and detector sensitivity makes it possible to determine absolute differential and integral cross sections resolved in vibrational and rotational states of the DF products. Interestingly, the backward scattered DF(vf=2) and DF(vf=3) vibrational products are found to present double-peaked (i.e., bimodal) rotational distributions. A three dimensional quantum mechanical calculation of the title reaction performed on the recent ab initio potential energy surface of Stark and Werner [J. Chem. Phys. 104, 6515 (1996)] is presented, which was carried out in the reagents arrangement channel within the coupled-states approximation, employing negative imaginary potentials. The calculated state-to-state differential cross sections show a very encouraging overall agreement with those evaluated from the scattering experiment. In particular, the bimodal structure of the rotational distributions is qualitatively well accounted for in the calculation. However, significant differences still persist between the calculated and the experimental results.
Observation of the 5 1Πu, 6 1Σu+, and 7 1Σu+ states of Na2 through a Franck–Condon window by all-optical triple resonance spectroscopy
Authors: Li Jing , Zhang Jianming , Wang He , Kim J. T. , Stwalley W. C.
Published: July 2002

We have observed the 5 1Πu, 6 1Σu+, and 7 1Σu+ states of Na2 by using all-optical triple resonance excitation and an ultrasensitive shielded cylindrical space-charge-limited ionization detector (presumably detecting Na3+ produced by Na2*+Na associative ionization). Although the absolute vibrational numbering is uncertain, the rotational constants are obtained. The Franck–Condon window concept is presented with calculated Franck–Condon factors based on the theoretical 5 1Πu, 6 1Σu+, and 7 1Σu+ potential energy curves of Magnier.
Polymer localization in attractive random media
Authors: Baumgaertner A.
Published: July 2002

A self-avoiding polymer embedded in a two-dimensional quenched random medium consisting of randomly distributed attractive sites has been studied using Monte Carlo methods. It is shown that at a critical temperature the adsorption energy exhibits a sharp transition to a localized state. The transition is characterized by a discontinuity of the adsorption energy at the critical point. The radius of gyration of the chain remains essentially unaffected by the disorder with respect to the chain length dependency. However, there is some evidence that at the critical point the size of the polymer starts to increase with decreasing temperature. Formulas for energy and critical temperature are suggested.
Electronic properties of CdSe nanocrystals in the absence and presence of a dielectric medium
Authors: Rabani Eran , Hetényi Balázs , Berne B. J. , Brus L. E.
Published: July 2002

We present a detailed study of the electronic properties of CdSe nanocrystals in the absence and presence of a dielectric medium. The electronic structure of the nanocrystal is modeled within the framework of the empirical pseudopotential method. We use a real-space grid representation of the wave function, and obtain the eigenvalues and eigenstates of the one-electron Hamiltonian using a slightly modified version of the filter-diagonalization method. The band gap, density of states, charge density, multipole moments, and electronic polarizabilities are studied in detail for an isolated nanocrystal. We discuss the implications of the results for the long range electrostatic and dispersion interactions between two CdSe nanocrystals. To study the effects of the surroundings we develop a self-consistent reaction field method consistent with the empirical pseudopotential method. We use the eigenstates of the isolated nanocrystal and iterate the self-consistent equations until converged results are obtained. The results show that the electronic properties of polar CdSe nanocrystals are quite sensitive to the environment.
Density matrix for an excess electron in a classical fluid: Results for a one-dimensional system
Authors: Sethia Ashok , Hirata Fumio , Singh Yashwant
Published: July 2002

We extend the theory of Chandler, Singh, and Richardson [J. Chem. Phys. 81, 1975 (1984)] to calculate the density matrix for an excess electron in a classical liquid like bath. For a one-dimensional fluid of hard rods and for two model potentials representing the electron fluid atom interaction (one representing the excluded volume effect and the other attractive interaction), we calculate the density matrix using the values of solvent induced potential surfaces for the electron found from our earlier calculations [Phys. Rev. B 42, 6090 (1990)]. The resulting density matrix is diagonalized and values of energies and wavefunctions of the electron including the effective mass and root mean square (RMS) displacement Rβ in imaginary time βℏ. The transition of the electron to a state of self-trapping is visualized through a sudden change in the value of Rβ or the effective mass m* at a value of β or solvent density ρs*. For a potential model of hard rods, we find that the RMS displacement Rβ for a given solvent density varies as (βℏ)ν. Values of ν are evaluated for several solvent densities.
Relativistic effects in gold chemistry. VI. Coupled cluster calculations for the isoelectronic series AuPt−, Au2, and AuHg+
Authors: Wesendrup Ralf , Laerdahl Jon K. , Schwerdtfeger Peter
Published: July 2002

Nonrelativistic and scalar relativistic pseudopotential calculations were carried out for the isoelectronic series of diatomic molecules AuPt−, Au2, and AuHg+ at the Hartree–Fock, second-order Mo/ller–Plesset (MP2), and coupled-cluster [CCSD(T)] level. For Au2 we performed large scale fully relativistic Dirac–Hartree–Fock and MP2 benchmark calculations in order to test the reliability of the pseudopotential approximation. Both methods yield almost identical spectroscopic properties for Au2. The comparison further reveals that pseudopotentials correctly describe the effects of relativity on the spectroscopic properties of Au2. The yet unknown diatomic species AuPt− and AuHg+ are stable compounds, and their rotational–vibrational constants are predicted. These show striking similarities compared to the values of Au2. MP2 results including a set of three g-functions per metal atom indicate that higher angular momentum functions are important for accurately predicting the bond distance of these molecules.
Speed of sound and equation of state for fluid oxygen to 10 GPa
Authors: Abramson E. H. , Slutsky L. J. , Harrell M. D. , Brown J. M.
Published: July 2002

The speed of sound in supercritical, fluid oxygen has been measured up to the freezing points of 6.0 GPa at 30 °C and 10.5 GPa at 200 °C. The oxygen was contained in a diamond–anvil cell and pressure was measured on the ruby scale. The measurements were used to establish an equation of state. Additionally, the fluid-β phase boundary was determined between 15 and 180 °C to a precision of 0.02 GPa.
Laser excitation and photoionization spectroscopy of the AO+ and B1 states of indium monoiodide: Ground state dissociation energy and photodissociation yield of In(6s 2S1/2)
Authors: King K. K. , Herring C. M. , Eden J. G.
Published: July 2002

The dissociation energy of the InI ground state (X 1Σ+(O+)) and the relative yield of In(6s 2S1/2) from the photodissociation of InI by sequential two-photon absorption have been measured by laser-induced fluorescence and excitation spectroscopy in the 390–431 nm region. Laser excitation spectroscopy and photoionization experiments demonstrate that the XO+ dissociation energy is 25 340±90 cm−1, which agrees with the value suggested by Vempati and Jones [J. Mol. Spectrosc. 127, 232 (1988)] if the InI ground state is covalent. Seven previously unreported vibrational bands of the InI(B←X) transition have been observed and the molecular emission spectra indicate that the B 3Π1(1) state is predissociated above v=6. Splitting between the fine structure levels of the In np 2P1/2,3/2 (15⩽n⩽17) states has also been measured by fluorescence suppression spectroscopy, following the three photon excitation of InI in the 450–470 nm interval.
Scattered and recoiled ion fractions from LiTaO3(100) surfaces with different electrical properties
Authors: Kim Y. , Kim S. S. , Ada E. , Yang Y. L. , Jacobson A. J. , Rabalais J. W.
Published: July 2002

Time-of-flight scattering and recoiling spectrometry (TOF-SARS) was used to investigate the scattered and recoiled ion fractions from 3 keV Ar+ ion beams on LiTaO3(100) single crystals. The TOF-SARS measurements were found to be sensitive to the electrical properties of the crystal. ac impedance measurements of the electrical conductivity showed that LiTaO3 is an insulator at room temperature and that its conductivity increases by ∼103 at temperatures in the range 100–200 °C. This increase in conductivity could be monitored in TOF-SARS by measuring the current through the crystal induced by the impinging Ar+ ions as a function of temperature. The activation energy for this transition was estimated from both the impedance and scattering measurements to be ∼1 eV. Azimuthal anisotropy of the scattered Ar+ ions from Ta atoms was observed at room temperature but not at elevated temperatures. Scattered Ar+ ion fraction measurements showed that scattered Ar+ ions are enhanced by charge buildup on the LiTaO3 surface, whereas recoiled ions are not affected. The effects of surface charging phenomena on TOF-SARS could be eliminated by either heating the LiTaO3 crystal to ∼200 °C or by application of a low energy electron beam to the crystal surface.
Self-diffusion of an asymmetric diblock copolymer above and below the order-to-disorder transition temperature
Authors: Fleischer Gerald , Rittig Frank , Kärger Jörg , Papadakis Christine M. , Mortensen Kell , Almdal Kristoffer , Štěpánek Petr
Published: July 2002

The self-diffusivity of an asymmetric poly(ethylenepropylene)–poly(dimethylsiloxane) diblock copolymer (PEP–PDMS) was investigated using pulsed field gradient NMR both in the ordered and the disordered state. In a temperature range below the order-to-disorder transition temperature, the diblock copolymer forms micelles which order in a simple cubic structure, and at lower temperatures, a noncubic structure is formed. We have found a broad distribution of self-diffusivities. The distribution width increases with decreasing temperature. The self-diffusivity as well as its distribution width changes only slightly at the order-to-disorder transition. In contrast to self-diffusion in symmetric diblock copolymers where single chains diffuse independently, our results are interpreted as a collective diffusion of chains confined to micelles which further cluster to larger aggregates. This behavior cannot be described by existing models of chain dynamics in the melt. The disordered state is characterized by a large temperature range above the order-to-disorder transition where concentration fluctuations dominate. This is revealed in the temperature dependence of the self-diffusivity and its distribution width, in the viscosity and in the inverse intensity of the first-order Bragg reflection in small angle neutron scattering (SANS).
Stochastic-trajectories and nonPoisson kinetics in single-molecule spectroscopy
Authors: Chernyak Vladimir , Schulz Michael , Mukamel Shaul
Published: July 2002

Microscopic correlation-function expressions for the stochastic evolution observed in single molecule spectroscopy are derived using Liouville-space projection operators. The kinetics of a multilevel quantum system coupled to a single collective overdamped Brownian-oscillator coordinate is exactly mapped onto a continuous-time-random-walk (CTRW) involving the transition states(curve-crossing points). Closed expressions are derived for the stochastic trajectories and the nonPoissonian distribution of number of flips. When the oscillator relaxation is fast compared with the reaction rates, the waiting time distribution becomes exponential and the standard Poisson kinetics is recovered.
Influence of the dispersivity of charge transport on the holographic properties of organic photorefractive materials
Authors: Jakob T. , Schloter S. , Hofmann U. , Grasruck M. , Schreiber A. , Haarer D.
Published: July 2002

The holographic properties of the photorefractive polymer composite PSX:DMNPAA:TNF are determined as a function of the grating spacing by use of two-beam coupling and degenerate four-wave mixing measurements. The phase shift was quantified with the grating translation technique. In particular, an almost constant mean drift length of the charge carriers of about 0.5 μm was obtained. The resulting discrepancies between the standard theory of crystals, which is generally used as an approximation for amorphous organic materials, and the experimental data are discussed and attributed to the different mechanisms of charge transport in amorphous organic materials. To verify our conclusions we performed time-of-flight and degenerate four-wave mixing measurements on the two photorefractive organic glasses DRDCTA:DOP:C60 and DRDCTA:EHMPA:C60, which differ in the degree of dispersivity of charge carrier transport and, hence, the involved trap energy distributions. Comparing the behavior of the two materials under investigation, we obtained a qualitative relationship between dispersivity and a theoretically unexpected drop in the diffraction efficiency: The larger the dispersivity the earlier the drop in the efficiency.
Fast radio-frequency amplitude modulation in multiple-quantum magic-angle-spinning nuclear magnetic resonance: Theory and experiments
Authors: Madhu P. K. , Goldbourt Amir , Frydman Lucio , Vega Shimon
Published: July 2002

Multiple-quantum magic-angle-spinning (MQMAS NMR) spectroscopy has become a routine method to obtain high-resolution spectra of quadrupolar nuclei. One of the main problems in the performance of this experiment has been the poor efficiency of the radio-frequency pulses used in converting multiple-quantum coherences to the observable single-quantum signals. As the MQMAS experiment is basically an echo experiment this problem can be related to the efficiency with which continuous wave pulses can normally achieve the multiple- to single-quantum conversion for different crystallites in a spinning powdered sample. In this paper we investigate various aspects involved in this multiple-to-single quantum conversion, in the hope to facilitate the devise of new experimental schemes that can lead to significant MQMAS signal enhancements. We examine in particular a recently suggested experiment for MQMAS spectroscopy which employs amplitude-modulated radio-frequency pulses, and which can yield substantial signal and even resolution enhancements over the commonly used pulse schemes in MQMAS experiments. The mechanisms of operation of continuous-wave and of amplitude-modulated pulses as applied to the selective manipulation of spin-3/2 coherence elements are examined in detail, with the aid of the fictitious spin-1/2 formalism in combination with quadrupolar adiabaticity arguments. New insight into the nature of the MQMAS experiment is thus revealed, and the superior performance of suitable amplitude modulations toward the formation of MQMAS powder echoes is justified. Experimental results highlighting the utility of this scheme in samples possessing multiple quadrupolar sites with varying quadrupolar anisotropies and chemical shift offsets are demonstrated, as is the relative insensitivity of the new signal-enhancement technique to the actual level of rf irradiation. Further implications and uses of this new irradiation scheme are also briefly discussed.
Solutions of the classical SU(2) Yang–Mills theory in (2+1) dimensions with the Chern–Simons term: Ansatz building
Authors: Teh Rosy
Published: July 2002

A general way of writing the gauge potentials Aaμ for which the SU(2) Yang–Mills equations of motion can be simplified and become solvable is shown. A number of exact solutions can be obtained from these simplified equations of motion.
A parametrization for independent variables of a two-matrix hypergeometric function
Authors: Wei Gaoyuan
Published: July 2002

A new parametrization for the independent variables of the two-matrix hypergeometric function 0F(k)0(a,b) is given. This parametrization results in a net reduction of two variables. The new arguments for the zonal polynomials in the series representation of 0F(k)0(a,b), multiplied by an exponential factor, are all in the interval [0,1], which greatly improves the convergence of the series. The results are of practical use in a number of applications, such as the configuration statistics of macromolecules, shapes of random walks, and multivariate statistics.
Nonperturbative square-well approximation to a quantum theory
Authors: Boettcher Stefan , Bender Carl M.
Published: July 2002

The possibility of expressing the solution to a φ2P quantum field theory as a series in powers of 1/P is proposed. Such a series would be nonperturbative in its dependence on the fundamental parameters of the theory such as the mass and the coupling constant. The first term in such a series describes a field in an infinite-dimensional square-well potential. In this paper, the quantum-mechanical Hamiltonian H=p2+q2P is studied as a model calculation and the expansion of the energy levels as series in powers of 1/P is examined. The method of matched asymptotic expansions to determine the first five terms in the series for all energy levels is used. The results are compared with extensive numerical calculations of the ground-state energy and it is found that the series is extremely accurate: When P=2, the five-term series has a relative error of 6%, when P=10 the relative error is 0.009%, and when P=200 the relative error is 3.4×10−9%.
On the quantization of the modified Pöschl–Teller potential
Authors: Wu Yihren
Published: July 2002

It is shown that the connection one-form on the prequantization line bundle that generates the correct energy spectrum for the modified Pöschl–Teller potential consists of the canonical one-form on the corresponding cotangent bundle, together with an adjustment term that arises from the Berry’s connection.
A mathematical treatment for a perturbation of the one-dimensional harmonic oscillator
Authors: Hervé Rose-Marie , Hervé Michel
Published: July 2002

A method is put forward for the exact computation of the transition amplitudes that describe the state of the harmonic oscillator after a sudden displacement of the equilibrium point: They appear in a paper by Guy Mayer [J. Phys. France 50, 2175 (1989)] on the multiphotonic Bremsstrahlung effects.
Energy-momentum tensor and transformation properties of the gauge potentials in gravitation theory
Authors: Sukhov Andrei M.
Published: July 2002

It is shown that the transformation properties of the translational gauge potentials eαi(x), will be chosen in another way [compared with the exposition of Hehl et al., Rev. Mod. Phys. 48, 393 (1976)]. The term containing the total (symmetric) energy-momentum tensor remains in the variation of the action. This approach allows us to change the transformation properties of the gauge potentials and the conservation laws of energy momentum.
General solutions of nonlinear Ianiro–Lebowitz model equation
Authors: Yuan Miao-En , Wang Achilaltu
Published: July 2002

The nonstationary spacially nonhomogeneous nonlinear Ianiro–Lebowitz model of Boltzmann equation is considered. Its whole range exact solutions are found. Analysis of the positivity behavior of the solutions are given.
On the structure of Yang–Mills fields in compactified Minkowski space
Authors: Minzoni A. A. , Muciño J. , Rosenbaum M.
Published: July 2002

In this work the Yang–Mills functional with gauge group SU(2) in compactified Minkowski space is reduced to a mechanical Lagrangian which enables one to find new classes of exact dual and nonself-dual solutions. The technique used in the reduction allows a simple interpretation of meron-type solutions. The formalism is then used to produce a good simple analytic approximation to static solutions of Skyrme’s field equation, relevant to low energy hadronic interactions.
Potentials derived geometrically for symmetry scattering
Authors: Wehrhahn Rodolfo Francisco
Published: July 2002

The scattering interaction in symmetry scattering is related to certain local potentials. The resulting potentials are calculated from the density function. This function is connected with the geometry of the space where scattering takes place. The potentials admit a quantum mechanical supersymmetric treatment. The corresponding superpotential is proportional to the logarithmic derivative of the density function.
Global potentials for general relativistic flows of ideal charged fluids
Authors: Debbasch Fabrice
Published: July 2002

It is shown that general relativistic nondissipative flows of a possibly charged one component fluid, submitted to the action of its own electromagnetic field, admit a representation in terms of global potentials. A corresponding variational principle is presented, from which the equations of motion for the fluid and the fields can be obtained.
Universal bundle for gravity, local index theorem, and covariant gravitational anomalies
Authors: Kelnhofer Gerald
Published: July 2002

Consistent and covariant Lorentz and diffeomorphism anomalies are investigated in terms of the geometry of the universal bundle for gravity. This bundle is explicitly constructed and its geometrical structure will be studied. By means of the local index theorem for families of Bismut and Freed, the consistent gravitational anomalies are calculated. Covariant gravitational anomalies are shown to be related with secondary characteristic classes of the universal bundle and a new set of descent equations which also contains the covariant Schwinger terms is derived. The relation between consistent and covariant anomalies is studied. Finally a geometrical realization of the gravitational BRS, anti-BRS transformations is presented which enables the formulation of a kind of covariance condition for covariant gravitational anomalies.
Linear operators with invariant polynomial space and graded algebra
Authors: Brihaye Y. , Giller Stefan , Kosinski Piotr
Published: July 2002

The irreducible, finite-dimensional representations of the graded algebras osp(j,2) (j=1,2,3) are expressed in terms of differential operators. Some quantum deformations of these algebras are shown to admit similar kinds of representations. These are formulated in terms of finite difference operators. The results are discussed in the framework of the quasi-exactly solvable equations.
The flow of the G2 periodic Toda lattice
Authors: McDaniel Andrew , Smolinsky Lawrence
Published: July 2002

In the study of the generalized periodic Toda lattices, Mark Adler and Pierre van Moerbeke showed that the flow of the G2 periodic Toda lattice has a 2-dimensional sub-Abelian variety of a 3-dimensional Prym variety as its Hamiltonian torus. In this paper it is shown that the 2-dimensional torus is a Prym–Tjurin variety and is explained in terms of the Weyl group of G2. This example is small enough to be explicitly computable.
Exact solutions of linearized Schwinger–Dyson equation of fermion self-energy
Authors: Zhou Bang-Rong
Published: July 2002

The Schwinger–Dyson equation of fermion self-energy in the linearization approximation is solved exactly in a theory with gauge and effective four-fermion interactions. Different expressions for the independent solutions, which, respectively, submit to irregular and regular ultraviolet boundary condition are derived and expounded.
Complementary group resolution of the SU(n) outer multiplicity problem. I. The Littlewood rules and a complementary U(2n−2) group structure
Authors: Pan Feng , Draayer J. P.
Published: July 2002

A complementary group to SU(n) is found that realizes all features of the Littlewood rules for Kronecker products of SU(n) representations. This is accomplished by considering a state of SU(n) to be a special Gel’fand state of the complementary group U(2n−2) with labels of the latter used to distinguish multiple occurrences of irreducible representations of SU(n) (irreps) in the SU(n)×SU(n)↓SU(n) decomposition that is obtained from the Littlewood rules. Furthermore, this realization also helps us to determine SU(n)⊃SU(n−1)×U(1) Reduced Wigner Coefficients (RWCs, frequently called Isoscalar Factors) and Clebsch–Gordan Coefficients [CGCs, or full (nonreduced) Wigner Coefficients] of SU(n), using algebraic or numeric methods, in either the canonical or a noncanonical basis. New explicit formulas for the SU(3) and SU(4) multiplicities are obtained by using this technique.
On the geometric equivalence of certain discrete integrable Heisenberg ferromagnetic spin chains
Authors: Daniel M. , Manivannan K.
Published: July 2002

Using a discrete curve mapping procedure, we reformulate the problem of nonlinear spin dynamics in three different discrete Heisenberg ferromagnetic spin chain models with different magnetic interactions. The procedure helps to rewrite the Landau–Lifshitz equations that govern the dynamics of spins in these ferromagnetic spin systems as equivalent to the integrable discretization of the completely integrable nonlinear Schrödinger family of equations. The elementary spin excitations in these spin systems are governed by lattice solitons.