bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined high resolution infrared and microwave study of bromochlorofluoromethane
Authors: Bauder Alfred , Beil Andreas , Luckhaus David , Müller Franz , Quack Martin
Published: July 2002

We report a detailed spectroscopic investigation of the chiral molecule bromochlorofluoromethane (CHBrClF) with rotational resolution using a pulsed nozzle beam Fourier transform microwave (FTMW) and a waveguide FTMW spectrometer as well as a supersonic jet interferometric Fourier transform infrared (FTIR) and infrared diode laser spectrometer. The rotational spectrum of CHBrClF has been measured between 8 and 18 GHz. The quadrupole hyperfine components have been fully resolved for the assigned rotational transitions with J⩽18. Three ground state rotational constants, five centrifugal distortion constants, and all five independent elements of the bromine and chlorine quadrupole coupling tensors have been determined for each of the four isotopomers CH79Br35CIF, CH81Br35CIF, CH79Br37CIF, and CH81Br37CIF from about 500 measured transition frequencies of the hyperfine components. The quadrupole coupling tensor has been transformed to its principal axes. The determinable sign combinations of the off-diagonal elements of the coupling tensor have been evaluated. Rotational transitions involving high J were measured by FTIR spectroscopy between 15 and 40 cm−1 (450–1200 GHz) using a light pipe cell, providing an estimate of the permanent dipole moment |μ|=(1.5±0.3) D from intensities. In the midinfrared, we have fully analyzed the rovibrational line structure of supersonic jet spectra of the CF-stretching fundamental ν4, giving band centers for the isotopomers CH79Br35CIF [ν̃ 40=1077.178 43(4) cm−1], CH81Br35CIF [ν̃=1077.133 06(4) cm−1], CH79Br37CIF [ν̃ 40=1076.7914(4) cm−1], and CH81Br37CIF [ν̃ 40=1076.730 26(5) cm−1]. A combined analysis of about 20 microwave frequencies, more than 100 infrared ground state combination differences, and about 70 infrared transition frequencies for each of the35Cl isotopomers finally provide accurate ground and excited state rotational parameters as well as structural parameters, which may be compared to ab initio calculations. The results are discussed in relation to the molecular structure as well as coincidences of ν4 absorptions with CO2 laser lines in view of CO2–laser pumping and possible spectroscopic studies of this chiral molecule at ultrahigh resolution.
Electron-impact total ionization cross sections of silicon and germanium hydrides
Authors: Ali M. A. , Kim Y.-K. , Hwang W. , Weinberger N. M. , Rudd M. E.
Published: July 2002

Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data—binding energies, average kinetic energies, and occupation numbers—which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH2, SiH3, SiH4, Si2H6, Si(CH3)4, GeH, GeH2, GeH3, GeH4, and Ge2H6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiHx, x=1–4, from thresholds to T<80 eV, while theoretical peaks occur at lower T than experimental peaks for SiHx, x=1–3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing.
Spin relaxation by collective director fluctuations and molecular diffusion in lamellar phases. Continuum theory of relaxation anisotropy and dispersion
Authors: Gustafsson Stefan , Halle Bertil
Published: July 2002

The orientation and frequency dependence of nuclear spin relaxation rates can provide detailed information about the amplitudes and rates of collective orientational fluctuations (director fluctuations) in liquid crystals. In particular, the low-frequency spin relaxation rates from a lamellar phase reflect the membrane bending rigidity and the intermembrane forces. This information is contained in three spectral density functions Jn(ω), n=0,1,2. We have recently presented a continuum-mechanical theory for the second-order spectral density J1(ω). Here we extend the theory to the fourth-order spectral densities J0(ω) and J2(ω), which dominate the transverse relaxation rate in the parallel and perpendicular configurations. These spectral densities have previously been considered in connection with director fluctuations in nematic phases, neglecting the elastic and hydrodynamic anisotropy of the phase. In lamellar phases, this anisotropy plays a crucial role and must be retained in the relaxation theory. Director fluctuations can be induced by elastic distortion modes as well as by molecular translational diffusion. In a lamellar phase, these independent processes give rise to qualitatively different spin relaxation behavior. In particular, J0(0) and J2(0) diverge in the limit of quenched disorder. The theoretical results presented here are directly applicable to spin relaxation data from a variety of lamellar systems, including phospholipid bilayers and sterically stabilized dilute lamellar phases. An analysis of published H2 and P31 relaxation data from phospholipid bilayer phases is presented, leading to a qualitatively different picture from what has previously been deduced in terms of a free membrane theory.
Interfaces between highly incompatible polymers of different stiffness: Monte Carlo simulations and self-consistent field calculations
Authors: Müller M. , Werner A.
Published: July 2002

We investigate interfacial properties between two highly incompatible polymers of different stiffness. The extensive Monte Carlo simulations of the binary polymer melt yield detailed interfacial profiles and the interfacial tension via an analysis of capillary fluctuations. We extract an effective Flory–Huggins parameter from the simulations, which is used in self-consistent field calculations. These take due account of the chain architecture via a partial enumeration of the single chain partition function, using chain conformations obtained by Monte Carlo simulations of the pure phases. The agreement between the simulations and self-consistent field calculations is almost quantitative, however, we find deviations from the predictions of the Gaussian chain model for high incompatibilities or large stiffnesses. The interfacial width at very high incompatibilities is smaller than the prediction of the Gaussian chain model, and decreases upon increasing the statistical segment length of the semiflexible component.
A molecular simulation study of freezing/melting phenomena for Lennard-Jones methane in cylindrical nanoscale pores
Authors: Maddox M. W. , Gubbins K. E.
Published: July 2002

A combination of grand canonical Monte Carlo and molecular dynamics simulation techniques are used to study the freezing and melting of Lennard-Jones methane in several different cylindrical pores. Two different types of pore wall are considered; a strongly attractive wall, and a weakly attractive wall, each with pore diameters in the range 1.5–3.5 nm. Freezing point depression is observed in the case of the weakly attractive pores, in agreement with several experimental studies. Freezing point elevation is observed at the walls of the strongly attractive pore, but freezing point depression occurs at the center of such pores, due to geometrical constraints.
A nonorthogonal CI treatment of symmetry breaking in sigma formyloxyl radical
Authors: Ayala Philippe Y. , Schlegel H. Bernhard
Published: July 2002

Spatial symmetry breaking can occur in Hartree–Fock wave functions when there are two or more close lying configurations that can mix strongly, such as in HCO2, NO2, and allyl radical. Like spin contamination, spatial symmetry breaking can cause sizeable errors when perturbation theory is used to estimate the correlation energy. With conventional methodology, very large MCSCF and MRCI calculations are necessary to overcome the spatial symmetry breaking problem. This paper explores an alternative approach in which a 2×2 nonorthogonal CI is used to recombine the two symmetry broken Hartree–Fock determinants. The necessary matrix elements closely resemble those used in the spin projection calculations. Second order perturbation theory is used to include electron correlation energy in this approach. With perturbative corrections for correlation energy, this approach predicts that the B22 structure is a minimum, in agreement with the best available calculations.
The density matrix renormalization group method: Application to the PPP model of a cyclic polyene chain
Authors: Fano G. , Ortolani F. , Ziosi L.
Published: July 2002

The density matrix renormalization group (DMRG) method introduced by White for the study of strongly interacting electron systems is reviewed; the method is variational and considers a system of localized electrons as the union of two adjacent fragments A,B. A density matrix ρ is introduced, whose eigenvectors corresponding to the largest eigenvalues are the most significant, the most probable states of A in the presence of B; these states are retained, while states corresponding to small eigenvalues of ρ are neglected. It is conjectured that the decreasing behavior of the eigenvalues is Gaussian. The DMRG method is tested on the Pariser-Parr-Pople Hamiltonian of a cyclic polyene (CH)N up to N=34. A Hilbert space of dimension 5.×1018 is explored. The ground state energy is 10−3 eV within the full CI value in the case N=18. The DMRG method compares favorably also with coupled cluster approximations. The unrestricted Hartree-Fock solution (which presents spin density waves) is briefly reviewed, and a comparison is made with the DMRG energy values. Finally, the spin-spin and density-density correlation functions are computed; the results suggest that the antiferromagnetic order of the exact solution does not extend up to large distances but exists locally. No charge density waves are present.
Formation and growth of ice particles in stationary ultrasonic fields
Authors: Bauerecker Sigurd , Neidhart Bernd
Published: July 2002

The formation of ice particles in stationary ultrasonic fields (SUSFs) from ice aerosol was observed. Under suitable experimental conditions aerosol particles gather in stable ellipsoidal systems at temperatures down to <50 K below ambient. We call these systems cold gas traps. The aerosol concentrates in the pressure node areas of the SUSF and conglomerates to form larger particles and snowflakes with diameters up to 10 mm. The resulting shapes are shown. Most of them are similar to those occurring in nature. An attempt is made to explain the effect. Three different processes of ice particle formation are visualized and discussed. Here the existence of a quasiliquid layer (QLL) on the particle surfaces seems to be essential because both the formation of ice particles and the QLL occur only at temperatures higher than about −25 °C. The observed trapping and generation process can be used, for example, in atmospheric physics for the study of particle aggregation, precipitation formation, and water and radiation transport phenomena.
Ionization of medium-sized silicon clusters and the geometries of the cations
Authors: Liu Bei , Lu Zhong-Yi , Pan Bicai , Wang Cai-Zhuang , Ho Kai-Ming , Shvartsburg Alexandre A. , Jarrold Martin F.
Published: July 2002

We have performed a systematic ground state geometry search for the singly charged Sin cations in the medium-size range (n⩽20) using density functional theory in the local density approximation (LDA) and generalized gradient approximation (GGA). The structures resulting for n⩽18 generally follow the prolate “stacked Si9 tricapped trigonal prism” pattern recently established for the lowest energy geometries of neutral silicon clusters in this size range. However, the global minima of Sin and Sin+ for n=6, 8, 11, 12, and 13 differ significantly in their details. For Si19 and Si20 neutrals and cations, GGA renders the prolate stacks practically isoenergetic with the near-spherical structures that are global minima in LDA. The mobilities in He gas evaluated for all lowest energy Sin+ geometries using the trajectory method agree with the experiment, except for n=18 where the second lowest isomer fits the measurements. The effect of gradient corrections for either the neutral or cationic clusters is subtle, but their inclusion proves to be critical for obtaining agreement with the mobility measurements in the n=15–20 range. We have also determined ionization potentials for our Sin neutral geometries and found that all experimental size-dependent trends are reproduced for n⩽19. This particularly supports our structural assignments for Si9, Si11, Si12, and Si17 neutrals. The good overall agreement between the measured and calculated properties supports the elucidation of the “prolate” family of silicon clusters as stacks of trigonal prisms.
Defect evolution in ultrathin films of polystyrene-block-polymethylmethacrylate diblock copolymers observed by atomic force microscopy
Authors: Hahm J. , Lopes W. A. , Jaeger H. M. , Sibener S. J.
Published: July 2002

We track individual defects in the microdomain patterns of cylinder-forming polystyrene-block-polymethylmethacrylate films with atomic force microscopy to elucidate the evolution of diblock domain topology during annealing. This evolution takes place through relinking, joining, clustering, and annihilation of defects. Such processes form the basis for predicting structural change in polymer films.
A density functional study of small neutral and cationic vanadium clusters Vn and Vn+ (n=2–9)
Authors: Wu Xueyuan , Ray A. K.
Published: July 2002

All electron density functional theory with gradient corrections to the exchange and correlation functionals has been used to investigate the properties of small neutral and cationic vanadium clusters. The energetically favorable structures of vanadium clusters are found to be those with maximized average coordinations. The binding energy is found to increase monotonically with the number of atoms in the cluster and it is predicted that a significantly large number of atoms is needed to reproduce the bulk cohesive energy. Except for the neutral vanadium tetramer, the preferred decay channels for all the neutral and cationic clusters contain the vanadium atom. The average magnetic moment per atom is found to oscillate with cluster size, with an upper bound of 0.33 μB in the range from V4 to V9. Results have been compared, in detail, with available experimental and theoretical data.
Nucleation in superheated gas-saturated solutions. I. Boiling-up kinetics
Authors: Baidakov V. G.
Published: July 2002

Nucleation in a superheated gas-saturated solution is regarded as a diffusional process in the space of three variables of a nucleus: Its volume υ and the partial pressures of the components p1″,p2″. The paper determines the surface relief of the thermodynamic potential in the vicinity of the saddle point and describes the growth of vapor bubbles in a solution with allowance for its viscosity, rate of evaporation of molecules of a solvent, and a dissolved substance, rate of diffusional supply of a substance to the bubble surface. The tensor of the generalized diffusion of nuclei, the decrement of increase of an unstable variable, the stationary nucleation rate have been calculated.
A new molecular dynamics method for simulating trapping site structures in cryogenic matrices
Authors: Ning Xi-Jing , Qin Qi-Zong
Published: July 2002

An ensemble model is proposed to describe the codeposition process of host and guest molecules. In this model, it is shown that the prepared matrix has a time related memory of the deposition process. A technique of time-going-backwards is developed to simulate the matrix structure around the guest molecule. In order to examine the reliability of this new method, a quantum fourth-order perturbation method is used for the first time to calculate the vibrational frequency shift of diatomic molecules in the matrix with respect to that in gas phase. The trapping site structures of some diatomic molecules (Br2, BrO, CS, CN, ClO, NBr, and NCl) in solid argon and corresponding frequency shifts have been calculated with simple pairwise potentials. The simulation results are in good agreement with the experimental measurements.
Molecular dynamics simulation of vibrational relaxation of highly excited molecules in fluids. II. Nonequilibrium simulation of azulene in CO2 and Xe
Authors: Heidelbach C. , Vikhrenko V. S. , Schwarzer D. , Schroeder J.
Published: July 2002

Results of nonequilibrium molecular dynamics simulations of vibrational energy relaxation of azulene in carbon dioxide and xenon at low and high pressure are presented and analyzed. Simulated relaxation times are in good agreement with experimental data for all systems considered. The contribution of vibration–rotation coupling to vibrational energy relaxation is shown to be negligible. A normal mode analysis of solute-to-solvent energy flux reveals an important role of high-frequency modes in the process of vibrational energy relaxation. Under all thermodynamic conditions considered they take part in solvent-assisted intramolecular energy redistribution and, moreover, at high pressure they considerably contribute to azulene-to-carbon dioxide energy flux. Solvent-assisted (or collision-induced) intermode energy exchange seems to be the main channel, ensuring fast intramolecular energy redistribution. For isolated azulene intramolecular energy redistribution is characterized by time scales from several to hundreds of ps and even longer, depending on initial excitation. The major part of solute vibrational energy is transferred to the solvent via solute out-of-plane vibrational modes. In-plane vibrational modes are of minor importance in this process. However, their contribution grows with solvent density. The distribution of energy fluxes via azulene normal modes strongly depends on thermodynamic conditions. The contribution of hydrogen atoms to the overall solute-to-solvent energy flux is approximately two to three times higher than of carbon atoms depending on the system and thermodynamic conditions as well. Carbon atoms transfer energy only in the direction perpendicular to the molecular plane of azulene, whereas hydrogen atoms show more isotropic behavior, especially at high pressure.
Connected quadruples for the frequencies of O3
Authors: Kucharski Stanisław A. , Bartlett Rodney J.
Published: July 2002

Coupled cluster methods with full inclusion of quadruples (T4) are not yet applicable to O3 frequencies, but a recently proposed noniterative quadruples method [CCSDT(Qf)] offers an ∼n7 evaluation. We report large basis set results for O3’s structure and harmonic vibrational frequencies, improving agreement with experiment over CCSDT.
The parametrization of a Thole-type all-atom polarizable water model from first principles and its application to the study of water clusters (n=2–21) and the phonon spectrum of ice Ih
Authors: Burnham Christian J. , Li Jichen , Xantheas Sotiris S. , Leslie Maurice
Published: July 2002

We present the parametrization of a new polarizable model for water based on Thole’s method [Chem. Phys. 59, 341 (1981)] for predicting molecular polarizabilities using smeared charges and dipoles. The potential is parametrized using first principles ab initio data for the water dimer. Initial benchmarks of the new model include the investigation of the properties of water clusters (n=2–21) and (hexagonal) ice Ih using molecular dynamics simulations. The potential produces energies and nearest-neighbor (H-bonded) oxygen–oxygen distances that agree well with the ab initio results for the small water clusters. The properties of larger clusters with 9–21 water molecules using predicted structures from Wales et al. [Chem. Phys. Lett. 286, 65 (1998)] were also studied in order to identify trends and convergence of structural and electric properties with cluster size. The simulation of ice Ih produces a lattice energy of −65.19 kJ/mol (expt. −58.9 kJ/mol) with an average dipole moment of 2.849 D. The calculated spectrum for the phonon density of states exhibits features that may correspond to the experimentally measured peaks at 28 and 37 meV. The many body contribution to the total energy is found to be close to 31% for both the water clusters and for ice Ih.
The influence of intramolecular chain dynamics on the diffusion of small penetrants in semicrystalline aromatic polymers
Authors: Mooney D. A. , MacElroy J. M. D.
Published: July 2002

A recently developed molecular model for diffusion in dense aromatic polymers, which attempts to explain penetrant jump frequencies in terms of phenyl ring partial flips, is investigated via molecular simulation. The model polymer system under consideration in this paper corresponds to the interfacial domains generated by the lateral chain invariant (LCI) grain boundaries between crystallites of a stiff chain polyamide, poly(p-phenylene terephthalamide) (PPTA), and the low molecular weight penetrant selected for study is water. Fully atomistic constraint molecular dynamics simulations are conducted with interatomic and intramolecular interactions described by the DREIDING potential [S. L. Mayo, B. D. Olafson, and W. A. Goddard III, J. Phys. Chem. 94, 8897 (1990).] The coupling of the diffusive motion of water with the local polymer chain dynamics is examined at two temperatures and over a range of grain boundary densities.
Simulation of self-diffusion of point-like and finite-size tracers in stochastically reconstructed Vycor porous glasses
Authors: Kainourgiakis M. E. , Kikkinides E. S. , Stubos A. K. , Kanellopoulos N. K.
Published: July 2002

Aim of the present study is to simulate self-diffusion in three-dimensional images of reconstructed Vycor porous glass, which have the same statistical content as the actual material in terms of porosity and autocorrelation function. Effective diffusivities are determined from a step-by-step random walk process at different porosities and diffusion regimes. In all cases, the effective diffusivity curves show a sharp decrease below 20% porosity and drop to zero below a porosity of about 15%, a value suggested independently from the theory of spinodal decomposition. Comparison between the computed and experimental diffusivity values obtained in the Knudsen regime, shows a relative difference of less than 6%. Additional simulations in the molecular diffusion regime are performed using inert tracers of finite size. In these simulations, a transition is found in the value of diffusivity from a high value at small time scales, to a lower constant value achieved at large times. The time at which this crossover takes place corresponds to a mean-square displacement value whose square root is roughly equal to the average pore radius of the material. Comparison between computed and experimental results taken from the literature, shows very good agreement, as in the case of point-like tracer diffusion. Thus, the reconstructed Vycor is shown to represent properly not only structural properties such as porosity and correlation function, but also dynamic properties such as effective diffusivity of inert gas molecules of various sizes.
Smoluchowski ripening of Ag islands on Ag(100)
Authors: Stoldt C. R. , Jenks C. J. , Thiel P. A. , Cadilhe A. M. , Evans J. W.
Published: July 2002

Using scanning tunneling microscopy, we study the post-deposition coarsening of distributions of large, two-dimensional Ag islands on a perfect Ag(100) surface at 295 K. The coarsening process is dominated by diffusion, and subsequent collision and coalescence of these islands. To obtain a comprehensive characterization of the coarsening kinetics, we perform tailored families of experiments, systematically varying the initial value of the average island size by adjusting the amount of Ag deposited (up to 0.25 ML). Results unambiguously indicate a strong decrease in island diffusivity with increasing island size. An estimate of the size scaling exponent follows from a mean-field Smoluchowski rate equation analysis of experimental data. These rate equations also predict a rapid depletion in the initial population of smaller islands. This leads to narrowing of the size distribution scaling function from its initial form, which is determined by the process of island nucleation and growth during deposition. However, for later times, a steady increase in the width of this scaling function is predicted, consistent with observed behavior. Finally, we examine the evolution of Ag adlayers on a strained Ag(100) surface, and find significantly enhanced rates for island diffusion and coarsening.
Trapping site structures of O3 isolated in argon matrices
Authors: Ning Xi-Jing , Qin Qi-Zong
Published: July 2002

A technique of time going backwards is used to simulate the deposition of ozone molecules mixed with argon atoms from the gas phase onto a cold surface. The relative probabilities of various trapping sites are obtained at different deposition temperatures (5, 10, and 20 K). Single substitutional sites are probably formed the most and they can be grouped into two subsites, specified by the doublet frequency splitting of the v3 mode acquired via the normal mode calculation of O3 in the matrix. The probability ratio of the two subsites depends upon the deposition temperatures. The normal frequencies of O3 calculated in double-, triple-, and multiple-substitutional sites distribute over a wide range, implying that they are not easily observable sites in an infrared spectrum. A series of experimental observations are interpreted well with the above calculations.
A CASSCF–MRCI study on the low-lying excited states of CH3OCl
Authors: Li Yumin , Francisco Joseph S.
Published: July 2002

A theoretical study on the excited states of methylhypochlorite (CH3OCl) has been carried out using high level ab initio molecular orbital methods. The vertical excitation energies for the lowest two A′1 states, three A″1 states, three A′1 states, and three A″1 states are calculated using the multireference configuration interaction (MRCI) method with cc-pVTZ and cc-pVTZ+sp basis sets. In addition, the potential energy curves for the lowest eight states are examined along both the ClO and CO coordinates at the complete active space SCF (CASSCF) level of theory with cc-pVTZ basis set. Except for the ground state, all seven excited states are strongly repulsive along the ClO coordinate, which is in good agreement with recent experimental work. Two absorption bands with maximums at 235 nm and 308 nm in the experimental UV spectra of CH3OCl can be assigned to the transitions X 1A′→1 1A″ and X 1A′→2 1A′.
Viscoelasticity and generalized Stokes–Einstein relations of colloidal dispersions
Authors: Banchio Adolfo J. , Nägele Gerhard , Bergenholtz Johan
Published: July 2002

The linear viscoelastic and diffusional properties of colloidal model dispersions are investigated and possible relations between the (dynamic) shear viscosity and various diffusion coefficients are analyzed. Results are presented for hard sphere and charge-stabilized dispersions with long-range screened Coulomb interactions. Calculations of the dynamic long-time properties are based on a (rescaled) mode coupling theory (MCT). For hard sphere suspensions a simple hydrodynamic rescaling of the MCT results is proposed which leads to good agreement between the theory and experimental data and Brownian dynamics simulation results. The rescaled MCT predicts that the zero-shear limiting viscosity of hard sphere dispersions obeys nearly quantitative generalized Stokes–Einstein (GSE) relations both with regard to the long-time self-diffusion coefficient and the long-time collective diffusion coefficient measured at the principal peak of the static structure factor. In contrast, the MCT predicts that the same GSEs are violated in the case of dispersions of highly charged particles. The corresponding short-time GSEs are found to be partially violated both for charged and uncharged colloidal spheres. A frequency dependent GSE, relating the elastic storage and viscous loss moduli to the particle mean squared displacement, is also investigated, According to MCT, this GSE holds fairly well for concentrated hard spheres, but not for charge-stabilized systems. Remarkably good agreement is obtained, however, with regard to the frequency dependence of the Laplace-transformed reduced shear stress relaxation function and the Laplace-transformed reduced time-dependent self-diffusion coefficient for both charged and uncharged particle dispersions.
On the identification of the vibrational spectrum of cyclic C8 in solid Ar
Authors: Wang S. L. , Rittby C. M. L. , Graham W. R. M.
Published: July 2002

A recent proposal to assign or reassign absorptions in Fourier transform infrared spectra of the products of evaporating graphite trapped in argon matrices to linear C13 and cyclic C8 has been examined. An analysis of the experimental and theoretical data presented indicates that the claimed identification of linear C13 is unwarranted. Simulations of spectra based on density functional theory calculations and isotopic shift data indicate that an absorption at 1818.0 cm−1 belongs to a carbon chain, and do not support a revision of our earlier identification of the ν12(eu) fundamental of cyclic C8 at 1844.2 cm−1.
The bonding of CO to metal surfaces
Authors: Föhlisch A. , Nyberg M. , Bennich P. , Triguero L. , Hasselström J. , Karis O. , Pettersson L. G. M. , Nilsson A.
Published: July 2002

The atom and symmetry specific properties of x-ray emission spectroscopy have been applied to the investigation of CO adsorbed on Ni(100) and Cu(100) surfaces. In comparison to ab initio electronic structure calculations, obtained in density functional theory, we develop a consistent electronic structure model of CO adsorption on transition and noble metals and extend to a conceptual model of the surface chemical bond. A strong CO–substrate interaction is found, characterized by significant hybridization of the initial CO orbitals and the metal bands. In the π system an allylic configuration is found as the result of orbital mixing between the CO 1π, 2π* and the metal dπ-band which is manifested experimentally in the observation of an oxygen lone-pair state. In the σ system experimental evidence of equally strong orbital mixing has been found. Energetically, the adsorbate–substrate complex is stabilized by the π-interaction but is destabilized by the σ-interaction. Furthermore, the internal C–O bond carried by the π-interaction is weakened upon adsorption, which is opposite for the internal C–O σ bond that is strengthened. The equilibrium properties of CO adsorbed on these metals are found to be the direct result of the balance between the σ- and π-interactions; both in terms of the total energy and the local bond properties.
Contact angle hysteresis generated by the residual gravitational field of the Space Shuttle
Authors: Ward C. A. , Rahimi P. , Sasges M. R. , Stanga D.
Published: July 2002

When the two fluid phases of a substance are present in a cylinder, one of the possible equilibrium configurations is for two liquid phases to be present, one above the vapor phase and one below. If surface tension dominates the gravitational effects, the two-interface configuration is the thermodynamically favored one. When the system is in the two-interface configuration, the difference in pressure between the two liquid phases is predicted to be the same as it would have been had no vapor phase been present! Although the pressure profile cannot be measured directly, it is predicted to cause the contact angle value at the upper three-phase line to be smaller than that at the lower three-phase line. This difference in contact angles can be measured, and from the measured values, the theory can be used to determine the value of the gravitational intensity. In an experiment conducted on a Space Shuttle flight, the configuration adopted when glass cylinders of different diameters were each partially filled with water was recorded. The fluid in each cylinder was found to adopt the two-interface configuration, as predicted. A 56 mm diam glass cylinder that had a height of 86 mm was observed to have a contact angle at the upper three-phase line of 6.7±1.3° and 26.5±4.0° at the lower. The value of the gravitational intensity inferred from the measured contact angles agrees with that reported from the (NASA) electronic Space Acceleration Measurement System (SAMS). This agreement supports the prediction that contact angle hysteresis is generated by a difference in pressure between the two liquid phases of the two-interface configuration.
The melting temperature of proton-disordered hexagonal ice: A computer simulation of 4-site transferable intermolecular potential model of water
Authors: Gao G. T. , Zeng X. C. , Tanaka Hideki
Published: July 2002

We report computer simulation results of free energies of proton-disordered hexagonal ice and liquid water at atmospheric pressure with the 4-site transferable intermolecular potential model of water. A new reference system is used to calculate the free energy of the ice phase. The melting point of proton-disordered hexagonal ice at atmospheric pressure is found to be Tm=238(±7) K. This result is consistent with a previous estimation, 230 K<Tm<250 K, from molecular dynamic simulation of the surface melting of the proton-disordered hexagonal ice [G.-J. Kroes, Surf. Sci. 275, 365 (1992)].
On the role of intermolecular interactions in establishing chiral stability
Authors: Vardi Amichay
Published: July 2002

I study the effect of intermolecular interactions on coherent tunneling racemization within the framework of the Hund double well model. Two self-consistent equations for the well population amplitudes, coupled by a tunneling matrix element, are used to describe the system dynamics. It is shown that the equations of motion are nonlinear due to the difference between homochiral interactions and heterochiral interactions. The consequence of this nonlinearity is that chiral molecular configurations are far more stable than expected by the Hund model for isolated molecules. Moreover, when the homochiral interactions are energetically favorable to heterochiral interactions (weaker homochiral repulsive interactions or stronger homochiral attractive interactions), spontaneous symmetry breaking may amplify the optical activity of a nearly racemic mixture.
Small angle x-ray scattering study on role of trapped entanglements in structure of swollen end-linked poly(dimethylsiloxane) networks
Authors: Kawamura Takanobu , Urayama Kenji , Kohjiya Shinzo
Published: July 2002

Amorphous structure of swollen end-linked poly(dimethylsiloxane) (PDMS) network has been investigated by means of small angle x-ray scattering (SAXS) technique as a function of molecular mass of precursor PDMS (Mp) and junction (cross-link) functionality. The Mp dependence of the SAXS profiles for tetra-functional PDMS networks shows a striking crossover at around Mp≈Mc where Mc represents the critical molecular mass to form entanglement couplings in the PDMS melt. These results strongly suggest that structure of swollen end-linked networks significantly depends on whether precursor chains are well entangled or not before end-linking, and that when precursor chain is long enough to form entanglement couplings, trapped entanglements formed in cross-linking (instead of cross-links) play a major role in elementary mesh of the resulting networks. For the networks of Mp≫Mc, the correlation length for the network structure is fairly small and comparable to that of dynamic density fluctuation for the solutions of the precursor polymer, and in addition, no appreciable effect of junction functionality on long-range network structure is observed. These observations imply that the contribution of cross-link to static heterogeneity in network structure is screened by trapped entanglement dominant in number.
To the complete integrability of long-wave–short-wave interaction equations
Authors: Roy Chowdhury A. , Chanda Pranab K.
Published: July 2002

It is shown that the nonlinear partial differential equations governing the interaction of long and short waves are completely integrable. The methodology used is that of Ablowitz et al. [M. J. Ablowitz, A. Ramani, and A. Segur, Lett. Nuovo Cimento 23, 333 (1980); M. J. Ablowitz, A. Ramani, and H. Segur, J. Math. Phys. 21, 715, 1006 (1980)], though in the last section of our paper the problem also has been discussed in the light of the procedure due to Weiss et al. [J. Weiss, M. Tabor, and G. Carnevale, J. Math. Phys. 24, 522 (1983)] and a Backlünd transformation has been obtained.
On discrete Schrödinger equations and their two-component wave equation equivalents
Authors: Bruckstein Alfred M. , Kailath Thomas
Published: July 2002

An approach to inverse scattering problems for discrete Schrödinger equations, which are discrete three-term recursions, is presented by systematically transforming them into discrete two-component wave-propagation equations. The wave-propagation equations permit the immediate application of certain computationally efficient and physically insightful ‘‘layer-peeling’’ algorithms for inverse scattering. The mapping of three-term recursions to two-component evolution equations is one to many, because the relation between the ‘‘potential’’ sequence parametrizing Schrödinger equations and the ‘‘reflection coefficient’’ sequence determining local wave interaction is a nonlinear difference equation. This mapping is examined in some detail and it is used to study both direct and inverse scattering problems associated with discrete Schrödinger equations.
Dirac constraints in field theory: Lifts of Hamiltonian systems to the cotangent bundle
Authors: Oevel Walter
Published: July 2002

To every Hamiltonian system is associated a degenerate Lagrangian formulation. Following Dirac’s theory of constraints one finds a family of lifts of the system to the cotangent bundle of the underlying manifold. The lifted system admits a reduction to the original equation such that the original Hamiltonian formulation is the pullback of the canonical symplectic form. Invariants of the original equation can be lifted to invariants of the extended system. This procedure is applied to integrable systems such as the Korteweg–de Vries equation.
Korteweg-de Vries–modified Korteweg-de Vries systems and Darboux transforms in 1+1 and 2+1 dimensions
Authors: Leble S. B. , Ustinov N. V.
Published: July 2002

The Jaulent–Miodek hierarchy [M. Jaulent and I. Miodek, Lett. Math. Phys. 1, 243 (1976)] and its two-dimensional analog are considered from the point of view of Darboux transforms structures. A new form of those transforms as well as old fashioned forms are presented. The determinant form of solitons is obtained. The combination of different transforms in the 2+1 case allows the buildup of localized solutions in both spatial dimensions, including the two-dimensional Korteweg-de Vries (KdV) equation.
The constraint algorithm for time-dependent Lagrangians
Authors: Chinea Domingo , de León Manuel , Marrero Juan C.
Published: July 2002

The aim of this paper is to develop a constraint algorithm for time-dependent Lagrangian systems which permit us to solve the motion equations. This algorithm extends the Gotay and Nester algorithm for autonomous Lagrangians which is, in fact, a particular case. To do this the almost stable tangent geometry of the evolution space and the notion of cosymplectic structure are used.
Spherically symmetric collapse of an anisotropic fluid body into an exotic black hole
Authors: Das A. , Tariq N. , Aruliah D. , Biech T.
Published: July 2002

The classical gravitational equations of Einstein are investigated for an anisotropic fluid body in the case of spherical symmetry. An equation of state T (4)(4)+k2T (1)(1)=0 is imposed. The junction conditions [T ba]nb=0 of Synge are required to be satisfied on the boundary of the fluid body. A class of exact, analytical solutions depending on four parameters is obtained. The solutions satisfy the equation of state and the weak energy conditions prior to the collapse of the boundary inside the event horizon. However, in the interior of the event horizon, the matter undergoes a transition into an exotic state. A portion of the fluid turns tachyonic with T44<0, a second portion has complex eigenvalues for [T ba], and a third part has signature +4.
Hecke algebraic properties of dynamical
R
-matrices. Application to related quantum matrix algebras
Authors: Hadjiivanov L. K. , Isaev A. P. , Ogievetsky O. V. , Pyatov P. N. , Todorov I. T.
Published: July 2002

The quantum dynamical Yang–Baxter (or Gervais–Neveu–Felder) equation defines an R-matrix R̂(p), where p stands for a set of mutually commuting variables. A family of SL(n)-type solutions of this equation provides a new realization of the Hecke algebra. We define quantum antisymmetrizers, introduce the notion of quantum determinant and compute the inverse quantum matrix for matrix algebras of the type R̂(p)a1a2=a1a2R̂. It is pointed out that such a quantum matrix algebra arises in the operator realization of the chiral zero modes of the WZNW model.
Cosmological and spherically symmetric solutions with intersecting p-branes
Authors: Ivashchuk V. D. , Melnikov V. N.
Published: July 2002

Multidimensional model describing the cosmological evolution and/or spherically symmetric configuration with n+1 Einstein spaces in the theory with several scalar fields and forms is considered. When electro-magnetic composite p-brane ansatz is adopted, n “internal” spaces are Ricci-flat, one space M0 has a nonzero curvature, and all p-branes do not “live” in M0, a class of exact solutions is obtained if certain block-orthogonality relations on p-brane vectors are imposed. A subclass of spherically symmetric solutions (containing nonextremal p-brane black holes) is considered. Post-Newtonian parameters are calculated.
Scattering of a radially symmetric spin wave on a magnetic vortex in a two-dimensional easy-plane ferromagnet
Authors: Ivanov B. A. , Yastremskiı̆ I. A.
Published: July 2002

The scattering amplitude for a radially symmetric spin wave (azimuthal number m=0) on a vortex in an easy-plane ferromagnet is found by analytical and numerical calculations in the long-wavelength approximation (wave number much larger than the inverse size of the vortex core). It is found that the scattering amplitude of a radially symmetric spin wave is smaller than that for a translational mode (m=±1) with the same value of the wave number.
Turbulent spots in plane Poiseuille flow — Measurements of the velocity field
Authors: Klingmann Barbro G. B. , Alfredsson P. Henrik
Published: July 2002

An experimental study on the development of turbulent spots in plane Poiseuille flow at a Reynolds number of 1600 has been carried out with the aim of achieving a better understanding of the transition to and maintenance of turbulence at low Reynolds numbers. Spots were triggered by a loudspeaker-induced jet of high velocity. The initial disturbance was found to undergo a first stage of rapid expansion, in which sharp internal shear layers form at locations away from the symmetry plane and precede the transition to turbulence. After this initial stage, a nearly self-similar structure develops with the typical features of a turbulent spot. The general features, turbulent properties, and spanwise spreading of the spot were investigated and compared both to previous experimental data and to numerical simulations. High-frequency fluctuations are absent at the front of the spot, whereas the turbulence is apparently self-sustained at the rear and displays features similar to fully turbulent Poiseuille flow at much higher Reynolds numbers. The waves accompanying the wing tips of the spot extend well within the spot, and reach amplitudes far in excess of those previously found outside the spot. The high level of random fluctuations in this part of the spot indicates that the breakdown of the waves is important for the spanwise propagation of the turbulent region.
Plane waves and structures in turbulent channel flow
Authors: Sirovich L. , Ball K. S. , Keefe L. R.
Published: July 2002

A direct simulation of turbulent flow in a channel is analyzed by the method of empirical eigenfunctions (Karhunen–Loève procedure, proper orthogonal decomposition). This analysis reveals the presence of propagating plane waves in the turbulent flow. The velocity of propagation is determined by the flow velocity at the location of maximal Reynolds stress. The analysis further suggests that the interaction of these waves appears to be essential to the local production of turbulence via bursting or sweeping events in the turbulent boundary layer, with the additional suggestion that the fast acting plane waves act as triggers.
Low-Reynolds number flow over a rotatable cylinder–splitter plate body
Authors: Xu John C. , Sen Mihir , Gad-el-Hak Mohamed
Published: July 2002

Uniform flow around a body consisting of a cylinder with a splitter plate attached to it is considered. The body is free to rotate about the axis of the cylinder. Numerical results show that on increasing the Reynolds number above a critical value a symmetry-breaking bifurcation appears and the splitter plate migrates to an asymmetric equilibrium position, confirming previous high-Reynolds number experiments. The present results reveal that this phenomenon is due to the flow in the separation bubble behind the cylindrical part of the body.
Relaxation rate of poloidal rotation in the banana regime in tokamaks
Authors: Shaing K. C. , Hirshman S. P.
Published: July 2002

The relaxation rate νp of poloidal rotation in the banana regime in tokamaks is calculated using a time-dependent parallel viscosity. It is found that νp is on the order of νii, the ion–ion collision frequency, with no geometric enhancement factor associated with toroidicity.
Modified Korteweg–deVries solitons in a warm plasma with negative ions
Authors: Kalita B. C. , Kalita M. K.
Published: July 2002

The propagation of ion-acoustic solitons in a warm plasma in the presence of negative ions has been investigated theoretically through the modified Korteweg–deVries (KdV) equation. In the case of the first-order velocity perturbation of the positive ions bearing a constant ratio to that of the negative ions, the existence of both compressive and rarefactive solitons at different critical densities for different temperature ratios has been established when the mass ratio is greater than unity. It is also demonstrated in this case that no modified KdV soliton exists at the critical density in a warm plasma with negative ions when the mass ratio is less than unity.
Parallel energy analyzer for pure electron plasma devices
Authors: Eggleston D. L. , Driscoll C. F. , Beck B. R. , Hyatt A. W. , Malmberg J. H.
Published: July 2002

A technique is presented for measuring the parallel energy distribution of magnetically confined electrons in a cylindrically symmetric pure electron plasma. In essence, the technique measures how many electrons are energetic enough to escape past applied confinement potentials. The technique does not require any secondary magnetic fields. Simplified variations of the technique are also presented which can be used at the expense of some loss of information. These techniques have been successfully used in three experimental contexts.
A differential equation for the ambipolar electric field in a multiple-helicity torsatron
Authors: Hastings D. E.
Published: July 2002

In a torsatron, the ambipolar electric field is obtained by equating the ion and electron fluxes. This formulation, when solved simultaneously with the density and temperature rate equations, gives continuous electric fields but may lead to the radial derivative of the electric field being discontinuous. This unphysical situation arises from the neglect of the finite orbit deviation from the flux surfaces. If the fluxes are calculated to higher order in inverse aspect ratio to include the finite orbit deviation, then a second-order differential equation is obtained that will give a continuous first derivative for the electric field.