bluuebunny/crossref_metadata_2025 huggingface dataset:
Structures and electronic properties of aluminum nanowires
Authors: Makita Toshiki , Doi Kentaro , Nakamura Koichi , Tachibana Akitomo
Published: June 2003

We report first-principle electronic-state calculations for aluminum (Al) nanowires, which receive much attention as a new device material. First-principle calculations of the periodic boundary nanowire models have been carried out by means of supercell approximation techniques with density functional theory. The stable structures of Al nanowires have been investigated by geometry optimization of model structures of various types. For each stable structure, we have discussed the properties of nanowire in detail, such as radius of wire, interatomic distances, and stability for deformation. Furthermore, the growth and the reconstruction of nanowire by adsoprtion of Al atom have been simulated. We have also discussed the electronic processes and the driving forces in the growing process of Al nanowire, in terms of the quantum mechanical energy densities based on the regional density functional theory [Tachibana, J. Chem. Phys. 115, 3497 (2001)]. They have disclosed the driving force of the stability in electronic processes and give new images of microscopic electronic stresses.
Torsional path integral Monte Carlo method for calculating the absolute quantum free energy of large molecules
Authors: Miller Thomas F. , Clary David C.
Published: June 2003

A new technique for evaluating the absolute free energy of large molecules is presented. Quantum-mechanical contributions to the intramolecular torsions are included via the torsional path integral Monte Carlo (TPIMC) technique. Importance sampling schemes based on uncoupled free rotors and harmonic oscillators facilitate the use of the TPIMC technique for the direct evaluation of quantum partition functions. Absolute free energies are calculated for the molecules ethane, n-butane, n-octane, and enkephalin, and quantum contributions are found to be significant. Comparison of the TPIMC technique with the harmonic oscillator approximation and a variational technique is performed for the ethane molecule. For all molecules, the quantum contributions to free energy are found to be significant but slightly smaller than the quantum contributions to internal energy.
A surface forces platform for dielectric measurements
Authors: Cho Yoon-Kyoung , Granick Steve
Published: June 2003

Methods are described to implement dielectric spectroscopy (frequency range 10−1–106 Hz) within a surface forces apparatus by using as electrodes silver sheets on the backside of mica. These methods are applied to study the competitive effects of surface alignment, confinement, and shear field on 5CB (5-cyanobiphenyl), a nematic liquid crystal at the experimental temperature of 25 °C. In the planar orientation, films could be squeezed to a minimum thickness of ≈5 Å, the molecule’s thickness. In the perpendicular (homeotropic) orientation, films could be squeezed to ≈25 Å, the expected thickness of the head-to-tail 5CB dimer. It was difficult to discuss responses at f>105 Hz quantitatively because the peak was not visible in the experimental frequency window. Nonetheless, the onset of the relaxation mode for the planar oriented molecules appears at higher frequency than for the homeotropic orientation. A slower relaxation mode, peaked at f≈10 Hz, was assigned to electrode polarization due to the mobility of trace ions within the 5CB samples although these samples were >99.7% pure. The peak frequency was a factor of 3 slower with homeotropic than planar alignment and, in both cases, independent of film thickness except when the film thickness exceeded 10 μm. This was explained using a simple model based on the assumption that trace ions move to oppositely charged electrodes to form electric double layers. A small influence of shear on the dielectric response was observed but only when the dielectric response was measured at the same frequency as the large-amplitude shear deformation. Also described is the use of capacitance to measure force–distance profiles.
On the nature of blueshifting hydrogen bonds: Ab initio and density functional studies of several fluoroform complexes
Authors: Pejov Ljupčo , Hermansson Kersti
Published: June 2003

Potential energy hypersurfaces (PESs) for four fluoroform complexes (with acetonitrile, ethyleneoxide, formaldehyde, and water) were explored at the HF, MP2, and B3LYP/6-311++G(d,p) levels of theory. Anharmonic C–H stretching vibrational frequency shifts are reported for all minima located on the studied PESs. In all cases, the lowest-energy minimum occurs for a C–H⋯O(N) hydrogen-bonded arrangement and is characterized by a significant C–H frequency blueshift (upshift), while additional minima [for “reversed” orientations, in which there is no direct C–H⋯O(N) contact] show only small C–H frequency upshifts. The large blueshifts found for the hydrogen-bonded arrangements are predominantly caused by the electronic exchange interaction, as revealed by Kitaura–Morokuma (KM) analysis, while the purely electrostatic+polarization interaction leads to C–H frequency redshifts, which was proven both by the KM analysis and the charge field perturbational (CFP) approach. The large net blueshifting effect of the exchange contribution is only possible thanks to the smallness of the redshifting electrostatic+polarization contribution, which, in turn, is a consequence of the fact that dμ(0)/drCH is negative for the fluoroform molecule. In all cases the charge transfer as well as the dispersion energy contributions lead to frequency redshifts. The small C–H blueshifts for the reversed orientations are almost completely governed by the electrostatic interaction, as shown by the KM and CFP analyses. All these characteristics of blueshifting H bonds are in line with a previously outlined general model concerning “standard” and “blueshifting” H-bonding interactions [K. Hermansson, J. Phys. Chem. A 106, 4695 (2002)].
Quantum chemistry calculation of excited three center systems: Theoretical study of He2++H2 collisions
Authors: Errea L. F. , Macı́as A. , Méndez L. , Pons B. , Riera A.
Published: June 2003

Close-coupling calculations of single (dissociative and nondissociative) and double electron capture cross sections in He2++H2 collisions in the range of impact energies 0.5–25 keV/amu are presented and compared with experimental data. The calculations have been carried out at the Franck–Condon level and employing both ab initio expansions, in terms of three-center electronic functions, and the independent particle model approximation. We discuss the mechanisms of the processes and the validity limits of these treatments.
Time-resolved small angle neutron scattering measurements of asphaltene nanoparticle aggregation kinetics in incompatible crude oil mixtures
Authors: Mason Thomas G. , Lin Min Y.
Published: June 2003

We use time-resolved-small angle neutron scattering to study the kinetics of asphaltene nanoparticle aggregation in incompatible crude oil mixtures. We induce asphaltene aggregation by mixing asphaltene-rich Syrian crude oil (SACO) with a paraffinic British crude oil and observe the scattered neutron intensity, I, as a function of wave number, q, over times, t, ranging from twenty minutes to about a week. We observe a growth in I at low q as the nanoscale asphaltenes agglomerate into microscale aggregates and interpret this growth as an increase in surface scattering from the aggregates. We fit I(q,t) to an empirical model and measure the growth in the power-law exponent, α, associated with the low-q logarithmic slope of I(q). We define a time, τα, associated with the first appearance of the aggregates when α>3; τα increases as a function of the volume fraction, φm, of SACO in the mixture. The surface scattering intensity initially increases and then saturates at long times when the aggregate structures no longer evolve at the length scales we probe. Based on this saturation, we define a time scale, τI, which is larger than τα but has essentially the same dependence on φm. We interpret τα(φm) and τI(φm) in terms of a simple aggregation model based on diffusion-limited kinetics and a repulsive potential barrier that models the effective solvent quality.
Magnetically insulated fission electric cells for direct energy conversion
Authors: Slutz S. A. , Seidel D. B. , Lipinski R. J. , Rochau G. E. , Brown L. C.
Published: June 2003

The principles of fission electric cells are reviewed. A detailed Monte Carlo model of the efficiency of a fission electric cell is presented and a theory of magnetically insulated fission electric cells (MIFECs) is developed. It is shown that the low operating voltages observed in previous MIFEC experiments were due to nonoptimal magnetic field profiles. Improved magnetic field profiles are presented. It is further shown that the large electric field present in a MIFEC limits the structure of the cathode and can lead to a displacement instability of the cathode toward the anode. This instability places constraints on the number of cells that can be strung together without some external cathode support. The large electric field stress also leads to electrical surface breakdown of the cathode. It is shown that this leads to the formation of a virtual cathode resulting in geometry constraints for spherical cells. Finally it is shown that the requirements of magnetic insulation and high efficiency leads to very low average density of the fissile material. Thus a reactor using fission electric cells for efficient direct energy conversion will be large and require a very large number of cells. This could be mitigated somewhat by the use of exotic fuels.
Exploiting both C3v symmetry and sparsity in vibrational calculations for methanelike molecules
Authors: Poirier Bill
Published: June 2003

In a recent article [J. Chem. Phys. 118, 6946 (2003)], X.-G. Wang and T. Carrington, Jr. presented an efficient method for computing the vibrational bend levels of five-atom molecules. The method is particularly useful if four of the five atoms are identical, in which case G4 symmetry may be exploited in conjunction with the iterative symmetry-adapted Lanczos method. In this paper, we demonstrate how to extend the group of exploitable symmetry operations to G12, without compromising any of the desirable numerical features of the Wang and Carrington approach. This reduces total CPU effort by at least a factor of 3.
Semiclassically optimized complex absorbing potentials of polynomial form. II. Complex case
Authors: Poirier Bill , Carrington Tucker
Published: June 2003

In a previous paper [J. Chem. Phys. 118, 17 (2003)], we presented an optimal, pure imaginary complex absorbing potential (CAP) of polynomial form, for use with resonance and scattering calculations. The optimal CAP was derived by minimizing reflection and transmission, and was found to greatly reduce CPU time. In this paper, the previous analysis is extended to more general complex polynomial functional forms, and new CAPs are developed which are even more efficient than those of the previous work, especially for highly accurate calculations.
Isospectrality of spherical MHD dynamo operators: Pseudo-hermiticity and a no-go theorem
Authors: Günther Uwe , Stefani Frank
Published: June 2003

The isospectrality problem is studied for the operator of the spherical hydromagnetic α2-dynamo. It is shown that this operator is formally pseudo-Hermitian (J-symmetric) and lives in a Krein space. Based on the J-symmetry, an operator intertwining Ansatz with first-order differential intertwining operators is tested for its compatibility with the structure of the α2-dynamo operator matrix. An intrinsic structural inconsistency is obtained in the set of associated matrix Riccati equations. This inconsistency is interpreted as a no-go theorem which forbids the construction of isospectral α2-dynamo operator classes with the help of first-order differential intertwining operators.
A contracted basis-Lanczos calculation of vibrational levels of methane: Solving the Schrödinger equation in nine dimensions
Authors: Wang Xiao-Gang , Carrington Tucker
Published: June 2003

We present a contracted basis-iterative method for calculating numerically exact vibrational energy levels of methane (a 9D calculation). The basis functions we use are products of eigenfunctions of bend and stretch Hamiltonians obtained by freezing coordinates at equilibrium. The basis functions represent the desired wavefunctions well, yet are simple enough that matrix-vector products may be evaluated efficiently. We use Radau polyspherical coordinates. The bend functions are computed in a nondirect product finite basis representation [J. Chem. Phys. 118, 6956 (2003)] and the stretch functions are computed in a product potential optimized discrete variable (PODVR) basis. The memory required to store the bend basis is reduced by a factor of ten by storing it on a compacted grid. The stretch basis is optimized by discarding PODVR functions with high potential energies. The size of the primitive basis is 33 billion. The size of the product contracted basis is six orders of magnitude smaller. Parity symmetry and exchange symmetry between two of the H atoms are employed in the final product contracted basis. A large number of vibrational levels are well converged. These include almost all states up to 8000 cm−1 and some higher local mode stretch bands.
Dynamics of beam-driven Langmuir and ion-acoustic waves including electrostatic decay
Authors: Li B. , Willes A. J. , Robinson P. A. , Cairns I. H.
Published: June 2003

The evolution of Langmuir waves and ion-acoustic waves stimulated by a hot electron beam in an initially homogeneous plasma is investigated numerically in time, position, and wave number space. Quasilinear interactions between the beam particles and Langmuir waves, nonlinear interactions between the Langmuir and ion-acoustic waves through Langmuir decay processes, and spontaneous emission are taken into account in the kinetic theory employed. For illustrative parameters of those in the solar wind near 1 a.u., nonlinear Langmuir decays are observed to transfer the beam-driven Langmuir waves rapidly out of resonance. The scattered Langmuir waves then undergo further decays, moving sequentially toward small wave numbers, until decay is kinematically prohibited. The main features of the evolution of Langmuir and ion-acoustic waves are spatially inhomogeneous. The scattered Langmuir spectra increase and eventually reach or exceed the beam-driven Langmuir spectra at a given spatial location (except in regions where further decays proceed). The ion-acoustic waves are relatively weak and subject to damping at the later stages of their evolution. The development of fine structures in the product Langmuir and ion-acoustic waves are observed, due to depletion of their energy by decay and dominant damping effects, respectively. The propagation of the beam is essentially unaffected by the operation of the decay process. The decay process is thus slaved to the primary beam–plasma evolution, as assumed in previous studies. A variation of the ratio of electron temperature to ion temperature is found to affect not only the ion-acoustic wave levels through effects on the damping rate, but also the dynamics of decay via effects on the decay rate. The latter was not addressed in previous studies. Furthermore, spontaneous emission of ion-acoustic waves is found to affect the dynamics of decay, thus its inclusion is necessary to correctly model the Langmuir and ion-acoustic spectra.
Bohmian versus semiclassical description of interference phenomena
Authors: Zhao Yi , Makri Nancy
Published: June 2003

The origin of quantum interference characteristic of bound nonlinear systems is investigated within the Bohmian formulation of time-dependent quantum mechanics. By contrast to time-dependent semiclassical theory, whereby interference is a consequence of phase mismatch between distinct classical trajectories, the Bohmian, fully quantum mechanical expression for expectation values has a quasiclassical appearance that does not involve phase factors or cross terms. Numerical calculations reveal that quantum interference in the Bohmian formulation manifests itself directly as sharp spatial/temporal variations of the density surrounding kinky trajectories. These effects are most dramatic in regions where the underlying classical motion exhibits focal points or caustics, and crossing of the Bohmian trajectories is prevented through extremely strong and rapidly varying quantum mechanical forces. These features of Bohmian dynamics, which constitute the hallmark of quantum interference and are ubiquitous in bound nonlinear systems, represent a major source of instability, making the integration of the Bohmian equations extremely demanding in such situations.
The parallel implementation of a full configuration interaction program
Authors: Gan Zhengting , Alexeev Yuri , Gordon Mark S. , Kendall Ricky A.
Published: June 2003

Both the replicated and distributed data parallel full configuration interaction (FCI) implementations are described. The implementation of the FCI algorithm is organized in a hybrid strings-integral driven approach. Redundant communication is avoided, and the network performance is further optimized by an improved distributed data interface library. Examples show linear scalability of the distributed data code on both PC and workstation clusters. The new parallel implementation greatly extends the hardware on which parallel FCI calculations can be performed. The timing data on the workstation cluster show great potential for using the new parallel FCI algorithm in expanding applications of complete active space self-consistent field applications.
Effects of ultraviolet radiation on dusty plasma structures at microgravity
Authors: Tsytovich V. N. , Nefedov A. P. , Fortov V. E. , Petrov O. F. , Morfill G. E.
Published: June 2003

It is found that the ultraviolet radiation exposed to dusty plasma can serve as an additional manipulator of dust cloud structures formed under microgravity conditions. Strong ultraviolet source of radiation, making the dust charges positive, is not favorable for the formation of compact dust structures, while a relative moderate ultraviolet source can help in changing the structures to confine larger amounts of dust grains. The possibility of using the ultraviolet irradiation for formation of compact dust structures at the center of the microgravity experimental device is investigated numerically by solving the set of self-consistent balance equations for parameters of the structure in the presence of an ultraviolet radiation source.
Structure of a simple fluid in the vicinity of the critical point: Approximate integral equation theory of liquids
Authors: Sarkisov G. N.
Published: June 2003

An approximate Ornstein–Zernike equation [J. Chem. Phys. 114, 9496 (2001)] is used in order to analyze properties of a simple fluid in the vicinity of the critical point. The heat capacity and compressibility of the fluid are considered involving their relations with the density and temperature derivatives of the thermal potential (or the correlation function). A new structural critical exponent approaching zero value of the first nontrivial minimum of the total correlation function is defined. Using our approximate equation and that derived by Duh, Henderson, and Haymet [J. Chem. Phys. 103, 2625 (1995); 104, 6742 (1996)] a set of the thermodynamic parameters along the isotherm T*=1.310, which is very close to the critical, is calculated. Computer simulation data are also given for comparison.
Theoretical study of the ambient-pressure dependence of sonochemical reactions
Authors: Yasui Kyuichi , Tuziuti Toru , Iida Yasuo , Mitome Hideto
Published: June 2003

Computer simulations of bubble oscillations are performed for various ambient pressures in order to study the mechanism of the ambient-pressure dependence of sonochemical reactions: sonochemiluminescence of aqueous luminol solutions [T. Tuziuti et al., J. Chem. Phys. 116, 6221 (2002)] and the oxidation of iodide [A. Henglein et al., J. Phys. Chem. 97, 158 (1993)]. It is shown that for air bubbles there exists an optimal bubble temperature for the production of the oxidants such as O, OH, H2O2, and O3 inside bubbles regardless of the ambient pressure because at higher bubble temperature the oxidants are consumed inside bubbles by oxidizing nitrogen. Correspondingly there exists an optimal acoustic amplitude for each ambient pressure, which shifts toward a lower value as the ambient pressure decreases because bubbles expand more. It results in the higher rate of sonochemical reactions for lower ambient pressure at relatively low acoustic amplitude. For oxygen bubbles, the amount of the oxidants created inside bubbles is larger for higher bubble temperature because in this case the oxidants are not consumed inside bubbles due to the absence of nitrogen. Regardless of the species of the gas inside bubbles, the decrease of the ambient pressure works as if the acoustic amplitude increases because bubbles expand more.
Critical point corrections for lattice systems
Authors: Aranovich G. L. , Donohue M. D.
Published: June 2003

Lattice gas is considered in the framework of three-dimensional Ono–Kondo theory. It is shown that a nonlinear correction to the configurational energy results in significant improvement of phase behavior, especially near the critical point.
Study of dipolar fluid inclusions in charged random matrices
Authors: Fernaud M. J. , Lomba E. , Martı́n C. , Levesque D. , Weis J.-J.
Published: June 2003

Structural, thermodynamic, and dielectric properties of a dipolar fluid confined in a charged random matrix are studied by means of grand canonical Monte Carlo simulation and replica Ornstein–Zernike integral equations in the hypernetted chain approximation. The fluid is modeled by a system of dipolar hard spheres. Two matrix topologies are considered: a frozen restricted primitive model matrix and a frozen hard sphere fluid with randomly distributed negative and positive charges. Both models lead to similar results in most cases, with significant deviations from the behavior of the corresponding equilibrated mixtures. The dielectric behavior is particularly interesting, since the effect of partial quenching on the equilibrated mixture recovers the electrostatics of the pure dipolar fluid but with the presence of Coulomb tails in the dipole–dipole total correlations. Differences between the two matrix models arise more vividly in the low density regime, in which the matrix with randomly distributed charges tends to enhance dipole association around the matrix particles. The integral equation results are in relatively good agreement with the computer simulation estimates.
Three-particle contribution to effective viscosity of hard-sphere suspensions
Authors: Cichocki B. , Ekiel-Jeżewska M. L. , Wajnryb E.
Published: June 2003

The virial expansion of the high-frequency effective viscosity is considered for hard sphere suspensions at equilibrium. The term of the third order in volume fraction, which involves three-particle hydrodynamic interactions, is calculated with high accuracy and the corresponding coefficient in the Saitô representation is also evaluated. The method is based on a regularization procedure, which gives the effective viscosity as the sum of convergent integrals over particle configurations. To calculate the hydrodynamic interactions, we apply the efficient algorithm based on the multipole expansion, corrected for lubrication, which has been earlier applied to evaluate the self-diffusion and the sedimentation coefficients. However, in the context of the effective viscosity, we have faced a slower convergence of the results with the increasing number of the included mulitipoles.
Millimeter-wave spectroscopy and coupled cluster calculations for a new phosphorus–carbon chain: HC5P
Authors: Bizzocchi L. , Degli Esposti C. , Botschwina P.
Published: June 2003

The linear, unstable HC5P molecule has been detected for the first time in the pyrolysis products of phosphorus trichloride and toluene mixtures. Its rotational spectrum has been investigated in the millimeter-wave region (78–195 GHz) for the ground and v11=1 excited state of both normal and deuterated species. Accurate values of rotational, centrifugal distortion and q11 l-type doubling constants have been obtained. The experimental work was assisted by coupled-cluster single double triple [CCSD(T)] calculations, which provided accurate predictions for the equilibrium structure and the dipole moment of this new carbon chain, phosphorus bearing molecule.
One- and two-photon excitation vibronic spectra of 2-methylallyl radical at 4.6–5.6 eV
Authors: Chen Chun-Cing , Wu Hsing-Chen , Tseng Chien-Ming , Yang Yi-Han , Chen Yit-Tsong
Published: June 2003

Vibronically excited 2-methylallyl radical [CH2C(CH3)CH2] at 4.6–5.6 eV has been studied by 1+1 and 2+2 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The 2-methylallyl radicals were produced by the flash pyrolysis of 3-bromo-2-methylpropene in a supersonic-jet expansion. The 2+2 REMPI spectrum of 2-methylallyl radical at 38 000–40 700 cm−1 is identified as B̃(1 2A1)←X̃(1 2A2) transition, i.e., the excitation of a nonbonding electron to the 3s Rydberg state (3s←n). Seven lowest-lying electronic states with excitation energy below 6 eV have been calculated in an MRCI level. Two new electronic bands have been observed at 38 500–41 000 cm−1 by 1+1 REMPI spectroscopy and assigned to C̃(1 2B2)←X̃(1 2A2) and Ẽ(2 2A2)←X̃(1 2A2). Much broader 1+1 REMPI signals at 41 000–43 5 00 cm−1 with HWHM of ∼80 cm−1 for each vibronic band could be due to D̃(2 2B2)←X̃(1 2A2) and/or F̃(3 2B2)←X̃(1 2A2) via an intensity borrowing from C̃(1 2B2)←X̃(1 2A2). Taking the computed geometries and vibrations of the ground- and excited electronic states, Franck–Condon factors (FCFs) have been calculated. Combining the FCFs with calculated excitation energies and oscillator strengths of the six electronic states at 4–6 eV, predicted spectral patterns have been used to assist spectroscopic analysis for the observed vibronic spectra of 2-methylallyl radical.
Two-pulse atomic coherent control spectroscopy of Eley–Rideal reactions: An application of an atom laser
Authors: Jørgensen Solvejg , Kosloff Ronnie
Published: June 2003

A spectroscopic application of the atom laser is suggested. The spectroscopy termed 2PACC (two-pulse atomic coherent control) employs the coherent properties of matter waves from a two-pulse atom laser. These waves are employed to control a gas–surface chemical recombination reaction. The method is demonstrated for an Eley–Rideal reaction of a hydrogen or alkali atom-laser pulse where the surface target is an adsorbed hydrogen atom. The reaction yields either a hydrogen or alkali hydride molecule. The desorbed gas-phase molecular yield and its internal state is shown to be controlled by the time and phase delay between two atom-laser pulses. The calculation is based on solving the time-dependent Schrödinger equation in a diabatic framework. The probability of desorption which is the predicted 2PACC signal has been calculated as a function of the pulse parameters.
Dissipative quantum dynamics of anharmonic oscillators with the multiconfiguration time-dependent Hartree method
Authors: Nest M. , Meyer H.-D.
Published: June 2003

We investigate the dissipative dynamics of a Morse oscillator coupled nonlinearly to a heat bath. To this end, we compare several reduced equations of motion with the dynamics of a full-dimensional wave packet with up to 61 spatial degrees of freedom. The discretized bath is converged for the relevant times considered in this paper. The propagations are done with a general purpose implementation of the multiconfiguration time-dependent Hartree method.
Theoretical study of transition radiation from hot electrons generated in the laser–solid interaction
Authors: Zheng Jian , Tanaka K. A. , Miyakoshi T. , Kitagawa Y. , Kodama R. , Kurahashi T. , Yamanaka T.
Published: June 2003

Transition radiation from a beam of hot electrons generated in ultraintense laser plasma interaction is theoretically studied. The total radiation is separated into two parts: one is incoherent transition radiation (ITR), the other is coherent transition radiation (CTR). The spectrum of ITR just depends on the particle velocity distribution in the beam. The angular distribution of ITR varies from sin2 θ, and approaches the angular distribution of the beam when the hot electron temperature increases from the nonrelativistic limit (T≪mc2) to the ultrarelativistic limit (T≫mc2). The spectrum of CTR is dependent on the particle configuration as well as their velocities. Any microbunching in the beam can greatly enhance the CTR intensity at the microbunching frequency, from which the dominant heating process can be inferred. The effects of target thickness and hot electron temperature on CTR intensity are also calculated. The simplified model shows that the CTR intensity decreases with the increase of the target thickness, and increases with the hot electron temperature. The divergence of the beam can broaden the CTR spectrum.
The scattering matrix for the Schrödinger operator with a long-range electromagnetic potential
Authors: Roux Ph. , Yafaev D.
Published: June 2003

We consider the Schrödinger operator H=(i∇+A)2+V in the space L2(Rd) with long-range electrostatic V(x) and magnetic A(x) potentials. Using the scheme of smooth perturbations, we give an elementary proof of the existence and completeness of modified wave operators for the pair H0=−Δ, H. Our main goal is to study spectral properties of the corresponding scattering matrix S(λ). We obtain its stationary representation and show that its singular part (up to compact terms) is a pseudodifferential operator with an oscillating amplitude which is an explicit function of V and A. Finally, we deduce from this result that, in general, for each λ>0 the spectrum of S(λ) covers the whole unit circle.
A geometric description of Routh’s procedure. Addendum: “Legendre transformation and analytical mechanics: A geometric approach” [J. Math. Phys. 44, 1709 (2003)]
Authors: Vignolo Stefano
Published: June 2003

The geometrical framework developed in J. Math. Phys. 44, 1709 (2003) is applied in order to obtain a geometric description of Routh’s procedure.
Group-invariant solutions of relativistic and nonrelativistic models in field theory
Authors: Grundland A. M. , Hariton A. J. , Hussin V.
Published: June 2003

In this paper we present a method of constructing explicit classes of solutions of the Chaplygin and Born–Infeld systems of equations in 1+1 dimensions. The approach adopted here is based on the symmetry reduction method for PDE’s. A systematic use of the subgroup structure of the invariance group is made to generate symmetry variables. We concentrate only on the case when the symmetry variables are invariants of the subgroups having dimension one. The set of symmetry variables enables us to reduce, after some transformation, the original equations to many possible ODE’s. We describe in detail how a composition of Lie subalgebras and singularity analysis applied to these systems provides us with classes of analytic solutions. Several new types of algebraic, rational and solitonlike solutions (among them kinks, bumps and multiple wave solutions) have been obtained in explicit form. We discuss also the existence of several classes of separable solutions admitted by the Chaplygin and Born–Infeld equations. Some physical interpretation of these results in the areas of fluid dynamics and field theory are given.
Quantum mechanical investigation of the O+H2→OH+H reaction
Authors: Balakrishnan N.
Published: June 2003

We report quantum mechanical calculations of cross sections and rate coefficients for the O+H2→OH+H reaction using the chemically accurate potential energy surfaces of A'3 and A"3 geometry by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)]. Calculations were performed for total angular momentum quantum number J=0 and the J-shifting approximation was applied to obtain cumulative reaction probabilities, initial state selected reaction cross sections, and thermal rate coefficients. The reliability of the J-shifting approximation was tested by performing accurate calculations for selected values of nonzero J. We obtain thermal rate coefficients in good agreement with experimental data at temperatures lower than 500 K but our calculations predict rate coefficients that are smaller than the experimental values at higher temperatures.
Oxygen atom Rydberg time-of-flight spectroscopy
Authors: Lin Cheng , Witinski Mark F. , Davis H. Floyd
Published: June 2003

The Rydberg atom time-of-flight method has been employed for velocity, angular and spin–orbit state-resolved detection of oxygen atoms, O (3PJ). The atoms were “tagged” by double-resonance two-photon excitation to high-n Rydberg levels and subsequently field ionized at a detector. The method was characterized by studying a well-known system, the photodissociation of NO2 at 355 nm. From the O atom time-of-flight spectra, the NO vibrational distribution for different O (3PJ) levels was obtained, with NO (v=1) rotational structure partially resolved.
Molecular structure and order of hexaoctyloxy-rufigallol in the solid and columnar phases: Analysis of H2–13C dipolar and C13 chemical-shift interactions
Authors: Dvinskikh Sergey V. , Sandström Dick , Luz Zeev , Zimmermann Herbert , Maliniak Arnold
Published: June 2003

We report a C13 NMR investigation of 1,2,3,5,6,7-hexaoctyloxy-rufigallol in the solid and columnar phases using various H2- and C13-labeled isotopomers. The measurements were performed under both static and magic-angle spinning conditions. The conformations of the aliphatic side chains were derived from an analysis of H2–13C dipolar and C13 chemical-shift interactions. The nonequivalent chains exhibit significantly different structural behavior in both solid and columnar phase. It emerged that one of the side chains adopts an in-plane structure, while the other two chains prefer antiparallel out-of-plane conformations. Quantum-chemical calculations of the C13 chemical-shift tensors were also carried out. These calculations support the experimental findings.
Dynamical and structural correlation in supercooled liquids: A molecular dynamics investigation of m-toluidine
Authors: Chelli Riccardo , Cardini Gianni , Procacci Piero , Righini Roberto , Califano Salvatore
Published: June 2003

Structural and dynamical properties of liquid and supercooled liquid m-toluidine are studied by molecular dynamics simulations. Approaching the liquid–glass transition, dynamical heterogeneities, a characteristic common to all supercooled glass formers, are observed. We prove the occurrence of strict correlation between these heterogeneities and the potential energy landscape of the system, expressed in terms of molecule–molecule interactions. A slowing down of the self-diffusive motion of the molecular centers of mass is observed for particular arrangements of pairs of H-bonded molecules. Previous studies on model systems provided evidence of the correlation between dynamical heterogeneities and potential energy landscape, described in terms of the inherent structure of the system. While in this last case the structure is viewed as a collective property of the system, in m-toluidine short-range interactions are sufficient to explain the dynamical behavior in a satisfactory way. This result agrees with the view, supported also by experimental observations, that m-toluidine can be considered as an ensemble of H-bonded subsystems weakly interacting among them.
Molecular simulation of diffusion and sorption of gases in an amorphous polymer
Authors: Lim Seong Y. , Tsotsis Theodore T. , Sahimi Muhammad
Published: June 2003

We report the results of equilibrium molecular dynamics (EMD) simulations of diffusion and sorption isotherms of CO2 and CH4 molecules in polyetherimide (PEI). Amorphous PEI structures are generated by MD simulations and energy minimizations, and are characterized by their density, glass transition temperature, and the radial distribution function. The self-diffusivities of CH4 and CO2 in the polymer are estimated by EMD simulations. The simulations indicate oscillatory motion of the molecules inside the temporal cavities of the polymer and hopping from one cavity to another in the PEI matrix as the mechanism of gas transport in the polymer. The accessible free volume of the polymer is calculated with the use of a probe molecule. It exhibits strong temporal fluctuations which indicates the existence of correlations between these fluctuations and those in the excess chemical potential of the gases. The solubility coefficients of the gases, calculated by the test particle insertion method, and the single gas sorption isotherms, are within the reported range of the experimental values. The computed self-diffusivities D of the gases differ from the experimental data by about one order of magnitude, although the range of the experimental values for D is quite large. We also compute the sorption isotherms for binary gas mixtures of CO2 and CH4 in the polymer.
The strongest bond in the universe? Accurate calculation of compliance matrices for the ions N2H+, HCO+, and HOC+
Authors: Grunenberg Jörg , Streubel Rainer , von Frantzius Gerd , Marten Wolfgang
Published: June 2003

Compliance matrices of protonated CO and N2 are calculated using coupled cluster methods and basis sets of quadruple zeta quality. Diagonal elements of the compliance matrices are used as unique bond strength descriptors. Going from CO (0.052 Å/mdyn) to CO–H+ the C–O bond is weakened (0.062 Å/mdyn), while the C–O bond in H–CO+ is getting stronger (0.045 Å/mdyn). After protonation, the N–N bond strength is getting stronger (from 0.043 to 0.042 Å/mdyn), too. The invariance of compliance matrix elements Cij under completion of (xi,xj) to a complete set (…,xi,…,xj,…) of internal coordinates is demonstrated.
Structures, energetics, and spectra of electron–water clusters, e−–(H2O)2–6 and e−–HOD(D2O)1–5
Authors: Lee Han Myoung , Lee Sik , Kim Kwang S.
Published: June 2003

Although various low-lying energy structures of electron–water clusters, e−–(H2O)2–6, have been reported, some of the global minimum energy structures (in particular, for the tetramer and pentamer) are still not clearly characterized yet. Therefore, using high-level ab initio calculations, we have investigated several new low-lying energy conformers in addition to previously reported ones. The lowest energy conformer for the pentamer is found to have a wedge-like structure which has never been studied before. Based on the experimental vertical electron-detachment energies and OH vibrational spectra of the electron–water clusters, we report the most probable structures and their nearly isoenergetic structures. The OH vibrational frequencies of e−(H2O)2–6 and e−HOD(D2O)1–5 are investigated, and are found to be in excellent agreement with the available experimental data. Their O–H stretch frequency shifts are classified in terms of the types of water molecules.
The algebraic entropy of classical mechanics
Authors: McLachlan Robert I. , Ryland Brett
Published: June 2003

We describe the “Lie algebra of classical mechanics,” modelled on the Lie algebra generated by kinetic and potential energy of a simple mechanical system with respect to the canonical Poisson bracket. It is a polynomially graded Lie algebra, a class we introduce. We describe these Lie algebras, give an algorithm to calculate the dimensions cn of the homogeneous subspaces of the Lie algebra of classical mechanics, and determine the value of its entropy limn→∞ cn1/n. It is 1.825 423 774 201 08… , a fundamental constant associated with classical mechanics.
Dynamical symmetry breaking and the Nambu–Goldstone theorem in the Gaussian wave functional approximation
Authors: Dmitrašinović V. , Nakamura Issei
Published: June 2003

We analyze the group-theoretical ramifications of the Nambu–Goldstone (NG) theorem in the self-consistent relativistic variational Gaussian wave functional approximation to spinless field theories. In an illustrative example we show how the Nambu–Goldstone theorem would work in the O(N) symmetric φ4 scalar field theory, if the residual symmetry of the vacuum were lesser than O(N−1), e.g., if the vacuum were O(N−2), or O(N−3),… symmetric. (This does not imply that any of the “lesser” vacua is actually the absolute energy minimum: stability analysis has not been done.) The requisite number of NG bosons would be (2N−3), or (3N−6),…, respectively, which may exceed N, the number of elementary fields in the Lagrangian. We show how the requisite new NG bosons would appear even in channels that do not carry the same quantum numbers as one of N “elementary particles” [scalar field quanta, or Castillejo–Dalitz–Dyson (CDD) poles] in the Lagrangian, i.e., in those “flavor” channels that have no CDD poles. The corresponding Nambu–Goldstone bosons are composites (bound states) of pairs of massive elementary (CDD) scalar fields excitations. As a nontrivial example of this method we apply it to the physically more interesting ’t Hooft σ model (an extended Nf=2 bosonic linear σ model with four scalar and four pseudoscalar fields), with spontaneously and explicitly broken chiral O(4)×O(2)≃SUR(2)×SUL(2)×UA(1) symmetry.
Spectrum and vibrational predissociation of the HF dimer. I. Bound and quasibound states
Authors: Vissers G. W. M. , Groenenboom G. C. , van der Avoird A.
Published: June 2003

We present full six-dimensional calculations of the bound states of the HF dimer for total angular momentum J=0,1 and of the quasibound states for J=0 that correspond with vibrational excitation of one of the HF monomers, either the donor or the acceptor in the hydrogen bond. Transition frequencies and rotational constants were calculated for all four molecular symmetry blocks. A contracted discrete variable representation basis was used for the dimer and monomer stretch coordinates R,rA,rB; the generation of the monomer basis in the dimer potential leads to significantly better convergence of the energies. We employed two different potential energy surfaces: the SQSBDE potential of Quack and Suhm and the SO-3 potential of Klopper, Quack, and Suhm. The frequencies calculated with the SO-3 potential agree very well with experimental data and are significantly better than those from the SQSBDE potential.
Spectrum and vibrational predissociation of the HF dimer. II. Photodissociation cross sections and product state distributions
Authors: Vissers G. W. M. , Groenenboom G. C. , van der Avoird A.
Published: June 2003

We study vibrational predissociation of the HF dimer both by a full coupled channels treatment as well as in the Fermi golden rule approximation. Photodissociation cross sections, linewidths, and rotational state distributions are computed for excitations from the ground state with rotational quantum numbers J=1, K=0 to monomer stretch excited states with J=K=0, both for even and odd permutation symmetry. The resonances investigated include excitation of the hydrogen bond donor and acceptor stretches, as well as combinations of one of these modes with the dimer stretch and dimer geared-bending modes. We find that dissociation is sufficiently slow for the Fermi golden rule approximation to be valid. The resonance positions and line strengths are compared with quasibound state calculations. The agreement with experimental data is fairly good for the photofragment angular distributions that were determined from the rotational state distributions, less good for some of the linewidths. Since we carefully checked that the results are converged with respect to the number of vibrational and rotational channels included, the remaining discrepancies are almost certainly due to small deficiencies in the SO-3 potential used in the calculations.
Dynamically accessible perturbations and magnetohydrodynamic stability
Authors: Hameiri Eliezer
Published: June 2003

It is shown that restricting the perturbations of a magnetohydrodynamic plasma equilibrium state with flow to those that are dynamically accessible yields the same stability criterion as the one obtained by minimizing the plasma energy subject to given values of all constants of the motion. This criterion is sharper than the classical one, which is based on the second variation of the potential energy (δW).
Formation of quadrupolar vortices in ion-temperature-gradient modes
Authors: Qamar Anisa , Mirza Arshad M. , Murtaza G. , Vranješ J. , Sakanaka P. H.
Published: June 2003

Nonlinear equations which govern the dynamics of low-frequency (ω≪ωci), ion-temperature gradient modes in the presence of equilibrium density, temperature, magnetic field, and electrostatic potential gradients are derived. For some specific profiles of the equilibrium flow velocity, number density, temperature, and magnetic field, new type of solutions in the form of quadrupole vortices are found for a nondissipative plasma. The results can have relevance to the understanding of the salient features of anomalous ion thermal transport and coherent vortex structure formation in magnetically confined plasmas, such as in tokamaks.
Photodissociation of oriented HXeI molecules generated from HI–Xen clusters
Authors: Nahler N. Hendrik , Baumfalk Reinhard , Buck Udo , Bihary Zsolt , Gerber R. Benny , Friedrich Bretislav
Published: June 2003

We report the production in the gas phase of ionically bound HXeI molecules. The molecules are generated by the photodissociation of HI molecules in large Xen clusters and are identified from the asymmetry of the detected H atom fragments arising from the dissociation of oriented HXeI. The orientation, resulting from a synergistic action of a pulsed laser field with a weak electrostatic field, is quite pronounced, due to a large ratio of the polarizability anisotropy to the rotational constant of HXeI.
Reaction of formaldehyde cation with methane: Effects of collision energy and H2CO+ and methane vibrations
Authors: Liu Jianbo , Van Devener Brian , Anderson Scott L.
Published: June 2003

The effects on the title reaction of collision energy (Ecol), five H2CO+ vibrational modes, and deformation vibrations of methane have been studied, including the measurement of product integral and differential cross sections over a center-of-mass Ecol range from 0.09–3.3 eV. Electronic structure and RRKM calculations are reported, providing an additional mechanistic insight. The total reaction efficiency is well below unity, despite there being two exoergic reaction pathways with no activation barriers. The energetically more favorable channel corresponds to H elimination (HE) from an intermediate complex, however, this channel accounts for only ∼15% of the total reaction cross section at low Ecol and is negligible at high energies. The dominant channel, hydrogen abstraction (HA) by H2CO+ from methane, is dominated by a complex-mediated mechanism at low Ecol, switching over to a direct hydrogen-stripping mechanism at high Ecol. Both HA and HE are inhibited in a strongly mode-specific fashion by H2CO+ vibrational excitations, and greatly enhanced by excitation of methane deformation vibrations. The strong mode specificity indicates that the reaction-limiting step occurs early in the collisions.
Dynamical tunneling in molecules: Role of the classical resonances and chaos
Authors: Keshavamurthy Srihari
Published: June 2003

The influence of classical phase space structures on the dynamical tunneling splittings is studied using an effective spectroscopic Hamiltonian for water. It is argued that the enhancements in the splittings due to resonances and chaos are best understood away from the fluctuations associated with avoided crossings. The essential differences between various mechanisms are investigated using perturbation theory.