bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the heat of formation of O3 using vacuum ultraviolet laser-induced fluorescence spectroscopy and two-dimensional product imaging techniques
Authors: Taniguchi Nori , Takahashi Kenshi , Matsumi Yutaka , Dylewski Scott M. , Geiser Joseph D. , Houston Paul L.
Published: July 2002

Two different techniques, vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy and two-dimensional (2D) ion counting product imaging, have been used to determine the bond energy for the dissociation of jet-cooled O3 into O(1D)+O2(a 1Δg). The photofragment excitation (PHOFEX) spectrum for O(1D) products is recorded by detecting the VUV-LIF signal associated with the 3s 1D0–2p 1D transition at 115.22 nm while scanning the photolysis laser wavelength between 305 and 313 nm. A clear cut-off corresponding to the appearance threshold into O(1D)+O2(a 1Δg) is observed in this PHOFEX spectrum. The 2D image of the O(1D) products from the O3 photolysis near 305 nm is measured using an ion-counting method, with the detection of O(1D) atoms by [2+1] resonance enhanced multiphoton ionization (REMPI) at 205.47 nm. The kinetic-energy distribution obtained from the 2D image shows rotational structure due to the O2(a 1Δg,v″=0) fragment. The bond energy into O(1D)+O2(a 1Δg) has been obtained from the rotational assignments in the kinetic-energy distribution. The two different experimental approaches give consistent results and an accurate value of the bond dissociation energy into O(1D)+O2(a 1Δg) is found to be 386.59±0.04 kJ/mol. The standard heat of formation of O3, ΔfH0(O3)=−144.31±0.14 kJ/mol, has also been calculated from the bond energy obtained, in conjunction with thermochemical data for O2 molecule and O atom. The uncertainty for the ΔfH0(O3) value obtained in the present study is smaller than the previous value which has been used widely.
Resonance Raman spectroscopy of matrix-isolated mass-selected Fe3 and Ag3
Authors: Haslett T. L. , Bosnick K. A. , Fedrigo S. , Moskovits M.
Published: July 2002

Raman spectroscopy of matrix-isolated, mass-selected Fe3 and Ag3 reveal that both are Jahn–Teller distorted triangular molecules. The observed spectrum of Ag3 can be accounted for adequately using an approximate Jahn–Teller potential truncated at the quadratic term [Wedum et al., J. Chem. Phys. 100, 6312 (1994)] with parameters ωa=119 cm−1, ωe=99 cm−1, k=1.92, and g=0.29. For Fe3, the spectrum is more complex, most likely due to the fact that spin–orbit coupling plays an important role in this high-spin cluster in addition to the quadratic Jahn–Teller terms. The overall pattern of the spectrum suggests that in Fe3 the Jahn–Teller distortion is likely small, and a peak at 249 cm−1 is tentatively assigned to its symmetric stretch.
Interplay between gelation and phase separation in tree polymers, and the calculation of macroscopic loop density in the postgel regime
Authors: Gujrati P. D. , Bowman Daniel
Published: July 2002

We consider a very general model of equilibrium polycondensation of tree polymers and elucidate (i) the conditions that must be met for gelation to compete with phase separation under a variety of conditions; (ii) how gelation is different from a thermal transition; and (iii) how gelation can be induced not only by lowering but also by raising the temperature, thereby giving rise to the [lower critical solution temperature for gelation] phenomenon observed recently. We also preset a new and direct scheme to calculate the contributions to various functional densities from finite (sol) and infinite (gel) clusters. The scheme presents us with an elegant method to calculate the loop density explicitly and helps settle a long-standing controversy about the presence and the nature of loops in the postgel regime. The loops are macroscopic in size. Other important features are also discussed.
High-resolution pulsed field ionization photoelectron–photoion coincidence study of CH4: Accurate 0 K dissociation threshold for CH3+
Authors: Weitzel Karl-Michael , Malow Marcus , Jarvis G. K. , Baer Tomas , Song Y. , Ng C. Y.
Published: July 2002

The formation of methyl cation (CH3+) from methane (CH4) has been investigated in high resolution using the newly perfected pulsed field ionization photoelectron–photoion coincidence (PFI-PEPICO) scheme. The PFI-PEPICO data reveal that fragmentation of CH4 in high-n Rydberg states occurs at energies above the dissociation threshold prior to pulsed field ionization. The crossover point of the breakdown curves is found to depend strongly on the Stark field in the ion source and thus traditional simulation procedures based on such a feature for ion dissociation energy determination are not appropriate in PFI-PEPICO studies. We show that for a prompt dissociation process, the disappearance energy of the parent molecule provides an accurate measure of the 0 K ion dissociation threshold, as that for CH3+ from CH4 is 14.323±0.001 eV.
Correlation length and amplitude scaling in critical polymer solutions
Authors: An Xueqin , Xia Ke-Qing , Shen Weiguo , Qiu Xin-Liang
Published: July 2002

We present a light scattering measurement of the correlation length for a series of critical solutions of polystyrene in methylcyclohexane with different molecular weights. Our results show that the correlation length ξ∼Nζνε−0.63, where N is the polymerization index and ε=(T−Tc)/Tc is the reduced temperature. The N exponent ζν is found to be 0.18±0.02, which is contrary to most earlier direct experimental results but in excellent agreement with theoretical predictions by de Gennes and Stepanow.
Effect of gravity on the deposition of colloidal particles on a planar surface
Authors: Choi H. S. , Rho C. H.
Published: July 2002

A steady state convective-diffusion equation is solved using a collocation method to find the concentration profile and flux of adsorbing particles near a particle adsorbed on the plane surface. At small values of the gravity number, NG=πd4Δρ/6kT, the concentration profile and flux vary slowly near the preadsorbed particle, while they are highly nonuniform at large values of NG. The effect of the position of the system boundary on the collocation calculation is discussed and it is shown how the concept of flux balance may be used to improve the accuracy of the results. Finally, we develop two fitting functions at high and low values of NG, respectively.
Lattice versus continuum models of a polymer chain
Authors: Taylor Mark P. , Lipson J. E. G.
Published: July 2002

A self-avoiding, self-interacting polymer chain is studied both on a lattice and in the continuum using a Born–Green–Yvon integral equation approach. Equivalent theoretical approximations are made in both cases, allowing for an unambiguous comparison between the lattice and continuum models. The theory preserves the universal scaling behavior for polymer chain dimensions in the high-temperature limit and, with a lowering of temperature, predicts a universal collapse transition behavior for both lattice and continuum chains. Implications for the modeling of polymer solutions are discussed.
Simulations of mobility and evaporation rate of adsorbate islands on solid surfaces
Authors: Mills Greg , Mattsson Thomas R. , Møllnitz Lone , Metiu Horia
Published: July 2002

We perform kinetic Monte Carlo simulations to examine the kinetic properties of one-atom-high islands formed by atoms adsorbed on a single-crystal surface. At sufficiently high temperature, the atoms can leave the island to migrate on the substrate. We call this process evaporation. We find that most of the evaporation events are described by a Poisson process characterized by a rate constant k(N,T), where N is the number of atoms in the island and T is the temperature. We also observe correlated evaporation events, which tend to follow each other in rapid succession. This complicated situation can be described, however, by an effective Poisson process that is defined to generate the correct vapor pressure. The dependence of k(N,T) on N follows an equation proposed by Metiu and Rosenfeld, and not a power law observed in previous work. The random motion of the atoms around the border of the island causes its center of mass to move along the surface. This island motion is diffusional, except at the shortest times. The dependence of the diffusion coefficient on N is a power law (if the smallest islands are excluded). The exponent is not universal and depends on temperature and the parameters of the model. Theory predicts universal behavior for very large islands and we assume that in our simulations we have not reached this regime.
Anion photoelectron spectroscopy of B2N−
Authors: Asmis Knut R. , Taylor Travis R. , Neumark Daniel M.
Published: July 2002

Vibrationally resolved 355 and 266 nm anion photoelectron spectra of B2N are presented. Photodetachment to two electronic states of linear B–N–B is observed and, aided by electronic structure calculations, assigned to the X̃ 1Σg+→X̃ 2Σu++e− and X̃ 1Σg+→Ã 2Σg++e− transitions. The electron affinity of B2N is 3.098±0.005 eV and the Ã 2Σg+ term energy T0 is 0.785±0.005 eV. Observation of excitations involving uneven quanta of the antisymmetric stretching mode (v3) indicates a breakdown of the Franck–Condon (FC) approximation and results from Herzberg–Teller vibronic coupling between the X̃ 2Σu+ and Ã 2Σg+ states involving the v3 mode. Measurement of the angular dependence of the photodetached electrons serves as a sensitive probe for the identification of these FC forbidden transitions. A linear vibronic coupling model qualitatively reproduces the perturbed v3 potentials of the X̃ and Ã states. Artifactual symmetry breaking along the v3 coordinate is observed in the ab initio wave functions for the neutral ground state up to the coupled-cluster level of theory, even when Brueckner orbitals are used. No evidence is found for an energetically low-lying cyclic state of B2N, which has been invoked in the assignment of the matrix infrared spectrum of B2N. However, the matrix infrared data agrees well with the peak spacing observed in the photoelectron spectra and reassigned to the linear X̃ 2Σu+ ground state.
Effect of beam energy and surface temperature on the dissociative adsorption of H2 on Si(001)
Authors: Dürr M. , Raschke M. B. , Höfer U.
Published: July 2002

Dissociative adsorption of H2 from a high-flux supersonic molecular beam on flat and vicinal Si(001) surfaces was investigated by means of optical second harmonic generation (SHG). The initial sticking coefficients for terrace adsorption varied between 10−8 and 10−4. They revealed a strongly activated dissociation process, both with respect to the kinetic energy of the incident molecules (70 meV⩽Ekin⩽380 meV) and the surface temperature (440 K⩽Ts⩽670 K). The results indicate that dynamical distortions of Si surface atoms can lower the effective adsorption barriers from 0.8±0.2 eV to almost negligible values. Previously proposed defect-mediated processes can be ruled out as a major adsorption channel.
Elastic sheet method for identifying atoms in molecules
Authors: Uberuaga Blas P. , Batista Enrique R. , Jónsson Hannes
Published: July 2002

We have developed a new method for finding and representing dividing surfaces which can, for example, be used to identify “atoms” in molecules or condensed phases based on Bader’s definition. Given the total electron density of the system, the dividing surface is taken to be the zero-flux surface, i.e., the surface on which the normal component of the gradient vanishes. Our method for finding this surface involves creating an “elastic sheet” represented by a swarm of fictitious particles which interact with each other so as to give a nearly uniform distribution of points on the sheet. Two kinds of forces act on the particles: (1) the component of the gradient of the density normal to the elastic sheet, and (2) an interparticle force which only acts in the local tangent plane of the sheet. Starting with a spherical surface and applying an optimization algorithm that minimizes the forces leads to convergence of the particles to the zero-flux surface. The elastic sheet tends to round off regions where the zero-flux surface has sharp cusps or points, but this appears not to be a serious problem in cases we have studied. The elastic sheet method is robust and can converge in situations where currently used methods fail. We demonstrate the method with a study of water clusters and a Si interstitial in a Si crystal.
Time propagation and spectral filters in quantum dynamics: A Hermite polynomial perspective
Authors: Vijay Amrendra , Wyatt Robert E. , Billing Gert D.
Published: July 2002

We present an investigation of Hermite polynomials as a basic paradigm for quantum dynamics, and make a thorough comparison with the well-known Chebyshev method. The motivation of the present study is to develop a compact and numerically efficient formulation of the spectral filter problem. In particular, we expand the time evolution operator in a Hermite series and obtain thereby an exponentially convergent propagation scheme. The basic features of the present formulation vı̀s a vı̀s Chebyshev scheme are as follows: (i) Contrary to the Chebyshev scheme Hamiltonian renormalization is not needed. However, an arbitrary time scaling may be necessary in order to avoid numerical hazards, and this time scaling also provides a leverage to accelerate the convergence of the Hermite series. We emphasize the final result is independent of the arbitrary scaling. (ii) As with the Chebyshev scheme the method is of high accuracy but not unitary by definition, and thus any deviation from unitarity may be used as a guideline for accuracy. The calculation of expansion coefficients in the present scheme is extremely simple. To contrast the convergence property of present method with that of the Chebyshev one for finite time propagation, we have introduced a time–energy scaling concept, and this has given rise to a unified picture of the overall convergence behavior. To test the efficacy of the present method, we have computed the transmission probability for a one-dimensional symmetric Eckart barrier, as a function of energy, and shown that the present method, by suitable time–energy scaling, can be very efficient for numerical simulation. Time–energy scaling analysis also suggests that it may be possible to achieve a faster convergence with the Hermite based method for finite time propagation, by a proper choice of scaling parameter. We have further extended the present formulation directed toward the spectral filter problem. In particular, we have utilized the Gaussian damping function for the purpose. The Hermite propagation scheme has allowed all the time integrals to be done fully analytically, a feature not completely shared by the Chebyshev based scheme. As a result, we have obtained a very compact and numerically efficient scheme for the spectral filters to compute the interior eigenspectra of a large rank eigensystem. The present formulation also allows us to obtain a closed form expression to estimate the error of the energies and spectral intensities. As a test, we have utilized the present spectral filter method to compute the highly excited vibrational states for the two-dimensional LiCN (J=0) system and compared with the exact diagonalization result.
Equation of state for polymer chains in good solvents
Authors: Lue L.
Published: July 2002

A free-energy model is developed for polymer chains in good solvents. This model, which combines the ideas of polymer field theory with liquid-state theory, is valid in the dilute, semidilute, and concentrated regimes. The model is compared against computer simulation data for the equation of state of tangent hard-sphere chain fluids. At low concentrations, it accurately describes the thermodynamics of tangent hard-sphere chains, reproducing the universal scaling behavior of long chains. At high concentrations, the model has an accuracy comparable to those of previous equations of state for tangent hard-sphere chains.
Laser driven ground state photodissociation of HCo(CO)4: An ab initio quantum molecular dynamics approach
Authors: Orel Ann E. , Zhao Yi , Kühn Oliver
Published: July 2002

The competition between laser selective dissociation of the axial Co–CO bond and intramolecular energy redistribution in HCo(CO)4 is investigated. Our approach is based on an ab initio calculation of the Cartesian reaction surface Hamiltonian along the Co–CO bond distance using density functional theory. The substrate degrees of freedom are treated within the harmonic approximation. We find only two modes which are strongly coupled to the dissociation reaction, one which can be approximately described as an H–Co stretching vibration while the second one is an umbrella type vibration of the equatorial carbonyls. The region of validity for harmonic motion of the substrate normal modes is explored.
Ab initio study of (NH3)2: Accurate structure and energetics
Authors: Lee Jae Shin , Park Sun Yong
Published: July 2002

The equilibrium and saddle point structures of the ammonia dimer were investigated employing a series of correlation-consistent basis sets, cc-pVXZ and aug-cc-pVXZ(X=D,T,Q) at the Hartree–Fock (HF), second order and fourth order Møller–Plesset perturbation theory (MP2, MP4) levels. It is shown that the energies and geometries of the stationary structures are sensitive to the basis set and electron correlation, and the proper combination of electron correlation treatment (MP2 or better) and basis set requirement (aug-cc-pVTZ or better) is necessary to determine the equilibrium structure and ordering of the stationary structures. The equilibrium structure of the ammonia dimer is found to be an asymmetric cyclic (eclipsed) structure with Cs symmetry. Although this is generally consistent with the equilibrium structure predicted from the model potential by Olthof et al. [J. Chem. Phys. 101, 8430 (1994)], it appears to be more shifted toward the linear structure than the centrosymmetric cyclic structure, which signifies a certain degree of hydrogen bonding in this dimer. The MP2 barrier height to proton donor–acceptor interchange at MP2/aug-cc-pVQZ//MP2/aug-cc-pVTZ is 7.6 cm−1, which is in excellent agreement with the value predicted from the model potential by Olthof et al. While the barrier height to rotation of one monomer (hydrogen-bond acceptor) about its C3 axis is relatively low, ∼20 cm−1, the corresponding value of the other monomer (hydrogen-bond donor) is shown to be rather high, probably more than 450 cm−1 at the equilibrium structure. The binding energies of the ammonia dimer are computed with and without counterpoise correction for basis set superposition error. The MP2 complete basis set (CBS) limit electronic binding energy of (NH3)2 is estimated to be within 13.2±0.3 kJ/mol.
The Shpol’skii system perylene in n-hexane: A computational study of inclusion sites
Authors: Wallenborn Ernst-Udo , Leontidis Epameinondas , Palewska Krystyna , Suter Ulrich W. , Wild Urs P.
Published: July 2002

We present a combined quantum mechanics/molecular mechanics study of the Shpol’skii system perylene/n-hexane. The system was modeled utilizing a customized pcff-derived force field optimized with a balanced set of optimization criteria based on geometry, vibrational modes, and the energies and forces in an ensemble of molecular geometries. Spectral shifts were calculated perturbatively using the method of Shalev et al. [J. Chem. Phys. 95, 3147 (1991)]. The calculated shifts are within the experimental uncertainty of the observed 0–0 lines and allow an unambiguous assignment of the three most prominent sites. The proposed assignment differs from that of a previous study.
Ring currents and charge stiffness in molecular and extended models of interacting fermions
Authors: Soos Z. G. , Pati Y. Anusooya , Pati S. K.
Published: July 2002

The diamagnetic susceptibility χ of half-filled fermion models with N=4n+2 sites is related to chemical shifts in molecules and charge stiffness in extended systems. The slow evolution of χ(N) with N in Hubbard models or spinless fermions indicates a small energy gap, as known from exact solutions of regular chains. A gap due to alternating transfer integrals (1±δ) suppresses χ for Nδ>1, but is a small correction for Nδ<1. Exact ring currents Nχ of Pariser–Parr–Pople (PPP) and Hubbard models are extended to N=18 in D18h symmetry. Hydrocarbon PPP parameters account for the anisotropy of proton shifts in 14 and 18 annulenes, for smaller shifts at larger N, and for larger shifts of anions with 4n+2 π-electrons. Fermion models with arbitrary spin-independent interactions are shown to have vanishing χ for open boundary conditions (chains) at half filling or finite N. Diamagnetic currents in molecules require rings but are not sensitive to small bond-length variations, while an energy gap rather than topology enters in the charge stiffness of extended systems. Although formally identical, χ has different applications in finite and extended systems and its convergence with N can be rapid or very slow. Spin–charge separation reflects correlations rather than topology in half-filled Hubbard, PPP, and spinless fermion models; 4n and 4n+2 rings with oppositely signed χ show similar spin–charge separation with increasing correlations.
Spin-restricted open-shell coupled-cluster theory for excited states
Authors: Szalay Péter G. , Gauss Jürgen
Published: July 2002

Using a linear-response approach, the recently introduced spin-restricted coupled-cluster (SR-CC) theory is extended to the treatment of excited states of high-spin open-shell molecules. Explicit equations are given within the usual singles and doubles approximation and our implementation (within an existing spin–orbital code) is described. It is shown that in SR-CC theory, due to spin constraints, the spin-expectation value for the excited states calculated as corresponding energy derivatives always corresponds to the exact value. In addition, the SR-CC singles and doubles (SR-CCSD) approach is extended to include also the so-called pseudotriple excitations (best described as double excitations with an additional spin–flip in one open-shell orbital) which are important for the description of so-called low-spin excited states. Exploratory calculations for a few diatomic systems (BeH, OH, NO, CN, and CO+) show that problems due to spin contamination in the unrestricted Hartree–Fock (UHF) CCSD treatment of excited states are rectified by using a restricted open-shell Hartree–Fock (ROHF) reference, as it is done in the SR-CC approach. While SR-CCSD performs well for high-spin excited states, the closely related partially spin-adapted (PSA) CC approach is shown to be inferior and errors in the computed excitation energies are generally larger than the typical accuracy of about 0.2 eV in CCSD excited state treatments. So-called low-spin states (e.g., the 2 2B1 state of NH2) are shown to require inclusion of pseudotriple excitations for even a qualitatively correct description. If they are included, ROHF-CC, SR-CC, and PSA-CC give essentially identical results.
Collisional energy transfer probabilities of highly excited molecules from kinetically controlled selective ionization (KCSI). II. The collisional relaxation of toluene: P(E′,E) and moments of energy transfer for energies up to 50 000 cm−1
Authors: Lenzer Thomas , Luther Klaus , Reihs Karsten , Symonds Andrew C.
Published: July 2002

Complete and detailed experimental transition probability density functions P(E′,E) have been determined for the first time for collisions between a large, highly vibrationally excited molecule, toluene, and several bath gases. This was achieved by applying the method of kinetically controlled selective ionization (KCSI) (Paper I [J. Chem. Phys. 112, 4076 (2000), preceding article]). An optimum P(E′,E) representation is recommended (monoexponential with a parametric exponent in the argument) which uses only three parameters and features a smooth behavior of all parameters for the entire set of bath gases. In helium, argon, and CO2 the P(E′,E) show relatively increased amplitudes in the wings—large energy gaps |E′−E|—which can also be represented by a biexponential form. The fractional contribution of the second exponent in these biexponentials, which is directly related to the fraction of the so-called “supercollisions,” is found to be very small (<0.1%). For larger colliders the second term disappears completely and the wings of P(E′,E) have an even smaller amplitude than that provided by a monoexponential form. At such low levels, the second exponent is therefore of practically no relevance for the overall energy relaxation rate. All optimized P(E′,E) representations show a marked linear energetic dependence of the (weak) collision parameter α1(E), which also results in an (approximately) linear dependence of 〈ΔE〉 and of the square root of 〈ΔE2〉. The energy transfer parameters presented in this study form a new benchmark class in certainty and accuracy, e.g., with only 2%–7% uncertainty for our 〈ΔE〉 data below 25 000 cm−1. They should also form a reliable testground for future trajectory calculations and theories describing collisional energy transfer of polyatomic molecules.
A theory of void formation in charge-stabilized colloidal suspensions at low ionic strength
Authors: Warren Patrick B.
Published: July 2002

Using a carefully justified development of Debye–Hückel theory for highly asymmetric electrolytes, one finds that a region of expanded phase instability, or miscibility gap, can appear for charge-stabilized colloidal suspensions at high charges and low ionic strengths. It is argued that this offers a straightforward explanation for the observations of void structures and other anomalies in such suspensions in this region. The nature of the interface between coexisting phases, and general arguments that many-body attractions form a key part of the underlying physical picture, are also examined. The present analysis may also generate new insights into old problems such as coacervation in oppositely charged colloid or protein–polyelectrolyte mixtures, and suggests interesting new possibilities such as the appearance of charge density wave phases in colloidal systems in the vicinity of the critical solution points.
Analysis of individual (macro)molecules and proteins using near-field optics
Authors: van Hulst Niek F. , Veerman Joost-Anne , Garcı́a-Parajó Marı́a F. , Kuipers L. (Kobus)
Published: July 2002

Recent achievements in single molecule detection using near-field optical excitation are presented. By proper control of technology, distinct advantages of near-field optics are exploited: (i) the nanometric excitation/emission volume (104–105 nm3), which provides high spatial resolution, localization of a single molecule within a few nm, and reduced background; (ii) the sensitivity for single molecule orientation in all three dimensions; (iii) the high local brightness, allowing real-time single molecule detection down to μs resolution; (iv) the simultaneous colocalization with nanometric surface topography. Real-time quantum jumps between singlet and triplet state of an individual molecule are observed. Distributions for triplet state lifetime and crossing yield are determined. Both triplet state lifetime and crossing yield of a single molecule appear to vary in time, due to the local heterogeneity. Individual dendritic molecules containing a single fluorescent core are investigated. The dendritic assemblies are discriminated from free fluorescent cores on the basis of accurate simultaneous localization of both the fluorescent core and the topography of the surrounding dendritic shell. Intramolecular rotational motion of the fluorescent core is observed. Individual green fluorescent proteins are visualized, both in fluorescence and topography. Photoinduced conformational changes to a nonemissive form of the protein are observed, leading to long dark intervals of several seconds.
Stabilization of transient negative ions by vibrational energy transfer: A cluster and thin film study on SF6 and C6F6
Authors: Weik F. , Sanche L. , Ingólfsson O. , Illenberger E.
Published: July 2002

Resonant low energy electron attachment to SF6 and C6F6 in argon clusters and on a multilayer krypton film is presented. The energy dependence of the absolute attachment cross sections for the condensed molecules is determined in the range 0–8 eV by measuring charge localization on the film. We find a cross section maximum of (3.0±0.8)×10−15 cm2 at 60 meV for SF6− formation, which is close to the gas phase value. For C6F6, we obtain a maximum value (4.8±1.2)×10−15 cm2 at 75 meV. In contrast to isolated gas phase molecules, where both ions are only observed in a very narrow energy range around 0 eV, SF6− resulting from electron attachment to clusters is observed up to 1.5 eV. The same is true for the condensed submonolayers, where charge localization is observed up to 1.5 eV for SF6. The extension of stable SF6− formation to much higher energies in condensed media is attributed to the transfer of intramolecular vibrational energy from SF6− to phonon vibrational modes of the Ar cluster or the Kr multilayer film. C6F6− formation is also observed up to 1.7 eV from clusters, but on the film, charge localization is only detected up to 0.7 eV. This difference is explained by the orientation of the C6F6 molecules on the rare gas film, which diminishes vibrational energy transfer to the phonon bath of the Kr lattice. Similar results are also obtained for the dimeric configurations of these molecules seeded into Ar clusters.
Quantum tunneling dynamics using hydrodynamic trajectories
Authors: Bittner Eric R.
Published: July 2002

In this paper we compute quantum trajectories arising from Bohm’s causal description of quantum mechanics. Our computational methodology is based upon a finite-element moving least-squares method (MWLS) presented recently by Wyatt and co-workers [Lopreore and Wyatt, Phys. Rev. Lett. 82, 5190 (1999)]. This method treats the “particles” in the quantum Hamilton–Jacobi equation as Lagrangian fluid elements that carry the phase, S, and density, ρ, required to reconstruct the quantum wave function. Here, we compare results obtained via the MWLS procedure to exact results obtained either analytically or by numerical solution of the time-dependent Schrödinger equation. Two systems are considered: first, dynamics in a harmonic well and second, tunneling dynamics in a double well potential. In the case of tunneling in the double well potential, the quantum potential acts to lower the barrier, separating the right- and left-hand sides of the well, permitting trajectories to pass from one side to another. However, as probability density passes from one side to the other, the effective barrier begins to rise and eventually will segregate trajectories in one side from the other. We note that the MWLS trajectories exhibited long time stability in the purely harmonic cases. However, this stability was not evident in the barrier crossing dynamics. Comparisons to exact trajectories obtained via wave packet calculations indicate that the MWLS trajectories tend to underestimate the effects of constructive and destructive interference effects.
Solvation effects in large binary van der Waals clusters with high doping rates
Authors: Vach Holger
Published: July 2002

We present a molecular-dynamics study of the pickup process for impurity rates around 50% for Ne, SiF4, Kr, and Xe dopants deposited onto Ar502 host clusters under quasiexperimental conditions. Under those conditions, the investigated mixed clusters never become liquid and only exhibit solid–solid structural transitions. For both Xe and SiF4 guest particles, we find strong solvation effects leading to final cluster structures dramatically different from those expected for small doping rates. While SiF4 molecules are normally believed to always reside in surface states of the argon cluster, we demonstrate that they can actually end up in deep permanent matrix states for sufficiently high guest particle concentrations.
Homonuclear 3d transition-metal diatomics: A systematic density functional theory study
Authors: Barden Christopher J. , Rienstra-Kiracofe Jonathan C. , Schaefer Henry F.
Published: July 2002

The equilibrium bond lengths, harmonic vibrational frequencies, and dissociation energies of the ground state homonuclear 3d transition-metal diatomics (scandium through copper) were determined using six density functional or hybrid Hartree–Fock/density functional theory (HF/DFT) methods and unrestricted Hartree–Fock theory. Results are compared to other theoretical studies and to experimental values when available. The accuracy of the DFT results is found to be highly dependent upon the functional employed, with the pure DFT methods, BLYP and BP86, often performing significantly better than the hybrid HF/DFT methods. For the van der Waals complex Mn2, all six functionals predict the ground state to be high-spin, disagreeing with experiment; the true (antiferromagnetic) ground state was not found for any functional. Average errors for theoretical geometries and vibrational frequencies are for B3LYP, 0.053 Å (2.4%) and 122 cm−1 (31.1%); for B3P86, 0.051 Å (2.4%) and 122 cm−1 (31.3%); for BHLYP, 0.077 Å (4.1%) and 208 cm−1 (49.3%); for BLYP, 0.024 Å (1.3%) and 98 cm−1 (24.5%); for BP86, 0.020 Å (1.1%) and 104 cm−1 (25.6%); and for LSDA, 0.056 Å (3.0%) and 158 cm−1 (37.9%). No functional gives results directly comparable for all nine species. Dissociation energy results are severely overestimated in many instances and negative in others. Anecdotal reports of success for density functional theory for these systems may have been overblown.
An optical–optical double resonance study of the perturbed O2 d3sσg(1Πg) Rydberg state excited via single rotational levels of the b(1Σg+) valence state
Authors: O’Keeffe P. , Ridley T. , Lawley K. P. , Donovan R. J. , Telle H. H. , Beddows D. C. S. , Urena A. G.
Published: July 2002

The perturbed v=3 level of the d3sσg(1Πg) Rydberg state of O2 has been excited in an optical–optical double resonance (OODR) experiment via J=0–16 of v=0 of the b(1Σg+) state. The d(1Πg) state resonances were detected by ionization with one further probe photon near 340 nm. The range of J levels of the d(1Πg) state now accessed reveals a lack of variation in line widths that is not predicted by previous models of state-dependent predissociation. Instead, intensities of rotational lines in the ionization spectrum appear to be controlled by a J-dependent mixing of the d(1Πg) state with a nearby valence state that has a much lower ionization cross section at the probe wavelengths used.
Space-times with intrinsic symmetries on the three-spaces t=constant
Authors: Martinez E. , Sanz J. L.
Published: July 2002

We consider metrics which possess a priori certain ‘‘intrinsic symmetries’’ on the three-spaces t=const. In the vacuum case, we obtain a generalization of Birkhoff’s theorem and a set of solutions with a translational isometry operating on the whole space-time. In the nonvacuum case, we assume a perfect fluid matter content and a fluid flow orthogonal to the three-spaces t=const, and obtain several exact analytical solutions, some of them satisfying the standard energy conditions. In particular, a stiff equation of state is obtained in some cases, and we also have found particular solutions where a plane, spherical, or hyperbolic intrinsic symmetry is manifest.
Spinorial infinite equations fitting metric-affine gravity
Authors: Cant A. , Ne’eman Y.
Published: July 2002

Two different approaches are used to construct infinite-component spinor equations based on the multiplicity-free irreducible representations of S̄L̄(4,R). These ‘‘manifield’’ equations are SL(2,C) invariant; they exist in special relativity, and can directly be coupled to gravitation in the metric-affine theory, i.e., in Einstein’s general relativity with nonpropagating torsion and nonmetricity. In the first approach the maximal compact subgroup S̄Ō(4) of S̄L̄(4,R) is ‘‘physical.’’ A vector operator X μ is constructed directly in the infinite-dimensional reducible representation 𝒟disc( 1/2 ,0) ⊕𝒟disc(0, 1/2 ). In the second approach, SL(2,C) and a vector operator γ μ are embedded directly in S̄L̄(4,R) via the Dirac representation. A manifield equation is then constructed (in a manner analogous to the Majorana equation) by taking an infinite-dimensional irreducible multiplicity-free representation of SL(4,R), spinorial in  j1, in the ( j1, j2) reduction over S̄Ō(4). Both manifields can fit the observed mass spectrum.
Fluctuation–dissipation theorem for QCD plasma
Authors: Chakrabarti J.
Published: July 2002

We explore a quantum-chromodynamic (QCD) plasma in stationary nonequilibrium states assuming that the process of thermalization is governed by Fokker–Planck dynamics. The generalized thermodynamic potential appropriate to the state is obtained. A relationship is developed between the response function and the fluctuations in the stationary state.
Simple calculation of Löwdin’s alpha function. II. Easier procedure for evaluating b
K k(L M‖l ), and vanishing of h
n,2n−i(L M‖l ) for special values of i and n
Authors: Suzuki Noboru
Published: July 2002

This paper subsequent to the one [J. Math. Phys. 25, 1133 (1984)] (referred to as Part I) presents the following new results: It is found out that for M=L and L−1 the coefficients bK k(L M‖l) in Löwdin’s α-function have properties other than manifested in Part I. The expression for bK k(L M‖l) is shown to be equivalent to the one into which Sharma’s expression, obtained in a different manner from that in Part I, is simplified by Rashid. The use of Rashid’s expression leads to the recurrence formula for bK k(L M‖l) with respect to M only. This formula and the expression for the bK k(L M‖l) with M=L provide an easier procedure for successively evaluating bK k(L M‖l) than in Part I. Furthermore, it is proved that the coefficients hn,2n−i(L M‖l) in the asymptotic form of the α-function vanish for i<l+M and for n<l.
Nonlinear spinor representations
Authors: Furlan P. , Ra̧czka R.
Published: July 2002

A systematic method for the construction of nonlinear carrier spaces for a class of nonlinear spinor representations of complex and pseudo-orthogonal rotation groups is presented. It is shown that Cartan pure spinors, which satisfy quadratic constraints, are special cases of our construction. A class of new nonlinear spinor representations is discovered, which is particularly interesting in the case of generalized conformal groups SO(ν+1,ν−1), ν=3,4,... . The nonlinearity condition considerably diminishes the number of independent spinor components and therefore the corresponding spinor fields are the most natural building blocks for grand unified field theories. The method presented here is universal and can be applied for the construction of new nonlinear representations of other higher-symmetry groups.
Dirac quantization of a three-dimensional gauge theory
Authors: Burnel A. , Van Der Rest-Jaspers M.
Published: July 2002

A model recently proposed by Hagen is examined from the point of view of Dirac quantization of constrained systems. This model exhibits interesting particular features for the Dirac method itself. Among them are the odd number of second-class constraints and the fact that, when a gauge is fixed, constraints result from compatibility conditions between Lagrange multipliers. From the point of view of the model itself, the invalidity of the axial gauge in the non-Abelian case is obtained by comparing the effective Hamiltonians for two different values of the arbitrary spacelike vector.
ζ-function method and the evaluation of fermion currents
Authors: Gamboa Saraví R. E. , Muschietti M. A. , Schaposnik F. A. , Solomin J. E.
Published: July 2002

Using the ζ-function method, a prescription for the evaluation of fermion currents in the presence of background fields is given. The method preserves gauge invariance at each step of the computation and yields to a finite answer showing the relevant physical properties for arbitrary background configurations. Examples for n=2,3 dimensions are worked out, emphasizing the connection between preservation of gauge invariance and violation of other symmetries (chiral symmetry for n=2, parity for n=3).
Formula for invariant integrations on SU(n)
Authors: Maekawa Takayoshi
Published: July 2002

The explicit formula for evaluating integrals of a product of the matrix elements of SU(n) is given in terms of Kronecker delta symbols.
Front form and point form formulation of predictive relativistic mechanics. Noninteraction theorems
Authors: Jaen X. , Molina A. , Iranzo V.
Published: July 2002

The front form and the point form of dynamics are studied in the framework of predictive relativistic mechanics. The noninteraction theorem is proved when a Poincaré-invariant Hamiltonian formulation with canonical position coordinates is required.
Penrose diagrams for the Einstein, Eddington–Lemaitre, Eddington–Lemaitre–Bondi, and anti-de Sitter universes
Authors: Tipler Frank J.
Published: July 2002

Penrose diagrams including the c boundary at infinity and the singularities for the Einstein, Eddington–Lemaitre, Eddington–Lemaitre–Bondi, and anti-de Sitter universes are constructed. Penrose diagrams for the Einstein, Eddington–Lemaitre, and anti-de Sitter universes have been published before, but these diagrams are incomplete in that the published diagrams do not contain the c-boundary points of the universes they are supposed to represent.
Remarks on bifurcation with symmetry, gradient property, and reducible representations
Authors: Cicogna Giampaolo , Gaeta Giuseppe , Rossi Pietro
Published: July 2002

The gradient property for bifurcation equations covariant with respect to a group representation that is reducible, but irreducible as a real representation, is examined. In this case, the Schur lemma does not hold in the usual form, and one is faced with problems not present in the irreducible case. It is shown how to handle these problems, and applications to the fundamental real representations of SO(2) and SU(2) are presented that, due to general group theoretical results, represent in a sense the more general situation.
Differentiation of retarded integrals and the divergence theorem for retarded functions with discontinuities
Authors: Cooperstock F. I. , Lim P. H.
Published: July 2002

Theorems expressing the time derivatives of retarded volume and surface integrals are presented as well as the Gauss divergence theorem for retarded functions with discontinuities. These theorems greatly facilitate the analysis of gravitational radiation from the motion of disjoint matter distributions in general relativity and could find useful application in other branches of physics.
Group analysis of the three-wave resonant system in (2+1) dimensions
Authors: Leo R. A. , Martina L. , Soliani G.
Published: July 2002

The three-wave resonant interaction equations (2D-3WR) in two spatial and one temporal dimension within a group framework are analyzed. The symmetry algebra of this system, which turns out to be an infinite-dimensional Lie algebra whose subalgebra is of the Kac–Moody type, is found. The one- and two-dimensional symmetry subalgebras are classified and the corresponding reduction equations are obtained. From these the new invariant and the partially invariant solutions of the original 2D-3WR equations are obtained.
A simple proof of duality for local algebras in free quantum field theory
Authors: Hislop Peter D.
Published: July 2002

New and simple proofs of duality for local von Neumann algebras in free-scalar field models associated with a general class of regions in Minkowski space are presented. The proofs are given for both the massive and massless cases and an abstract result of Araki [H. Araki, J. Math. Phys. 4, 1343 (1963)] is assumed. The properties of the local algebras are analyzed using the associated real linear manifolds. Duality is proved in the massive models using elementary properties of Sobolev spaces and in the massless model using dilatation covariance. A proof of the factor property and the cyclicity and separability of the vacuum for these local algebras is also given.
Continued fractions and Rayleigh–Schrödinger perturbation theory at large order
Authors: Vrscay E. R. , Cizek J.
Published: July 2002

Concern with the continued fraction representations of divergent Rayleigh–Schrödinger perturbation expansions in quantum mechanics is expressed. The following relation between the large-order behavior of the continued fraction coefficients cn and the perturbation series coefficients E(n) is shown to exist: If E(n) ∼(−1)n+1Γ( pn+a),  p=0,1,2,..., as n→∞, then cn=O(np) as n→∞. The case  p=1 is studied in detail here, using the problems of the quartic anharmonic oscillator and the hydrogen atom in a linear radial potential as illustrative examples. For  p=1 the asymptotics of the cn are shown to be linked to the infinite field limit E(λ)∼F(0)λα, predicting α and providing convergent estimates of F(0).
The Cauchy problem for the coupled Maxwell–Schrödinger equations
Authors: Nakamitsu Kuniaki , Tsutsumi Masayoshi
Published: July 2002

The Cauchy problem for the coupled Maxwell–Schrödinger equations in Rd in the Lorentz gauge is considered. The viscosity method is used to establish local existence. In one and two space dimensions, global solutions are obtained.
Continuity of entropy and mutual entropy in C*-dynamical systems
Authors: Ohya Masanori , Matsuoka Takashi
Published: July 2002

The lower semicontinuities of the entropy and the mutual entropy of a state for C*-dynamical systems are proved with respect to the set of all KMS states and the set of all α-invariant states.
On the construction of perfect Morse functions on compact manifolds of coherent states
Authors: Berceanu S. , Gheorghe A.
Published: July 2002

Perfect Morse functions on the manifold of coherent states are effectively constructed. The case of a compact, connected, simply connected Lie group of symmetry, having the same rank as the stationary group of the manifold of coherent states, such that the manifold of coherent states is a Kählerian C-space, is considered. It is proved that the set of perfect Morse functions is dense in the set of energy functions for linear Hamiltonians in the elements of the Cartan algebra of the Lie algebra of the representation of the group considered. It is proved that the maximum number of orthogonal vectors on a coherent vector manifold is equal to the Euler–Poincaré characteristic of the manifold.
Exact solutions for discrete kinetic models with ternary collisions
Authors: Cornille Henri
Published: July 2002

Discrete velocity Boltzmann models with three or four independent densities and only one independent binary collision term are considered. As has been suggested, multiplying the binary collision term by 1+τM, M being the total mass (the sum of all densities), one could include ternary collisions. However, a phenomenological point of view is adopted, τ being an effective parameter for multiparticle collisions, while the restriction 1+τM>0 ensures the validity of the H theorem. Exact solutions for three (1+1)-dimensional models, the six-velocity Broadwell model and the four- and the six-velocity planar models, are discussed. Both similarity shock-wave solutions and (1+1)-dimensional solutions with two exponential variables are obtained. These last solutions are either periodic solutions or infinitely weak shock solutions.
On the GKP and BS constructions of the c-boundary
Authors: zhi-quan Kuang , can-bin Liang
Published: July 2002

Two examples are presented in this paper, the first is unfavorable to the c-boundary construction given by Geroch, Kronheimer, and Penrose [Proc. R. Soc. London Ser. A 327, 545 (1972)] but in favor of that given by Budic and Sachs [J. Math. Phys. 15, 1302 (1974)], while the second plays an opposite role. The second example is also an example of a causally continuous space-time with a ‘‘really big gap,’’ contrary to what was believed in the literature.