bluuebunny/crossref_metadata_2025 huggingface dataset:
Europe and the world
Authors: Hanson David P.
Published: January 2003

Michelle Egan. 2001. Constructing a European Market. Standards, Regulation and Governance.
Oxford: Oxford University Press. 362 pages; ISBN 0‐9‐24405‐7.

Brigid Gavin. 2001. The European Union and Globalization; Towards Global Democratic
Governance. Cheltenham, UK: Edward Elgar. 242 pages; ISBN 1‐84064‐005‐7.

Patrick A. Messerlin. 2001. Measuring the Costs of Protection in Europe: European Commercial Policies
in the 2000s. Washington: Institute for International Economics. 370 pages; ISBN
0‐88132‐273‐3.
Quasisaddles of liquids: Computational study of a bulk Lennard-Jones system
Authors: Shah Pooja , Chakravarty Charusita
Published: January 2003

Inherent saddles of the potential energy surface, U, of a liquid are defined as configurations which correspond to the absolute minima of the pseudopotential surface, W=|∇U|2. Given finite numerical precision, multidimensional minimization procedures will sample both absolute and low-lying minima which are referred to collectively as quasisaddles. The sensitivity of statistical properties of these quasisaddles to the convergence criteria of the minimization procedure is investigated using, as a test system, a simple liquid bound by a quadratically shifted Lennard-Jones pair potential. The variation in statistical properties of quasisaddles is studied over a range of error tolerances spanning five orders of magnitude. Based on our results, it is clear that there are no qualitative changes in statistical properties of saddles over this range of error tolerances and even the quantitative changes are small. The results also show that it is not possible to set up an unambiguous numerical criterion to classify the quasisaddles into true saddles which contain no zero curvature, nontranslational normal modes, and inflexion points which have one or more zero-curvature normal mode directions.
Field-effect detection of chemical species with hybrid organic/inorganic transistors
Authors: Bartic C. , Campitelli A. , Borghs S.
Published: January 2003

In this letter, we demonstrate that organic-based transistors are able to detect charged/uncharged chemical species in aqueous media via the field effect. The chemical sensitivity of the organic transistors is illustrated for protons and glucose. The electrochemical potential developed at the solution/dielectric interface depends on the proton concentration in solution and it modifies the current flowing in the transistor according to this concentration. Glucose can also be detected if an enzymatic layer is coupled to the dielectric surface. An inorganic proton-sensitive dielectric, Ta2O5, is used in the transistor structure in order to reduce the operational voltages. The field-effect detection of chemical species allows us to realize sensors for a variety of ions/molecules if layers with a specific functionality are added to the transistor. Organic-based sensing devices show great potential for low-cost, health-related, and environmental applications because of their very simple fabrication process, which leads to disposability.
Electronic rectification in protein devices
Authors: Rinaldi R. , Biasco A. , Maruccio G. , Arima V. , Visconti P. , Cingolani R. , Facci P. , De Rienzo F. , Di Felice R. , Molinari E. , Ph. Verbeet M. , Canters G. W.
Published: January 2003

We show that the electron-transfer protein azurin can be used to fabricate biomolecular rectifiers exploiting its native redox properties, chemisorption capability and electrostatic features. The devices consist of a protein layer interconnecting nanoscale electrodes fabricated by electron beam lithography. They exhibit a rectification ratio as large as 500 at 10 V, and operate at room temperature and in air.
Hydrogen molecular ion and molecule in two dimensions
Authors: Patil S. H.
Published: January 2003

We discuss some general properties of the wave functions of H2+ in two dimensions, when the electron is close to the nucleus, and when it is far away from the nucleus. Based on these properties, some simple, parameter-free wave functions are developed for some of the states. They lead to quite accurate energies and give an insight into the structure of H2+ in two dimensions. These wave functions and appropriate correlation functions, are then used to develop reliable wave functions for H2 in two dimensions. They provide a clear and interesting comparison with the corresponding results in three dimensions.
Organic single-layer white light-emitting diodes by exciplex emission from spin-coated blends of blue-emitting molecules
Authors: Mazzeo M. , Pisignano D. , Della Sala F. , Thompson J. , Blyth R. I. R. , Gigli G. , Cingolani R. , Sotgiu G. , Barbarella G.
Published: January 2003

We report on white electroluminescence (EL) emission from a single-layer light-emitting diode based on a binary blend of organic soluble blue-emitting molecules, i.e., a diamine derivative and a substituted thiophene-1,1-dioxide. Weakly voltage-dependent white color, of coordinates (0.39, 0.40) according to the standard of the Commission Internationale de l’Eclairage, is obtained from the superposition of the blue emission from the donor and a low-energy peak due to a charge-transfer complex between the two molecules (exciplex). The EL spectrum is broader and more structured than the photoluminescence one: this could be due to the activation of exciplexes with different conformations as inferred from quantum-chemistry calculations.
Time-dependent interplay between electron emission and fragmentation in the interatomic Coulombic decay
Authors: Scheit S. , Cederbaum L. S. , Meyer H.-D.
Published: January 2003

The electronic decay of the Ne2+ cation by electron emission is studied. This interatomic Coulombic decay (ICD) follows inner valence ionization of the neon dimer and the decay rate depends strongly on the internuclear distance. The time-dependent theory of wave packet propagation is applied allowing to follow the evolution of the decay process in time. The impact of nuclear dynamics on the decay spectrum is investigated. Among others, the spectrum corresponding to the decay of the 2 2Σu+ electronic state of the Ne2+ cation is calculated at different times. Its characteristics are found to be influenced considerably by the nuclear motion. A pronounced oscillatory structure appears: Its origin is explained and related to the interatomic nature of the ICD process. Particularly enlightening for the understanding of the ICD process is the analysis of the total energy distribution in the final system resulting after the fragmentation of the Ne22+ dication, produced by the ICD of Ne2+.
Locally coupled coherent states and Herman–Kluk dynamics
Authors: Child M. S. , Shalashilin D. V.
Published: January 2003

An exact analysis of coupled coherent state (CCS) theory in the moving locally quadratic Hamiltonian approximation is shown to reproduce both the linearized coherent state matrix element of the Herman–Kluk propagator and the coherent state overlap with Heller’s thawed Gaussian wave function. The derivation is applicable to anharmonic as well as harmonic systems, because the quadratic approximation is taken to apply only in the vicinity of a particular classical trajectory. New compact expressions for the linearized Herman–Kluk coherent state matrix element are given, and improvements for the practical application of CCS theory are discussed.
Photoelectron spectroscopy of Tin− clusters (n=1–130)
Authors: Liu Shu-Rong , Zhai Hua-Jin , Castro Miguel , Wang Lai-Sheng
Published: January 2003

Photoelectron spectra of cold Tin− anion clusters for n=1–130 were investigated at four detachment photon energies: 532, 355, 266, and 193 nm. Improved spectral resolution provides well-resolved electronic structures of the clusters, and the spectral evolution as a function of cluster size was probed systematically. Narrow and well-resolved spectral features were observed at n=13, 19, and 55, consistent with the high symmetry icosahedral structures proposed for these clusters. The measured electron affinities as a function of size in the studied size range do not extrapolate to the bulk work function, indicating that Ti clusters with n=130 may not assume the bulk structure.
Structural and electronic properties of small titanium clusters: A density functional theory and anion photoelectron spectroscopy study
Authors: Castro Miguel , Liu Shu-Rong , Zhai Hua-Jin , Wang Lai-Sheng
Published: January 2003

Density functional theory calculations using the generalized-gradient approximation have been carried out on the structural and electronic properties of Tin− and Tin clusters for n=3–8 and 13. Many low-lying states, of different spins and geometries, were found for each Tin− and Tin species. We observed that the calculated density of states (DOS) and the adiabatic electron binding energies for the ground state of a given anion are in good agreement with experimental photoelectron spectroscopy (PES) data, lending credence to the assignments of the ground state structures. Comparison between the calculated DOS and the PES data for other low-lying states made it possible to affirm contributions of these states to the spectra, allowing the characterization of the ensemble or composition of a given Tin− system. We found that all the clusters possess highly compact structures, and Ti7 and Ti13 have distorted pentagonal bipyramidal and icosahedral structures, respectively. From the ground state spin states, insight into the magnetic properties of the clusters and their evolution with size was also obtained. Small Ti clusters with n<5 are highly magnetic, but the magnetic moment drops rapidly with size.
Spectroscopically determined potential energy surface of H216O up to 25 000 cm−1
Authors: Shirin Sergei V. , Polyansky Oleg L. , Zobov Nikolai F. , Barletta Paolo , Tennyson Jonathan
Published: January 2003

A potential energy surface for the major isotopomer of water is constructed by fitting to observed vibration–rotation energy levels of the system using the exact kinetic energy operator nuclear motion program DVR3D. The starting point for the fit is the ab initio Born–Oppenheimer surface of Partridge and Schwenke [J. Chem. Phys. 106, 4618 (1997)] and corrections to it: both one- and two-electron relativistic effects, a correction to the height of the barrier to linearity, allowance for the Lamb shift and the inclusion of both adiabatic and nonadiabatic non-Born–Oppenheimer corrections. Fits are made by scaling the starting potential by a morphing function, the parameters of which are optimized. Two fitted potentials are presented which only differ significantly in their treatment of rotational nonadiabatic effects. Energy levels up to 25 468 cm−1 with J=0, 2, and 5 are fitted with only 20 parameters. The resulting potentials predict experimentally known levels with J⩽10 with a standard deviation of 0.1 cm−1, and are only slightly worse for J=20, for which rotational nonadiabatic effects are significant. The fits showed that around 100 known energy levels are probably the result of misassignments. Analysis of misassigned levels above 20 000 cm−1 leads to the reassignment of 23 transitions.
Computation of molecular Hartree–Fock Wigner intracules
Authors: Besley Nicholas A. , O’Neill Darragh P. , Gill Peter M. W.
Published: January 2003

The computation of molecular Wigner intracules from Hartree–Fock wave functions using Gaussian basis functions is described. The Wigner intracule is a new type of intracule that contains information about both the relative position and momentum of the electrons. Two methods for evaluating the required integrals are presented. The first approach uses quadrature while the second requires summation of an infinite series.
The reaction HCl++CF4→HCF4++Cl: Implications for the heat of formation of CF3+
Authors: Ferguson Eldon E. , Miller Thomas M. , Viggiano A. A.
Published: January 2003

For some years there has been a dispute concerning the appearance energy of CF3+ from CF4 [AE(CF3+/CF4)], or alternatively, the ionization energy of CF3[IE(CF3)] or the heat of formation of CF3+[ΔfH(CF3+)]. In an earlier work [M. Tichy, G. Javahery, N. D. Twiddy, and E. E. Ferguson, Int. J. Mass Spectrom. Ion Processes 79, 231 (1987)] the reaction between HCl+ was used to support a low value, AE(CF3+/CF4)=14.2 eV. A remeasurement of this reaction over the temperature range 173–500 K shows that the original study was in error, both in the reported rate constant and the ion product. In the present work, the rate constant was found to be collisional, producing HCF4+. The rate constant for thermal decomposition of HCF4+ into HF+CF3+ was measured in the course of this work. These new measurements bring into harmony AE(CF3+/CF4) obtained from the HCl+ reaction and the value AE(CF3+/CF4)=14.67±0.04 eV reported by R. L. Asher and B. Ruscic [J. Chem. Phys. 106, 210 (1997)].
A monomers-in-dimers model for carboxylic acid dimers
Authors: Emmeluth Corinna , Suhm Martin A. , Luckhaus David
Published: January 2003

The OH stretching fundamental band system of carboxylic acid dimers is studied using acetic acid and its isotopomers as a model system. Comparing experimental jet spectra with multidimensional quantum mechanical calculations the origin of the extremely broad vibrational band structure (Δν̃≈800 cm−1) is found in strong anharmonic resonances involving the OH stretching vibration. Within an adiabatic picture of hydrogen bonding a new monomers-in-dimers model allows to analyze the observed vibrational band structure in terms of the anharmonic quantum dynamics of the CO2H functional group. The results are discussed in terms of the time-dependent population dynamics and its implications for the mode-specificity of the vibrational predissociation of the hydrogen bonds. On a subpicosecond time scale the intramolecular vibrational energy redistribution of the dimer remains effectively localized within the six-dimensional manifold of the internal vibrations of the carboxyl group, conserving its local CS symmetry.
Solution effects and the order of the helix–coil transition in polyalanine
Authors: Peng Yong , Hansmann Ulrich H. E. , Alves Nelson A.
Published: January 2003

We study helix–coil transitions in an all-atom model of polyalanine. Molecules of up to length 30 residues are investigated by multicanonical simulations. Results from two implicit solvent models are compared with each other and with that from simulations in gas phase. While the helix–coil transition is in all three models a true thermodynamic phase transition, we find that its strength is reduced by the protein–solvent interaction term. The order of the helix–coil transition depends on the details of the solvation term.
Non-Gaussian dynamics from a simulation of a short peptide: Loop closure rates and effective diffusion coefficients
Authors: Portman John J.
Published: January 2003

Intrachain contact formation rates, fundamental to the dynamics of biopolymer self-organization such as protein folding, can be monitored in the laboratory through fluorescence quenching measurements. The common approximations for the intrachain contact rate given by the theory of Szabo, Schulten, and Schulten (SSS) [J. Chem. Phys. 72, 4350 (1980)] and Wilemski–Fixman (WF) [J. Chem. Phys. 60, 878 (1973)] are shown to be complementary variational bounds: The SSS and WF approximations are lower and upper bounds, respectively, on the mean first contact times. As reported in the literature, the SSS approximation requires an effective diffusion coefficient 10 to 100 times smaller than expected to fit experimentally measured quenching rates. An all atom molecular dynamics simulation of an eleven residue peptide sequence in explicit water is analyzed to investigate the source of this surprising parameter value. The simulated diffusion limited contact time is ≈6 ns for a reaction radius of 4 Å for solvent viscosity corresponding to that of water at 293 K and 1 atm (η=1.0 cP). In analytical work, the polymer is typically modeled by a Gaussian chain of effective monomers. Compared to Gaussian dynamics, the simulated end-to-end distance autocorrelation has a much slower relaxation. The long time behavior of the distance autocorrelation function can be approximated by a Gaussian model in which the monomer diffusion coefficient D0 is reduced to D0/6. This value of the diffusion coefficient brings the mean end-to-end contact time from analytical approximations and simulation into agreement in the sense that the SSS and WF approximations bracket the simulated mean first contact time.
Continuum description of solvent dielectrics in molecular-dynamics simulations of proteins
Authors: Egwolf Bernhard , Tavan Paul
Published: January 2003

We present a continuum approach for efficient and accurate calculation of reaction field forces and energies in classical molecular-dynamics (MD) simulations of proteins in water. The derivation proceeds in two steps. First, we reformulate the electrostatics of an arbitrarily shaped molecular system, which contains partially charged atoms and is embedded in a dielectric continuum representing the water. A so-called fuzzy partition is used to exactly decompose the system into partial atomic volumes. The reaction field is expressed by means of dipole densities localized at the atoms. Since these densities cannot be calculated analytically for general systems, we introduce and carefully analyze a set of approximations in a second step. These approximations allow us to represent the dipole densities by simple dipoles localized at the atoms. We derive a system of linear equations for these dipoles, which can be solved numerically by iteration. After determining the two free parameters of our approximate method we check its quality by comparisons (i) with an analytical solution, which is available for a perfectly spherical system, (ii) with forces obtained from a MD simulation of a soluble protein in water, and (iii) with reaction field energies of small molecules calculated by a finite difference method.
Inelastic collision cross sections of CH(X 2Π) with He(1S) on new ab initio surfaces
Authors: Ben Abdallah D. , Jaidane N. , Ben Lakhdar Z. , Spielfiedel A. , Feautrier N.
Published: January 2003

Full close-coupled (CC) integral inelastic cross sections were determined for collisions between CH(X 2Π)(N′=1) and He. These calculations are based on new ab initio CEPA (coupled electron pair approach) potential energy surfaces computed by Abdallah et al. These theoretical CC cross sections confirm a previous prediction of preferential population of final states levels in which the electronic wave function of the CH molecule is antisymmetric with respect to reflection in the plane of the molecule. These results are compared with the experimental results of Macdonald et al. At all energies the discrepancies were in most cases less than 7% of the ratio of the sum of the cross sections for the four transitions into levels of nominal A″ reflection symmetry divided by the sum of the cross sections for the four transitions into levels of nominal A′ reflection symmetry. Nevertheless, there is substantial disagreement in the magnitudes of the ratios particularly for the transitions with larger inelasticity.
The excited electronic state of the silver–ammonia complex
Authors: Miyawaki Jun , Sugawara Ko-ichi
Published: January 2003

The first excited electronic state of the silver–ammonia 1:1 complex AgNH3 was studied by resonantly enhanced two-photon ionization. The complex was formed using laser ablation and cooled in a free jet expansion. The origin of the Ã 2E1/2–X̃ 2A1 band system located at 467 nm is redshifted by 8142 cm−1 from the corresponding 5p 2P1/2–5s 2S transition of Ag, indicating a significant stabilization upon electronic excitation. The splitting of the origins of the spin–orbit substates, E1/22 and E3/22, was determined to be 805 cm−1. The intermolecular stretching (ν3) overtones and their combination bands with the intermolecular bending (ν6) mode are observed for the E1/22 state, whereas only the ν3 mode appears in the E3/22–A12 bands. The vibronic assignment was supported by the spectrum of its deuterated isotopomer, AgND3. The vibrational frequencies of the ν3 and ν6 mode in the Ã 2E1/2 state of AgNH3 were determined to be 371 and 185 cm−1, respectively. The anomalously small frequency of the ν6 mode is explained as a result of Jahn–Teller interaction and spin–orbit interaction in the Ã 2E state.
Absolute total and partial cross sections for the electron impact ionization of diborane (B2H6)
Authors: Basner R. , Schmidt M. , Becker K.
Published: January 2003

We measured absolute partial cross sections for the formation of all singly charged positive ions formed by electron impact on diborane (B2H6) from threshold to 200 eV using a time-of-flight mass spectrometer. The absolute total ionization cross section of B2H6 was obtained as the sum of all measured partial ionization cross sections. Dissociative ionization resulting in thirteen different fragment ions was found to be the dominant ionization process, although we found evidence of the presence of the B2H6+ parent ion. The ion spectrum at all impact energies including in the energy region below 40 eV, which is of special interest for low-temperature plasma technology, is dominated by B2H5+, B2H4+, and B2H2+ fragment ions. The B2H5+ fragment ion has the largest partial ionization cross section with a maximum value of 2.87×10−16 cm2 at 60 eV. We also observed H+, H2+, and H3+ fragment ions, but no ion signals were found that can be attributed to the formation of doubly charged ions. Additional measurements using a sector-field mass spectrometer revealed that all fragment ions containing one boron atom (B+, BHy+, y=1–3) and H+ are formed with significant excess kinetic energy. The mass spectrum of ions formed by electron impact on B2H6 at 70 eV in our experiments revealed distinctly larger abundances of the fragment ions BH3+, BH2+, and BH+ than earlier mass spectrometric measurements.
The asymmetric dimer N2–O2: Characterization of the potential energy surface and quantum mechanical calculation of rotovibrational levels
Authors: Aquilanti V. , Bartolomei M. , Carmona-Novillo E. , Pirani F.
Published: January 2003

The potential energy surface for the N2–O2 system has been characterized through a combined analysis of scattering experiments and second virial coefficient data. A spherical harmonic expansion functional form has been used to describe the intermolecular features in the salient geometries of the complex and to account for the relative contributions arising from interaction components of different nature. The most stable geometry is an X conformation where the potential well exhibit a depth of −16.08 meV at a distance of 3.66 Å. In order to relate structure dynamics and spectroscopic features of this weakly bound asymmetric dimer, we carried out extensive calculations of the bound rotovibrational states permitted to the complex. Calculations have been carried out with both exact and approximate quantum mechanical methods, where, respectively, the Coriolis coupling is both included and neglected.
Equivalent core model: Extended theory and applications
Authors: Kryzhevoi Nikolai V. , Dobrodey Nickolay V. , Cederbaum Lorenz S.
Published: January 2003

The ability of the recently developed corrected equivalent core model (cECM) to predict properties of core hole states is examined for the CO molecule. It is shown that systematic corrections derived in this approach significantly improve the results of the conventional equivalent core model (ECM). This opens new possibilities to apply the equivalent core formalism to calculate the energy of core hole states which cannot be usefully done by the ECM itself. On the self-consistent-field level the predictions of geometry changes upon core ionization made by the cECM and those of direct core hole calculations are found to be very similar to each other. There exists, however, an appreciable difference between the total energies of the core hole states obtained in both approaches. A new procedure enabling us to improve the results of the cECM, in particular, to reduce this energy difference is proposed. In contrast to the cECM, where the corrections to the ECM energy are found by deriving the Hamiltonian HZ of the Z system from the Hamiltonian HZ+1 of the (Z+1) system, the corrections are straightforwardly obtained in this new method (c′ECM) by deriving HZ+1 from HZ. The importance of the various systematic corrections to the ECM is discussed.
Diffusion-controlled reactions with a binding site hidden in a channel
Authors: Dagdug Leonardo , Berezhkovskii Alexander , Bezrukov Sergey M. , Weiss George H.
Published: January 2003

The rate of a diffusion-controlled reaction with a buried binding site is smaller than the rate for the same site on the surface. We study the slowdown of the reaction rate when the site is hidden in a pore that connects two bulk media. On the assumption that the pore is cylindrical we derive an expression for the Laplace transform of the rate coefficient from which we infer the long-time limit of the reaction rate. This provides information on how the reaction rate depends on the channel radius, the location of the site, and the diffusion constant in the pore, which is allowed to differ from that in the bulk. The validity of approximations was checked by simulations that indicated excellent agreement between the analytical and and numerical results.
Semiclassical calculation of thermal rate constants in full Cartesian space: The benchmark reaction D+H2→DH+H
Authors: Yamamoto Takeshi , Miller William H.
Published: January 2003

Semiclassical (SC) initial-value representation (IVR) methods are used to calculate the thermal rate constant for the benchmark gas-phase reaction D+H2→DH+H. In addition to several technical improvements in the SC-IVR methodology, the most novel aspect of the present work is use of Cartesian coordinates in the full space (six degrees of freedom once the overall center-of-mass translation is removed) to carry out the calculation; i.e., we do not invoke the conservation of total angular momentum J to reduce the problem to fewer degrees of freedom and solve the problem separately for each value of J, as is customary in quantum mechanical treatments. With regard to the SC-IVR methodology, we first present a simple and straightforward derivation of the semiclassical coherent-state propagator of Herman and Kluk (HK). This is achieved by defining an interpolation operator between the Van Vleck propagators in coordinate and momentum representations in an a priori manner with the help of the modified Filinov filtering method. In light of this derivation, we examine the systematic and statistical errors of the HK propagator to fully understand the role of the coherent-state parameter γ. Second, the Boltzmannized flux operator that appears in the rate expression is generalized to a form that can be tuned continuously between the traditional half-split and Kubo forms. In particular, an intermediate form of the Boltzmannized flux operator is shown to have the desirable features of both the traditional forms; i.e., it is easy to evaluate via path integrals and at the same time it gives a numerically well-behaved flux correlation function at low temperatures. Finally, we demonstrate that the normalization integral required in evaluating the rate constant can be expressed in terms of simple constrained partition functions, which allows the use of well-established techniques of statistical mechanics.
Large area, high resolution, dry printing of conducting polymers for organic electronics
Authors: Blanchet Graciela B. , Loo Yueh-Lin , Rogers J. A. , Gao F. , Fincher C. R.
Published: January 2003

We show here that thermal imaging, a nonlithographic technique which enables printing multiple, successive layers via a dry additive process can be used in combination with tailored printable conductors in the fabrication of organic electronic devices. This method is capable of patterning a range of organic materials at high speed over large areas with micron size resolution and excellent electrical performance avoiding the solvent compatibility issues currently faced by alternative techniques. Such a dry, potentially reel-to-reel printing method may provide a practical route to realizing the expected benefits of plastics for electronics. We illustrate the viability of thermal imaging and imageable organics conductors by printing a functioning, large area (4000 cm2) active matrix backplane display circuit containing several thousand transistors.
Mechanism of linear and nonlinear optical effects of KDP and urea crystals
Authors: Lin Zheshuai , Wang Zhizhong , Chen Chungtian , Lee Ming-Hsien
Published: January 2003

First-principles calculations of the linear and nonlinear optical properties of KH2PO4 (KDP) and CO(NH2)2 are presented. The calculations are an extension of methods we developed earlier and applied to borate crystals. Electronic band structure obtained from a pseudopotential method is input to the calculation. For two crystals considered, the resulting indices of refraction, birefringence, and nonlinear optical coefficients are in good agreement with experiments. The origin of nonlinear effects has been explained through real-space atom-cutting analysis. For KDP, the contributions of PO4 groups to second-harmonic generation effect are dominant, and the hydrogen bonds contribute much more to birefringence. For both KDP and urea, the contributions from the virtual electron process to nonlinear optical responses are dominant.
Eley–Rideal reactions of H atoms with Cl adsorbed on Au(111): Quantum and quasiclassical studies
Authors: Quattrucci Joseph G. , Jackson Bret , Lemoine Didier
Published: January 2003

The Eley–Rideal reactions of H atoms with Cl adsorbed on Au(111) surfaces are examined. Electronic structure calculations based on density functional theory are used to construct a model potential energy surface. Both quantum and quasiclassical methods are used to compute reaction cross sections and product state distributions. Steering of the incident H atom towards the adsorbed Cl leads to relatively large reaction cross sections of 2–3 Å2. The product HCl in this strongly exothermic reaction has over an eV of energy in vibrational motion, and a bit less than one eV each in rotation and translation.
Bond-forming reactions of dications: Production of ArO+ and ArO2+ in the reaction of Ar2+ with O2
Authors: Ascenzi Daniela , Franceschi Pietro , Tosi Paolo , Bassi Davide , Kaczorowska Malgorzata , Harvey Jeremy N.
Published: January 2003

We present cross sections as a function of the collision energy for the bond-forming reactions of argon dications with oxygen molecules, producing ArO2++O and ArO++O+, respectively. Both the reactions are exothermic, and have cross sections much smaller than those of the competitive charge-transfer processes. The low-lying electronic states of ArO2+ have been calculated at the MR–AQCC/cc-pV5Z level. In contrast to previous results we found that the ground Σ-3 state has a local minimum. However, the estimated lifetime of this metastable state is too short to be detected in our setup. Thus the observed ArO2+ ions must be in the higher-lying Δ1 or Σ+1 states.
Decay dynamics of the vibrationally activated OH–CO reactant complex
Authors: Pond Bethany V. , Lester Marsha I.
Published: January 2003

The decay dynamics of the OH–CO reactant complex have been examined following infrared excitation in the OH overtone region using various IR pump–UV probe methods. The time scale for overall decay of the OH–CO (2vOH) complex has been bracketed between 0.19 and 5 ns through linewidth and direct time-domain measurements. The inelastically scattered OH (v=1) fragments exhibit a bimodal internal energy distribution, which reveals that vibrational predissociation proceeds through two pathways. The dominant inelastic decay channel involves vibrational energy transfer from OH to CO with little excess energy remaining for rotational excitation of the OH fragment, while a slower secondary channel releases most of the excess energy as OH rotational excitation. Intermolecular bending excitation of the OH–CO complex through combination bands results in increased rotational excitation of the OH fragments. The most probable OH product states display a strong lambda-doublet preference indicating that the singly occupied pπ orbital of OH is aligned perpendicular to the OH rotation plane following vibrational predissociation of the complex. These product states also minimize the translational recoil of the fragments and maximize the rotational angular momentum of the OH fragment. Abrupt cutoffs in the OH (v=1) fragment internal energy distributions are utilized to determine an upper limit for the ground state binding energy of OH–CO, D0⩽410 cm−1, which is in good accord with ab initio predictions. Finally, a comparison of infrared band intensities obtained using action and depletion detection methods suggests that geared bend and H-atom bend excitation may promote reactive decay of the OH–CO reactant complex.
A concerted variational strategy for investigating rare events
Authors: Passerone Daniele , Ceccarelli Matteo , Parrinello Michele
Published: January 2003

A strategy for finding transition paths connecting two stable basins is presented. The starting point is the Hamilton principle of stationary action; we show how it can be transformed into a minimum principle through the addition of suitable constraints like energy conservation. Methods for improving the quality of the paths are presented: for example, the Maupertuis principle can be used for determining the transition time of the trajectory and for coming closer to the desired dynamic path. A saddle point algorithm (conjugate residual method) is shown to be efficient for reaching a “true” solution of the original variational problem.
A density-functional theory for polymer liquids based on the interaction site model
Authors: Sumi Tomonari , Hirata Fumio
Published: January 2003

The density-functional theory (DFT) for molecular fluids [J. Chem. Phys. 115, 6653 (2001)] is extended to the case of polymer liquids. A system consisting of the ideal chains is employed as a reference system for the DFT, where many-body effects are considered as an effective field that acts on each site of the ideal chains. We derived a relation between the site–site pair distribution functions and the site–density distribution functions under a mean field arising from a single polymer molecule. An integral equation for the site–site pair distribution functions is obtained by the DFT, where the external field is taken to be the mean field. We propose an approximate expression of the intramolecular correlation functions for isolated single-polymer chains to take account for the excluded volume effects inside a polymer chain. The intramolecular correlation function considering the excluded volume effects was in qualitative agreement with those obtained from a simulation for liquid consisting of freely jointed tangent-soft-core chains. The site–density integral equation under the mean field, using the intramolecular correlation function, reproduces the simulation results for site–site pair distribution functions of the system of freely jointed tangent-soft-core chains.
Atomic scale fractal dimensionality in proteins
Authors: Medini Duccio , Widom Allan
Published: January 2003

The soft condensed matter of biological organisms exhibits atomic motions whose properties depend strongly on temperature and hydration conditions. Due to the superposition of rapidly fluctuating alternative motions at both very low temperatures (quantum effects) and very high temperatures (classical Brownian motion regime), the dimension of an atomic “path” is in reality different from unity. In the intermediate temperature regime and under environmental conditions which sustain active biological functions, the fractal dimension of the sets upon which atoms reside is an open question. Measured values of the fractal dimension of the sets on which the hydrogen atoms reside within the azurin protein macromolecule are reported. The distribution of proton positions was measured employing thermal neutron elastic scattering from azurin protein targets. As the temperature was raised from low to intermediate values, a previously known and biologically relevant dynamical transition was verified for the azurin protein only under hydrated conditions. The measured fractal exponent of the geometrical sets on which protons reside in the biologically relevant temperature regime is given by D=(0.65±0.1). The relationship between fractal dimensionality and biological function is qualitatively discussed.
Thermodynamically consistent equation of state of hard sphere fluids
Authors: Eu Byung Chan , Ohr Young Gie
Published: January 2003

The Wiener–Hopf technique has been been applied to solve the Ornstein–Zernike equation for hard sphere fluids and to calculate thereby a thermodynamically consistent equation of state. An analytic form of a thermodynamically consistent equation of state for hard sphere fluids is obtained in which the correlation range is treated as an adjustable parameter. With a suitable choice of the range parameter the equation of state presented is found to be numerically comparable to the Carnahan–Starling equation of state in accuracy.
An effective-colloid pair potential for Lennard-Jones colloid–polymer mixtures
Authors: Guzmán Orlando , de Pablo Juan J.
Published: January 2003

We propose an effective one-component model that accurately reproduces the colloid–colloid radial distribution function gcc(r) of a colloid–polymer mixture. The particles of this effective model interact through an effective potential ueff(r), obtained by inversion of the Ornstein–Zernike equation and a closure suited for fluids with repulsive cores. The consistency of this approach was tested by simulation of the effective one-component fluid and comparison to the original radial distribution function. The effective potential can be separated into a repulsive part (corresponding to the “bare” pair potential between colloids), and a depletion potential, v(r). The strength and range of v(r) are well represented by simple functions of the total volume fraction.
Macroscopic dynamics of ferronematics
Authors: Jarkova E. , Pleiner H. , Müller H.-W. , Brand H. R.
Published: January 2003

We derive the complete set of macroscopic dynamic equations for ferrofluids in the nematic liquid crystal phase under an external magnetic field. We include the magnetization as an independent dynamic degree of freedom. Special emphasis is laid on possible static and dynamic cross couplings between magnetization, director reorientations and flow. As examples we discuss the field dependence of the sound spectrum and the rheology of shear flow.
Quantal study of the exchange reaction for N+N2 using an ab initio potential energy surface
Authors: Wang Dunyou , Stallcop James R. , Huo Winifred M. , Dateo Christopher E. , Schwenke David W. , Partridge Harry
Published: January 2003

The N+N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground A″4 state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N+N2(J=0). The J–K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasiclassical calculation using a London–Eyring–Polanyi–Sato PES. Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate three-dimensional quantal dynamics study for the N+N2 reaction system and the ab initio PES reported here is the first such surface for N3.
Optical four wave mixing spectroscopy for multilevel systems coupled to multimode Brownian oscillators
Authors: Sung Jaeyoung , Silbey Robert J.
Published: January 2003

We generalize the multimode Brownian oscillator model for a two-level system to optical four wave mixing spectroscopy of a multilevel system, based on the recent work of Sung and Silbey [J. Chem. Phys. 115, 9266 (2001)]. For the Ohmic limit where the phenomenological Langevin equation becomes correct, we present exact expressions for energy-gap correlation functions in the strong damping case as well as in the weak damping case.
C
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dipolar-driven C13–13C recoupling without C13 rf irradiation in nuclear magnetic resonance of rotating solids
Authors: Takegoshi K. , Nakamura Shinji , Terao Takehiko
Published: January 2003

Two recently proposed C13–13C recoupling methods under magic angle spinning (MAS), resonant interference recoupling (RIR), and C13–1H dipolar-assisted rotational resonance (DARR), are examined on a common theoretical foundation using the average Hamiltonian theory. In both methods, a rf field is applied on not C13 but H1 to recouple the C13–1H dipolar interactions, and spectral overlap necessary to conserve energy for C13–13C polarization transfer is achieved by the C13–1H dipolar line broadening. While DARR employs time-independent C13–1H interactions recoupled by suitable rf irradiation to H1 spins, RIR uses time-dependent C13–1H interactions modulated appropriately by H1 rf irradiation. There are two distinct cases where C13–1H line broadening realizes C13–13C spectral overlap. For a pair of a carbonyl or aromatic carbon and an aliphatic carbon, spectral overlap can be achieved between one of the spinning sidebands of the former C13 resonance and the C13–1H dipolar powder pattern of the latter. On the other hand for a pair of spins with a small chemical shift difference, the two center bands are overlapped with each other due to C13–1H dipolar broadening. For the former, we show that both RIR and DARR occur in the first order, while for the latter, DARR recoupling is appreciable for time-independent C13–1H interactions. We refer to the former DARR as the first-order DARR recoupling and the latter as the second-order DARR. Experimentally, we examined the following C13–1H recoupling methods for DARR: H1 CW irradiation fulfilling a rotary-resonance condition or a modulatory-resonance condition, and H1 π pulses applied synchronously to MAS. For RIR, the FSLG-m2m¯m sequence is applied to H1. Several one-dimensional DARR and RIR experiments were done for N-acetyl[1,2-13C, 15N] DL-valine, and [2,3-13C] L-alanine. It was found that the polarization transfer rate for RIR is larger than that for DARR except for fast spinning, while the rate for DARR is less sensitive to the spinning speed. Further, we showed that the efficiency of the second-order DARR recoupling is not significantly less than that of the first-order DARR. Among the C13–1H recoupling methods examined, CW irradiation at the n=1 rotary-resonance condition is superior for DARR because it gives a larger C13–1H dipolar broadening, leading to broadband recoupling. We showed that a broadband-recoupling experiment with the first and the second-order DARR by CW irradiation at the n=1 rotary-resonance condition is applicable to signal assignment as well as structural determination of a multiply/uniformly C13 labeled molecule as demonstrated by two-dimensional C13–13C DARR polarization-transfer experiments of uniformly C13, N15-labeled glycylisoleucine.
Ferromagnetic spin coupling in the manganese trimer ion evidenced by photodissociation spectroscopy
Authors: Terasaki Akira , Briere Tina M. , Kulawik Maria , Minemoto Shinichirou , Tono Kensuke , Matsushita Akira , Kondow Tamotsu
Published: January 2003

The optical spectrum of the manganese trimer ion, Mn3+, was obtained by measurement of the photodissociation cross section in the photon-energy range between 1.43 and 4.13 eV. Analysis of the spectrum by quantum-chemical calculations derived its electronic and geometric structures. The geometric structure was found to be an isosceles triangle (C2v) with bond lengths of 3.03 Å and an apex angle of 144°. The ground electronic state was found to be B217. The electronic structure of the valence orbitals indicates that the chemical bond is formed weakly by the 4s electrons. The 3d electrons are localized on the atomic sites, as is suggested by the nonbonding nature of the nearly degenerate occupied orbitals. All of the local spins are in the majority-spin state, and give rise to a total spin magnetic moment as large as 16μB. The ferromagnetic nature is due to the weak binding among constituent atoms and to the strong 3d-4s exchange interaction in the manganese atom. This finding is in marked contrast to the antiferromagnetism of bulk manganese.
Optical spectroscopy of jet-cooled NiSi
Authors: Lindholm Ned F. , Brugh Dale J. , Rothschopf Gretchen K. , Sickafoose Shane M. , Morse Michael D.
Published: January 2003

The electronic states of gaseous diatomic NiSi have been investigated using the combined techniques of resonant two-photon ionization spectroscopy, dispersed fluorescence spectroscopy, and density functional computations. A single electronic band system, designated as the [18.0]1←X 1Σ+ system, has been found in the 17 500–19 500 cm−1 range, and three bands of this system have been rotationally resolved and analyzed. To shorter wavelengths, the spectrum becomes much more congested and intense, and four bands in this region have been rotationally resolved and analyzed as well. A dispersed fluorescence investigation has allowed the measurement of 17 vibrational levels of the ground state. Through this work, the ground state of Ni58Si28 is demonstrated to have Σ+1 symmetry, with r0=2.0316(4) Å, ωe=467.43(30) cm−1, and ωexe=2.046(21) cm−1. These results are in good agreement with the results of density functional computations performed on the ground state. Comparisons to AlCu and CuSi demonstrate that NiSi has a double bond, while these related molecules are best considered as having a single σ-bond.
Stress analysis of AlxGa1−xN films with microcracks
Authors: Rudloff D. , Riemann T. , Christen J. , Liu Q. K. K. , Kaschner A. , Hoffmann A. , Thomsen Ch. , Vogeler K. , Diesselberg M. , Einfeldt S. , Hommel D.
Published: January 2003

Thick AlxGa1−xN epilayer with microcracks grown by metalorganic vapor-phase epitaxy on a GaN buffer above a (0001) sapphire substrate was comprehensively characterized by spatially and spectrally resolved cathodoluminescence (CL) and micro-Raman (μ-Raman) spectroscopy. The variation of the CL line shift and the μ-Raman measurements between the microcracks are consistent with the interpretation that AlGaN is to a large extent stressed like a two dimensional film between the microcracks with nearly full relaxation close to the cracks. A satisfactory theoretical confirmation of this stress distribution was obtained by a three-dimensional finite-element application of the elasticity theory.
Association in a four-coordinated, water-like fluid
Authors: Peery Travis B. , Evans Glenn T.
Published: January 2003

A four-site, network forming fluid is investigated as a model for the thermodynamic and structural properties of water. Water is represented as a hard sphere with intermolecular association interactions between hydrogen and electron lone pair sites described using the sticky hard sphere limit. This primitive model is analyzed using Wertheim’s multidensity graph formalism within the ideal network approximation. Both the associated Ornstein–Zernike integral equation theory, under Percus–Yevick-type closure conditions, and first-order thermodynamic perturbation theory are used to derive analytical results, that mimic, at least qualitatively, some of the features of water. Equations of state, the isothermal compressibility, the heat of vaporization, the heat capacity, and the (classical) critical exponents are determined. The pair correlation function and the structure factor are derived, the latter displaying a prepeak at small k indicative of cluster formation. Both the thermodynamic and structural properties are expressible using the average number of hydrogen bonds per molecule Nhb, which is determined self-consistently within the theory.