bluuebunny/crossref_metadata_2025 huggingface dataset:
Unambiguous exchange-correlation energy density
Authors: Burke Kieron , Cruz Federico G. , Lam Kin-Chung
Published: July 2002

An exact exchange-correlation energy density is constructed using only knowledge of the density dependence of the exchange-correlation energy functional, EXC. The energy density does not depend on the choice of origin, and allows direct comparison between any functional approximation and the exact quantity. The asymptotic behavior of this energy density contains the exact ionization potential. The relative performance of approximation energy functionals is reflected in this energy density, i.e., the local approximation is moderately accurate, generalized gradient approximations work better, while hybrids with exact exchange work best. The intershell spike in atoms is highlighted in this energy density. The energy density can also be calculated for solids, and has implications for many areas of density-functional theory.
Role of the second-order memory function on the dielectric relaxation
Authors: Dı́az-Calleja R. , Sanchis M. J. , del Castillo L. F.
Published: July 2002

In this paper the use of the second-order memory function to represent experimental results of dielectric relaxation data of amorphous and glass forming materials is presented, and particularly, its interpretation in terms of the frequency dependence of the complex shear modulus, shear viscosity, and diffusion coefficient is pointed out. The method used for its evaluation is applied to consider the experimental results for three ester substances, and their particular features are discussed.
Photoproducts ejected from liquid surfaces: The importance of photochemical, diffusional, kinetic, and surface structural effects
Authors: Furlan Alan , Hall Gregory E.
Published: July 2002

Gas-phase products of liquid surface photochemistry in high vacuum were analyzed by time-of-flight/quadrupole mass spectroscopy. A thin liquid film of a long-chain alkyl iodide, C18H37I, dissolved in squalane (C30H62) was irradiated with nanosecond laser pulses at 275 nm. The photoproducts leaving the liquid after a low-fluence laser pulse (0.5 mJ/cm2) were I, HI, and I2. Since these species may desorb at times delayed by diffusion in the liquid phase, time-of-flight profiles were also recorded using a chopper wheel in front of the surface. This allowed a reconstruction of the time-dependent flux from the surface. The flight time distributions were compared to model calculations which take into account laser photolysis of C18H37I, diffusion and surface evaporation of I, HI, and I2, and the condensed-phase kinetics of radical reactions, and allow for a component of direct photodissociation of surface layer molecules, leading to hyperthermal I atoms. Simulations based on a comprehensive kinetic scheme are in good agreement with our measurements, with no specific surface processes other than evaporation of thermalized species formed at, or diffusing to the surface. However, compared to results previously found for liquid C2H5I, the caging of the geminate pair is much stronger in our system, and the fraction of I atoms promptly reacting to HI is smaller. The absence of prompt hyperthermal I fragments is interpreted by a preferential orientation of the C18H37I molecules in the topmost liquid layer with the I atom pointing into the liquid. The sensitivity of the method is discussed with respect to surface-specific processes, as well as primary and secondary radical reactions occurring in the bulk liquid.
Fractionated crystallization in a polydisperse mixture of hard spheres
Authors: Bartlett Paul
Published: July 2002

We consider the nature of the fluid–solid phase transition in a polydisperse mixture of hard spheres. For a sufficiently polydisperse mixture (σ>0.085) crystallization occurs with simultaneous fractionation. At the fluid–solid boundary, a broad fluid diameter distribution is split into a number of narrower fractions, each of which then crystallize. The number of crystalline phases increases with the overall level of polydispersity. At high densities, freezing is followed by a sequence of demixing transitions in the polydisperse crystal.
Unimolecular reaction dynamics from kinetic energy release distributions. III. A comparative study of the halogenobenzene cations
Authors: Urbain P. , Leyh B. , Remacle F. , Lorquet A. J. , Flammang R. , Lorquet J. C.
Published: July 2002

The translational kinetic energy release distribution (KERD) in the halogen loss reaction of the chloro-, bromo-, and iodobenzene cations has been experimentally determined in the microsecond time scale and theoretically analyzed by the maximum entropy method. The KERD is constrained by the square root of the translational energy, i.e., by the momentum gap law. This can be understood in terms of quantum-mechanical resonances controlled by a matrix element involving a localized bound state and a rapidly oscillating continuum wave function, as in the case of a vibrational predissociation process. The energy partitioning between the reaction coordinate and the set of the remaining coordinates is nearly statistical, but not quite: less translational energy is channeled into the reaction coordinate than the statistical estimate. The measured entropy deficiency leads to values of the order of 80% for the fraction of phase space sampled by the pair of fragments with respect to the statistical value. In the case of the dissociation of the chlorobenzene ion, it is necessary to take into account a second process which corresponds to the formation of the chlorine atom in the excited electronic state 2P1/2 in addition to the ground state 2P3/2. The observations are compatible with the presence of a small barrier (of the order of 0.12 eV) along the reaction path connecting the D̃ 2A1 state of C6H5Cl+ to the Cl(2P1/2)+C6H5+(X̃ 1A1) asymptote.
Structure and dynamics of 9-ethylfluorene-Arn van der Waals complexes
Authors: Pitts Jonathan D. , Knee J. L.
Published: July 2002

The neutral S1 excited state and the ion ground state of 9-ethylfluorene-Arn van der Waals complexes have been studied for n=1–3. Resonance enhanced multiphoton ionization spectroscopy of the S1 state of the argon clusters reveals multiple isomeric structures for each of the cluster sizes studies coupled with the two monomer conformations. The n=1 cluster shows three isomers, one of the symmetric 9-ethylfluorene and two of the unsymmetric. The n=2 clusters has four possible isomers all of which are assigned to a (1|1) conformation, although each represents a unique structure with different argon binding sites. The n=3 cluster collapses down to two dominate isomers, one for each conformation of the parent. Mass analyzed threshold ionization (MATI) spectroscopy was used to investigate the ion, as well as assisting in isomer assignment of the S1 spectrum. IVR and dissociation of the argon complexes have also been studied with MATI spectroscopy. Ab initio calculations are used to determine the binding energy for all conformers and isomers of the n=1 complex. These values are in excellent agreement with the experimentally bracketed values, and prove useful in isomer assignments. Redistribution of the 208 cm−1 band of the n=2 symmetric conformation shows dynamics suggesting interconversion of all isomers to a new unassigned structure. Preferential dissociation of the argon located on the ethyl chain side of the sym-9-ethylfluorene-Ar2 complex is observed in both isomers.
Crack propagation induced heating in crystalline energetic materials
Authors: Holmes W. , Francis R. S. , Fayer M. D.
Published: July 2002

A model is presented for time and spatial dependences of the heating of molecular vibrations and the possible initiation of chemical reaction from heat dissipated in the vicinity of a propagating crack in a molecular crystal. In the model, energy from a moving crack tip is released as phonons in proximity to the crack. Initially the phonons and the molecular vibrations are not in thermal equilibrium. Subsequently, there is a competition between excitation of molecular vibrations by multiphonon up-pumping and diffusion of phonons from the crack region. If the coupling between the locally hot phonon bath and the molecular vibrations is sufficiently large, a transitory high vibrational temperature will be achieved prior to eventual thermal equilibration with the bulk of the crystal. It is found that the peak vibrational temperature can be sufficiently high for a significant time period for chemical reactions to occur. The model calculates the local time-dependent vibrational temperature using reasonable values of the physical input parameters. For a crack tip moving near the speed of sound, the calculations show that vibrational temperatures can reach ∼800 K in 55 ps and exceed 550 K for ∼1 ns after the initial heating. This temperature change is sufficient to produce chemical reaction in a secondary explosive such as HMX, but given the duration and size of the heated region, a single crack should not result in self-sustaining chemical reaction. The role that cracks may play in shock sensitivity is discussed.
Ionization potentials of LinO (2⩽n⩽70) clusters: Experiment and theory
Authors: Lievens Peter , Thoen Peter , Bouckaert Steven , Bouwen Wim , Vanhoutte Frederik , Weidele Horst , Silverans Roger E. , Navarro-Vázquez Armando , von Ragué Schleyer Paul
Published: July 2002

We report on experimental and theoretical investigations of the ionization potentials and structures of lithium monoxide clusters. The clusters were produced by a laser vaporization source, laser ionized, and mass selected by a time-of-flight mass spectrometer. Threshold photoionization spectroscopy was performed using photon energies of 3–5.52 eV and 6.4 eV. Ionization potentials of LinO (2⩽n⩽70) were derived from the photoionization efficiency curves. The evolution of the ionization potentials as a function of cluster size shows distinct steps at n=10, 22, and 42, and a pronounced odd–even staggering up to n≈42. These steps are in agreement with the shell model for metallic clusters, provided that the oxygen atom localizes two of the lithium valence electrons while leaving the other valence electrons delocalized in a metallic cluster. For the small clusters (n<6), fine structure is observed in the threshold spectra, possibly due to the presence of isomeric states in the cluster beam. Geometries and relative stabilities of the smaller LinO clusters (2⩽n⩽8) were computed by means of density functional theory using the B3LYP functional, and adiabatic and vertical ionization potentials were calculated. A comparison with the experimental ionization potentials provides evidence for the greater importance of rigid geometrical structures over metal-like characteristics for the small clusters.
MRCI calculations on the helium dimer employing an interaction optimized basis set
Authors: van de Bovenkamp J. , van Duijneveldt F. B.
Published: July 2002

Multireference configuration interaction (MRCI) calculations are presented for the helium dimer employing a new, 301-orbital basis set consisting of a [8s]6p5d4f3g2h atom-centered set and a set of 3s3p2d2 f1g midbond functions. The basis was specifically designed to optimally describe the [self-consistent field+second-order Möller–Plesset (SCF+MP2)] He2 interaction energy (at R=4.0 bohr), using a procedure recently developed for calculations on the water dimer. The MRCI calculations employ an 78-configuration reference set, which is capable of reaching full CI quality. Using the difference between the limiting (coupled-cluster single double triple [CCSD(T)]) values of Klopper and Noga [J. Chem. Phys. 103, 6127 (1995)] and the present values in order to account for basis set incompleteness, the final He2 well depth is found to be ΔE(R=5.6)=−10.99±0.02 K while at R=4.0 bohr one finds 292.72±0.2 K. These values are in excellent agreement with the results of Komasa and Rychlewski [Mol. Phys. 91, 909 (1997)], obtained in variational calculations using explicitly correlated Gaussian-type geminal wave functions. This paper also considers the role of the Möller–Plesset polarization dispersion energy Edisp(20) as well as the correlated first-order interaction energy E(1), as arising in the symmetry-adapted perturbation theory (SAPT) theory, in determining the binding energy at different levels of correlation [MP2, MP3, CCSD(T) and 78-MRCI]. From these results it appears that the SAPT calculations of Korona et al. [J. Chem. Phys. 106, 5109 (1997)] incorrectly predicted significantly more attraction at both distances.
Intermolecular potential of carbon dioxide dimer from symmetry-adapted perturbation theory
Authors: Bukowski Robert , Sadlej Joanna , Jeziorski Bogumił , Jankowski Piotr , Szalewicz Krzysztof , Kucharski Stanisław A. , Williams Hayes L. , Rice Betsy M.
Published: July 2002

A four-dimensional intermolecular potential energy surface for the carbon dioxide dimer has been computed using the many-body symmetry-adapted perturbation theory (SAPT) and a large 5s3p2d1f basis set including bond functions. The SAPT level applied is approximately equivalent to the supermolecular many-body perturbation theory at the second-order level. An accurate fit to the computed data has been obtained in a form of an angular expansion incorporating the asymptotic coefficients computed ab initio at the level consistent with the applied SAPT theory. A simpler site-site fit has also been developed to facilitate the use of the potential in molecular dynamics and Monte Carlo simulations. The quality of the new potential has been tested by computing the values of the second virial coefficient which agree very well with the experimental data over a wide range of temperatures. Our potential energy surface turns out to be substantially deeper than previous ab initio potentials. The minimum of −484 cm−1 has been found for the slipped parallel geometry at the intermolecular separation R=3.54 Å and a saddle point at −412 cm−1 for the T-shaped configuration and R=4.14 Å. Three minima and two first-order saddle points have been located on the pairwise-additive potential energy surface of the CO2 trimer. The nonplanar structure of C2 symmetry has been found to be 48.8 cm−1 more stable than the cyclic planar form of C3h symmetry, in disagreement with experimental observation. It is suggested that the relative stability of the two isomers cannot be reliably determined by pairwise-additive potential and inclusion of three-body forces is necessary for this purpose.
The disilaketenyl radical (HSiSiO) in its ground and first excited electronic states
Authors: Brown Shawn T. , Yamaguchi Yukio , Schaefer Henry F.
Published: July 2002

The disilaketenyl (HSiSiO) radical, an isovalent isomer of the ketenyl (HCCO) radical, has been investigated theoretically using ab initio electronic structure theory. For the two lowest-lying electronic states (X̃ 2A″ and Ã 2A′) of HSiSiO, total energies and physical properties including equilibrium geometries, dipole moments, harmonic vibrational frequencies, and associated infrared (IR) intensities were predicted at the self-consistent-field (SCF) and configuration interaction with single and double excitations (CISD) levels of theory with a wide range of basis sets. At the CISD optimized geometries coupled cluster with single and double excitations (CCSD) and CCSD with perturbative triple excitations [CCSD(T)] energies were also determined. The ground and first excited electronic states of HSiSiO were predicted to be transplanar bent structures, while the linear 1 2Π state was found to be a saddle point with two imaginary vibrational frequencies. The X̃ 2A″ and Ã 2A′ states of HSiSiO are more distorted from linearity and more polar than the corresponding states of HCCO. In particular the HSiSiO ground state is predicted to have a peculiarly acute HSiSi bond angle of only 75°, almost suggesting an Si–Si bridging hydrogen. At the CCSD(T) level of theory with the largest basis set, Dunning’s cc-pVQZ, the first excited state was predicted to lie 36.3 kcal/mol (1.57 eV, 12 700 cm−1) classically above the ground state. With the same method the barriers to linearity were determined to be 45.2 kcal/mol (1.96 eV, 15 800 cm−1) for the ground state and 8.9 kcal/mol (0.39 eV, 3100 cm−1) for the first excited state, respectively. Due to their large dipole moments and relatively large vibrational infrared (IR) intensities, the two lowest-lying electronic states of HSiSiO may be suitable for IR spectroscopic studies, and the ground state for microwave spectroscopic investigations.
A new six-dimensional analytical potential up to chemically significant energies for the electronic ground state of hydrogen peroxide
Authors: Kuhn Bernd , Rizzo Thomas R. , Luckhaus David , Quack Martin , Suhm Martin A.
Published: July 2002

We report calculations of the electronic ground state potential energy surface (PES) of hydrogen peroxide covering, in an almost global fashion, all six internal degrees of freedom by two different ab initio techniques. Density functional theory (DFT) calculations using the Becke 3 parameter Lee–Yang–Parr (B3LYP) hybrid functional and multiconfigurational second order perturbation theory (CASPT2) calculations, both using large basis sets, are performed for a wide range of geometries (8145 DFT and 5310 CASPT2 single-point energies). We use a combined data set of mostly DFT with additional CASPT2 ab initio points and the complete CASPT2 surface to fit a total of four different 6D analytical representations. The resulting potentials contain 70–76 freely adjusted parameters and represent the ground state PES up to 40000 cm−1 above the equilibrium energy with a standard deviation of 100–107 cm−1 without any important artifacts. One of the model surfaces is further empirically refined to match the bond dissociation energy D0 for HOOH→2OH. The potentials are designed for energy regions accessible by vibrational fundamental and overtone spectroscopy including the dissociation channel into hydroxyl radicals. Characteristic properties of the model surfaces are investigated by means of stationary point analyses, torsional barrier heights, harmonic frequencies, low-dimensional cuts and minimum energy paths for dissociation. Overall good agreement with high-level ab initio calculations, especially for the CASPT2 based potentials, is achieved. The drastic change in geometry at intermediate O–O distances, which reflects the transition from covalent to hydrogen bonding, is reproduced quantitatively. We calculate fully 6D anharmonic zero point energies and ground state torsional splittings with the diffusion quantum Monte Carlo method in perfect agreement, within statistical error bars, with experiment for the CASPT2 based potentials. Variational vibrational calculations in the (4+2)D adiabatic approximation yield energy levels and torsional splittings from the ground state up to predissociative states, satisfactorily reproducing the experimental transition wavenumbers.
The reaction of O+(4S) and N2(X 1Σg+) revisited: Recoil velocity analysis of the NO+ product
Authors: Levandier Dale J. , Dressler Rainer A. , Chiu Yu-hui , Murad Edmond
Published: July 2002

The guided-ion beam method has been used to measure time-of-flight (TOF) spectra of the NO+ produced in the reaction of O+(4S) and N2(X 1Σg+). Particular care was taken to minimize the participation of the O+(2D,2P) metastables in the reactions, the success of which is validated by measuring the absolute cross section for the reaction as a function of collision energy in the near-thermal to 1.5 eV range. In this range, the cross section exhibits a region of low reactivity at near-thermal energies, which can be obscured by reactions of metastables and other effects, and a region of sharply increasing reactivity above a threshold of collision energy ≈0.3 eV. The velocity-transformed TOF spectra, at collision energies of 0.51 eV, 0.80 eV, 3.2 eV, and 6.3 eV, indicate two reaction mechanisms: in the first, product ions are scattered backward with inefficient translational to internal energy conversion; in the second, product ions arise from intermediate collision complexes with efficient translational energy conversion. The first mechanism is associated with the passage through the spin-forbidden doublet ground state N2O+ intermediate, while the second involves passage through an endothermic quartet intermediate.
Wave packet motion during thermalization of the relaxed excited state in the one-dimensional platinum dimethylglyoxime complex
Authors: Iwai Shinichiro , Kamata Toshihide , Murata Shigeo , Yamamoto Kaoru , Ohta Toshiaki
Published: July 2002

Pump–probe spectroscopic studies were made for a one-dimensional (1D) platinum dimethylglyoxime complex (Pt(dmg)2) under excitation in the exciton absorption band using 40 fs pulses. Oscillation with a period of 0.11 ps which is superimposed on the rise of the induced absorption due to the self-trapped exciton (STE) was found for the first time in this system. The oscillation damped with a time constant of 0.1 ps. In a previous work in which 150 fs pulses were used for excitation at various wavelengths, we found that the spectral shape of the induced absorption changed with time in 0.1–0.3 ps after instantaneous rise up. These results were reasonably explained by the formation and the thermalization of the STE. In the framework of the interpretation we have presented, the oscillation superimposed on the induced absorption is considered to originate from the wave packet motion of the STE during thermalization.
Quantum mechanical study of intramolecular vibrational energy redistribution in the third CH stretch overtone state in benzene
Authors: Rashev S.
Published: July 2002

The absorption spectrum and dynamical evolution of the third CH stretch overtone state CH(v=4) in benzene has been studied quantum mechanically using a completely symmetrized vibrational basis set, in terms of a combined local mode-normal mode description, including all 30 molecular vibrational modes in the calculations. The calculated spectrum in this work has a smaller bandwidth than spectra of benzene CH(v=4) obtained by other authors so far.
Tricapped tetrahedral Ag7: A structural determination by resonance Raman spectroscopy and density functional theory
Authors: Bosnick K. A. , Haslett T. L. , Fedrigo S. , Moskovits M. , Chan W-T. , Fournier R.
Published: July 2002

The resonance Raman spectrum of Ag7, mass selected out of a cation beam of sputtered silver, neutralized, and codeposited with solid Ar, is presented. By comparing the observed spectrum with one calculated using density functional theory one concludes the structure of the silver septamer to be a tricapped tetrahedron. A partial resonance Raman spectrum of Ag9 is also included. Both spectra are dominated by totally symmetric “breathing” modes at ∼165 cm−1 (as is also true for Ag5 [T. L. Haslett et al., J. Chem. Phys. 108, 3453 (1998)]). This frequency is close to the Debye frequency (156 cm−1) of solid silver, implying that the nature of the chemical bond in these silver clusters already approximates closely that which exists in bulk silver.
Enhanced photoluminescence in a novel photobleached dithienylbenzo[c]thiophene oligomer derivative
Authors: Tan Shida , Bhowmik Achintya K. , Thakur Mrinal , Lakshmikantham M. V. , Cava Michael P.
Published: July 2002

Photoluminescence of a novel dithienylbenzo[c]thiophene oligomer has been studied in detail. Significant enhancement of photoluminescence has been observed in the material after photobleaching. The bleached oligomer was observed to be stable over time and had a photoluminescence peak significantly blue shifted compared to the fresh material. UV-visible and FTIR spectroscopic analyses indicated photooxidation to be the origin of bleaching. Photoluminescence efficiencies have been measured for both fresh and photobleached solutions. The PL quantum efficiencies have been determined to be 92% for the photobleached material, and 9% for the fresh solution. Spectral narrowing was observed in solid films of the bleached oligomer for excitation with 1 nJ, 200 fs pulses at 400 nm.
Emission by collisional D2–He pairs at temperatures from 2 to 20 kK
Authors: Hammer Dominik , Frommhold Lothar
Published: July 2002

From the existing ab initio dipole surface of H2–He collisional complexes we calculate the collision-induced emission spectra of D2–He pairs for all possible rotovibrational transitions |vJ〉→|v′J′〉, with v and v′=0,…,20, for frequencies from 100 to 100 000 cm−1 and temperatures from 2000 to 20 000 K. The results are compared to the H2–He spectra calculated previously [D. Hammer, L. Frommhold, and W. Meyer, J. Chem. Phys. 111, 6283 (1999)] and isotope effects are investigated. While the general features of the spectra are similar, for D2–He the peak of the spectrum is shifted to lower frequencies and the intensities are smaller.
An evaluation of the semiclassical Herman–Kluk (HK) propagator for molecule–surface reactive scattering
Authors: McCormack Drew A.
Published: July 2002

The Herman–Kluk (HK) semiclassical propagator is applied to two-dimensional (2D) and four-dimensional (4D) activated reactive scattering of H2 from a Cu(100) surface. Flux analysis is used to calculate collision-energy-dependent reaction probabilities from the time dependence of the semiclassical wave function; several different variations of this analysis method are implemented. Direct comparison is made between the reaction probabilities calculated using the HK method, and numerically exact quantum results, as well as quasiclassical (QC) trajectory calculations. Although aspects of results obtained using the HK propagator are an improvement over the QC results—for example, reproduction of the quantum reaction threshold and quantum resonances—overall the HK reaction probabilities are no more accurate than the QC probabilities. Furthermore, the HK method is relatively expensive to apply, and the computational expense does not scale with dimension as favorably as might be expected. The reasons for this are discussed.
Light scattering by fluctuations within a nematic wetting layer in a isotropic phase of a liquid crystal
Authors: Sigel Reinhard , Strobl Gert
Published: July 2002

Wetting of a solid surface by a homeotropically oriented nematic layer in the isotropic phase of the liquid crystal CB8 is examined by static light scattering experiments under evanescent illumination. For angles of incidence between the critical angle of total internal reflection and a larger second critical angle, an enhanced off-specular scattering is observed, which can be attributed to orientational fluctuations within the surface layer. In contrast to the scattering of the isotropic bulk there is a marked dependence on the scattering vector component parallel to the interface. The effect is observable only within a range of 0.4 K above the clearing point. The second critical angle gives experimental access to the order parameter S(0) at the interface. By combination of the scattering data with ellipsometric measurements, the thickness of the layer at a temperature close to the clearing point is estimated to d=6.9 nm. This value is comparable to the isotropic bulk correlation length ξni=5.6 nm determined by conventional light scattering.
Monte Carlo simulations of diblock copolymer thin films confined between two homogeneous surfaces
Authors: Wang Qiang , Yan Qiliang , Nealey Paul F. , de Pablo Juan J.
Published: July 2002

Thin films of symmetric diblock copolymers confined between two hard, flat and homogeneous surfaces have been investigated by means of Monte Carlo simulations on a simple cubic lattice. For such simulations, the match between bulk lamellar period L0 and the simulation box size is crucial to obtain meaningful results. The simulations have been performed in an expanded grand-canonical ensemble, where the chemical potential and the temperature of the confined films are specified and the density is allowed to fluctuate. The dependence of morphology, density, and chain conformation in the confined films on the type of surfaces, surface separation, and the strength of surface-block interactions has been studied systematically. Our results are consistent with experimental findings.
The stability of nonequilibrium molecular dynamics simulations of elongational flows
Authors: Todd B. D. , Daivis Peter J.
Published: July 2002

We show that nonequilibrium molecular dynamics simulations of elongational flows are inherently unstable over long periods of time. This instability leads to a catastrophic nonequilibrium phase transition that destroy the true structure of the fluid. We identify the source of this instability as a lack of momentum conservation, resulting from numerical round-off errors. We show that this error grows exponentially in the direction of compression, and present two numerical recipes that involve only minor perturbations to the particle trajectories to guarantee momentum conservation.
Relativistic all-electron coupled-cluster calculations on Au2 in the framework of the Douglas–Kroll transformation
Authors: Hess Bernd A. , Kaldor Uzi
Published: July 2002

We report relativistic all-electron coupled-cluster calculations on the gold dimer, using methods based on the Douglas–Kroll transformation. We use basis sets comprising up to i-type functions and study the dependence of Re, De, and ωe on basis set size, correlation method, and basis set superposition error. It is found that the dispersion interaction (electron correlation) between the gold d shells is described satisfactorily only if basis sets with angular momenta up to at least h functions are used. Mo/ller–Plesset calculations up to fourth order tend to underestimate the bond distance, while averaged coupled-pair functional and coupled-cluster calculations including perturbative triples converge to molecular parameters close to experiment. Correlating the 5p semicore of the gold atoms is found to have a non-negligible contribution.
Chemisorption of NH3 on Si(100)-(2×1): A study by first-principles ab initio and density functional theory
Authors: Loh Zhi-Heng , Kang H. Chuan
Published: July 2002

The energetics involved in the chemisorption of NH3 on Si(100)-(2×1) have been examined using ab initio and nonlocal density functional theory. One- and two-dimer cluster models were employed to model the Si(100)-(2×1) surface. By using various exchange-correlation functionals and Gaussian split-valence basis sets, we have obtained the geometries of the molecularly adsorbed and dissociatively chemisorbed states, as well as the hitherto unreported geometry of the transition state which exists between the two states. The geometries of the various states have been rationalized based on either electrostatic or orbital interactions. In addition, calculations were also performed on models which contain a second-adlayer ammonia molecule to yield several possible geometries for the extrinsic precursor state. The extrinsic precursor ammonia binding energies for the various geometries found are in the range of 3.93–8.80 kcal/mol. The energetics of the chemisorption process and the binding energies of the extrinsic precursor ammonia are in good agreement with available experimental data.
Finite-size corrections to the free energies of crystalline solids
Authors: Polson J. M. , Trizac E. , Pronk S. , Frenkel D.
Published: July 2002

We analyze the finite-size corrections to the free energy of crystals with a fixed center of mass. When we explicitly correct for the leading (ln N/N) corrections, the remaining free energy is found to depend linearly on 1/N. Extrapolating to the thermodynamic limit (N→∞), we estimate the free energy of a defect-free crystal of particles interacting through an r−12 potential. We also estimate the free energy of perfect hard-sphere crystal near coexistence: at ρσ3=1.0409, the excess free energy of a defect-free hard-sphere crystal is 5.918 89(4)kT per particle. This, however, is not the free energy of an equilibrium hard-sphere crystal. The presence of a finite concentration of vacancies results in a reduction of the free energy that is some two orders of magnitude larger than the present error estimate.
Fluorescence and electronic absorption spectra of phthalan: Two-dimensional vibrational potential energy surface for the ring-puckering and flapping in the S1(π,π*) state
Authors: Bondoc Eugene , Sakurai Sachie , Morris Kevin , Chiang Whe-Yi , Laane Jaan
Published: July 2002

The ring-puckering and ring-flapping vibrations of phthalan in its S1(π,π*) electronic excited state have been studied using fluorescence excitation spectroscopy of jet-cooled molecules, dispersed fluorescence spectroscopy, and ultraviolet absorption spectroscopy. This electronic state has A1 symmetry resulting from a B2→B2 orbital transition. Thus type A absorption bands result from A1→A1 and B2→B2 transitions to the S1 vibronic levels. The ring-puckering levels for the S1(π,π*) electronic state were determined for both the flapping ground (vF=0) and excited states (vF=1) and these were used to calculate both one- and two-dimensional potential energy surfaces which fit the observed spectra. In the S1(π,π*) state phthalan was found to be planar and more rigid than in the ground state in terms of the puckering coordinate. However, the molecule is less rigid along the flapping coordinate. This study shows how several types of spectroscopy and computations must be used in conjunction with each other to attain a comprehensive analysis of the electronic excited state.
Microscopic calculation of surface-induced second-harmonic generation in crystals of para-nitroaniline
Authors: Malagoli M. , Munn R. W.
Published: July 2002

Previous results for surface linear optical response in centrosymmetric para-nitroaniline crystals are combined with literature values for the molecular first hyperpolarizability to calculate the surface-induced quadratic response. The average surface quadratic susceptibilities for incident light at a wavelength of 803 nm are calculated to be 71 and 50×10−22 m2 V−1 for different surface terminations normal to the [001] direction, and 9 and 7×10−22 m2 V−1 for different surface terminations normal to the [101] direction (the natural cleavage plane). The latter values are three orders-of-magnitude below that determined by Kobayashi and Kotani, consistent with their evidence for bulk second-harmonic generation from a new phase at the surface.
Self-diffusion and interaction of the polystyrene–polyisoprene blend in chloroform probed by quasielastic light scattering
Authors: Sun Z. , Wang C. H.
Published: July 2002

Solutions of an incompatible polystyrene (PS)–polyisoprene (PIP) blend dissolved in CHCl3 are investigated by light scattering as a function of total polymer concentration at a fixed composition in the semidilute regime. Two diffusive modes are observed in the intensity–intensity time-correlation function. As the total polymer concentration increases, it is found that the rate constant of the fast mode increases and that of the slow mode as well as the relative amplitude of the fast mode decrease. With the help of a theory developed in this laboratory, we deduce from the light scattering data the self-diffusion coefficients and the Flory–Huggins interaction parameter χF of the two polymers. The self-diffusion coefficients of both polymers decrease as the total polymer concentration increase. Meanwhile, the Flory–Huggins interaction parameter χF between PS and PIP in CHCl3 (equal to 0.017) is nearly independent of polymer concentration. After making corrections for the excluded volume effect between unlike polymer using polymer solution theory, we obtain from χF a net segment–segment interaction parameter χF0, which is rather close to that obtained from the solvent free dry blend.
Radiative and predissociative rates for NO A 2Σ+v′=0–5 and D 2Σ+v′=0–3
Authors: Luque Jorge , Crosley David R.
Published: July 2002

Two-photon laser-induced fluorescence of the NO A–X(0–5,0) and D–X(0–3,0) bands is used to obtain collision-free lifetimes of the A v′=0–5 and D v′=0–3 levels in a flow cell. The vibrational trend from NO A v′=0 to v′=3 is small, with radiative lifetimes between 205±7 to 184±8 ns, respectively, in agreement with recent calculations derived from branching ratio measurements and ab initio calculations. Rotationally resolved measurements in the NO A 2Σ+ and D 2Σ+ states reveal very different lifetime behavior for these nearly isoenergetic levels above the NO X 2Π state dissociation limit. The rotational lifetimes of A 2Σ+v′=4,5 and D 2Σ+v′=0 are basically constant with rotation. However, D 2Σ+v′=1, 2, and 3 have a strong rotational dependence, decreasing nearly threefold between N′=0 and 20. These observations suggest weak coupling with the ground-state continuum to be the most likely predissociation mechanism for the high A 2Σ+ levels, and rotational on heterogeneous (gyroscopic) predissociation by the C 2Π is the dominant mechanism for the D 2Σ+ state above v′=0. The collision-free lifetime of E 2Σ+v′=0 is 40±3 ns, and that for F 2Δv′=0 is 27±3 ns.
Normal modes of vibration of the C60 isotopomers C5912C13 and C5812C213
Authors: Soto J. R. , Calles A. , Morán-López J. L.
Published: July 2002

The vibrational excitation spectra of the isotopomers C5912C13 and C5812C213 has been calculated within the framework of a first principle calculation. The force constants between the carbon atoms we obtained by performing the second derivatives of the energy within the Hartree–Fock approximation. A comparison of the frequency shifts in the vibrational spectra produced by the isotopes with Raman spectroscopy experiments is also presented.
Polarized infrared study on the structure of two-dimensional nanoclusters of partially fluorinated long-chain fatty acid salts at ambient and elevated temperatures
Authors: Ren Yanzhi , Iimura Ken-ichi , Kato Teiji
Published: July 2002

Atomic force microscopy (AFM) images of the single monolayer of five partially fluorinated fatty acid salts [CF3(CF2)m(CH2)nCOO−]2Cd2+ [(m,n)=(7,10), (7,16), (7,22), (5,22), and (3,22)] transferred from aqueous Cd2+ subphase to solid substrate revealed that the molecules had assembled into monodispersed two-dimensional clusters of tens of nanometers, whose morphology developed systematically with (m,n). Polarized infrared measurements detected a corresponding change with (m,n) in the –(CF2)–m and –(CH2)–n orientation angles. It is found that the van der Waals interaction between the C–C–C trans zig–zag planes of adjacent hydrocarbon segments is the driving force for the cluster formation, while the overlapping interaction between the fluorocarbon tails of neighbor salt molecules is responsible for cluster compactness. Grazing incidence reflection absorption spectra of the (m,n)=(7,10) single monolayer recorded during temperature elevation from 25 to 150 °C show that heating has caused the hydrocarbon chain and the terminal C–CF3 axis to be gradually randomly oriented, while the carboxylate C2 symmetry axis and the fluorocarbon long axis to realign toward the substrate normal. It is discovered that the single monolayer has thermal memory and cyclic heating-cooling treatment can render an excellent thermal stability of 120 °C to the –(CH2)–10 and CF3(CF2)–7 orientations. The different thermal behavior of the corresponding five-layer Y-type LB films, reported by Naselli, Swalen, and Rabolt [J. Chem. Phys. 90, 3855 (1989)] was explained as due to the longitudinal interaction between the headgroups of adjacent layers.
Ultrahigh-vacuum multitechnique study of AuCN monolayers on Au(111) formed by electrochemical deposition
Authors: Yamada Taro , Sekine Rika , Sawaguchi Takahiro
Published: July 2002

The two kinds of monolayers of AuCN electrodeposited on Au(111), indexed (1.15×√3R−30°) and (1.41×2√3R−30°), have been subjected to x-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and high resolution electron energy loss spectroscopy (HREELS) as well as low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM) to determine the geometrical, electronic, and vibrational properties. The -AuCN- chain structure was taken into consideration. XPS yielded Au 4f signals from AuCN indicating fractional charges on the Au atom incorporated in AuCN. The UPS of AuCN/Au(111) was composed mainly of the Au orbitals with weak signals from CN orbitals, attributed by DV-Xα relativistic molecular orbital calculation. By HREELS, the C–N stretching frequencies were found to be 2140–2160 cm−1, which are consistent with the electronic structure. In the frequency region below 300 cm−1, loss peaks related to the Au–N bonds were seen. The structures of -AuCN- chains in the (1.15×√3R−30°) and (1.41×2√3R−30°) adlayers are discussed upon these new findings.
On reduction of two degrees of freedom Hamiltonian systems by an S1 action, and SO(1,2) as a dynamical group
Authors: Iwai Toshihiro
Published: July 2002

Reduction by an S1 action is a method of finding periodic solutions in Hamiltonian systems, which is known rather as the method of averaging. Such periodic solutions can be reconstructed as S1 orbits by pulling back the critical points of an associated ‘‘reduced Hamiltonian’’ on a ‘‘reduced phase space’’ along the reduction. For Hamiltonian systems of two degrees of freedom, a geometric setting of the reduction is already accomplished in the case where the reduced phase space is a two-sphere in the Euclidean space R3, and the reduced Hamilton’s equations of motion are Euler’s equations. This article deals with the case where the reduced phase space will be a two-hyperboloid in the three-Minkowski space, and the reduced Hamilton’s equations of motion will be Euler’s equations with respect to the Lorentz metric. This reduction is associated with SU(1,1) symplectic action on the phase space R4. As a consequence of this association the reduced Hamiltonian system proves to admit a dynamical group SO0(1,2). A well-known reduction by an S1 action occurs in the case of rotational-invariant Hamiltonian systems, which will be associated with SL(2,R) symplectic action on R4. It is shown that the reduction associated with SU(1,1) and with SL(2,R) are symplectically equivalent.
Linearization of nonlinear differential equations by means of Cauchy’s integral
Authors: Kröger Helmut
Published: July 2002

It is suggested to transform a class of nonlinear differential equations with a holomorphic type of nonlinearity into linear integrodifferential equations. The method is presented in detail for first-order ordinary differential equations. The transformed equation is studied and is found to have a unique solution with an analytical representation. In a numerical test calculation rapid convergence of an approximate solution of the linearized equation towards the reference solution is found. The method can be applied to higher-order ordinary and partial differential equations. The transformation can be generalized also to operator-valued differential equations.
Wigner quantum systems. Two particles interacting via a harmonic potential. I. Two-dimensional space
Authors: Kamupingene A. H. , Palev T. D. , Tsaneva S. P.
Published: July 2002

A noncanonical quantum system, consisting of two nonrelativistic particles, interacting via a harmonic potential, is considered. The center-of-mass position and momentum operators obey the canonical commutation relations, whereas the internal variables are assumed to be the odd generators of the Lie superalgebra sl(1,2). This assumption implies a set of constraints in the phase space, which are explicitly written in the paper. All finite-dimensional irreducible representations of sl(1,2) are considered. Particular attention is paid to the physical representations, i.e., the representations corresponding to Hermitian position and momentum operators. The properties of the physical observables are investigated. In particular, the operators of the internal Hamiltonian, the relative distance, the internal momentum, and the orbital momentum commute with each other. The spectrum of these operators is finite. The distance between the constituents is preserved in time. It can take no more than three different values. For any non-negative integer or half-integer l there exists a representation, where the orbital momentum is l (in units of 2ℏ). The position of any one of the particles cannot be localized, since the operators of the coordinates do not commute with each other. The constituents are smeared with a certain probability within a finite surface, which moves with a constant velocity together with the center of mass.
Path integration over compact and noncompact rotation groups
Authors: Böhm Manfred , Junker Georg
Published: July 2002

Applications of group theoretical methods in the path integral formalism of nonrelativistic quantum theory are considered. Analysis of the symmetry of the Lagrangian leads to the expansion of the short time propagator in matrix elements of unitary irreducible representations of the symmetry group. Identification of the coordinates with the group parameters transforms the path integral to integrals over the group manifold. The integration is performed using the orthogonality of the representations. Compact and noncompact rotation groups are considered, where the corresponding path integral is embedded in Euclidean and pseudo-Euclidean spaces, respectively. The unit sphere and unit hyperboloid may either be viewed as the group manifold itself or at least as a group quotient. In the first case Fourier analysis leads to an expansion in group characters. In the second case an expansion in zonal spherical functions is obtained. As examples the groups SO(n), SU(2), SO(n−1,1), and SU(1,1) are explicitly discussed. The path integral on SO(n+m) and SO(n,m) in bispherical coordinates is also treated.
A class of integrable potentials
Authors: Sen Tanaji
Published: July 2002

A class of time independent two-dimensional integrable potentials, all possessing an invariant of the same general form, is constructed. One of these potentials is superintegrable, its invariants realize the symmetry algebra sO(3) for negative energies, e(2) for zero energy, and sO(2,1) for positive energies. A transformation of coupling constants reveals that in parabolic coordinates this potential is the harmonic oscillator acted on by constant forces. This and another potential in the class may be considered as successive extensions of the Kepler potential. The analytic properties of these integrable systems in the complex time plane are also discussed.
Linear de Sitter gravity
Authors: Fronsdal C. , Heidenreich W. F.
Published: July 2002

It is shown that there are two equivalent field potentials for massless spin-2 fields in (3,2)–de Sitter space; a symmetric two-tensor and a three-tensor of mixed symmetry. Each theory carries two inequivalent Gupta–Bleuler triplets, which correspond to the two helicities. They differ in their behavior at spatial infinity. All four fields appear when writing linear conformal gravity in de Sitter space. Two of them describe the unitary conformal gravitons, and two describe part of the conformal ghost.
Detailed behavior of the phase-integral approximations at zeros and singularities of the square of the base function
Authors: Skorupski Andrzej A.
Published: July 2002

Approximate solutions to the one-dimensional time independent wave equation, called the phase-integral approximations, are analyzed in the vicinity of characteristic points. The approximations are of arbitrary order and are generated from an unspecified base function. The general theory is illustrated by examples involving the power and/or the exponential behavior of the square of the base function. In these cases simple estimates are derived for the integrals which define the accuracy of the phase-integral approximation, and the optimum approximation order is determined.
An infinite sum of products of Jacobi polynomials
Authors: Farrell R. A. , Gray E. P. , Hart R. W.
Published: July 2002

Starting with a formula by Noble [Proc. Cambridge Philos. Soc. 59, 363 (1963), Eq. (16)] for a certain sum of products of Jacobi polynomials, another sum of this type is evaluated.