bluuebunny/crossref_metadata_2025 huggingface dataset:
Random phase approximation for complex charged systems: Application to copolyelectrolytes (polyampholytes)
Authors: González-Mozuelos P. , de la Cruz M. Olvera
Published: July 2002

We study binary polyelectrolytes in the melt state and in concentrated solutions using the random phase approximation (RPA). We compute the thermodynamics and electrostatics of chemically linked polyelectrolytes chains into block copolymer molecules (copolyelectrolytes). Polyelectrolytes blends and copolyelectrolytes in the presence of free ions have Debye–Hückel-type effective monomer–monomer interactions, even when the polymer chains are not charged. Copolyelectrolyte of chemically linked chains of opposite charge in the absence of counterions, have ion–ion effective interactions characteristic of a dielectric medium, contrary to the case of polyelectrolyte blends where these effective interactions are Debye–Hückel type, even on the absence of free ions. The dielectric constant in such a diblock copolymer melt is proportional to the square of the degree of polymerization Np. In the reference state (without interactions) RPA assumes random walk statistics, which are nearly unperturbed in the dielectric; we find the scaling of the end-to-end vector square of a chain in the dielectric. We also discuss the physics of other copolyelectrolytes (polyampholytes).
Multiconfiguration self-consistent field quadratic response calculations of the two-photon transition probability rate constants for argon
Authors: Sundholm Dage , Rizzo Antonio , Jo/rgensen Poul
Published: July 2002

The two-photon transition probability rate constant for the transition from the ground state (1Se) to the 1De excited state of argon has been calculated by the means of multiconfiguration self-consistent field quadratic response methods. The rate constant for the 1De transition in the Hartree–Fock approximation is 0.119×10−50 cm4 s, while in the multiconfiguration Hartree–Fock calculation it is 0.191×10−50 cm4 s. The calculated rate constant is in an excellent agreement with the experimental rate constant of 0.205×10−50 cm4 s obtained as the sum of the rate constants for the transitions to the spin–orbit mixed 3p54p[3/2]J=2 (1De), 3p54p[5/2]J=2 (3De), and 3p54p′[3/2]J=2 (3Pe) states.
Exact solutions of regular approximate relativistic wave equations for hydrogen-like atoms
Authors: van Leeuwen R. , van Lenthe E. , Baerends E. J. , Snijders J. G.
Published: July 2002

Apart from relativistic effects originating from high kinetic energy of an electron in a flat potential, which are treated in first order by the Pauli Hamiltonian, there are relativistic effects even for low-energy electrons if they move in a strong Coulomb potential. The latter effects can be accurately treated already in the zeroth order of an expansion of the Foldy–Wouthuysen transformation, if the expansion is carefully chosen to be nondivergent for r→0 even for Coulomb potentials, as shown by Van Lenthe et al. [J. Chem. Phys. 99, 4597 (1993)] (cf. also Heully et al. [J. Phys. B 19, 2799 (1986)] and Chang et al. [Phys. Scr. 34, 394 (1986)]). In the present paper, it is shown that the solutions of the zeroth order of this two-component regular approximate (ZORA) equation for hydrogen-like atoms are simply scaled solutions of the large component of the Dirac wave function for this problem. The eigenvalues are related in a similar way. As a consequence, it is proven that under some restrictions, the ZORA Hamiltonian is bounded from below for Coulomb-like potentials. Also, an exact result for the first order regular approximate Hamiltonian is given. The method can also be used to obtain exact results for regular approximations of scalar relativistic equations, like the Klein–Gordon equation. The balance between relativistic effects originating from the Coulombic singularity in the potential (typically core penetrating s and p valence electrons in atoms and molecules) and from high kinetic energy (important for high-energy electrons in a flat potential and also for core-avoiding high angular momentum (d, f, and g states in atoms) are discussed.
Molecular dynamics study of nucleation and melting of n-alkanes
Authors: Esselink K. , Hilbers P. A. J. , van Beest B. W. H.
Published: July 2002

We present the results of computer simulations of the melting and crystallization behavior of n-alkanes, using the molecular dynamics technique. We study the effect of changing simulation parameters such as coupling to a heat bath, we determine the temperature interval in which crystallization occurs for decane, and we construct a table of crystallization and melting temperatures for the normal alkanes butane till dodecane. We introduce and apply a new method to identify crystalline regions and compute the crystallization rate of a nucleus. Size dependence of the crystallization rate and melting temperature is studied using nonane and decane. We believe that the concepts introduced here will help in studying the effect of various molecules and processes on melting and nucleation behavior better.
The effect of grid quality and weight derivatives in density functional calculations
Authors: Baker Jon , Andzelm Jan , Scheiner Andrew , Delley Bernard
Published: July 2002

Full density functional geometry optimizations on hydrogen peroxide and heptane/dimethyl pentane using six different numerical grids are presented. The grids vary in quality and gradients are calculated (1) assuming a fixed grid and no weight derivatives, and (2) with full allowance for a ‘‘moving’’ atom-centered grid and inclusion of the weight derivatives. The results clearly demonstrate that accurate energies and geometries can be obtained with around 3500 points per atom for medium-sized systems (up to say 30 atoms) without the necessity of including the weight derivatives. The latter only begin to influence the results for grids which are of insufficient quality to guarantee reliable values in any case.
Low-energy excitations in glass-forming aqueous lithium–chloride
Authors: Achibat T. , Duval E. , Dupuy-Philon J. , Jal J. F. , Prevel B. , Zorkani I.
Published: July 2002

Low frequency Raman and inelastic neutron scattering from glass-forming aqueous lithium chloride (LiCl,4H2O; LiCl,6H2O) are compared. The measurements were carried out from the vitreous to liquid states. The scattering from anharmonic oscillations (light scattering excess), which was separated from the one from harmonic vibrations, is zero in the vitreous state, and increases rapidly in the supercooled state. The frequency dependence of light-vibration coupling coefficient is linear for low-energy harmonic vibrations. It is different for anharmonic oscillations. From the frequency dependence of the density of vibrational states and the absence of light scattering excess in the glassy state, it is deduced that the structure is compact in the glassy state.
Formation of atomic cloth observed by Penning ionization electron spectroscopy
Authors: Ozaki Hiroyuki , Kasuga Mayumi , Tsuchiya Takao , Funaki Tsutomu , Mazaki Yasuhiro , Aoki Masaru , Masuda Shigeru , Harada Yoshiya
Published: July 2002

A single sheet of a clothlike macromolecule (atomic cloth; 4 Å thick) comprising the columns of polydiacetylene and polyacetylene chains alternately crosslinked to the rows of alkyl chains was prepared by the photopolymerization of 1,15,17,31-dotriacontatetrayne molecules laid flat in a monolayer. This process was monitored by Penning ionization electron spectroscopy.
Solid-fluid equilibrium in a nonlinear hard sphere triatomic model of propane
Authors: Shen W.-N. , Monson P. A.
Published: July 2002

We describe a study of the phase diagram of a nonlinear triatomic molecule with hard sphere interactions between the sites using isobaric ensemble Monte Carlo simulations. The model is constructed so as to serve as a hard sphere interaction site model of propane. Several different crystal structures were used to initialize the solid phase simulations. An apparently optimum crystal geometry was located by allowing the Monte Carlo simulation cell shape to fluctuate. The fluid phase was found to be stable over a range of volume fractions, which is 35% greater than for a system of hard spheres with the same molecular volume. The fractional density change on freezing is about 4%. When the free energy for the model is used in a generalized van der Waals theory of solid–fluid equilibrium it predicts low values of the triple point temperature and fractional density change on freezing which are qualitatively similar to those for propane.
Modern He–He potentials: Another look at binding energy, effective range theory, retardation, and Efimov states
Authors: Janzen A. R. , Aziz R. A.
Published: July 2002

We compare a number of helium–helium potentials with respect to their predictions of dimer binding energy, scattering length, effective range and Efimov states. We also study the effect of retardation on the ‘‘best’’ potential. All realistic potentials support a weakly bound dimer, while none supports an Efimov state. We agree with other authors that retardation decreases the binding energy by about 10%. Finally, we investigated the effect on the binding energy from the application of retardation over different ranges of separation. The precise effects of retardation at short range in realistic potentials require further study.
A periodic orbit analysis of the vibrationally highly excited LiNC/LiCN: A comparison with quantum mechanics
Authors: Prosmiti R. , Farantos S. C. , Guantes R. , Borondo F. , Benito R. M.
Published: July 2002

By constructing continuation/bifurcation diagrams of families of periodic orbits of LiNC/LiCN system the spectroscopy and dynamics for this species are deduced and compared with accurate quantum mechanical calculations up to 13 000 cm−1. The interesting phenomenon of the appearance of gaps in the continuation diagram of the principal family that corresponds to the bend motion is shown to occur in both isomers, LiNC and LiCN. Through semiclassical quantization a one to one correspondence of specific periodic orbits to certain eigenstates is demonstrated. One interesting example is the case of periodic orbits that are generated from a saddle-node bifurcation and describe rotations of the Li+ ion around the CN− fragment. The correspondence of these periodic orbits to regular rotating type eigenfunctions is shown, thus, demonstrating in a clear way the importance of the saddle-node bifurcations in locating localized wavefunctions in highly energized molecules.
Third-order nonlinear time domain probes of solvation dynamics
Authors: Joo Taiha , Jia Yiwei , Yu Jae-Young , Lang Matthew J. , Fleming Graham R.
Published: July 2002

Several closely related third-order nonlinear time-resolved spectroscopic techniques, pump/probe transient absorption, transient grating, and three pulse stimulated photon echo peak shift measurements, are investigated theoretically and experimentally. It is shown in detail, through the consideration of response functions and numerical simulations including both finite pulse durations and detuning from exact resonance, how the solvation dynamics are manifested in these third-order nonlinear time-resolved spectroscopies. It is shown that the three pulse stimulated photon echo peak shift measurement and the transient grating measurement can give accurate dynamical information, whereas transient absorption may not be a reliable technique for a study of solvation dynamics in some cases. The contribution of very slow or static (inhomogeneous) components to the dynamics, however, can only be obtained from the three pulse echo peak shift measurements. Comprehensive experimental measurements are presented to illustrate and corroborate the calculations. We show that it is possible to separate the intramolecular vibrational and solvent contributions to the dephasing (or optical lineshape). Furthermore it is shown that the solvation of polar solutes in polar protic solvents has rather universal characteristics. The initial ultrafast process, usually identified as an inertial response of solvent molecules, occurs on a ∼100 fs time scale, and is essentially identical in methanol, ethanol, and butanol. The amplitude of this ultrafast component does, however, decrease with increasing alcohol size in 1-alkanols. The diffusive (≳0.5 ps) regime of the solvation process shows a strong solvent dependence, and may be described satisfactorily by dielectric relaxation theories.
Dielectric study on coupling constant of lower critical solution of poly (vinylmethylether) in water
Authors: Shinyashiki Naoki , Matsumura Yasuhide , Mashimo Satoru , Yagihara Shin
Published: July 2002

Dielectric relaxation measurements by time domain reflectometry were performed on a lower critical solution of poly (vinylmethylether) in water over a frequency region from 100 kHz to 10 GHz and at temperatures between 5 °C and the phase separation temperature TP. Two relaxation peaks could be observed. One observed around 10 GHz is caused by reorientation of water molecules and the other observed at 10–100 MHz is due to a micro-Brownian motion of polymer chain. Absorption and dispersion curves of the latter process can be fitted well to those calculated by the coupling model. Coupling constant n observed increases with temperature. This is the first finding and gives an evidence of validity of the coupling model.
The motion of protons in water–ammonia clusters
Authors: Cheng Hai-Ping
Published: July 2002

The dynamics of clusters (H2O)nH+ (n=1,2,3,4) interacting with an NH3 molecule has been studied by first-principles Born–Oppenheimer molecular dynamics (BOMD) simulations. These small clusters are chosen as prototype systems for studying the mechanisms of proton transfer at atomistic level. We focus on the fundamental steps of proton motion in molecular clusters, the dynamical consequences of proton affinities, and the interplay between proton motion and proton affinity in these systems. A characteristic feature of the motion, the forming and breaking of O–H bonds in H3O+ is analyzed in detail. The transfer process is found to be consecutive along a quasi-one-dimensional channel. The umbrella mode in NH3 can easily be excited to direct the lone pair of the ammonia molecule to the water clusters. The hydronium ion, however, reorients mainly via rotation. When NH3 reaches one terminal water molecule of a protonated water cluster, the system undergoes a series of intermediate states in which the mobile protons travel within the water clusters, H3O+ transients are formed as protons approach individual water molecules. The lifetime of the H3O+ transient is 8–20 fs, or 1–3 vibrational periods of the O–H stretch mode. Proton transfer is observed for n=1, 2, 3, although for n=3 NH+4(H2O)3 is in existence with NH3(H2O)2H+. For n=4, NH3(H2O)4H+ is the dominant statistical configuration. Vibrational spectrum of NH3(H2O)4H+ is analyzed in detail. The features of the spectrum can be used, in principle, to probe the proton motion in the transition state region reactions. In these calculations, the electronic charge distribution is calculated concurrently with the nuclear dynamics. An analysis of isocharge density surfaces gives qualitative and quantitative descriptions of the dynamics of electronic redistribution. The BOMD is performed in the framework of density functional theory with local spin density and generalized gradient approximations.
Large-scale calculations of excitation energies in coupled cluster theory: The singlet excited states of benzene
Authors: Christiansen Ove , Koch Henrik , Halkier Asger , Jo/rgensen Poul , Helgaker Trygve , Sánchez de Merás Alfredo
Published: July 2002

Algorithms for calculating singlet excitation energies in the coupled cluster singles and doubles (CCSD) model are discussed and an implementation of an atomic-integral direct algorithm is presented. Each excitation energy is calculated at a cost comparable to that of the CCSD ground-state energy. Singlet excitation energies are calculated for benzene using up to 432 basis functions. Basis-set effects of the order of 0.2 eV are observed when the basis is increased from augmented polarized valence double-zeta (aug-cc-pVDZ) to augmented polarized valence triple-zeta (aug-cc-pVTZ) quality. The correlation problem is examined by performing calculations in the hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3, as well as by using the CCSDR(3) perturbative triples corrections. The effect of triple excitations are less than 0.2 eV for all excitations except for the 2 1E2g state. The calculated excitation energies are compared with experiment and other theoretical results.
Collision effects in nitrogen and methane coherent anti-Stokes Raman isotropic Q-branch spectra at high densities
Authors: Ridder M. , Suvernev A. A. , Dreier T.
Published: July 2002

Using coherent anti-Stokes Raman spectroscopy (CARS) the spectral shift and width of the collisionally narrowed Q-branch structures of nitrogen and the ν1 symmetric stretch vibration in methane were investigated at high densities. The gas samples either contained the pure substance or, for the case of nitrogen and methane, were diluted with argon, methane and carbon monoxide or argon and nitrogen, respectively, in the pressure range 50–2000 bar and at temperatures between 300 and 700 K. The simultaneous recording of spectra at ambient conditions ensured a frequency measurement accuracy of 0.07 cm−1. Contributions to the line shapes and frequency shifts are determined that originate from narrowing of the rotational structure and from vibrational dephasing in nitrogen, methane, and its mixtures. The results are compared with quasiclassical calculations of the band shape and shift to determine thermally averaged collision cross sections for energy relaxation and vibrational dephasing as a function of temperature. In the investigated density regime, for nitrogen the band shape is dominated by collisional narrowing. The peak position of the band does not strongly depend on composition of the sample and the maximum red shift of the Raman frequency diminishes with increasing temperature. For methane at densities above 50 amagat effects from rotational relaxation are no longer detectable and dephasing collisions are dominant. In addition to vibration–translation relaxation, vibrational energy transfer is an important process for line broadening at high densities. The frequency shift of the Q-band strongly depends on mixture composition and temperature.
Molecular dynamics simulations of a fully hydrated dipalmitoylphosphatidylcholine bilayer with different macroscopic boundary conditions and parameters
Authors: Tieleman D. P. , Berendsen H. J. C.
Published: July 2002

We compared molecular dynamics simulations of a bilayer of 128 fully hydrated phospholipid (DPPC) molecules, using different parameters and macroscopic boundary conditions. The same system was studied under constant pressure, constant volume, and constant surface tension boundary conditions, with two different sets of charges, the single point charge (SPC) and extended single point charge (SPC/E) water model and two different sets of Lennard-Jones parameters for the interaction between water and methyl/methylene. Some selected properties of the resulting bilayer systems are compared to each other, previous simulations, and experimental data. It is concluded that in relatively high water concentration it is possible to use ab initio derived charges with constant pressure boundary conditions. The SPC water model gives a larger area per head group and a broader interface than the SPC/E model. Increasing the repulsion between water oxygens and CH2/CH3 groups has a large effect on the width of the interface and the area per head group. There is little difference between simulations with constant pressure and constant surface tension. The use of constant volume, using a reasonable estimate for the initial box dimensions, easily introduces artefacts.
Transition from an unstable synchronization state with transient oscillation cessations to spiral rotation in a coupled chemical oscillator system
Authors: Nishiyama Nobuaki , Matsuyama Tomoko
Published: July 2002

Spatiotemporal patterns of chemical wave propagation in the assemblies of nine cation-exchange beads loaded with the catalyst ferroin of Belousov–Zhabotinsky reaction are reported. The beads are immersed in the reaction mixture, on which periodic chemical waves are emerged. In the bead assemblies, abrupt changes of initiation site and direction of the periodic chemical waves were observed. In some cases, it was observed that transient oscillation cessations and the following rotating spiral wave occur.
Hybrid schemes combining the Hartree–Fock method and density-functional theory: Underlying formalism and properties of correlation functionals
Authors: Görling Andreas , Levy Mel
Published: July 2002

Hybrid schemes that combine elements of the Hartree–Fock and the Kohn–Sham procedures are shown here to have a rigorous formal basis within exact density-functional theory. Properties of the exact correlation energy and its functional derivative, corresponding to each hybrid scheme, are introduced and the correlation energy is expressed by a coupling constant integral. The coupling constant expansions of hybrid correlation energies are considered.
A high-resolution vacuum ultraviolet photoionization, photoelectron, and pulsed field ionization study of CS2 near the CS2+(X 2Π3/2,1/2) thresholds
Authors: Huang J.-C. , Cheung Y.-S. , Evans M. , Liao C.-X. , Ng C. Y. , Hsu C.-W. , Heimann P. , Lefebvre-Brion H. , Cossart-Magos C.
Published: July 2002

High-resolution photoionization efficiency (PIE) and pulsed field ionization photoelectron (PFI-PE) spectra for CS2 have been measured using coherent vacuum ultraviolet (VUV) laser radiation in the energy range of 81 050–82 100 cm−1. The PIE and threshold photoelectron (TPE) spectra for CS2 in the energy range of 80 850–82 750 cm−1 have also been obtained using synchrotron radiation for comparison with results of the VUV laser study. The analysis of the PIE spectra reveals three Rydberg series converging to the excited CS2+(2Π1/2) spin–orbit state. These series, with quantum defects of 1.430, 1.616, and 0.053, are associated with the [2Π1/2]npσu, [2Π1/2]npπu, and [2Π1/2]nfu configurations, respectively. The Stark shift effect on the ionization threshold of CS2 has been examined as a function of dc electric fields (F) in the range of 0.65–1071 V/cm. The observed F dependence of the Stark shift for the ionization onset of CS2 is consistent with the prediction by the classical adiabatic field ionization formula. The extrapolation of the ionization onset to zero F yields accurate values for IE[CS2+(X̃ 2Π3/2)]. This study shows that in order to determine accurate IEs and to probe autoionizing structures for molecular species by PIE measurements, it is necessary to minimize the electric field used for ion extraction. The assignment of Renner–Teller structures resolved in the VUV PFI-PE spectrum is guided by the recent nonresonant two-photon (N2P) PFI-PE and theoretical studies. The analysis of the PFI-PE spectrum also yields accurate values for IE[CS2+(X̃ 2Π3/2,1/2)]. Taking average of the IE values determined by VUV-PFI-PE, N2P-PFI-PE, and Stark field extrapolation methods, we obtain a value of 81 285.7±2.8 cm−1 for IE[CS2+(X̃ 2Π3/2)]. For IE[CS2+(2Π1/2)], we recommend a value of 81 727.1±0.5 cm−1 determined by the Rydberg series analysis. A theoretical simulation of the 2Π3/2(000) and 2Π1/2(000) VUV-PFI-PE band profiles reproduces the observed branching ratio of 1.9±0.3 for CS2+(X̃ 2Π3/2)/CS2+(2Π1/2). The relative intensities of vibronic structures observed in the VUV PFI-PE and TPE spectra are in agreement. Evidence is found, indicating that the strongly (Stark field induced) autoionizing Rydberg state, 17pσu, which is ≈10 cm−1 below the IE of CS2, has a minor contribution to the observed profile for the X̃ 2Π3/2(000) PFI-PE band.
Reduced multireference CCSD method: An effective approach to quasidegenerate states
Authors: Li Xiangzhu , Paldus Josef
Published: July 2002

Standard multireference (MR) coupled cluster (CC) approaches are based on the effective Hamiltonian formalism and generalized Bloch equation. Their implementation, relying on the valence universal or state universal cluster Ansatz, is very demanding and their practical exploitation is often plagued with intruder state and multiple solution problems. These problems are avoided in the so-called state selective or state specific (SS) MR approaches that concentrate on one state at a time. To preserve as much as possible the flexibility and generality offered by the general MR CC approaches, yet obtaining a reliable and manageable algorithm, we propose a novel SS strategy providing a size-extensive CC formalism, while exploiting the MR model space and the corresponding excited state manifold. This strategy involves three steps: (i) The construction of a variational configuration interaction (CI) wave function within the singly (S) and doubly (D) excited state manifold, (ii) the cluster analysis of this CI wave function providing the information about the higher than pair cluster amplitudes, and (iii) the exploitation of these amplitudes in the so-called externally corrected CCSD procedure. This approach is referred to as the reduced MR (RMR) SS CCSD method and is implemented at the ab initio level and applied to several model systems for which the exact full CI results are available. These include two four electron H4 systems (usually referred to as the H4 and S4 models), an eight electron H8 model and the singlet-triplet separation problem in CH2. It is shown that the RMR CCSD approach produces highly accurate results, is free from intruder state problems, is very general and effective and applicable to both closed and open shell systems.
Infrared and Raman studies on high pressure phases of solid N2: An intermediate structural modification between ε and δ phases
Authors: Bini Roberto , Jordan Matthias , Ulivi Lorenzo , Jodl Hans J.
Published: July 2002

The vibrational properties of high pressure phases of solid nitrogen have been studied along several isobars between 30 and 300 K by infrared and Raman spectroscopy. The existence of an intermediate phase (δloc) between the high temperature δ and the low temperature ε phases has been confirmed. The analysis of the infrared spectrum in the fundamental region, combined to the knowledge of the Raman spectrum both in the fundamental and in the lattice region, furnishes direct information on the structural properties of the δloc phase. In the δloc phase the disklike molecules are ordered in fixed positions while the spherelike units behave as hindered rotors. An insight on the localization dynamics of the nitrogen molecules is given. A different structure from that of the δ phase is obtained from a group theoretical analysis of the observed Raman and infrared components. As to the ε phase, a temperature dependent reorganization of the molecules located on the faces of the rhombohedral cell is suggested.
A comparative study of anharmonicity and matrix effects on the complexes XH:NH3, X=F, Cl, and Br
Authors: Del Bene Janet E. , Jordan Meredith J. T.
Published: July 2002

Ab initio calculations have been performed to investigate the structures and infrared spectra of the complexes FH:NH3, ClH:NH3, and BrH:NH3, and the effects of the presence of inert gas atoms on structures and spectra. Two-dimensional MP2/6-31+G(d,p) potential energy surfaces were constructed for the complexes XH:NH3, and model two-dimensional Schrödinger equations were solved for the proton stretching and dimer (heavy-atom) stretching modes. Although all complexes have equilibrium structures characterized by traditional hydrogen bonds, their infrared spectra differ significantly. In FH:NH3 both the ground (v=0) and first excited state for the proton stretching mode (v=1) are confined to the potential well describing the equilibrium structure. In this case the harmonic approximation is appropriate, and matrix effects are unimportant. In ClH:NH3 the v=1 proton stretching vibration accesses the more polar, proton-shared region of the potential surface. Here the harmonic treatment leads to a significant overestimation of the experimental proton-stretching frequency. Significant improvement results from an anharmonic treatment, which shows some coupling between proton and dimer modes. The presence of rare gas atoms preferentially stabilizes the proton-shared region of the surface, lowering the energy of the v=1 state. Further improvement results if the MP2/aug’-cc-pVDZ potential energy surface is used. In BrH:NH3 the proton-shared region of the potential surface is accessible in both v=0 and v=1 vibrational states, and an anharmonic treatment is required to obtain reasonable agreement with experiment. In BrH:NH3 proton stretching and dimer stretching modes are highly coupled, and rare gas atoms have structural and spectral effects.
Ten-dimensional wave packet simulations of methane scattering
Authors: Milot R. , Jansen A. P. J.
Published: July 2002

We present results of wave packet simulations of scattering of an oriented methane molecule from a flat surface including all nine internal vibrations. At a translational energy up to 96 kJ/mol we find that the scattering is almost completely elastic. Vibrational excitations when the molecule hits the surface and the corresponding deformation depend on generic features of the potential-energy surface. In particular, our simulation indicate that for methane to dissociate the interaction of the molecule with the surface should lead to an elongated equilibrium C–H bond length close to the surface.
The role of sticking and reaction probabilities in hot-atom mediated abstraction reactions of D on metal surfaces by gaseous H atoms
Authors: Kammler Th. , Wehner S. , Küppers J.
Published: July 2002

Recent experiments on the abstraction of D adsorbed on metal surfaces with gaseous hydrogen atoms revealed a kinetics of HD formation which is not compatible with the operation of Eley–Rideal (ER) mechanisms. Furthermore, homonuclear products were observed during abstraction, which are not expected through an ER reaction scheme. It was therefore suggested that hot-atom (HA) mechanisms are more appropriate to explain the measured kinetics and products. Random walk calculations of the abstraction kinetics are presented based on a model which exclusively relies on elementary reaction steps which are HA mediated processes. Within this model, the ratio of two variables, the probabilities for hot-atom sticking at empty sites ps and hot-atom reaction with adsorbed species pr, was found to control the kinetics of HD and D2 formation. The essential features of measured kinetic data at Ni(100), Pt(111), and Cu(111) surfaces were reproduced by simple and reasonable assumptions on ps/pr.
Comparison of infrared and Raman wave numbers of neat molecular liquids: Which is the correct infrared wave number to use?
Authors: Bertie John E. , Michaelian Kirk H.
Published: July 2002

This paper is concerned with the peak wave number of very strong absorption bands in infrared spectra of molecular liquids. It is well known that the peak wave number can differ depending on how the spectrum is measured. It can be different, for example, in a transmission spectrum and in an attenuated total reflection spectrum. This difference can be removed by transforming both spectra to the real, n, and imaginary, k, refractive index spectra, because both spectra yield the same k spectrum. However, the n and k spectra can be transformed to spectra of any other intensity quantity, and the peak wave numbers of strong bands may differ by up to 6 cm−1 in the spectra of the different quantities. The question which then arises is “which infrared peak wave number is the correct one to use in the comparison of infrared wave numbers of molecular liquids with wave numbers in other spectra?” For example, infrared wave numbers in the gas and liquid phase are compared to observe differences between the two phases. Of equal importance, the wave numbers of peaks in infrared and Raman spectra of liquids are compared to determine whether the infrared-active and Raman-active vibrations coincide, and thus are likely to be the same, or are distinct. This question is explored in this paper by presenting the experimental facts for different intensity quantities. The intensity quantities described are macroscopic properties of the liquid, specifically the absorbance, attenuated total reflectance, imaginary refractive index, k, imaginary dielectric constant, ε″, and molar absorption coefficient, Em, and one microscopic property of a molecule in the liquid, specifically the imaginary molar polarizability, αm″, which is calculated under the approximation of the Lorentz local field. The main experimental observations are presented for the strongest band in the infrared spectrum of each of the liquids methanol, chlorobenzene, dichloromethane, and acetone. Particular care was paid to wave number calibration of both infrared and Raman spectra. Theoretical arguments indicate that the peak wave number in the αm″ spectrum is the correct one to use, because it is the only one that reflects the properties of molecules in their local environment in the liquid free from predictable long-range resonant dielectric effects. However, it is found that the comparison with Raman wave numbers is confused when the anisotropic local intermolecular forces and configuration in the liquid are significant. In these cases, the well known noncoincidence of the isotropic and anisotropic Raman scattering is observed, and the same factors lead to noncoincidence of the infrared and Raman bands.
Crystal-field splitting, magnetic interaction, and vibronic excitations of 244Cm3+ in YPO4 and LuPO4
Authors: Liu G. K. , Li S. T. , Zhorin V. V. , Loong C.-K. , Abraham M. M. , Boatner L. A.
Published: July 2002

The electronic and lattice-dynamical properties of 244Cm3+ doped orthophosphate crystals of YPO4 and LuPO4 were studied using site-selective fluorescence line narrowing (FLN) techniques. Although radiation damage caused substantial inhomogeneous line broadening, FLN gave rise to sharp resonant and satellite lines. Samples were annealed at 500 °C to eliminate satellite lines due to Cm3+ ions at different lattice environments. The crystal–field splitting of the nominal 8S7/2 ground state and the 6D7/2 excited state was determined from an analysis of the excitation and fluorescence spectra using an exchange charge model of crystal field interaction within the scheme of intermediate coupling. The effective g factors of the four Kramers doublets of the J=7/2 ground state and the lowest doublet of the excited state were evaluated from a least-squares fit of the observed Zeeman splitting to an effective-operator Hamiltonian. The energies of phonon modes were estimated from the observed vibronic spectra of the 244Cm3+ ion in both hosts and compared with the results of previous optical and neutron measurements.
Derivation of the Matalon-Packter law for Liesegang patterns
Authors: Antal T. , Droz M. , Magnin J. , Rácz Z. , Zrinyi M.
Published: July 2002

Theoretical models of the Liesegang phenomena are studied and simple expressions for the spacing coefficients characterizing the patterns are derived. The emphasis is on displaying the explicit dependences on the concentrations of the inner and the outer electrolytes. Competing theories (ion-product supersaturation, nucleation and droplet growth, induced sol-coagulation) are treated with the aim of finding the distinguishing features of the theories. The predictions are compared with experiments and the results suggest that the induced sol-coagulation theory is the best candidate for describing the experimental observations embodied in the Matalon-Packter law.
Solvation of cyclopentadienyl and substituted cyclopentadienyl radicals in small clusters. I. Nonpolar solvents
Authors: Fernandez J. A. , Yao J. , Bernstein E. R.
Published: July 2002

Cyclopentadienyl (cpd), methylcpd (mcpd), fluorocpd (Fcpd), and cyanocpd (CNcpd) are generated photolytically, cooled in a supersonic expansion, and clustered with nonpolar solvents. The solvents employed are Ar, N2, CH4, CF4, and C2F6. These radicals and their clusters are studied by a number of laser spectroscopic techniques: Fluorescence excitation (FE), hole burning (HB), and mass resolved excitation (MRE) spectroscopies, and excited state lifetime studies. The radical D1←D0 transition is observed for these systems: The radical to cluster spectroscopic shifts for the clusters are quite large, typically 4 to 5 times those found for stable aromatic species and other radicals. Calculations of cluster structure are carried out for these systems using parameterized potential energy functions. Cluster geometries are similar for all clusters with the solvent placed over the cpd ring and the center-of-mass of the solvent displaced toward the substituent. The calculated cluster spectroscopic shifts are in reasonable agreement with the observed ones for N2 and CF4 with all radicals, but not for C2F6 with the radicals. The Xcpd/Ar data are sacrificed to generate excited state potential parameters for these systems. CH4 is suggested to react with all but the CNcpd radical and may begin to react even with CNcpd. van der Waals vibrations are calculated for these clusters in the harmonic approximation for both D1 and D0 electronic states; calculated van der Waals vibrational energies are employed to assign major cluster vibronic features in the observed spectra.
Effect of pressure on fragility and glass transition temperature in fragile glass-former
Authors: Paluch M. , Hensel-Bielówka S. , Zioło J.
Published: July 2002

This paper presents the effect of pressure on liquid fragility in poly(bisphenol A-co-epichlorohydrin), glycidyl end capped. On the basis of temperature dependences of dielectric relaxation times measured for several different pressures, the steepness or fragility index mT has been calculated. We proved that liquid fragility is independent of pressure within experimental error. The influence of pressure on glass transition temperature has also been studied. It turned out that pressure dependence of glass transition temperature is well represented by the second-order polynomial.
Fractional approximations to the Bessel function J0(x)
Authors: Martín Pablo , Guerrero Antonio L.
Published: July 2002

A method to obtain fractional approximations to the Bessel function J0(x) is reported here. This method improves a recently published one principally in that all the parameters are uniquely determined by linear equations. Our approximations give fairly good accuracy for all real, positive values. The maximum absolute error for the first-degree approximation is about 0.0035, and for the fourth-degree one, about 2.8×10−6.
Conditions for the convolution of two Wigner distributions to be itself a Wigner distribution
Authors: Narcowich Francis J.
Published: July 2002

The convolution of two Wigner distribution functions (WDF’s) is always non-negative, but not always a WDF, as Jagannathan et al. [Phys. Lett. A 120, 161 (1987)] have shown. In this paper conditions are given that are sufficient, and probably necessary, for such a convolution to be a WDF, and a new characterization of Gaussian WDF’s is obtained as a by-product.
Mixed boundary conditions in quantum field theory
Authors: Luckock Hugh
Published: July 2002

When quantum field theory is formulated in terms of transition amplitudes between initial and final configurations, it is important to impose mathematically consistent boundary conditions on the fields. The choice of boundary conditions is also important when dealing with elliptic complexes and index theorems on bounded manifolds. Although Dirichlet and Neumann boundary conditions are adequate for many purposes, they are not always appropriate. However, a number of the remaining cases can be handled by imposing Dirichlet conditions on certain field components and Neumann conditions on the others. Quantum gravity and supergravity, spinor field theory, and various elliptic complexes all lend themselves to mixed boundary conditions of this sort. The mathematical significance of mixed boundary conditions is investigated, and a simple rule is obtained for determining which field components should obey which boundary conditions. It will be shown that gauge transformations on a bounded manifold give rise to intrinsic gauge transformations within the boundary. This result is used to define gauge-invariant and BRS-invariant quantum amplitudes for boundary configurations. The most general form for mixed boundary conditions on the Dirac operator and the de Rham complex will also be derived.
Finiteness of physics and its possible consequences
Authors: Lev Felix
Published: July 2002

The modular analog of representations of the so(1,4) algebra for a system of two spinless particles is considered in the framework of approach (proposed by the author earlier), in which physical systems are described by the elements of a linear space over a finite field, and operators of physical quantities by linear operators in this space. The eigenvalues of the free mass operator and corresponding eigenvectors are found. It is shown that if the finite field under consideration satisfies some properties then the particles necessarily interact with each other. The corresponding interaction is universal, since it is fully defined by the masses of particles and characteristics of the finite field. The formula for the kernel of the interaction operator is derived, but since the kernel is defined by the sum over the Galois field and this sum cannot be calculated explicitly, then it cannot be determined how far the above interaction manifests itself in the usual conditions.
On integrable models related to the osp(1,2) Gaudin algebra
Authors: Brzeziński T. , Macfarlane A. J.
Published: July 2002

The osp(1,2) Gaudin algebra is defined and integrable models described by it are considered. The models include the osp(1,2) Gaudin magnet and the Dicke model related to it. Detailed discussion of the simplest cases of these models is presented. The effect of the presence of fermions on the separation of variables is indicated.
Hypersymmetry: A ℤ3-graded generalization of supersymmetry
Authors: Abramov Viktor , Kerner Richard , Le Roy Bertrand
Published: July 2002

We propose a generalization of non-commutative geometry and gauge theories based on ternary ℤ3-graded structures. In the new algebraic structures we define, all products of two entities are left free, the only constraining relations being imposed on ternary products. These relations reflect the action of the ℤ3-group, which may be either trivial, i.e., abc=bca=cab, generalizing the usual commutativity, or non-trivial, i.e., abc=jbca, with j=e(2πi)/3. The usual ℤ2-graded structures such as Grassmann, Lie, and Clifford algebras are generalized to the ℤ3-graded case. Certain suggestions concerning the eventual use of these new structures in physics of elementary particles and fields are exposed.
Backscattering and inverse problem in random media
Authors: Shevtsov Boris M.
Published: July 2002

With use of the invariant imbedding method and Markov process approximation, the statistical characteristics of the backscattering field from the impulse point source in a nonstationary multidimensional random medium are considered. The equations for the characteristic function and the density of the probability in the functional space of the backscattering are obtained. The equations for the statistical moments of the field are yielded and then solutions are presented in the matrix form. The additional averaging of the fast field variations is used for the simplification of the statistical equations. The procedures for the investigation of the direct and inverse statistical problem are proposed. The role of the phenomenological transfer theory is discussed from the statistical point of view.
Nonisospectral scattering problems: A key to integrable hierarchies
Authors: Gordoa Pilar R. , Pickering Andrew
Published: July 2002

We show that certain partial differential equations associated to nonisospectral scattering problems in 2+1 dimensions provide a key to associated integrable hierarchies of both ordinary and partial differential equations. This is illustrated using (an extension of) a known second-order and two new third-order nonisospectral scattering problems. These scattering problems allow us to derive new hierarchies of integrable partial differential equations, in both 1+1 and 2+1 dimensions, together with their underlying linear problems (isospectral and nonisospectral); and also new hierarchies of integrable ordinary differential equations, again with their underlying linear problems.
An inverse scattering scheme for the regularized long-wave equation
Authors: Dye J. M. , Parker A.
Published: July 2002

The regularized long-wave (RLW) equation was proposed as an alternative model to the Korteweg–de Vries (KdV) equation to describe small-amplitude long waves in shallow water. However, unlike the KdV equation—which is exactly solvable by the inverse scattering method—the RLW equation is deemed not to be completely integrable. In this paper, an inverse scattering scheme is described for solving the RLW equation which is based on the “dressing method” of Zakharov and Shabat. Significantly, the compatibility of the “dressed” operators leads to two governing equations which, taken together, reduce to the RLW equation. One of these equations links the RLW equation to the (completely integrable) shallow water wave (ASWW) equation due to Ablowitz et al.; the second is a linear wave constraint that signals the nonintegrability of the RLW equation and prohibits the existence of multisoliton solutions. Contrary to results already reported in the literature, the proposed scheme associates the RLW equation with a third-order scattering problem. Moreover, as a special case of the RLW scheme, we obtain an inverse scattering procedure for the integrable ASWW equation; its formulation via the dressing method would appear to be given here for the first time. Explicit solutions are constructed for both equations using the respective inverse scattering schemes.
Analysis of thermodynamic properties of fullerite C60
Authors: Aksenova N. A. , Isakina A. P. , Prokhvatilov A. I. , Strzhemechny M. A.
Published: July 2002

The thermal expansion coefficients of pure fullerite are determined on the basis of powder x-ray studies in the temperature range 30–293 K. The obtained results are in good agreement with dilatometric and neutron-scattering data. The data on thermal expansion are used to analyze the heat capacity at constant volume CV. The intramolecular component of CV is analyzed consistently and accurately taking into account the complete set of temperature-dependent intramolecular eigenfrequencies. The rotational component of heat capacity is obtained by subtracting the intramolecular and phonon contributions from the total CV. The phonon component is evaluated on the basis of the Debye model using the Debye temperature (ΘD(0)=55.4 K) calculated from the known sound velocities. The general and partial Grüneisen parameters are calculated as functions of temperature. The results obtained for the high-temperature phase indicate that rotations of C60 molecules are strongly hindered and intercorrelated.