bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotationally inelastic collisions between a molecule in a 2S+1Σ electronic state and an open-shell target: General quantum analysis and experimental measurement of state-resolved cross sections for CaCl(X 2Σ+)+NO(X 2Σ)
Authors: Corey Gregory C. , Alexander Millard H. , Dagdigian Paul J.
Published: July 2002

The general quantum treatment for the scattering of molecules in 2S+1∑ electronic states by open-shell 2S atoms is investigated, with particular emphasis given to the influence of the open-shell character of the atomic perturber on the collisional propensity for conservation of the e/f molecular symmetry index. The molecule-state-resolved cross sections are expressed as a sum of spin-independent and spin-correlated terms. The spin-independent term is formally equivalent to the cross section for state-resolved transitions in a 2S+1∑-state molecule upon collision with a structureless target. The spin-correlated term is due solely to the electrostatic exchange forces arising from the open-shell nature of both the molecule and the atomic target. Recently calculated CaCl(X 2∑+)–Ar cross sections are used to investigate the extent to which e/f conservation depends on the relative magnitudes of these two contributions. Experimental state-to-state rotationally inelastic cross sections for the scattering of CaCl(X 2∑+) by the open-shell NO(X 2∏) molecule are presented and analyzed by means of this formalism.
Time-dependent self-consistent field (TDSCF) approximation for a reaction coordinate coupled to a harmonic bath: Single and multiple configuration treatments
Authors: Makri Nancy , Miller William H.
Published: July 2002

This paper explores the usefulness of the time-dependent self-consistent field (TDSCF) approximation for treating the dynamics of a reaction coordinate coupled to a bath of harmonic degrees of freedom. The reaction coordinate is a one-dimensional double well potential, typical of a hydrogen atom isomerization process. The standard (i.e., one configuration) TDSCF approximation is found to provide a very poor description of the effect of coupling to the bath on the isomerization rate. A multiconfiguration (MC-TDSCF) treatment is thus developed and found to provide a much improved description.
X-ray structural studies of freely suspended ordered hydrated DMPC multimembrane films
Authors: Smith G. S. , Sirota E. B. , Safinya C. R. , Plano R. J. , Clark N. A.
Published: July 2002

We have performed x-ray scattering studies of freely suspended, thick (∼2μ), oriented dimyristoyl–phosphatidyl–choline (DMPC)–water multilamellar films with the emphasis on the ordered phases. These stable films were drawn in situ on a triple axis x-ray spectrometer at a controlled, continuously variable temperature (T) and relative humidity (RH). The structure was determined at several temperatures and humidities and a T–RH phase diagram was constructed. We have found that the previously labeled ordered Lβ′ phase is in fact three distinct two-dimensional phases differentiated by the direction of chain tilt with respect to the in-plane lattice. The line shapes of the scattering data indicate that a lower limit of ∼200 Å may be placed on the in-plane chain–chain correlation length, while the chain positions are uncorrelated across the water layers.
Infrared spectra of hydrogen dimers
Authors: McKellar A. R. W.
Published: July 2002

Weakly bound complexes of molecular hydrogen have been studied using an infrared Fourier transform spectrometer and a long absorption path (112 m) through equilibrium gas mixtures at temperatures ∼20 K. Spectra of the dimers (H2)2, (HD)2, and (D2)2 were recorded, along with those of the mixed species H2–D2 and HD–D2. They lie in the 2900–8700 cm−1 (1.15–3.35 μm) spectral region corresponding to the monomer fundamental and first overtone bands. Since the rotation and vibration of the monomers remain largely unperturbed in a dimer, each dimer band is centered around a monomer rotation–vibration transition. The structure within these bands is associated with motions of the dimer as a whole, and particularly its end-over-end rotation, denoted by l. The spectra are quite detailed and well resolved, especially for the heavier isotopes HD–D2, and (D2)2, and in many cases, their rotational structure can be fully assigned. Although a detailed analysis is beyond the scope of the present paper, it should ultimately be possible to obtain precise multidimensional pair potential and induced dipole moment surfaces for molecular hydrogen directly from this experiment.
Surface-induced enhancement of internal structure in polymers and proteins
Authors: Wattenbarger M. R. , Chan H. S. , Evans D. F. , Dill K. A.
Published: July 2002

We study the conformations of chain molecules near interfaces by exhaustive simulation. We explore all the conformations accessible to a short isolated chain (16 monomers) on a 2-dimensional square lattice as a function of the distance of the center of mass of the chain from an interface. Our principal focus is on the ‘‘internal structure’’ of the chain, certain simple patterns of intrachain contacts such as helices and sheets (planar zigzags). In the process of enumeration, we confirm the well-known result that chains near interfaces have fewer conformations than chains in the bulk. We also find that the persistence length increases, and the radius of gyration and end-to-end length become anisotropic as the chain approaches the interface. The main conclusion of this work is that chain molecules are predicted to often have enhanced amounts of internal structure when they are at or near interfaces. Steric constraints imposed by the interface are selective and exclusive, eliminating open conformations but not eliminating compact conformations such as helices and sheets. Therefore when a polymer, protein, or peptide chain is weakly attracted to an interface, internal structure should be induced or, if already present, it should be enhanced. In 2 dimensions, stronger attraction in some cases flattens the chain and obliterates this structure.
Multiple steady states and dissipative structures in a circular and linear array of three cells: Numerical and experimental approaches
Authors: Marmillot Philippe , Kaufman Marcelline , Hervagault Jean-François
Published: July 2002

The steady-state behavior of a circular and linear array of three cells containing a substrate-inhibited-like kinetics catalyzed by immobilized thylakoids is studied. The photobiochemical reaction used to model the system is based on previous studies concerning a single and a two-cell system. In a general model all the cells in the array are considered to be continuously fed by the substrate and under diffusional relation with each others. Several models are then considered (circular and linear arrangements) depending upon the presence or the absence of these previous characteristics on each cell. The behavior of the various configurations is studied as a function of both the external substrate input concentration a0, and the ratio between the transport terms λ. The results given by bifurcation analysis and limit point continuation allows to determine three domains of stable stationary behavior: I, monostability; II, bistability and multistability; III, multistability and occurrence of dissipative structures. The existence of domain III is strictly dependent on the existence of a topological and functional symmetry in the arrangement. The experimental occurrence of both stable symmetric and asymmetric steady states in a circular and linear array of cells is also illustrated.
Hard particles in narrow pores. Transfer-matrix solution and the periodic narrow box
Authors: Kofke David A. , Post Albert J.
Published: July 2002

We derive an exact transfer-matrix solution for an infinite system of hard particles confined in a manner that precludes non-nearest-neighbor interactions. The solution takes the form of a functional eigenvalue equation which may be solved numerically for the thermodynamic and structural properties of the confined fluid. Barker [Aust. J. Phys. 15, 127 (1962)] originally derived this solution by a different route, and we apply it in a number of new ways. We present the first calculations based on this solution for systems of hard disks between parallel lines, and for hard spheres in a cylindrical pore. Through comparison with Monte Carlo simulations, we examine the range of validity of the solution when applied to systems in which non-nearest-neighbor interactions may occur. We find that the transfer-matrix approach provides acceptable results for pore widths up to two particle diameters, and that the approximation becomes quite poor as the pore is widened further, particularly at high density. This solution may be used to test the narrow-pore limit of more versatile theories of confined fluids. We further apply the solution to the so-called ‘‘periodic narrow box,’’ which has previously been solved in only two dimensions. We reproduce the two-dimensional result, and present the solution (which may be formulated explicitly rather than as an eigenvalue equation) for the three-dimensional, hard sphere version of the model. This simple model provides a remarkably accurate description of the thermodynamic behavior of a bulk hard sphere crystal.
Relativistic energies of the ground state of the hydrogen molecule
Authors: Wolniewicz L.
Published: July 2002

Relativistic corrections, Born–Oppenheimer energies and adiabatic corrections are computed for R ≤ 12.0 bohr for the electronic ground state of the hydrogen molecule. The Born–Oppenheimer potential is slightly lower than ever reported. The problem of linear dependencies in the basis set is removed and the same set is used for all internuclear distances which assures continuity of the results. The radiative corrections are evaluated approximately and—for that purpose—the polarizability of the molecule is also computed. Vibrational energies are computed and— corrected for nonadiabatic effects—compared with experiment for several isotopes. It is argued on the basis of the remaining discrepancies that an improvement in the ab initio nonadiabatic corrections is necessary.
Molecular dynamics results for stretched water
Authors: Ruocco G. , Sampoli M. , Torcini A. , Vallauri R.
Published: July 2002

Detailed computer simulation results of several static and dynamical properties of water, obtained by using a realistic potential model proposed by Jorgensen et al., in the supercooled region, at densities well below the coexistence curve, are reported. We have analyzed the structural properties by evaluating the volume distributions of Voronoi polyhedra as well as angular and radial distributions of molecular clusters. In particular, the homogeneity of the system has carefully been checked. The investigated dynamical properties mainly concern the density and temperature dependence of the diffusion coefficient. The results are compared both with previous simulations, performed with different models, and with experimental findings. Some differences stress the fact that the conclusions drawn on the physical process underlying density and temperature behavior, can strongly be influenced by the use of different potential models.
CH3SH ultraviolet absorption cross sections in the region 192.5–309.5 nm and photodecomposition at 222 and 193 nm and 296 K
Authors: Vaghjiani Ghanshyam L.
Published: July 2002

The absolute ultraviolet absorption cross sections of methyl mercaptan (CH3SH) have been determined in the wavelength region 192.5–309.5 nm at 296 K. The uv absorbance, A, in a column of slowly flowing standard CH3SH/helium gas mixtures, was monitored in long Pyrex absorption cells of path length, l, at several different pressures at the ambient cell temperature using a diode-array spectrometer with an instrumental resolution ranging from 0.25 to 1.10 nm. The absorption cross sections, σ=A/l[CH3SH], were calculated using the Beer–Lambert law from the known partial pressure of CH3SH in the gas mixture. The primary quantum yields of H atom produced in the 222 and 193 nm laser photolysis of CH3SH have been determined to be 0.95±0.10 and 0.49±0.08 relative to 248 nm CH3SH photolysis and 193 nm HBr photolysis, respectively, at 296 K. The H atoms were directly monitored in the photolysis by resonance fluorescence detection of H(2S).
Collision dynamics of OH(X 2Π, v=9)
Authors: Chalamala Babu R. , Copeland Richard A.
Published: July 2002

Collisional removal rate constants for the OH(X 2Π, v=9) radical are measured for the colliders O2, CO2, and N2O and upper limits are established for He, H2, Ar, and N2. OH(v=6) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to v=9 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the v=9 population is probed as a function of the collider gas partial pressure by a time-delayed pulsed ultraviolet laser. The probe laser light is resonant with the B 2Σ+–X 2Π(0,9) transition and the resulting visible B 2Σ+–A 2Σ+ fluorescence is detected with a filtered photomultiplier tube. We measure rate constants for N2O: (6.4±1.0)×10−11; CO2: (5.7±0.6)×10−11; O2: (1.7±1.1)×10−11; H2: <3×10−12; He: <2×10−12; N2: <5×10−13; Ar: <2×10−13 (all in units of cm3 s−1). For O2 and CO2 these rate constants are significantly faster than those for low vibrational levels and comparable to those for v=12.
Bound–bound A 2Σ+–X 2Π transition of NO–Ar van der Waals complexes
Authors: Tsuji Kazuhide , Shibuya Kazuhiko , Obi Kinichi
Published: July 2002

The bound–bound excitation spectrum of the NO–Ar van der Waals complex associated with the NO A 2Σ+–X 2Π transition has been measured by the resonance enhanced two-photon ionization (RE2PI) method using a time-of-flight (TOF) mass spectrometer. The van der Waals bands characterized by red-shaded rotational contours present no regularity in the progression. The photodissociation action spectra obtained by probing the NO A 2Σ+(v′=0, N′=1–8) products have also been measured, and the binding energies (D0) of the complex in the A 2Σ+ and X 2Π states are determined as 44 and 88 cm−1, respectively. The action spectrum corresponding to the NO A 2Σ+(v′=0, N′=1 and 2) product shows several shape resonance peaks, which implies that the intermolecular potential between NO A 2Σ+ and Ar has a potential barrier of about 24 cm−1.
Nonresonant two-photon pulsed field ionization of CH3S formed in photodissociation of CH3SH and CH3SSCH3
Authors: Hsu C.-W. , Ng C. Y.
Published: July 2002

Threshold photoelectron (PE) spectra for CH3S formed in the photodissociation of CH3SH and CH3SSCH3 in the photon energy range of 36 850–38 150 cm−1 have been measured using the nonresonant two-photon pulsed field ionization (N2P-PFI) technique. Both spin–orbit states CH3S(X̃ 2E3/2) and CH3S(2E1/2) are observed from CH3SH and CH3SSCH3 in this photodissociation energy range. However, negligible intensities of vibrationally excited CH3S radicals are produced from CH3SH. In the case of CH3S from CH3SSCH3, the population ratio CH3S(ν3=1)/CH3S(ν3=0) is estimated to be ≊0.18. The simulation of the N2P-PFI-PE spectra reveals that the rotational temperature for CH3S(X̃ 2E3/2,1/2) formed by photodissociation of CH3SH is ≊200–250 K and the branching ratio CH3S(2E1/2)/CH3S(X̃ 2E3/2) is 0.5±0.1. For CH3S(X̃ 2E3/2,1/2) produced from CH3SSCH3, the rotational temperature for CH3S(X̃ 2E3/2,1/2) is ≊800–900 K and the branching ratio CH3S(2E1/2)/CH3S(X̃ 2E3/2) is 1.1±0.2. This experiment demonstrates that the PFI-PE spectroscopic method can be a sensitive probe for nascent rovibronic state distributions of photoproducts. Furthermore, the simulation also shows that the photoionization dynamics of CH3S may involve rotational angular momentum changes up to ±4. The ionization energy and C–S stretching frequency for CH3S+(X̃ 3A2) are determined to be 74 726±8 cm−1 (9.2649±0.0010 eV) and 733±5 cm−1, respectively. The spin–orbit splitting for CH3S(X̃ 2E3/2,1/2) is 257±5 cm−1, in agreement with the literature values.
A molecular explanation of the transition from viscous to hopping mechanism of mass transport in the supercooled liquid near the glass transition
Authors: Bagchi Biman
Published: July 2002

When the viscosity of a supercooled liquid becomes large, the mechanism of mass transport is known to undergo a change from viscosity dependent, Stokes–Einstein behavior to an activated hopping dominated, almost viscosity independent behavior. This change is known to occur rather sharply near the temperature Tc where the mode coupling theory predicts singularities in the transport properties of the liquid. However, the origin of this change in the transport mechanism is not well-understood. Here we suggest a simple microscopic interpretation of this crossover. Our analysis is based on a scaled particle theory calculation of the activation energy for hopping and the non-Markovian rate theory of activated barrier crossing. We find that as the liquid is progressively supercooled, the activation barrier for hopping increases rapidly which makes the curvature at the barrier top also to increase. At high densities the latter gives almost a viscosity independent hopping rate which becomes more dominant at large viscosities where the collective diffusion becomes inefficient. The suddenness of the crossover is because as the density is increased, the hopping rate also decreases rapidly because of the increase in the activation energy, and a rapid increase in viscosity is required to tilt the balance in favor of the hopping mechanism. The latter can only happen at a dynamic singularity where the viscosity undergoes a sharp increase. The present analysis also offers an explanation of the decoupling of structural relaxation from the viscosity at large values of latter—such a decoupling has been suggested recently by Angell. Our analysis also provides a tentative explanation of the recent simulation results of Keyes and co-workers.
V–E energy transfer in ethylene and alkali gas mixtures using infrared multiphoton excitation
Authors: Li Quanxin , Yu Shuqin , Chen Congxiang , Ma Xingxiao
Published: July 2002

V–E energy transfer in C2H4 and alkali gas system C2H‡4+M→C2H4+M*(M=Na, K, Rb, and Cs, ‡ denotes high vibrationally excited state, * denotes electronically excited state) was investigated by using IR multiphoton excitation of C2H4 and probing the atomic fluorescence due to the above process. The atomic decay rates were determined as a function of alkali or ethylene gas concentration. The rate constants of V–E energy transfer were originally obtained by comparing the decay rate under different experimental conditions with the solution of the set of equations based on a proposed kinetic model. The kinetic information with respect to the inverse E–V energy transfer and the deexcitation process of the highly vibrationally excited state C2H‡4 were also obtained which agreed well with the results obtained from other methods. The large cross sections of the V–E energy transfer and their weak dependence on temperature obtained were interpreted based on a harpooning mechanism.
Statistical morphology of random interfaces in microemulsions
Authors: Likos C. N. , Mecke K. R. , Wagner H.
Published: July 2002

We introduce a phenomenological lattice model of interacting surfaces to relate the phase behavior of microemulsions with the random geometry and topology of microstructures formed by the self-assembling surfactants. The model rests upon an effective Hamiltonian whose morphological character is manifest. In contrast to earlier membrane models, we focus attention on energy parameters favoring multiply connected microstructures. By employing mean-field and related approximations supported by Monte Carlo simulations, we study phase diagrams, liquid structure factors, and macroscopic surface tensions to demonstrate that the model reflects prominent features of microemulsions.
Collapse of single DNA molecule in poly(ethylene glycol) solutions
Authors: Vasilevskaya V. V. , Khokhlov A. R. , Matsuzawa Y. , Yoshikawa K.
Published: July 2002

The compactization of a single DNA molecule in polyethylene glycol (PEG) solution was investigated both theoretically and experimentally. A theory is proposed taking into account the polyelectrolyte effect and redistribution of PEG within DNA coils. This approach makes it possible to describe the dependence of critical value, c, of PEG concentration at the point of DNA collapse on the degree of PEG polymerization, P, and on the concentration of low-molecular salt, ns. Observation of single DNA molecule in solution of PEG has been carried out by means of fluorescence microscopy which allows one to observe the conformation of individual DNA directly. Direct evidence that the coil–globule transition of DNA occurs as first order phase transition was obtained. It was confirmed that the critical concentration of PEG decreases with an increase of the degree of PEG polymerization and salt concentration. The width of the coexistence region of coil and globule was found to be dependent on salt concentration and degree of polymerization of PEG. It was found that DNA undergoes re-entrant globule–coil transition in concentrated solution of high-molecular weight PEG. These experimental results correspond well to the theoretical predictions.
Molecular dynamics simulation of vapor deposited amorphous ice
Authors: Essmann Ulrich , Geiger Alfons
Published: July 2002

We report a molecular dynamics simulation of the vapor deposition of amorphous ice on a cold surface. We compare the obtained structure with neutron scattering data of high and low density amorphous ice formed by pressure induced transformation of crystalline ice. The structure of our vapor deposited ice is intermediate between these two, although closer to high density amorphous ice. Its radial distribution functions resemble the results of a simulation of cluster formation in the gas phase as well as of a recent neutron scattering experiment on vapor deposited amorphous ice. The occurrence of an intermediate structure is also in agreement with a recent electron diffraction study. Structural differences are discussed in terms of the hydrogen-bond network. The amorphous surface layer is deeply fissured, suggesting a high porosity of vapor deposited ice.
The anomalous Debye–Waller factor and the fragility of glasses
Authors: Roland C. M. , Ngai K. L.
Published: July 2002

The correlation between the magnitude of the Debye–Waller anomaly and the temperature dependence of the relaxation time and viscosity of glass-forming liquids (i.e., their fragility) is investigated using the coupling model of relaxation. The correlation is shown to be a natural consequence of the relationship between the noncooperative and intermolecularly cooperative relaxation times of the model. Specifically, the deviation of the mean squared displacement from a linear temperature dependency increases as the fragility (in the Angell sense) of the glass-forming liquid increases because more fragile glasses exhibit substantially more short-time, noncooperative relaxation. This latter fact arises from their shorter noncooperative relaxation times, as deduced from the coupling model.
Molecular dynamics study of entangled hard-chain fluids
Authors: Smith Steven W. , Hall Carol K. , Freeman Benny D.
Published: July 2002

By applying efficient computational algorithms to the simplest off-lattice polymer model–the freely-jointed tangent hard-sphere chain–we have been able to perform molecular dynamics simulations long enough to probe chain dynamics in the entangled regime. Chain lengths range from 8 to 192 segments while volume fractions range from 0.3 to 0.45. Analysis of the mean-square displacement (MSD), Rouse modes, scattering functions, and end-to-end vector correlations provides information about chain motion. Chain dynamics are compared with predictions of the Rouse model for short chains and the tube model of Doi and Edwards for long chains. The mean-square displacement for the inner segments of the longest chains are consistent with predictions of the tube model, reproducing the three scaling regimes that are postulated to occur. In addition, anomalous diffusive behavior in the atomic MSD of the inner segments is observed at long times as the inner segments cross over into the free diffusion limit. Rouse-mode autocorrelation functions decay non-exponentially and do not exhibit scaling consistent with the tube model. Definitive plateau-like behaviors are observed in the density–density correlations, normal coordinate decay, and end-to-end vector relaxation of the 192-mer fluids at the highest density.
Anomalous pulse-angle and phase dependence of Hahn’s electron spin echo and multiple-quantum echoes in a photoinduced spin-correlated radical pair
Authors: Tang Jau , Thurnauer Marion C. , Kubo Atsushi , Hara Hideyuki , Kawamori Asako
Published: July 2002

Formation of two- and three-pulse electron spin echoes and their anomalous pulse-angle and phase dependence in a photoinduced spin-correlated radical pair are examined. Analytical formulae for the unusual Hahn’s spin-echo signals and the two-pulse double-quantum echo are derived in terms of the pulse angle, microwave phase, and the time intervals between the laser pulse and the microwave pulses. Such anomalies are shown to be present in both cases of singlet and triplet precursors. Phase dependence and formation of the three-pulse stimulated echo and multiple-quantum echoes are also examined.
Dynamics of lipid bilayers from comparative analysis of H2 and C13 nuclear magnetic resonance relaxation data as a function of frequency and temperature
Authors: Nevzorov Alexander A. , Brown Michael F.
Published: July 2002

Analysis of the nuclear spin relaxation rates of lipid membranes provides a powerful means of studying the dynamics of these important biological representatives of soft matter. Here, temperature- and frequency-dependent H2 and C13 nuclear magnetic resonance (NMR) relaxation rates for vesicles and multilamellar dispersions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in the liquid–crystalline state have been fitted simultaneously to various dynamic models for different positions of the acyl chains. The data include H2 R1Z rates (Zeeman order of electric quadrupolar interaction) acquired at 12 external magnetic field strengths from 0.382 to 14.6 T, corresponding to a frequency range from ωD/2π=2.50–95.3 MHz; and H2 R1Q rates (quadrupolar order of electric quadrupolar interaction) at 15.3, 46.1, and 76.8 MHz. Moreover, C13 R1Z data (Zeeman order of magnetic dipolar interaction) for DMPC are included at six magnetic field strengths, ranging from 1.40 to 17.6 T, thereby enabling extension of the frequency range to effectively (ωC+ωH)/2π=938.7 MHz. Use of the generalized approach allows formulation of noncollective segmental and molecular diffusion models, as well as collective director fluctuation models, which were tested by fitting the H2 R1Z data at different frequencies and temperatures (30 °C and 50 °C). The corresponding C13 relaxation rates were predicted theoretically and compared to experiment, thus allowing one to unify the C13 and H2 NMR data for bilayer lipids in the fluid state. A further new aspect is that the spectral densities of motion have been explicitly calculated from the H2 R1Z and R1Q data at 40 °C. We conclude that the relaxation in fluid membrane bilayers is governed predominantly by relatively slow motions, which modulate the residual coupling remaining from faster local motions (order fluctuations). Only the molecular diffusion model, including an additional slow motional process, and the membrane deformation model describing three-dimensional collective fluctuations fit the H2 NMR data and predict the C13 NMR data in the MHz range. Orientational correlation functions have been calculated, which emphasizes the importance of NMR relaxation as a unique tool for investigating the dynamics of lipid bilayers and biological membranes.
Theoretical study on the Rydberg states of NeH: Ab initio quantum defect and complex coordinate calculations
Authors: Petsalakis Ioannis D. , Theodorakopoulos Giannoula , Li Yan , Hirsch Gerhard , Buenker Robert J. , Child Mark S.
Published: July 2002

Ab initio calculations have been carried out on the potential energy curves of the Rydberg states of NeH up to 3d. Quantum defect functions have been calculated from the ab initio potentials and potential energy curves and vibrational levels for higher n (s,p,d) Rydberg states have been generated. The interaction of the 2p B 2Π state with the 2s and 2p, A 2Σ+ and C 2Σ+ states and their predissociation by X 2Σ+ has been treated by multi-state complex coordinate scaling calculations for both NeH and NeD. The results are consistent with previous 2×2 calculations on the predissociation of the A 2Σ+ and C 2Σ+ states. Finally, a calculation of the interaction between the Π2, Σ+2, and Δ2 3d states in NeH and NeD shows appreciable mixing between the states at high values of the rotational quantum number.
Positron chemistry by quantum Monte Carlo. II. Ground-state of positron-polar molecule complexes
Authors: Bressanini Dario , Mella Massimo , Morosi Gabriele
Published: July 2002

The stability of the ground-state of positron-polar molecule complexes [M,e+] has been explored for M=LiH,HF,H2O,BeO,LiF using variational and diffusion Monte Carlo techniques. Our simulations show that the ground-state of the complexes [LiH,e+]2,1Σ+, [BeO,e+]2,1Σ+, and [LiF,e+]2,1Σ+ is stable against the dissociation either in the two fragments M and e+ or in the other two fragments M+ and Ps=[e+,e−], while the ground-state of [H2O,e+]2,1A1, and of [HF,e+]2,1Σ+ has an energy equal to the dissociation threshold, M and e+. We also compare the predicted vertical positron affinity (PA) with high quality vertical electron affinity (EA) and discuss the relevant difference between the two values.
Vortex structure of the tunneling flow in long-range electron transfer reactions
Authors: Daizadeh Iraj , Guo Jian-xin , Stuchebrukhov Alexei
Published: July 2002

Ab initio calculations of tunneling current along a model 25-Å-long polypeptide chain, and similar extended hydrocarbon molecular wires, show that in the tunneling flow there exist “topological defects,” viz. the lines on which the wave function of the tunneling electron is zero, and the phase of the wave function is not defined. As a result, the flow of quantum mechanical probability experiences circular motions (vortices) around such nodal lines, and the overall structure of the flow becomes remarkably complex. The vortices in the tunneling flow are quantized, and are similar in their mathematical nature to those in a quantum superfluid liquid.
Positron and positronium chemistry by quantum Monte Carlo. IV. Can this method accurately compute observables beyond energy?
Authors: Mella Massimo , Morosi Gabriele , Bressanini Dario
Published: July 2002

Many different properties of the positron containing systems PsH, [Li,e+], LiPs, and [LiH,e+], were computed using both variational Monte Carlo and fixed node diffusion Monte Carlo methods, and explicitly correlated trial wave functions. Our results show that these techniques can accurately compute not only energy values, but also other observables. Our 〈δ(r+−)〉 values for PsH, [Li,e+], and LiPs are in good agreement with the most recent state of the art correlated calculations, while for [LiH,e+] our calculations are the first to give reliable results.
The anomalous diffusion of polymers in random media
Authors: Dua Arti , Cherayil Binny J.
Published: July 2002

We re-examine the problem of the diffusion of a Gaussian chain in a fixed array of obstacles using the projection operator formalism introduced by Loring [J. Chem. Phys. 88, 6631 (1988)]. We show that in the limit of long wavelengths, the frequency-dependent monomer friction coefficient that is used in the calculation of the mean square displacement of the center of mass can be rewritten exactly in terms of the time correlation function of the total force on the chain. When the decay profile of the force correlation function is assumed to be exponential, and its dependence on the density of obstacles written in an approximate resummed form, the dynamics of the center of mass is found to be diffusive at long and short times, and subdiffusive (anomalous) at intermediate times. Moreover, the diffusion coefficient D that describes the long-time behavior of the chain at high concentrations of small obstacles is found to vary with chain length N as N−2, which is in qualitative agreement with the predictions of the reptation model. These results are obtained in the absence of any mechanism that might incorporate the notion of reptation directly into the calculations, in contrast to Loring’s approach, which treats the monomer friction coefficient approximately using a decoupling of segmental motion into parallel and perpendicular components.
Photodissociation of water. I. Electronic structure calculations for the excited states
Authors: van Harrevelt Rob , van Hemert Marc C.
Published: July 2002

Results of ab initio calculations for the four lowest excited states of both A′ and A″ have been discussed. In the multireference configuration interaction calculations, a large Rydberg basis set has been used. Three-dimensional potential energy surfaces, and matrix elements of the transition dipole moment between the excited states and the ground X̃ state, and the electronic angular momentum operator between the Ã state and the B̃ and X̃ states have been presented. The calculations show that above about 124 nm the photodissociation can be well described by the three lowest electronic states, X̃, Ã, and B̃. The ab initio results of matrix elements of the electronic angular momentum operator allow a realistic nonadiabatic treatment of the photodissociation in the B̃ band. At wavelengths smaller than about 124 nm, the dynamics will be more complicated because of the coupling between various electronic states.
Dielectric properties of glucose and maltose solutions
Authors: Höchtl P. , Boresch S. , Steinhauser O.
Published: July 2002

We report molecular dynamics (MD) simulations of aqueous solutions of glucose and maltose. For each sugar, two concentrations were studied. The static and frequency-dependent dielectric properties of the solutions were calculated from MD trajectories of at least 5 ns length and compared to those of pure water. The contributions from the solute, the solvent, and the solute–solvent cross term were analyzed. In addition, for the more dilute glucose and maltose solutions a Voronoi analysis was carried out to distinguish between contributions from the first water shell and from unbound bulk water. The results of the glucose simulations were compared to available experimental data. While the static dielectric constant of the four solutions was found to be very similar to that of pure water, a number of differences could be discerned in the dielectric spectra. These findings for the overall frequency-dependent dielectric susceptibilities were rationalized by a dielectric component analysis. The importance of contributions from cross terms and from the solute depended on solute type (glucose or maltose) and concentration. In particular, we observed a linear correlation between the contribution of the solute–solvent cross term and the total number of hydroxyl groups of the solute (i.e., the number of solute molecules times the number of hydroxyl groups in a glucose or maltose molecule, respectively). The dielectric properties of water in the solutions could be rationalized as the superposition of two contributions, one originating from the bulklike free waters, the other from the waters in the first hydration shell of the saccharides.
The aqueous solvation of sodium chloride: A Monte Carlo transition path sampling study
Authors: Martı́ J. , Csajka F. S.
Published: July 2002

We study the dissociation of sodium chloride in an environment of simple point charged model waters using a stochastic transition path sampling method. The method is able to analyze the structure and dynamics (including transition states) of rare events without any a priori assumption. After an ensemble of reactive paths between stable states has been constructed, a set of transition state configurations can be derived. Technical details of the simulation are discussed. We observe that the structure found from the ensemble of transition state configurations is qualitatively equal to the structure obtained when the interionic distance is assumed as the reaction coordinate. We also discuss energetic aspects of the ion pair dissociation: A free energy profile of the dynamical process reveals the contribution of solvent degrees of freedom to the reaction barrier.
Gauge and dual symmetries and linearization of Hirota’s bilinear equations
Authors: Saito S. , Saitoh N.
Published: July 2002

In Hirota’s [Hiroshima University Technical Report Nos. A 6, A 9, 1981; J. Phys. Soc. Jpn. 50, 3785 (1981)] bilinear difference equation which is satisfied by solutions to the Kadomtsev–Petviashvili (KP) hierarchy, gauge and dual symmetries are found, which enable one to reduce the problem of solving the nonlinear equation to solving a single linear equation.
Elliptical billiards and Poncelet’s theorem
Authors: Chang Shau-Jin , Friedberg Richard
Published: July 2002

Two- and three-dimensional billiard systems with elliptical and ellipsoidal boundaries, respectively, are studied. It is known that the trajectory of such a two-dimensional system generates a caustic conic curve. Many properties of the elliptical billiard system in the language of projective geometry can be described. One of these properties is that if a trajectory is closed after p bounces, then all trajectories sharing the same caustic conic are also closed after p bounces. In projective geometry, this is known as Poncelet’s theorem. Many of the two-dimensional results are extended to three dimensions. In particular, it is shown that all straight segments of a trajectory in a three-dimensional ellipsoidal billiard system are always tangent to two caustic quadrics. If a trajectory is closed after p bounces, then all trajectories sharing the same two caustic quadrics are also closed after p bounces. A generalized Poncelet’s theorem in three dimensions is thus established. On the basis of numerical studies, it is conjectured that this generalized Poncelet’s theorem is also valid for an arbitrary finite number field. The implications of the results are discussed and their extension to n dimensions is outlined.
Taylor series and δ-perturbation expansions for a nonlinear semiconductor transport equation
Authors: Abraham-Shrauner B. , Bender Carl M. , Zitter R. N.
Published: July 2002

A one-dimensional, nonlinear equation for steady-state carrier transport in semiconductors is solved by two approaches: a Taylor series–first integral method and the δ-perturbation method. The square of the carrier speed is found as a function of the distance where collisions are treated by an energy-independent mean-free time. The coefficients of the Taylor series at the first maximum are exact expressions in the function determined from the first integral. In the perturbation expansion the function is evaluated to first order in δ. For both methods expressions for the distance from the first maximum to the emitting electrode are found and the distance is evaluated numerically for the Taylor series–first integral method.
Elliptical billiard systems and the full Poncelet’s theorem in n dimensions
Authors: Chang Shau-Jin , Crespi Bruno , Shi Kang-Jie
Published: July 2002

In this work is presented a generalization of Poncelet’s theorem to n dimensions which is refered to as the full Poncelet’s theorem. The theorem states that if the reflections of a trajectory by a sequence of confocal quadrics lead to a closed skew polygon, then there exists an (n−1)-parameter family of polygons having the same property. A physical realization and a projective geometrical proof of this theorem are given. If all the reflecting quadrics coincide, the above theorem reduces to the n-dimensional Poncelet’s theorem presented by Chang and Friedberg. The geometrical proof is a finite construction based on a preliminary theorem which extends Hart’s lemma. The full Poncelet’s theorem may thus be extended to projective geometries over most fields, including discrete ones.
The Weiss–Tabor–Carnevale Painlevé test and Burgers’ hierarchy
Authors: Pickering Andrew
Published: July 2002

The Weiss–Tabor–Carnevale (WTC) Painlevé test, and its recent perturbative extension, provide necessary conditions for a partial differential equation to have the Painlevé property. It follows that Burgers’ hierarchy must pass the WTC Painlevé test. The aim here is to prove this explicitly. In addition the Bäcklund transformation for Burgers’ equation, obtained by WTC via truncation, is extended to the entire hierarchy. The recursion operator is found to be related to a simple first order system.
Taub numbers at future null infinity. II
Authors: Naber M. G. , Glass E. N.
Published: July 2002

This work extends the ideas presented in Taub I [Phys. Rev. D 47, 474 (1993)]. Taub numbers are studied as a set of tensorial conservation laws derivable from curves of solutions to the Einstein equations. The zeroth-order Taub numbers for mass and angular momentum are computed using the Penrose–Goldberg superpotential [Phys. Rev. D 41, 410 (1990)]. A superpotential for the higher-order Taub vectors is given and is gauge invariant with respect to the perturbation gauge. Taub numbers are computed for the Schwarzschild and Kerr solutions, Schwarzschild and Kerr viewed as perturbations of Minkowski and Schwarzschild, respectively, and for the stationary perturbations of Schwarzschild. Taub numbers are found to give a tensorial formulation for mass and angular momentum for asymptotically flat spacetimes. A new solution generation technique for asymptotically flat solutions is also presented.
Supersymmetric Yang–Mills theory on a four-manifold
Authors: Witten Edward
Published: July 2002

By exploiting standard facts about N=1 and N=2 supersymmetric Yang–Mills theory, the Donaldson invariants of four-manifolds that admit a Kahler metric can be computed. The results are in agreement with available mathematical computations, and provide a powerful check on the standard claims about supersymmetric Yang–Mills theory.
Vertex operators in solvable lattice models
Authors: Foda Omar , Jimbo Michio , Miwa Tetsuji , Miki Kei , Nakayashiki Atsushi
Published: July 2002

The basic properties of q-vertex operators are formulated in the context of the Andrews–Baxter–Forrester (ABF) series, as an example of face interaction models, the q-difference equations satisfied by their correlation functions are derived, and their connection with representation theory established. The q-difference equations of the Kashiwara–Miwa (KM) series are discussed as an example of edge interaction models. Next, the Ising model, the simplest special case of both ABF and KM series, is studied in more detail using the Jordan–Wigner fermions. In particular, all matrix elements of vertex operators are calculated.
Group quantization of parametrized systems. I. Time levels
Authors: Hájíček P.
Published: July 2002

A method of quantizing parametrized systems is developed that is based on a kind of ‘‘gauge invariant’’ quantities—the so-called perennials (a perennial must also be an ‘‘integral of motion’’). The problem of time in its particular form (frozen time formalism, global problem of time, multiple choice problem) is met, as well as a related difficulty characteristic for this type of theory: the paucity of perennials. The present paper is an attempt to find some remedy in the ideas on ‘‘forms of relativistic dynamics’’ by Dirac. Some aspects of Dirac’s theory are generalized to all finite-dimensional first-class parametrized systems. The generalization is based on replacing the Poincaré group and the algebra of its generators as used by Dirac by a canonical group of symmetries and by an algebra of elementary perennials. A number of insights are gained; the following are the main results. First, conditions are revealed under which the time evolution of the ordinary quantum mechanics, or a generalization of it, can be constructed. The construction uses a kind of gauge and time choice and it is described in detail. Second, the theory is structured so that the quantum mechanics resulting from different choices of gauge and time are compatible. Third, a practical way is presented of how a broad class of problems can be solved without the knowledge of explicit form of perennials.
Feynman identity: A special case. I
Authors: da Costa G. A. T. F.
Published: July 2002

There is an identity due to Feynman which relates graphs and closed curves on a lattice and it was used by Feynman in his combinatorial proof of Onsager’s closed formula for the partition function of the two-dimensional Ising model. Long ago Sherman considered a special case of this identity and pointed out similarities with the Witt identity of Lie algebra theory. In this paper and following, we revisit this special case and solve some problems related with it. In particular, the weights are computed explicitly using paths and words and a direct connection with the Witt formula is found.
Instability of vector fields induced by first integrals
Authors: Gascón F. G. , Salas D. Peralta
Published: July 2002

It is shown that when a first integral of a R3 vector field X is known, instabilities are induced on the equilibrium points of X.
Liquid-metal flows in current collectors for homopolar machines: Fully developed solutions for the primary azimuthal velocity
Authors: Talmage Gita , Walker John S. , Brown Samuel H. , Sondergaard Neal A.
Published: July 2002

Liquid metals in the small radial gaps between the rotors and stators of homopolar machines represent low-resistance electric current collectors. Design predictions for these liquid-metal current collectors require a thorough knowledge of liquid-metal flows in a narrow gap between a fixed and a moving surface, with a strong applied magnetic field and a free surface beyond each end of the gap. The radial and axial velocities in the secondary flow are reduced by a strong axial or radial magnetic field. For a sufficiently strong field, the azimuthal momentum transport by the secondary flow can be neglected. This assumption reduces the problem for the primary azimuthal velocity to a fully developed magnetohydrodynamic duct flow problem with a moving wall and two free surfaces. Asymptotic solutions for large Hartmann numbers are presented for skewed magnetic fields with both radial and axial components. Collectors without any electrical insulation or with insulation on the stator sides, or rotor sides, or both are considered. Solutions for a purely axial magnetic field and arbitrary Hartmann numbers are also presented.
Rotational–translational energy transfer in rarefied nonequilibrium flows
Authors: Boyd Iain D.
Published: July 2002

A new model for simulating the transfer of energy between the translational and rotational modes is derived for a homogeneous gas of diatomic molecules. The model has been developed specifically for use in discrete particle simulation methods where molecular motion and intermolecular collisions are treated at the molecular level. In such methods it is normal to assume a constant rotational collision number for the entire flow field. The new model differs in that a temperature dependence is introduced, which has been predicted by theory and observed in experiment. The new model is applied to the relaxation of rotational temperature, and is found to produce significant differences in comparison with the model normally employed at both high and low temperatures. Calculations have also been performed for a Mach 7 normal shock wave. Large differences in the solutions are again observed, with the new model offering an improved correspondence to the available experimental data.