bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave operator and artificial intelligence contraction algorithms in quantum dynamics: Application to CD3H and C6H6
Authors: Iung Christophe , Leforestier Claude , Wyatt Robert E.
Published: July 2002

We have established in this study the capabilities of the wave operator (WO) algorithm to extract from a huge primitive space a smaller subspace (the active space) containing all of the zero order states which play an active role during the intramolecular vibrational energy redistribution (IVR) from an initial state ‖i≳0. While exact methods such as the recursive residue generation method (RRGM) or the Chebychev algorithms can only be applied in a primitive space containing less than about 200 000 states, the WO algorithm can be used efficiently in ultralarge basis sets containing billions of states. The recursive residue generation method (RRGM) or Chebychev methods can then be applied in this active space which typically contains less than 10 000 states. In order to draw general conclusions on the efficiency of such a method and on the main features of IVR phenomena, we have concurrently studied IVR from the fifth CH overtone in the nine mode CD3H molecule and from the second CH overtone in the 16 mode C6H6 system. We have analyzed the main features of the active space and have shown that the WO algorithm selects the important states. A very broad energy distribution of states in the active space has been obtained for these two systems. We have also shown that C6H6 is a very complex system to study; while only a few hundred states are effectively populated during the IVR from the fifth CH overtone in CD3H, about 8000 states have to be considered in order to accurately study IVR from the second CH overtone in C6H6. However, we have shown that the WO method is able to reproduce correctly both the survival probability of the initial state and the intricate energy flow through the molecule during the first picosecond. Finally, we have shown that the WO algorithm builds a far more efficient active space than a more traditional artificial intelligence (Al) tree pruning procedure.
Theoretical study of intramolecular vibrational relaxation of acetylenic CH vibration for v=1 and 2 in large polyatomic molecules (CX3)3YCCH, where X=H or D and Y=C or Si
Authors: Stuchebrukhov A. A. , Marcus R. A.
Published: July 2002

Quantum calculations are reported for the intramolecular vibrational energy redistribution and absorption spectra of the first two excited states of the acetylenic CH stretch vibration in the polyatomic molecules (CX3)3YCCH, where X=H or D and Y=C or Si. Using approximate potential energy surfaces, comparison is made with the corresponding recent experimental spectra. It is found that a model of intramolecular vibrational relaxation based on the assumption of sequential off-resonance transitions via third and fourth order vibrational couplings (as opposed to direct high order couplings) is in agreement with experimental results on spectral linewidths. In a semiclassical limit this type of relaxation corresponds to a dynamic tunneling in phase space. It is shown that the local density of resonances of third and fourth order, rather than the total density of states, plays a central role for the relaxation. It is found that in the Si molecule an accidental absence of appropriate resonances results in a bottleneck in the initial stages of relaxation. As a result, an almost complete localization of the initially prepared excitation occurs. It is shown that an increase of the mass alone of the central atom from C to Si cannot explain the observed difference in the C and Si molecules. The spectral linewidths were calculated with the Golden Rule formula after prediagonalization of the relevant vibrational states which are coupled in the molecule to the CH vibration, directly or indirectly. For the spectral calculations, in addition to the direct diagonalization, a modified recursive residue generation method was used, allowing one to avoid diagonalization of the transformed Lanczos Hamiltonian. With this method up to 30 000 coupled states could be analyzed on a computer with relatively small memory. The efficiency of C programming language for the problem is discussed.
A configuration bias Monte Carlo method for ionic solutions
Authors: Shelley J. C. , Patey G. N.
Published: July 2002

A version of configuration bias Monte Carlo suitable for the insertion and deletion of ions in grand canonical Monte Carlo simulations of ionic solutions has been developed. The method has been optimized and applied to a system where the straightforward insertion and deletion of ions is prohibitively impractical. The present approach is likely to be useful in other systems as well.
Laser induced fluorescence spectroscopy of the B′ 1u–X 0+g transition of Xe2: Determination of the B′ state potential and evidence for a barrier to dissociation
Authors: Pibel Charles D. , Yamanouchi Kaoru , Tsuchiya Soji
Published: July 2002

We report the observation of discrete and continuous laser induced fluorescence (LIF) spectra of the B′ 1u–X 0+g transition of Xe2, near 68 000 cm−1. The discrete features continue 5 cm−1 above the predicted atomic asymptote, which indicates the presence of a barrier to dissociation in the excited state. The dissociation energy (De′=48±12 cm−1), and excited state constants (re′=5.46±0.05 Å, ωe′=5.9±0.7 cm−1, and ωexe′=0.17±0.02 cm−1) for the B′ state were obtained from a Franck–Condon fit to the spectrum. The resulting potential is more shallow and has a longer equilibrium bond length compared with a previous experimentally derived potential. The barrier to dissociation (2 cm−1≤h≤10 cm−1, r≊10 Å) is attributed to the presence of a long-range (∝1/r3) repulsion, arising from a dipole–dipole resonant interaction.
Tunable vacuum ultraviolet photofragment excitation spectroscopy of OCS
Authors: Pibel Charles D. , Ohde Kyoko , Yamanouchi Kaoru
Published: July 2002

Photofragment excitation (PHOFEX) spectroscopy of OCS in the vacuum ultraviolet (VUV) has been carried out using tunable VUV excitation of jet-cooled OCS, followed by ultraviolet laser induced fluorescence (LIF) detection of the S (1S) photofragment via the S (3D°1–1S) transition. The PHOFEX spectrum near 154 nm is better resolved than previous absorption spectra, and new features are visible. The LIF spectrum of the S (1S) photofragment may be successfully modeled using the product recoil anisotropy (β=1.8±0.2) and CO (v,J) product state distribution previously measured for photodissociation of OCS at 157 nm [Strauss et al., J. Chem. Phys. 90, 5364 (1989)].
Calculation of expectation values of molecular systems using diffusion Monte Carlo in conjunction with the finite field method
Authors: Sandler P. , Buch V. , Clary D. C.
Published: July 2002

A scheme employing the finite field method is proposed for extracting expectation values of molecular properties from diffusion Monte Carlo calculations. The method enables calculation of expectation values of nonlocal operators, such as kinetic energies of molecular components of the system. The method is demonstrated for the H2O...N2 cluster.
Dissociative attachment in hot CH3Cl: Experiment and theory
Authors: Pearl D. M. , Burrow P. D. , Fabrikant I. I. , Gallup G. A.
Published: July 2002

The dissociative attachment (DA) cross section of hot CH3Cl has been measured in a crossed electron–molecule beam apparatus at temperatures up to 750 K and electron energies from 0–0.5 eV. The results are compared to cross sections computed using a mixed ab initio-semiempirical approach, treating CH3Cl as a quasidiatomic molecule. The theoretical treatment requires an anion potential curve in the stable region as a portion of the input data. Computations with three different basis sets show the results to be sensitive to the size of basis set from which the potential is determined. At high temperatures, the experimental DA cross sections are found to be in very good agreement with those derived from theory using the potential curve computed with the most flexible of the basis sets. At room temperature the theory suggests that the measured DA cross section is still limited by the presence of impurities.
A configuration bias Monte Carlo method for water
Authors: Shelley J. C. , Patey G. N.
Published: July 2002

A configuration bias Monte Carlo (CBMC) procedure suitable for the insertion and deletion of water molecules (SPC/E) in grand canonical and Gibbs ensemble Monte Carlo (GEMC) simulations under ambient conditions is presented. This CBMC technique involves sampling a number of orientations of the molecule at the chosen site and selecting one with a probability proportional to its Boltzmann weight. The Swendsen–Wang technique is used to reject improbable insertions or deletions before performing expensive CBMC calculations. This approach yields significant gains in efficiency and should be applicable to many other systems. Water molecules are frequently inserted and deleted in the same locations indicating that the overall acceptance rate for such moves is somewhat misleading. A better measure is to only consider deletions of molecules that have remained in the system for a sufficiently long time. Based upon this measure insertions and deletions should be attempted at least as often as displacements in grand canonical Monte Carlo simulations of water.
Infrared emission spectra of C3: the Renner effect in the ã3Πu and b̃3Πg electronic states
Authors: Tokaryk D. W. , Civiš Svatopluk
Published: July 2002

Five new triplet bands of 12C3, and three corresponding bands of 13C3, have been observed in emission between 6000 and 6600 cm−1 with a Fourier transform spectrometer. Rotational analysis shows that these bands arise from excited bending vibrations of the b̃3Πg→ã3Πu electronic transition, and that all components of the (010) vibrational level of the b̃3Πg state exhibit unusual perturbations. Renner parameters for both electronic states have been extracted from an analysis of the spin-orbit parameters of the (000) 3Π, (010) 3Δ, (020) 3Φ, and (030) 3Γ levels. The Renner effect is shown to be large in both electronic states (ε′ = +0.447, ε″ = +0.566). Approximate bending vibrational frequencies are also obtained (ω2′∼345 cm−1, ω2″∼505 cm−1).
6D quantum calculation of energy levels for HF stretching excited (HF)2
Authors: Wu Qian , Zhang Dong H. , Zhang John Z. H.
Published: July 2002

Converged full-dimensional (6D) quantum mechanical calculation of energy levels of intramolecular stretching excited (HF)2(ν1ν2) is presented for (ν1ν2)=(01), (10), (02), (20), and (11). The bound state calculation for the excited HF dimer employs the SQSBDE potential energy surface of Quack and Suhm and is for total angular momentum J=0. This calculation provides the first rigorous theoretical result of energy levels for HF stretching excited HF dimer in full dimensions. The calculated fundamental transition frequencies are ν1=3940.6 cm−1 and ν2=3896.4 cm−1. These values are somewhat larger than the corresponding experimental measurement of 3930.9 cm−1 for ν1 and 3868.3 cm−1 for ν2. The overtone frequencies are calculated to be 2ν1=7713.5 cm−1, 2ν2=7642.5 cm−1, and ν1+ν2=7841.8 cm−1. The theoretical tunneling splittings of the fundamentals ν2 and ν1 are, respectively, a factor of 5.3 and 3.7 smaller than the ground state splitting, compared to a factor of 3 from the experimental measurement. The splittings of the overtone states 2ν2, 2ν1, and ν1+ν2 are smaller than that of the ground state by factors of 9.6, 48, and 1.8, respectively. Some of the calculated energy levels of excited (HF)2 are spectroscopically characterized and assigned.
Microscopic theory of molecular crystal surface second-harmonic generation
Authors: Munn R. W.
Published: July 2002

Second-harmonic generation (SHG) is induced in molecular crystals by the variation through the surface region of the electric fields associated with the optical wave and with the permanent electric multipole moments of the molecules. It arises from the molecular first hyperpolarizability, whether permanent or induced by electric fields at noncentrosymmetric sites in the bulk crystal or at sites in the surface region where centrosymmetry is lost. Algebraic expressions suitable for iterative numerical evaluation are derived for the molecular response coefficients as affected by the multipole fields in the surface region. Detailed expressions are then derived for the surface second-harmonic generation in terms of the spatially varying molecular response and a microscopic expression that is derived for the variation of optical electric field through the surface region. The treatment does not require the introduction of a surface dielectric constant but incidentally yields a microscopic expression for it. The quadratic susceptibilities for surface SHG in anthracene and pyrene are roughly estimated as respectively 1/80 and 1/20 that in p-nitroaniline, reported to be 4 fm V−1; the coefficients could vary by one or two orders of magnitude among different surfaces.
Instability of nonequilibrium fluctuation in electrochemical nucleation. II. Determination of the critical condition
Authors: Aogaki Ryoichi , Yamada Akito , Tadano Atsushi
Published: July 2002

In the foregoing paper, part I, the mechanism of the fluctuations which are necessarily induced by the breakdown of the electrostatic equilibrium was examined. Consequently, it was found that nonspecific adsorption of ions onto electrode surface is essential to the progress of nucleation. It was also deduced that the critical condition for the unstable growth corresponds to the flat potential distribution in the diffuse layer within the electric double layer. Therefore, using the facts that at the stable region of the fluctuations, the electrode is kept in the electrostatic equilibrium and apparently behaves as an ideal polarized electrode, a method to determine the critical potential by the extrapolation from the stable region was theoretically developed. As a result, the critical potential equations corresponding to the flat distribution of the potential in the diffuse layer were obtained for various experimental conditions. By applying these equations to actual systems, the adsorbed states of ions at the interface can be examined. Therefore, the critical potential for silver nucleation onto platinum electrode in AgNO3+NaNO3 solution were measured. Consequently, no intense specific adsorption of ions was observed, and it was concluded that a pair of Ag+ ion and NO−3 ion are simultaneously adsorbed by the electrostatic interaction.
Molecular scattering: Very-short-range imaginary potentials, absorbing-potentials, and flux-amplitude expressions
Authors: Neuhauser Daniel
Published: July 2002

This article has a few goals. First, a new highly accurate and anomaly free time-independent approach to reactive scattering is presented, based on the use of very-short-range imaginary potentials. The range of the imaginary potentials is extremely short—in successful one-dimensional simulations they cover only two grid points. The savings are incurred by limiting the role of the imaginary potentials to shifting the eigenvalues of the Hamiltonian away from the real axis, thereby avoiding anomalies; the imaginary potentials are not required to impose outgoing boundary conditions. Another goal is a rigorous derivation of a flux-amplitude (FA) expression, whereby (for any scattering approach, whether using negative imaginary potentials or not) reactive S-matrix amplitudes are extracted from the wavefunction at a single surface of any desired ‘‘internal’’ coordinate system—there is no need to project the wave function to the asymptotic products coordinates before determining its flux. With the FA expression, expensive volume integrals in state-to-state scattering are reduced to simple surface integrals. The FA expression also leads to a rigorous derivation of various alternate expressions for the scattering matrix which are useful whenever negative imaginary potentials are utilized. Finally, a new expression is presented for estimating the errors in absorbing potentials single-column calculations due to imperfections in the absorbing potentials.
Vibrational frequencies of the HF dimer from the coupled cluster method including all single and double excitations plus perturbative connected triple excitations
Authors: Collins Charlene L. , Morihashi Kenji , Yamaguchi Yukio , Schaefer Henry F.
Published: July 2002

Dissociation energies, equilibrium structures, equilibrium dipole moments, harmonic vibrational frequencies, infrared (IR) intensities, and zero-point vibrational energies (ZPVEs) are presented for the hydrogen fluoride monomer and dimer at the coupled cluster with single and double excitations plus perturbative connected triple excitations [CCSD(T)] level of theory with a series of large basis sets. Discussion focuses on the results from the largest basis set, triple zeta plus double polarization and one set of higher angular momentum functions [TZ2P(f,d)]. The structural parameters and dissociation energy agree well with the recent theoretical values reported in a high level ab initio study by Peterson and Dunning [J. Chem. Phys. 102, 2032 (1995)] and with experimental results. Here, the harmonic vibrational frequencies and IR intensities for the dimer are also predicted. The predicted vibrational frequency shifts relative to the monomer for the HF and DF stretching coordinates in the dimer are close to the experimental estimates.
Fragmentation of C+60 and higher fullerenes by surface impact
Authors: Beck Rainer D. , Rockenberger Jörg , Weis Patrick , Kappes Manfred M.
Published: July 2002

Fragmentation of various fullerenes was studied by surface impact on highly oriented pyrolytic graphite at collision energies Ecol of 150–1050 eV/molecule. The projectiles C+60, C+70, C+76, C+84, and C+94 were formed by laser desorption of chromatographically separated samples, while large carbon clusters C+94, C+110, C+164 were produced by laser-induced coalescence reactions. Except at the highest impact energies, the fragment distributions consist of even numbered C+n species with abundance maxima similar to those observed in fullerene synthesis. With increasing Ecol, we observe a size evolution in the fragment distributions characteristic of a sequential fragmentation process. Simulated fragment distributions based on statistical rate theory and a sequential C2 loss mechanism reproduce the experimental data well up to a maximum Ecol. They are used to determine the mean energy transfer during surface impact as a function of collision energy as well as its dependence on several experimental parameters such as the nature (cleanliness) of the target surface, the internal energy of the incident ion, and the incident fullerene size. Both internal and kinetic energy of the incident ion are found to contribute to the observed fragmentation although with different efficiencies. For the higher fullerenes we find a tendency towards increasing transfer efficiency of incident kinetic to internal energy with increasing projectile size. Finally, above a size-dependent impact energy threshold, a transition to a different high energy fragmentation process is indicated by changes in the fragment distributions. These go from exclusively even numbered fullerene fragments at low impact energy to smaller even and odd numbered C+n fragments at high Ecol. It is suggested that this change indicates the formation of high energy, nonfullerene isomers.
Molecular dynamics calculation of elastic constants in Gay–Berne nematic liquid crystals
Authors: Allen Michael P. , Warren Mark A. , Wilson Mark R. , Sauron Alain , Smith William
Published: July 2002

In this paper we present a molecular dynamics calculation of the Frank elastic constants of a nematic liquid crystal. We study two well-known variants of the Gay–Berne potential, and determine the elastic constants by measuring orientational fluctuations as a function of wave vector, using reasonably large system sizes in the range 1000–8000 molecules. For some of the simulations, a set of Lagrangian constraints was applied in order to keep the director fixed along one of the box axes, facilitating the measurement of fluctuations in components of the reciprocal-space order tensor Q̂(k) in the director frame.
Fully coupled six-dimensional calculations of the water dimer vibration-rotation-tunneling states with a split Wigner pseudo spectral approach
Authors: Leforestier Claude , Braly Linda B. , Liu Kun , Elrod Matthew J. , Saykally Richard J.
Published: July 2002

A novel and efficient pseudospectral method for performing fully coupled six-dimensional bound state dynamics calculations is presented, including overall rotational effects. A Lanczos based iterative diagonalization scheme produces the energy levels in increasing energies. This scheme, which requires repetitively acting the Hamiltonian operator on a vector, circumvents the problem of constructing the full matrix. This permits the use of ultralarge molecular basis sets (up to over one million states for a given symmetry) in order to fully converge the calculations. The Lanczos scheme was conducted in a symmetry adapted spectral representation, containing Wigner functions attached to each monomer. The Hamiltonian operator has been split into different terms, each corresponding to an associated diagonal or nearly diagonal representation. The potential term is evaluated by a pseudospectral scheme of Gaussian accuracy, which guarantees the variational principle. Spectroscopic properties are computed with this method for four of the most widely used water dimer potentials, and compared against recent terahertz laser spectroscopy results. Comparisons are also made with results from other dynamics methods, including quantum Monte Carlo (QMC) and reversed adiabatic approximation calculations. None of the potential surfaces produces an acceptable agreement with experiments. While QMC methods yield good results for ground (nodeless) states, they are highly inaccurate for excited states.
Spectroscopic characterization of the excited valence MgKr(3dδ 3Δ1) and MgKr(3dπ 3Π) van der Waals states
Authors: Kaup John G. , Breckenridge W. H.
Published: July 2002

The Mg(3s3dπ 3DJ)⋅Kr(3Π0+,0−) and Mg(3s3dδ 3DJ)⋅Kr(3Δ1) valence excited states have been characterized via resonance enhanced two-photon ionization (R2PI) spectroscopy of transitions from the long-lived Mg(3s3pπ 3PJ)⋅Kr(3Π0+,0−) metastable states of the MgKr van der Waals molecule. Because the excited Mg(3d) orbital is quite diffuse and the Kr atom can approach along the nodal axis of the aligned 3d orbital, minimizing repulsion, the MgKr(3s3dδ 3Δ1) state is very strongly bound (D0=1874±80 cm−1), closely approaching the bond energy of the MgKr+ core ion (for which D0=1891±80 cm−1). In contrast, the MgKr(3s3dπ 3Π0−) state is more weakly bound (D0=587±80 cm−1), although it has a greater bond strength than the MgKr(3s3pπ 3Π0−) lower state (for which D0 is 250±80 cm−1). We have also observed interesting spin–orbit effects which are attributed to mixing of Kr character into molecular orbitals which are nominally of Mg* excited-state character.
Structural investigation of copper(II) chloride solutions using x-ray absorption spectroscopy
Authors: D’Angelo P. , Bottari E. , Festa M. R. , Nolting H.-F. , Pavel N. V.
Published: July 2002

The local environment of the Cu2+ ion in copper chloride solutions has been investigated by x-ray absorption spectroscopy. Three aqueous solutions of CuCl2 with increasing Cl−/Cu2+ ratio have been examined. An advanced data analysis including multiple-scattering effects produced quantitative information on the chlorocuprate complexes present in solution and provided evidence for an increasing degree of complex formation between Cu2+and Cl− ions with increasing chloride concentration. The presence of Cu–Cl interactions at the axial site has been detected in a 0.1 M CuCl2 solution for the first time. At higher chloride concentrations (Cl−/Cu2+ratios equal 10 and 30) the equatorial positions in the distorted octahedral copper coordination are occupied by 3.2 and 3.0 oxygens and 0.8 and 1.0 chloride ions, respectively, while the axial positions are occupied by 1.2 and 1.0 oxygens and 0.8 and 1.0 chloride ions, respectively. The results are found to be consistent with previous x-ray and neutron diffraction studies and with experimental data on the complex formation.
Collisional energy transfer of highly vibrationally excited NO2: The role of intramolecular vibronic coupling and the transition dipole coupling mechanism
Authors: Hartland Gregory V. , Qin Dong , Dai Hai-Lung , Chen Carl
Published: July 2002

The collisional relaxation of highly vibrationally excited NO2 has been studied for a variety of collision partners (He, Ar, CO, N2, O2, N2O, NO2, CO2, SF6, and toluene) by time-resolved Fourier transform infrared emission spectroscopy. The average energy 〈E〉 of the vibrationally excited NO2 molecules during collisional quenching was obtained from the IR spectra by modeling the ν3 and ν1+ν3 bands, using the known harmonic frequencies and anharmonicity constants. The average amount of energy lost per collision 〈ΔE〉 was determined from the 〈E〉 versus time data. The results show that there is a dramatic increase in the amount of energy transferred for all bath gases at NO2 energies above 10 000–12 000 cm−1, which is near the origin of the NO2 Ã2B2/B̃2B1 states. This threshold in the energy-transfer rate occurs because of strong vibronic coupling between the X̃2A1 and Ã2B2/B̃2B1 electronic states. The increase in vibration-to-vibration (V-V) energy transfer can be understood within the context of the transition dipole coupling model. Vibronic coupling in NO2 produces extensive broadband emission in the IR and near-IR, which enhances the V-V energy-transfer rate by relaxing the resonance conditions in dipole coupling. The V-V energy-transfer probability was calculated using the dipole coupling model, where the transition dipole moment of excited NO2 was directly extracted from the IR emission spectra. These calculations successfully reproduced the observed threshold in the V-V energy transfer probability. The transition dipole coupling model was also used to estimate the relative contribution of V-V versus vibration-to-translation, rotation (V-T,R) energy transfer for NO2 deactivation. The calculations showed that V-T,R energy transfer is the major relaxation channel for triatomic or smaller collision partners. For larger species like SF6, however, V-V energy transfer is the dominant channel. Vibronic coupling may cause an increase in the V-T,R energy-transfer rate by allowing electronic potential related terms, possibly the electronic transition dipole moment, to contribute to the matrix elements responsible for V-T,R energy transfer.
Accuracy of electronic wave functions in quantum Monte Carlo: The effect of high-order correlations
Authors: Huang Chien-Jung , Umrigar C. J. , Nightingale M. P.
Published: July 2002

Compact and accurate wave functions can be constructed by quantum Monte Carlo methods. Typically, these wave functions consist of a sum of a small number of Slater determinants multiplied by a Jastrow factor. In this paper we study the importance of including high-order, nucleus-three-electron correlations in the Jastrow factor. An efficient algorithm based on the theory of invariants is used to compute the high-body correlations. We observe significant improvements in the variational Monte Carlo energy and in the fluctuations of the local energies but not in the fixed-node diffusion Monte Carlo energies. Improvements for the ground states of physical, fermionic atoms are found to be smaller than those for the ground states of fictitious, bosonic atoms, indicating that errors in the nodal surfaces of the fermionic wave functions are a limiting factor.
Vibronic analyses of the mass-resolved NeXe spectra near Xe*(6p)
Authors: Mao D. M. , Hu X. K. , Bascal H. A. , Dimov S. S. , Lipson R. H.
Published: July 2002

New mass-resolved two-photon spectra of NeXe involving molecular Rydberg states that dissociate to Ne+Xe*(6p) have been recorded using the combined techniques of (2+1) resonance enhanced multiphoton ionization and time-of-flight mass spectrometry. Excited state symmetries were deduced from separate spectra recorded with linearly and circularly polarized light. Vibronic analyses show that most of the excited states in this spectral region are essentially repulsive except for shallow minima whose electronic origins lie above their asymptotic dissociation limits. The magnitude of the potential humps for the excited states have been estimated. These results are rationalized in terms of an excited state bonding scheme that is dominated predominately by the interplay between repulsive exchange interactions and attractive long-range forces.
Electron impact dissociative ionization of CO2: Measurements with a focusing time-of-flight mass spectrometer
Authors: Tian Cechan , Vidal C. R.
Published: July 2002

For reliable cross section data a focusing time-of-flight mass spectrometer has been presented which collects all the ions produced by the electron impact dissociative ionization of molecules. The focusing characteristic of the mass spectrometer generates the ions close to the axis and focuses the energetic ions back to the detector. By observing the deflection curves we can measure the cross sections conclusively. The complete collection allows one to extract the initial kinetic energy distribution of the ions from the time-of-flight profiles of the mass peaks. As a first example we measured the cross sections of electron impact dissociative ionization of CO2  for electron energies from threshold to 300 eV. The results agree very well with recent measurements of Straub et al. [J. Chem. Phys. 105, 4015 (1996)], although previous data are in very poor agreement with each other. We measured the initial translational energy distribution of the fragment ions from the dissociative ionization of CO2 . With respect to the kinetic energy distribution of the ions we analyzed the techniques which make use of the quadrupole mass spectrometer. We discuss why the results from the quadrupole mass spectrometer underestimate the cross sections for the fragment ions. Finally we suggest to recheck the data from earlier quadrupole mass spectrometer measurements.
Adsorption hysteresis and pore critical temperature in a single cylindrical pore
Authors: Morishige K. , Shikimi M.
Published: July 2002

The effect of temperature on adsorption isotherms of Ar, N2, O2, C2H4, and CO2 on model mesoporous adsorbents (MCM-41) with different pore sizes (pore radius rp=1.2, 1.4, 2.1 nm) has been measured. The results clearly show that the hysteresis loop shrinks with increasing temperature and eventually disappears at the hysteresis critical temperature (Tch), which depends on the average pore size but lies substantially below the pore critical temperature (Tcp). A plot of (Tc−Tch)/Tc against d/rp for all the gases examined, except for CO2, forms a single straight line passing through the origin, where d is the molecular diameter. This relationship predicts that the adsorption hysteresis never occurs in the cylindrical pore of radius smaller than twice the molecular diameter. On the other hand, the same plot for conventional adsorbents with an interconnected network of irregular pores seems to be smoothly linked to the data points of Tcp on MCM-41 rather than those of Tch on MCM-41.
Deactivation of highly excited CS2 and SO2 by rare gases
Authors: Chimbayo Alexander , Toselli Beatriz M. , Barker John R.
Published: July 2002

The time dependent thermal lensing (TDTL) technique has been used to study collisional energy transfer from highly excited CS2 in baths of Xe, Kr, and Ar, and from highly excited SO2 in Kr and Ar. Bath gas pressures ranged from about 50 to about 600 Torr. The data were analyzed by simulating the observed TDTL signals with a unified hydrodynamic TDTL theory. The results are expressed in terms of 〈ΔE〉, the bulk average energy transferred per collision as a function of 〈E〉, the mean energy content. The results show that 〈ΔE〉 increases dramatically at 〈E〉≈17 500–23 500 cm−1 for CS2 deactivation, and at 〈E〉≈18 000–22 500 cm−1 for SO2 deactivation. This enhancement of energy transfer, which was observed previously in NO2 and CS2 deactivation, has been linked to the presence of nearby excited electronic states. Furthermore, at lower energy, our results reveal an unusual systematic dependence of 〈ΔE〉 on bath pressure; energy transfer per collision is significantly more efficient at lower collision frequency. These results and data from the literature can be explained with a phenomenological model which includes collisional vibrational relaxation within each of two sets of vibronic levels, and collision-induced intersystem crossing (CIISC), which exhibits mixed order kinetics.
Monte Carlo study of adsorption of a polyelectrolyte onto charged surfaces
Authors: Kong C. Y. , Muthukumar M.
Published: July 2002

By using off-lattice Monte Carlo simulations, the conditions of adsorption of a uniformly charged polyelectrolyte onto oppositely charged planar and spherical surfaces have been investigated. These conditions are functions of the strength of the electrostatic interaction, Debye screening length, chain length, and charge density and curvature of the surface. The adsorption can be tuned by using any one of these parameters. The chain’s conformation, adsorption energy and thickness of the adsorbed polymer are obtained under different adsorption conditions. We find the Monte Carlo simulation data to be in good agreement with the theoretical prediction derived previously by using the assumptions of ground state dominance and separability.
Electron transfer reaction dynamics in non-Debye solvents
Authors: Bicout D. J. , Szabo Attila
Published: July 2002

The dynamics of electron transfer in a non-Debye solvent is described by multidimensional Markovian reaction-diffusion equation. To highlight differences with existing approaches in the simplest possible context, the irreversible outer-sphere reaction in a solvent with a biexponential energy-gap autocorrelation function, Δ(t), is studied in detail. In a Debye solvent, Δ(t)=exp(−t/τL) and the rate can be rigorously expressed as an explicit functional of exp(−t/τL). It has been suggested that the exact rate in a non-Debye solvent can be found by replacing exp(−t/τL) with the appropriate (nonexponential) Δ(t). For a “biexponential” solvent, our approach is based on an anisotropic diffusion equation for motion on a harmonic surface in the presence of a two-dimensional delta function sink. Three approximations, which reduce the solution of this equation to effective one-dimensional ones, are considered and compared with exact Brownian dynamics simulation results. The crudest approximation replaces the non-Debye solvent with an effective Debye one with τeff−1=(−dΔ/dt)t=0. The second is obtained by invoking the Wilemski–Fixman-type closure approximation for the equivalent two-dimensional integral equation. This approximation turns out to be identical to the above mentioned “substitution” procedure. When the relaxation times of the two exponentials are sufficiently different, it is shown how the two-dimensional problem can be reduced to a one-dimensional one with a nonlocal sink function. This anisotropic relaxation time approximation is in excellent agreement with simulations when the relaxation times differ by at least a factor of three and the activation energy is greater than kBT. Finally, it is indicated how the influence of intramolecular vibrational modes (i.e., nonlocal sink functions) can be treated within the framework of this formalism.
Charge carrier transport in conjugated polymers
Authors: Hertel D. , Bässler H. , Scherf U. , Hörhold H. H.
Published: July 2002

The charge carrier mobility in a ladder-type poly(paraphenylene) (MeLPPP) and a phenylamino-substituted poly(phenylenevinylene) (PPV) derivative (PAPPV) has been studied in detail by using the time-of-flight (TOF) method. In most cases, the TOF signals feature characteristics of nondispersive charge transport in terms of the disorder formalism, although the transition from nondispersive to the dispersive transport regime was observed in PAPPV. Hole mobilities in the range of 10−4 to 7×10−3 cm2/Vs were obtained, depending on electric field and temperature. The influence of disorder on charge transport of the investigated conjugated polymers is discussed.
Toward a global and causal understanding of the unusual Rydberg state potential energy curves of the heteronuclear rare gas dimers
Authors: Lipson R. H. , Field R. W.
Published: July 2002

Primitive calculations, based on simple physical concepts, have been found to explain the unusual excited state potential energy curves deduced from RgXe (Rg=Kr, Ar, Ne), two-photon spectra. The irregularities in the potentials and their dependence on the effective principle quantum number, n*, are attributed to repulsive exchange interactions between electrons in closed shell orbitals of the ground state Rg atom and the Xe* Rydberg electron. The internuclear distance dependence of these exchange interactions reflect the nodal structure of the radial probability distribution of the Rydberg orbital.
On the dimensional reduction of invariant fields and differential operators
Authors: Nikolov P. A.
Published: July 2002

In the present paper the most general type of group action introducing some relevant exact sequences for the dimensional reduction of invariant fields and differential operators is studied.
Quantum mechanics as an infinite-dimensional Hamiltonian system with uncertainty structure: Part I
Authors: Cirelli Renzo , Manià Alessandro , Pizzocchero Livio
Published: July 2002

Schrödinger quantum mechanics is formulated as an infinite-dimensional Hamiltonian system whose phase space carries an additional structure (uncertainty structure) to account for the probabilistic character of the theory. The algebra of observables is described as an algebra of smooth functions on the quantal phase space, with a product naturally induced by the geometrical structures living on that manifold. The possibility of generalizing Schrödinger mechanics along these lines is discussed.
Poisson structures on the cotangent bundle of a Lie group or a principle bundle and their reductions
Authors: Alekseevsky D. , Grabowski J. , Marmo G. , Michor P. W.
Published: July 2002

On a cotangent bundle T*G of a Lie group G one can describe the standard Liouville form θ and the symplectic form dθ in terms of the right Maurer Cartan form and the left moment mapping (of the right action of G on itself), and also in terms of the left Maurer–Cartan form and the right moment mapping, and also the Poisson structure can be written in related quantities. This leads to a wide class of exact symplectic structures on T*G and to Poisson structures by replacing the canonical momenta of the right or left actions of G on itself by arbitrary ones, followed by reduction (to G cross a Weyl-chamber, e.g.). This method also works on principal bundles.
q-exponential and q-gamma functions. II. q-gamma functionsa)
Authors: McAnally D. S.
Published: July 2002

For ‖q‖ ≠ 1, the integral definition of the gamma function in terms of the exponential function is generalized to a definition of a q-gamma function, or a family of q-gamma functions, in the standard and symmetric cases, using the q-exponential functions and their asymptotic behavior as z → ∞ on geometric sequences {zn(ζ)= qnζ}n∈Z with common ratio q. The properties of the q-gamma functions (poles, zeros, product expansions) are also determined.
On the simplest (2+1) dimensional integrable spin systems and their equivalent nonlinear Schrödinger equations
Authors: Myrzakulov R. , Vijayalakshmi S. , Syzdykova R. N. , Lakshmanan M.
Published: July 2002

Using a moving space curve formalism, geometrical as well as gauge equivalence between a (2+1) dimensional spin equation (M-I equation) and the (2+1) dimensional nonlinear Schrödinger equation (NLSE) originally discovered by Calogero, discussed then by Zakharov and recently rederived by Strachan, have been estabilished. A compatible set of three linear equations are obtained and integrals of motion are discussed. Through stereographic projection, the M-I equation has been bilinearized and different types of solutions such as line and curved solitons, breaking solitons, induced dromions, and domain wall type solutions are presented. Breaking soliton solutions of (2+1) dimensional NLSE have also been reported. Generalizations of the above spin equation are discussed.
From time-ordered products to Magnus expansion
Authors: Oteo J. A. , Ros J.
Published: July 2002

Recent work by Lam on the decomposition of time-ordered products appearing in the time-evolution operator in terms of sums of products of nested commutators is endowed with a recursive algorithm. A sufficient condition for absolute convergence is subsequently obtained. Connection with Magnus expansion is established.
An asymptotic description of transient settling and ultrafiltration of colloidal dispersions
Authors: Davis K. E. , Russel W. B.
Published: July 2002

Sedimentation and ultrafiltration are important processes for removing solids from suspensions. The Kynch theory describes the transient settling of noncolloidal particles forming an incompressible sediment by providing a solution to the convective conservation equation. This solution predicts the existence of several different regions as settling progresses. Subsequent treatments have accounted for compressibility within the sediment. These modifications focus largely on stretching the Kynch theory to fit the problem at hand rather than on formulating a new model to include the relevant physics. In this paper a model of sedimentation for colloidal systems is presented by including a diffusion term in the governing equation. In the regions above the sediment, this term acts as a small perturbation to the Kynch theory. Within the sediment, owing to the high solid volume fraction, diffusion is comparable to convection. Slow compression to the maximum sediment volume fraction contrasts the incompressibility of the Kynch theory. Application of the method of matched asymptotic expansions to the conservation equation enables the formulation of a complete description of the settling process, and, in particular, the volume fraction evolution in the sediment. This method is also applied to the related ultrafiltration process. Where the properties of the sediment, or filtercake, are important, such as in ceramics manufacturing, a quantitative understanding of its formation is of obvious value.
Molecular mixing in Rayleigh–Taylor instability. Part I: Global mixing
Authors: Linden P. F. , Redondo J. M.
Published: July 2002

This paper describes experiments on the mixing produced by Rayleigh–Taylor instability between two miscible fluids. A layer of brine is placed over a layer of fresh water in a gravitational field, and the ensuing flow is visualized by laser-induced fluorescence and measurements are made of the concentration fields as the flow develops. It is found that large-scale disturbances develop which produce intermingling of the fluids, but molecular mixing occurs as a result of small-scale instabilities which grow on the edges of the larger scale motions. When the system overturns stably stratified fluid is produced, and the mixing efficiency of the process is measured and found to be large compared with other forms of mixing. It is suggested that this increased efficiency is due to the fact that much of the mixing occurs when the system is unstably stratified.
The deformation and breakup of liquid drops in low Reynolds number flow through a capillary
Authors: Olbricht W. L. , Kung D. M.
Published: July 2002

The deformation and breakup of a freely suspended, immiscible liquid drop are examined experimentally for low Reynolds number flow in a straight circular capillary tube. Results are reported for capillary numbers from 0.05 to greater than unity and for values of the viscosity ratio that span more than three orders of magnitude. In every case, the size of the drop is comparable to the tube diameter. The steady-state shapes of the drops are compared with previous numerical studies of the problem. However, for a critical value of the capillary number that depends on drop size and viscosity ratio, drop breakup is observed in the experiment. When the viscosity ratio is small, i.e., the drop fluid is less viscous than the outer phase liquid, an indentation in the trailing edge of the drop grows and entrains outer phase liquid inside the boundaries of the original drop. When the viscosity ratio is O(1), the drop stretches along the axis of the tube until it breaks.
The calculation of the low Reynolds number resistance functions for two unequal spheres
Authors: Jeffrey D. J.
Published: July 2002

The resistance functions that relate the forces, couples, and stresslets exerted on ambient fluid by two unequal rigid spheres in low Reynolds number flow are calculated for the case in which the spheres are immersed in an ambient linear flow. In conjuction with earlier works, this paper completes the tabulation of all of the two-sphere resistance functions at present needed in investigations of the mechanics of suspensions. Each function is calculated first as a series in inverse powers of the center-to-center separation, and then, in order to handle the singular behavior caused by lubrication forces, the asymptotic form which the function takes when the spheres are close is combined with the series expansion into a single expression valid for all separations of the spheres.
High-beta operation and magnetohydrodynamic activity on the TFTR tokamak
Authors: McGuire K. , Arunasalam V. , Barnes C. W. , Bell M. G. , Bitter M. , Boivin R. , Bretz N. L. , Budny R. , Bush C. E. , Cavallo A. , Chu T. K. , Cohen S. A. , Colestock P. , Davis S. L. , Dimock D. L. , Dylla H. F. , Efthimion P. C. , Ehrhrardt A. B. , Fonck R. J. , Fredrickson E. , Furth H. P. , Gammel G. , Goldston R. J. , Greene G. , Grek B. , Grisham L. R. , Hammett G. , Hawryluk R. J. , Hendel H. W. , Hill K. W. , Hinnov E. , Hoffman D. J. , Hosea J. , Howell R. B. , Hsuan H. , Hulse R. A. , Janos A. C. , Jassby D. , Jobes F. , Johnson D. W. , Johnson L. C. , Kaita R. , Kieras-Phillips C. , Kilpatrick S. J. , LaMarche P. H. , LeBlanc B. , Manos D. M. , Mansfield D. K. , Mazzucato E. , McCarthy M. P. , McCune M. C. , McNeill D. H. , Meade D. M. , Medley S. S. , Mikkelsen D. R. , Monticello D. , Motley R. , Mueller D. , Murphy J. A. , Nagayama Y. , Nazakian D. R. , Neischmidt E. B. , Owens D. K. , Park H. , Park W. , Pitcher S. , Ramsey A. T. , Redi M. H. , Roquemore A. L. , Rutherford P. H. , Schilling G. , Schivell J. , Schmidt G. L. , Scott S. D. , Sinnis J. C. , Stevens J. , Stratton B. C. , Stodiek W. , Synakowski E. J. , Tang W. M. , Taylor G. , Timberlake J. R. , Towner H. H. , Ulrickson M. , von Goeler S. , Wieland R. , Williams M. , Wilson J. R. , Wong K.-L. , Yamada M. , Yoshikawa S. , Young K. M. , Zarnstorff M. C. , Zweben S. J.
Published: July 2002

Magnetohydrodynamic (MHD) activity within three zones (core, half-radius, and edge) of TFTR [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 51] tokamak plasmas are discussed. Near the core of the plasma column, sawteeth are often observed. Two types of sawteeth are studied in detail; one with complete, and the other with incomplete, magnetic reconnection. Their characteristics are determined by the shape of the q profile. Near the half-radius the m/n=3/2 and 2/1 resistive ballooning modes are found to correlate with a beta collapse. The pressure and the pressure gradient at the mode rational surface are found to play an important role in stability. MHD activity is also studied at the plasma edge during limiter H modes. The edge localized modes (ELM’s) are found to have a precursor mode with a frequency between 50–200 kHz and a mode number m/n=1/0. The mode does not show a ballooning structure. While these instabilities have been studied on many other machines, on TFTR the studies have been extended to high pressure (plasma pressure greater than 4×105 Pa) and low collisionality [vi*(a/2)<0.002, ve*(a/2)<0.01].