bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic investigation of the AlNC and AlCN isomers by Knudsen cell mass spectrometry
Authors: Meloni G. , Gingerich K. A.
Published: July 2002

Equilibria involving the isomers AlNC and AlCN above a mixture of aluminum nitride, graphite, and gold contained in a graphite Knudsen cell were investigated with a mass spectrometer. The enthalpies of formation, ΔfH0o, and of atomization, ΔaH0o, in kJ mol−1, for AlNC and AlCN, were derived as 281.3±14 and 303.8±14, and as 1228.1±15 and 1205.6±15, respectively.
Nonlinear dynamical properties of an oscillating tip–cantilever system in the tapping mode
Authors: Nony L. , Boisgard R. , Aimé J. P.
Published: July 2002

The dynamical properties of an oscillating tip–cantilever system are now widely used in the field of scanning force microscopy. The aim of the present work is to get analytical expressions describing the nonlinear dynamical properties of the oscillator in noncontact and intermittent contact situations in the tapping mode. Three situations are investigated: the pure attractive interaction, the pure repulsive interaction, and a mixing of the two. The analytical solutions obtained allow general trends to be extracted: the noncontact and the intermittent contact show a very discriminate variation of the phase. Therefore the measurement of the phase becomes a simple way to identify whether or not the tip touches the surface during the oscillating period. It is also found that the key parameter governing the structure of the dynamical properties is the product of the quality factor by a reduced stiffness. In the attractive regime, the reduced stiffness is the ratio of an attractive effective stiffness and the cantilever one. In the repulsive regime, the reduced stiffness is the ratio between the contact stiffness and the cantilever one. The quality factor plays an important role. For large values of the quality factor; it is predicted that a pure topography can be obtained whatever the value of the contact stiffness. For a smaller quality factor, the oscillator becomes more sensitive to change of the local mechanical properties. As a direct consequence, varying the quality factor, for example with a vacuum chamber, would be a very interesting way to investigate soft materials either to access topographic information or nanomechanical properties.
Stark effect on the S1←S transition of cis-free base isobacteriochlorin in an n-octane single crystal at 5 K
Authors: Singh Amarnauth , Huang Wen-Ying , Johnson Lawrence W.
Published: July 2002

High-resolution Stark effect measurements on the S1←S0(ππ*) origin of cis-free base isobacteriochlorin in single crystals of n-octane at 5 K are reported. The spectral splittings of the band at 15 822 cm−1 are linearly dependent on the applied electric field. The change in dipole moment (Δμ) was found to be 1.32 D and is parallel to the crystal’s b-axis. This band blueshifted as the polarity of the solvents at room temperature was increased, which implies that Δμ is negative. To rationalize the large magnitudes and opposite signs of the cis and trans tautomers’ Δμ values, we propose a simple valence-bond model based on ionic resonance structures.
Theory of lamellar–lamellar phase transitions in pure and mixed surfactant solutions
Authors: Noro Massimo G. , Gelbart William M.
Published: July 2002

There is a variety of experimental evidence for lamellar-to-lamellar phase transitions in aqueous solutions of single- and two-component surfactant systems. We develop here the statistical thermodynamics of alternative scenarios for lamellar–lamellar coexistence. In one case the transition involves phase separation driven by demixing of the two amphiphiles within each bilayer; a purely repulsive interaction between bilayers is sufficient, because of its dependence on bilayer composition. In the complementary case, a condensation-type phase change is involved, caused by the competition between attractive and repulsive interactions; the primary order parameter for this transition is the overall surfactant concentration.
Thickness-dependent melting transition in Langmuir–Blodgett films
Authors: Fontana M. P. , Facci Paolo
Published: July 2002

Fatty acid Langmuir–Blodgett films, a quartz crystal microbalance, and Fourier-transform infrared dichroism have been used to study the evolution of the melting transition upon the variation of the sample thickness, from bulk to a few monolayers. Whereas ordinary bulk behavior was observed for samples all the way down to n=12 layers, a crossover range of 12⩽n⩽8 was identified to a continuous transition, characterized also by the existence of an intermediate orientationally ordered phase. Measurements on annealed samples indicated the strong sensitivity of such a phase and the order of the transition to defects and sample metastability.
Mass spectroscopic studies of laser ablated carbon clusters as studied by photoionization with 10.5 eV photons under high vacuum
Authors: Wakabayashi Tomonari , Momose Takamasa , Shida Tadamasa
Published: July 2002

Neutral carbon clusters Cn (n=1–30) produced along with ionic clusters in laser vaporized graphite are studied under high vacuum by combined use of time-of-flight (TOF) mass spectroscopy and one photon ionization with a photon energy of 10.5 eV. The TOF mass distribution pattern shows intensification of the C4n+2 (n⩾2) clusters more clearly than the previous work by Kaizu et al. [J. Chem. Phys. 106, 9954 (1997)] who employed the same 10.5 eV photon but photoionized the neutral clusters generated by laser vaporization of graphite in helium buffer gas. The intensification is attributed to the intrinsic stability of the C4n+2 (n⩾2) neutral clusters, probably due to the monocyclicity. Two different line shapes of the mass spectral peak are observed for one and the same cluster size. The line shape with a tailing toward longer flight times is associated with the neutral clusters produced by relatively slow fragmentation of larger clusters (n≫30) followed by autoionization of the fragmented clusters. The other sharp line shape is associated with prompt ionization by the 10.5 eV photon. It is concluded that only the electronically excited neutral clusters are ionized for n⩽5 whereas the clusters with n>5 are ionized irrespective of their electronic state.
Proton tunneling of tropolone in durene single crystal as studied by time-resolved EPR detected excitation spectroscopy
Authors: Ikoma Tadaaki , Akiyama Kimio , Tero-Kubota Shozo , Ikegami Yusaku
Published: July 2002

We have measured the excitation spectra for tropolone–OH in durene single crystal and tropolone–OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm−1 was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S1 state. Moderately asymmetric potentials of the S0 and S1 states, where the energetic imbalance between two wells in the S1 state potential is opposite the S0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (01+<01−). A well-resolved progression of a phonon band with a 15 cm−1 separation was also obtained in durene crystal at very low temperature. From a Franck–Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state.
Ab initio near edge soft x-ray absorption fine structure (AI-NEXAFS) spectrum of ethylene
Authors: Nicolas G. , Gadea F. X.
Published: July 2002

We present here an ab initio calculation of the C(1s−1,π*) absorption band of ethylene. The linear vibronic coupling model is used with the aid of large configuration interaction (CI) ab initio calculations. The vibronic model involves the three totally symmetric vibrational motions (ν1,ν2,ν3) and the two non-totally symmetric ones (ν11,ν12). For all these in-plane modes, the ab initio potential energy curves are obtained for the electronic ground state and for the two lowest core-excited (1s→π*) states by multireference CI calculations including variational and pertubative contributions. The potential curves are fitted by polynomial expansions from which two sets of effective parameters are extracted for the linear coupling model. In this way, through the effective parameters, anharmonicities of the potentials and changes in the frequency from the ground to the core-excited states are taken into account without any adjustment. The contribution of the out-of-plane modes (ν4,ν7,ν8) is also considered assuming the commutation of in-plane and out-of-plane Hamiltonians. The final calculated spectrum involving the in-plane and the out-of-plane vibrational modes is found to be in good agreement with the experimental one, showing evidence for symmetry breaking and core-hole localization.
Stability of bicontinuous cubic phases in ternary amphiphilic systems with spontaneous curvature
Authors: Schwarz U. S. , Gompper G.
Published: July 2002

We study the phase behavior of ternary amphiphilic systems in the framework of a curvature model with nonvanishing spontaneous curvature. The amphiphilic monolayers can arrange in different ways to form micellar, hexagonal, lamellar, and various bicontinuous cubic phases. For the latter case we consider both single structures (one monolayer) and double structures (two monolayers). Their interfaces are modeled by the triply periodic surfaces of constant mean curvature of the families G, D, P, C(P), I-WP, and F-RD. The stability of the different bicontinuous cubic phases can be explained by the way in which their universal geometrical properties conspire with the concentration constraints. For vanishing saddle-splay modulus κ̄, almost every phase considered has some region of stability in the Gibbs triangle. Although bicontinuous cubic phases are suppressed by sufficiently negative values of the saddle-splay modulus κ̄, we find that they can exist for considerably lower values than obtained previously. The most stable bicontinuous cubic phases with decreasing κ̄<0 are the single and double gyroid structures since they combine favorable topological properties with extreme volume fractions.
Autoionization-detected infrared spectroscopy of intramolecular hydrogen bonds in aromatic cations. II. Unconventional intramolecular hydrogen bonds
Authors: Fujimaki Eiji , Fujii Asuka , Ebata Takayuki , Mikami Naohiko
Published: July 2002

A newly developed infrared spectroscopic technique, called autoionization-detected infrared (ADIR) spectroscopy, was applied for a study on hydroxyl–alkyl interactions in cresol and ethylphenol cations. In this technique, vibrational transitions in the ion core of high Rydberg states, which has almost the same vibrational structure as the corresponding bare molecular ion, are measured by detecting the vibrational autoionization signal. The OH stretching vibrations in the rotational isomers of the ortho-, meta-, and para-cresol cations and those of the ethylphenol cations were observed. Remarkable low-frequency shifts of the OH vibration were found only for the cis rotational isomers of the ortho-cresol and ortho-ethylphenol cations, whereas no such shift was found for all the other rotational and structural isomer cations. On the other hand, no remarkable shift of the OH stretch frequency was found for all the isomers in the neutral ground state. These results indicate that an intramolecular hydrogen bond is formed between the hydroxyl and alkyl groups in the cationic ground state of ortho-cresol and ortho-ethylphenol. The remarkable low-frequency shift of the OH vibration also indicates that the alkyl group acts as a proton acceptor in the hydrogen bond. This is a new type of intramolecular hydrogen bond, and the origin of such unconventional hydrogen bond in the cations is discussed.
Crystal field analysis and Monte Carlo simulation of lattice disordering for Cm3+ in YPO4 and LuPO4
Authors: Liu G. K. , Zhorin V. V. , Li S. T. , Beitz J. V.
Published: July 2002

A method of analyzing inhomogeneous line broadening with crystal-field theory is presented. For actinide ions with unfilled f-shells in solids, the most important contribution to line broadening of f-electron transitions is from short-range interactions with distorted lattice. Optically active curium ions are used to measure the degree of radiation damage in the vicinity of their lattice site. The radiation damage was produced by decay of distant 244Cm3+ ions. Fluorescence line narrowing (FLN) spectra show that inhomogeneous line broadening induced by α-decay of the actinide ion 244Cm3+ in single crystals of LuPO4 and YPO4 has a microscopic nature. Namely, correlation is absent between energy levels of the Cm3+ ions at different local environments. Monte Carlo simulation of lattice distortion and crystal-field calculation of Cm3+ energy levels have been conducted to provide a quantitative interpretation of the experimental results. This method should be applicable to 4f- and 3d-ions in crystalline materials with lattice distortion.
Gated escaping of ligand out of protein
Authors: Sheu Sheh-Yi , Yang Dah-Yen
Published: July 2002

We construct a new gating model and develop a new theory to study the escaping process of a ligand out of a spherical cavity with a puncture (or gate) on the surface. The gate undulation can be regulated by any time-dependent function and the motion of the ligand inside the spherical cavity is mapped into a two-dimensional entropy potential surface. Hence the driving force of our model is entropy only. For a static gate, the escaping process corresponds to climbing a two-dimensional entropy barrier. When the gate open angle is small, the escaping rate is proportional to the square of the opening angle. The prefactor of the escaping rate constant depends on the curvature of the entropy potential surface. For coherent gating, the survival time depends not only on the gate undulation frequency but also on how the initial state is defined. On the escaping from protein, our escaping rate shows it is qualitatively consistent with the experimental result of ligand recombination in myoglobin.
Rotationally resolved pulsed-field ionization photoelectron bands for O2+(A 2Πu,v+=0–12) in the energy range of 17.0–18.2 eV
Authors: Song Y. , Evans M. , Ng C. Y. , Hsu C.-W. , Jarvis G. K.
Published: July 2002

We have obtained rotationally resolved pulsed-field ionization photoelectron (PFI-PE) spectra for O2 in the energy range of 17.05–18.13 eV, covering the ionization transitions O2+(A 2Πu,v+=0–12,N+)←O2(X 3Σg−,v″=0,N″). Although these O2+(A 2Πu,v+) PFI-PE bands have significant overlaps with vibrational bands for O2+(a 4Πu) and O2+(X 2Πg), we have identified all the O2+(A 2Πu,v+=0–12) bands by simulation of spectra obtained using supersonically cooled O2 samples with rotational temperatures ≈20 and 220 K. While these v+=0–12 PFI-PE bands represent the first rotationally resolved photoelectron data for O2+(A 2Πu), the PFI-PE bands for O2+(A 2Πu,v+=9 and 10) are the first rotationally resolved spectroscopic data for these levels. The simulation also allows the determination of accurate ionization energies, vibrational constants, and rotational constants for O2+(A 2Πu,v+=0–12). The analysis of the PFI-PE spectra supports the conclusion of the previous emission study that the O2+(A 2Πu,v+=9 and 10) states are strongly perturbed by a nearby electronic state.
Diffusion anomaly from analytical formula
Authors: Sarkar Subir , Kumar A. V. Anil , Yashonath Subramanian
Published: July 2002

An analytic expression is derived for the diffusion coefficient of a sorbate in a crystalline porous solid with bottlenecks. The diffusion coefficients obtained from the analytic expression is found to agree well with the molecular dynamics results. It is also found to reproduce the temperature dependence of the levitation effect for zeolites Y and A. The present calculations provide a strong theoretical support for the levitation effect obtained so far purely from molecular dynamics calculations.
Resonance Raman study of the solvatochromic electronic transitions of [Ru(NH3)4bipyridine]2+ in methanol and dimethylsulfoxide
Authors: Streiff John , McHale Jeanne L.
Published: July 2002

The electronic transitions of [Ru(NH3)4bipyridine]2+(R4AB) in the visible region are solvatochromic due to hydrogen bonding interactions with the solvent. In this work, we employ resonance Raman and absorption spectroscopy to separate the static and dynamic contributions to the solvatochromic shift. Raman excitation profiles for R4AB in methanol (MeOH) and dimethylsulfoxide (DMSO) were obtained at wavelengths within the lowest energy absorption band, which comprises two overlapping metal-to-ligand charge transfer (MLCT) transitions (the red band), and preresonant with a higher energy blue band. The absorption and Raman profiles of R4AB were analyzed using time-dependent theory to determine the 0–0, internal, and solvent reorganization energies, the sum of which is the energy of maximum absorption. It is concluded that the solvatochromic shift in the transition energy of each of the two visible MLCT bands is due mainly to changes in the 0–0 energy, while the internal and solvent reorganization energies are found to be similar in MeOH and DMSO. Preresonance enhancement via the blue band is larger in methanol than in DMSO. The question of the composite nature of the visible absorption band is addressed by modeling the low-temperature absorption spectrum, where two peaks in the red are resolved. The dimensionless displacements derived from the Raman modeling are shown to be consistent with attributing the structure to two overlapping electronic transitions rather than a vibrational progression. Depolarization ratio dispersion was found to be difficult to model, probably due to strong preresonance enhancement which is only accounted for phenomenologically in this work.
Experimental detection of nucleation rate surface singularity
Authors: Anisimov M. P. , Nasibulin A. G. , Shandakov S. D.
Published: July 2002

As a rule, the modern theories of nucleation represent only modifications of classical theory, and they still remain unsuitable for quantitative prediction of experimental results. In order to create the universal description of supersaturated vapor nucleation, as well as evaluate other theories, we need to get the reliable experimental results. Now experimental skills are high enough for precision measurements of the vapor nucleation rates as well as for detecting and evaluating, for example, temperatures of phase transitions in the new phase critical embryos. That is, one can find experimentally the singularity of the nucleation rate surface at conditions for the critical embryo phase transitions. Visual analysis of the experimental results has the low potential to detect the nucleation rate surface singularity and the surface singularity can be missed sometimes. One major problem for singularity detection is the noise of experimental results. This problem still exists even if one has experimental results of high accuracy. The condition for surface continuity and monotony could be applied as a criterion for analysis of experimental data for the vapor nucleation rates. The criterion is tested for the broad spectrum of the experimental results in the vapor nucleation. As an example of the criterion being used, the experimental results for the n-pentanol–water binary system of nucleation have been analyzed. A peculiarity of this system is the existence of a miscibility gap between the components. It was found that the criterion as a function of n-pentanol mole fraction has the singularity in the vicinity of this gap. This singularity was smoothed in the experimental results presentation and omitted in the original research. The proposed criterion can be used to search the experimental data set singularity as a function of their variable(s).
Electronic bath approach to thermal effects in ion-surface scattering
Authors: Sulston Kenneth W. , Goodman Frank O.
Published: July 2002

McDowell’s 1985 electronic bath theory of charge transfer is used to investigate the effect of varying surface temperature on the process of ion scattering from a solid surface. As a specific example, the system of Na+ scattered from W is modeled. The neutralization probability is found to have a significant temperature dependence only if the ion orbital energy is fairly close (within 1 eV) to the Fermi level, at closest approach. As well, the temperature effect is greatest when the ion’s incident energy is small (on the order of a few eV).
Calculations on the stability of low temperature solid nitrogen phases
Authors: Fabianski Robert , Kuchta Bogdan , Firlej Lucyna , Etters Richard D.
Published: July 2002

The thermodynamic stability of the low temperature α, γ, and ε phases of nitrogen is examined using an energy minimization technique. Three of the most successful potential forms available are studied and the results are not satisfactory. A recent potential form is modified by optimizing its parameters to seek agreement with experiment. This search yields phase transitions between the α, γ, and ε phases that are in good agreement with experiment, as are other important thermodynamic properties. The reason for this success is explained.
Surface aligned photochemistry: Photodissociation of Cl2 and Cl2⋯Cl adsorbed on LiF(001)
Authors: Giorgi Javier B. , Naumkin Fedor Y. , Polanyi John C. , Raspopov Sergei A. , Sze Newman S.-K.
Published: July 2002

Photodissociation of chlorine adsorbed on a LiF(001) surface at 25–70 K has been investigated by means of angularly resolved resonantly enhanced multiphoton ionization spectroscopy (REMPI). The translational-energy distributions and angular distributions for forming Cl(g) photofragments were determined. Photolysis was performed employing 351 nm radiation, with laser pulse energies of 0.3–1.2 mJ/cm2. A peak in the translational energy of Cl(g) at about 0.4 eV was identified as being due to the direct photodissociation of the Cl2(ad) molecule by 3.5 eV photons. Particular interest attached to the observation of a further channel (termed “A”) for photodissociation leading to Cl(g) with translational energy peaking at ∼1 eV and extending to 1.5 eV. The available photon energy renders it highly unlikely that this “high-energy” Cl(g) originates in Cl2(ad). Channel A had the same linear dependence of Cl-atom flux on laser pulse-energy as did the lower energy (0.4 eV) channel, termed “B,” but differed from it in exhibiting a slow approach to steady state. It appears that channel A requires the prior build-up of Cl(ad) concentration due to the photodissociation of Cl2. It is proposed that this leads to the formation of a steady-state concentration of Cl2⋯Cl which when photolyzed yields high-energy Cl(g) via channel A. Channel A exhibits a distinctive angular distribution at low coverage and a characteristic Cl*/Cl ratio, as compared with channel B. The suggested mechanism for channel A is Cl2⋯Cl+hν→Cl3*→Cl2•Cl→Cl2+Cl (where* is an electronically excited state and • represents repulsion in the lower electronic state to which Cl3* reverts). This mechanism is interpreted in terms of an extensive diatomics-in-molecules (DIM) model for the trichlorine radical, shown to be in agreement with high level ab initio multireference internally contracted configuration interaction (MRCI) calculations, and consistent with the observations.
The 1-silaketenyl radical (HSiCO): Ground and first excited electronic states
Authors: Yamaguchi Yukio , Petraco Nicholas D. K. , Brown Shawn T. , Schaefer Henry F.
Published: July 2002

The two lowest-lying (X̃ 2A″ and Ã 2A′) electronic states and lowest linear stationary point (1 2Π) of the 1-silaketenyl radical (HSiCO) have been investigated systematically using ab initio electronic structure theory. The lowest linear stationary point possesses two distinct imaginary vibrational frequencies along the HSiC bending coordinates, indicating a strong Renner–Teller interaction. The ground and first excited states of HSiCO are found to have trans-planar bent structures and they are more distorted from linearity but less polar than the corresponding states of HCCO. Specifically, the X̃ 2A″ structure features a small HSiC bond angle of 84°. With our most reliable method, cc-pVQZ CCSD(T), the classical X̃−Ã splitting has been predicted to be 35.7 kcal/mol (1.55 eV, 12 500 cm−1). The barriers to linearity were determined to be 53.5 kcal/mol (2.32 eV, 18 700 cm−1) for the X̃ 2A″ state and 17.8 kcal/mol (0.77 eV, 6240 cm−1) for the Ã 2A′ state. The ground state of HSiCO was found to be relatively stable thermodynamically against the two dissociation reactions HSiCO(X̃ 2A″)→H(2S)+SiCO(X̃ 3Σ−) and HSiCO(X̃ 2A″)→SiH(X̃ 2Π)+CO(X̃ 1Σ+). Due to the large infrared (IR) intensities of some of the vibrational modes, IR spectroscopic investigation of the HSiCO radical may be feasible. HSiCO is the global minimum for these four atoms, lying energetically below SiCOH (38.5 kcal/mol), HCSiO (40.7 kcal/mol), and CSiOH (76.3 kcal/mol) at the TZ2P(f,d) configuration interaction with single and double excitations (CISD) level of theory.
Two-dimensional hard dumbbells. I. Fluctuating cell model
Authors: Gay Shawn C. , Rainwater James C. , Beale Paul D.
Published: July 2002

We apply the fluctuating cell model to the calculation of free energies and pressures of high density phases of two-dimensional hard dumbbells using the Metropolis algorithm to generate configurations in the NVT ensemble. The natural logarithm of the average free volume is found to yield a better approximation of the free energy of the system than the value obtained from simple cell theory for all reduced bond lengths except very near the previously calculated hard disk limit. The proposed approximation for the free energy, when used in combination with a semianalytic algorithm to calculate free volumes, is found to be of comparable efficiency to the lattice-coupling method of Frenkel and Ladd. Unlike the simple cell model, the fluctuating cell model is applicable to molecules that freeze into plastic crystals as well as orientationally ordered crystals. We also calculate the distribution of free volumes in the solid phase. The nature of the distribution of free volumes changes abruptly near the hard-disk limit, similarly to the sudden change in validity of the fluctuating cell theory approximation.
Static dielectric constant of aqueous electrolyte solutions: Is there any dynamic contribution?
Authors: Chandra Amalendu
Published: July 2002

We investigate the presence of dynamic cross correlation between ionic current and collective dipole moment fluctuations and the contribution of such dynamic cross correlations to the static dielectric constant of electrolyte solutions by means of a series of sufficiently long molecular dynamics simulations of aqueous NaCl and KCl solutions at different concentrations ranging from 0.88 M to 4.5 M.
Localized-density-matrix method and nonlinear optical response
Authors: Liang WanZhen , Yokojima Satoshi , Chen GuanHua
Published: July 2002

The linear scaling localized-density-matrix (LDM) method is generalized to calculate the nonlinear optical responses of large polyacetylene oligomers. The ground state reduced single-electron density matrix is initialized by the divide-and-conquer approach and is obtained subsequently using the LDM method. The third-harmonic generation spectra of large oligomers are calculated. The saturation of off-resonant second hyperpolarizability χ(3)(0) has been reinvestigated, and the value of χ(3)(0) is found to depend mainly on the optical gap and the number of double bonds.
Dissociative photoionization of CF4 from 23 to 120 eV
Authors: Masuoka Toshio , Kobayashi Ataru
Published: July 2002

Using synchrotron radiation as a continuum light source, dissociative photoionization of CF4 has been studied in the photon-energy region of 23–120 eV. Ion branching ratios were obtained by analyzing time-of-flight mass spectra and were converted to the absolute partial cross sections for the production of singly charged CF3+, CF2+, CF+, F+, and C+ ions, as well as doubly charged CF32+ and CF22+ ions by using the reported total absorption cross sections of CF4. Ion branching ratios were differentiated with respect to the incident photon energy. The results obtained by this analytical photoion spectroscopy clearly show dissociation pathways of the CF4+ and CF42+ ions, many of which are observed for the first time in the present study. These pathways are discussed by comparing with the reported electronic states of the ions.
Field equations and the tetrad connection
Authors: Urani John R. , Kutchko Frank J.
Published: July 2002

A fundamental result of Geroch is that a space-time admits a spinor structure if and only if it is parallelizable. A nonsymmetric, metric-compatible curvature-free connection is associated with a global orthonormal tetrad field on such a parallelizable space-time. This connection is used to examine reported inconsistencies for S> 1/2 spinor field equations on general space-times. It is shown that the assumed Levi–Civita transport of Clifford units causes the inconsistencies at the Klein–Gordon stage. The relation of the torsion tensor of the parallelization connection to the space-time topology is indicated and the Lorentz covariance of the modified Klein–Gordon equations is demonstrated. A particularly simple plane-wave solution form for free-field equations is shown to result for locally flat space-times for which the torsion tensor is necessarily zero.
On the spectra of SO(3) scalars in the enveloping algebra of SU(3)
Authors: De Meyer H. , Vanden Berghe G. , Van der Jeugt J.
Published: July 2002

Formulas are given that make it possible to calculate the eigenvalues of the two independent SO(3) scalars O0l and Q0l in the SU(3) enveloping algebra.
The four-dimensional conformal Kepler problem reduces to the three-dimensional Kepler problem with a centrifugal potential and Dirac’s monopole field. Classical theory
Authors: Iwai Toshihiro , Uwano Yoshio
Published: July 2002

The four-dimensional conformal Kepler problem is reduced by an S1 action, when the associated momentum mapping takes nonzero fixed values. The reduced Hamiltonian system proves to be the three-dimensional Kepler problem along with a centrifugal potential and Dirac’s monopole field. The negative-energy surface turns out to be diffeomorphic to S3×S2, on which the symmetry group SO(4) acts. Constants of motion of the reduced system are also obtained, which include the total angular momentum vector and a Runge–Lenz-like vector. The Kepler problem is thus generalized so as to admit the same symmetry group.
Positivity and unimodality as stabilizers of the analytic extrapolation of a function known with errors
Authors: Antolín J. , Cruz A.
Published: July 2002

Positivity and unimodality hypotheses on an unknown function χ1(x) confer Stieltjes character to another function H1(z), known in a discrete set of real points and affected by errors caused by experimental measurements, and impose constraints on the coefficients of its formal expansion which limit the universe of approximant functions, so acting as stabilizers of the analytic extrapolation. The type I Padé approximants, built with the coefficients of the formal expansion, provide rigorous bounds on the function in the cut complex plane. The application of a Stieltjes–Chebyshev technique allows approximations to the function, even on the cut, to be obtained. The physical problem of K±p forward elastic scattering is approached by the previous method, and bounds on the coupling constant and real part of the amplitude are found.
Eigenvalues and eigenvectors of the finite Fourier transform
Authors: Mehta M. L.
Published: July 2002

The eigenvalues and eigenvectors of the n×n unitary matrix of finite Fourier transform whose j, k element is (1/(n)1/2)exp[(2πi/n)jk], i=(−1)1/2, is determined. In doing so, a multitude of identities, some of which may be new, are encountered. A conjecture is advanced.
States and derivations on quasi-*-algebras
Authors: Trapani Camillo
Published: July 2002

The Gel’fand–Naimark–Segal representation is extended to quasi-*-algebras, provided that a suitable choice of states is made. Derivations of quasi-*-algebras and, in particular, of left-Hilbert quasi-*-algebras are studied.
Solutions of reaction-diffusion integral equations describing explosive evolution of densities for localized structures
Authors: Wilhelmsson Hans
Published: July 2002

Reaction-diffusion integral equations are studied with special regard to explosive-type solutions. Certain localized structures can grow explosively in time without change in spatial structure. The characteristic shapes can be described in terms of elliptic functions.
Electromagnetic angular momentum radiated by two-point charges
Authors: Aguirregabiria J. M. , Etxebarria J. R.
Published: July 2002

A previous covariant approach in classical field theory to the definition of the energy and linear momentum radiated by two-point charges is extended to the case of angular momentum. First, the mixed contribution to the radiation rate of angular momentum for two proper time infinitesimal intervals is defined, shown to be independent of the hypersurface used, and computed in an exact covariant way. With this result a definition of the radiated angular momentum for a system of interacting particles is given in the framework of predictive relativistic mechanics. The lowest order of this quantity is calculated and compared with a previous result obtained by means of a different method. The agreement of the results obtained in both approaches can be interpreted as a test for the Lorentz–Dirac equation.
Origin of the Lagrangian constraints and their relation with the Hamiltonian formulation
Authors: Cariñena José F. , López Carlos , Román-Roy Narciso
Published: July 2002

The theory of presymplectic systems is used for the study of mechanical systems described by singular Lagrangians in order to clarify the geometric meaning of the Euler–Lagrange equations for such systems. The two different types of primary constraint functions arising in the Lagrangian formulation are analyzed by means of the relation between the image under the vertical endomorphism of the kernel of the presymplectic form ωL and its vertical part. The connection with the Hamiltonian Dirac theory is also studied and the theory is illustrated with several examples.
Splitting methods and invariant imbedding for time-independent wave propagation in focusing media and wave guides
Authors: Evans J. W.
Published: July 2002

For time-independent wave propagation in focusing media or wave guides, backscattering and coupling between propagation modes are caused by deterministic or random variations of the refractive index in the distinguished (x) direction of propagation. Various splittings of the wave field into forward and backward traveling components, which lead to coupled equations involving abstract operator coefficients, are presented. Choosing a natural explicit representation for these operators immediately yields a coupled mode form of these equations. The splitting procedure also leads naturally to abstract transmission and reflection operators for slabs of finite thickness (a≤x≤b), and abstract invariant imbedding equations satisfied by these. The coupled mode form of these equations, together with such features as reciprocity (associated with an underlying symplectic structure) are also discussed. The example of a square law medium is used to illustrate some of these concepts.
Structure of the space of solutions of Einstein’s equations: A new variables approach
Authors: Saraykar R. V.
Published: July 2002

Following Ashtekar’s new Hamiltonian formulation of general relativity [‘‘A new Hamiltonian formulation of general relativity,’’ Syracuse University preprint, 1986; Phys. Rev. Lett. 57, 2244 (1986); Proceedings of the Florence Conference on ‘‘Constrained Systems’’ (World Scientific, Singapore, 1986)], the results of Arms, Fischer, Marsden, and Moncrief [Ann. Inst. H. Poincaré 33, 147 (1980); Ann. Phys. (NY) 144, 81 (1982)] on the structure of the space of solutions of vacuum Einstein equations in the case of space-times admitting a compact Cauchy hypersurface are rederived and extended.
Stochastic calculus on distorted Brownian motion
Authors: Pantić Dražen
Published: July 2002

Relations between Malliavin’s calculus and the formulation of Schrödinger dynamics in terms of local Dirichlet forms are investigated. It is proved that under mild regularity conditions there exists a directional derivative of the solution of the stochastic equation associated with the corresponding Dirichlet form. Also, sufficient conditions are given so that E{ f(Xt,x)} is a strong solution of the Cauchy problem (∂/∂t) h(t,x)=(−Δ+Q(x))h(t,x), where {Xt,x, t>0}, x∈Rd, is a distorted Brownian motion.
Transformation group acting on a self-dual Yang–Mills hierarchy
Authors: Nakamura Yoshimasa
Published: July 2002

A GL(n,C) self-dual Yang–Mills hierarchy is introduced; it is an infinite system of self-dual Yang–Mills equations having an infinite number of independent variables. Cauchy problems for the hierarchy are formally solved by using Lie transforms of a wave matrix. A relationship between the Kadomtsev–Petviashvili hierarchy and the self-dual Yang–Mills hierarchy is discussed. Furthermore, it is shown that an infinite-dimensional transformation group acts on a solution space to the (n≥2) self-dual Yang–Mills hierarchy. A parametric solution to the hierarchy is also given as a representation of the transformation group.
Global hyperbolicity of a spatially closed space-time
Authors: Matori Yoshihiro
Published: July 2002

A spatially closed space-time is shown to be globally hyberbolic.
Lie algebra automorphisms, the Weyl group, and tables of shift vectors
Authors: Bouwknegt Peter
Published: July 2002

The canonical lift of the Weyl group in the automorphism group of a simple Lie algebra is discussed. A constructive algorithm is given to compute the shift vector for every Weyl group conjugacy class, and tables for the simply laced Lie algebras of rank ≤8 are provided. Applications in physics, such as the equivalence of certain orbifold and twisted WZW string models, as well as the implication for the moduli space of 2-D conformal field theories are discussed.
Blow-up of the SU(2,C) Yang–Mills fields
Authors: Yang Yisong
Published: July 2002

It is remarked that, if the gauge group is not compact, finite−time blowing−up Yang–Mills fields over the Minkowski spaces may exist. The example taken is G=SU(2,C). It is shown that blow−up can occur in an arbitrarily small time interval when the initial data of the fields are suitably chosen.
Bargmann–Wigner equations in de Sitter space
Authors: Heidenreich W. F. , Lorente M.
Published: July 2002

Bargmann–Wigner equations in (3,2)-de Sitter space are found for all spins s≥1 and all masses. The massless fields have gauge freedom; they can be extended to indecomposable representations of the form of Gupta–Bleuler triplets.
Comment on ‘‘Some results from a Mellin transform expansion for the heat kernel’’ [J. Math. Phys. 3
0, 1226 (1989)]
Authors: Malbouisson A. P. C. , Simào F. R. A. , Ferraz de Camargo Fo A.
Published: July 2002

In this note the inaccuracies contained in the above mentioned paper are corrected and some of the results therein are modified and extended. In particular, formulae are given for directly calculating the coefficients of the heat kernel expansion, not making appeal to recurrence in the heat equation. The nonexistence of a class of anomalies in odd dimension is proved.
A Hamiltonian-free description of single particle dynamics for hopelessly complex periodic systems
Authors: Forest Étienne
Published: July 2002

A picture of periodic systems that does not rely on the Hamiltonian of the system, but on maps between a finite number of time locations, is developed. Moser or Deprit-like normalizations are done directly on the maps, thereby avoiding the complex time-dependent theory. Linear and nonlinear Floquet variables are redefined entirely in terms of maps. This approach relies heavily on the Lie representation of maps introduced by Dragt and Finn [J. Math. Phys. 20, 2649 (1979); J. Geophys. Res. 81, 13 (1976)]. One might say that although the Hamiltonian is not used in the normalization transformation, Lie operators are used, which are themselves, in some sense, pseudo-Hamiltonians for the maps they represent. The techniques find application in accelerator dynamics or in any field where the Hamiltonian is periodic, but hopelessly complex, such as magnetic field design in stellarators.
An example of a nontrivial causally simple space-time having interesting consequences for boundary constructions
Authors: Rübe Petra
Published: July 2002

An example is given of a causally simple space-time that may serve as a counterexample for various purposes, such as showing that for a general causally simple space-time the chronological common past of a terminal indecomposable future set need not be an indecomposable set.
Renormalized equations for linear transport in stochastic media
Authors: Malvagi F. , Pomraning G. C.
Published: July 2002

The master equation is used to obtain a model describing the ensemble-averaged intensity corresponding to linear particle transport in randomly mixed immiscible fluids. An asymptotic limit corresponding to small amounts of opaque fluids admixed with large amounts of transparent fluids is employed to reduce the complexity of the description. In the limit of a single transparent fluid, a renormalized transport equation is obtained, involving an effective source and effective interaction coefficients that account, in a simple way, for the statistical nature of the problem in this asymptotic limit.
Ricci and contracted Ricci collineations of the Robertson–Walker space-time
Authors: Núñez L. , Percoco U. , Villalba V. M.
Published: July 2002

Ricci collineations and contracted Ricci collineations of the Robertson–Walker metric, associated with a vector field of the form ξ=(ξ0(t,r),ξ1(t,r),0,0) are presented.
Multiple scattering of elastic waves by a distribution of identical spheres
Authors: Phanord D. D. , Berger N. E.
Published: July 2002

Self-consistent integral equations for multiple scattering amplitudes and dispersion relations for coherent propagation of elastic waves, are obtained from general reciprocity, two space scatterer formalism and by averaging the functional equations relating the multiple and single scattering amplitudes of the spheres. Approximations for bulk wave propagation numbers are derived.
Reciprocity relations and energy theorems for multiple scattering of elastic waves
Authors: Phanord D. D. , Berger N. E.
Published: July 2002

Reciprocity relations, energy theorems, and scattering cross sections are derived for a fixed configuration of N-identical and similarly aligned lossless scatterers whose centers are uniformly distributed in a given volume. The general results are specialized to scattering in the forward direction.
A geometrical formulation of fermionic integrable systems
Authors: Das Ashok , Huang Wen-Jui , Roy Shibaji
Published: July 2002

A fermionic Hamiltonian system is formulated on a supermanifold. It is shown that if the system possesses a bi-Hamiltonian structure, one can naturally define a Lax equation associated with a (1,1) tensor on this supermanifold and this allows one to construct a set of conserved quantities. Furthermore, if the corresponding Nijenhuis tensor vanishes, it is shown that all these conserved quantities would be in involution which is a sufficient condition for integrability of the system. The fermionic extension of the KdV equation with a bi-Hamiltonian structure within this geometrical approach is studied.
Asymptotic representations of the running parameters in Yang–Mills theories
Authors: Maximov S. I. , Vovk V. I.
Published: July 2002

A unique perturbative solution to the renormalization group (RG) equation for the running coupling constant (RCC) will be proven to exist. The general representations of the running coupling constant and mass in the form of asymptotic expansions are explicitly derived. A two-parametric ambiguity is discovered in these expansions which leaves the full result invariant. This feature is observed to be an attribute of the particular type of transcendental equations resulting from the differential RG equation for the RCC.
Three-body plane wave at zero angular momentum and some addition theorems
Authors: Kvitsinsky A. A. , Merkuriev S. P.
Published: July 2002

A quantum three-body system with zero angular momentum is considered. The plane wave ℱ related to this problem is studied. It is proved to be a function of two variables that have a meaning of the eikonals on the internal space. A number of explicit formulas for ℱ and its asymptotics are derived. New addition theorems for the scalar hyperspherical harmonics as well as for some special functions are obtained.
On the Wigner and the Racah coefficients of suq(2) and suq(1,1)
Authors: Maekawa Takayoshi
Published: July 2002

An explicit expression for the Wigner coefficients coupling two positive (or negative) discrete series of the representations is obtained and the Racah coefficients for these cases are found with a single sum.
C-integrable nonlinear PDEs. II
Authors: Calogero F. , Xiaoda Ji
Published: July 2002

A technique to perform a convenient Change of (independent) variables in a PDE is reported, and it is used to generate C-integrable nonlinear PDEs, i.e., nonlinear PDEs solvable by an appropriate Change of variables. Several examples of such PDEs are exhibited.
Hilbert space representations of the Poincaré group for the Landau gauge
Authors: Cassinelli G. , Truini P. , Varadarajan V. S.
Published: July 2002

The theory of the electromagnetic quantum field in the Landau gauge has always lacked a treatment based on a Hilbert space of C4 -valued functions (the one particle space) on which the Poincaré group acts via a continuous representation realized by bounded operators. In the present paper the gap will be filled and it will be shown, through the mathematical technique of jets on the forward light cone in momentum space, how the theory presented extends the previous treatments of the problem. In order to show that the massless vector field theory in the Landau gauge can be obtained, the equation of motion and the two-point function will be derived in the present model according to the Wightman axioms.
The covariant many-body problem in quantumelectrodynamics
Authors: Barut A. O.
Published: July 2002

The two-body covariant equation recently applied to QED problems is here generalized to N spin 1/2 particles interacting via the exchange of massless vector bosons and derived from an action principle. This is a nonperturbative one-time equation whose Hamiltonian is additive in the center of mass and relative variables. All recoil corrections and radiative effects are included. In this formulation, the relativistic many-body problem has the same structure as the Schrödinger many-body problem.
A new invariant of superconformal OSp(n‖1)
Authors: D’Hoker Eric
Published: July 2002

A new invariant under extended superconformal OSp(n‖1) transformations acting on three points in the superplane is discussed. Under the linear action of OSp(n‖1), this results in an invariant multilinear form or tensor of degree 3n, which acts on vectors of dimension n‖2.
On interpretation of the magnetized Kerr–Newman black hole
Authors: Karas V. , Vokrouhlický D.
Published: July 2002

An electromagnetic field in the vicinity of the magnetized Kerr–Newman black hole is studied. In the extreme case, the field does not thread the horizon of an electrically neutral configuration. Analogically, the magnetic field is expelled out of an extreme black hole with zero angular momentum. Uniqueness of the magnetized Schwarzschild black hole is discussed.
Coinciding versus noncoinciding: Is the topological spin-statistics theorem already proven in quantum mechanics?
Authors: Tscheuschner Ralf D.
Published: July 2002

It will be demonstrated that subtle features in the topologization of the configuration space of positive and negative objects determine the spin-statistics relation of the associated quantum theories.