bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristic features of the electrostatic potentials of singly negative monoatomic ions
Authors: Sen K. D. , Politzer Peter
Published: July 2002

We show that a monoatomic negative ion has a minimum in its electrostatic potential V(r) occurring at the radial distance rm that encompasses a quantity of electronic charge exactly equal to the nuclear charge. Thus, V(rm) is due entirely to the excess electronic charge on the ion. We suggest that rm can be identified with the radius of the ion, while V(rm) indicates the strength of its interactions with positive ions.
Approximate radii for singly negative ions of 3d, 4d, and 5d metal atoms
Authors: Sen K. D. , Politzer Peter
Published: July 2002

The radii and electrostatic potential of singly−negative ions of the 3d,4d and 5d transition series have bee calculated. This gives a quantitative estimate of the size of these ions.(AIP)
Structural steps to oxidation of Ni(100)
Authors: Wang W.-D. , Wu N. J. , Thiel P. A.
Published: July 2002

In this paper, we emphasize the temperature- and exposure-dependent development of low-energy electron diffraction patterns,measured quantitatively during oxidation of Ni(100) at 80 to 400 K. We find a strong temperature dependence in the development of LEED patterns associated with NiO. NiO(111) is favored by adsorption temperatures below 300 K, whereas a (7×7)-like structure is favored by adsorption temperatures of 300 to 400 K. Room temperature is a ‘‘crossover’’ point between these two forms of the oxide. The final oxide depth is independent of adsorption temperature and, therefore, of epitaxial orientation, between 80 and 400 K. When the sample is heated in vacuum after adsorption, massive rearrangements take place above 500 K. Some of the nickel reverts to metallic nickel covered by a c(2×2) oxygen overlayer, and some forms NiO crystallites which are probably deeper than the initial oxide skin. Effectively, the parent oxide disproportionates into a less-oxygen-rich phase and a more-oxygen-rich phase. This is again independent of the orientation of the initial oxide epitaxy.
Dielectric dispersion of primary alcohols in polymer complex
Authors: Asaka Nobuyuki , Shinyashiki Naoki , Umehara Toshihiro , Mashimo Satoru
Published: July 2002

Dielectric measurements using a frequency region 106–1010 Hz were performed on methanol and ethanol-polyvinyl pyrolidone systems by a time domain reflectometry. Two relaxation peaks were observed for each system. The high frequency process is the primary process of the alcohols. Relaxation time varies little with the polymer concentration. In the case of the ethanol system, its extrapolated value for pure polymer is 280 ps and does not differ much from the value of 130 ps for pure alcohol. For the methanol system, it changes from 280 to 55 ps. It is suggested that the process is due to reorientation of two hydroxyl groups in the alcohol chain, which involves breakage and remaking of a hydrogen bond and the low frequency process, of which relaxation time is about 10 ns, is due to reorientation of alcohol molecules bonded to the polymer.
Coupled-cluster open-shell analytic gradients: Implementation of the direct product decomposition approach in energy gradient calculations
Authors: Gauss Jürgen , Stanton John F. , Bartlett Rodney J.
Published: July 2002

Analytic energy gradients for the coupled-cluster singles and doubles (CCSD) method have been implemented for closed-shell systems using restricted Hartree–Fock (RHF) and open-shell systems using unrestricted Hartree–Fock (UHF) reference functions. To achieve maximum computational efficiency, the basic theory has been reformulated in terms of intermediates, thus reducing the number of required floating-point operations, and all computational steps are given in terms of matrix products in order to exploit the vector capabilities of modern supercomputers. Furthermore, the implementation has been designed to take full advantage of Abelian symmetry operations. To illustrate the computational efficiency of our implementation and in particular to demonstrate the possible savings due to the exploitation of symmetry, computer timings and hardware requirements are given for several representative chemical systems. In addition, the newly developed analytic CCSD gradient methods are applied to calculate the equilibrium geometry and energy splitting of the lowest singlet and triplet states of the C4O2 molecule.
Radial behavior of the average local ionization energies of atoms
Authors: Politzer Peter , Murray Jane S. , Grice M. Edward , Brinck Tore , Ranganathan Shoba
Published: July 2002

The radial behavior of the average local ionization energy Ī(r) has been investigated for the atoms He–Kr, using ab initio Hartree–Fock atomic wave functions. Ī(r) is found to decrease in a stepwise manner with the inflection points serving effectively to define boundaries between electronic shells. There is a good inverse correlation between polarizability and the ionization energy in the outermost region of the atom, suggesting that Ī(r) may be a meaningful measure of local polarizabilities in atoms and molecules.
Reconstruction of the one-particle density matrix from expectation values in position and momentum space
Authors: Schmider Hartmut , Smith Vedene H. , Weyrich Wolf
Published: July 2002

For the beryllium atom, it is demonstrated that coherent form factors F(k) can be insufficient for inferring the one-particle reduced density matrix (ODM). The description in terms of reciprocal form factors B(s) as the complementary momentum-space property is compared with the results for a least-squares fit to F(k) data. A virtually complete description of the true ODM may be obtained by using a combined data set, as can be shown by representing the ODM in spherically averaged form.
One-particle density matrices along the molecular bonds in linear molecules
Authors: Schmider Hartmut , Edgecombe Kenneth E. , Smith Vedene H. , Weyrich Wolf
Published: July 2002

The bonding in a number of σ-bonded diatomic and linear triatomic molecules is interpreted in terms of the one-particle density matrix (ODM) along the bond axis. Special attention is drawn to the off-diagonal contributions of the ODM in a two-dimensional position space representation, which are shown to be indicative of a bonding or antibonding covalent interaction between the atomic centers.
Intracavity C atom absorption in the tuning range of the ArF excimer laser
Authors: Versluis Michel , Meijer Gerard
Published: July 2002

Our tunable ArF excimer laser has no laser action in a region around 51 790 cm−1 due to an intracavity 3 1P←2 1D C atom absorption. This has a direct consequence for the interpretation of the photodissociation processes in CO at 193 nm.
Millimeter-wave spectroscopy of MgF: Structure and bonding in alkaline–earth monofluoride radicals
Authors: Anderson M. A. , Allen M. D. , Ziurys L. M.
Published: July 2002

The pure rotational spectrum of the MgF radical in its ground electronic state (X 2Σ+) has been recorded using millimeter/submillimeter direct absorption techniques. Transitions arising from the v=0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, 24MgF, have been observed. In addition, spectra of the isotopomers 26MgF and 25MgF in the natural abundances of magnesium have been detected. Rotational and fine structure constants have been determined for these species, as well as hyperfine parameters for the fluorine nucleus (I=1/2). For 25MgF, the hyperfine structure was also resolved arising from the magnesium nucleus, which has I=5/2, yielding the 25Mg hyperfine and quadrupole constants. Comparison of these hyperfine parameters with those of the heavier alkaline–earth monofluorides and the free 25Mg+ atom suggests that there is an increase in covalent bonding in MgF vs its heavier fluoride counterparts. This behavior is also apparent in the hybridization of the wave function of the unpaired electron in MgF, which appears to consist of almost equal s and p character.
Photoinduced large amplitude motion as mechanism for pure electronic dephasing and its manifestation in continuous-wave and time-resolved spectroscopy
Authors: Stock Gerhard
Published: July 2002

It is demonstrated that photoinduced large amplitude (LA) dynamics on a picosecond time scale may result in electronic pure dephasing on a time scale of a few tens of femtoseconds. It is shown that LA photodynamics affects continuous-wave (cw) spectra (e.g., absorption and resonance-Raman) and transient spectra (e.g., photon-echo and pump–probe) in a rather different way. Calculations are presented for a two-dimensional model problem, consisting of a fast vibrational mode and a slow LA mode, which is considered as a simple model for isomerization. The spectroscopic signals for this model are compared to the results for a complementary model, where the fast vibrational mode interacts with a bath (e.g., the environment). It is shown that standard cw techniques such as absorption and resonance-Raman spectroscopy fail to clearly distinguish the two (physically rather different) model problems, as the ultrafast optical dephasing results in strong line broadening of these spectra. Time-resolved pump–probe spectroscopy, on the other hand, is not limited by electronic pure dephasing and thus allows for a clear discrimination of the two photophysical processes. Simulations of photon-echo experiments furthermore elucidate that slow intramolecular LA motion results in inhomogeneous broadening of optical spectra. Finally a novel time-resolved technique is proposed that is capable to reveal ‘‘sub-linewidth’’ information on electronic transitions which are strongly broadened by homogeneous and inhomogeneous pure dephasing processes.
Free energy and cluster structure in the coexistence region of the restricted primitive model
Authors: Caillol J.-M. , Weis J.-J.
Published: July 2002

The method of thermodynamic integration is used to determine the free energy of the restricted primitive model of electrolytes along two subcritical isotherms. The densities of liquid-gas coexistence derived from these data are found to be in good agreement with recent estimates from Gibbs ensemble Monte Carlo calculations. The difficulties of the free energy approach—which reside in the necessity of obtaining extremely accurate free energy values at near critical temperatures—is stressed. A detailed account is given of the clustering properties of the ions in the vapor phase, including cluster populations and energies, as well as intercluster contributions to the thermodynamic properties. The validity of several cluster theories for the free energy is investigated.
The soft x-ray photochemistry of physisorbed SiF4. I. Reactions of the molecular species through desorption and dissociation
Authors: Frigo S. P. , Simons J. K. , Rosenberg R. A.
Published: July 2002

We present evidence that demonstrates photolysis of SiF4 adsorbed on Ge(100) at 30 K. Silicon 2p soft x-ray photoemission spectroscopy (PES) indicates that upon irradiation, the molecularly adsorbed SiF4 dissociates into SiFn species (where n=0,1,2,3) and desorbs as molecular SiF4. Also, the Si 2p PES from undissociated molecules exhibits a number of distinct kinetic-energy shifts. These are attributed to anisotropic adsorption in which different molecular sites have different apparent Si 2p binding energies. A structure of the adsorbate layer is proposed to account for the varying core hole screening. Examination of the gas phase during irradiation confirms molecular desorption and shows the system to have a significant neutral molecular desorption yield. Changes in the valence-level photoemission structure and signal intensity are consistent with the observed fragmentation and desorption, both of which lead to disappearance of the molecularly adsorbed species.
The soft x-ray photochemistry of physisorbed SiF4. II. Mechanisms and kinetics
Authors: Frigo S. P. , Simons J. K. , Rosenberg R. A.
Published: July 2002

We present an analysis of the extensive photolysis of an adsorbate resulting from adsorbate core-level excitation. The system studied was SiF4 adsorbed on Ge(100) at 30 K. Photolysis fragments and molecular species (identified with Si 2p soft x-ray photoemission spectroscopy) were measured as a function of monochromatic (140-eV) photon exposure and adsorbate coverage. The photolysis cross sections for 55–140-eV photons were determined and the neutral photon-stimulated desorption cross section for a selected SiF4 excitation is also presented. In the Si 2p absorption region, it was found that the photolysis cross section was one to three times the preedge value and comparable in magnitude to that of gas phase photoabsorption, while the total yield increased at most by a factor of 1.4. Both of these observations indicate that direct core excitation of the adsorbate is a major path by which photolysis occurs as opposed to an indirect, substrate-driven one.
Failure of linear mixture rule in vibrational relaxation in CO2–CF2Cl2 and CO2–C4H4S mixtures
Authors: Sircar Amit , Sarkar K. Lalita , Chalapati Rao Y. V.
Published: July 2002

The experimental data for the deactivation of CO2(00°1) in CO2–CF2Cl2 and CO2–C4H4S mixtures are presented in the temperature range 323–463 K for different compositions. The relaxation rate per unit pressure (Pτ)−1 showed deviations from the linear mixture rule.
Molecular electrostatic potentials as indicators of covalent radii
Authors: Wiener John J. M. , Edward Grice M. , Murray Jane S. , Politzer Peter
Published: July 2002

Through nonlocal density functional calculations (B/LYP/6-31G**), we show that the minimum of the molecular electrostatic potential along an internuclear axis provides a more realistic boundary point between two bonded atoms than does the electronic density minimum. We also suggest that the two bonded atoms contribute approximately equally to the magnitude of the minimum potential along the axis.
Normalized fluctuations, H2O vs n-hexane: Site-correlated percolation
Authors: Koga Yoshikata , Westh Peter , Sawamura Seiji , Taniguchi Yoshihiro
Published: July 2002

Entropy, volume and the cross fluctuations were normalized to the average volume of a coarse grain with a fixed number of molecules, within which the local and instantaneous value of interest is evaluated. Comparisons were made between liquid H2O and n-hexane in the range from −10 °C to 120 °C and from 0.1 MPa to 500 MPa. The difference between H2O and n-hexane in temperature and pressure dependencies of these normalized fluctuations was explained in terms of the site-correlated percolation theory for H2O. In particular, the temperature increase was confirmed to reduce the hydrogen bond probability, while the pressure appeared to have little effect on the hydrogen bond probability. According to the Le Chatelier principle, however, the putative formation of ‘‘ice-like’’ patches at low temperatures due to the site-correlated percolation requirement is retarded by pressure increases. Thus, only in the limited region of low pressure (<300 MPa) and temperature (<60 °C), the fluctuating ice-like patches are considered to persist.
Exchange-correlation potentials
Authors: Tozer David J. , Ingamells Victoria E. , Handy Nicholas C.
Published: July 2002

We describe our implementation of the Zhao, Morrison, and Parr method [Phys. Rev. A 50, 2138 (1994)] for the calculation of molecular exchange-correlation potentials from high-level ab initio densities. The use of conventional Gaussian basis sets demands careful consideration of the value of the Lagrange multiplier associated with the constraint that reproduces the input density. Although formally infinite, we demonstrate that a finite value should be used in finite basis set calculations. The potential has been determined for Ne, HF, N2, H2O, and N2(1.5re), and compared with popular analytic potentials. We have then examined how well the Zhao, Morrison, Parr potential can be represented using a computational neural network. Assuming vxc=vxc(ρ), we incorporate the neural network into a regular Kohn–Sham procedure [Phys. Rev. A 140, 1133 (1965)] with encouraging results. The extension of this method to include density derivatives is briefly outlined.
Time-resolved infrared diode laser spectroscopy of the ν1 band of the iron carbonyl radical (FeCO) produced by the ultraviolet photolysis of Fe(CO)5
Authors: Tanaka Keiichi , Sakaguchi Kouichi , Tanaka Takehiko
Published: July 2002

The infrared spectrum of the iron carbonyl radical FeCO generated by the 193 nm excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved diode laser spectroscopy. The 85 lines, mostly observed as triplets split by the electron spin-spin interaction, were assigned to the ν1 (CO stretch) band of FeCO. The electronic ground state of FeCO was confirmed experimentally to have 3Σ− symmetry. Molecular constants in the ground and ν1 vibrational states were derived from an analysis of the infrared spectrum combined with pure rotational lines in the lowest spin component Ω=0 observed by Fourier transform microwave (FTMW) spectroscopy. The rotational and centrifugal distortion constants in the ground state were determined as B0=4364.266(55) MHz and D0=1.378(25) kHz, where the figures in parentheses are standard errors to be attached to the last digit. The spin-spin and spin-rotation coupling constants are λ0=663.1(40) GHz and γ0=−974(27) MHz, respectively. The origin of the ν1 vibrational band determined is 1946.470 60(12) cm−1, which is consistent with the value derived from photodetachment spectroscopy of the FeCO− anion. The collisional quenching rate of FeCO by Fe(CO)5 was measured to be 1.13(4)×10−10 cm3 molec −1 s−1 by a kinetic study.
Mixed semiclassical–classical approaches to the dynamics of complex molecular systems
Authors: Sun Xiong , Miller William H.
Published: July 2002

Starting with the semiclassical initial value representation (IVR) for the description of a composite molecular system consisting of a “system’’ and a “bath,’’ we show a systematic procedure whereby one can retain the semiclassical IVR description of the “system’’—thus including quantum interference and tunneling effects for these degrees of freedom—while neglecting these effects in the “bath’’ degrees of freedom, thus reducing them to a classical description. The zeroth order version of this mixed semiclassical–classical model is seen to be the semiclassical equivalent of the Ehrenfest model (closely related to the TDSCF approximation), but higher order versions are also developed that go beyond this level of approximation. Two levels of this theory are explicitly worked out. Numerical tests on simple but illustrative problems are used to discuss the merit of these approaches.
Semiclassical dynamics in up to 15 coupled vibrational degrees of freedom
Authors: Brewer Mark L. , Hulme Jeremy S. , Manolopoulos David E.
Published: July 2002

The threshold photodetachment spectra of the ArnI− (n=2–6) anions measured recently by Neumark and co-workers have been simulated semiclassically using the cellularized frozen Gaussian approximation of Walton and Manolopoulos. This is the first time that a semiclassical initial value method has been applied to a series of molecular problems with so many coupled degrees of freedom. It is found that the number of trajectories required for convergence and the absolute error in the semiclassical approximation both increase approximately linearly with the number of degrees of freedom. The simulated photodetachment spectra of the smaller anions Ar2I−, Ar3I−, and Ar4I− are in satisfactory agreement with experiment and the simulated spectra of the larger anions show that the corresponding experimental spectra are dominated by hot bands.
Static structure factor and electron correlation effects studied by inelastic x-ray scattering spectroscopy
Authors: Watanabe Noboru , Hayashi Hisashi , Udagawa Yasuo , Ten-no Seiichiro , Iwata Suehiro
Published: July 2002

Inelastic x-ray scattering spectra of methanol, acetonitrile, benzene, and cyclohexane have been measured with 2 eV resolution for momentum transfer q between 0.69 and 2.77 a.u. using synchrotron radiation from the photon factory (PF) storage ring. By utilizing the Bethe sum rule, the spectra were brought onto an absolute scale, so that the static structure factor S(q) has been obtained. S(q) of these molecules has also been calculated at the single reference configuration interaction (CI) with several types of basis sets. A new formula is proposed to carry out spherical averaging accurately. It is concluded that the CI singles and doubles (CISD) treatment is necessary to predict correct S(q), and that an inclusion of polarization function influences S(q) significantly at this level. An addition of f functions also improves the agreement with the experiments. S(q)’s based on CISD wave functions are in good agreement with the experimental ones, in particular at large q.
Kinetically accessible compact conformations of chain molecules
Authors: Yoshie Naoko , Yamamoto Keigo
Published: July 2002

The kinetic accessibility of various compact conformations of chain molecules is studied using a short self-avoiding chain on a three-dimensional cubic lattice. The kinetic accessibility of a compact conformation depends on the conformational energy and the distances from the other conformations along kinetically possible trajectories. We focus on the kinetic distances. We consider a chain in a poor solvent, having multiple lowest-energy compact conformations. The chain collapse from an arbitrary conformation to one of the lowest energy conformations is investigated. Though the lowest energy states would be occupied with the same probability in equilibrium, the probabilities for a first hit are not necessarily all the same and they indeed are not. We show that the hit probability at low temperature can be used as a measure of the kinetic distances from other conformations. The hit probability is investigated under two kinetic processes. One is a Monte Carlo dynamic process and the other is a “contact-set stepping” process, in which kinetic distances between conformations are defined based on sets of contacts. The two kinetic processes exhibit similar results showing that both processes well reproduce the kinetic behavior of chain molecules. Through the characterization of the states with large hit probability at low temperature, we show that the influence of the kinetic distances on the kinetic accessibility can be explained by domain structure or locality of contacts.
Ordinary and thermal diffusions in polyatomic binary fluid mixtures
Authors: Singh G. S. , Kumar B.
Published: July 2002

General formulas for the ordinary and Soret diffusion coefficients D12 and DT, and the thermal-diffusion ratio kT (or the thermal-diffusion factor α12) of a binary and dilute fluid mixture consisting of nonspherical molecules have been obtained utilizing the classical transport theory recently developed by us [G. S. Singh and B. Kumar, J. Chem. Phys. 104, 5604 (1996)]. The general results involve up to the infinite order of approximations but in the present work we have restricted ourselves up to the second order only. We thus obtain general expressions for the second approximation to both D12 and DT, and the first approximation to kT (or α12) in terms of different square bracket integrals. The velocity as well as angular velocity parts of these integrals for the fluid mixtures of hard biaxial ellipsoids have been analytically performed with the help of the modified Hoffman procedure. The expressions for [D12]2, [DT]2, and [kT]1 have thus ultimately been obtained in terms of five four-dimensional quadratures over the orientational coordinates of like or unlike pairs of colliding ellipsoidal molecules.
Surface kinetics of a nonlinear oxygen-induced (1×5)→(1×1) phase transition on Ir{100}
Authors: Ali T. , Klötzer B. , Walker A. V. , Ge Q. , King D. A.
Published: July 2002

The interaction of oxygen with the stable Ir{100}-(1×5) and the metastable (1×1) surfaces has been studied using supersonic molecular beams in the surface temperature range 200–1080 K. Starting from the clean (1×5) substrate, the adsorption kinetics are dominated by the adsorbate-induced lifting of the reconstruction. The formation of (1×1) islands occurs between two limiting oxygen surface coverages, as confirmed by helium scattering and low-energy electron diffraction (LEED) measurements. Two distinct temperature regimes are observed in the sticking probability measurements; between 350 and 600 K the local oxygen coverage on the (1×1) phase is about 0.28 monolayers (ML) during the prevailing phase transformation, whereas it is 0.20 ML in the temperature range 700–900 K. This “biphasic” behavior is explained by the enhancement of surface diffusion of adsorbed oxygen atoms at sample temperatures above 650 K and has been investigated further using thermal energy atom scattering (TEAS). In contrast to the (1×5) phase, TEAS measurements show that random adsorption of O2 takes place on the clean metastable (1×1) surface. At 1080 K a pronounced flux dependence of the sticking probability is observed due to a nonlinear growth law for the formation of (1×1) islands, r=c(θO1×5)4.5. Thermal desorption measurements accompanied by LEED show that the desorption rate is strongly influenced by the (1×1) to (1×5) surface phase transition; repulsive lateral interactions exist between adsorbed oxygen atoms on the (1×1) substrate. We present a mathematical model which takes these effects into account in reproducing the salient features of the temperature programmed desorption (TPD) spectra. Sticking probability, TEAS, and TPD data are all consistent with a defect concentration of 0.03 ML on the clean (1×5) surface annealed at 1400 K.
Nonadiabatic photodissociation dynamics of ICN in the Ã continuum: A semiclassical initial value representation study
Authors: Coronado Eduardo A. , Batista Victor S. , Miller William H.
Published: July 2002

In this paper we investigate the nonadiabatic photodissociation dynamics of ICN in the Ã continuum, using a semiclassical initial value representation method which is able to describe electronically nonadiabatic processes through the quantization of the classical electron–nuclear model Hamiltonian of Meyer and Miller [J. Chem. Phys. 70, 3214 (1979)]. We explore the capabilities of this semiclassical technique as applied to studying the ICN absorption spectrum, and the CN rotational distribution, through direct comparison of our semiclassical results with experimental data, and with full quantum mechanical calculations. We find that the Meyer–Miller Hamiltonian, quantized according to the semiclassical prescription, describes the ICN photodissociation dynamics in excellent agreement with full-quantum mechanical calculations.
Photolysis of CF3Cl adsorbed on Si(111)(7×7) surface by monochromatic synchrotron radiation
Authors: Wen C.-R. , Chou L.-C.
Published: July 2002

We present an analysis of the photolysis of an adsorbed molecule by monochromatic synchrotron radiation. The system studied was CF3Cl adsorbed on Si(111)(7×7) at 30 K, and the techniques employed were photoemission spectroscopy (PES) and photon-stimulated desorption (PSD). The valence-level photoemission spectra, under various photon exposures, show that the photolysis effect induced by the incident monochromatic synchrotron radiation photons (hν=98 or 110 eV) occurs on this adsorbed gas–solid system. Variations of the F− and F+ PSD ion yields were measured as a function of monochromatic (110 eV) photon exposure at three adsorbate coverages (the lowest dose=0.3×1015, the medium dose=0.8×1015, and the highest dose=2.2×1015 mol/cm2). For the lowest CF3Cl-dosed surface, the photon-exposure dependencies of the F− and F+ yields show the characteristics: (a) at early stages of photolysis, the desorption of F− yields is mainly due to dissociative attachment (DA) and dipolar dissociation (DD) of the adsorbed CF3Cl molecules induced by the photoelectrons emitting from the silicon substrate, while at high photon exposure the F− formation by electron capture of the F+ ion is the dominant mechanism; (b) the F+ ion desorption is associated with the bond breaking of the surface SiF which is formed by reaction of the surface Si atom with the neutral fluorine atom or F− ion produced by scission of the C–F bond of CF3Cl, CF2Cl, or CFCl species. A kinetic model was proposed for the explanation of the photolysis of the lowest CF3Cl-dosed surface. Based on this model and the variation rates of the F−/F+ signals during 110 eV photon bombardment, a photolysis cross section of ∼1.9×10−17 cm2 was determined. The photolysis cross section as a function of incident photon energy in the range 98–110 eV, near Si(2p), was also obtained, which shows a threshold at around 100 eV, corresponding to the same rise as the total electron yield (TEY) spectrum of the clean silicon substrate. This edge-jump indicates an enhancement of the photolysis efficiency by indirect excitation of the substrate core-level [Si(2p)] electrons, and confirms the substrate-mediated excitation as the photolysis mechanism for the lowest-dosed surface. However, for the medium- and the highest-dosed surfaces both the direct photodissociation and the substrate-mediated dissociation of the adsorbed CF3Cl occur at early stages of photolysis, while only the substrate-mediated dissociation was observed at higher photon exposure. For photolysis of all three surfaces the SiF is the only fluorosilyl product observed on the surface.
Affine collineations in Robertson–Walker space-time
Authors: Maartens R.
Published: July 2002

In a recent paper [M. L. Bedran and B. Lesche, J. Math. Phys. 27, 2360 (1986)], an attempt was made to find an affine collineation in Robertson–Walker space-time. However, only a homothetic affine collineation was found, in the case of a linear scale factor, R(t)∼t. It is pointed out that another homothetic affine collineation exists when R(t)∼tb, and a proper (nonhomothetic) affine collineation in the Einstein static space-times has been found.
Hamiltonian reduction for massive fields coupled to sources
Authors: Marzban C. , Whiting B. F. , Van Dam H.
Published: July 2002

The Dirac–Bergmann formalism for handling constrained dynamical systems is applied to massive and massless spin-2 field theories in Minkowski space. In the process, it is shown that an extension of the formalism is required before the true Hamiltonian on the reduced phase space can be calculated. With this extension, the approach then allows a revealing exposition of the m→0 limit of the massive theory, particularly of the requirement for the conservation of sources, and reconfirms the experimentally observable discontinuity which occurs at m=0.
Generalized coherent states and Berry’s phase
Authors: Giavarini G. , Onofri E.
Published: July 2002

The quantum dynamics of time-dependent Hamiltonians of the kind H(t)=U(t)H(0)U(t)° is studied in the framework of generalized coherent states. It is shown that the quantum and the classical dynamics are isomorphic and that the phase of ‖ψ(t)〉 is simply the classical action. In adiabatic approximation it is easy to extract Berry’s phase from this. A discussion of generalized coherent states (CS’s) necessary to deal with excited states is given; in particular for SU(2), SU(1,1) and E(2) their structure is completely characterized, showing that the deep connection with geometric quantization extends to these generalized CS’s. This technique may be employed to estimate higher-order correction to the adiabatic approximation.
Deformations of the Galilean algebra
Authors: Figueroa-O’Farrill José M.
Published: July 2002

All the infinitesimal deformations of the Galilean algebra with and without central extension are computed, as well as their integrability properties. Among the four-parameter family of infinitesimal deformations of the unextended algebra is found the Newton algebras, the Euclidean algebra E(4), the Poincaré algebra, the de Sitter algebras, and SO(5). For the centrally extended algebra there is found, in particular, an infinitesimal deformation containing a Poincaré subalgebra (although the embedding is not the natural one), and centrally extended versions of the Newton algebras.
Noncommutative geometry and reality
Authors: Connes Alain
Published: July 2002

We introduce the notion of real structure in our spectral geometry. This notion is motivated by Atiyah’s KR-theory and by Tomita’s involution J. It allows us to remove two unpleasant features of the ‘‘Connes–Lott’’ description of the standard model, namely, the use of bivector potentials and the asymmetry in the Poincaré duality and in the unimodularity condition.
Gamow states as continuous linear functionals over analytical test functions
Authors: Bollini C. G. , Civitarese O. , De Paoli A. L. , Rocca M. C.
Published: July 2002

The space of analytical test functions ξ, rapidly decreasing on the real axis (i.e., Schwartz test functions of the type 𝒮 on the real axis), is used to construct the rigged Hilbert space (RHS) (ξ,ℋ,ξ′). Gamow states (GS) can be defined in RHS starting from Dirac’s formula. It is shown that the expectation value of a self-adjoint operator acting on a GS is real. We have computed exactly the probability of finding a system in a GS and found that it is finite. The validity of recently proposed approximations to calculate the expectation value of self-adjoint operators in a GS is discussed.
A geometrical angle on Feynman integrals
Authors: Davydychev A. I. , Delbourgo R.
Published: July 2002

A direct link between a one-loop N-point Feynman diagram and a geometrical representation based on the N-dimensional simplex is established by relating the Feynman parametric representations to the integrals over contents of (N−1)-dimensional simplices in non-Euclidean geometry of constant curvature. In particular, the four-point function in four dimensions is proportional to the volume of a three-dimensional spherical (or hyperbolic) tetrahedron which can be calculated by splitting into birectangular ones. It is also shown that the known formula of reduction of the N-point function in (N−1) dimensions corresponds to splitting the related N-dimensional simplex into N rectangular ones.
Numerical solution of axisymmetric, unsteady free-boundary problems at finite Reynolds number. II. Deformation of a bubble in a biaxial straining flow
Authors: Kang I. S. , Leal L. G.
Published: July 2002

Numerical solutions of the full Navier–Stokes equations are used to investigate the steady and unsteady deformation of a bubble in a biaxial straining flow for Reynolds numbers in the range 0≤R≤400, and Weber numbers up to O(10). The steady-state bubble shape and the frequency of small amplitude oscillations of shape are both identical for biaxial and uniaxial straining flows in the potential flow limit. However, for a large, but finite Reynolds number, the bubble shape in the biaxial straining flow is found to be fundamentally different from the shape in uniaxial flows. This is shown to be a consequence of vorticity enhancement via vortex line stretching in the biaxial flow, which does not occur in the uniaxial flow. At the highest Reynolds number considered here, R=400, the steady-state bubble behavior for low W is qualitatively similar to the potential flow case, with a limit point for existence of the low W branch of steady solutions occurring at W∼6. However, in this case a second branch of steady solutions is found for larger W≥7, which exhibits oblate bubble shapes for large W, and has no counterpart in the potential flow limit. In unsteady flows, the behavior of bubble deformation is fundamentally different in the uniaxial and biaxial flows for both high Reynolds numbers and the potential flow limit. This suggests that breakup will occur in far different ways in the two cases.
On the effective viscosity of a nondilute emulsion of two Stokes fluids with small capillary number
Authors: Miloh T. , Benveniste Y.
Published: July 2002

A rigorous analytical framework is presented for the computation of the effective viscosity of a neutrally buoyant nondilute emulsion of two immiscible Newtonian Stokes fluids. The capillary number, which is a relative measure of viscous forces that tend to distort the drop and of the interfacial tension that favors sphericity, is assumed to be small. Thus drop distortion is ignored to first order and sphericity is preserved under small shear rates. The so-called ‘‘direct method,’’ which does not involve any energy concepts, is used and also is shown to be equivalent to the traditional approach based on the dissipation function. The micromechanics model is based on the ‘‘generalized self-consistent model’’ commonly used in composite media. At low concentrations the present theoretical prediction reduces to Taylor’s formula [Proc. R. Soc. London Ser. A 138, 41 (1932)] and is also compared against other approximate theories and experimental data for the nondilute case. The agreement is in general surprisingly good. The present model is also shown to fall between some existing bounds, which result from the application of various variational principles. A critical comparison between these bounds is also given.
Analysis of molecular mixing and chemical reaction in a vortex pair
Authors: Cetegen B. M. , Aguirre J. P.
Published: July 2002

This paper concerns an analytical/numerical study of molecular mixing and infinitely fast chemical reactions in the field of a two-dimensional vortex pair. Calculations of scalar concentration fields and its mixing statistics are presented for a range of nondimensional vortex strengths, Γ/2πν=10–50, Schmidt numbers, ν/D=1–100, and a time parameter. A measure of molecular mixing ‘‘mixedness,’’ defined as the variance of the spatial concentration field from its well-mixed value, shows that the augmentation of mixedness resulting from the presence of vortex pair is linearly proportional to the vortex pair strength and time elapse since the inception of the vortex pair.
Streamwise vorticity and entrainment in the near field of a round jet
Authors: Liepmann Dorian
Published: July 2002

The transition in round jets is accompanied by the transport of azimuthal to streamwise vorticity in the near field of the flow. In free shear layers, this forms Bernal–Roshko structures which are streamwise vortex pairs. Similar structures are shown to exist in round jets. The vortical ring structures form, grow, and amalgamate as they move downstream; they develop azimuthal instabilities. The resulting radial component of vorticity in the flow is tilted backward and stretched by the axial shear in the braid region of the flow. As the vortex filaments stretch backward, the vorticity increases and the induced velocity of the resulting vortex pair moves it farther outward, away from the shear layer into the stagnant fluid. The end of the pair is then left behind the braid and forms a streamerlike structure. This process is identified via flow visualization and confirmed by detailed entrainment measurements. The structures are shown to grow in the braid region. The streamwise structures have a major impact on the instantaneous entrainment field and, therefore, on the mixing process of the jet.
The spectrum of fractal dimensions of passively convected scalar gradients in chaotic fluid flows
Authors: Városi Frank , Antonsen Thomas M. , Ott Edward
Published: July 2002

The passive convection of scalar fields by an incompressible fluid flow in two dimensions is investigated numerically. The prescribed flow is chaotic meaning that nearby fluid elements diverge exponentially with time. The gradient of the convected scalar field is of primary interest, and a measure is defined, reflecting the spatial distribution of the regions having large gradient. The dimension spectrum for this measure is computed by the standard box counting technique, and it is found to be fractal. A recent theory proposes that the fractal structure of the scalar gradient can be related to the nonuniform stretching properties of the flow. Using this theory, the fractal dimension spectrum is computed from the distribution of finite time Lyapunov exponents of the flow, and it is found to be in reasonable agreement with the dimension spectrum computed directly by means of box counting.
Lagrangian and Eulerian time correlations in turbulence
Authors: Kaneda Yukio
Published: July 2002

A dynamical analysis is made of the Lagrangian and Eulerian two-time velocity correlations QL and QE for small time difference in turbulence at very high Reynolds number. The short-time analysis yields a refinement of the so-called random sweeping model approximation for the Eulerian correlation QE. An estimate of the Lagrangian frequency spectrum of the Lagrangian correlation QL in the inertial subrange is derived on the basis of a deductive Lagrangian renormalized approximation (LRA), which is consistent with the short-time analysis. Estimates of some nondimensional constants associated with the Eulerian and Lagrangian time microscales are also obtained by making use of the energy spectrum predicted by the LRA.
Effects of dynamic screening on the electrical conductivity of fully ionized, nondegenerate hydrogen plasma
Authors: Redmer R. A. , Röpke G. , Morales F. , Kilimann K.
Published: July 2002

The electrical conductivity of fully ionized, nondegenerate hydrogen plasma is expressed within the Zubarev method by equilibrium correlation functions. Using the Green’s function technique, the Lenard–Balescu–Gurnsey collision integral of a generalized Boltzmann equation is derived that accounts for the effects of dynamic screening. Applying the usual random phase approximation, numerical results for the collision integral and the electrical conductivity are compared with the case of static screening (ω=0) and the long-wavelength limit (q→0) for the dielectric function Ε(q,ω). Effective low-density expansions are given for the collision integrals as well as for the electrical conductivity that are applicable for a wide range of density and temperature.
Gyrokinetic analysis of ion temperature gradient modes in the presence of sheared flows
Authors: Artun M. , Tang W. M.
Published: July 2002

The linearized gyrokinetic equation governing electrostatic microinstabilities in the presence of sheared equilibrium flows in both the ẑ and ŷ directions has been systematically derived for a sheared slab geometry, where in the large-aspect-ratio limit ẑ and ŷ directions correspond to the toroidal and poloidal directions, respectively. In the familiar long perpendicular wavelength regime (k⊥ρi<1), the analysis leads to a comprehensive kinetic differential eigenmode equation that is solved numerically. The numerical results have been successfully cross-checked against analytic estimates in the fluid limit. For typical conditions, the ion temperature gradient (ηi) modes are found to be stabilized for ŷ direction flows with a velocity shear scale comparable to that of the ion temperature gradient and velocities of a few percent of the sound speed. Sheared flows in the ẑ direction taken alone are usually destabilizing, with the effect being independent of the sign of the flow. However, when both types are simultaneously considered, it is found that in the presence of sheared ẑ-direction flow, sheared ŷ-direction flow can be either stabilizing or destabilizing depending on the relative sign of these flows. However, for sufficiently large values of v′y the mode is completely stabilized regardless of the sign of vzv′y. The importance of a proper kinetic treatment of this problem is supported by comparisons with fluid estimates. In particular, when such effects are favorable, significantly smaller values of sheared ŷ-direction flow are required for stability than fluid estimates would indicate.
Particle transport and rotation damping due to stochastic magnetic field lines
Authors: Finn John M. , Guzdar Parvez N. , Chernikov Alexander A.
Published: July 2002

It is suggested that sound wave propagation along stochastic magnetic field lines contributes to particle transport, described by a quasilinear diffusion coefficient D=Dmcs, where Dm is the magnetic field line diffusion coefficient [Nucl. Fusion 6, 297 (1966)]. In this calculation, the perturbed magnetic field δB is taken to be specified, either due to global modes or due to external perturbations, such as toroidal ripple, divertor coils, or an ergodic magnetic limiter. The transport, which proceeds by the propagation of electrostatic sound waves along the stochastic field lines, is not intrinsically ambipolar. The importance of this process is that it represents the shorting out of a radial electric field in the presence of δBr, and therefore provides a mechanism for damping of plasma rotation, and may therefore be an important factor for L–H transition in tokamaks. This part of particle transport and momentum transport are therefore related and are of the same order of magnitude. However, experiments (without an ergodic magnetic limiter) appear to indicate that another source of particle transport, perhaps by E×B advection due to electrostatic modes, can dominate the particle transport due to sound wave propagation along stochastic field lines.
Acceleration of an electron ring in a modified betatron with transverse pressure
Authors: Grossmann John M. , Finn John M. , Manheimer Wallace M.
Published: July 2002

An analytic and numerical scheme is developed to follow the adiabatic evolution of a beam with nonzero transverse pressure in a modified betatron. These calculations are made using improvements to previous zero pressure models in regimes where, as before, the poloidal inertia is ignored. The evolution of the beam is determined as a series of time-independent equilibria with pressure appearing in our fluid approach as a gradient in the fluid equations of motion. The evolution of the pressure during adiabatic acceleration is determined by kinetic theory. The series of equilibria are then characterized by the constant number of particles within a drift (Pθ) surface, the conserved toroidal flux inside a Pθ surface, and the self-consistently evaluated pressure distribution (from magnetic moment conservation.) As in the case of zero pressure, it is found that the beam makes a transition from diamagnetic to paramagnetic orbits when it reaches a certain energy, and that the transition manifests itself by a change in the topology of the Pθ surfaces during acceleration. As compared to our zero pressure results, it is found that the poloidal drift of the beam is significantly faster, so that measurement of this rotation frequency is a possible diagnostic for pressure. Despite the faster drift, however, the paramagnetic transition occurs at about the same energy in both cases. Finally it is observed that the higher poloidal drift frequency associated with this pressure forces the beam toward the Brillouin limit much sooner than in the cold beam case, and that contrary to simple estimates, the pressure increases rather than decreases during acceleration because of coupling between toroidal and poloidal motion.
The temporal evolution of a potential double layer formed by ion beam reflection in a magnetized plasma
Authors: Fujita H. , Yagura S.
Published: July 2002

The temporal evolution of a potential double layer in a collisionless plasma is observed. The layer is formed by injecting a pulsed ion beam along converging magnetic field lines into a boundary drawing electron current and by applying a pulsed positive potential to the boundary in the presence of a continuous ion beam injection. The formation and destruction processes are reversible in the former case, whereas they are irreversible in the latter case. Diorect measurements of ion beam reflection estimated from spatial profiles of ion density are made at various times to facilitate the understanding of the temporal evolution of double layer formation.
On a Korteweg–de Vries equation with variable coefficients in cylindrical coordinates
Authors: Shen S. P. , Shen M. C.
Published: July 2002

An equation of the Korteweg–de Vries (KdV) type with variable coefficients in cylindrical coordinates for nonlinear wave propagation on water of variable depth is presented. The special case concerning water motion with cylindrical symmetry reduces to an equation of the KdV type obtained from approximate equations for long waves.