bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum-classical correspondence in the O(3P)+HCl and Cl(2P)+OH reactions for total angular momentum J=0
Authors: Lin Yongjing , Ramachandran B. , Nobusada Katsuyuki , Nakamura Hiroki
Published: July 2002

A method for carrying out quasiclassical trajectory (QCT) calculations of A+BC(v,j) reactive collisions for the special case of the total angular momentum J=0 is described. Since quantum reactive scattering calculations involving heavier atoms are not straightforward for the J>0 case, this method is useful to establish the extent to which classical mechanics is applicable to a particular reaction. The method is tested by comparing the results of trajectory calculations for the J=0 case with analogous quantum-mechanical (QM) calculations for the O(3P)+HCl reaction and the reverse reaction Cl(2P)+OH. The S4 potential surface, which is based on MRCI+Q/cc-pVTZ energies scaled by the scaled external correlation method [B. Ramachandran et al., J. Chem. Phys. 111, 3862 (1999)], is used for these calculations. The QCT and QM cumulative reaction probabilities are found to be in good agreement, especially for the Cl+OH reaction. The agreement between the two types of state-resolved reaction probabilities is less striking but improves considerably as the initial diatomic rotational quantum number j increases. A comparison is also made between the exact and J-shifted QCT thermal rate coefficients. These are found to be in excellent agreement, which is in keeping with similar agreement observed in the case of the quantum-mechanical exact and J-shifted thermal rate coefficients.
Photodissociation of glyoxal: Resolution of a paradox
Authors: Li Xiaosong , Schlegel H. Bernhard
Published: July 2002

Photofragmentation of glyoxal, C2H2O2, under collision free conditions proceeds by internal conversion from S1 to vibrationally excited S0, which is observed to dissociate into H2+CO+CO (28%), H2CO+CO (65%), and HCOH+CO (7%). Early molecular orbital calculations placed the barrier for the formaldehyde channel 12–20 kcal/mol above the three body fragmentation channel, contrary to what would have been expected from the branching ratios. The best calculational estimate of the barrier for the three body fragmentation was ≈8 kcal/mol higher than the reported activation energy for the thermal decomposition of glyoxal. These problems have been resolved by the more accurate ab initio molecular orbital calculations reported in the present note. With the complete basis set extrapolation method of G. Petersson and co-workers using an atomic pair natural orbital basis set (CBS-APNO), the calculated heats of reaction that are within 0.4–0.8 kcal/mol of the experimental values for glyoxal→H2+2CO, H2CO+CO, and 2 HCO. The barrier computed for H2CO+CO is 54.4 kcal/mol, in excellent agreement with the high pressure limit of the activation energy for thermal decomposition of glyoxal. The computed barrier for the three body fragmentation is 4.8 kcal/mol higher than the H2CO+CO channel, in agreement with the observed lower yield for this channel.
Resonant interaction of fast particles with neoclassical tearing modes
Authors: Marchenko V. S. , Lutsenko V. V.
Published: July 2002

Cherenkov resonance between rotating neoclassical tearing mode (NTM) and energetic ions has been considered. Resonant interaction drives the current, which is in phase quadrature with the magnetic island and thus produces a toroidal torque accelerating island in the direction of the fast ion diamagnetic drift. This torque has been included in the coupled nonlinear first-order differential equations governing evolution of the NTM rotation frequency and amplitude. It has been shown that due to resonant interaction with energetic ions, this autonomous system exhibits Hopf bifurcation from the unstable stationary solution to the stable limit cycle describing nonlinear oscillations of the mode frequency and amplitude. Such behavior resembles the frequency jump events observed during NTM activity in ASDEX Upgrade [S. Guenter et al., Phys. Plasmas 7, 935 (2000)].
Semiclassical description of quantum coherence effects and their quenching: A forward–backward initial value representation study
Authors: Wang Haobin , Thoss Michael , Sorge Kathy L. , Gelabert Ricard , Giménez Xavier , Miller William H.
Published: July 2002

The forward–backward (FB) version of the semiclassical (SC) initial value representation (IVR) is used to study quantum coherence effects in the time-dependent probability distribution of an anharmonic vibrational coordinate and its quenching when coupled to a thermal bath. It is shown that the FB-IVR accurately reproduces the detailed quantum coherent structure in the weak coupling regime, and also describes how this coherence is quenched with an increase of the system–bath coupling and/or the bath temperature. Comparisons are made with other approximations and the physical implications are discussed.
Stabilization of the resistive wall mode by differentially rotating walls
Authors: Freidberg J. P. , Betti R.
Published: July 2002

The effect of differentially rotating walls on external resistive wall instabilities is investigated for a general cylindrically symmetric diffuse pinch configuration. It is found that when the relative wall rotation velocity exceeds a critical value, the resistive wall mode is stabilized. The critical rotation frequency is, however, quite large, well above the growth rate with a single wall and probably impractical for a realistic experiment. Though the presence of a finite vacuum gap between the walls reduces the critical velocity for stabilization, the required flow is still likely to be too large for practical applications.
Dynamical theory of time-resolved fluorescence with pulse excitation
Authors: Lu Jing , Shao Fang-wei , Fan Kang-nian , Du Si-de
Published: July 2002

A uniform theory of time-resolved resonance fluorescence and resonance Raman with pulse excitation is developed and an approach describing the evolution of a wave packet during vibrational relaxation is given. Then, the theory is applied to the spontaneous emission of a model system with two harmonic electronic states. The evolution of the wave packet during vibrational relaxation obtained leads to the changing of fluorescence signal with time.
Investigation of one- and two-dimensional vibrational density of states using two-phonon infrared absorption spectroscopy
Authors: Jakob P.
Published: July 2002

The coherent excitation of two-phonon states using infrared absorption spectroscopy (IRAS) is employed to investigate band structure effects of vibrational modes. Examples representative of one-dimensional (1D), two-dimensional (2D) as well as mixed lateral coupling behavior are presented. It is demonstrated that each of these examples displays a characteristic signature which can be traced to its dissimilar spectral density of states. Momentum compensation of pairs of coherently excited adsorbate phonon modes is held responsible for the excitation of vibrational modes far from the Γ point using infrared absorption spectroscopy. The line shape of the resulting absorption feature (two-phonon continuum of states) then represents an average of all possible (νq,ν−q′) phonon pairs. It is shown that despite inherently lacking the ability to probe phonon dispersion curves, IRAS nevertheless is able to extract the vibrational density of states with a perfect average over the surface Brillouin zone. In particular, the two-phonon spectra contain sufficient information to derive the dimensionality of an adsorbate system and to extract the bandwidth of the contributing modes.
Hydrodynamic instability of ablation fronts in inertial confinement fusion
Authors: Piriz A. R.
Published: July 2002

An analytical model for the Rayleigh–Taylor instability of an ablation front is developed by decoupling the instability analysis from the corona physics. Thus, the validity of the resulting dispersion relation is not limited by a particular approximation for the unperturbed profiles. In consequence, it turns out to be suitable for calculating the instability growth rate by using the corona profiles obtained from one-dimensional simulations. The model applies to the regime with large and intermediate Froude numbers, for which Fr⩾10−2. However, it is well behaved also for Fr⩽10−2, allowing for its application to situations with arbitrary Froude numbers. Besides, the model shows the relevance of the stabilizing effects of the lateral transport of mass and momentum.
Comment on the accuracy of absolute electron-impact ionization cross sections for molecules
Authors: Stebbings R. F. , Lindsay B. G.
Published: July 2002

Electron impact ionization of molecules has been studied extensively in many laboratories and it is perhaps surprising therefore that uncertainty in the values of many cross sections has persisted. In an effort to rectify this situation absolute partial and total electron-impact ionization cross sections have been measured in this laboratory for a range of molecular targets, including H2, N2, O2, CO, NO, CO2, CH4, and SF6. These total cross sections for these molecules are compared here to those measured by Rapp and Englander-Golden, which have long been widely adopted as the de facto standard. The excellent agreement observed between these two independent data sets would seem to warrant a high level of confidence in them, and in the corresponding partial cross sections determined in this laboratory.
The photodissociation of CH3SCH3 and CD3SCD3 at 220–231 nm investigated by velocity map ion imaging
Authors: Martı́nez-Haya B. , Quintana P. , Bañares L. , Samartzis P. , Smith D. J. , Kitsopoulos T. N.
Published: July 2002

The photodissociation of the two isotopomers of dimethyl sulfide, CH3SCH3 and CD3SCD3, through the first electronic absorption band at wavelengths 220–231 nm has been studied employing velocity map ion imaging to detect the methyl products. Translational energy and recoil angle distributions have been determined for the CH3 and CD3 fragments either in the vibrational ground state or without product state selection. The measurements indicate that the S–C bond photolysis yields strongly anisotropic product scattering distributions characterized by β parameters within the range (−0.4, −1.0). The β values closest to the limiting value of −1.0 (corresponding to a dipole perpendicular transition) are observed for the methyl fragments produced in the vibrational ground state. The product recoil energy distributions are centered at ≈1.5–1.7 eV (i.e., 65%–75% of the available energy) and are quite narrow (full width at half maximum, FWHM≈0.3–0.5 eV), which indicates that methyl and methylthio fragments are born internally cold but with substantial translational excitation. The recoil energy distribution is practically independent of the photolysis wavelength within the interval studied, indicating that changes in the photon energy correlate primarily with the rovibrational excitation of the CH3S (or CD3S) fragment whose internal dynamics appear to be more active in the dissociation process than that of the CH3 (or CD3) partner.
A phase-locked loop
Authors: Shahruz S. M.
Published: July 2002

In this article, a phase-locked loop (PLL) is introduced. The proposed PLL, denoted by NPLL, is similar to the standard PLL except that it incorporates a nonlinear element and a low pass filter in its loop. The NPLL outperforms the standard PLL: (i) it has a large acquisition range, i.e., it can achieve locking in situations where the standard PLL cannot; and (ii) it achieves locking much faster than the PLL. The superior performance of the NPLL is due to the nonlinear element and the low pass filter added to the loop. Results of many tests, only three of which are reported in this article, show the superior performance of the NPLL.
Piezoelectric-field-enhanced lateral ambipolar diffusion coefficient in InGaN/GaN multiple quantum wells
Authors: Huang Yin-Chieh , Liang Jian-Chin , Sun Chi-Kuang , Abare Amber , DenBaars Steven P.
Published: July 2002

Lateral diffusion behavior of two-dimensional carrier gas in InGaN/GaN multiple quantum wells was investigated using optical transient transmission measurements. A large ambipolar diffusion coefficient was observed, which was attributed to the enhancement by a strong piezoelectric field. This large ambipolar diffusion coefficient was found to increase with increased well width with a value on the order of 3000 cm2/s for a 62 Å well-width sample.
The infrared spectra of the NH3-dn+ cations trapped in solid neon
Authors: Thompson Warren E. , Jacox Marilyn E.
Published: July 2002

When a dilute mixture of NH3 in neon is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 eV and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes three relatively prominent product absorptions which agree well with the positions determined in earlier gas-phase studies for the three infrared-active fundamentals of NH3+14. The corresponding fundamentals of NH3+15, ND3+14, and ND3+15 have been observed for the first time, as have been many of the fundamentals of the partially deuterium-substituted cations, in experiments on isotopically enriched NH3 samples. When the effects of anharmonicity are considered (including the occurrence of “negative anharmonicity” for the out-of-plane deformation fundamental), the positions of these absorptions agree satisfactorily with those predicted in an earlier study from the fit of an ab initio potential surface to the experimental data for NH3+14, as well as with those predicted in the present study from a least-squares force constant adjustment to the frequencies observed for the various isotopomers.
The stereodynamics of the O(1D)+HD reaction on the ground 1 1A′ and excited 1 1A″ potential energy surfaces
Authors: Aoiz F. J. , Bañares L. , Castillo J. F. , Martı́nez-Haya B. , de Miranda Marcelo P.
Published: July 2002

The stereodynamics of the O(1D)+HD(v=0,j=0) reaction has been studied theoretically on the Dobbyn–Knowles (DK) ab initio potential energy surfaces (PES). Quasiclassical trajectory (QCT) calculations have been carried out on the 1 1A′ ground state PES and both QCT and quantum mechanical (QM) calculations have been performed on the 1 1A″ excited state PES. The product rotational angular momentum (j′) polarization in the (k,k′) scattering frame (i.e., the k–k′–j′ vector correlation) has been determined for selected rovibrational states of the OH(v′,j′)+D and OD(v′,j′)+H product channels at the collision energy of 0.196 eV. The agreement between the QM and QCT results is very good and indicates that the “abstraction” reaction occurring on the excited 1 1A″ PES yields OH and OD products strongly polarized, in strong contract with the “insertion” reaction occurring on the ground 1 1A′ PES, which leads to an essentially isotropic distribution of the product rotational angular momentum. The differentiated stereodynamics on the 1 1A′ and 1 1A″ surfaces constitutes a reference for experimental research with the aim of assessing the contribution of the excited 1 1A″ surface to the overall reactivity of this system.
Influence of intraband transitions on the electron thermoreflectance response of metals
Authors: Smith Andrew N. , Norris Pamela M.
Published: July 2002

Ultrashort pulsed lasers have repeatedly been demonstrated as effective tools for the observation of transport properties on atomistic time and length scales. Transient thermoreflectance scans of a Au thin film taken using a 200 fs pulsed laser are compared to the parabolic two step model using both the assumption of a linear relationship between reflectance and temperature and using an intraband reflectance model. In this study, the incident photon energy was less than the interband transition energy, therefore the thermoreflectance response is primarily due to intraband transitions. The intraband transitions are influenced by the electron and lattice temperatures through the electron collisional frequency.
Effective Hamiltonians in Floquet theory of magic angle spinning using van Vleck transformation
Authors: Ramesh R. , Krishnan Mangala Sunder
Published: July 2002

In this article, we propose to use van Vleck’s contact transformation method for the study of time-dependent interactions in solid state nuclear magnetic resonance (NMR) by Floquet theory [A. Schmidt and S. Vega, J. Chem. Phys. 96, 2655 (1992)]. Floquet theory has been used for studying the spin dynamics of magic angle spinning (MAS) NMR experiments. The contact transformation method is an operator method in time-independent perturbation theory and has been used to obtain effective Hamiltonians in molecular spectroscopy. Here the above method is combined with Floquet theory to study the dynamics of a dipolar coupled spin (I=1/2) system. In order to determine the frequencies and intensities of bands in MAS spectra, we need to diagonalize the Floquet–Hamiltonian matrix. This is generally done numerically, by truncating the infinite dimensional Floquet–Hamiltonian matrix. Here we propose an effective Floquet–Hamiltonian for the system. We demonstrate the application of the above method to a homonuclear dipolar coupled spin system (I=1/2). The eigenvalues obtained from the above are compared with those obtained using numerical diagonalization. The eigenvalues of the effective Hamiltonian compare quite well with those computed using numerical diagonalization of Floquet matrices.
Plasma diagnostics at electron cyclotron resonance ion sources by injection of laser ablated fluxes of metal atoms
Authors: Mironov V. , Runkel S. , Stiebing K. E. , Hohn O. , Shirkov G. , Schmidt-Böcking H. , Schempp A.
Published: July 2002

Short pulses of neutral particles generated by laser ablation of metal targets have been injected into the Frankfurt 14 GHz electron cyclotron resonance (ECR) ion source. Rise/fall times of pulses of highly charged ions of Cd and Mg were registered as a function of microwave power and gas pressure. From a comparison of the measured data to numerical simulations, values of the electron density and the temperature in the ECR plasma were estimated to be about 0.75×1012 cm−3 and a few keV. The effective electron temperature increases with increasing microwave power and decreases with increasing gas pressure. The electron density is only a weak function of the microwave power, but increases significantly with the gas pressure. In the Ar/O2 gas-mixing mode of operation, an improved confinement of lowly charged ions was observed.
Organic light-emitting devices with saturated red emission using 6,13-diphenylpentacene
Authors: Picciolo L. C. , Murata H. , Kafafi Z. H.
Published: July 2002

Organic electroluminescent devices with saturated red emission were developed using 6,13-diphenylpentacene (DPP) doped into tris(8-hydroxyquinolinato) aluminum III (Alq3). DPP exhibits a narrow emission spectrum giving rise to a saturated red peak, centered around 625 nm, with excellent chromaticity coordinates (x=0.63 and y=0.34) in accordance with the Commission Internationale de l’Eclairage. An absolute photoluminescence (PL) quantum yield (φPL) of ∼30% was measured for a composite film of 0.55 mol % of DPP doped into Alq3. An electroluminescence (EL) quantum efficiency of 1.3% at 100 A/m2, close to the estimated theoretical limit (1.5%), was measured for an unoptimized device structure that consists of an active emissive layer sandwiched between hole- and electron-transport layers. In addition, the EL quantum efficiency is constant or stable over a wide range of current densities (1–1000 A/m2) or luminance values (1–1000 cd/m2).
Temperature-dependent valence band offset and band-gap energies of pseudomorphic GaAsSb on GaAs
Authors: Teissier R. , Sicault D. , Harmand J. C. , Ungaro G. , Le Roux G. , Largeau L.
Published: July 2002

The band-gap (Egp) and valence band offset (ΔEv) energies of pseudomorphic GaAsSb layers on GaAs substrate are determined from temperature-dependent photoluminescence measurements on GaAsSb/GaAs and GaAsSb/GaAlAs quantum wells grown by molecular beam epitaxy. A clear evidence of staggered type-II band alignment of GaAsSb relative to GaAs and a value of 1.05 for the valence band offset ratio (Qv) are proposed. Finally, through a detailed comparison of these values with those published previously, we have shown that the scatter in Qv found in the literature (<1 to 2.1) is closely dependent on the exact determination of Egp. Particularly, we have shown that the strain dependence of the deformation potential is important in the calculation of the strain energy contribution to Egp.
Low frequency scattering excess in supercooled confined water
Authors: Venturini F. , Gallo P. , Ricci M. A. , Bizzarri A. R. , Cannistraro S.
Published: July 2002

Inelastic neutron scattering data on water confined in Vycor glass are presented for temperatures ranging from 268 to 220 K and hydration levels of 12% and 8%. The data have been analyzed in the framework of the mode coupling theory, in the region of the β relaxation. Strong deviations from the theoretical predictions are found and ascribed to the existence of a low frequency scattering excess.
Identification of the 3pπue′ 3Δu Rydberg state of O2 by (3+1) resonance-enhanced multiphoton-ionization spectroscopy
Authors: Lewis B. R. , Gibson S. T. , Tucay Aurea A. , Robertson Robert , Hwang Eunsook S. , Bergman Aaron , Copeland Richard A.
Published: July 2002

The diffuse v=0 to 4 levels of the 3pπu e′ 3Δu Rydberg state of O2 are identified and characterized using (3+1) resonance-enhanced multiphoton-ionization spectroscopy. An experimental potential-energy curve for the e′ state, together with the magnitude of its interaction with the A′ 3Δu valence state, are determined semiempirically by analyzing the predissociated spectra using the coupled-channel Schrödinger-equation method. The experimental Rydberg-valence coupling (930 cm−1) exceeds significantly the value calculated ab initio by Buenker and Peyerimhoff [Chem. Phys. Lett. 34, 225 (1975)] (<320 cm−1), but is in good agreement with the single-configuration model prediction of Lewis et al. [J. Chem. Phys. 113, 2214 (2000)] (900 cm−1).
Induction of poloidal rotation by a radial ponderomotive force of electron cyclotron waves
Authors: Martinell Julio J. , Gutiérrez-Tapia César
Published: July 2002

The nonlinear ponderomotive (PM) force due to high-power rf waves is studied as a drive for plasma rotation. It is shown that poloidal rotation may be driven by a radial PM force, in addition to the usual mechanism of direct angular momentum transfer from a poloidal PM force. Here, the effect of a radial PM force producing a radial plasma flow in the presence of viscous damping and neutral collisions is considered. The PM force is produced around an electron cyclotron resonant surface at a specific poloidal location, which naturally creates a poloidally asymmetric steady radial flow, when friction is present. The flow can also arise as a result of poloidal or toroidal PM force components, even in the absence of friction. In toroidal geometry this situation is unstable due to the Stringer spin-up mechanism, for a high enough power of the rf waves. This process is most important near the outer regions of the plasma, where it can then give rise to a high confinement mode (H mode), once a sheared poloidal flow is established. The advantage of this method of driving rotation is that the wave can propagate radially and when it is absorbed at the resonant surface the radial PM force is produced, instead of launching a wave in the poloidal direction. It is shown that this effect may be large enough for electron-cyclotron resonance heating, due to the small width of the resonant surface.
Effects of incomplete ionization of impurities in poly-Si gate and band gap narrowing on direct tunneling gate leakage current
Authors: Watanabe Hiroshi , Takagi Shin-ichi
Published: July 2002

In this article the ionization rate of phosphorus doped in poly-Si gate and band gap narrowing caused by carrier–carrier interactions and carrier–ion interactions are self-consistently calculated by using a simple algorithm that is formulated phenomenologically. As a result, the ionization rate is found to be unity when the phosphorus concentration is less than 3×1019 cm−3, and becomes lower rapidly with the increase of the concentration larger than 3×1019 cm−3. Using this result, in a wide oxide voltage region, we can reproduce the oxide voltage dependence of the measured tunneling current from the gate in various samples (tOX=2.1, 2.8, and 3.4 nm) with the same tunneling mass (mOX=0.42m0), where m0 is the free electron mass. In particular, we show why the incomplete ionization can reproduce the tunneling current from the gate even in a lower oxide voltage region where the complete ionization cannot do so. Furthermore, a local band gap narrowing, which is described by an additional band gap narrowing due to exchange–correlation interactions of carriers induced by a local potential, is included in the present calculation.
Complete ab initio three-body nonadditive potential in Monte Carlo simulations of vapor–liquid equilibria and pure phases of argon
Authors: Bukowski Robert , Szalewicz Krzysztof
Published: July 2002

Complete ab initio three-body nonadditivity, including the short-range contributions, has been used for the first time in Monte Carlo simulations of liquid, gas, and liquid–vapor equilibrium of argon. Very good overall agreement with experiment has been achieved for phase equilibrium parameters and pV data of pure phases. The importance of various three-body interaction components has been assessed and their relationship to the liquid structure has been investigated. Although the short-range contributions to the nonadditivity are quite large, cancellations occurring between these and other components at the interatomic distances typical for the liquid make the total three-body nonadditive effect very similar to that given by a simple triple-dipole potential. Performance of the three-term virial equation of state is assessed based on the results of simulations.
Production of positive ion pairs by electron-impact ionization of CH4
Authors: Lindsay B. G. , Rejoub R. , Stebbings R. F.
Published: July 2002

Absolute partial cross sections for formation of (CH2+,H+), (CH+,H+), and (C+,H+) ion pairs resulting from electron-impact ionization of CH4 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector.
Fowler–Nordheim conduction in polysilicon (n+)-oxide–silicon (p) structures: Limit of the classical treatment in the barrier height determination
Authors: Hadjadj A. , Salace G. , Petit C.
Published: July 2002

Fowler–Nordheim current in Si-poly (n+)-SiO2–Si(p) structures, with an oxide thickness varying between 3 and 12 nm, has been measured and numerically computed with the exact electric field in the oxide, the field dependence of the barrier shape with the image force, and the temperature effects. The fit of the experimental data leads to an accurate determination of the electron affinity difference and the barrier height at the emitting Si–poly (n+)-gate-electrode–oxide interface. The evolution of these two parameters with temperature is discussed in relation with the oxide thickness.
Electrorheology of a zeolite/silicone oil suspension under dc fields
Authors: Tian Yu , Meng Yonggang , Wen Shizhu
Published: July 2002

The electrorheology of electrorheological (ER) fluids based on zeolite and silicone oil under dc fields was investigated at room temperature. ER fluids with volume fractions of 27% and 30% were prepared and tested. When a 5 kV/mm dc field was applied, shear yield stress of 26.7 kPa was obtained for the latter. The ER fluid with a higher volume fraction of zeolite had a higher current density and a higher shear yield stress under the same electric field. Compared with other ER fluids based on zeolite particles with low shear yield stress, the zeolite employed by us was found to have high dielectric constant and conductivity. The high permittivity mismatch and the high conductivity mismatch of the components of the fluids were considered responsible for the high shear yield stress.
Torsional analyses of trans-2-butene and propene cations: A comparative investigation of two prototypical ions with different degrees of symmetry
Authors: Burrill A. B. , Johnson P. M.
Published: July 2002

The mass analyzed threshold ionization spectra of trans-2-butene and propene have been obtained using single-step vacuum ultraviolet excitation. The ionization potential for trans-2-butene is 73 605±4 cm−1, while for propene it is 78 587±4 cm−1. Both species have progressions of the low frequency, torsional, normal modes. Using the torsional normal mode and first overtone from a trans-2-butene cation the torsional barrier is determined to be approximately 453 cm−1, assuming a sinusoidal potential. Normal mode analysis indicates that all low frequency normal modes of the propene cation involve substantial internal motion of the vinyl component, and the spectrum shows a very anharmonic torsional mode progression. These factors complicate direct torsional barrier analysis from the experimental lines, but through the use of various ab initio methods the propene torsional barrier is determined to be approximately 429 cm−1. Due to the anharmonicity found in propene, the correlation corrected vibrational self-consistent field method in GAMESS was used to verify the assignments of the experimental lines. The torsional barriers for both cations are found to lie approximately 275–300 cm−1 below the barrier heights of the neutral species.
Anharmonic vibrational spectroscopy of the glycine–water complex: Calculations for ab initio, empirical, and hybrid quantum mechanics/molecular mechanics potentials
Authors: Chaban Galina M. , Gerber R. Benny
Published: July 2002

Effects of intermolecular hydrogen bonding between glycine and one water molecule on the vibrational spectrum are investigated, using ab initio (at the level of second order Møller–Plesset perturbation theory), empirical (OPLS-AA), and mixed ab initio/empirical quantum mechanics/molecular mechanics (QM/MM) potentials. Vibrational spectroscopy is calculated using the correlation corrected vibrational self-consistent field method that accounts for anharmonicities and couplings between different vibrational normal modes. The intermolecular hydrogen bonding interactions are found to be very strong and to affect vibrational frequencies and infrared intensities of both the glycine and the water molecule to a very large extent. The predicted ab initio anharmonic spectra can be used to identify amino acids in complexes with water in experimental studies. The OPLS-AA potential is found to describe hydrogen bonding between glycine and water incorrectly, and to predict erroneous vibrational spectra. Hybrid (QM/MM) techniques can, however, be used to calculate more reliable vibrational spectra, in agreement with full ab initio treatment of the whole system, provided that the regions that contain hydrogen bonds are described by ab initio potentials.
Effective-medium Gaussian-chain theory for semidilute polymer solutions confined to a slit
Authors: Teraoka Iwao , Wang Yongmei
Published: July 2002

Theoretical formulation for the thermodynamics of a nondilute polymer solution in a confined space is presented. The interactions between polymer chains were taken into account as an effective potential field in which a chain of the Gaussian conformation grows. We determined the potential so that, when applied to the bulk solution, the theory reproduces the osmotic pressure of the bulk solution calculated within renormalization group theory. The Green function for the polymer chains confined to a slit was calculated self-consistently, since the density profile obtained from the Green function determines the potential field within the slit. The chemical potential, the partition coefficient, the density profile, and the dimension of the polymer chain perpendicular to the slit walls were obtained as a function of the concentration for different slit widths. The results agree with those obtained in the computer simulations.
Defect generation in Cu(In,Ga)Se2 heterojunction solar cells by high-energy electron and proton irradiation
Authors: Jasenek A. , Rau U.
Published: July 2002

We investigate irradiation-induced defects in high-efficiency Cu(In,Ga)Se2/CdS/ZnO heterojunction solar cells after electron irradiation with energies of 0.5, 1, and 3 MeV and after 4 MeV proton irradiation. We use electron and proton fluences of more than 1018 cm−2 and up to 1014 cm−2, respectively. The reduction of the solar cell efficiency in all experiments is predominantly caused by a loss ΔVOC of the open circuit voltage VOC. An analytical model describes ΔVOC in terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se2 absorber material. From our model, we extract defect introduction rates for recombination centers in Cu(In,Ga)Se2 for the respective particles and energies. We directly monitor the defect generation of these radiation-induced defects by admittance spectroscopy. The decrease of effective doping density in the Cu(In,Ga)Se2 absorber layer under particle irradiation is analyzed with capacitance voltage measurements at low temperatures. Furthermore, data on the relative damage coefficients for high-energy electron irradiation in Cu(In,Ga)Se2 solar cells are presented. All data, from electron as well as proton irradiations, merge to a single characteristic degradation curve.
Role of sp2 phase in field emission from nanostructured carbons
Authors: Ilie A. , Ferrari A. C. , Yagi T. , Rodil S. E. , Robertson J. , Barborini E. , Milani P.
Published: July 2002

It is shown that sp2 phase organization plays an important role in the field emission from nanostructured carbons. Emission is found to depend on the cluster size, anisotropy, and mesoscale bonding of the sp2 phase, and the electronic disorder. It is found by Raman spectroscopy that increasing the size of sp2 clusters in the 1–10 nm range improves emission. Anisotropy in the sp2 phase orientation can help or inhibit the emission. sp2 clusters embedded in the sp3 matrix or electronic disorder induced by localized defects oriented in the field direction can provide a local field enhancement to facilitate the emission.
Detailed analysis of forces influencing lateral resolution for Q-control and tapping mode
Authors: Jäggi Rainer D. , Franco-Obregón Alfredo , Studerus Paul , Ensslin Klaus
Published: July 2002

The recently introduced active quality factor control for dynamic force microscopy (Q-control) in liquids promises higher sensitivity, and thus, smaller interaction forces compared to normal tapping (intermittent contact) mode. By a careful analysis of force distance curves, we show that the lateral resolution obtained on fragile biological membranes is actually comparable for both modes if scan parameters are optimized accordingly. In addition, Q-control is limited to small scan rates only.
Compensation of beam deflection due to the magnetic field using beam steering by aperture displacement technique in the multibeamlet negative ion source
Authors: Hamabe M. , Takeiri Y. , Ikeda K. , Oka Y. , Osakabe M. , Tsumori K. , Asano E. , Kawamoto T. , Kaneko O. , Tanaka M.
Published: July 2002

A beam steering technique using aperture displacement was examined to correct the negative ion beam deflection due to the magnetic field for electron suppression in a large-area multibeamlet H− source. The total deflection angle was estimated, including the effect of the deflection by the electron suppression magnetic field and the beam steering by the aperture displacement, both by linear optics theory and by three-dimensional beam trajectory simulation. Two methods were compared; one used the displacement both of the grounded grid (GG) apertures and of the exit part of the extraction grid (EG exit) apertures, and the other used the displacement only of the EG exit. The beam steering experiments were performed using a large-area multibeamlet H− source with both displacement methods, and the results were compared with the theoretical estimations. As a result, both methods were effective to correct the beam deflection. In particular, the displacement of only the EG exit with a simplified displacement structure achieved a large steering angle by a small displacement. The steering angle in the experiment was a few mrad smaller than the estimations. Based on these results, the aperture displacement of the EG exit was applied to the 1/5 segment of a H− source in the Large-Helical-Device neutral beam injector, where the GG apertures are displaced only focusing of the large-area multibeamlet. In this case, 1.0 mm of the displacement is concluded to be proper to sufficiently compensate the beam deflection at 180 keV, from extrapolation of the beam energy characteristics at 100–140 kev.
Unconventional magnetic behavior of iron-oxide nanoparticles in polymeric matrices
Authors: Testa A. M. , Foglia S. , Suber L. , Fiorani D. , Casas Ll. , Roig A. , Molins E. , Grenèche J. M. , Tejada J.
Published: July 2002

We report the results of magnetization and Fe57 Mössbauer spectroscopy measurements performed in the temperature range 5–300 K on composites containing iron–oxide nanoparticles encased in polystyrene type resins. After carrying out a suitable field treatment in order to decouple the particles from the matrix, a fraction of the particles freely rotate in response to an applied magnetic field.
The average bond length in Pd clusters Pdn, n=4–309: A density-functional case study on the scaling of cluster properties
Authors: Krüger Sven , Vent Stefan , Nörtemann Folke , Staufer Markus , Rösch Notker
Published: July 2002

For a series of clusters Pdn (n=4–309) the average metal–metal bond distance has been determined with an accurate all-electron density functional approach. In contrast to experimental data on supported or ligand stabilized palladium clusters, bond lengths of gas-phase Pd clusters are calculated to increase with size, exhibiting remarkably linear scaling with the average coordination number. To achieve good agreement of extrapolated nearest-neighbor distances with EXAFS data and the experimental bulk value, relativistic effects have to be taken into account in the electronic structure calculations. For the example of Pd55O20, the effect of surface oxidation has been examined, indicating a strong increase of the nearest-neighbor distance.
Direct correlation between microstructure and mechanical tensile properties in Pb-free solders and eutectic SnPb solder for flip chip technology
Authors: Jang J. W. , De Silva A. P. , Lee T. Y. , Lin J. K. , Frear D. R.
Published: July 2002

The relationship between the microstructure and the mechanical tensile properties of lead-free solders and eutectic SnPb solders is presented for flip chip scale interconnects. Eutectic Sn–37Pb and Sn–0.7Cu solder (in wt %) exhibited a ductile fracture after tensile testing. Eutectic Sn–3.5Ag solder (in wt %) had greater strength and exhibited a brittle fracture at the interface. The different fracture behavior of the lead-free solders was attributed to the grain size and configuration of the intermetallics. Minor additions of alloying elements to the high Sn lead-free solder dramatically affected the microstructure and mechanical properties.
Effect of dust charge fluctuation on the Alfvén wave propagation in a magnetized dusty plasma
Authors: Alam Md. Khurshed , Begum Bilkis Ara , Chowdhury A. Roy
Published: July 2002

Growth rates of propagating waves in a magnetized dusty plasma are studied for various values of natural decay rate for the presence of dust charge fluctuation in the case of hot ions and electrons and for a weak magnetic field. The dispersion relation is obtained for the waves that propagate through low-frequency plasma with velocity, VA=B0/(μominio)1/2. Consistency of the results with previous work [Alam et al., Astrophys. Space Sci. 259, 15 (1998)] is discussed and the physical situation is also seen to be the situation considered in Varma et al. [Phys. Rev. E 47, 3612 (1993)] and Melandsø et al. [Planet Space Sci. 41, 321 (1993)]. At last, numerical estimates of the growth rate as a function of the attachment frequency, the decay rate for its various range of values have been done and are displayed graphically.
Domain wall pinning on strain relaxation defects in FePt(001)/Pt thin films
Authors: Attané J. P. , Samson Y. , Marty A. , Halley D. , Beigné C.
Published: July 2002

Thin FePt (001) films, grown by molecular-beam epitaxy on Pt(001), exhibit a very large perpendicular magnetic anisotropy (Ku=5×106 J m−3) and a 100% magnetic remanence in perpendicular field. The lattice misfit between FePt and Pt (1.5%) relaxes through the pileup of a/6 〈112〉 partial dislocations along {111} planes, leading to the formation of microtwins. Atomic force microscopy images demonstrate that this process induces a spontaneous rectangular nanostructuration of the sample, while magnetic force microscopy shows that the microtwins act as pinning sites for the magnetic walls. This leads to square magnetic domains and explains the large coercivity associated with the domain wall propagation.
Photodissociation studies of microsolvated metal cation complexes Mg+(NCCH3)n (n=1–4)
Authors: Liu Haichuan , Guo Wenyue , Yang Shihe
Published: July 2002

Acetonitrile-solvated Mg+ complexes Mg+(NCCH3)n were produced in a pick-up source. The Mg+(NCCH3)n clusters were subjected to photodissociation in a time-of-flight reflectron mass spectrometer. Except for a minor reactive product Mg+-NC at short wavelengths, only nonreactive (or evaporation) fragments were observed from photodissociation of Mg+(NCCH3)n (n=1–4). Action spectra of Mg+(NCCH3)n (n=1–4) were recorded in the spectral region of 230–560 nm, which provide insight into the structure and photodissociation dynamics of the complexes. For all the complexes we studied, the ligands are believed to be in the first solvation shell. Both the evaporation and reaction processes occur on the ground state surfaces of the complexes. By using the DFT/B3LYP and CIS methods, the most stable ground-state structures and the excitation spectra for Mg+(NCCH3)1–3 were obtained. The ab initio predictions appear to be consistent with the experimental results.
Temperature in multibubble sonoluminescence
Authors: Yasui Kyuichi
Published: July 2002

Computer simulations of bubble oscillations revealed that the bubble temperature at the collapse is highest for a moderately low acoustic amplitude because at higher acoustic amplitudes the bubble content is mostly vapor. The light emission of multibubble sonoluminescence is a combination of chemiluminescence and plasma emissions.
Pierce gain analysis for a sheet beam in a rippled waveguide traveling-wave tube
Authors: Carlsten Bruce E.
Published: July 2002

A Pierce-type mode analysis is presented for a planar electron beam in a rippled planar waveguide. This analysis describes the gain of a traveling-wave tube consisting of that geometry. The dispersion relation is given by the determinant of a matrix based on the coupling of different free-space modes through the boundary conditions. For the case of high-frequency, low-power amplifiers, the dispersion relation reduces to a simple cubic expression for the Compton regime, leading to three roots analogous to the Pierce solution of a standard traveling-wave tube. The analysis shows that this type of traveling-wave tube is capable of very high gain at extremely high frequencies.
Measurements of conserved scalar filtered density function in a turbulent jet
Authors: Tong Chenning
Published: July 2002

Conserved scalar (temperature) filtered density function (FDF) is studied experimentally in the fully developed region of a turbulent jet with Taylor-microscale Reynolds numbers of 293 and 190. We obtain the FDFs using one-dimensional box filters of widths Δ ranging from 30 to 248 scalar dissipation scales (ηφ) as well as a two-dimensional box filter (Δ/ηφ=90) which consists of three discrete sensors. Taylor’s hypothesis is used to perform streamwise filtering operations. The mean conserved scalar FDF conditioned on the resolvable-scale scalar fluctuations 〈φ〉L and the subgrid scale (SGS) variance 〈φ″2〉L (log-normally distributed) is found to be bimodal when 〈φ″2〉L/〈φ″2〉 is large, indicating that the conditional SGS mixing is nearly binary. For small 〈φ″2〉L/〈φ″2〉 (<1) the conditional FDF is approximately Gaussian. The kurtosis of the conditional FDF decreases with increasing SGS variance and is independent of the filter widths for large SGS variance. The bimodal distribution can be symmetric or asymmetric depending on the curvature of the resolvable-scale scalar. As the SGS variance increases, the conditional scalar differences for separations comparable to the filter widths also change from Gaussian to bimodal distributions. At the same time the conditional SGS scalar changes from approximately isotropic to strongly anisotropic. The results show that the contributions to the bimodal distributions come primarily from the SGS scales comparable to the filter width. It is remarkable that similarities exist between the bimodal conditional FDFs obtained here in a fully developed jet and bimodal probability density functions observed in the early stages of binary scalar mixing. The present study provides a physical basis for the assumed FDF method for conserved scalars used in large-eddy simulation of turbulent combustion.
Nonstationary oscillations in gyrotrons
Authors: Airila M. I. , Dumbrajs O. , Reinfelds A. , Strautiņš U.
Published: July 2002

The onset of stochastic oscillations in gyrotrons is studied by means of the self-consistent theory describing nonstationary processes. Complicated alternating sequences of regions of stationary, automodulation, and chaotic oscillations are found in the plane of the generalized gyrotron variables: cyclotron resonance mismatch and dimensionless current. The results of the investigations are important in connection with attempts to increase the output power of gyrotrons by raising the current.
Existence conditions of surface spin waves in ferromagnetic nanowires and nanoparticles
Authors: Ferchmin A. R. , Puszkarski H.
Published: July 2002

A theoretical treatment of spin-wave excitations in ferromagnetic wires and particles in the presence of single-ion surface anisotropy is developed within the framework of the matrix theory. Two different models of surface anisotropy are considered, one of which assumes the anisotropy axes are perpendicular to the surfaces (current model) and the other one with a single selected axis for the whole system (Aharoni model). The results obtained indicate the possibility of the existence of surface exchange spin waves in ferromagnetic nanowires and nanoparticles in both models. However, under assumptions of the Aharoni model, this occurs only for the surface anisotropy of the proper sign (the single ion anisotropy constant at the surface of the wire or particle has to be negative, D<0), while under the assumptions of the current model, in the grains the surface states are always present, but—depending on the sign of D—they are localized at different faces. Therefore, both models are hardly distinguishable when applied to wires, but essentially nonequivalent when used to describe grains. It is suggested that resonance experiments on small magnetic grains should point out which of these models can be applied.