bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrogen and deuterium ion species mix and injected neutral beam power fractions of the TEXTOR–PINIs for 20–60 kV determined by Doppler shift spectroscopy
Authors: Uhlemann R. , Hemsworth R. S. , Wang G. , Euringer H. 
Published: July 2002

The ion species fractions of the multimegawatt neutral beam ion sources for Torus Experiment for Technological Oriented Research (TEXTOR) were determined by Hα/Dα-light Doppler shift spectroscopy. The ion sources are modified Joint European Torus (JET) plug in neutral injectors (PINIs) with a three-grid acceleration system and a magnetic field in the plasma box produced by permanent magnets in checkerboard arrangement. The ion species mix of the extracted beam was measured for energies of 20–60 keV and beam currents of 13–100 A of hydrogen and deuterium produced by the two ion sources (PINI) mounted on the neutral beam injectors of TEXTOR. The maximum H+/D+ fraction at full power operation is 66%–69%. No significant difference between the two ion sources was found. The results of the hydrogen ion species mix are in good agreement with prior optical and momentum analysis made on the NI-Testbed. The additionally measured dependence of the extracted species mix from the source gas pressure is small in the pressure range above 3 μbar where the ion sources are usually operated. Measurements over the beam pulse length from 0.1 to 3 s show no change in the species mix. For calculating the deuterium ion species mix at low energies, several cross sections for Hα-light excitation, charge exchange, and dissociation available from the literature were extrapolated to about 3 keV per nucleon.
The correction factors used for calculating the ion species fraction from the ratio of the relevant integrated Doppler shift light peaks are given as a function of the gas target density in the neutralizer and of the energy per nucleon. The optical spectrometers specially designed and constructed for neutral beam Hα-light Doppler shift spectroscopy give a sufficient resolution of 1 Å and enough light intensity also at smaller beam energies and currents. The subsequent injected neutral beam power fractions H0(E), H0(E/2), and H0(E/3) and the molecular fractions H02(E) and H02(2/3E) are given as a function of acceleration voltage considering the beam line transmission and 90% of equilibrium gas target density. The injected full energy neutral beam component at 55 keV is for hydrogen 48% or 0.7 MW and 66% or 1.1 MW for deuterium.
Synchrotron-radiation plane-wave GID topography (abstract)
Authors: Novikov D. V. , Gog T. , Griebenow M. , Materlik G. 
Published: July 2002

X-ray-diffraction topography is a traditional tool for investigating the real structure of crystals and provides high sensitivity to lattice constant variations with good space resolution. However, recent advances in technology and the growing importance of surface regions of single-crystal and multilayer systems require new approaches to this method, which are made possible by the high brightness and wide tunability of synchrotron radiation. In this work the SR plane-wave grazing-incidence diffraction (GID) topography is discussed as an effective tool for depth-resolved investigations of near-surface defect structures in single crystals and epitaxial layers. The favorable properties of synchrotron radiation enable one to avoid the usual limitations on applicability of this diffraction geometry and investigate all classes of defects in real materials. The experiments were performed at the beamlines ROEMO1 and CEMO of HASYLAB, using double-crystal Ge/asymmetric Si monochromators. The image formation of near-surface dislocations and the effects of refraction on rough surfaces were investigated. Oblique diffraction planes were used to compare the topography in skew incoplanar and coplanar geometries. The latter is shown to be more effective, as it utilizes the wavelength tunability of SR and allows one to vary the diffraction conditions in a wide range from usual highly asymmetric to grazing incidence below the critical angle of total external reflection (and the penetration depth from hundreds to tens of nanometers) without off-plane rotations and provides pictures free of complicated geometrical distortions.
The dislocation images at different diffraction conditions proved to be qualitatively the same for near-surface defects, while the structure distortions, produced by the defects in the underlying layers, become invisible at grazing incidence, due to both depth resolution of the method and inevitable loss of lattice-parameter resolution. This might be a substantial advantage for characterization of films on substrates with a low perfection. Thus SR based plane-wave GID topography provides all the features of usual asymmetric topography and has substantial advantages for surface defect analysis.
Analysis and design of microwave amplifiers employing field-emitter arrays
Authors: Calame J. P. , Gray H. F. , Shaw J. L. 
Published: July 2002

An analysis of the microwave ( f≳1 GHz) properties of field-emitter arrays (FEAs) and several representative medium power (10–100 W) microwave amplifiers employing FEAs is presented. The FEA analysis is limited to parallel-plate structures having discrete pointlike vertical emitter tips and gate apertures aligned to each tip. A transmission line analysis of wave propagation in this structure is presented and used to evaluate the geometries and materials needed for microwave operation. This analysis is used to investigate the performance capabilities and emitter requirements of both modulated-emission linear beam tubes and microdevices based on FEAs. Specific microtriode designs are used to investigate practical problems such as space charge and thermal effects. Competitive performance should be achievable in gated-emission linear beam tubes by using FEAs that perform at levels previously reported by several laboratories. Existing FEA technology (currents of 10 μA per emitter, transconductances of 1 μS per emitter, 1 μm oxide thickness, and 3 μm emitter spacing) is suitable for use in cavity klystrodes(r) at frequencies through 10 GHz, and in moderately bunched beam (bunch width of 180°), octave-bandwidth traveling-wave-tube applications through 3 GHz. Extending the operating frequency and/or reducing the bunch width will require a larger ratio of transconductance to current. Microtriodes operating at 10 GHz will benefit from a modified FEA structure and improved emitter performance.
An extra acceleration electrode must be added above the gate aperture to alleviate problems due to space charge between the gate and collector, and the gate oxide thickness must be increased to at least 2 μm. A FEA incorporating these features and capable of producing 5 μS and 100 μA per emitter could generate 130 W from a 5-mm-wide device with 8.6 dB gain, 7% bandwidth, and 36% power added efficiency. To allow higher gain and wideband operation, the transconductance at a given current must be increased. A FEA capable of producing 5 μS at only 10 μA per emitter would result in a microtriode with more than 1 octave bandwidth, 45 W output power, 10 dB gain, and 34% power added efficiency. Anode-to-case temperature differences of less than 100 °C appear possible in this device if BeO is used as the dielectric.
On the nature of the two low-lying singlet states of anthracene: Vibronic activity in the two-photon excitation spectrum
Authors: Salvi P. R. , Marconi G. 
Published: July 2002

The two-photon excitation spectrum of anthracene in a n-heptane matrix at 10 K has been measured in the energy region 26 000–32 000 cm−1. Experimental evidence of two-photon band assignment to vibronically induced B1u ×b1u and B2u ×b2u transitions is given. In particular, the two-photon spectrum above ≂28 000 cm−1 shows several vibronic origins built on b2u vibrations and progressions of ag modes on them. The lowest ππ* absorption region (&lt;28 000 cm−1) has, on the contrary, negligible intensity and very weak B1u ×b1u bands are observed. These data can be rationalized in terms of vibronic coupling between electronic states induced by normal
coordinates of b1u and b2u symmetry. By means of the Herzberg–Teller theory and displacing the molecule away from equilibrium along the normal coordinate we have calculated the vibronic interaction between electronic states in the orbital following approach. The results based on CNDO/S-CI wave functions show that B2u ×b2u transitions have a larger vibronic activity than the B1u ×b1u transitions. The 1132, 1384, and 1393 cm−1 b2u modes are particularly strong in inducing two-photon intensity through a vibronic coupling mechanism involving essentially the ground and the final 1 1B2u state. The B2u ×b2u two-photon amplitude tensors are not sensitive to the method of calculation. B1u ×b1u tensors have instead a more pronounced dependence on the method used. This is due to the fact that in the two-photon sums most of the intermediate states play an equivalent
role in determining the amplitude tensor, in contrast with the B2u ×b2u case. It is important to use a reasonably correct representation of the excited state wave functions. It is shown that more accurate calculations (INDO/S and CNDO/S with increased CI) lead to better agreement of the total vibronic intensity of the 1 1B1u state with experiment and predict the largest activity for the 648 cm−1 b1u mode, as observed in the spectrum.
High resolution S1←S fluoescence excitation spectra of the 1- and 2-hydroxynaphthalenes. Distinguishing the c
i
s and t
r
a
n
s rotamers
Authors: Johnson J. R. , Jordan K. D. , Plusquellic D. F. , Pratt D. W. 
Published: July 2002

Both fluorescence excitation and dispersed emission techniques have been used to study the S1←S0 electronic spectra of 1- and 2-hydroxynaphthalene (1/2HN) in the collision-free environments of a supersonic jet and a twice-skimmed molecular beam, using both pulsed and high-resolution cw lasers operating in the ultraviolet. In the jet experiments, we observe that each molecule exhibits two electronic origins, separated by 274 cm−1 in 1HN and by 317 cm−1 in 2HN. In the beam experiments, we resolve the rotational structure of each of the four bands and determine the inertial constants of all eight zero-point vibrational levels, accurate to ±0.1 MHz. We also determine the orientations of the four optical transition moments in the molecular frame. Significant differences in both the inertial constants and the transition moment orientations are observed in each band. Similar experiments have been performed on the hydroxy-deuterated 1/2HN (1/2DN).
A comparison of the results obtained for 1/2DN with those for the corresponding bands in 1/2HN makes possible the determination of the center-of-mass coordinates of the hydroxy hydrogen in both electronic states, accurate to ± 0.02 Å. Differences in these coordinates reveal that the two electronic origins in each spectrum are caused by the presence of two N–O–H(D) rotamers in both 1H(D)N and 2H(D)N, one with a cis (or syn) geometry and one with a trans (or anti) geometry with respect to the naphthalene frame. We make an unambiguous assignment of each origin to a specific rotamer. The lower energy origin in the spectrum of 1HN is that of the cis rotamer, whereas the lower energy origin in the spectrum of 2HN is that of the trans rotamer. We then use these results, together with those of ab initio calculations on the ground electronic states of all four isomers, to explore the reasons for the differences in their energies, to account for the orientations of their transition moments, and to specify other features of the S0 and S1 potential energy surfaces along the cis–trans isomerization coordinate. Motion along this coordinate requires significant displacement of the oxygen atom and selected ring hydrogens as well as rotation about the C–O bond, in both electronic states.
Role of local configurations in a Langmuir–Hinshelwood surface reaction: Kinetics and compensation
Authors: Kang H. C. , Jachimowski T. A. , Weinberg W. H. 
Published: July 2002

We have employed Monte Carlo sampling to calculate the rate coefficient of a Langmuir–Hinshelwood reaction between species A and B on a square lattice. The experimental situation that is simulated is the reaction between a preadsorbed overlayer of species A with species B. The preadsorbed overlayer of A is allowed to equilibrate prior to the adsorption of B. Upon adsorption of B, the initial reaction rate is calculated assuming that A is irreversibly adsorbed and immobile, and that the equilibrium between adsorbed B and gas-phase B is established much more rapidly than the time scale of the reaction between A and B. Reaction is allowed only between nearest-neighbor AB pairs. We examine the parametrization of the reaction rate coefficient into an effective activation energy and an effective preexponential factor.
We find that correlations between nearest-neighbor particles affect the reaction rate coefficient significantly. We also find that if the distribution of local configurations of nearest-neighbor pairs of reactant particles changes with temperature, the corresponding Arrhenius plot is nonlinear. The effective activation energy and the effective preexponential factor vary strongly with the fractional coverage of A and show a large compensation effect, similar to that observed experimentally in many desorption and surface-reaction systems. We conclude that variations in the distribution of local configurations of pairs of reactant molecules is a function of temperature and fractional surface coverage can be responsible for these experimentally observed compensation effects.
N,N′-dicyanoquinonediimines as a molecular constituent of organic conductors: Vibrational behavior and electron–molecular vibration coupling
Authors: Lunardi G. , Pecile C. 
Published: July 2002

The results of a vibrational analysis of neutral N,N′-dicyanoquinonediimine (DCNQI) and of 2,5-X,Y-DCNQI (X■Y■Cl; X■Cl, Y■CH3; X■Y■CH3 or CD3) are presented. A sound assignment of the in-plane fundamental vibrational modes is discussed also in terms of a normal coordinate analysis (NCA) based on a modified valence force field. For light and deuterated 2,5-dimethyl-dicyanoquinonediimine (DMDCNQI) the vibrational analysis is extended to the corresponding radical anion. The comparison of the vibrational assignment of neutral and fully ionized species, together with the results of the NCA, leads to the identification of a strong Duschinsky effect, as well as of the frequency shifts relative to the ionization process. The buν47 fundamental mode (quinoid C■N stretch) is recognized as diagnostic of the degree of charge transfer (CT) for DMDCNQI component units of CT systems. The relative values of the linear electron–molecular vibration (e–mv) coupling constants for the neutral and ionized DMDCNQI molecular structure, evaluated by a spectroscopic version of the complete neglect of differential overlap (CNDO/S) calculation associated with the eigenvectors coming from the NCA, are also reported.
The infrared vibronic features of the Ba(DMDCNQI)2 salt are sorted out by exploiting their intensity evolution with the temperature and are interpreted by applying Rice’s model for a dimerized linear chain together with the calculated e–mv coupling constants. Furthermore, the visible absorption spectrum of the DMDCNQI radical anion is analyzed and its vibronic structure is attributed to a coupling with the three vibrational modes agν′5, 1585; ν8, 1290; and ν′18, 395 cm−1. The dependence of the vibrational frequencies on ionicity and the vibronic features of the optical spectra are discussed with a view to their application in the investigation of the physical properties and the temperature and/or pressure-dependent phase transitions of conductors based on the DCNQI structure, particularly in the case of the open questions raised by the physical properties of the highly conducting Cu (DMDCNQI)2 salt.
Scaling theory for radial distributions of star polymers in dilute solution in the bulk and at a surface, and scaling of polymer networks near the adsorption transition
Authors: Ohno Kaoru , Binder Kurt 
Published: July 2002

Monomer density profiles ρ(r) and center–end distribution functions g(rCE) of star polymers are analyzed by using a scaling theory in arbitrary dimensions d, considering dilute solutions and the good solvent limit. Both the case of a free star in the bulk and of a center-adsorbed star at a free surface are considered. In the latter case of a semi-infinite problem, a distinction is made between repulsive walls, attractive walls—where for large arm length l the configuration of the star is quasi-(d−1) dimensional—, and ‘‘marginal walls’’ where for l→∞ the transition from d-dimensional structure occurs. For free stars, ρ(r) behaves as r−d+1/ν for small r, where ν is the exponent describing the linear dimensions of the star, e.g., the gyration radius Rgyr∼lν. For center-adsorbed stars at repulsive or marginal walls, ρ(r∥,z) behaves as ρ(r∥,0) ∼r−d+λ( f )∥ and ρ(0,z)∼z−d+1/ν, where r∥ and z denote the distances parallel and perpendicular to the surface, respectively; the new exponent λ( f ) depends explicitly on the number of arms  f  in general. For center-adsorbed stars at attractive walls, ρ(r∥,z) behaves as ρ(r∥,0)∼r−(d−1)+1/ν(d−1)∥, ν(d−1) being the exponent describing (d−1)-dimensional stars, while ρ(0,z) decays exponentially.
On the other hand, the center–end distribution function at short distances is described by nontrivial exponents. For free stars with  f  arms, g(rCE)∼(rCE)θ( f ) for small rCE, where θ( f ) is expressed in terms of the configuration-number exponent γ( f ) and the exponent γ of linear polymers as θ( f ) =[γ−γ( f+1) +γ( f )−1]/ν. For center-adsorbed stars, at repulsive or marginal walls gs(rCE∥,ze) behaves as gs(rCE∥,0) ∼(rCE∥)θ∥( f ), gs(0,zE) ∼(zE)θ⊥( f ) with θ∥( f ) =[γ1−γs( f+1) +γs( f )−1]/ν and θ⊥( f ) =[γ−γs( f+1) +γs( f )−1]/ν, γ1 being the exponent of a linear polymer with one end at the surface. The scaling theory of general polymer networks at the adsorption transition is also presented.
The configuration-number exponent γ𝒢 for a polymer network 𝒢 with nh h functional units in the bulk, n′h h-functional units at the surface and totally composed of  f  linear polymers with the same length is given by γSB𝒢 =α−1−f+ν +∑∞h=1[nhΔh +nhΔSBh]. Δh and ΔSBh are related, respectively, to the exponents of star polymers as γ( f )=α−1+(γ−α)f/2+Δf and γSBs( f ) =α−1+ν+(γ−α)f/2 +ΔSBf, with α given by α=2−νd. The exponent γSBs( f ) is evaluated by means of the renormalization-group ε=4−d expansion to the first order.
Accurate a
b i
n
i
t
i
o potential energy computations for the H4 system: Tests of some analytic potential energy surfaces
Authors: Boothroyd Arnold I. , Dove John E. , Keogh William J. , Martin Peter G. , Peterson Michael R. 
Published: July 2002

The interaction potential energy surface (PES) of H4 is of great importance for quantum chemistry, as a test case for molecule–molecule interactions. It is also required for a detailed understanding of certain astrophysical processes, namely, collisional excitation and dissociation of H2 in molecular clouds, at densities too low to be accessible experimentally. Accurate ab initio energies were computed for 6046 conformations of H4, using a multiple reference (single and) double excitation configuration interaction (MRD-CI) program. Both systematic and ‘‘random’’ errors were estimated to have an rms size of 0.6 mhartree, for a total rms error of about 0.9 mhartree (or 0.55 kcal/mol) in the final ab initio energy values. It proved possible to include in a self-consistent way ab initio energies calculated by Schwenke, bringing the number of H4 conformations to 6101. Ab initio energies were also computed for 404 conformations of H3; adding ab initio energies calculated by other authors yielded a total of 772 conformations of H3. (The H3 results, and an improved analytic PES for H3, are reported elsewhere.) Ab initio energies are tabulated in this paper only for a sample of H4 conformations; a full list of all 6101 conformations of H4 (and 772 conformations of H3 ) is available from Physics Auxiliary Publication Service (PAPS), or from the authors.
The best existing analytic PESs for H4 are shown to be accurate only for pairs of H2 molecules with intermolecular separations greater than about 3 bohr (1.6 Å). High energy collisions (such as might lead to direct collisional dissociation) cannot be well represented by such surfaces. A more general analytic PES for H4 is required, which will be accurate for compact (high-energy) conformations and for conformations that cannot be subdivided into a pair of H2 molecules. Work in progress on devising such a surface (fitted to the 6101 conformations of this work) will be reported in a forthcoming paper.
Formation of highly excited oxygen atoms O(2p33p,5P) and O(2p33s,5S) in electron irradiation of mixtures of rare gases and O2
Authors: Mori Tomoo , Kanou Kouichiro , Ishikawa Yo-ichi , Arai Shigeyoshi 
Published: July 2002

The 777 nm emission and absorption observed for electron-irradiated He and Ne containing O2 are attributed to the optical transition between O(2p33p,5P) and O(2p33s,5S). He*2(2s 3Σ+u) produces these excited oxygen atoms in its reaction with O2 and the rate constant is (4.2±0.4)×10−10 cm3 s−1. In irradiated Ne and irradiated Ne containing O2, we found the absorption due to Ne*2 (3p 3Πg, v′=1←3s 3Σ+u, v″=0, v′=2←v″=1, and v′=3←v″=2) and the sharp absorption due to O(2p33s,5S) at ∼777 nm, together with the emission of O(2p33p,5P) at the same wavelength.
The vibrational constants of Ne*2 for the 3p 3Πg state are ωe=647 cm−1 and ω′exe=28 cm−1. Ne*2(3s 3Σ+u) may produce O(2p33s,5S) in its reaction with O2. On the other hand, the reactions of excited Ne atoms with O2 appear to be responsible for the emission. The formation of O(2p33s,5S) in irradiated Ar containing O2 is explained in terms of the mechanism involving highly excited Ar** (E≥14.3 eV) and O2. The rate constant for the reaction of Ar** with O2 and the deactivation constant of Ar** by Ar were determined to be (3.2±0.2)×10−10 and (8.9±1.3)×10−15 cm3 s−1, respectively. O(2p33s,5S) disappears by its reaction with O2 in He, Ne, and Ar. The rate constants were found to be (1.8±0.2)×10−10 cm3 s−1 in He, (1.7±0.2)×10−10 cm3 s−1 in Ne, and (1.7±0.2)×10−10 cm3 s−1 in Ar. Ar deactivates O(2p33s,5S) at a rate constant of (2.9±0.2)×10−15 cm3 s−1. Similar deactivation rate constants of O(2p33s,5S) by He and Ne are (1.8±0.1)×10−15 and (3.4±0.3)×10−15 cm3 s−1, respectively. The rough estimation of the radiation chemical yield for O(2p33s,5S) gives G=1×10−2 for the mixture of 7600 Torr He and 0.1 Torr O2.