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1

Helium atom scattering investigation of the Sb(111) surface.  

PubMed

The Sb(111) surface was studied with helium atom scattering (HAS). Elastic HAS at different energies of the incident helium beam (15.3, 21.9, 28.4 meV) was applied for structural investigations. The lattice constants derived from the positions of the observed diffraction peaks up to third order were found to be in perfect agreement with previous structure determinations of Sb(111). The observed diffraction patterns with clear peaks up to second order were used to model the electronic surface corrugation with the GR method. As an estimation for the attractive part of the interaction potential a well depth of (4.0 ± 0.5) meV was found. Best fit results were obtained with a corrugation height of 12-13% of the lattice constant, which is rather large compared to other surfaces with metallic character. Intensity measurements of the specular peak as a function of incident energy were analysed to determine the distribution of terraces on the surface. The results show a quite flat Sb(111) surface and a step height of 3.81 ? of the remaining terraces. PMID:23969322

Mayrhofer-Reinhartshuber, M; Tamtögl, A; Kraus, P; Ernst, W E

2013-10-01

2

Getting the Elastic Scattering Length by Observing Inelastic Collisions in Ultracold Metastable Helium Atoms  

NASA Astrophysics Data System (ADS)

We report an experiment measuring simultaneously the temperature and the flux of ions produced by a cloud of triplet metastable helium atoms at the Bose-Einstein critical temperature. The onset of condensation is revealed by a sharp increase of the ion flux during evaporative cooling. Combining our measurements with previous measurements of ionization in a pure Bose-Einstein condensate, we extract an improved value of the scattering length a=11.3+2.5-1.0 nm. The analysis includes corrections that take into account the effect of atomic interactions on the critical temperature, and thus an independent measurement of the scattering length would allow a new test of these calculations.

Seidelin, S.; Gomes, J. Viana; Hoppeler, R.; Sirjean, O.; Boiron, D.; Aspect, A.; Westbrook, C. I.

2004-08-01

3

Unveiling mode-selected electron-phonon interactions in metal films by helium atom scattering.  

PubMed

The quasi two-dimensional electron gas on a metal film can transmit to the surface even minute mechanical disturbances occurring in the depth, thus allowing the gentlest of all surface probes, helium atoms, to perceive the vibrations of the deepest atoms via the induced surface-charge density oscillations. A density functional perturbation theory (DFPT) and a helium atom scattering study of the phonon dispersion curves in lead films of up to 7 mono-layers on a copper substrate show that: (a) the electron-phonon interaction is responsible for the coupling of He atoms to in-depth phonon modes; and (b) the inelastic HAS intensity from a given phonon mode is proportional to its electron-phonon coupling. The direct determination of mode-selected electron-phonon coupling strengths has great relevance for understanding superconductivity in thin films and two-dimensional systems. PMID:24473191

Benedek, G; Bernasconi, M; Bohnen, K-P; Campi, D; Chulkov, E V; Echenique, P M; Heid, R; Sklyadneva, I Yu; Toennies, J P

2014-04-28

4

Quantum mechanical studies of helium atom scattering from isolated CO molecules on metal surfaces  

NASA Astrophysics Data System (ADS)

We review two distinct quantum mechanical theories of atomic scattering from a point defect, single adsorbate or vacancy, inducing a corrugation much larger than that of the crystal surface. They are both based upon unrestricted motion of the probe and involve a realistic interaction potential. The most sophisticated one is a pseudospectral wavepacket method that is presented in both Cartesian and cylindrical representations. The physically attractive, albeit more approximate, close-coupling gas phase approach is also considered. We report the first realistic comparison with the experimental measurements of helium atom scattering on CO/Cu(100), at a beam energy of 20 meV. The combined use of the gas phase and of the reference models enables the unambiguous interpretation of all experimental peaks.

Nave, Sven; Lemoine, Didier

2002-06-01

5

Surface Debye temperature and vibrational dynamics of Antimony(111) from helium atom scattering measurements  

NASA Astrophysics Data System (ADS)

The surface Debye temperature and the vibrational dynamics of Sb(111) were studied using helium atom scattering. The Debye-Waller attenuation of the elastic diffraction peaks was measured at surface temperatures between 98 K and 447 K. A surface Debye temperature of (155 ± 3)K is obtained within the description originally derived for electron diffraction. The attractive well depth for the He-Sb(111) interaction is determined to be (4.5 ± 0.5) meV. The perpendicular mean-square displacement for the surface at room temperature is estimated to be (1.8 ± 0.4) × 10- 2Å2.

Tamtögl, Anton; Mayrhofer-Reinhartshuber, Michael; Kraus, Patrick; Ernst, Wolfgang E.

2013-11-01

6

Vibrational dynamics and surface structure of Bi(111) from helium atom scattering measurements  

NASA Astrophysics Data System (ADS)

The Bi(111) surface was studied by elastic scattering of helium atoms at temperatures between 118 and 423 K. The observed diffraction patterns with clear peaks up to third order were used to model the surface corrugation using the eikonal approximation as well as the GR method. Best fit results were obtained with a rather large corrugation height compared to other surfaces with metallic character. The corrugation shows a slight enhancement of the surface electron density in between the positions of the surface atoms. The vibrational dynamics of Bi(111) were investigated by measurements of the Debye-Waller attenuation of the elastic diffraction peaks and a surface Debye temperature of (84 ± 8) K was determined. A decrease of the surface Debye temperature at higher temperatures that was recently observed on Bi nanofilms could not be confirmed in the case of our single-crystal measurements.

Mayrhofer-Reinhartshuber, M.; Tamtögl, A.; Kraus, P.; Rieder, K. H.; Ernst, W. E.

2012-03-01

7

Atomic scattering from an adsorbed monolayer solid with a helium beam that penetrates to the substrate  

SciTech Connect

Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated by propagating a wavepacket and including the effect of a feedback of the inelastic wave onto the diffracted wave, which represents a coherent re-absorption of the created phonons. Parameters are chosen to be representative of an observed p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/NaCl(001) and a conjectured p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/KCl(001). For the latter, there are cases where part of the incident beam is trapped in the interlayer region for times exceeding 50 ps, depending on the spacing between the monolayer and the substrate and on the angle of incidence. The feedback effect is large for cases of strong transient trapping.

Hansen, F. Y. [Department of Chemistry, Technical University of Denmark, IK-207-DTU, DK-2800 Lyngby (Denmark); Bruch, L. W. [Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, Wisconsin 53706 (United States); Dammann, B. [Department of Informatics and Mathematical Modeling, Technical University of Denmark, 321-DTU, DK 2800 Lyngby (Denmark)

2013-03-14

8

Breakdown of atomic superposition for the helium scattering potential of c(2×2) oxygen on nickel (001)  

NASA Astrophysics Data System (ADS)

Self-consistent calculations of the charge density of the c(2×2) phase of oxygen on nickel (001) (i) give a helium scattering potential which in excellent agreement with the shape, height and width of that obtained by Rieder by fitting his atom-surface scattering data: (ii) justify th use of a hard-wall fit because of a 4.2 Å -1 averrage softness parameter; and (iii) rule out superposition of atomic or ionic charge densities for this and similar systems.

Godby, R. W.; Garcia, N.

1985-11-01

9

Breakdown of atomic superposition for the helium scattering potential of c(2×2) oxygen on nickel (001)  

NASA Astrophysics Data System (ADS)

Self-consistent calculations of the charge density of the c(2×2) phase of oxygen on nickel (001) (i) give a helium scattering potential which is in excellent agreement with the shape, height and width of that obtained by Rieder by fitting his atom-surface scattering data; (ii) justify the use of a hard-wall fit because of a 4.2 Å -1 average softness parameter; and (iii) rule out superposition of atomic or ionic charge densities for this and similar systems.

Godby, R. W.; Garcia, N.

10

Inelastic x-ray scattering study of the state-resolved differential cross section of Compton excitations in helium atoms  

SciTech Connect

The state-resolved differential cross sections for both the 1s{sup 2} {sup 1}S{sub 0}{yields}1s2s {sup 1}S{sub 0} monopolar transition and the 1s{sup 2} {sup 1}S{sub 0}{yields}1s2p {sup 1}P{sub 1} dipolar transition of atomic helium had been measured over a large momentum transfer region by high-resolution inelastic x-ray scattering (IXS). The almost-perfect match of the present measurement with the theoretical calculations gives a stringent test of the theoretical method and the calculated wave functions. Our results demonstrate that high-resolution IXS is a powerful tool for studying the excitations in atoms and molecules.

Xie, B. P.; Yang, K.; Zhou, B.; Feng, D. L. [Department of Physics, Surface Physics Laboratory (National Key Laboratory), and Advanced Materials Laboratory, Fudan University, Shanghai 200433 (China); Zhu, L. F.; Wang, E. L. [Hefei National Laboratory for Physical Sciences at Microscale, Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Hiraoka, N.; Cai, Y. Q. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Yao, Y.; Wu, C. Q. [Department of Physics, Fudan University, Shanghai 200433 (China)

2010-09-15

11

Reconstruction of the CoGa(100) surface studied by thermal-energy helium-atom scattering, LEED, and AES  

NASA Astrophysics Data System (ADS)

The surface structure of CoGa(100) has been studied by means of thermal-energy helium-atom scattering (TEAS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). A c(4×2) surface reconstruction is revealed by LEED and TEAS measurements. Sometimes this reconstruction is mixed with a (5×5) reconstruction, which is found to be due to a very minor contamination with oxygen. Only double-layer steps are found on the surface. Above 500 K, the reconstructed layer starts to disorder, but short-range ordering in this layer is still observed until 700 K. Near 900 K, segregation of Co is observed with AES. The increase of the cobalt concentration is consistent with filling up the 0.25 ML, necessary for the c(4×2) reconstruction, to a completed monolayer at 900 K. This interpretation implies that the surface is always terminated by Co.

Pan, F. M.; Pflitsch, Ch.; David, R.; Verheij, L. K.; Franchy, R.

2001-03-01

12

Vibrational properties of the clean W(110) surface and of different hydrogen adsorbate phases studied by helium atom scattering  

NASA Astrophysics Data System (ADS)

We have investigated the clean and the hydrogen covered W(110) surface with elastic and inelastic helium atom scattering (HAS). At low temperatures two different hydrogen superstructures can be detected in accordance with earlier LEED investigations. Further hydrogen exposure leads to a weakening of all superstructure spots and at saturation the (1 × 1) periodicity of the clean surface is restored. The surface phonon dispersion curves of the clean surface and of all hydrogen adsorbate phases have been measured by inelastic HAS. The clean surface displays "normal" surface lattice dynamics while the surface phonon dispersion curves of the superstructures show backfolded phonon branches due to the reduced Brillouin zones of these phases. This behaviour contrasts with the hydrogen saturated surface where a sharp surface phonon anomaly has been found. The connection of these properties with an earlier report of a top layer shift reconstruction induced by adsorbed hydrogen is still not known.

Hulpke, E.; Lüdecke, J.

13

Measurement of surface phonon dispersion relations for LiF, NaF, and KCL through energy-analyzed inelastic scattering of a helium atomic beam  

NASA Astrophysics Data System (ADS)

The scattering from a crystal surface of a high intensity low energy, high velocity resolution, narrow helium atomic beam was investigated. The scattered beam was velocity-analyzed using standard time of flight (TOF) techniques. The TOF spectra showed multiple sharp energy-shifted maxima corresponding to creation and annihilation of surface phonons directed both parallel and antiparallel to the incoming beam. From these TOF shifts and the known scattering angles, the surface phonon frequency and wavevector were calculated. Different points of the phonon dispersion curve were probed. Interaction is found to be primarily with Rayleigh surface modes although the presence of bulk-like modes at the surface is also observed. Selective adsorption plays an important role in inelastic scattering. The bound life times of the helium atoms are calculated to range from 6 to 60 psec for the lowest to the highest bound states on LiF, respectively.

Doak, R. B.

1981-09-01

14

Investigations of the dynamics and growth of insulator films by high resolution helium atom scattering. Final report, May 1, 1985--April 30, 1997  

SciTech Connect

Over the twelve years of this grant from the U.S. Department of Energy, DE-FG05-85ER45208, the over-reaching aims of this work have been to explore and to attempt to understand the fundamental physics and chemistry of surfaces and interfaces. The instrument we have employed m in this work is high-resolution helium atom scattering (HAS) which we have become even more convinced is an exceptionally powerful and useful tool for surface science. One can follow the evolution of the development and progress of the experiments that we have carried out by the evolution of the proposal titles for each of the four three-year periods. At first, m in 1985-1988, the main objective of this grant was to construct the HAS instrument so that we could begin work on the surface vibrational dynamics of crystalline materials; the title was {open_quotes}Helium Atom-Surface Scattering Apparatus for Studies of Crystalline Surface Dynamics{close_quotes}. Then, as we became more interested m in the growth of films and interfaces the title m in 1988-1991 became {open_quotes}Helium Atom Surface Spectroscopy: Surface Lattice Dynamics of Insulators, Metal and Metal Overlayers{close_quotes}. In 1991-1994, we headed even more m in this direction, and also recognized that we should focus more on insulator materials as very few techniques other than helium atom scattering could be applied to insulators without causing surface damage. Thus, the proposal title became {open_quotes}Helium Atom-Surface Scattering: Surface Dynamics of Insulators, Overlayers and Crystal Growth{close_quotes}. M in the final period of this grant the title ended up {open_quotes}Investigations of the Dynamics and Growth of Insulator Films by High Resolution Helium Atom Scattering{close_quotes} m in 1994-1997. The list of accomplishments briefly discussed in this report are: tests of the shell model; multiphoton scattering; physisorbed monolayer films; other surface phase transitions; and surface magnetic effects.

Safron, S.A.; Skofronick, J.G.

1997-07-01

15

Atomic Spectra in a Helium Bubble  

Microsoft Academic Search

Density functional theory (DFT) is applied to atomic spectra under perturbations of superfluid liquid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and

Takashi Nakatsukasa; Kazuhiro Yabana; George F. Bertsch

2002-01-01

16

Phonon dynamics of the Sn\\/Ge (111) surface at room temperature and low temperature determined by helium-atom scattering  

Microsoft Academic Search

We report on a high-resolution helium atom scattering study of the surface lattice dynamics, for both the room temperature (3×3)R30° and the low-temperature (3×3) structures formed by 1\\/3 of a monolayer of Sn on Ge(111). At room temperature a pronounced lowering of the energy of the transversally polarized phonons along the Gamma Mmacr direction is observed for wave vectors in

J. Lobo; D. Farías; E. Hulpke; E. G. Michel

2005-01-01

17

Interstellar Helium Atom Flux Halo  

NASA Astrophysics Data System (ADS)

Relative motion of the Sun with respect to the surrounding local interstellar medium (LISM) results in interstellar helium atoms entering the heliosphere. These atoms have been experimentally studied in detail by observing their glow, measuring as pickup ions, and by directly detecting them on the Ulysses and IBEX space missions. Local helium fluxes are characterized by velocity distributions with their angular width and direction determined by the velocity, temperature, and number density of helium in the LISM. Dynamics of atom propagation to an observational point in the gravitational field of the sun and atom losses are well understood. The observed wings [e.g., Bzowski et al., Ap. J. Suppl., 198(2), 12, 2012] of directional distributions of interstellar helium fluxes show higher intensities than predicted by conventional theoretical models. This wing enhancement (in contrast to the flux core), the helium flux halo, could be caused by non-Maxwellian conditions in the LISM, which is not in a state of thermodynamical equilibrium, and by interactions of helium atoms in the heliosphere. The nature of the interstellar helium flux halo is examined, constraining its possible physical causes.

Gruntman, M.

2012-12-01

18

Positronium and Electron Scattering on Helium  

NASA Technical Reports Server (NTRS)

A recent work [1] establishes experimentally that Positronium scattering by atoms of various elements is surprisingly close in total cross-section to that of an isolated electron of the same velocity. In this work we will look at the scattering of Ps on Helium and compare it to a determination of the scattering of an e- with the same element. For both the Ps scattering and the e- scattering on He, we assume the symmetrization of the e- with the closed shell He electrons is the dominant interaction. A local effective potential employed in [2] and [3] is used to model the electron exchange and cross- sections are determined for a set of partial waves. For the Ps scattering we include as a secondary effect the Van der Waals interaction. For single e- scattering of He, we also employ a short range Coulomb potential and dispersion as contributing effects. Results of the cross-sections determined in each case are then compared

DiRienzi, Joseph

2011-01-01

19

The first stages of epitaxial growth of Pb atoms on Cu(100) studied by scattering of thermal helium  

NASA Astrophysics Data System (ADS)

We studied the initial stages of the growth of Pb layers on a Cu(100) substrate by means of thermal energy atom scattering (TEAS). We found that the coverage dependence of the intensity of the specularly reflected He beam is well described by a simple mathematical formula based on random adsorption on substrate lattice sites including lateral repulsive interactions between adatoms. Equilibrium measurements of the adsorbed layer for very low coverages (3 × 10 -3 monolayers) allowed to determine the 2D heat of evaporation of Pb atoms from step to terrace sites. This was accomplished by measuring the temperature dependence of the cross section for diffuse scattering.

Sánchez, A.; Ibañez, J.; Miranda, R.; Ferrer, S.

1986-12-01

20

Surface structure of niobium-doped potassium tantalate KTa1 - xNbxO3 obtained from helium atom scattering studies  

NASA Astrophysics Data System (ADS)

Helium atom scattering experiments have been carried out on the (001) surface of KTaO3 doped with 6, 10 and 15% Nb, produced by cleaving in situ single crystal samples. Several phenomena were observed through He atom diffraction measurements, including metastable behavior immediately after cleaving, reconstruction of a fraction of the surface to (2 × 1) domains after thermally cycling the surface temperatures, and the distribution of step heights of terraces at the surface as multiples of the unit cell dimension of ~ 4 Å. In addition, a large hysteresis effect was found in the lang100rang azimuth in the variation of surface reflectivity with surface temperature; a much smaller hysteresis effect was found in the lang110rang azimuth. The hysteresis effects appear for all Nb doping concentrations. Finally, small oscillations in the specular and Bragg diffraction intensities near the surface temperature 80 K were also observed.

Trelenberg, T. W.; Fatema, Rifat; Li, Jaime A.; Akhadov, E. A.; Van Winkle, David H.; Skofronick, J. G.; Safron, Sanford A.; Flaherty, F. A.; Boatner, L. A.

2010-08-01

21

Kaonic helium atoms  

NASA Astrophysics Data System (ADS)

The KEK experiment E570 has measured the Balmer-series x-rays of kaonic 4He atoms using large-area silicon drift x-ray detectors (SDDs) in order to study the low-energy K¯-nucleus strong interaction. The energy of the 3d?2p transition was determined to be 6467±3(stat)±2(syst)eV. The resulting strong-interaction energy-level shift is in agreement with theoretical calculations, thus eliminating a long-standing discrepancy between theory and experiment. Using a similar setup, the E17 experiment at J-PARC, the first experiment to be carried out in the hadron hall of J-PARC, will measure the 3d?2p x-rays of kaonic 3He.

Hayano, Ryugo S.; KEK E570 Collaboration; J-PARC E17 Collaboration

2009-08-01

22

Positronium and electron scattering on Helium  

NASA Astrophysics Data System (ADS)

A recent work [1] establishes experimentally that Positronium scattering by atoms of various elements is surprisingly close in total cross-section to that of an isolated electron of the same velocity. In this work we will look at the scattering of Ps on Helium and compare it to a determination of the scattering of an e- with the same element. For both the Ps scattering and the e- scattering on He, we assume the symmetrization of the e- with the closed shell He electrons is the dominant interaction. A local effective potential employed in [2] and [3] is used to model the electron exchange and cross- sections are determined for a set of partial waves. For the Ps scattering we include as a secondary effect the Van der Waals interaction. For single e- scattering of He, we also employ a short range Coulomb potential and dispersion as contributing effects. Results of the cross-sections determined in each case are then compared. [4pt] [1] S. J. Bromley, S. Armitage, J. Beale, D. E. Leslie, A. I. Williams, G. Laricchia, Science 330, 789 (2010)[0pt] [2] R. J. Drachman, S.K. Houston, J. Phys. B: At. Mol. Phys. 3 1657 (1970)[0pt] [3] J. Di Rienzi, R. J. Drachman, J. Phys. B. 36 2409 (2003)

di Rienzi, Joseph; Drachman, Richard

2011-06-01

23

Atom lithography with metastable helium  

SciTech Connect

A bright metastable helium (He*) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He* atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He{sup *} was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of {lambda}=1083 nm light was used to channel and focus the He* atoms into lines separated by {lambda}/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.

Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold [Physics and Astronomy, Stony Brook University, Stony Brook. New York 11794-3800 (United States)

2010-02-15

24

Atomic Spectra in a Helium Bubble  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) is applied to atomic spectra under perturbations of superfluid liquid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and D2 absorption lines are quite well reproduced by theory, suggesting that the DFT may be useful for describing spectral perturbations in more complex environments.

Nakatsukasa, Takashi; Yabana, Kazuhiro; Bertsch, George F.

2002-09-01

25

Effects of chain branching on the monolayer structure of alkanes at interfaces: a neutron and helium atom scattering study  

NASA Astrophysics Data System (ADS)

A study comparing the monolayer structures of intermediate-length alkanes adsorbed on various substrates using He-atom scattering (HAS) and neutron scattering (NS) reveals significant differences in the ordering of branched and unbranched molecules. HAS measurements of tetracosane ( n-C 24H 50) adsorbed on hydrogen-covered Pt(1 1 1) and NS experiments with tetracosane on graphite basal-plane surfaces show the formation of well-ordered monolayers. For squalane monolayers, on the other hand, no diffraction peaks were observed by HAS for adsorption on hydrogen-covered Pt(1 1 1) and only a broad diffraction peak was found by NS for adsorption on graphite, corresponding to the nearest-neighbor separation in a direction perpendicular to the principal molecular axis. We conclude that unbranched alkanes form highly ordered monolayers at a close-packed interface whereas the translational order in monolayers of the branched squalane molecule is either shorter range or nonexistent. These results demonstrate the importance of molecular branching for the structure of these organic layers and may have implications for the interfacial ordering of alkane-based lubricants and coatings.

Fuhrmann, D.; Graham, A. P.; Criswell, L.; Mo, H.; Matthies, B.; Herwig, K. W.; Taub, H.

2001-06-01

26

Characterisation and O 2 titration of CO islands on Pt 100: helium atom scattering and reactive sticking probability measurements  

NASA Astrophysics Data System (ADS)

Thermal energy atom scattering (TEAS) has been used simultaneously with molecular beam adsorption and thermal desorption to probe the lateral distribution of CO on a Pt 100 single-crystal surface. On the initial hex-R phase at 350 K, (1 × 1) island growth occurs at a constant local coverage ( ?(1 × 1)CO) of 0.4 ML. However, during desorption the surface remains wholly in the (1 × 1) state until ( ?(1 × 1)CO) ? 0.25 ML. Subsequent reconstruction to hex occurs at a constant local coverage of 0.19 ML in the remaining (1 × 1) domains. Hysteresis is not observed for the pre-prepared (1 × 1) surface, on which a random CO distribution is observed during adsorption. The scattering cross-section ? for a single CO molecule on the hex-R and (1 × 1) surfaces at 350 K has been determined as 71 ± 10 and 130 ± 18Å 2 respectively. The behaviour during oxidation of (1 × 1)-CO islands on the initial hex-R surface prepared by either adsorption or desorption is found to be consistent with the TEAS data. The first sticking probabilities for O 2 and CO on the CO ad-freed and O ad-freed (1 × 1) phase of Pt 100 are also reported.

Pasteur, A. T.; Guo, X.-C.; Ali, T.; Gruyters, M.; King, D. A.

1996-11-01

27

Surface Phonon Dispersion Curves of Rubidium Chloride, Potassium Bromide, Rubidium Bromide and Sodium Iodide Studied by Inelastic Helium Atom Scattering  

NASA Astrophysics Data System (ADS)

The alkali halide surfaces were the first for which full surface phonon dispersion curves were measured. Most of the early work was mainly concerned with the low-energy modes for the lighter alkali halides, such as LiF and NaF, and a full survey of a more representative sampling of these crystals was never made. A recent theoretical calculation has also suggested that relaxation effects might provide interesting features on the surface phonon modes especially for the optical modes of the heavier compounds. The work of this dissertation is an effort to measure the surface dynamics of other, usually heavier, alkali halide crystals. This work describes measurements on the surfaces of RbCl(001), RbBr(001), KBr(001), and NaI(001) with the inelastic He atom scattering technique. The energy gain or loss and the momentum change is measured by the time of flight method. For the four crystals, the surface phonon dispersion curves are obtained along both high symmetry directions. The general agreement between the theory and the experimental results is very good. Some new features of the surface vibration have been found. First, the optical mode, crossing resonance and acoustic modes were clearly seen from the KBr surface over the entire zone. The strong interaction coupling between the He and the optical mode is rather unique. Secondly, crossing resonances (S_8 mode) were observed for the KBr, RbBr and NaI surfaces. This observation suggests that this mode is a general feature of all the alkali halide surfaces. The origin of this mode might be due to the perpendicular polarized bulk acoustic motion. Thirdly, NaI results show that bound-state resonance effects could strongly enhance the bulk mode especially when there is a high density of phonon states. Finally, there is no experimental evidence supporting any surface relaxation effects. In fact, the experimental results seem to agree better with the unrelaxed calculations. In addition to the inelastic scattering measurements, we also did angular distribution, low pressure He beam scattering and a temperature-dependent dynamical study. Information such as the surface corrugation, He-surface potential, bound state energies, the surface Debye-Waller temperature and a measure of multi-phonon contributions can be obtained from these experimental results.

Chern, Gung

28

A neutron scattering investigation of the collective excitations of superfluid helium in porous media  

Microsoft Academic Search

Inelastic neutron scattering has been used to probe the microscopic dynamics of superfluid helium adsorbed in various porous materials. The substrates used to confine the superfluid were porous vycor glass, silica aerogel of two different porosities, and silica xerogel. As in bulk superfluid helium, the confined helium atoms exhibit well-defined cooperative motions, or collective excitations, but modified due to the

Robert Michael Dimeo

1999-01-01

29

Interaction of Helium Rydberg State Atoms with Superfluid Helium  

NASA Astrophysics Data System (ADS)

The pair potentials between ground state helium and Rydberg He atoms are calculated by the full configuration interaction electronic structure method for both the electronic singlet and the triplet manifolds. The obtained pair potentials are validated against existing experimental molecular and atomic data. Most states show remarkable energy barriers at long distances ( Å), which can effectively stabilize He against the formation of He at low nuclear kinetic energies. Bosonic density functional theory calculations, based on the calculated pair potential data, indicate that the triplet ground state He reside in spherical bubbles in superfluid helium with a barycenter radius of 6.1 Å at the liquid saturated vapor pressure. The pressure dependency of the relative He absorption line blue shift in the liquid was obtained through both the statistical line broadening theory as well as the dynamic adiabatic following method. The pronounced difference between the results from the static and dynamic models is attributed to the dynamic Jahn-Teller effect that takes places in the electronically excited state within the dephasing time of 150 fs. Transient non-thermalized liquid surroundings near He may contribute to an artificial reduction in the absorption line blue shift by up to 30 cm.

Fiedler, Steven L.; Eloranta, Jussi

2014-03-01

30

Atomic Scattering Factors  

NSDL National Science Digital Library

From the Lawrence Berkeley Laboratory's Center for X-Ray Optics, these "atomic scattering factors are based upon photoabsorption measurements of elements in their elemental state." These easy-to-use tables allow users to search out atomic scattering factor data by element and look up the x-ray properties of elements, the index of refraction for a compound material, the x-ray attenuation length of a solid, the x-ray transmission of a solid or a gas, and more. Most of the tables are accessed by way of an online query form with variables such as material, density, and photon energy range entered by the user. Most outputs come in plot form for quick viewing, or results may be retrieved as a text or postscript file for use with a personal plotting software.

31

Elastic and inelastic scattering of He atoms from Bi(111)  

NASA Astrophysics Data System (ADS)

Elastic and inelastic scattering of helium atoms has been used to study the Bi(111) surface. Sharp diffraction peaks are found with results in excellent agreement with previous structure determinations of the Bi(111) surface. The rather large first order peaks with respect to the zero order peak indicate a stronger surface corrugation than observed in helium scattering from other metallic surfaces. Time-of-flight spectra of scattered He atoms clearly reveal two inelastic scattering maxima, which allow a first report on phonon creation and annihilation events on the Bi(111) surface. An estimate of the group velocity shows that the phonon creation peak is likely to correspond to a Rayleigh mode.

Tamtögl, A.; Mayrhofer-Reinhartshuber, M.; Balak, N.; Ernst, W. E.; Rieder, K. H.

2010-08-01

32

Cold elastic and reactive atom-molecule collisions in helium-helium-alkali-metal triatomic systems  

NASA Astrophysics Data System (ADS)

Atom-molecule collisions in helium-helium-alkali-metal triatomic systems at cold energies are studied using the adiabatic hyperspherical representation. We consider the elastic collision processes He4X+He4?He4X+He4 and He24+X?He24+X, as well as the reactive collision processes He4X+He4?He24+X, where X is one of the bosonic alkali-metal atoms: Li7, Na23, K39, Rb85, or Cs133. The elastic and reactive collision cross sections are calculated at nonzero collision energies by including not only zero atom-molecule relative angular momentum, L =0, processes but also L >0 processes. The total cross section for He4X+He4?He4X+He4 is found to increase with the scattering length between He4 and X, while the other collision processes are not found to have any systematic dependence on the alkali-metal species X.

Suno, Hiroya; Esry, B. D.

2014-05-01

33

Nondispersive Two-Electron Wave Packets in a Helium Atom  

SciTech Connect

We demonstrate the existence of stable nondispersing two-electron wave packets in the helium atom in combined magnetic and circularly polarized microwave fields. These packets follow circular orbits and we show that they can also exist in quantum dots. Classically the two electrons follow trajectories which resemble orbits discovered by Langmuir and which were used in attempts at a Bohr-like quantization of the helium atom. Eigenvalues of a generalized Hessian matrix are computed to investigate the classical stability of these states. Diffusion Monte Carlo simulations demonstrate the quantum stability of these two-electron wave packets in the helium atom and quantum-dot helium with an impurity center.

Kalinski, Matt; Hansen, Loren; Farrelly, David [Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300 (United States)

2005-09-02

34

Elastic and inelastic helium beam scattering from Cu(100) surfaces and vibrational modes in incommensurate systems  

SciTech Connect

Structural and vibrational properties of clean and oxygen covered, single crystal Cu(100) surfaces were studied, using the technique of high resolution helium beam scattering. To carry out these investigations it was necessary to first design and build a high performance neutral atom scattering experimental setup, consisting of: (1) a high intensity, supersonic neutral atom beam source; (2) a UHV scattering chamber with sample manipulation and diagnostic facilities; (3) a novel, metastable atom detector system. Experimental results pertaining to the following are presented: (1) new information on quasi-elastic electron helium atom scattering observed in the metastable atom detector: (2) elastic He atom scattering from clean and oxygen covered Cu(100) surfaces; and (3) inelastic He atom scattering from clean Cu(100) surfaces. These experiments were performed with the detector moving in and out of the scattering plane, the latter being a novel feature of this setup. The analysis of these data gives the inherent vibrational modes of the surface. Finally, a computational investigation of the structural and dynamic properties of a model incommensurate system, the one-dimensional, finite Frenkel-Kontorova chain, is reported.

Martini, K.M.

1986-01-01

35

Classical helium atom with radiation reaction  

NASA Astrophysics Data System (ADS)

We study a classical model of helium atom in which, in addition to the Coulomb forces, the radiation reaction forces are taken into account. This modification brings in the model a new qualitative feature of a global character. Indeed, as pointed out by Dirac, in any model of classical electrodynamics of point particles involving radiation reaction one has to eliminate, from the a priori conceivable solutions of the problem, those corresponding to the emission of an infinite amount of energy. We show that the Dirac prescription solves a problem of inconsistency plaguing all available models which neglect radiation reaction, namely, the fact that in all such models, most initial data lead to a spontaneous breakdown of the atom. A further modification is that the system thus acquires a peculiar form of dissipation. In particular, this makes attractive an invariant manifold of special physical interest, the zero-dipole manifold that corresponds to motions in which no energy is radiated away (in the dipole approximation). We finally study numerically the invariant measure naturally induced by the time-evolution on such a manifold, and this corresponds to studying the formation process of the atom. Indications are given that such a measure may be singular with respect to that of Lebesgue.

Camelio, G.; Carati, A.; Galgani, L.

2012-06-01

36

Classical helium atom with radiation reaction  

SciTech Connect

We study a classical model of helium atom in which, in addition to the Coulomb forces, the radiation reaction forces are taken into account. This modification brings in the model a new qualitative feature of a global character. Indeed, as pointed out by Dirac, in any model of classical electrodynamics of point particles involving radiation reaction one has to eliminate, from the a priori conceivable solutions of the problem, those corresponding to the emission of an infinite amount of energy. We show that the Dirac prescription solves a problem of inconsistency plaguing all available models which neglect radiation reaction, namely, the fact that in all such models, most initial data lead to a spontaneous breakdown of the atom. A further modification is that the system thus acquires a peculiar form of dissipation. In particular, this makes attractive an invariant manifold of special physical interest, the zero-dipole manifold that corresponds to motions in which no energy is radiated away (in the dipole approximation). We finally study numerically the invariant measure naturally induced by the time-evolution on such a manifold, and this corresponds to studying the formation process of the atom. Indications are given that such a measure may be singular with respect to that of Lebesgue.

Camelio, G. [Universita degli Studi di Milano, Corso di Laurea in Fisica, Via Celoria 16, I-20133 Milano (Italy); Carati, A.; Galgani, L. [Dipartimento di Matematica, Universita degli Studi di Milano, Via Saldini 50, I-20133 Milano (Italy)

2012-06-15

37

Collisions of cold antiprotonic helium atoms and ions with ordinary helium atoms  

Microsoft Academic Search

We consider two types of collisional processes with excited antiprotonic helium systems. (i) Transitions between hyperfine structure sublevels in (p?He+)nLFJ are considered at T ? 25 K using the coupled-channels method and a model of scalar and tensor interactions between antiprotonic and ordinary He atoms. Inelastic cross sections for the single and double spin-flip transitions are less than elastic ones

G Ya Korenman; S N Yudin

2007-01-01

38

Helium nanobubble release from Pd surface: An atomic simulation  

SciTech Connect

Molecular dynamic simulations of helium atoms escaping from a helium-filled nano-bubble near the surface of crystalline palladium reveal unexpected behavior. Significant deformation and cracking near the helium bubble occur initially, and then a channel forms between the bubble and the surface, providing a pathway for helium atoms to propagate towards the surface. The helium atoms erupt from the bubble in an instantaneous and volcano-like process, which leads to surface deformation consisting of cavity formation on the surface, along with modification and atomic rearrangement at the periphery of the cavity. The present simulation results show that, near the palladium surface, there is a helium-bubble-free zone, or denuded zone, with a typical thickness of about 3.0 nm. Combined with experimental measurements and continuum-scale evolutionary model predictions, the present atomic simulations demonstrate that the thickness of the denuded zone, which contains a low concentration of helium atoms, is somewhat larger than the diameter of the helium bubbles in the metal tritide. Furthermore, a relationship between the tensile strength and thickness of metal film is also determined.

Wang, Liang; Hu, Wangyu; Deng, Huiqiu; Xiao, Shifang; Yang, Jianyu; Gao, Fei; Heinisch, Howard L.; Hu, Shilin

2011-02-14

39

Deep Inelastic Neutron Scattering Study of Nanoconfined Liquid Helium Mixtures  

NASA Astrophysics Data System (ADS)

The single-particle momentum distribution n(p) plays a central role in the contemporary understanding of quantum many- body systems, especially the helium liquids. The superfluid behavior of liquid He^4 below the famous lambda-point temperature is associated with the Bose condensation of a macroscopic fraction of the He^4 atoms to the zero momentum state. This manifests itself in n(p) as a ?-function singularity at p = 0. Similarly, the Fermi liquid character of He^3 is associated with a sharp discontinuity in the Fermi surface at the Fermi momentum pF. Using the Wide Angular Chopper Spectrometer at the Spallation Neutron Source, we recently carried out a deep inelastic neutrons scattering study of dilute He^3 + He^4 solutions confined in mesoporous MCM-41 in order to investigate the effects of confinement on the non-classical momentum distribution of an isotopic helium solution. The Bose condensate fraction, Fermi surface, average isotopic kinetic energies, and related work in the literature will be discussed.

Sokol, Paul; Prisk, Timothy; Das, Narayan

2011-03-01

40

Application of density-functional theory to line broadening: Cs atoms in liquid helium  

Microsoft Academic Search

We test the applicability of density-functional theory (DFT) to spectral perturbations taking an example of a Cs atom surrounded by superfluid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The

Takashi Nakatsukasa; Kazuhiro Yabana; George F. Bertsch

2002-01-01

41

Low-Energy HELIUM(+) and LITHIUM(+) Ion Scattering from Surfaces  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. A 150^circ ion scattering spectrometer has been commissioned and utilized to investigate several adsorbate systems on Cu(110). Firstly, the experimental parameters were determined by using 3keV Li^+ ions in the ICISS mode to investigate the clean Cu(110) surface. The inelastic background normally observed in Li^+ ion scattering energy distributions was found to be more sensitive to the sublayer shadowing conditions than was the substrate's elastic scattering peak. Most of the observed lower layer scattering features corresponded to multiple scattering events. Using computer modelling it was deduced that for the clean Cu(110) surface the 1st to 2nd layer spacing was compressed by (8 +/- 3)%, and the 2nd to 3rd was expanded by (11 +/- 8)% compared to the bulk values. 3keV Li^+ and 2keV He ^+ ions were then used to study the Cu(110)(2 x 1)-O and Cu(110)(2 x 3)-N adsorbate systems. In the former case the Li^+ data exhibited a doubling of the Cu-Cu distance in the < 110> and the < 211 > azimuths and were found to favour a missing row type reconstruction, in which every other < 100> row had been removed. In addition, He^+to O scattering indicated that the oxygen atoms resides in the < 100> long bridge site (0.0 +/- 0.2)A above the surface. Li ^+ ion scattering from the Cu(110)(2 x 3)-N indicated a substantial reconstruction of the surface, with an apparent reduction in the Cu-Cu spacing in the < 110> azimuth and an increase in the < 211> azimuth. Many of the observations are found to be quantitatively consistent, and all are qualitatively consistent, with a reconstruction in which a local Cu(100)c(2 x 2)-N structure is formed. Additionally, the He ^+to N scattering results favour a N adsorption site slightly above the surface. Adsorption of Na, K and Cs onto Cu(110) at room temperature was studied using 1keV He^+ ions, 1keV Li^+ ions were used to investigate Cs adsorption. The intensity of the alkali elastic scattering signal exhibited a 'dip' with increasing alkali coverage. For lithium this was attributed to the change in the reionization probability with changes in the surface's work function. For helium this was thought to be due to changes in the neutralization mechanism within the alkali adlayer. Additionally, the alkali metal adsorbates induced an inelastic background in the He^+ ion energy distributions, and this is ascribed to changes in the neutralization probability as the ion returns through the alkali metal overlayer.

Ashwin, Mark John

1990-01-01

42

A collimated pulsed supersonic metastable helium atomic beam  

NASA Astrophysics Data System (ADS)

The supersonic short-pulse helium atomic beam and its metastables were studied. A pulsed high-density helium atomic beam was ejected from a nozzle, collimated by a skimmer and then flowed through a penning-type discharge device. After discharging, the metastable density of the pulsed helium atomic beam was up to 1.24×1011 cm-3. Excellent symmetry of atomic beam profile was obtained. The deviation of angle of the atomic beam with respect to the axis was less than 0.14°. The mean diffusion angle of the pulsed beam was 4°, and a mean velocity of atomic beam was up to 1350 ms-1. Laser induced fluorescence of metastable atoms has been studied.

Feng, P. X.; Weiner, B.

2007-04-01

43

PREFACE: Atom-surface scattering Atom-surface scattering  

Microsoft Academic Search

It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific

Salvador Miret-Artés

2010-01-01

44

Three-body interactions in proton-helium angular scattering  

SciTech Connect

H/sup +/+He scattering at 0.5 MeV has been investigated using a coincidence technique that completely determines the three-body transverse momentum exchange in single ionization collisions. Three scattering regions could be distinctly recognized that are dominated by proton--helium-nucleus, proton-electron, or electron--helium-nucleus interactions. Calculations and the experimental data show that the coupling between the electronic and nuclear degrees of freedom is required to understand the dynamics for more than 97% of the ionizing collisions.

Dorner, R.; Ullrich, J.; Schmidt-Bocking, H.; Olson, R. E.

1989-07-10

45

Development of a helium cryostat for laser spectroscopy of atoms with unstable nuclei in superfluid helium  

NASA Astrophysics Data System (ADS)

We are developing a new nuclear laser spectroscopic technique for the study of nuclear structure that can be applied to short-lived low-yield atoms with unstable nuclei. The method utilizes superfluid helium (He II) as a trapping medium for high-energy ion beams. A liquid helium cryostat with optical windows is a key apparatus for this type of experiment. We describe the design and the performance of the cryostat which is developed for the present project.

Imamura, Kei; Furukawa, Takeshi; Wakui, Takashi; Yang, Xiaofei; Yamaguchi, Yasuhiro; Tetsuka, Hiroki; Mitsuya, Yosuke; Tsutsui, Yoshiki; Fujita, Tomomi; Ebara, Yuta; Hayasaka, Miki; Arai, Shino; Muramoto, Sosuke; Ichikawa, Yuichi; Ishibashi, Yoko; Yoshida, Naoki; Shirai, Hazuki; Hatakeyama, Atsushi; Wada, Michiharu; Sonoda, Tetsu; Ito, Yuta; Odashima, Hitoshi; Kobayashi, Tohru; Ueno, Hideki; Shimoda, Tadashi; Asahi, Koichiro; Matsuo, Yukari

2013-12-01

46

Midlatitude incoherent scatter observations of helium and hydrogen ions  

Microsoft Academic Search

We have successfully employed a constrained non-linear least squares analysis of incoherent scatter data from the topside ionosphere over Arecibo, Puerto Rico to simultaneously deduce concentrations of helium ions, protons, and oxygen ions as well as ion and electron temperatures. The constraint encourages smooth temperature profiles, and its use avoids unrealistic parameter values in regions where light ions are more

Philip J. Erickson; Wesley E. Swartz

1994-01-01

47

The Weakest Link: Bonding between Helium Atoms  

ERIC Educational Resources Information Center

A highly simplified model for helium dimers that reproduces their essential features without the need for elaborate computation is presented. The He-He potential is predicted to have minimum of 10.9 K at a nuclear separation of 5.61 bohrs.

Lohr, Lawrence L.; Blinder, S. M.

2007-01-01

48

Heuristic theory of positron-helium scattering.  

NASA Technical Reports Server (NTRS)

An error in a previous modified adiabatic approximation (Drachman, 1966), due to a lack of generality in the form of the short-range correlation part of the wave function for L greater than zero, is corrected heuristically by allowing the monopole suppression parameter to depend on L. An L-dependent local potential is constructed to fit the well-known positron-hydrogen s, p, and d wave phase shifts below the rearrangement threshold. The same form of potential yields a positron-helium cross-section in agreement with a recent experimental measurement near threshold.

Drachman, R. J.

1971-01-01

49

Atomic Theory of Liquid Helium Near Absolute Zero  

Microsoft Academic Search

The properties of liquid helium at very low temperatures (below 0.5°K) are discussed from the atomic point of view. It is argued that the lowest states are compressional waves (phonons). Long-range motions which leave density unaltered (stirrings) are impossible for Bose statistics since they simply permute the atoms. Motions on an atomic scale are possible, but require a minimum energy

R. P. Feynman

1953-01-01

50

Spectra of helium clusters with up to six atoms using soft-core potentials  

NASA Astrophysics Data System (ADS)

In this paper, we investigate small clusters of helium atoms using the hyperspherical harmonic basis. We consider systems with A=2,3,4,5,6 atoms with an interparticle potential which does not present a strong repulsion at short distances. We use an attractive Gaussian potential that reproduces the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the widely used He-He interactions, the Aziz and Slaman potential, called LM2M2. In systems with more than two atoms, we consider a repulsive three-body force that, by construction, reproduces the trimer binding energy of the LM2M2 potential. With this model, consisting of the sum of a two- and three-body potential, we have calculated the spectrum of clusters formed by four, five, and six helium atoms. We have found that these systems present two bound states, one deep and one shallow, close to the threshold fixed by the energy of the (A-1)-atom system. Universal relations between the energies of the excited state of the A-atom system and the ground-state energy of the (A-1)-atom system are extracted, as well as the ratio between the ground state of the A-atom system and the ground-state energy of the trimer.

Gattobigio, M.; Kievsky, A.; Viviani, M.

2011-11-01

51

Recent Progress in Electron-Atom Scattering  

NASA Astrophysics Data System (ADS)

The application of multi-parameter data collection techniques to electron-atom collision-experiments allows statistically significant results to be obtained for weak physical effects [1]. In addition to improved count rates, if the spin projection of the primary electron is determined, the roles of electron exchange and relativity in the scattering process can be highlighted. Examples of recent measurements from our laboratories will be discussed in the context of work from other groups. These will include benchmark measurements on the electronic excitation of helium employing the time-of-flight technique [2]. The technique allows inelastic cross sections to be accurately placed on an absolute scale by normalization to well-established elastic cross sections. Measurements on the (e,2e) ionization/excitation of helium through the application of energy-dispersive toroidal-analyzers will also be discussed [3]. The results provide a stringent test to theory and indicate the strengths and limitations of state-of-the art calculations in describing the Coulomb 4-body problem. Finally I will describe results from (e,2e) measurements on argon [4] and xenon [5] targets performed with spin polarized electrons which probe the many-body nature of electron exchange-scattering. [1] J. Ullrich et al, Rep. Prog. Phys. 66 (2003) 1463. [2] M. Lange et al, J. Phys. B: At. Mol. Opt. Phys. 39 (2006) 4179. [3] S. Bellm, J. Lower and K. Bartschat, Phys. Rev. Lett. 96, 223201 (2006). [4] S. Bellm, J. Lower, Marco Kampp and Colm T. Whelan, J. Phys. B: At. Mol. Opt. Phys. 39 (2006) 4759. [5] R. Panajotovic, J. Lower, E. Weigold A. Prideaux and D. H. Madison, Phys. Rev. A 73, 52701, (2006).

Lower, Julian

2007-06-01

52

Photoionization of atoms and molecules. [of hydrogen, helium, and xenon  

NASA Technical Reports Server (NTRS)

A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

Samson, J. A. R.

1976-01-01

53

Stimulated Brillouin Scattering from Helium-Hydrogen Plasmas  

SciTech Connect

An extensive study of the stimulated Brillouin scattering (SBS) in helium-hydrogen plasmas has been performed using a gas jet at the Janus Laser Facility. We observe three regions of reflectivity by varying the probe intensity from 10{sup 14} to 10{sup 16}: saturated region, linear region, and near SBS threshold region. In the linear regime, adding small amounts of H to a He plasma reduces the SBS reflectivity by a factor of 4.

Froula, D H; Divol, L; Price, D; Gregori, G; Williams, E A; Glenzer, S H

2003-08-22

54

Semiclassical quantization of Bohr orbits in the helium atom  

NASA Astrophysics Data System (ADS)

We use the complex WKB-Maslov method to construct the semiclassical spectral series corresponding to the resonance Bohr orbits in the helium atom. The semiclassical energy levels represented as the Rydberg tetra series correspond to the doubly symmetrically excited states of helium-like atoms. This level series contains the Rydberg triple series reported by Richter and Wintgen in 1991, which corresponds to the Z2+e-e- configuration of electrons observed by Eichmann and his collaborators in experiments on the laser excitation of the barium atom in 1992. The lower-level extrapolation of the formula obtained for the semiclassical spectrum gives the value of the ground state energy, which differs by 6% from the experimental value obtained by Bergeson and his collaborators in 1998. We also calculate the fine structure of the semiclassical spectrum due to the spin-orbit and spin-spin interactions of electrons.

Belov, V. V.; Maksimov, V. A.

2007-05-01

55

Atomically thin superfluid helium films on solid hydrogen  

NASA Astrophysics Data System (ADS)

We have measured both adsorption isotherms and third-sound resonance of atomically thin 4He films on solid hydrogen. We find helium more weakly bound to a hydrogen surface than to other rare-gas surfaces, with a van der Waals cofficient of 4.6+/-0.4 K (layers)3. We have also measured third sound, at 0.18 K, down to a total helium coverage of 0.45+/-0.01 atomic layer, indicating an inert coverage at T=0 K of 0.29 atomic layer or less. In common with other weak-binding substrates we also see depressions in third-sound velocity near half-layer intervals.

Shirron, P. J.; Mochel, J. M.

1991-08-01

56

Raman Scattering from Solid and Fluid Helium at High Pressure  

NASA Astrophysics Data System (ADS)

Raman spectra were measured in solid helium at two molar volumes: 7.74 cm('3) ("10 kbar") and 9.06 cm('3) ("5 kbar"). The Raman-active E(,2g) phonon has been observed in the hcp phase of each crystal. The volume dependence measured for this phonon frequency is well represented by the mode Gruneisen parameter (gamma) = 1.06 + 0.097 V. Conventional lattice dynamics, using modern helium potentials, predicts a frequency and volume dependence for the E(,2g) phonon in good agreement with the measurements over this range of volume. Temperature dependence of the E(,2g) phonon frequency and linewidth was measured under isochoric conditions. Over the limited range of temperature in which the hcp phase exists, the thermal shift of frequency was measured to be negative by an amount no more than 1 cm('-1). The phonon linewidth was observed to be non-zero at 0 K, increasing in width with increasing temperature. The temperature dependence is compatible with a strong interaction between the E(,2g) phonon and zone-edge phonons, where the optical phonon combines with a transverse acoustic phonon to create a longitudinal acoustic phonon. In addition, second-order Raman spectra were collected for both high-pressure solid phases, hcp and fcc. Structure has been observed in the two-phonon portion of the solid helium spectra and is remarkably similar in both phases. Significant intensity extends beyond the expected cut-off for two-phonon processes, though to a decreasing extent with increasing pressure. Thus multi-phonon processes remain important in helium even at high pressure. Raman scattering from dense fluid helium shows clear departure from the behavior of collision-induced scattering from the more classical fluids. Even at room temperature, a departure from the usual roughly-exponential behavior is observed at low frequency in helium at high pressure. The departure becomes even more pronounced near the freezing temperature, with a dramatic reduction in low-frequency intensity. Helium in the quantum regime (low-density, low-temperature) has previously been shown to have a Raman spectrum consisting of a broad peak with no intensity at low frequency. Further study of the change in this low-frequency behavior from classical to quantum by variation of the density may lead to an increased understanding of dense fluids.

Watson, George Henry, Jr.

57

Ionization potential of the helium atom.  

PubMed

The ground-state ionization potential of the He4 atom is found to be 5 945 204 223 (42) MHz. Along with lower-order contributions, this result includes all effects of relative order alpha4, alpha(3)m(e)/m(alpha), and alpha(5)ln(2)alpha. Effective operators derived in dimensionally regularized nonrelativistic quantum electrodynamics are employed. The average values of these operators are evaluated using a high-accuracy variational wave function constructed in an exponential basis. PMID:11713750

Korobov, V; Yelkhovsky, A

2001-11-01

58

Spectroscopy of Lithium Atoms and Molecules on Helium Nanodroplets  

PubMed Central

We report on the spectroscopic investigation of lithium atoms and lithium dimers in their triplet manifold on the surface of helium nanodroplets (HeN). We present the excitation spectrum of the 3p ? 2s and 3d ? 2s two-photon transitions for single Li atoms on HeN. The atoms are excited from the 2S(?) ground state into ?, ?, and ? pseudodiatomic molecular substates. Excitation spectra are recorded by resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) mass spectroscopy, which allows an investigation of the exciplex (Li*–Hem, m = 1–3) formation process in the Li–HeN system. Electronic states are shifted and broadened with respect to free atom states, which is explained within the pseudodiatomic model. The assignment is assisted by theoretical calculations, which are based on the Orsay–Trento density functional where the interaction between the helium droplet and the lithium atom is introduced by a pairwise additive approach. When a droplet is doped with more than one alkali atom, the fragility of the alkali–HeN systems leads preferably to the formation of high-spin molecules on the droplets. We use this property of helium nanodroplets for the preparation of Li dimers in their triplet ground state (13?u+). The excitation spectrum of the 23?g(?? = 0–11) ? 13?u+(?? = 0) transition is presented. The interaction between the molecule and the droplet manifests in a broadening of the transitions with a characteristic asymmetric form. The broadening extends to the blue side of each vibronic level, which is caused by the simultaneous excitation of the molecule and vibrations of the droplet (phonons). The two isotopes of Li form 6Li2 and 7Li2 as well as isotope mixed 6Li7Li molecules on the droplet surface. By using REMPI-TOF mass spectroscopy, isotope-dependent effects could be studied.

2013-01-01

59

PREFACE: Atom-surface scattering Atom-surface scattering  

NASA Astrophysics Data System (ADS)

It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific contributions. J R Manson, or Dick to his friends and colleagues, is one of the founding fathers, together with N Cabrera and V Celli, of the 'Theory of surface scattering and detection of surface phonons'. This is the title of the very well-known first theoretical paper by Dick published in Physical Review Letters in 1969. My first meeting with Dick was around twenty years ago in Saclay. J Lapujoulade organized a small group seminar about selective adsorption resonances in metal vicinal surfaces. We discussed this important issue in surface physics and many other things as if we had always known each other. This familiarity and warm welcome struck me from the very beginning. During the coming years, I found this to be a very attractive aspect of his personality. During my stays in Göttingen, we had the opportunity to talk widely about science and life at lunch or dinner time, walking or cycling. During these nice meetings, he showed, with humility, an impressive cultural background. It is quite clear that his personal opinions about history, religion, politics, music, etc, come from considering and analyzing them as 'open dynamical systems'. In particular, with good food and better wine in a restaurant or at home, a happy cheerful soirée is guaranteed with him, or even with only a good beer or espresso, and an interesting conversation arises naturally. He likes to listen before speaking. Probably not many people know his interest in tractors. He has an incredible collection of very old tractors at home. In one of my visits to Clemson, he showed me the collection, explaining to me in great detail, their technical properties; all of them were ready for use! We cannot imagine him without his two old-fashioned Mercedes, also in his collection. He also has technical skills in construction and music and always has time for jogging. I would finally say that he is an even-tempered person. In brief, mens sana in corpore sano 1 . Dick is a theorist bound to experimental work, extremely intuitive and very dedicated. In his long stays outside Clemson, he always visited places where experiments were being carried out. He has been, and still is, of great help to experimental PhD students, postdocs or senior scientists in providing valuable advice and suggestions towards new measurements. Plausible interpretations of their results developing theoretical models or always searching for good agreement with experiment are two constants in his daily scientific work. Experimental work is present in most of his 150 papers. One of the main theoretical challenges in this field was to develop a formalism where the plethora of experimental results reported in the literature were accommodated. His transition matrix formalism was also seminal in the field of atom-surface scattering. Elastic and inelastic (single and double phonon) contributions were determined as well as the multiphonon background. This work was preceded by a theory for diffuse inelastic scattering and a posterior contribution for multiphonon scattering, both with V Celli. In a similar vein, a theory of molecule-surface scattering was also derived and, more recently, a theory for direct scattering, trapping and desorption. Very interesting extensions to scattering with molten metal and liquid surfaces have also been carried out. Along with collaborators he has studied energy accommodation and sticking coefficients, providing a better understanding of their meaning. G Armand and Dick proposed the well-known corrugated Morse potential as an interaction potential model providing reliable results of diffraction patterns and selective adsorption resonances. This proposal was, in a certain sense, the result of many previous studies carried out by t

Miret-Artés, Salvador

2010-08-01

60

Further Examination of a Simplified Model for Positronium-Helium Scattering  

NASA Technical Reports Server (NTRS)

While carrying out investigations on Ps-He scattering we realized that it would be possible to improve the results of a previous work on zero-energy scattering of ortho-positronium by helium atoms. The previous work used a model to account for exchange and also attempted to include the effect of short-range Coulomb interactions in the close-coupling approximation. The 3 terms that were then included did not produce a well-converged result but served to give some justification to the model. Now we improve the calculation by using a simple variational wave function, and derive a much better value of the scattering length. The new result is compared with other computed values, and when an approximate correction due to the van der Waals potential is included the total is consistent with an earlier conjecture.

DiRienzi, J.; Drachman, Richard J.

2012-01-01

61

Motion of a helium atom in a quartz crystal with dislocations  

NASA Astrophysics Data System (ADS)

The motion of a helium atom through the quartz crystal structure disturbed by dislocations has been considered. Two cases of their action on the motion of the helium atom have been discussed. (1) Dislocations, in particular, screw dislocations, can be represented as contracted or extended helical (six-, four-, three-membered) channels consisting of SiO4 tetrahedra. In this case, the helium atom moves inside the dislocation as in the crystallographic channel with changed parameters. (2) Dislocations can cross the crystallographic channel. This leads to an excess or a deficit of oxygen atoms of SiO4 tetrahedra in the immediate environment of the helium atom located in the channel. In both cases, the displacement of the helium atom appears as a Frenkel-Kontorova soliton. However, in the latter case, the dependence of the activation energy of this soliton on the number of defects is discontinuous and exhibits a “mobility gap” of the helium atom.

Kalashnikov, E. V.; Tolstikhin, I. N.; Pevzner, B. Z.

2010-07-01

62

Application of density-functional theory to line broadening: Cs atoms in liquid helium  

NASA Astrophysics Data System (ADS)

We test the applicability of density-functional theory (DFT) to spectral perturbations taking an example of a Cs atom surrounded by superfluid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and D2 absorption lines are quite well reproduced by theory, suggesting that the DFT may be useful for describing spectral perturbations in more complex environments.

Nakatsukasa, Takashi; Yabana, Kazuhiro; Bertsch, George F.

2002-03-01

63

The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows  

Microsoft Academic Search

Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a

J. C. Hoppe; W. C. Honaker

1979-01-01

64

Binding of two helium atoms in confined geometries  

SciTech Connect

The authors carry out a comprehensive study of the binding of two helium atoms in unrestricted and, in particular, in restricted geometries in both two and three dimensions. Besides the well known binding of the {sup 4}He dimer in unrestricted geometry in two and three dimensions, the authors also find weakly bound states of the {sup 3}He-{sup 4}He molecule and the {sup 3}He dimer in 2 dimensions. Furthermore, any combination of two {sup 4}He or {sup 3}He atoms can form a molecule if their motion is sufficiently confined. The calculations are carried out by numerically solving the Schroedinger equation as well as by constructing a suitable variational wave function.

Kilic, S. [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik] [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik; [Univ. of Split (Croatia). Faculty of Natural Sciences; Krotscheck, E.; Zillich, R. [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik] [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik

1999-08-01

65

Modeling of Atom-Diatom Scattering.  

National Technical Information Service (NTIS)

This report entails the work performed on modeling atom-diatom scattering processes utilizing the Impulse Approach (IA). Results of the model, obtained with a computer code, have proven to be in remarkable agreement with laboratory measurements for severa...

J. M. Sindoni

1992-01-01

66

Alkali-Metal Atoms as Spin Labels on Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

We have recently achieved electron spin resonance (ESR) of single alkali-metal atoms isolated on helium (He) nanodroplets A two-laser pump/probe setup for optically detected magnetic resonance is applied, which is based on magnetic circular dichroism to selectively address spin states. The influence of the helium droplet on the alkali-metal valence-electron wave function is directly noticeable as a shift of the ESR transitions with respect to that of free atoms. This perturbation depends on the size of the droplets and can be modeled with an increase of the hyperfine constant, that is an increase of the Fermi contact interaction. After careful characterization of the Rb--He-droplet system the method is being developed into a more universal diagnostic tool to study spin dynamics. ESR silent species located inside the droplet can be investigated by utilizing the surface Rb atom as spin label, and the droplet size is a convenient handle to control the distance between the two. In case of species with a nuclear spin (e.g., 129Xe) spin exchange between the optically pumped Rb atom and the nuclear spin can be studied. We are also extending our method to study magnetically active materials of technological importance, such as Cr, Cu, and small clusters thereof, and we strive to present the first results at the meeting. M. Koch, G. Auböck, C. Callegari, and W.E. Ernst, Phys. Rev. Lett. 103, 035302 (2009) M. Koch, J. Lanzersdorfer, C. Callegari, J.S. Muenter, and W.E. Ernst, J. Phys. Chem. A 113, 13347 (2009) M. Koch, C. Callegari, and W.E. Ernst, Mol. Phys., in press.

Koch, Markus; Ratschek, Martin; Callegari, Carlo; Ernst, Wolfgang E.

2010-06-01

67

Neutral Atom Lithography Using a Bright Metastable Helium Beam  

NASA Astrophysics Data System (ADS)

We have performed neutral atom lithography using a bright beam of metastable 2^3S1 Helium (He*) that is collimated with the bichromatic force, followed by three optical molasses velocity compression stages. Because bichromatic collimation makes such an intense He* beam, our exposure time is measured in minutes instead of hours. We have exploited the focusing and channeling of the He* beam into lines by the dipole force the atoms experience while traversing a standing wave of ? = 1083 nm light tuned 500 MHz below the 2^3S1-> 2^3P2 transition. Focused He* atoms damage the molecules of a self assembled monolayer (SAM) of nonanethiol by depositing their 20 eV of internal energy on its surface. The undisturbed SAM then protects a 200 å,ayer of gold that has been evaporated onto a prepared Silicon wafer from a wet chemical etch. Samples created with this method have an edge resolution of 63 nm that was observed using an atomic force microscope. The lines are separated by ?/2 and cover the entire exposed length of the substrate, about 3 mm. They are about 3 mm long, corresponding to about twice the beam waist of the laser standing wave. Thus there are ˜6 x10^3 lines of length ˜1500 ?. These results agree with our numerical simulations of the experiment.

Allred, Claire; Reeves, Jason; Corder, Chris; Metcalf, Harold

2009-05-01

68

Study of Injection of Helium into Supersonic Air Flow Using Rayleigh Scattering  

NASA Technical Reports Server (NTRS)

A study of the transverse injection of helium into a Mach 3 crossflow is presented. Filtered Rayleigh scattering is used to measure penetration and helium mole fraction in the mixing region. The method is based on planar molecular Rayleigh scattering using an injection-seeded, frequency-doubled ND:YAG pulsed laser and a cooled CCD camera. The scattered light is filtered with an iodine absorption cell to suppress stray laser light. Preliminary data are presented for helium mole fraction and penetration. Flow visualization images obtained with a shadowgraph and wall static pressure data in the vicinity of the injection are also presented.

Seaholtz, Richard G.; Buggele, Alvin E.

1997-01-01

69

Neutral Atom Lithography Using a Bright Metastable Helium Beam  

NASA Astrophysics Data System (ADS)

We have performed neutral atom lithography using a bright beam of metastable Helium (He*) that is collimated with the bichromatic force followed by two Doppler molasses velocity compression stages. We have previously demonstrated this lithography method using a metal grid to project its image on a self assembled monolayer (SAM) of nonanethiol. The open areas of the grid allow incident He* to damage the SAM molecules by depositing their 20 eV of internal energy on the surface. The undisturbed SAM regions then protect a gold coated Silicon wafer from a wet chemical etch. Samples created with this method have an edge resolution of 63 nm that was observed using an atomic force microscope. We have now achieved focusing of the He* beam into lines by the dipole force that the atoms experience while traversing a standing wave of ? = 1083 nm light tuned 500 MHz above the 2^3S1-->2^3P2 transition. The lines are separated by ?/2 and their length is comparable to the laser beam waist. Because bichromatic collimation makes such an intense He* beam, our exposure time can be as short as 10 minutes.

Shean, Claire; Reeves, Jason; Metcalf, Harold

2008-05-01

70

Analogies in the Microscopic Behavior of Superfluid and Classical Helium Studied by Neutron Scattering (Analogieen in het Microscopische Gedrag van Superfluid en Klassiek Helium).  

National Technical Information Service (NTIS)

Contents: Introduction; Overdamped Phonons in Fluid Helium at 4 K; Comment and Reply on 'Overdamped Phonons in Fluid Helium at 4 K'; Dynamics in He at 4 and 8 K from Inelastic Neutron Scattering; Structure of Helium at 4 and 8 K from Neutron Diffraction; ...

R. M. Crevecoeur

1996-01-01

71

Formation of Triplet Positron-helium Bound State by Stripping of Positronium Atoms in Collision with Ground State Helium  

NASA Technical Reports Server (NTRS)

Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.

Drachman, Richard J.

2006-01-01

72

Rearrangement and annihilation in antihydrogen-atom scattering  

SciTech Connect

I review some results for annihilation and rearrangement processes in low-energy antihydrogen-hydrogen and antihydrogen-helium scattering. For the strong nuclear force results using a {delta}-function potential are compared to a scattering length approach. It is found that the {delta}-function potential does not give correct annihilation cross sections in the case of antihydrogen-helium scattering. Problem associated with the use of the Born-Oppenheimer approximation for rearrangement calculations are reviewed.

Jonsell, Svante [Department of Physics, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom)

2008-08-08

73

The adsorption of H 2 and D 2 on Fe(110) . I. Helium scattering as a probe of adsorption  

NASA Astrophysics Data System (ADS)

Results of thermal energy atom scattering (TEAS) measurements of H 2 and D 2 adsorption-desorption kinetics on Fe(110) are presented in detail, with emphasis on the strengths and pitfalls inherent in this recently developed technique. It is shown that, for this system, adlayer coverage is directly related to the height of the specularly scattered peak from an incident helium atomic or deuterium molecular beam. The scattered peak height was used to monitor surface concentration as adsorption or desorption occurred, and at equilibrium. Measurements were carried out both at constant temperatures and during temperature programmed desorption. The cross sections for helium scattering from deuterium and hydrogen on Fe(110) were found to be 3.4 and 3.5 Å 2, respectively. The cross section for D 2 scattering from adsorbed deuterium on Fe(110) was measured as 11.0 Å 2. The initial sticking coefficient and the rate of adsorption were found to be independent of temperature for both H 2 and D 2. The desorption kinetics were found to be second order, with activation energies of 26.5 kcal/mol (D 2) and 25.0 kcal/mol (H 2). The isosteric heats of adsorption are 24.7 kcal/mol (D 2) and 24.2 kcal/mol (H 2).

Kurz, Edward A.; Hudson, John B.

74

Probing crystalline insulator surfaces with neutral helium atom scattering: A study of mixed potassium tantalate/niobate and thin films of potassium chloride and p-quaterphenyl on sodium chloride(001)  

NASA Astrophysics Data System (ADS)

Results from experiments using a thermal-energy beam of helium atoms as a probe in studying three crystalline insulator surfaces are presented. The primary focus is the simple ferroelectric perovskite, KTa1- xNbxO3 (or KTN when not specifying an Nb concentration) with x = 0.06, 0.10, 0.20, 0.30, and 0.52. Thin films of KCl and p-quaterphenyl grown onto NaCl(001) were also studied. Extending an earlier work on potassium tantalate (KTaO3), freshly cleaved (001) surfaces of niobium-doped potassium tantalate (KTN) were studied. While KTaO3 is an incipient ferroelectric undergoing no bulk phase changes, KTN, with Nb concentration greater than ˜1.5%, is a tunable ferroelectric, existing in several bulk phases depending on the temperature of the material. A metastable feature observed in KTN immediately after cleaving results in satellite peaks around the specular peak which decay over time. Also, small, broad half-order peaks were observed when the surface temperature was cycled between 50 K and 270 K for the first time. Surface hysteresis effects and responses to electric fields were also studied. Surface dispersion curves for the two high-symmetry directions are given for various Nb doping levels and substrate temperatures. This work compares the above phenomena to similar occurrences observed previously in KTaO3, and notes how the responses differ as a function of niobium doping. Also building on previous experience, the growth of KCl on NaCl was studied. Several recent works have focused on the physical interpretation of 3/4-order peaks observed during LEED investigations of this system. A HAS study of this system revealed, at best, a weak indication of several n/4-order peaks, but at film thicknesses well above those reported. In our first attempt to examine the surfaces of films of large organic molecules using HAS, p-quaterphenyl (p-4P) was deposited onto an NaCl surface held at 300K. Diffraction intensities from the NaCl were reduced but produced no other effects. However, cooling the surface to 50 K revealed many smaller diffraction peaks from the p-4P in addition to the larger NaCl peaks. The organic film peaks were isotropic, appearing as a two-dimensional diffraction powder pattern.

Trelenberg, Thomas Walter

75

Method and means for helium/hydrogen ratio measurement by alpha scattering  

NASA Technical Reports Server (NTRS)

An apparatus for determining helium to hydrogen ratios in a gaseous sample is presented. The sample is bombarded with alpha particles created by a self contained radioactive source and scattering products falling within a predetermined forward scattering angular range impact a detector assembly. Two detectors are mounted in tandem, the first completely blocking the second with respect to incident scattering products. Alpha particle/hydrogen or alpha particle/helium collisions are identified by whether scattering product impacts occur simultaneously in both detectors or only in the first detector. Relative magnitudes of the two pulses can be used to further discriminate against other effects such as noise and cosmic ray events.

Whitehead, A. B.; Tombrello, T. A. (inventors)

1980-01-01

76

Observing atom motion by electron-atom Compton scattering  

NASA Astrophysics Data System (ADS)

A very elemental method of observing the motion of the nucleus in molecules or solids is described. The observations for copper, graphite, and formvar films can be understood assuming that the electrons scatter from a moving target (vibrating atoms). The method is the complete electron analog for neutron Compton scattering. The nuclear motion causes a doppler shift in the energy of elastically scattered electrons. It is rather unusual among the methods of studying vibrations (e.g., molecular vibrations in individual molecules or phonons in solids) in that the information obtained is directly related to the momentum distribution of the probed atoms, rather than the energy difference between different vibrational states. The application of the semiclassical picture described here could fail to describe more detailed measurements. Gas-phase experiments may be more suitable for fully quantitative measurements. Indeed the experiment could be used to study the breakup of molecules after a well-defined perturbation.

Vos, Maarten

2002-01-01

77

Three-body recombination of cold helium atoms  

NASA Astrophysics Data System (ADS)

Three-body recombination is an important loss mechanism for Bose-Einstein condensates. Previous investigations( B.D. Esry, C.H. Greene, and J.P. Burke, Jr., Phys. Rev. Lett. 83), 1751 (1999); E. Nielsen and J.H. Macek, ibid. 83, 1566 (1999); P.F. Bedaque, E. Braaten, and H.-W. Hammer, ibid. 85, 908 (2000). have been limited to the ultracold limit where only the J=0 symmetry needed to be considered. This work(H. Suno, B.D. Esry, C.H. Greene, and J.P. Burke, Jr., accepted in Phys. Rev. A) extends these studies and treats not only J=0 but also J>0 states, so that the recombination rate K3 at finite collision energies can be calculated. In addition, the rates for the time-reversed process, namely collision-induced dissociation, are also obtained. In particular we study the case of ground-state helium atoms, including collisions of both ^4He and ^3He.

Suno, H.; Esry, B. D.; Greene Burke, Chris H., Jr.

2002-05-01

78

Measurement of a Long Electronic Spin Relaxation Time of Cesium Atoms in Superfluid Helium  

SciTech Connect

The longitudinal electronic spin relaxation time of Cs atoms optically polarized in superfluid helium (He II, 1.5 K) has been measured with special care to cope with a serious decrease in the number of Cs atoms in the observation region. This decrease, mainly caused by helium convection in introducing the atoms into He II by laser sputtering, was significantly reduced using a new atom implantation method. Combined with a careful correction for the number of atoms, we have determined the relaxation time to be 2.24(19) s or longer, roughly twice as long as that in solid He.

Furukawa, T.; Izumi, H.; Shimoda, T. [Department of Physics, Graduate School of Science, Osaka University, Osaka 560-0043 (Japan); Matsuo, Y.; Fukuyama, Y.; Kobayashi, T. [RIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-0198 (Japan); Hatakeyama, A. [Institute of Physics, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo 153-8902 (Japan)

2006-03-10

79

Resonant charge-exchange involving excited helium atoms and reactive transport of local thermodynamic equilibrium helium plasma  

SciTech Connect

The cross sections for charge-exchange and charge-transfer processes are evaluated for collisions of helium ions with parent-atoms in ground and excited states, with the principal quantum number n= 1-5, in the collision energy range from thermal up to 10 eV. Corresponding diffusion-type collision integrals are derived, and the role of 'abnormal' transport of electronically excited states on the reactive thermal conductivity of equilibrium helium plasma, at atmospheric pressure, estimated in the frame of a simplified approach.

Kosarim, A. V.; Smirnov, B. M. [Joint Institute for High Temperatures RAS, Moscow (Russian Federation); Laricchiuta, A. [CNR IMIP Bari, Bari (Italy); Capitelli, M. [CNR IMIP Bari, Bari (Italy); Department of Chemistry, University of Bari, Bari (Italy)

2012-06-15

80

Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms  

Microsoft Academic Search

Collisions of metastable antiprotonic helium with atoms of medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between antiprotonic and ordinary helium atoms. S-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F=L\\\\pm

G. Ya. Korenman; S. N. Yudin

2004-01-01

81

a Neutron Scattering Study of Liquid HELIUM-4.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. The results of high-resolution, high-accuracy, high-precision neutron inelastic measurements on liquid ^4He are presented. In the collective excitation region, the temperature -dependence of the sharp one-phonon peak is studied and seen to exhibit a qualitative change at T_ {lambda}. The Woods-Svensson hypothesis that the scattering separates naturally into parts proportional to the macroscopic normal and superfluid densities is tested and is found to be too simplistic to describe the detailed temperature dependence. A novel theoretical approach by Glyde and Griffin is evaluated. Their formulation establishes the microscopic connection between the Bose condensate and the phonon excitations in superfluid ^4He. The present parameterisation of their model describes the qualitative temperature dependence well. At high momentum transfer we obtain estimates of the momentum distribution above and below T _lambda, by extracting the Q-dependence of the fourth central moment of the scattering. The obtained n(p) at T > T_lambda is in very good agreement with theoretical calculations. Our low-temperature momentum distribution is more sharply peaked than at high temperature, but reflects the lack of higher -order terms in the short-time expansion used for extraction of the fourth moment. Estimates of the mean kinetic energy per atom are obtained and are slightly higher than previous experimental estimates, but in agreement with theoretical calculations. From this, we evaluate the magnitude of the condensate fraction, and find n_0(T=0) = 10.3 +/- 1.0%.

Andersen, Ken Holst

82

The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows  

NASA Technical Reports Server (NTRS)

Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.

Hoppe, J. C.; Honaker, W. C.

1979-01-01

83

MISSE Scattered Atomic Oxygen Characterization Experiment  

NASA Technical Reports Server (NTRS)

An experiment designed to measure the atomic oxygen (AO) erosion profile of scattered AO was exposed to Low Earth Orbital (LEO) AO for almost four years as part of the Materials International Space Station Experiment 1 and 2 (MISSE 1 and 2). The experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), Tray 1, attached to the exterior of the International Space Station (ISS) Quest Airlock. The experiment consisted of an aperture disk lid of Kapton H (DuPont) polyimide coated on the space exposed surface with a thin AO durable silicon dioxide film. The aperture lid had a small hole in its center to allow AO to enter into a chamber and impact a base disk of aluminum. The AO that scattered from the aluminum base could react with the under side of the aperture lid which was coated sporadically with microscopic sodium chloride particles. Scattered AO erosion can occur to materials within a spacecraft that are protected from direct AO attack but because of apertures in the spacecraft the AO can attack the interior materials after scattering. The erosion of the underside of the Kapton lid was sufficient to be able to use profilometry to measure the height of the buttes that remained after washing off the salt particles. The erosion pattern indicated that peak flux of scattered AO occurred at and angle of approximately 45 from the incoming normal incidence on the aluminum base unlike the erosion pattern predicted for scattering based on Monte Carlo computational predictions for AO scattering from Kapton H polyimide. The effective erosion yield for the scattered AO was found to be a factor of 0.214 of that for direct impingement on Kapton H polyimide.

Banks, Bruce A.; deGroh, Kim K.; Miller, Sharon K.

2006-01-01

84

Capture of a continuous beam of Li atoms in a cryogenic, supersonic helium jet.  

NASA Astrophysics Data System (ADS)

We are developing an intense cold atom source based on continuous post-nozzle injection of lithium atoms into a supersonic helium jet. The jet operates at a temperature of 5 Kelvin and with a continuous flux of approximately10^20 helium atoms per second, corresponding to a helium phase space density of order 10-3. By adiabatic expansion, the temperature in the moving frame will be reduced into the mK regime. Lithium atoms injected into the beam will become entrained in the helium flow, and subsequently extracted from it with a magnetic lens. Numerical simulations show that high efficiency of capture and extraction may simultaneously be realized. We anticipate that the extracted lithium beam will have a brightness that is substantially larger than what can be achieved with laser-cooling. We have completed studies of the capture of Li atoms by the helium jet with laser-induced fluorescence. The fluorescence images show clear evidence of entrainment of the Li atoms.

Borysow, Michael; Stoll, Brady; Heinzen, Daniel

2010-03-01

85

Atom-interferometric studies of light scattering  

SciTech Connect

We have used an echo-type atom interferometer that manipulates laser-cooled atoms in a single ground state to investigate the effect of light scattering from pulsed and continuous-wave light. The interferometer uses two off-resonant standing-wave pulses applied at times t=0 and t=T to diffract and recombine momentum states separated by 2({Dirac_h}/2{pi})k at t=2T. Matter wave interference is associated with the formation of a density grating with period {lambda}/2 in the vicinity of this echo time. The grating contrast is measured by recording the intensity of coherently backscattered light. The interferometer is perturbed by an additional pulse applied at t=2T-{delta}T or by continuous-wave background light. If the additional pulse is a standing wave, the momentum states interfering at t=2T are displaced and the grating contrast can be completely recovered due to constructive interference. In this case, the contrast shows a periodic modulation at the atomic recoil frequency as a function of {delta}T. In a recent work, it was shown that the atomic recoil frequency can be measured easily and precisely when using coherence functions to model the signal shape. This paper provides an alternative description of the signal shape through an analytical calculation of echo formation in the presence of an additional standing-wave pulse. Using this treatment, it is possible to model the effects of spontaneous emission and spatial profile of the laser beam on the signal shape. Additionally, the theory predicts scaling laws as a function of the pulse area and the number of additional standing-wave pulses. These scaling laws are investigated experimentally and can be exploited to improve precision measurements of the atomic recoil frequency. We also show that coherence functions can be used to make a direct measurement of the populations of momentum states associated with the ground state under conditions where the Doppler-broadened velocity distribution of the sample is much larger than the recoil velocity. These measurements are consistent with Monte Carlo wave-function simulations. If the additional pulse is a traveling wave, we find that the grating contrast measured as a function of {delta}T can be modeled by a quasiperiodic coherence function as in previous experiments that utilized atomic beams. In this work, we investigate the dependence of the photon scattering rate on the intensity and detuning of the traveling wave. We also study the effects of perturbing the interferometer with continuous-wave light and find that the dependence of the photon scattering rate on the intensity and detuning of the perturbing field is consistent with expectations.

Beattie, S.; Barrett, B.; Chan, I.; Mok, C.; Kumarakrishnan, A. [Department of Physics and Astronomy, York University, Toronto, Ontario, M3J 1P3 (Canada); Yavin, I. [Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States)

2009-07-15

86

Optical pumping in a flowing helium afterglow with additive metal impurity atoms  

Microsoft Academic Search

It is demonstrated that in a Penning collision of optically oriented metastable helium atoms with an impurity metal atom such as barium, both the longitudinal and transverse components of spin angular momentum are conserved. This results in a polarization of the ion which may be detected by optical emission in the case of excited ion levels or absorption for the

L. D. Schearer

1974-01-01

87

Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms  

Microsoft Academic Search

Collisions of metastable antiprotonic helium with atoms of a medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between and He atoms. S-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F =

G Ya Korenman; S. N. Yudin

2006-01-01

88

Interpretation of diffuse He-atom scattering from steps  

SciTech Connect

With the recent improvements in dynamic range of He-surface scattering experiments, the measurement of diffuse scattered intensity from surface defects: step edges or point defects: has become a frequently executable experiment. There remain, however, certain features in the experimental data that, to date, have not been fully explained. A calculational method applicable to the scattering from step edges is developed here, firstly to calculate the basic oscillatory form of the intensities, and then to look at the previously unexplained finer structure. In particular, the paper attempts to reproduce some experimental data; that is, helium-atom scattering from a randomly stepped Pt(111) crystal, in a fixed 90/sup 0/-angle geometry (see A. M. Lahee, J. R. Manson, J. P. Toennies, and Ch. Woell, Phys. Rev. Lett. 57, 471 (1986)). Even under a simple, hard-wall, eikonal approximation some of the previously unexplained features can be reproduced by the inclusion of a ''natural periodicity'' corrugation in the neighborhood of a step. This corrugation, with the periodicity of the lattice parameter, is allowed to decay away from the step. It is this decay length that is found to determine the characteristic width of the fine structure. The diffuse diffraction from a randomly stepped Pt(111), incidentally, now exhibits a certain degree of threefold symmetry. The enhanced corrugation amplitude in the neighborhood of a step is believed to be, of order at least, six times that observed on an unstepped Pt(111) surface. However, this enhancement factor is certainly very surface-orientation, and/or material, dependent.

Hinch, B.J.

1988-09-15

89

Scattering of electrons from neon atoms  

NASA Technical Reports Server (NTRS)

Scattering of electrons from neon atoms is investigated by the polarized-orbital method. The perturbed orbitals calculated with use of the Sternheimer approximation lead to the polarizability 2.803 a(0)-cube in fairly good agreement with the experimental value 2.66 a(0)-cube. Phase shifts for various partial waves are calculated in the exchange, exchange-adiabatic, and polarized-orbital approximations. They are compared with the previous results. The calculated elastic differential, total, and momentum-transfer cross sections are compared with the experimental results. The polarized-orbital approximation yields results which show general improvement over the exchange-adiabatic approximation.

Dasgupta, A.; Bhatia, A. K.

1984-01-01

90

Theory of Inelastic Scattering of Cold Neutrons from Liquid Helium  

Microsoft Academic Search

A measurement of the energy losses of monoenergetic neutrons scattered from liquid He II would permit a determination of the energy-versus-momentum relation for the elementary excitations (phonons and rotons) in the liquid. A major part of the scattering at a fixed angle arises from production or annihilation of a single excitation and appears as sharp lines in the energy spectrum.

Michael Cohen; Richard P. Feynman

1957-01-01

91

Spectroscopy of antiprotonic helium atoms and its contribution to the fundamental physical constants  

PubMed Central

Antiprotonic helium atom, a metastable neutral system consisting of an antiproton, an electron and a helium nucleus, was serendipitously discovered, and has been studied at CERN’s antiproton decelerator facility. Its transition frequencies have recently been measured to nine digits of precision by laser spectroscopy. By comparing these experimental results with three-body QED calculations, the antiproton-to-electron massratio was determined as 1836.152674(5). This result contributed to the CODATA recommended values of the fundamental physical constants.

Hayano, Ryugo S.

2010-01-01

92

Small-angle scattering of neutrons on normal and superfluid liquid helium  

NASA Astrophysics Data System (ADS)

Experiments on small-angle scattering of neutrons on liquid helium at temperatures of 1.0-5 K at the ISIS pulsed neutron source (England) are reported. Detailed measurements of the angular distribution of the scattered neutrons reveal a significant change in the temperature dependence of the second moment of the pairwise correlation function (the first derivative of the angular distribution for small scattering angles). At high temperatures the angular distribution of the scattered neutrons follows the classical description for small-angle scattering, but at temperatures below the ?-point, quantum mechanical behavior is observed (scattering of neutrons on quantum fluctuations). It is confirmed experimentally that over the entire temperature range the neutron scattering cross section at zero angle is determined by classical thermodynamic fluctuations in the density.

Tsipenyuk, Yu. M.; Kirichek, O.; Petrenko, O.

2013-09-01

93

Thermal desorption from ordered chemisorbed phases studied by helium scattering: Oxygen on Ag(110)  

NASA Astrophysics Data System (ADS)

We relate the helium specular beam intensity during adsorbate desorption (He desorption curve) to the instantaneous surface coverage. In this way the He desorption curve is shown to provide a picture of the desorption process which can be fruitfully compared to the one coming from thermal desorption mass spectra (TDS), obtained under strictly comparable experimental conditions. We tested the combination of thermal energy atom scattering (TEAS) and TDS in the case of the associative desorption from long range ordered O(2×1)-Ag(110) phase. Using the so-called overlap approach and assuming intense adsorbate-adsorbate (and vacancy-vacancy) attractions along Ag-O-Ag rows we obtain an instantaneous coverage which is in good agreement with TDS results. He desorption curves confirm the extreme sharpness of the desorption transition further indicating that the tails of the TDS peak bear small contributions from oxygen which did not belong to the O(2×1) phase. Opportunities and limitations inherent to the use of the He desorption curve (and its first derivative) as a marker of the temperature position and sharpness of the desorption transition are also addressed.

Canepa, M.; Terreni, S.; Narducci, E.; Mattera, L.

1999-01-01

94

Three-body recombination in cold helium-helium-alkali-metal-atom collisions  

SciTech Connect

Three-body recombination in helium-helium-alkali-metal collisions at cold temperatures is studied using the adiabatic hyperspherical representation. The rates for the three-body recombination processes {sup 4}He+{sup 4}He+X->{sup 4}He+{sup 4}HeX and {sup 4}He+{sup 4}He+X->{sup 4}He{sub 2}+X, with X={sup 7}Li, {sup 23}Na, {sup 39}K, {sup 85}Rb, and {sup 133}Cs, are calculated at nonzero collision energies by including not only zero total angular momentum, J=0, states but also J>0 states. The three-body recombination rates show a relatively weak dependence on the alkali-metal species, differing from each other only by about one order of magnitude, except for the {sup 4}He-{sup 4}He-{sup 23}Na system.

Suno, Hiroya; Esry, B. D. [The Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001 (Japan); Department of Physics, Kansas State University, Manhattan, Kansas 66506 (United States)

2009-12-15

95

Bounds for the scattering length of spin-polarized helium from high-accuracy electronic structure calculations.  

PubMed

We developed a series of correlation-consistent, polarized multiple zeta basis sets optimized specifically for the energy of the 2 3S state of helium atom. These basis sets were subsequently augmented with diffuse functions optimized for the van der Waals constants C6 through C14 which determine the asymptotic behavior of the second-order dispersion interaction between 2 3S helium atoms at large interatomic separation R. The resulting bases were applied to compute the Born-Oppenheimer (BO) potential for the lowest 5Sigmag+ state of the helium dimer. The coupled cluster and the full configuration-interaction techniques were employed to account for the electron correlation effects. The cardinal number extrapolation technique was used to obtain the complete-basis-set limit V(R) for the interaction potential and to find its lower VL(R) and upper VU(R) bounds. The resulting potentials were fitted to an analytical function containing accurate van der Waals constants C6 through C12 (including C11). We found that the complete-basis-set BO potential has a well depth De=1048.24+/-0.36 cm-1. The highest rotationless vibrational level is bound by D14=90.2+/-4.7 MHz, much stronger than the previous most accurate estimation of 15.2 MHz. The error bounds for De and D14 were obtained using the VL(R) and VU(R) potentials. The S-wave scattering length computed using the VL(R), V(R), and VU(R) potentials (assuming atomic masses) is aL=7.41 nm, a=7.54 nm, and aU=7.69 nm, respectively. We also computed the adiabatic, relativistic, and quantum electrodynamics (QED) corrections to the BO potential. When these corrections are taken into account the values of D14 and of a (both computed assuming nuclear masses) are 87.4+/-6.7 MHz and 7.64+/-0.20 nm; the error bounds reflect now also the uncertainty of the included adiabatic, relativistic, and QED corrections. The value of the scattering length resulting from our investigation lies outside the error bounds of all experimental determinations based on the properties of Bose-Einstein condensate of spin-polarized helium atoms. PMID:16223296

Przybytek, Micha?; Jeziorski, Bogumil

2005-10-01

96

Multipole polarizabilities and London dispersion forces between neon and helium atoms using double perturbation theory  

Microsoft Academic Search

Using an interchange theorem the polarizability of the neon atom at imaginary frequencies is calculated correct to first order in electron correlation. These results are then used to evaluate the long-range dispersion interactions between two neon atoms and between neon and helium atoms. For neon-neon interactions we find ?(5.308 ? R6) [1+(11.53 ? R2) + (189.5 ? R4)], while for

J. T. Broussard; Neil R. Kestner

1973-01-01

97

Small-angle Neutron Scattering Measurements of Liquid Helium Mixtures Confined in MCM-41  

NASA Astrophysics Data System (ADS)

Small-angle neutron scattering (SANS) was used to study the isotopic distribution of liquid helium mixtures confined in MCM- 41, a silica glass with a 2D hexagonal net of monodisperse cylindrical pores, as a function of filling and He^3 concentration. The ordered pore array of MCM-41 gives rise to Bragg reflections with intensities determined by both how the liquid fills the pores and how the isotopes are distributed within the pores. The modulation in peak intensity can be modeled by writing down a form factors for cylindrical objects with varying scattering length density. Comparison will be made with small-angle X-ray (SAXS) scattering measurements performed with synchrotron light on liquid helium mixtures confined in aerogel.

Kaiser, Helmut; Prisk, Timothy; Sokol, Paul; Steward, Ian; Pantalei, Claudia

2011-03-01

98

Evidence of scattering of bulk elementary excitations in isotopically pure liquid helium-II at low temperatures  

NASA Astrophysics Data System (ADS)

This short report is concerned with experimental investigations of bulk elementary excitations (BEEs) in the isotopically pure liquid helium-II at low temperatures below 100 mK. The evidence of BEEs? scattering is introduced in this work. Two identical Au-heaters were used to generate BEEs. The first pulsed heater generates BEE beams to record them. The second heater serves to generate BEE beams in order to scatter the first beams, operating delay time between pulses of the heaters. Experimental signals were recorded by several bolometers situated both above and below the liquid surface: scattered BEEs are travelling in the liquid from the pulsed heater to the bolometer; scattered BEEs, reaching the liquid surface, evaporate 4He-atoms detected by two bolometers positioned in a vacuum; scattered signals are reflected from the liquid surface back to the liquid and are detected by the other bolometer situated in the liquid. It is manifested that the experimental results showed a dramatic decrease in peaks of recorded signals. Also, signal losses for different heater powers were calculated.

Zakharenko, A. A.

2010-07-01

99

Hartree-Fock Interaction between a Helium Atom and Lithium-Metal: A Test for the Effective Medium Theory.  

National Technical Information Service (NTIS)

The interaction of a helium atom with 6 and 10 atom clusters of lithium has been calculated using the unrestricted Hartree-Fock method, Hartree-Fock method with correlation corrections, and the effective medium theory. Inside the cluster the helium embedd...

B. K. Rao P. Jena D. Schillady A. Hintermann M. Manninen

1985-01-01

100

BRIEF COMMUNICATIONS: Raman scattering of laser radiation to the far ultraviolet by excited states of helium and neon  

NASA Astrophysics Data System (ADS)

An investigation was made of spontaneous Raman scattering of YAG:Nd3+ laser radiation with the wavelength ?=1.064? by the metastable state 21S of the helium atom and the 2p53p[5/2]2 state of neon, both excited in a hollow-cathode discharge. This scattering produced radiation at the wavelengths of 56.9 and 62.8 nm, respectively. The spectral brightness of the source was 1.5×1015 and 1.0×1014 photons·sec-1·cm-2·sr-1·cm when the population of the He(21S) state was 1.4×1011cm-3 and the population of the Ne(2/p53p[5/2]2) state was 3.5×108cm-3. It was found that the Raman scattering by the atomic or ionic levels excited in a gas-discharge plasma made it possible to generate strong far ultraviolet radiation and could be used for plasma diagnostics.

Mailyan, A. É.; Nersisyan, G. Ts; Papanyan, V. O.

1986-05-01

101

Helium AtomSCF-LCAO Calculation of the (1s)2 Ground State of the  

NSDL National Science Digital Library

Using a double-zeta basis of Slater-type orbitals [STOs], this Java applet calculates the single determinant singlet ground state 1s2 wavefunction of the helium atom. The doubly occupied orbital is expanded in terms of two basis functions, 1s and 1s`.

102

On the Coupling between Electronic and Nuclear Motion and Van der Waals' Interaction between Helium Atoms  

Microsoft Academic Search

The analytical expression for the potential due to the coupling between the electronic and the nuclear motion for two normal helium atoms has been obtained for a wave function of the form of that of P. Rosen. This coupling interaction is a repulsive potential and is to be added to the usual ``valence'' and Van der Waals' potential obtained in

Ta-You Wu

1956-01-01

103

Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms  

Microsoft Academic Search

Collisions of metastable antiprotonic helium with atoms of a medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between (\\\\barp\\\\,He^+)_{nL} and He atoms. S-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F

G. Ya Korenman; S. N. Yudin

2006-01-01

104

Complex-Angular-Momentum Analysis of Atom-Atom Scattering Experiments  

Microsoft Academic Search

S-matrix elements typically encountered in atom-atom scattering may be phenomenologically parametrized using meromorphic functions of complex angular momenta. The contribution to the scattering amplitude of each pole of the S matrix is of such a simple nature (effectively, decaying oscillations for parameters encountered in practice) as to greatly facilitate the deduction of the phase shifts from scattering data. Some of

E. A. Remler

1971-01-01

105

Efimov physics in bosonic atom-trimer scattering  

SciTech Connect

Bosonic atom-trimer scattering is studied in the unitary limit using momentum-space equations for four-particle transition operators. The impact of the Efimov effect on the atom-trimer scattering observables is explored, and a number of universal relations is established. Positions and widths of tetramer resonances are determined. The trimer relaxation rate constant is calculated.

Deltuva, A. [Centro de Fisica Nuclear da Universidade de Lisboa, P-1649-003 Lisboa (Portugal)

2010-10-15

106

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures  

Microsoft Academic Search

There has been a resurgence of interest in the properties of solid helium due to the recent discovery of non-classical rotational\\u000a inertia (NCRI) in solid 4He by Chan and coworkers below 200 mK which they have interpreted as a transition to a ‘supersolid’ phase. We have carried\\u000a out a series of elastic and inelastic neutron scattering measurements on single crystals

Elizabeth Blackburn; John Goodkind; Sunil K. Sinha; Collin Broholm; John Copley; Ross Erwin

2008-01-01

107

Thomson Scattering Measurements of Helium Recombining Plasmas in the Divertor Simulator MAP-II  

NASA Astrophysics Data System (ADS)

Laser Thomson Scattering (LTS) measurements of Electron Ion Recombining (EIR) Helium plasma were performed in the divertor/edge simulator MAP-II. Upgrades of our LTS system, in the stray-light level and in the notch filter, allowed the measurement of electron temperatures as low as 0.1 eV and further investigation of EIR processes. Electron temperature and electron density profiles of EIR He recombining plasmas with different background neutral pressures have been measured.

Scotti, Filippo; Kado, Shinichiro; Okamoto, Atsushi; Shikama, Taiichi; Tanaka, Satoru

108

Adsorption of H/sub 2/ and D/sub 2/ on Fe(110). 1. Helium scattering as a probe of adsorption. Interim report  

SciTech Connect

Results of thermal-energy atom scattering (TEAS) measurements of hydrogen and deuterium adsorption-desorption kinetics on iron (110) are presented in detail, with emphasis on the strength and pitfalls inherent in this recently developed technique. It is shown that, for this system, adlayer coverage is directly related to the height of the specularly scattered peak from an incident helium atomic or deuterium molecular beam. The scattered peak height was used to monitor surface concentration as adsorption or desorption occurred, and at equilibrium. Measurements were carried out both at constant temperatures and during temperature programmed desorption. The cross sections for helium scattering from deuterium and hydrogen on Iron (110) were found to be 3.4 A squared and 3.5 A squared, respectively. The cross section for D/sub 2/ scattering from adsorbed deuterium on Fe(110) was measured as 11.0 A squared. The initial sticking coefficient and the rate of adsorption were found to be independent of temperature for both H/sub 2/ and D/sub 2/. The desorption kinetics were found to be second order, with activation energies of 26.5 kcal/mole (D/sub 2/) and 25.0 kcal/mole (H/sub 2/). The isosteric heats of adsorption are 24.7 kcal/mole (D/sub 2/) and 24.2 kcal/mole (H/sub 2/).

Kurz, E.A.; Hudson, J.B.

1987-07-30

109

Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel.  

PubMed

Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters. PMID:20733871

Shirinzadeh, B; Hillard, M E; Balla, R J; Waitz, I A; Anders, J B; Exton, R J

1992-10-20

110

Stimulated Brillouin Scattering from Helium-Hydrogen Plasmas  

NASA Astrophysics Data System (ADS)

In order to reduce stimulated Brillouin scattering (SBS) from NIF hohlraums, it has been proposed that a gas mixture of He/H be used. It is predicted that SBS can be controlled by varying the relative concentrations of H and He. We will present results from experiments performed at the Janus Laser Facility. We have used a two beam configuration to investigate the SBS from a He/H gas jet. A 1-? interaction beam was used to drive SBS in the plasma. This beam was focused to ˜ 80 microns with a maximum intensity of 2 × 10^15 W-cm-2 in 1-ns. We measured up to 10% SBS backscatter for pure He plasmas. A dramatic reduction in SBS backscatter (down to 2%) was observed when adding a small fraction of H (<10%) to a He plasma. Comparison with linear theory predictions will be shown. This Work was performed under the auspices of the U.S. Dept. of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

Froula, Dustin; Divol, Laurent; Price, Dwight; Gregori, Gianluca; Williams, Ed; Glenzer, Siegfried

2003-10-01

111

A helium film coated quasi-parabolic mirror to focus a beam of ultra-cold spin polarized atomic hydrogen  

Microsoft Academic Search

A 350 mK helium-4-coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an

V. G. Luppov; W. A. Kaufman; K. M. Hill; R. S. Raymond; A. D. Kirsch

1993-01-01

112

The spectral decomposition of the helium atom two-electron configuration in terms of hydrogenic orbitals  

NASA Astrophysics Data System (ADS)

The two-electron configuration in the helium atom is known to very high precision. Yet, we tend to refer to this configuration as a 1s?1s? singlet, where the designations refer to hydrogen orbitals. The high precision calculations utilize basis sets that are suited for high accuracy and ease of calculation, but do not really aid in our understanding of the electron configuration in terms of product states of hydrogen orbitals. Since undergraduate students are generally taught to think of helium, and indeed the rest of the periodic table, in terms of hydrogenic orbitals, we present in this paper a detailed spectral decomposition of the two-electron ground state for helium in terms of these basis states. The 1s?1s? singlet contributes less than 93% to the ground state configuration, with other contributions coming from both bound and continuum hydrogenic states.

Hutchinson, Joel; Baker, Marc; Marsiglio, Frank

2013-01-01

113

Convergence of Symmetry-Adapted Perturbation Theory for the Interaction between Helium Atoms and between a Hydrogen Molecule and a Helium Atom  

NASA Astrophysics Data System (ADS)

Convergence properties of perturbation expansions for the interaction energy are investigated by performing high-order calculations for the interaction between helium atoms and between a hydrogen molecule and a helium atom. It is shown that for small intermonomer distances the standard Rayleigh-Schrödinger (polarization) expansion converges to a Pauli forbidden state of the dimer. At large separations the exchange component of the interaction energy is not recovered in a practically low order and an apparent convergence to the Coulomb part of the interaction energy is observed. The symmetrized Rayleigh-Schrödinger (SRS) theory provides in low order very accurate values of both the Coulomb and the exchange parts of the interaction energy for the physical, Pauli allowed state. In the region of the van der Waals minimum already the second-order treatment reproduces the full configuration interaction (FCI) energy with an error of a few percent. In very high orders the convergence of the SRS theory becomes extremely slow and the series appears to converge to a nonphysical limit very close to the exact interaction energy. The symmetry-adaptation characteristic of the Hirschfelder-Silbey (HS) theory is shown to correct this pathological behavior although the improved convergence is observed only in very high orders, so from the practical point of view the HS theory is not superior to the SRS approach. The HS series converges to the FCI interaction energy only if the latter is corrected for the basis set superposition error using the full counterpoise correction of Boys and Bernardi.

Korona, Tatiana; Moszynski, Robert; Jeziorski, Bogumil

114

Rydberg States of rb and cs Atoms on Helium Nanodroplets: a Rydberg-Ritz Analysis  

NASA Astrophysics Data System (ADS)

Rydberg series of Rb and Cs atoms on the surface of helium nanodroplets (He_{N}) have been studied by resonance enhanced multi-photon ionization spectroscopy and laser induced fluorescence spectroscopy. The recorded excitation spectra are analyzed by using a Rydberg-Ritz approach. The dependence of the quantum defects on the principal quantum number within a Rydberg series gives insight into the interaction between the alkali atom's valence electron and the superfluid helium droplet. For higher excited states a screening of the valence electron from the alkali atom core by the helium droplet is observed. For lower states the strength of the screening effect decreases and the quantum defects are found to lie closer to free atom values. In addition, the large spin-orbit (SO) constant of the Cs-He_{N} nP(^{2}?) states allows a detailed study of the influence of the helium droplet on the SO splitting as function of the principal quantum number. Within the pseudo-diatomic picture the alkali-He_{N} system represents a diatomic molecule. The coupling of the Cs valence electrons spin and the orbital angular momentum with the intermolecular axis, which is defined by the connection between the droplet center and the alkali nucleus, depends on the strength of the atomic SO interaction. While the splitting of the 6^{2}P_{1/2}(^{2}?_{1/2}) and 6^{2}P_{3/2}(^{2}?_{3/2}) components has an atom-like character (Hund's case (c) coupling), the SO splitting of higher n states is lower than the atomic value (Hund's case (a) coupling). C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) F. Lackner, G. Krois, M. Theisen, M. Koch, and W.E. Ernst, Phys. Chem. Chem. Phys., 13, 18781-18788 (2011) F. Lackner, G. Krois, and W.E. Ernst, J. Phys. Chem. Lett., 3, 1404-1408 (2012)

Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.

2013-06-01

115

Creation evidence of the second non-dispersive Zakharenko wave by helium atomic beams in superfluid helium-II at low temperatures  

NASA Astrophysics Data System (ADS)

In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave (C_{ph}=C_{g} ? 0) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures ˜100 mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and negative roton signals together. It is natural that the negative roton creation by the beams requires the ^{4}He-atom energies ˜12 K, while the positive roton creation by the atomic beams requires energies ˜35 K. Therefore, successive increase in the heater power resulting in an increase in the ^{4}He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.

Zakharenko, A. A.

2007-10-01

116

"Fast Atom Diffraction" IBA in the regime of quantum scattering  

NASA Astrophysics Data System (ADS)

Recently, quantum effects were observed for the scattering of fast atoms from surfaces under a grazing angle of incidence. We discuss basic features of Fast Atom Diffraction (FAD) which adds a further powerful method to the established tools in ion beam analysis. Attractive features of FAD in studies on the structure of surfaces comprise negligible radiation damage, no charging effects, and an extreme sensitivity to the topmost layer of surface atoms. Scanning the quantum wavelength associated with the motion of a massive particle by the variation of its kinetic energy allows one to apply interferometric concepts to surface analysis based on the scattering of fast atoms.

Winter, H.

2014-08-01

117

Atomic Theory of the Two-Fluid Model of Liquid Helium  

Microsoft Academic Search

It is argued that the wave function representing an excitation in liquid helium should be nearly of the form if(ri)phi, where phi is the ground-state wave function, f(r) is some function of position, and the sum is taken over each atom i. In the variational principle this trial function minimizes the energy if f(r)=exp(ik.r), the energy value being E(k)=ℏ2k22mS(k), where

R. P. Feynman

1954-01-01

118

Photon scattering from atoms in an atom interferometer: Coherence lost and regained  

Microsoft Academic Search

We have scattered single photons from interfering de Broglie waves in an atom interferometer and observed contrast loss and revivals as the separation of the interfering paths at the point of scattering is increased. Additionally, we have demonstrated that the lost coherence can be recovered by observing only atoms that are correlated with photons emitted into a limited angular range.

Michael S. Chapman; Troy D. Hammond; Alan Lenef; Jörg Schmiedmayer; Richard A. Rubenstein; Edward Smith; David E. Pritchard

1995-01-01

119

Resonant x-ray Raman scattering from atoms and molecules  

SciTech Connect

Inelastic x-ray scattering and elastic x-ray scattering are fundamentally related processes. When the x-ray photon energy is near the ionization threshold for an inner shell, the inelastic channel is dominated by resonant x-ray Raman scattering. Studies of this emission not only illuminate the resonant scattering process in general, they also point to new opportunities for spectral studies of electronic structure using x-rays. Atoms in the form of a free gas provide an ideal target for testing the current theoretical understanding of resonant x-ray Raman scattering. In addition, x-ray scattering from molecular gases demonstrates the effect of bonding symmetry on the polarization and angular distribution of the scattered x-rays. Comparisons of experimental data with theory demonstrate both the successes and limitations of simple, single-electron interpretations of the scattering process.

Cowan, P.L.

1992-12-31

120

Resonant x-ray Raman scattering from atoms and molecules  

SciTech Connect

Inelastic x-ray scattering and elastic x-ray scattering are fundamentally related processes. When the x-ray photon energy is near the ionization threshold for an inner shell, the inelastic channel is dominated by resonant x-ray Raman scattering. Studies of this emission not only illuminate the resonant scattering process in general, they also point to new opportunities for spectral studies of electronic structure using x-rays. Atoms in the form of a free gas provide an ideal target for testing the current theoretical understanding of resonant x-ray Raman scattering. In addition, x-ray scattering from molecular gases demonstrates the effect of bonding symmetry on the polarization and angular distribution of the scattered x-rays. Comparisons of experimental data with theory demonstrate both the successes and limitations of simple, single-electron interpretations of the scattering process.

Cowan, P.L.

1992-01-01

121

Design and construction of a spectrometer facility and experiment for intermediate energy proton scattering on helium. [Wave functions, preliminary experimental techniques  

SciTech Connect

The goal of the research was to investigate proton scattering on nuclei at intermediate energies and in particular to investigate proton scattering on helium. A theoretical investigation of the helium nucleus and the nature of the intermediate energy interaction, design and optimization of an energy-loss spectrometer facility for proton-nucleus scattering, and the unique superfluid helium target and experimental design are discussed.

Rolfe, R.M.

1976-12-01

122

CASCADE CALCULATION OF EXOTIC HELIUM ATOMS -- s-orbit vs. p-orbit absorption rates  

NASA Astrophysics Data System (ADS)

We construct a new model for the Stark-mixing process of exotic helium atoms using the impact-parameter method, and compared it with a phenomenological one used so far (sliding transition model). It turns out that the sliding transition model is justified only for low-n states and largely overestimates the Stark-mixing transition rate at high-n states. As a result of the atomic-cascade calculation, the s-(p-)orbit absorption rates in our new model are considerably smaller (larger) than those in the phenomenological one, although both our new model and old one well reproduce the experimental x-ray yields.

Koike, T.; Akaishi, Y.

2000-09-01

123

Use of helium nanodroplets for assembly, transport, and surface deposition of large molecular and atomic clusters  

NASA Astrophysics Data System (ADS)

The utility of continuous beam of helium droplets for assembly, transport, and surface deposition of metal and molecular clusters is studied. Clusters of propyne having from about 10 to 104 molecules were obtained via sequential pickup of molecules by He droplets with average sizes in the range of 104-107 atoms. The maximum attainable flux of the propyne molecules carried by He droplets was found to be in the range of (5-15)×1015 molecules sr-1 s-1, being larger in larger droplets. The size of the clusters and the flux of the transported species are ultimately limited by the evaporative extinction of the entire helium droplet upon capture of particles. It is shown that the attenuation of the He droplet beam in the process of the cluster growth can be used in order to obtain the average size and the binding energy of the clusters. Furthermore, we used He droplets for assembling and surface deposition of gold and silver clusters having about 500 atoms. Typical deposition rate of metal atoms of about 3×1015 atoms sr-1 s-1 is comparable to or larger than obtained with other beam deposition techniques. We propose that doping of He droplets by Au and Ag atoms in two separate pickup chambers leads to formation of the bimetal clusters having core-shell structure.

Mozhayskiy, Vadim; Slipchenko, Mikhail N.; Adamchuk, Vera K.; Vilesov, Andrey F.

2007-09-01

124

Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass  

NASA Astrophysics Data System (ADS)

Metastable pionic helium (?He+) is a three-body atom composed of a helium nucleus, an electron occupying the 1s ground state, and a negatively charged pion ?- in a Rydberg state with principal and orbital angular momentum quantum numbers of n ˜?+1˜16. We calculate the spin-independent energies of the ?3He+ and ?4He+ isotopes in the region n =15-19. These include relativistic and quantum electrodynamics corrections of orders R??2 and R??3 in atomic units, where R? and ? denote the Rydberg and fine structure constants. The fine-structure splitting due to the coupling between the electron spin and the orbital angular momentum of the ?- and the radiative and Auger decay rates of the states are also calculated. Some states (n,?)=(16,15) and (17,16) retain nanosecond-scale lifetimes against ?- absorption into the helium nucleus. We propose the use of laser pulses to induce ?- transitions from these metastable states to states with large (˜1011 s-1) Auger rates. The ?He2+ ion that remains after Auger emission of the 1s electron undergoes Stark mixing with the s, p, and d states during collisions with the helium atoms in the experimental target. This leads to immediate nuclear absorption of the ?-. The resonance condition between the laser beam and the atom is thus revealed as a sharp spike in the rates of neutrons, protons, deuterons, and tritons that emerge. A resonance curve is obtained from which the ?He+ transition frequency can in principle be determined with a fractional precision of 10-8-10-6 provided the systematic uncertainties can be controlled. By comparing the measured ?He+ frequencies with the calculated values, the ?- mass may be determined with a similar precision. The ?He+ will be synthesized by allowing a high-intensity (>108 s-1) beam of ?-produced by a cyclotron to come to rest in a helium target. The precise time structure of the ?- beam is used to ensure a sufficient rate of coincidence between the resonant laser pulses and the ?He+ atoms.

Hori, Masaki; Sótér, Anna; Korobov, Vladimir I.

2014-04-01

125

NONLINEAR OPTICAL PHENOMENA: Interference of laser-induced resonances in the continuous structures of a helium atom  

NASA Astrophysics Data System (ADS)

Coherent effects in the interference of overlapping laser-induced resonances in helium atoms are considered. The simultaneous action of single-mode radiation of the 294-nm second harmonic of a cw dye laser and a 1064-nm Nd:YAG laser on helium atoms provides the overlap of two resonances induced by transitions from the 1s2s1S and 1s4s1S helium levels. The shape of the overlapping laser-induced resonances in the rotating-wave approximation is described by analytic expressions, which depend on the laser radiation intensities and the ratio of laser frequencies.

Magunov, A. I.; Strakhova, S. I.

2003-03-01

126

Thomson scattering in the average-atom approximation.  

PubMed

The average-atom model is applied to study Thomson scattering of x-rays from warm dense matter with emphasis on scattering by bound electrons. Parameters needed to evaluate the dynamic structure function (chemical potential, average ionic charge, free electron density, bound and continuum wave functions, and occupation numbers) are obtained from the average-atom model. The resulting analysis provides a relatively simple diagnostic for use in connection with x-ray scattering measurements. Applications are given to dense hydrogen, beryllium, aluminum, and titanium plasmas. In the case of titanium, bound states are predicted to modify the spectrum significantly. PMID:23031036

Johnson, W R; Nilsen, J; Cheng, K T

2012-09-01

127

Thomson scattering in the average-atom approximation  

NASA Astrophysics Data System (ADS)

The average-atom model is applied to study Thomson scattering of x-rays from warm dense matter with emphasis on scattering by bound electrons. Parameters needed to evaluate the dynamic structure function (chemical potential, average ionic charge, free electron density, bound and continuum wave functions, and occupation numbers) are obtained from the average-atom model. The resulting analysis provides a relatively simple diagnostic for use in connection with x-ray scattering measurements. Applications are given to dense hydrogen, beryllium, aluminum, and titanium plasmas. In the case of titanium, bound states are predicted to modify the spectrum significantly.

Johnson, W. R.; Nilsen, J.; Cheng, K. T.

2012-09-01

128

Dynamics of entanglement between two atomic samples with spontaneous scattering  

SciTech Connect

We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement and to compare it with the predictions obtained when spontaneous scattering is neglected. We provide numerical evidence that the interferometric scheme to entangle atomic samples is only marginally affected by the presence of spontaneous scattering and should thus be robust even in more realistic situations.

Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio [Dipartimento di Fisica 'E. R. Caianiello', Universita di Salerno, INFM-UdR di Salerno, INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via. S. Allende, I-84081 Baronissi, SA (Italy)

2004-07-01

129

Classical theory of atom-surface scattering: The rainbow effect  

NASA Astrophysics Data System (ADS)

The scattering of heavy atoms and molecules from surfaces is oftentimes dominated by classical mechanics. A large body of experiments have gathered data on the angular distributions of the scattered species, their energy loss distribution, sticking probability, dependence on surface temperature and more. For many years these phenomena have been considered theoretically in the framework of the “washboard model” in which the interaction of the incident particle with the surface is described in terms of hard wall potentials. Although this class of models has helped in elucidating some of the features it left open many questions such as: true potentials are clearly not hard wall potentials, it does not provide a realistic framework for phonon scattering, and it cannot explain the incident angle and incident energy dependence of rainbow scattering, nor can it provide a consistent theory for sticking. In recent years we have been developing a classical perturbation theory approach which has provided new insight into the dynamics of atom-surface scattering. The theory includes both surface corrugation as well as interaction with surface phonons in terms of harmonic baths which are linearly coupled to the system coordinates. This model has been successful in elucidating many new features of rainbow scattering in terms of frictions and bath fluctuations or noise. It has also given new insight into the origins of asymmetry in atomic scattering from surfaces. New phenomena deduced from the theory include friction induced rainbows, energy loss rainbows, a theory of super-rainbows, and more. In this review we present the classical theory of atom-surface scattering as well as extensions and implications for semiclassical scattering and the further development of a quantum theory of surface scattering. Special emphasis is given to the inversion of scattering data into information on the particle-surface interactions.

Miret-Artés, Salvador; Pollak, Eli

2012-07-01

130

Classical theory of atom-surface scattering: The rainbow effect  

NASA Astrophysics Data System (ADS)

The scattering of heavy atoms and molecules from surfaces is oftentimes dominated by classical mechanics. A large body of experiments have gathered data on the angular distributions of the scattered species, their energy loss distribution, sticking probability, dependence on surface temperature and more. For many years these phenomena have been considered theoretically in the framework of the "washboard model" in which the interaction of the incident particle with the surface is described in terms of hard wall potentials. Although this class of models has helped in elucidating some of the features it left open many questions such as: true potentials are clearly not hard wall potentials, it does not provide a realistic framework for phonon scattering, and it cannot explain the incident angle and incident energy dependence of rainbow scattering, nor can it provide a consistent theory for sticking. In recent years we have been developing a classical perturbation theory approach which has provided new insight into the dynamics of atom-surface scattering. The theory includes both surface corrugation as well as interaction with surface phonons in terms of harmonic baths which are linearly coupled to the system coordinates. This model has been successful in elucidating many new features of rainbow scattering in terms of frictions and bath fluctuations or noise. It has also given new insight into the origins of asymmetry in atomic scattering from surfaces. New phenomena deduced from the theory include friction induced rainbows, energy loss rainbows, a theory of super-rainbows, and more. In this review we present the classical theory of atom-surface scattering as well as extensions and implications for semiclassical scattering and the further development of a quantum theory of surface scattering. Special emphasis is given to the inversion of scattering data into information on the particle-surface interactions.

Miret-Artés, Salvador; Pollak, Eli

131

Electronically excited rubidium atom in helium clusters and films. II. Second excited state and absorption spectrum.  

PubMed

Following our work on the study of helium droplets and film doped with one electronically excited rubidium atom Rb(?) ((2)P) [M. Leino, A. Viel, and R. E. Zillich, J. Chem. Phys. 129, 184308 (2008)], we focus in this paper on the second excited state. We present theoretical studies of such droplets and films using quantum Monte Carlo approaches. Diffusion and path integral Monte Carlo algorithms combined with a diatomics-in-molecule scheme to model the nonpair additive potential energy surface are used to investigate the energetics and the structure of Rb(?)He(n) clusters. Helium films as a model for the limit of large clusters are also considered. As in our work on the first electronic excited state, our present calculations find stable Rb(?)He(n) clusters. The structures obtained are however different with a He-Rb(?)-He exciplex core to which more helium atoms are weakly attached, preferentially on one end of the core exciplex. The electronic absorption spectrum is also presented for increasing cluster sizes as well as for the film. PMID:21241108

Leino, Markku; Viel, Alexandra; Zillich, Robert E

2011-01-14

132

How do hydrogen atoms on surfaces affect the trajectories of heavier scattered atoms?  

NASA Astrophysics Data System (ADS)

The recently developed technique of scattering and recoiling imaging spectrometry (SARIS) is used to probe the effect of hydrogen atoms on the trajectories of 5 keV Ne+ scattering from a Pt(111) surface. Classical kinematic calculations and ion trajectory simulations, using the scattering and recoiling imaging code (SARIC), are carried out in order to probe the details of the interaction and the nature of the perturbation. It is demonstrated that adsorbed hydrogen atoms are capable of deflecting these low kilo-electron-volt Ne trajectories scattering from a Pt surface. These perturbations result in spatial shifts and broadenings of the anisotropic features of the SARIS images that are readily detectable. The scattered Ne atoms lose 0-18% of their initial kinetic energy as a result of the perturbation by the H atoms. The physics of the perturbation on the trajectories can be understood from straightforward classical kinematic calculations and SARIC ion trajectory simulations.

Lui, K. M.; Bolotin, I.; Kutana, A.; Bykov, V.; Lau, W. M.; Rabalais, J. W.

1999-12-01

133

Charge Scattering and Mobility in Atomically Thin Semiconductors  

NASA Astrophysics Data System (ADS)

The electron transport properties of atomically thin semiconductors such as MoS2 have attracted significant recent scrutiny and controversy. In this work, the scattering mechanisms responsible for limiting the mobility of single-layer semiconductors are evaluated. The roles of individual scattering rates are tracked as the two-dimensional electron gas density is varied over orders of magnitude at various temperatures. From a comparative study of the individual scattering mechanisms, we conclude that all current reported values of mobilities in atomically thin transition-metal dichalcogenide semiconductors are limited by ionized impurity scattering. When the charged impurity densities are reduced, remote optical phonon scattering will determine the ceiling of the highest mobilities attainable in these ultrathin materials at room temperature. The intrinsic mobilities will be accessible only in clean suspended layers, as is also the case for graphene. Based on the study, we identify the best choices for surrounding dielectrics that will help attain the highest mobilities.

Ma, Nan; Jena, Debdeep

2014-01-01

134

Scattering processes in atomic physics, nuclear physics, and cosmology  

NASA Astrophysics Data System (ADS)

The universal way to probe a physical system is to scatter a particle or radiation off the system. The results of the scattering are governed by the interaction Hamiltonian of the physical system and scattered probe. An object of the investigation can be a hydrogen atom immersed in a laser field, heavy nucleus exposed to a flux of neutrons, or space-time metric perturbed by the stress-energy tensor of neutrino flux in the early Universe. This universality of scattering process designates the Scattering Matrix, defined as the unitary matrix of the overlapping in and out collision states, as the central tool in theoretical physics. In this Thesis we present our results in atomic physics, nuclear physics, and cosmology. In these branches of theoretical physics the key element that unifies all of them is the scattering matrix. Additionally, within the scope of Thesis we present underlying ideas responsible for the unification of various physical systems. Within atomic physics problems, namely the axial anomaly contribution to parity nonconservation in atoms, and two-photon resonant transition in a hydrogen atom, it was the scattering matrix which led to the Landau-Yang theorem, playing the central role in these problems. In scattering problems of cosmology and quantum optics we developed and implemented mathematical tools that allowed us to get a new point of view on the subject. Finally, in nuclear physics we were able to take advantage of the target complexity in the process of neutron scattering which led to the formulation of a new resonance width distribution for an open quantum system.

Shchedrin, Gavriil

135

Reversal of photon-scattering errors in atomic qubits.  

PubMed

Spontaneous photon scattering by an atomic qubit is a notable example of environment-induced error and is a fundamental limit to the fidelity of quantum operations. In the scattering process, the qubit loses its distinctive and coherent character owing to its entanglement with the photon. Using a single trapped ion, we show that by utilizing the information carried by the photon, we are able to coherently reverse this process and correct for the scattering error. We further used quantum process tomography to characterize the photon-scattering error and its correction scheme and demonstrate a correction fidelity greater than 85% whenever a photon was measured. PMID:23005287

Akerman, N; Kotler, S; Glickman, Y; Ozeri, R

2012-09-01

136

Reversal of Photon-Scattering Errors in Atomic Qubits  

NASA Astrophysics Data System (ADS)

Spontaneous photon scattering by an atomic qubit is a notable example of environment-induced error and is a fundamental limit to the fidelity of quantum operations. In the scattering process, the qubit loses its distinctive and coherent character owing to its entanglement with the photon. Using a single trapped ion, we show that by utilizing the information carried by the photon, we are able to coherently reverse this process and correct for the scattering error. We further used quantum process tomography to characterize the photon-scattering error and its correction scheme and demonstrate a correction fidelity greater than 85% whenever a photon was measured.

Akerman, N.; Kotler, S.; Glickman, Y.; Ozeri, R.

2012-09-01

137

Time-resolved Thomson scattering on high-intensity laser-produced hot dense helium plasmas  

NASA Astrophysics Data System (ADS)

The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm and hot dense matter states, i.e. systems at solid-like densities and temperatures of one to several hundred eV. Such extreme conditions are relevant for high-energy density studies such as, e.g., in planetary physics and inertial confinement fusion. We consider here a liquid helium jet pumped with a high-intensity optical short-pulse laser that is subsequently probed with brilliant soft x-ray radiation. The optical short-pulse laser generates a strongly inhomogeneous helium plasma which is characterized with particle-in-cell simulations. We derive the respective Thomson scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We observe plasmon modes that are generated in the interior of the target and study their temporal evolution. Such pump-probe experiments are promising tools to measure the important plasma parameters density and temperature. The method described here can be applied to various pump-probe scenarios by combining optical lasers, soft x-rays and hard x-ray sources.

Sperling, P.; Liseykina, T.; Bauer, D.; Redmer, R.

2013-02-01

138

Ultrahigh-resolution study of protein atomic displacement parameters at cryotemperatures obtained with a helium cryostat.  

SciTech Connect

Two X-ray data sets for a complex of human aldose reductase (h-AR) with the inhibitor IDD 594 and the cofactor NADP(+) were collected from two different parts of the same crystal to a resolution of 0.81 A at 15 and 60 K using cold helium gas as cryogen. The contribution of temperature to the atomic B values was estimated by comparison of the independently refined models. It was found that although being slightly different for different kinds of atoms, the differences (deltaB) in the isotropic equivalents B of atomic displacement parameters (ADPs) were approximately constant (about 1.7 A(2)) for well ordered atoms as the temperature was increased from 15 to 60 K. The mean value of this difference varied according to the number of non-H atoms covalently bound to the parent atom. Atoms having a B value of higher than 8 A(2) at 15 K showed much larger deviations of deltaB from the average value, which might reflect partial occupancy of atomic sites. An analysis of the anisotropy of ADPs for individual atoms revealed an increase in the isotropy of ADPs with the increase of the temperature from 15 to 60 K. In a separate experiment, a 0.93 A resolution data set was collected from a different crystal of the same complex at 100 K using cold nitrogen as a cryogen. The effects of various errors on the atomic B values were estimated by comparison of the refined models and the temperature-dependent component was inferred. It was found that both decreasing the data redundancy and increasing the resolution cutoff led to an approximately constant increase in atomic B values for well ordered atoms.

Petrova, T.; Ginell, S.; Mitschler, A.; Hazemann, I.; Schneider, T.; Cousido, A.; Lunin, V.; Joachimiak, A.; Podjarny, A,; Biosciences Division; Russian Academy of Sciences; IGBMC; Inst. of Molecular Oncology

2006-01-01

139

Millimeter-Wave Spectra of Carbon Monoxide Solvated with Helium Atoms  

NASA Astrophysics Data System (ADS)

Millimeter-wave spectra of He_N-CO (^{12}C^{16}O, ^{13}C^{16}O, ^{12}C^{18}O, ^{13}C^{18}O) clusters with N up to 10, produced in a molecular expansion, were observed using intracavity OROTRON jet spectrometer in the frequency range of 110-150 GHz. The R(0) transitions were detected, which correspond to the known b-type (K = 1 - 0) R(0) lines of the binary system, He_1-CO. Further, the a-type (K = 0 - 0) rotational transitions of He_N-CO (N = 7, 8) in the frequency range of 20-40 GHz were measured combining OROTRON spectrometer with a double resonance technique. The isotopic shifts of the cluster transitions show remarkably smooth behavior with N from 1 to 6 and become rather scattering for N ? 7. The dependence of the rotational constant (cluster moment of inertia) and of the shift of the CO fundamental vibration on the number of He atoms in cluster were obtained for He_N-CO isotopologues from the analysis of their infrared spectra and very recent microwave data for the normal He_N-^{12}C^{16}O isotopologue. This study explores the microscopic evolution of superfluidity, which becomes apparent even in such small clusters as He_4-CO. The obtained results are compared with those from recent quantum Monte-Carlo calculations. and used to further interpret recent infrared measurements of CO in helium nanodroplets. J. Tang, A. R. W. McKellar, J. Chem. Phys. 119, 763 (2003) A. R. W. McKellar, J. Chem. Phys. 121, 6868 (2004) A. R. W. McKellar, J. Chem. Phys. 125, 164328 (2006). L. A. Surin, A. V. Potapov, B. S. Dumesh, S. Schlemmer, Y. Xu, P. L. Raston, and W. Jäger, Phys. Rev. Lett. 101, 233401 (2008) T. Škrbi?, S. Moroni, and S. Baroni, J. Phys. Chem. A 111, 7640 (2007). K. von Haeften, S. Rudolph, I. Simanovski, M. Havenith, R. E. Zillich, and K. B. Whaley, Phys. Rev. B 73, 054502 (2006).

Surin, L. A.; Giesen, T. F.; Schlemmer, S.; Potapov, A. V.; Dumesh, B. S.

2009-06-01

140

Diagnostic based modeling for determining absolute atomic oxygen densities in atmospheric pressure helium-oxygen plasmas  

SciTech Connect

Absolute atomic oxygen ground state densities in a radio-frequency driven atmospheric pressure plasma jet, operated in a helium-oxygen mixture, are determined using diagnostic based modeling. One-dimensional numerical simulations of the electron dynamics are combined with time integrated optical emission spectroscopy. The population dynamics of the upper O 3p {sup 3}P ({lambda}=844 nm) atomic oxygen state is governed by direct electron impact excitation, dissociative excitation, radiation losses, and collisional induced quenching. Absolute values for atomic oxygen densities are obtained through comparison with the upper Ar 2p{sub 1} ({lambda}=750.4 nm) state. Results for spatial profiles and power variations are presented and show excellent quantitative agreement with independent two-photon laser-induced fluorescence measurements.

Niemi, K.; Reuter, S.; Graham, L. M.; Waskoenig, J.; Gans, T. [Centre of Plasma Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland (United Kingdom)

2009-10-12

141

Optical Pumping and Electron Spin Resonance of Single 87Rb Atoms on Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Our recent development of electron spin resonance (ESR) spectroscopy on superfluid helium nanodroplets (HeN) provides a sensitive tool to investigate interactions between a surface located alkali-metal atom and an ESR silent species inside the droplet. Highest sensitivity is expected for alkali-metal atoms with large hyperfine coupling. We present hyperfine resolved ESR spectra of single 87Rb (hyperfine constant a_HFS = 3417 MHz) atoms isolated on HeN. In accordance with our previous work on 85Rb (AHFS= 1012 MHz) we find a droplet size dependent increase of AHFS between 400 and 450 ppm, due to the electronic perturbation by the helium environment. The process of optical pumping and of optical detection on HeN is investigated in detail in order to optimize the ESR signal. A simple model for optical pumping on HeN is presented, which agrees well with the experimental results. M. Koch, G. Auböck, C. Callegari, and W.E. Ernst, Phys. Rev. Lett. 103, 035302 (2009) A. Volk, J. Poms, M. Koch, and W.E. Ernst, J. Phys. Chem. A, in press

Koch, Markus; Poms, Johannes; Volk, Alexander; Ernst, Wolfgang E.

2011-06-01

142

Two photon laser spectroscopy of antiprotonic helium atoms at CERN's AD  

NASA Astrophysics Data System (ADS)

The ASACUSA collaboration of CERN has carried out two-photon laser spectroscopy of antiprotonic helium atoms using counter-propagating ultraviolet laser beams. This excited some non-linear transitions of the antiproton at the wavelengths ? = 139.8-197.0 nm, in a way that reduced the thermal Doppler broadening of the observed resonances. The resulting narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3-5 parts in 109. By comparing these values with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these results.

Hori, M.

2014-06-01

143

Quasifree electron scattering on atoms in the inverse kinematic system  

Microsoft Academic Search

The measurement of elastic electron scattering is a sensitive tool to test ionic and atomic potentials. Because a dense ionic target is difficult to produce, we use inverse kinematics, i.e. we exchange the roles of projectile and target and transform the cross sections. The absolute singly and doubly differential cross sections for the projectile ionization of He0 (0.1 MeV\\/u) scattered

T. Jalowy; M. Kuzel; R. Wünsch; R. Neugebauer; D. Hofmann; L. Sarkadi; A. Báder; L. Víkor; G. Víkor; P. Focke; D. H. Jakubaßa-Amundsen; M. W. Lucas; G. Sigaud; K. O. Groeneveld

1997-01-01

144

Elastic scattering of electrons from Rb, Cs and Fr atoms  

NASA Astrophysics Data System (ADS)

Differential, integrated elastic, momentum-transfer and total cross sections as well as differential S, T and U spin parameters for scattering of electrons from rubidium, caesium and francium atoms in the incident energy range up to 300 eV are calculated using a relativistic Dirac equation. The projectile electron-target atom interaction is represented by both real and complex parameter-free optical potentials for obtaining the solution of a Dirac equation for scattered electrons. The Dirac-Fock wavefunctions have been used to represent the Rb, Cs and Fr target atoms. The results of differential cross sections and spin asymmetry parameter S for e-Rb and e-Cs have been compared with the available experimental and theoretical results. Detailed results are reported for the elastic scattering of electrons from the ground states of a francium atom for the first time in the wide range of incident electron energies. The results of electron-Fr elastic scattering show the similar features to those obtained in the case of e-Rb and e-Cs elastic scattering.

Gangwar, R. K.; Tripathi, A. N.; Sharma, L.; Srivastava, R.

2010-04-01

145

Formation of the muonic helium atom /alpha particle-muon-electron/ and observation of its Larmor precession  

NASA Technical Reports Server (NTRS)

Experiments are described in which it proved possible to form the muonic helium atom by stopping polarized negative muons in a helium gas with a 2% xenon admixture at a pressure of 14 atm. The observed Larmor precession amplitudes are plotted against the gyromagnetic ratio for both muons and antimuons stopped in He + 2% Xe. In addition, a non-zero residual polarization of 0.06 plus or minus 0.01 was measured for muons stopped in pure helium gas, which corresponds to a depolarization factor of 18 plus or minus 3.

Souder, P. A.; Casperson, D. E.; Crane, T. W.; Hughes, V. W.; Lu, D. C.; Yam, M. H.; Orth, H.; Reist, H. W.; Zu Putlitz, G.

1975-01-01

146

Electron elastic scattering off a semifilled-shell atom: The Mn atom  

NASA Astrophysics Data System (ADS)

The impact of both exchange interaction and electron correlation, as well as their combined impact, on electron elastic scattering off a semifilled-shell Mn(⋯3d54s2, 6S) atom are theoretically studied in the electron energy range of ?=0-25 eV. Corresponding elastic-scattering phase shifts ??(?) as well as partial ??(?) and total ?(?) cross sections are found to be subject to a strong correlation impact. The latter is shown to drastically differ for oppositely spin-polarized scattered electrons in some cases, thereby bringing significant differences in corresponding ??(?)s, ??(?)s, and ?(?)s between these electrons. This is proven to be an inherent feature of electron scattering off a semifilled-shell atom in general. Electron correlation is accounted for in the framework of the self-energy part ? of the Green function of a scattered electron concept. The latter is calculated both in the second-order perturbation theory in the Coulomb interelectron interaction as well as beyond it by solving the Dyson equation for ?. The significance of the “Dyson” correlation corrections in e-+Mn scattering is unraveled. They are shown to noticeably increase the inherent differences between elastic-scattering phase shifts and cross sections of spin-up (?) and spin-down (?) polarized electrons scattered off a spin-polarized Mn atom, in some cases. In particular, the existence of a narrow resonant maximum in ??(?) near ??8 eV but the absence of such in ??(?) in e-+Mn scattering is predicted.

Dolmatov, V. K.; Amusia, M. Ya.; Chernysheva, L. V.

2013-10-01

147

Hydrogen-Assisted Laser-Induced Resonant Transitions between Metastable States of Antiprotonic Helium Atoms  

SciTech Connect

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of H{sub 2} molecules. By selectively shortening the lifetimes of states with higher principal quantum number n as compared to those of lower n, this method for the first time provides access to all initially populated metastable states of {ital {bar p}}He{sup +} atoms. This was demonstrated by observing the transitions (n,l)=(38,l){r_arrow}(39,l+1), l=35,36,37 and (n,l)=(37,l){r_arrow}(38,l+1), l=34,35,36. {copyright} {ital 1997} {ital The American Physical Society}

Ketzer, B.; Hartmann, F.; von Egidy, T.; Maierl, C.; Pohl, R. [Physik-Department, Technische Universitaet Muenchen, D-85747 Garching (Germany)] [Physik-Department, Technische Universitaet Muenchen, D-85747 Garching (Germany); Eades, J.; Widmann, E.; Yamazaki, T. [CERN, CH-1211 Geneva 23 (Switzerland)] [CERN, CH-1211 Geneva 23 (Switzerland); Kumakura, M.; Morita, N. [Institute for Molecular Science, Myodaiji, Okazaki 444 (Japan)] [Institute for Molecular Science, Myodaiji, Okazaki 444 (Japan); Hayano, R.; Hori, M.; Ishikawa, T.; Torii, H. [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113 (Japan)] [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113 (Japan); Sugai, I. [Institute for Nuclear Study, University of Tokyo, 3-2-1 Midori-cho, Tanashi, Tokyo 188 (Japan)] [Institute for Nuclear Study, University of Tokyo, 3-2-1 Midori-cho, Tanashi, Tokyo 188 (Japan); Horvath, D. [Central Research Institute for Physics, Research Institute for Particle and Nuclear Physics, H-1525 Budapest (Hungary)] [Central Research Institute for Physics, Research Institute for Particle and Nuclear Physics, H-1525 Budapest (Hungary)

1997-03-01

148

Non-radiative inelastic processes in lithium-helium ion-atom collisions  

NASA Astrophysics Data System (ADS)

Aims: The aims are to estimate efficiencies of non-radiative inelastic processes in lithium-helium ion-atom collisions and to compare them to those for radiative processes. Methods: Non-radiative inelastic cross-sections and rate coefficients for different lithium-helium ion-atom collisions are estimated by means of the recently proposed branching probability current method, which is based on the accurate ab initio adiabatic Born-Oppenheimer potentials that have been recently calculated for the low-lying 1,3?+ and 1,3? states of the LiHe+ ion. Results: It is shown that at low temperatures the radiative depopulation in Li+ + He and Li + He+ collisions dominates over the non-radiative processes, while in Li+ + He(2s 3S) collisions the non-radiative processes dominate over the radiative association at temperatures above 3000 K, which can be expected to have some influence on depopulations of metastable He in high temperature astrophysical environments.

Belyaev, Andrey K.; Augustovi?ová, Lucie; Soldán, Pavel; Kraemer, Wolfgang P.

2014-05-01

149

Enhanced ion backscattering near 180/sup 0/ scattering angles in the two-atom scattering model. [Ion scattering from solids  

SciTech Connect

An analytical two-atom scattering model has been developed to treat the recent discovery of the enhancement near 180/sup 0/ of Rutherford backscattering yields from disordered solids. In contrast to conventional calculations of Rutherford backscattering that treat scattering from a single atom only (the backscattering atom), the present model includes the interaction of a second atom lying between the target surface and the backscattering atom. The projectile ion makes a glancing collision with this second atom both before and after it is backscattered. A weighted average is made over all possible positions of this second atom. The model predicts an enhancement effect whose physical origin arises from the tolerance of path for those ions whose ingoing and outgoing trajectories lie in the vicinity of the critical impact parameter. Results using Moliere scattering show how the yield enhancement depends on ion energy, backscattering depth, exit angle, scattering potential, atomic numbers of the projectile and target, and target density. In the model the critical impact parameter and critical angle play important roles. It is shown that these quantities depend on a single dimensionless parameter and formulas accurate to better than 1% are given for them.

Oen, O.S.

1982-08-01

150

Comparisons of sets of electron-neutral scattering cross sections and swarm parameters in noble gases: II. Helium and neon  

NASA Astrophysics Data System (ADS)

This paper is the second of a series of four reports, describing work carried in 2011 in the context of the Plasma Data Exchange Project with the Gaseous Electronics Conference, devoted to intercomparisons between different sets of electron-neutral scattering cross sections from ground-state noble gas atoms, in the energy range from thermal to about 1 keV. The present work compares cross section sets for helium and neon, determined independently, which are available on the open access LXCat website (www.lxcat.laplace.univ-tlse.fr/). The cross sections are used as input data in an electron Boltzmann solver or in Monte Carlo simulations, to calculate different swarm parameters (transport parameters and rate coefficients). The calculated quantities are compared with measurements to assess the quality of the cross sections in providing data for modelling low-temperature plasmas or analysing experiments. The paper includes several appendices prepared by co-authors to the work, presenting details on how the various cross section datasets were compiled or evaluated.

Alves, L. L.; Bartschat, K.; Biagi, S. F.; Bordage, M. C.; Pitchford, L. C.; Ferreira, C. M.; Hagelaar, G. J. M.; Morgan, W. L.; Pancheshnyi, S.; Phelps, A. V.; Puech, V.; Zatsarinny, O.

2013-08-01

151

Dynamics of entanglement between two atomic samples with spontaneous scattering  

Microsoft Academic Search

We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement

Antonio Di Lisi; Silvio De Siena; Fabrizio Illuminati

2004-01-01

152

Influence of thermal vibrations on ion surface scattering near 180° scattering angle in the two-atom scattering model  

NASA Astrophysics Data System (ADS)

Based on the two-atom scattering model, the ion surface scattering near 180° scattering angle is investigated for the analysis of a new ion beam technique, i.e., impact collision ion scattering spectroscopy (ICISS). The shadowing effect of elastic scattering and the ion trajectory focusing effect play important roles for large-angle backscattering at the solid surface. Numerical results show that these two effects are very sensitive to the thermal vibrations of surface atoms, especially to their anisotropy. The angle of incidence at the maximum intensity and the peak width (fwhm) of the backscattering intensity is an increasing function of uz/ ux, where ux and uz are the rms displacements parallel to and perpendicular to the surface, respectively. In the case of a TiC crystal, it was found that the ratio of uz/ ux is nearly 1.6.

Takeuchi, W.; Yamamura, Y.

1984-03-01

153

Emergence of a measurement basis in atom-photon scattering.  

PubMed

After measurement, a wave-function is postulated to collapse on a predetermined set of states--the measurement basis. Using quantum process tomography, we show how a measurement basis emerges in the evolution of the electronic spin of a single trapped atomic ion after spontaneous photon scattering and detection. This basis is determined by the excitation laser polarization and the direction along which the photon was detected. Quantum tomography of the combined spin-photon state reveals that although photon scattering entangles all superpositions of the measurement-basis states with the scattered photon polarization, the measurement-basis states themselves remain classically correlated with it. Our findings shed light on the process of quantum measurement in atom-photon interactions. PMID:23471403

Glickman, Yinnon; Kotler, Shlomi; Akerman, Nitzan; Ozeri, Roee

2013-03-01

154

Atomic Beam Scattering Methods to Study Overlayer Structures and H-Surface Interaction Relevant to Astrophysics  

NASA Astrophysics Data System (ADS)

In this thesis we present results of experimental methods for studying surface structures of ultra-thin films and describe a new apparatus to study the recombination of atomic hydrogen on well characterized low temperature surface using atomic and molecular beam methods. We have used atomic beam scattering (ABS) to characterize the growth of mercury and lead overlayers on Cu(001) surface. The structures of ordered phases have been identified using ABS and low-energy electron diffraction (LEED). A model to analyze diffraction data from these phases is presented. The new apparatus we are going to describe includes a high performance atomic hydrogen source using radio-frequency (RF) dissociation. The dissociation efficiency can be as high as 90% in the optimized pressure range. An atomic hydrogen beam line has been added to our ultra-high vacuum (UHV) scattering apparatus. We have also designed and constructed a low temperature sample manipulator for experiments at liquid helium temperatures. The manipulator has one degree of freedom of rotation and the capability of heating the sample to 700K and cooling down to 12K. The first sample studied was a single graphite surface. We have used a He beam to characterize the sample surface and to monitor deposition of H on the sample surface in real time. A series of "adsorption curves" have been obtained at different temperature and doses. We found that at temperatures below 16K, both H and H_2 have formed a partial layer on the surface. From adsorption curve, we deduce that the initial sticking coefficient for H is about 0.06 when surface at 16K. When the H beam is interrupted, the He specularly reflected beam recovers partially, indicating that hydrogen atoms desorb, while others remain on the surface. The residual coverage of H is estimated to be about 2% of a monolayer.

Lin, Jingsu

155

Electron Shell Ionization of Atoms with Classical, Relativistic Scattering  

NASA Astrophysics Data System (ADS)

We investigate forward scattering of ionization from neon, argon, and xenon in ultrahigh intensities of 2×1019W/cm2. Comparisons between the gases reveal the energy of the outgoing photoelectron determines its momentum, which can be scattered as far forward as 45° from the laser wave vector klaser for energies greater than 1 MeV. The shell structure in the atom manifests itself as modulations in the photoelectron yield and the width of the angular distributions. We arrive at an agreement with theory by using an independent electron model for the atom, a dipole approximation for the bound state interaction, and a relativistic, three-dimensional, classical radiation field including the laser magnetic field. The studies provide the atomic physics within plasmas, radiation, and particle acceleration in ultrastrong fields.

Ekanayake, N.; Luo, S.; Grugan, P. D.; Crosby, W. B.; Camilo, A. D.; McCowan, C. V.; Scalzi, R.; Tramontozzi, A.; Howard, L. E.; Wells, S. J.; Mancuso, C.; Stanev, T.; Decamp, M. F.; Walker, B. C.

2013-05-01

156

Towards Realization of an Atomic de Broglie Microscope: Helium Atom Focusing Using Fresnel Zone Plates  

Microsoft Academic Search

A neutral, ground-state, 4He atom beam has been focused using Fresnel zone plates. At only moderate demagnification \\\\(0.40×\\\\), a focused spot diameter of <=2.0 mum is achieved at a signal intensity of 500 counts\\/s. This is an improvement over previous work by a factor of 10 in resolution, 103 in signal intensity, and 108 in focused beam density, and allows

R. B. Doak; R. E. Grisenti; S. Rehbein; G. Schmahl; J. P. Toennies; Ch. Wöll

1999-01-01

157

Neutrino-helium ionizing collisions: Electromagnetic contribution  

NASA Astrophysics Data System (ADS)

In terrestrial experiments searching for neutrino magnetic moments one investigates the ionization channel in the neutrino-atom scattering. We present numerical calculations that disprove the recent theoretical claim about large enhancement of the electromagnetic-interaction contribution to the neutrino impact ionization of helium relative to the case of the neutrino scattering on free electrons.

Kouzakov, Konstantin A.; Rodina, Yulia A.; Studenikin, Alexander I.

2014-04-01

158

Retardation or Casimir Effects in a Rydberg Helium Atom and Other Atomic Systems.  

NASA Astrophysics Data System (ADS)

A retardation effect, an effect due to the finiteness of the speed of light, can manifest itself in the interaction between two polarizable systems as a change in the form of the long-range interaction potential. With the interaction viewed as mediated by virtual photons, retardation effects become important when the time required for a photon to travel back and forth between the two systems becomes larger than or of the order of the characteristic period of the motion of either system. The form of the potential under retardation is characterized in general by the dynamic electric dipole polarizabilities alpha_ {d}(omega) of each of the systems, where omega is the virtual photon frequency, the separation r of the systems, hbar, and c. The high-precision verification of a retardation effect on the potential V(r) between a pair of systems probably demands that the systems be microscopic and form a bound state. The ideal pair would seem to be a helium ionic core (an alpha particle and an electron in the 1 s state) interacting with an electron in a state with n and l not too small, possibly in a high Rydberg state. Making use of time-ordered Feynman diagrams, with the electrons treated nonrelativistically, an expression for V(r) valid for r greater than several a _0 is obtained. The approach can be interpreted as an extension of the physical arguement that for r > 137alpha_0 the retardation component of V(r) follows easily from considerations of the interactions between electromagnetic vacuum fluctuations and each member of the pair, with each member characterized solely by its frequency-dependent electric dipole polarizability, alpha_{d}(omega); the extension from r > 137 a_0 down to just several a _0 is achieved by including in the characterization of each member not only its alpha_ {d}(omega), but its frequency-dependent nonadiabatic dipole polarizability, beta( omega). Effects originating in the finite nuclear mass are discussed. Retardation effects for Rydberg systems with many-electron cores are also of interest and so a qualitative discussion of retardation effects is provided to help one guess, for a given system with l ~ n gg 1, whether the size of the retardation energy shift is such as to warrant consideration.

Babb, James Frederick

159

Time-resolved mapping of correlated electron emission from helium atom in an intense laser pulse  

NASA Astrophysics Data System (ADS)

We apply and analyze the concept of mapping ionization time on to the final momentum distribution to the correlated electron dynamics in the nonsequential double ionization of helium in a strong laser pulse (?=800 nm) and show how the mapping provides insight into the double ionization dynamics. To this end, we study, by means of numerical integration of the time-dependent Schrödinger equation of a fully correlated model atom, the temporal evolution of the center-of-mass momentum in a short laser pulse. Our results show that in the high intensity regime (I0=1.15×1015 W cm-2), the mapping is in good agreement with a classical model including binary and recoil rescattering mechanisms. In the medium intensity regime (I0=5×1014 W cm-2), we identify additional contributions from the recollision-induced excitation of the ion followed by subsequent field ionization (RESI).

Ruiz, C.; Becker, A.

2008-02-01

160

Absorption non-symmetric ion-atom processes in helium-rich white dwarf atmospheres  

NASA Astrophysics Data System (ADS)

In this work, the processes of absorption charge exchange and photoassociation in He+H+ collisions, together with the process of ion HeH+ photodissociation, are considered as factors influencing the opacities of the atmospheres of helium-rich white dwarfs in the far-UV and extreme ultraviolet (EUV) regions. It is shown that they should be taken into account even in the case of atmospheres of white dwarfs with H:He = 10-5. It is then established that in the case of white dwarfs with H:He ? 10-4, particularly when H:He ? 10-3, these processes have to be included ab initio in the corresponding models of their atmospheres, since in the far-UV and EUV regions they become dominant with respect to known symmetric ion-atom absorption processes.

Ignjatovi?, Lj. M.; Mihajlov, A. A.; Sre?kovi?, V. A.; Dimitrijevi?, M. S.

2014-04-01

161

Excitation of {sup 1}S and {sup 3}S Metastable Helium Atoms to Doubly Excited States  

SciTech Connect

We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed {sup 1,3}P{sup o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s {sup 3}S{sup e}) and singlet (from 1s2s {sup 1}S{sup e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.

Alagia, M. [CNR-ISMN Sezione Roma, Piazzale A. Moro 5, I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy); Coreno, M. [CNR-IMIP, Montelibretti, I-00016 Roma (Italy); Farrokhpour, H.; Omidyan, R.; Tabrizchi, M. [Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Franceschi, P. [Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Tunisia) (Italy); Mihelic, A.; Zitnik, M. [Jozef Stefan Institute, P.O. Box 3000, SI-1001 Ljubljana (Slovenia); Moise, A.; Prince, K. C.; Richter, R. [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza, Trieste (Italy); Soederstroem, J. [Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden); Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Stranges, S. [Dipartimento di Chimica, Universita'La Sapienza', I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy)

2009-04-17

162

Electron emission from Na/Fe(100) surfaces by deexcitation of spin-polarized helium metastable atoms  

NASA Astrophysics Data System (ADS)

A pulsed helium metastable atom beam was generated by the pulsed nozzle-skimmer discharge and a high degree of spin polarization of the helium beam was obtained using the optical pumping method. Spin polarization of the outermost surface electron was detected for clean and sodium covered Fe(100) films deposited on MgO(100) by measuring the secondary electrons ejected by the irradiation of the spin-polarized helium metastable atom beam. Secondary electrons correspond to the Fermi level for a clean iron surface and those corresponding to the Na 3s level for the sodium-covered surface show a positive asymmetry, which indicates the negative polarization of electrons at these levels. The negative polarization of the Na 3s electrons rapidly decreases with the thickness increasing of the Na layer up to 0.5 ML but remains almost constant at a higher coverage (3ML). .

Yamauchi, Yasushi; Kurahashi, Mitsunori; Suzuki, Taku

2001-06-01

163

Optically-Detected Magnetic Resonance of Alkali Atoms Isolated on Helium Nano-Droplets  

NASA Astrophysics Data System (ADS)

Sharp, hyperfine-resolved, ESR spectra of alkali atoms isolated on helium nanodroplets are measured by optically-detected magnetic resonance (ODMR). A net spin polarization is created inside a magnetic field (B=0.2 to 4.2 T) by a pump laser beam. Microwave radiation in a resonant cavity at 9.4 GHz causes a spin transition which is detected by a probe laser beam. For ultimate precision the spectrum of free atoms is concurrently measured and serves as a reference. The shift of the ESR lines on the droplet with respect to free atoms directly reflects the distortion of the valence-electron wavefunction due to the He nanodroplet. While the electron g-factor remains unchanged within experimental uncertainties (<5 ppm), the increase of the hyperfine constant (typically +400 ppm) is consistent with an increase of the Fermi contact interaction. We are able to follow this change as a function of droplet size attesting the sensitivity of the method for the measurement of chemical shifts. The observation of Rabi oscillations indicates a long decoherence time and proves our ability to perform coherent manipulation of the spin.

Koch, Markus; Callegari, Carlo; Ernst, Wolfgang E.

2009-06-01

164

Elastic positron scattering by radon and radium atoms  

NASA Astrophysics Data System (ADS)

Relativistic calculations of the differential, integral, momentum transfer cross-sections and spin polarization parameters of positron scattering by radon and radium atoms have been performed using an optical potential. The aim of such calculations is to represent the interaction between a positron and target atoms in the energy range 2.0-500.0 eV. The theoretical results are obtained from the relativistic approach based on solving the Dirac equation using the Hartree-Fock and Dirac-Fock wave functions to calculate cross-sections at all the energies measured.

Sharma Kapil, K.; Vats, R. P.

2012-04-01

165

Single- and double-ionization cross sections for angular scattering of fast protons by helium  

SciTech Connect

The angular scattering of H{sup +} by He has been investigated for single ionization at energies of 0.5, 1.0, and 3.0 MeV; and for double ionization at 1.0 MeV. The classical-trajectory Monte Carlo method has been used within one- and two-electron models to illustrate the collision dynamics. The angular differential single-ionization cross sections are in good agreement with experiment, and display the combined effects of proton scattering from the He nucleus and its electrons. The relative fraction of double ionization, as a function of scattering angle, shows a maximum at {similar to}0.9 mrad that is in agreement with the experiments of Giese and Horsdal (Phys. Rev. Lett. 60, 2018 (1988)). This maximum is found to be due to two uncorrelated scattering events between the H{sup +} and the He atom's two electrons in the double-ionization reaction from impact parameters different than that for the single-ionization reaction.

Olson, R.E. (Gesellschaft fur Schwerionenforschung Darmstadt m.b.H., D-6100 Darmstadt 11, Federal Republic of Germany (DE) Physics Department, University of Missouri-Rolla, Rolla, Missouri 65401); Ullrich, J.; Dorner, R.; Schmidt-Bocking, H. (Institut fur Kernphysik, Universitat Frankfurt, D-6000 Frankfurt am Main, Federal Republic of Germany)

1989-09-01

166

Cs atoms on helium nanodroplets and the immersion of Cs+ into the nanodroplet.  

PubMed

We report the non-desorption of cesium (Cs) atoms on the surface of helium nanodroplets (He(N)) in their 6(2)P(1/2) ((2)?(1/2)) state upon photo-excitation as well as the immersion of Cs(+) into the He(N) upon photo-ionization via the 6(2)P(1/2) ((2)?(1/2)) state. Cesium atoms on the surface of helium nanodroplets are excited with a laser to the 6(2)P states. We compare laser-induced fluorescence (LIF) spectra with a desorption-sensitive method (Langmuir-Taylor detection) for different excitation energies. Dispersed fluorescence spectra show a broadening of the emission spectrum only when Cs-He(N) is excited with photon energies close to the atomic D(1)-line, which implies an attractive character of the excited state system (Cs?-He(N)) potential energy curve. The experimental data are compared with a calculation of the potential energy curves of the Cs atom as a function of its distance R from the center of the He(N) in a pseudo-diatomic model. Calculated Franck-Condon factors for emission from the 6(2)P(1/2) ((2)?(1/2)) to the 6(2)S(1/2) ((2)?(1/2)) state help to explain the experimental data. The stability of the Cs?-He(N) system allows to form Cs(+) snowballs in the He(N), where we use the non-desorbing 6(2)P(1/2) ((2)?(1/2)) state as a springboard for ionization in a two-step ionization scheme. Subsequent immersion of positively charged Cs ions is observed in time-of-flight mass spectra, where masses up to several thousand amu were monitored. Only ionization via the 6(2)P(1/2) ((2)?(1/2)) state gives rise to a very high yield of immersed Cs(+) in contrast to an ionization scheme via the 6(2)P(3/2) ((2)?(3/2)) state. When resonant two-photon ionization is applied to cesium dimers on He droplets, Cs(2) (+)-He(N) aggregates are observed in time-of-flight mass spectra. PMID:21861569

Theisen, Moritz; Lackner, Florian; Ernst, Wolfgang E

2011-08-21

167

Photoionization of atomic ions and related electron scattering processes  

SciTech Connect

A selection of recent theoretical results revealing new phenomenology in the photoionization and electron elastic scattering properties of multicharged atomic ions. Particularly striking is the non-smooth behavior of cross sections along isoelectronic and isonuclear sequences of ions, indicating that, although ionic phenomena become simpler eventually, this does not happen monotonically or quickly. This has importance concerning the possibility of transferring our vast knowledge of neutrals to ionic species.

Manson, Steven T.; Turner, Clay S. [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Altun, Zikri [Department of Physics, Marmara University, Istanbul (Turkey); Chakraborty, Himadri; Dias, Eric; Deshmukh, Pranawa C. [Department of Physics, Indian Institute of Technology-Madras, Madras, India 600 036 (India)

1998-09-28

168

Inversion problem for ion-atom differential elastic scattering.  

NASA Technical Reports Server (NTRS)

The paper describes a practical application of Remler's (1971) method by which one constructs a set of phase shifts from high resolution measurements of the differential elastic scattering of protons by rare-gas atoms. These JWKB phase shifts are then formally inverted to determine the corresponding intermolecular potentials. The validity of the method is demonstrated by comparing an intermolecular potential obtained by direct inversion of experimental data with a fairly accurate calculation by Wolniewicz (1965).

Rich, W. G.; Bobbio, S. M.; Champion, R. L.; Doverspike, L. D.

1971-01-01

169

Excitation of helium in He+He and HeHe collisions: the influence of metastable helium atoms  

Microsoft Academic Search

The excitation of helium by 20-100 keV He+ and He beams has been investigated by the spectroscopic analysis of radiation emitted in the spectral range 3900-6000 AA during the spontaneous decay of the excited products of single collisions. Observations have been made at 54.5 deg with respect to the primary beam to permit a Doppler shift separation of target and

W. G. F. Blair; R. W. McCullough; F. R. Simpson; H. B. Gilbody

1973-01-01

170

Coherence effects in scattering order expansion of light by atomic clouds  

NASA Astrophysics Data System (ADS)

We interpret cooperative scattering by a collection of cold atoms as a multiple scattering process. Starting from microscopic equations describing the response of $N$ atoms to a probe light beam, we represent the total scattered field as an infinite series of multiple scattering events. As an application of the method, we obtain analytical expressions of the coherent intensity in the double scattering approximation for Gaussian density profiles. In particular, we quantify the contributions of coherent backward and forward scattering.

Rouabah, Mohamed-Taha; Samoylova, Marina; Bachelard, Romain; Courteille, Philippe W.; Kaiser, Robin; Piovella, Nicola

2014-05-01

171

Inelastic helium scattering from the Ag(001) and Ag(001)c(2 × 2)Cl surfaces  

NASA Astrophysics Data System (ADS)

Inelastic He atom scattering has been used to investigate the surface phonon spectra of the Ag(001) surface and the change in the vibrational spectra when an ordered adsorbate, c(2 × 2)Cl, is present. The lowest energy transversely polarized surface mode is resolved and found to lie above the lower edge of the bulk band for both Ag(001) and Ag(001)c(2 × 2)Cl. Higher energy ( >10 meV) adsorbate-substrate vibrations were not observed. Although these results are not comprehensive, they provide an opportunity to evaluate the application of this technique to the study of high energy surface vibrations. Some quantitative assessments are described.

Lambert, W. R.; Cardillo, M. J.; Trevor, P. L.; Doak, R. B.

1984-10-01

172

Electron-helium and electron-neon scattering cross sections at low electron energies using a photoelectron source  

NASA Technical Reports Server (NTRS)

Absolute electron-helium and electron-neon scattering cross sections have been measured at low electron energies using the powerful technique of photoelectron spectroscopy. The measurements have been carried out at 17 electron energies varying from 0.7 to 10 eV with an accuracy of + or - 2.7 percent. The results obtained in the present work have been compared with other recent measurement and calculations.

Kumar, Vijay; Subramanian, K. P.; Krishnakumar, E.

1987-01-01

173

Two-photon double ionization of the helium atom by ultrashort pulses  

SciTech Connect

Two-photon double ionization of the helium atom was the subject of early experiments at FLASH and will be the subject of future benchmark measurements of the associated electron angular and energy distributions. As the photon energy of a single femtosecond pulse is raised from the threshold for two-photon double ionization at 39.5 eV to beyond the sequential ionization threshold at 54.4 eV, the electron ejection dynamics change from the highly correlated motion associated with nonsequential absorption to the much less correlated sequential ionization process. The signatures of both processes have been predicted in accurate \\textit{ab initio} calculations of the joint angular and energy distributions of the electrons, and those predictions contain some surprises. The dominant terms that contribute to sequential ionization make their presence apparent several eV below that threshold. In two-color pump probe experiments with short pulses whose central frequencies require that the sequential ionization process necessarily dominates, a two-electron interference pattern emerges that depends on the pulse delay and the spin state of the atom.

Palacios, Alicia; Horner, Daniel A; Rescigno, Thomas N; McCurdy, C William

2010-05-14

174

Regge Oscillations in Electron-Atom Total Scattering Cross Sections?  

NASA Astrophysics Data System (ADS)

In quantum scattering, the presence of a sufficiently narrow resonance allows the collision partners to form a long-lived intermediate complex which rotates as it decays to preserve the total angular momentum. Here we consider a system trapped in such a resonance state and allow it to decay at zero scattering angle, which through the optical theorem can be related to the total cross section (TCS). If the complex has a large angular life, it will return to forward scattering %?=0^o many times. For the resonance to contribute to the TCS requires: (i) Several rotations of the complex (Regge trajectory stays close to real axis) and (ii) Coherent addition of forward scattering sub-amplitudes (real part of Regge pole is close to an integer). Our analysis is based on the recent complex angular momentum approach [1] used to explain low energy oscillations in proton-H collision. Specifically, we want to establish whether similar oscillations can also be observed in electron-atom scattering. To this end, we present a detailed analysis of Regge trajectories and their contributions to the TCS for the model Thomas-Fermi potential. J. H. Macek et al., Phys. Rev. Lett. 93, 183203 (2004).

Sokolovski, D.; Ovchinnikov, S. Yu.; Felfli, Z.; Macek, J. H.; Msezane, A. Z.

2006-05-01

175

X and Rb Atoms on Helium Nanodroplets: is the Van Der Waals Attraction Strong Enough to Form a Molecule?  

NASA Astrophysics Data System (ADS)

Chemical reactions in the cold environment of a helium nanodroplet currently attract high interest and can be spectroscopically observed with typical molecular beam techniques. In order to estimate the influence of surrounding helium on the van der Waals interaction between heliophilic and heliophobic dopants that could be investigated in our lab with ESR spectroscopy, we apply density-functional theory to simulate a double-dotation of He-clusters with Rb and Xe atoms. Simulations of a double-doped He_{N} droplet with N = 500 show that the alkali metal atom stays on the surface, whereas the Xe atom sits in the middle of the droplet. The van der Waals attraction between Rb and Xe is not strong enough to compensate the separation of the heliophilic Xe and the heliophobic Rb caused by the helium droplet: a potential barrier of 23.4 K has to be overcome, which is to be compared with the 0.4 K internal temperature of the droplet. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester (2011) M. Koch, C. Callegari, and W. E. Ernst, Mol. Phys. 108 (7), 1005-1011 (2010) J. Poms, A. W. Hauser, and W. E. Ernst, Phys. Chem. Chem. Phys. 14, 15158-15165 (2012)

Poms, Johannes; Hauser, Andreas W.; Ernst, Wolfgang E.

2013-06-01

176

Shifts in the ESR Spectra of Alkali-Metal Atoms (Li, Na, K, Rb) on Helium Nanodroplets  

PubMed Central

He-droplet-induced changes of the hyperfine structure constants of alkali-metal atoms are investigated by a combination of relativistically corrected ab initio methods with a simulation of the helium density distribution based on He density functional theory. Starting from an accurate description of the variation of the hyperfine structure constant in the M–He diatomic systems (M=Li, Na, K, Rb) as a function of the interatomic distance we simulate the shifts induced by droplets of up to 10 000 4He atoms. All theoretical predictions for the relative shifts in the isotropic hyperfine coupling constants of the alkali-metal atoms attached to helium droplets of different size are then tied to a single, experimentally derived parameter of Rb.

Hauser, Andreas W; Gruber, Thomas; Filatov, Michael; Ernst, Wolfgang E

2013-01-01

177

Observation of correlated X-ray scattering at atomic resolution  

PubMed Central

Tools to study disordered systems with local structural order, such as proteins in solution, remain limited. Such understanding is essential for e.g. rational drug design. Correlated X-ray scattering (CXS) has recently attracted new interest as a way to leverage next-generation light sources to study such disordered matter. The CXS experiment measures angular correlations of the intensity caused by the scattering of X-rays from an ensemble of identical particles, with disordered orientation and position. Averaging over 15 496 snapshot images obtained by exposing a sample of silver nanoparticles in solution to a micro-focused synchrotron radiation beam, we report on experimental efforts to obtain CXS signal from an ensemble in three dimensions. A correlation function was measured at wide angles corresponding to atomic resolution that matches theoretical predictions. These preliminary results suggest that other CXS experiments on disordered ensembles—such as proteins in solution—may be feasible in the future.

Mendez, Derek; Lane, Thomas J.; Sung, Jongmin; Sellberg, Jonas; Levard, Clement; Watkins, Herschel; Cohen, Aina E.; Soltis, Michael; Sutton, Shirley; Spudich, James; Pande, Vijay; Ratner, Daniel; Doniach, Sebastian

2014-01-01

178

Observation of correlated X-ray scattering at atomic resolution.  

PubMed

Tools to study disordered systems with local structural order, such as proteins in solution, remain limited. Such understanding is essential for e.g. rational drug design. Correlated X-ray scattering (CXS) has recently attracted new interest as a way to leverage next-generation light sources to study such disordered matter. The CXS experiment measures angular correlations of the intensity caused by the scattering of X-rays from an ensemble of identical particles, with disordered orientation and position. Averaging over 15 496 snapshot images obtained by exposing a sample of silver nanoparticles in solution to a micro-focused synchrotron radiation beam, we report on experimental efforts to obtain CXS signal from an ensemble in three dimensions. A correlation function was measured at wide angles corresponding to atomic resolution that matches theoretical predictions. These preliminary results suggest that other CXS experiments on disordered ensembles-such as proteins in solution-may be feasible in the future. PMID:24914148

Mendez, Derek; Lane, Thomas J; Sung, Jongmin; Sellberg, Jonas; Levard, Clément; Watkins, Herschel; Cohen, Aina E; Soltis, Michael; Sutton, Shirley; Spudich, James; Pande, Vijay; Ratner, Daniel; Doniach, Sebastian

2014-07-17

179

Excitation of the hyperfine transitions of atomic hydrogen, deuterium, and ionized helium 3 by Lyman-alpha radiation  

Microsoft Academic Search

The profile of Lyman-alpha radiation in an expanding gas cloud is calculated in detail in order to determine the color temperature of the radiation scattered by an H I atom within the cloud. Scattering of Lyalpha is likely to dominate in the excitation of the 21 cm transition of H I in astronomical gas clouds with very low densities. The

S. Deguchi; W. D. Watson

1985-01-01

180

Scattering of positrons and electrons by alkali atoms  

NASA Technical Reports Server (NTRS)

Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.

Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.

1990-01-01

181

Electroweak constraints from atomic parity violation and neutrino scattering  

SciTech Connect

Precision electroweak physics can provide fertile ground for uncovering new physics beyond the standard model (SM). One area in which new physics can appear is in so-called 'oblique corrections', i.e., next-to-leading-order expansions of bosonic propagators corresponding to vacuum polarization. One may parametrize their effects in terms of quantities S and T that discriminate between conservation and nonconservation of isospin. This provides a means of comparing the relative contributions of precision electroweak experiments to constraints on new physics. Given the prevalence of strongly T-sensitive experiments, there is an acute need for further constraints on S, such as provided by atomic parity-violating experiments on heavy atoms. We evaluate constraints on S arising from recently improved calculations in the Cs atom. We show that the top quark mass m{sub t} provides stringent constraints on S within the context of the SM. We also consider the potential contributions of next-generation neutrino scattering experiments to improved (S,T) constraints.

Hobbs, Timothy; Rosner, Jonathan L. [Department of Physics, Indiana University, Bloomington, Indiana 47405 (United States); Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)

2010-07-01

182

Electroweak constraints from atomic parity violation and neutrino scattering  

NASA Astrophysics Data System (ADS)

Precision electroweak physics can provide fertile ground for uncovering new physics beyond the standard model (SM). One area in which new physics can appear is in so-called “oblique corrections,” i.e., next-to-leading-order expansions of bosonic propagators corresponding to vacuum polarization. One may parametrize their effects in terms of quantities S and T that discriminate between conservation and nonconservation of isospin. This provides a means of comparing the relative contributions of precision electroweak experiments to constraints on new physics. Given the prevalence of strongly T-sensitive experiments, there is an acute need for further constraints on S, such as provided by atomic parity-violating experiments on heavy atoms. We evaluate constraints on S arising from recently improved calculations in the Cs atom. We show that the top quark mass mt provides stringent constraints on S within the context of the SM. We also consider the potential contributions of next-generation neutrino scattering experiments to improved (S,T) constraints.

Hobbs, Timothy; Rosner, Jonathan L.

2010-07-01

183

Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2 Laser Bombardment  

NASA Astrophysics Data System (ADS)

To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H--He and F--He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

Lie, Zener Sukra; Khumaeni, Ali; Kurihara, Kazuyoshi; Kurniawan, Koo Hendrik; Lee, Yong Inn; Fukumoto, Ken-ichi; Kagawa, Kiichiro; Niki, Hideaki

2011-12-01

184

He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth  

SciTech Connect

Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.

Not Available

1992-01-01

185

Born Series for Electron Hydrogen Molecule Scattering.  

National Technical Information Service (NTIS)

It is shown that one single relationship exists between the corresponding Born terms for the elastic and inelastic scatterings of electrons, including exchange, by hydrogen molecule and helium like atom. Such a relationship is not valid for hydrogenic ato...

S. P. Khare

1983-01-01

186

One-phonon transitions observed in the scattering of He atoms from a LiF/001/ surface.  

NASA Technical Reports Server (NTRS)

For the scattering of a nearly monoenergetic beam of thermal-energy He atoms from a cleaved (001)LiF crystal surface, speed distributions of the reflected atoms are measured at suitably spaced scattering angles within the plane of incidence. From the measurements, elastic and one-phonon inelastic scattering processes are identified. Elastically scattered atoms distribute themselves in a set of sharp diffraction peaks. One-phonon inelastically scattered atoms are dispersed about each diffraction peak. The most probable velocities of the inelastically scattered atoms exhibit a characteristic sawtooth variation with scattering angle which, to first approximation, corresponds to conservation of the component of atom momentum tangent to the surface.-

Fisher, S. S.; Bledsoe, J. R.

1972-01-01

187

Double photoionization of helium with synchrotron x-rays: Proceedings  

SciTech Connect

This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.

Not Available

1994-01-01

188

Optimization of polarized helium-3 neutron spin filters for neutron scattering  

NASA Astrophysics Data System (ADS)

Nuclear spin-polarized 3He gas has been widely used in neutron scattering experiments. Spin-exchange optical pumping (SEOP) is one of the primary methods to produce polarized 3He. In SEOP, 3He is polarized via spin exchange collisions with optically pumped rubidium (Rb) atoms. At Indiana University, we have developed a boat system and a compact system based on the SEOP method to produce hyperpolarized 3He. A nuclear magnetic resonance (NMR) system has been built to monitor the relative 3He polarization as well as to flip the polarization. In order to get an absolute measure of the 3He polarization, an electron paramagnetic resonance (EPR) system has also been constructed. The NMR and EPR combined offer a robust 3He polarimetry to our SEOP systems. To get better performance, a new SEOP method called Hybrid SEOP is applied, which uses a rubidium/potassium (K) mixture instead of a pure Rb vapor. We have successfully achieved up to 69% 3He polarization with this method on our compact system. One important application of polarized 3He is used as neutron spin filters. We provided a neutron polarizer imbedded with a NMR-based neutron spin flipper for the HB-2A powder diffractometer at Oak Ridge National Laboratory, which make the HB-2A the first powder diffractometer in US capable of performing polarized studies.

Jiang, Chenyang

189

Effective-range approximations for resonant scattering of cold atoms  

NASA Astrophysics Data System (ADS)

Studies of cold atom collisions and few-body interactions often require the energy dependence of the scattering phase shift, which is usually expressed in terms of an effective-range expansion. We use accurate coupled-channel calculations on 6Li, 39K, and 133Cs to explore the behavior of the effective range in the vicinity of both broad and narrow Feshbach resonances. We show that commonly used expressions for the effective range break down dramatically for narrow resonances and near the zero crossings of broad resonances. We present an alternative parametrization of the effective range that is accurate through both the pole and the zero crossing for both broad and narrow resonances. However, the effective-range expansion can still fail at quite low collision energies, particularly around narrow resonances. We demonstrate that an analytical form of an energy and magnetic-field-dependent phase shift, based on multichannel quantum defect theory, gives accurate results for the energy-dependent scattering length.

Blackley, Caroline L.; Julienne, Paul S.; Hutson, Jeremy M.

2014-04-01

190

Positron scattering from hydrogen atom embedded in dense quantum plasma  

SciTech Connect

Scattering of positrons from the ground state of hydrogen atoms embedded in dense quantum plasma has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in dense quantum plasma have been represented by exponential cosine-screened Coulomb potentials. Variationally determined hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s?1s and 2s?2s elastic collisions, 1s?2s excitation, positronium formation, elastic proton-positronium collisions, have been reported in the energy range 13.6-350 eV. Furthermore, a comparison has been made on the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which the plasma screening effect has been represented by the Debye model. Our results for the unscreened case are in fair agreement with some of the most accurate results available in the literature.

Bhattacharya, Arka [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India)] [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India); Kamali, M. Z. M. [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)] [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India) [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India); Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)] [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)

2013-08-15

191

Interaction of rare gas metastable atoms. [Differential and total cross sections, elastic scattering, ionization, potential scattering, phase shifts, rate constants  

SciTech Connect

The physical and chemical properties of metastable rare gas atoms are discussed and summarized. This is followed by a detailed examination of the various possible pathways whereby the metastable's excess electronic energy can be dissipated. The phenomenon of chemi-ionization is given special emphasis, and a theoretical treatment based on the use of complex (optical) potential is presented. This is followed by a discussion on the unique advantages offered by elastic differential cross section measurements in the apprehension of the fundamental forces governing the ionization process. The methodology generally adopted to extract information about the interaction potential for scattering data is also systematically outlined. Two widely studied chemi-ionization systems are then closely examined in the light of accurate differential cross section measurements obtained in this work. The first system is He(2/sup 3/S) + Ar for which one can obtain an interaction potential which is in good harmony with the experimental results of other investigators. The validity of using the first-order semiclassical approximation for the phase shifts calculation in the presence of significant opacities is also discussed. The second reaction studied is He*+D/sub 2/ for which measurements were made on both spin states of the metastable helium. A self-consistent interaction potential is obtained for the triplet system, and reasons are given for not being able to do likewise for the singlet system. The anomalous hump proposed by a number of laboratories is analyzed. Total elastic and ionization cross sections as well as rate constants are calculated for the triplet case. Good agreement with experimental data is found. Finally, the construction and operation of a high power repetitively pulsed nitrogen laser pumped dye laser system is described in great details. Details for the construction and operation of a flashlamp pumped dye laser are likewise given.

Wang, A.Z.F.

1977-11-01

192

Measurement of the Coherent Neutron Scattering Length of 3He by Reflection from a Quartz-Liquid-Helium Interface  

NASA Astrophysics Data System (ADS)

The real part of the bound-atom coherent neutron scattering length of 3He has been measured by comparing the reflectivities of quartz-liquid-3He and quartz-liquid-4He interfaces and has been found to have the value (6.1 +/- 0.6) × 10- 13 cm.

Kitchens, T. A.; Oversluizen, T.; Passell, L.; Schermer, R. I.

1974-04-01

193

Helium atom reflectivity study of physisorption and chemisorption on single crystal metal surfaces  

NASA Astrophysics Data System (ADS)

A new helium atomic beam reflectivity apparatus has been developed to measure adsorption and desorption rates for hydrocarbons and alkanethiols on Au(111) and to study the internal energy dependence of the chemisorption of methane on transition metal surfaces. Twenty-five hydrocarbons (alkanes, alkenes, and related cyclic molecules) were measured and found to be only capable of physisorption on Au(111) with an adsorption energy which is proportional to bulk properties of the molecule such as heat of vaporization or polarizability. Since polarizability is an additive property, an empirical additive model has been developed to predict the adsorption energy based on the composition of the molecule. In addition, the sticking coefficients of the linear hydrocarbons were measured as a function of surface temperature. As the surface temperature is increased and desorption becomes significant, the sticking coefficient decreases due to incomplete accommodation of the translational energy of the incident molecule. On a Au(111) surface, alkanethiols are capable of both physisorption and chemisorption. Although the physisorption energy of the 1-alkanethiols increases linearly as a function of chain length, the activation energy for desorption from the chemisorbed state is constant at 124 kJ/mol. As a result, at very long chain lengths (tetradecanethiol and above), the activation energy for desorption from the physisorbed state exceeds that for chemisorption. The rate of chemisorption of the thiols from their physisorbed state was also found to be a function of the chain-length of the molecule. While the energy of activation for chemisorption was found to be the same for all alkanethiols studied, the pre- exponential factor (attempt frequency) decreases with increasing alkanethiol chain length. With the development and installation of an external resonant cavity system, high fluxes of vibrationally excited methane could be generated for mode-specific adsorption experiments. Although the rate, of activated methane chemisorption on Pt(111) increases with increasing impinging translational energy, the rate appears to be independent of excitation of the 2? 3 asymmetric stretch vibration. Preliminary experiments for methane adsorption on Ni(111) also indicate that the vibrational energy of the 2? 3 mode is less effective than an equivalent amount of translational energy for the promotion of chemisorption.

Wetterer, Sean Michael

194

Neutralization of low energy helium ions scattered from Au adatoms on Si(111)-?3 × ?3-Au  

NASA Astrophysics Data System (ADS)

The neutralization of 5 keV He + ions scattered from Au adatoms on the Si(111)-?3 × ?3-Au surface was studied by impact-collision ion-scattering spectroscopy (ICISS). The He + ICISS data contained false shadowing features that were actually the result of local neutralization effects. The radially dependent ion-atom neutralization theory of Woodruff, when used in our simulations of the ion scattering results, was reasonably successful in describing the neutralization of the He + ions by the Au atoms. Good agreement for both the [112¯] and [1¯10] azimuths was obtained for a neutralization rate R = A exp(- ar), where A and a are 15.5 fs -1 and 1.94 Å -1 , respectively. An Auger neutralization model assuming a planar ion-solid interaction surface was also tested, yielding much poorer agreement.

Daley, Richard S.; Huang, Judy H.; Williams, R. Stanley

1988-08-01

195

Decoherence due to Multiple-Photon Scattering in an Atom Interferometer  

Microsoft Academic Search

A famous Feynman gedankenexperiment proposes using scattered light to determine through which of the slits in a Young's double slit interferometer a given interfering particle has passed---noting that, in the process, any observable interference pattern is lost. We have realized this experiment in a separated-beam atom interferometer where the scattered light reveals which path through the interferometer the atom has

David A. Kokorowski; Tony D. Roberts; Alexander D. Cronin; David E. Pritchard

2000-01-01

196

Coherent Atom Optics With Fast Metastable Beams: Metastable Helium Diffraction By 1D and 2D Magnetized Reflection Gratings  

SciTech Connect

1D and 2D reflection gratings (Permalloy stripes or dots deposited on silicon), immersed in an external homogeneous static magnetic field, are used to study 1D and 2D diffraction of fast metastable helium atoms He* (23S1). Both the grazing incidence used here and the repulsive potential (for sub-level m = -1) generated by the magnetisation reduce the quenching effect. This periodically structured potential is responsible for the diffraction in the incidence plane as well as for the diffraction in the perpendicular plane.

Grucker, J.; Baudon, J.; Karam, J.-C.; Perales, F.; Ducloy, M. [Laboratoire de Physique des Lasers, UMR-CNRS 7538, Universite Paris 13, 99, Avenue J.B. Clement, 93430-Villetaneuse (France); Bocvarski, V. [Institute of Physics, Pregrevica 118, 11080 - Belgrade-Zemun (Serbia and Montenegro)

2007-04-23

197

Infrared rubidium atomic resonant filters for low wavenumber scattering  

Microsoft Academic Search

This dissertation presents new approaches for low wavenumber scattering (LWS) based on infra-red rubidium filters, including blocking filters, dispersion filters, and passband filters. LWS is scattering of light with a small frequency change, such as rotational Raman scattering and Thomson scattering, which enables the measurement of species specific properties. The rubidium filters are used in conjunction with a tunable, pulsed

Zhen Tang

2001-01-01

198

Solutions of the Schrödinger equations for lithium and excited helium (2 1S) atoms with a correlation-function hyperspherical harmonic and generalized Laguerre-function expansion method  

Microsoft Academic Search

By introducing a simple spatially symmetric correlation function, we have modified a hyperspherical harmonic and generalized Laguerre function (HHGLF) into a correlation function HHGLF (CFHHGLF) expansion method and used it to solve directly the Schrödinger equations of ground-state lithium and excited helium (2 1S) atoms. In such a scheme, the wave function of the lithium atom is decomposed into the

Yixuan Wang; Conghao Deng; Dacheng Feng

1995-01-01

199

Antiproton annihilation in very low-energy antihydrogen scattering by simple atoms and molecules  

NASA Astrophysics Data System (ADS)

The aim of experimentalists currently working on the preparation of antihydrogen is to trap it at very low temperatures so that its properties can be studied. Of concern to experimentalists are processes that lead to a loss of antihydrogen through annihilation. The dominant annihilation process that leads to the loss of antihydrogen is the annihilation of the antiproton with nuclei through the strong interaction. A recent scattering calculation of antihydrogen with hydrogen at very low energy, using the complex strong interaction potential of Kohno and Weise, has found an average annihilation cross-section of 0.13Ea0-2, where E is the energy of relative motion. The antihydrogen-helium system is of particular interest to experimentalists as helium may be present as an impurity in the trap. Also there is interest in the possibility of using it to cool antihydrogen. We present a treatment of antihydrogen scattering with helium at very low temperatures. The annihilation cross-sections obtained are much larger than antihydrogen-hydrogen scattering cross-section, making it very unlikely that helium can be used to cool antihydrogen.

Armour, E. A. G.; Gregory, M. R.; Liu, Y.

2006-06-01

200

Structure of ultrathin oxide layers on metal surfaces from grazing scattering of fast atoms  

NASA Astrophysics Data System (ADS)

The structure of ultrathin oxide layers grown on metal substrates is investigated by grazing scattering of fast atoms from the film surface. We present three recent experimental techniques which allow us to study the structure of ordered oxide films on metal substrates in detail. (1) A new variant of a triangulation method with fast atoms based on the detection of emitted electrons, (2) rainbow scattering under axial surface channeling conditions, and (3) fast atom diffraction (FAD) for studies on the structure of oxide films. Our examples demonstrate the attractive features of grazing fast atom scattering as a powerful analytical tool in surface physics.

Winter, H.; Seifert, J.; Blauth, D.; Busch, M.; Schüller, A.; Wethekam, S.

2009-10-01

201

Elastic scattering of polarized protons on helium three at 800 MeV  

SciTech Connect

A set of spin dependent parameters and cross sections has been measured for p vector-/sup 3/He elastic scattering over the range of q 0.7-4.2 fm/sup -1/. The experiment was done at the Los Alamos Meson Physics Facility (LAMPF) using the High Resolution Spectrometer (HRS) with a polarized proton beam at 0.8 GeV. The focal plane polarimeter of the HRS was used to determine the spin direction of the scattered proton. Since /sup 3/He is one of the simplest nuclei, p vector-/sup 3/He scattering provides a very sensitive test of multiple scattering theories. The theoretical analysis was done by using two different wave functions for /sup 3/He as input to the multiple scattering theory. The theoretical calculations and experimental data together give useful information about nucleon-nucleon amplitudes and also help obtain a better understanding of the scattering process.

Azizi, A.

1985-01-01

202

Reactive scattering of electronically excited alkali atoms with molecules  

SciTech Connect

Representative families of excited alkali atom reactions have been studied using a crossed beam apparatus. For those alkali-molecule systems in which reactions are also known for ground state alkali and involve an early electron transfer step, no large differences are observed in the reactivity as Na is excited. More interesting are the reactions with hydrogen halides (HCl): it was found that adding electronic energy into Na changes the reaction mechanism. Early electron transfer is responsible of Na(5S, 4D) reactions, but not of Na(3P) reactions. Moreover, the NaCl product scattering is dominated by the HCl/sup -/ repulsion in Na(5S, 4D) reactions, and by the NaCl-H repulsion in the case of Na(3P). The reaction of Na with O/sub 2/ is of particular interest since it was found to be state specific. Only Na(4D) reacts, and the reaction requires restrictive constraints on the impact parameter and the reactants' relative orientation. The reaction with NO/sub 2/ is even more complex since Na(4D) leads to the formation of NaO by two different pathways. It must be mentioned however, that the identification of NaO as product in these reactions has yet to be confirmed.

Mestdagh, J.M.; Balko, B.A.; Covinsky, M.H.; Weiss, P.S.; Vernon, M.F.; Schmidt, H.; Lee, Y.T.

1987-06-01

203

Pressure shifts and electron scattering in atomic and molecular gases  

SciTech Connect

In this work, the authors focus on one aspect of Rydberg electron scattering, namely number density effects in molecular gases. The recent study of Rydberg states of CH{sub 3}I and C{sub 6}H{sub 6} perturbed by H{sub 2} is the first attempt to investigate number density effects of a molecular perturber on Rydberg electrons. Highly excited Rydberg states, because of their ``large orbital`` nature, are very sensitive to the surrounding medium. Photoabsorption or photoionization spectra of CH{sub 3}I have also been measured as a function of perturber pressure in 11 different binary gas mixtures consisting of CH{sub 3}I and each one of eleven different gaseous perturbers. Five of the perturbers were rare gases (He, Ne, Ar, Kr, Xe) and six were non-dipolar molecules (H{sub 2}, CH{sub 4}, N{sub 2}, C{sub 2}H{sub 6}, C{sub 3}H{sub 8}). The goal of this work is to underline similarities and differences between atomic and molecular perturbers. The authors first list some results of the molecular study.

Rupnik, K.; McGlynn, S.P. [Louisiana State Univ., Baton Rouge, LA (United States). Chemistry Dept.; Asaf, U. [Hebrew Univ., Jerusalem, IL (United States). Racah Inst. of Physics

1994-11-01

204

Cross section angular momentum dependence and the factorisation approximation for electron-atom scattering in the first Born approximation  

Microsoft Academic Search

The factorisation approximation in electron-atom scattering usually consists of eliminating the exchange contribution to the scattering by writing the scattering cross section as the product of the square of a direct scattering target form factor times the Mott cross section for electron-electron scattering. It is shown that a factorisation approximation is only possible for scattering angles less than 30' and

R. A. Bonham

1990-01-01

205

Exploring the helium (e, 2e) differential cross section at 64.6 eV with symmetric scattering angles but nonsymmetric energies  

Microsoft Academic Search

Helium (e, 2e) measurements are presented for an incident energy of 64.6 eV over a wide range of scattering angles from the coplanar to the perpendicular plane geometry. These measurements were taken for symmetric scattering angles and a range of detection energies from symmetric energy sharing where each electron has an excess energy of 20 eV to asymmetric sharing where

A. J. Murray; F. H. Read

1993-01-01

206

Dissipative light scattering by a trapped atom approaching electromagnetically-induced-transparency conditions  

SciTech Connect

We study the time dependence of the spectrum of inelastically scattered radiation from a trapped atom. The atom is illuminated by two lasers tuned to the electromagnetically induced transparency (EIT) of the free atom. For counterpropagating laser beams, rapid removal of vibrational energy is observed as the atom approaches near-EIT conditions. We show that the imbalance in the sidebands of the scattered radiation spectrum explains quantitatively the cooling of the center-of-mass motion of the trapped atom. We also examine parameters critical for EIT cooling in situations far from the Lamb-Dicke limit.

Roghani, Maryam; Breuer, Heinz-Peter; Helm, Hanspeter [Institute of Physics, Albert-Ludwigs University, Hermann-Herder Strasse 3, D-79104 Freiburg (Germany)

2010-03-15

207

Phonon scattering and thermal conductance properties in two coupled graphene nanoribbons modulated with bridge atoms  

NASA Astrophysics Data System (ADS)

The phonon scattering and thermal conductance properties have been studied in two coupled graphene nanoribbons connected by different bridge atoms by using density functional theory in combination with non-equilibrium Green's function approach. The results show that a wide range of thermal conductance tuning can be realized by changing the chemical bond strength and atom mass of the bridge atoms. It is found that the chemical bond strength (bridge atom mass) plays the main role in phonon scattering at low (high) temperature. A simple equation is presented to describe the relationship among the thermal conductance, bridge atom, and temperature.

Tan, Shi-Hua; Tang, Li-Ming; Chen, Ke-Qiu

2014-05-01

208

Double-to-single photoionization ratio of plasma-embedded helium atom at X-ray energies  

NASA Astrophysics Data System (ADS)

The double photoionization of helium by absorption of a high-frequency photon have gained considerable interest in theoretical [1-2] and experimental [3] studies during the last decades. In this work, we have investigated the asymptotic ratios of double-to-single photoionization of plasmas-embedded helium atom at very high photon but non-relativistic energies in the framework of the Debye model for weakly coupled plasmas [4]. The ratio of double-to-single photoionization for free atom is determined as 1.644%, in good agreement with the synchrotron measurements [3] and other theoretical predictions [1, 2]. The asymptotic ratio of double-to-single photoionization cross-sections for different screening parameters along with the single, the double, and the total photoionization asymptotic cross sections will be presented at the meeting. [1] R. C. Forrey, et al., Phys. Rev. A 51, 2112 (1995). [2] R. Krivec, M. Ya. Amusia, and V. B. Mandelzweig, Phys. Rev. A 62, 064701 (2000). [3] J. C. Levin et al., Phys. Rev. Lett. 67, 968 (1991); 76, 1220 (1996). [4] S. Kar and Y. K. Ho, Phys. Rev. A, to be published (2008).

Kar, Sabyasachi; Ho, Yew Kam

2008-05-01

209

Evolution from the coplanar to the perpendicular plane geometry of helium ([ital e],2[ital e]) differential cross sections symmetric in scattering angle and energy  

Microsoft Academic Search

Experimentally determined differential cross sections are presented for the ([ital e],2[ital e]) process in helium, in which the two outgoing electrons have the same energy and the same scattering angle with respect to the incident beam. At four incident energies from 20 to 50 eV above the ionization threshold the detection plane defined by the outgoing electrons was varied from

A. J. Murray; F. H. Read

1993-01-01

210

Evolution from the coplanar to the perpendicular plane geometry of helium (e,2e) differential cross sections symmetric in scattering angle and energy  

Microsoft Academic Search

Experimentally determined differential cross sections are presented for the (e,2e) process in helium, in which the two outgoing electrons have the same energy and the same scattering angle with respect to the incident beam. At four incident energies from 20 to 50 eV above the ionization threshold the detection plane defined by the outgoing electrons was varied from being coplanar

A. J. Murray; F. H. Read

1993-01-01

211

Relativistic distorted-wave calculation of electron scattering from alkali atoms  

Microsoft Academic Search

In electron scattering from alkali atom systems, the distortion of the target atom by the incident electron plays a important role and is represented by a polarization potential. The perturbative formulation (Temkin 1959) works well for systems with moderate polarizability such as the ground states of noble gases. A simple non-relativistic non-perturbative method was developed for the alkali atoms and

Weixing Ji

2002-01-01

212

Low-Energy Elastic Scattering of Electrons from Highly Polarizable Atoms  

Microsoft Academic Search

In elastic scattering of electrons from atomic systems it is necessary to include the effect of the polarization of the atomic target by the incident electron in order to obtain reliable results for cross sections and spin polarization parameters. For highly polarizable systems such as the alkalis or excited states of atoms, the perturbative polarized-orbital method [1] does not yield

Weixing Ji; R. P. McEachran; A. D. Stauffer

2000-01-01

213

Spectral theory of quantum memory and entanglement via Raman scattering of light by an atomic ensemble  

Microsoft Academic Search

We discuss theoretically quantum interface between light and a spin polarized ensemble of atoms with the spin =>1 based on an off-resonant Raman scattering. We present the spectral theory of the light atom interaction and show how particular spectral modes of quantum light couple to spatial modes of the extended atomic ensemble. We show how this interaction can be used

O. S. Mishina; D. V. Kupriyanov; J. H. Müller; E. S. Polzik

2007-01-01

214

Light Scattering Studies of Solids and Atomic Vapors.  

National Technical Information Service (NTIS)

The general technique of light scattering and luminescence was used to study the properties of a number of material systems. First, multi-phonon resonant Raman scattering up to four phonons in GaSe and one- and two-phonon resonant Raman scattering in the ...

T. C. Chiang

1978-01-01

215

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1991--April 30, 1994  

SciTech Connect

This progress report describes work carried out in the study of surface structure and dynamics of ionic insulators, the microscopic interactions controlling epitaxial growth and the formation of overlayers, and energy exchange in multiphonon surface scattering. The approach used is to employ high resolution helium atom scattering to study the geometry and structural features of the surfaces. Experiments have been carried out on the surface dynamics of RbCl and preliminary studies done on CoO and NiO. Epitaxial growth and overlayer dynamics experiments on the systems NaCl/NaCl(001), KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been performed. They have collaborated with two theoretical groups to explore models of overlayer dynamics with which to compare and to interpret their experimental results. They have carried out extensive experiments on the multiphonon scattering of helium atoms from NaCl and, particularly, LiF. Work has begun on self-assembling organic films on gold and silver surfaces (alkyl thiols/Au(111) and Ag(111)).

Safron, S.A.; Skofronick, J.G.

1994-04-01

216

Interacting double dark resonances in a hot atomic vapor of helium  

SciTech Connect

We experimentally and theoretically study two different tripod configurations using metastable helium ({sup 4}He*), with the probe field polarization perpendicular and parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances interact incoherently and merge together into a single electromagnetically induced transparency peak with increasing coupling power. In the second case, we observe destructive interference between the two dark resonances inducing an extra absorption peak at the line center.

Kumar, S.; Ghosh, R. [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India); Laupretre, T.; Bretenaker, F.; Goldfarb, F. [Laboratoire Aime Cotton, CNRS-Universite Paris Sud 11, F-91405 Orsay Cedex (France)

2011-08-15

217

Elastic scattering of polarized protons on helium three at 800 MeV  

SciTech Connect

A set of spin dependent parameters and cross sections has been measured for polarized p-/sup 3/He elastic scattering over the range of q .7 to 4.2 fm/sup -1/. The experiment was done at the Los Alamos Meson Physics Facility (LAMPF) using the High Resolution Spectrometer (HRS) with a polarized proton beam at .8 GeV. The focal plane polarimeter of the HRS was used to determine the spin direction of the scattered proton. Since /sup 3/He is one of the simplest nuclei, polarized p-/sup 3/He scattering provides a very sensitive test of multiple scattering theories. The theoretical analysis was done by using two different wave functions for /sup 3/He as input to the multiple scattering theory. The theoretical calculations and experimental data together will give us useful information about nucleon-nucleon amplitudes and also help us to obtain a better understanding of the scattering process. 68 refs., 55 figs., 9 tabs.

Azizi, A.

1985-07-01

218

Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics  

SciTech Connect

We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without optical access to a single site) and pair correlations between different sites. As a striking example we consider scattering from transversally illuminated atoms into an optical cavity mode. For the Mott-insulator state, similar to classical diffraction, the number of photons scattered into a cavity is zero due to destructive interference, while for the superfluid state it is nonzero and proportional to the number of atoms. Moreover, we demonstrate that light scattering into a standing-wave cavity has a nontrivial angle dependence, including the appearance of narrow features at angles, where classical diffraction predicts zero. The measurement procedure corresponds to the quantum nondemolition measurement of various atomic variables by observing light.

Mekhov, Igor B. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria); Faculty of Physics, St. Petersburg State University, St. Petersburg (Russian Federation); Maschler, Christoph; Ritsch, Helmut [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria)

2007-11-15

219

Cross section for diffuse scattering from random steps on Cu(100) determined by TEAS (thermal energy atom scattering)  

NASA Astrophysics Data System (ADS)

The cross section for diffuse scattering from random steps in Cu(100) has been measured by TEAS. The result is 13 Å per unit step length, meaning that this is the distance normal to the step edge over which the surface is not specularly reflective for scattering of thermal He atoms. This result was obtained in an experimentally direct way that basically consisted in growing Cu islands on top of the Cu substrate and in decorating these islands with Pb atoms in order to titrate the step density.

Sánchez, Alejandro; Ferrer, Salvador

220

Cross section for diffuse scattering from random steps on Cu(100) determined by teas (thermal energy atom scattering)  

NASA Astrophysics Data System (ADS)

The cross section for diffuse scattering from random steps in Cu(100) has been measured by TEAS. The result is 13 Å per unit step length, meaning that this is the distance normal to the step edge over which the surface is not specularly reflective for scattering of thermal He atoms. This result was obtained in an experimentally direct way that basically consisted in growing Cu islands on top of the Cu substrate and in decorating these islands with Pb atoms in order to titrate the step density.

Sánchez, Alejandro; Ferrer, Salvador

1987-08-01

221

Spectroscopy of li Atoms and li Dimers in the Triplet Manifold on the Surface of Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Helium nanodroplets (He_{N}) have attracted strong interest as superfluid nanocryostats and can serve as a tool for the efficient preparation of tailored molecules and clusters. Alkali-metal atoms and molecules are bound only weakly to the He_{N} surface. The fragility of these systems leads preferably to the formation of high-spin molecules on He_{N}. We use this property of helium nanodroplets for the preparation of Li dimers in their triplet ground state (1^{3}?_{u}^{+}). We present an excitation spectrum of the 2^{3}?_{g}(? ' = 0 - 10) ? 1^{3}?_{u}^{+}(? '' = 0) transition. The interaction between the molecule and the droplet manifests in a broadening of the transitions with a characteristic asymmetric form. The broadening extents to the blue side of each vibronic level, which is caused by the simultaneous excitation of the molecule and vibrations of the droplet (phonons). The two isotopes of Li form ^{6}Li_{2}, ^{7}Li_{2} as well as the isotope mixed ^{6}Li^{7}Li molecule on the droplet surface. By using resonance enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy isotope dependent effects could be studied. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) J. Higgins, C. Callegari, J. Reho, F. Stienkemeier, W.E. Ernst, M. Gutowski and G. Scoles, J. Phys. Chem. A, 102, 4952-4965 (1998) J. Higgins, C. Callegari, J. Reho, F. Stienkemeier, W.E. Ernst, K.K. Lehmann, M. Gutowski and G. Scoles, Science, 273, 629-631, (1996)

Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.

2013-06-01

222

Evalutation of integrals in the theory of atomic scattering of electrons  

Microsoft Academic Search

Summary  It is shown how using methods recently developed in field theory, one may exactly evaluate some integrals appearing in the\\u000a calculation of the differential cross section for the scattering of electrons by atoms.

E. Corinaldesi; L. Trainor

1952-01-01

223

Measurement of rate coefficients for electron-atom collisions in a helium plasma by laser-induced fluorescence  

NASA Astrophysics Data System (ADS)

We present experimentally obtained rate coefficients for electron-atom collisions for icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> n = 0 transitions of neutral helium. Results for the dipole-allowed transitions 3 3S-3 3P, 3 3P-3 3D, 3 1S-3 1P, 3 1D-3 1P, 4 1S-4 1P and 4 1D-4 1P are given for an electron temperature range of 3-7 eV. For the transitions 3 3S-3 3P and 3 3P-3 3D results down to temperatures below 1 eV were obtained. The measurements were performed in a magnetic multipole plasma source by a laser perturbation method. The plasma parameters were measured by employing a Langmuir probe. The electron density was in the range of 1011 to several 1012 cm-3 at helium filling pressures of a few Pascal. The results are compared with the theoretical and experimental data available in the literature.

Denkelmann, R.; Maurmann, S.; Lokajczyk, T.; Drepper, P.; Kunze, H.-J.

1999-10-01

224

Elastic Scattering of Polarized Protons on Helium Three at 800 MeV.  

National Technical Information Service (NTIS)

A set of spin dependent parameters and cross sections has been measured for polarized p- sup 3 He elastic scattering over the range of q .7 to 4.2 fm exp -1 . The experiment was done at the Los Alamos Meson Physics Facility (LAMPF) using the High Resoluti...

A. Azizi

1985-01-01

225

Supersonic beam formation and helium-scattering from GaAs(110)  

SciTech Connect

The author describes (1) his contributions to the science of supersonic beam formation, (2) the results of a {sup 4}He-scattering study from ion-damaged GaAs(110) surfaces, and (3) some preliminary results of 4He-scattering from MBE-grown GaAs(100). In our study of supersonic beam formation, we measure the angular distribution of flux from electron microscope apertures used as supersonic nozzles. This allows (1) the ideal on-axis beam intensity to be calculated and a comparison to be made with effusive beams (a fourfold intensity enhancement occurs), and allows (2) accurate calculations of flow rates through the differential stages of a supersonic beam source. He also studied (3) beam attenuation due to collisions with background gases, and show how skimmer-beam interference and condensation are avoided. The contributions (1)-(3) allow specification of the operating parameters leading to maximum beam signal. {sup 4}He-beams are then used in comparing scattering intensities from clean and Ar{sup +} ion-damaged GaAs(110). He found that the average residual surface damage due to single ion impacts decreases from small groups of defects (vacancies and adatoms) at low sample temperature T during bombardment to isolated monovacancies at higher T. This decrease occurs even in the absence of thermal annealing, and is possibly due to the T-dependent accommodation of adatom energy by the crystal. He also showed {sup 4}He-scattering data from MBE-grown As-stabilized (2 {times} 4) reconstructed GaAs(100). The scattering intensity decays with a time constant of {approximately}1 hour, about 100 times faster than a (110) surface under comparable vacuum conditions, but the cause of this instability is unknown.

Weaver, B.D.

1989-01-01

226

ATLAS OF CROSS SECTIONS FOR SCATTERING OF MUONIC HYDROGEN ATOMS ON HYDROGEN ISOTOPE MOLECULES  

Microsoft Academic Search

The total cross sections of the elastic, spin-flip, and charge-exchange processes for the scattering of muonic hydrogen isotope atoms (p?,d?,t?) in the ground state on hydrogen isotope molecules (H2, D2, T2, HD, HT, DT) are calculated. The scattering cross sections of muonic hydrogen isotope atoms on hydrogen isotope nuclei obtained earlier in the multichannel adiabatic approach are used in the

A. Adamczak; M. P. FAIFMAN; L. I. Ponomarev; V. I. Korobov; V. S. MELEZHIK; R. T. SIEGEL; J. Wozniak

1996-01-01

227

Intershell correlations in nonresonant Compton scattering of an X-ray photon by an atom  

SciTech Connect

The role of intershell correlations in nonresonant Compton scattering of an X-ray photon by a free multielectron atom is studied theoretically for the Ar atom. The results of calculation are of a predictive nature. The developed mathematical formalism is general in nature and can be applied to a wide set of elements from the Periodic Table, for which the description of the wavefunctions of scattering states in the nonrelativistic Hartree-Fock approximation remains correct.

Hopersky, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinsky, A. M.; Ikoeva, K. Kh.; Khoroshavina, O. A. [Rostov State Railway University (Russian Federation)

2011-11-15

228

Microscopic theory of scattering of weak electromagnetic radiation by a dense ensemble of ultracold atoms  

SciTech Connect

Based on the developed quantum microscopic theory, the interaction of weak electromagnetic radiation with dense ultracold atomic clouds is described in detail. The differential and total cooperative scattering cross sections are calculated for monochromatic radiation as particular examples of application of the general theory. The angular, spectral, and polarization properties of scattered light are determined. The dependence of these quantities on the sample size and concentration of atoms is studied and the influence of collective effects is analyzed.

Sokolov, I. M., E-mail: IMS@IS12093.spb.edu; Kupriyanov, D. V. [St. Petersburg State Technical University (Russian Federation); Havey, M. D. [Old Dominion University, Department of Physics (United States)

2011-02-15

229

Theory of light and atom scattering in the Bose-Einstein condensate of a dilute gas  

SciTech Connect

A semiclassical theory of superradiant light scattering from a Bose-Einstein condensate of a dilute gas is developed without recourse to the mean field approximation. The dynamics and spectrum of superradiant field, as well as the kinetics of formation of coherent atomic states with various translational momenta are calculated. The results are qualitatively consistent with experimental data for atoms scattered in the backward direction relative to that of the exciting laser beam propagation.

Avetisyan, Ya. A. [Russian Academy of Sciences, Institute of Problems of Fine Mechanics and Control (Russian Federation); Trifonov, E. D. [Herzen State Pedagogical University (Russian Federation)], E-mail: thphys@herzen.spb.ru

2006-11-15

230

Elastic scattering of electrons and positrons by atoms. Schrödinger and Dirac partial wave analysis  

NASA Astrophysics Data System (ADS)

Two FORTRAN 77 codes are described which provide a complete description of elastic scattering of electrons and positrons by atoms using the static field approximation with non-relativistic (Schrödinger) and relativistic (Dirac) partial wave analysis. The delivered information includes phase shifts, differential cross-sections, scattering amplitudes and percentage points of the single scattering angular distribution. The scattering field may be internally generated by the codes (which incorporate an accurate analytical approximation to the Dirac-Hartree-Fock-Slater field of free atoms) or read from the input file. Solid state effects for scattering in solids are described by means of a simple muffin-tin model. For electron scattering, exchange corrections are also taken into account. Phase shifts are obtained by using the RADWEQ subroutine package [Comput. Phys. Commun. 62 (1991) 65] to solve the radial equations. The relativistic code provides reliable cross-section data for kinetic energies between ? 1 keV and ? 1 MeV.

Salvat, Francesc; Mayol, Ricardo

1993-03-01

231

Observation of a coherence loss of an atomic wave scattered from the optical potential in a Talbot-Lau atom interferometer  

SciTech Connect

A coherence loss of an atomic wave scattered from the optical potential in an interferometer is observed. A Talbot-Lau atom interferometer is developed for that measurement using a laser-cooled lithium atomic beam. The long de Broglie wavelength of slow lithium atoms gives a short Talbot length and makes it possible to construct a small and stable atom interferometer.

Kohno, Takuya; Suzuki, Shinya; Shimizu, Kazuko [Institute for Laser Science, University of Electro-Communications, Chofu-shi, Tokyo 182-8585 (Japan)

2007-11-15

232

Advances in the helium-jet coupled on-line mass separator RAMA. [Recoil Atom Mass Analyzer  

SciTech Connect

General improvements to the on-line mass separator RAMA (Recoil Atom Mass Analyzer) have yielded a greater reliability and efficiency for some elements. A new utilitarian helium-jet chamber has been installed to facilitate quick target and degrader foil changes in addition to a new ion source holder. A higher efficiency hollow-cathode, cathode-extraction ion source, for lower melting point elements (< 1200/sup 0/C) has also been designed. Tests with the beta-delayed proton emitter /sup 37/Ca showed a factor of five increase in yield over the old hollow-cathode, anode-extraction source. A differentially-pumped-tape drive system compatible with both ..gamma..-..gamma.. and ..beta..-..gamma.. experiments has been incorporated into the general detection system. All major operating parameters will soon be monitored by a complete stand-alone microprocessor system which will eventually be upgraded to a closed-loop control system.

Moltz, D M; Aysto, J; Cable, M D; Parry, R F; Haustein, P E; Wouters, J M; Cerny, J

1980-01-01

233

Laser scattering by density fluctuations of ultra-cold atoms in a magneto-optical trap  

Microsoft Academic Search

We study the spectrum of density fluctuations in the ultra-cold gas of neutral atoms, confined in a magneto-optical trap. We determine the corresponding amplitude and spectra of laser light scattered by this medium. We derive an expression for the dynamical structure function, by using a test particle method. We propose to use the collective laser scattering as a diagnostic method

J. T. Mendonça; H. Terças

2011-01-01

234

Comparison of atomic oxygen measurements by incoherent scatter and satellite-borne mass spectrometer techniques  

NASA Technical Reports Server (NTRS)

Atomic oxygen densities determined by the incoherent scatter technique are compared to densities deduced from satellite-borne mass spectrometer measurements and are found to agree within experimental error. The diurnal variations inferred from the incoherent scatter measurements do show, however, some departure from diurnal variations found by modeling the mass spectrometer results. Some implications of these departures are briefly discussed.

Hedin, A. E.; Alcayde, D.

1974-01-01

235

Ordering of metal overlayers on metal substrates studied using atom beam scattering  

Microsoft Academic Search

We will illustrate how atom beam scattering (ABS) can be used to study the growth and ordering of adsorption of Hg on Cu(001). At low coverage (less than 2% of a monolayer), we obtain that the scattering cross section of He with (adsorbed) Hg is about 50 A². We find that mercury forms two stable phases on Cu(001) in the

G. Vidali; C. W. Hutchings; P. A. Dowben; M. Karimi; C. Moses; M. Foresti

1990-01-01

236

Analysis of an atom laser based on the spatial control of the scattering length  

SciTech Connect

In this paper we analyze atom lasers based on the spatial modulation of the scattering length of a Bose-Einstein condensate. We demonstrate, through numerical simulations and approximate analytical methods, the controllable emission of matter-wave bursts and study the dependence of the process on the spatial shape of the scattering length along the axis of emission. We also study the role of an additional modulation of the scattering length in time.

Carpentier, Alicia V.; Michinel, Humberto; Rodas-Verde, Maria I.; Perez-Garcia, Victor M. [Area de Optica, Facultade de Ciencias de Ourense, Universidade de Vigo, As Lagoas s/n, Ourense, ES-32004 Spain (Spain); Departamento de Matematicas, ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)

2006-07-15

237

Analyzing Power in Elastic Scattering of Polarized Protons from Neutron-rich Helium Isotopes  

NASA Astrophysics Data System (ADS)

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He from polarized protons at 71 MeV/nucleon. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a 6He nucleus. An optical model analysis revealed that the spin-orbit potential for 6He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semi-microscopic analysis with a ? + n + n cluster folding model suggests that the inclusion of realistic interaction between a proton and the ? core is important in describing the p-6He elastic scattering.

Sakaguchi, S.; Iseri, Y.; Uesaka, T.; Tanifuji, M.; Aoi, N.; Hiyama, E.; Ichikawa, Y.; Ishikawa, S.; Itoh, K.; Itoh, M.; Iwasaki, H.; Kawabata, T.; Kawahara, T.; Kuboki, H.; Maeda, Y.; Nakao, T.; Okamura, H.; Sakai, H.; Sasamoto, Y.; Sasano, M.; Satou, Y.; Sekiguchi, K.; Suda, K.; Suzuki, D.; Tamii, A.; Wakui, T.; Yako, K.; Yamaguchi, M.; Yamamoto, Y.

2013-08-01

238

Electron Diffraction of Superfluid Helium Droplets  

PubMed Central

We present experimental results of electron diffraction of superfluid helium droplets and droplets doped with phthalocyanine gallium chloride and discuss the possibility of performing the same experiment with a laser aligned sample. The diffraction profile of pure droplets demonstrates dependence on the nozzle temperature, that is, on the average size of the droplets. Larger clusters demonstrate faster decay with increasing momentum transfer, whereas smaller clusters converge to isolated gas phase molecules at source temperatures of 18 K and higher. Electron diffraction of doped droplets shows similar modified molecular scattering intensity as that of the corresponding gas phase molecules. On the basis of fittings of the scattering profile, the number of remaining helium atoms of the doped droplets is estimated to be on the order of hundreds. This result offers guidance in assessing the possibility of electron diffraction from laser aligned molecules doped in superfluid helium droplets.

2014-01-01

239

Plane wave packet formulation of atom-plus-diatom quantum reactive scattering  

NASA Astrophysics Data System (ADS)

We recently interpreted several reactive scattering experiments using a plane wave packet (PWP) formulation of quantum scattering theory [see, e.g., S. C. Althorpe, F. Fernández-Alonso, B. D. Bean, J. D. Ayers, A. E. Pomerantz, R. N. Zare, and E. Wrede, Nature (London) 416, 67 (2002)]. This paper presents the first derivation of this formulation for atom-plus-diatom reactive scattering, and explains its relation to conventional time-independent reactive scattering. We generalize recent results for spherical-particle scattering [S. C. Althorpe, Phys. Rev. A 69, 042702 (2004)] to atom-rigid-rotor scattering in the space-fixed frame, atom-rigid-rotor scattering in the body-fixed frame, and finally A+BC rearrangement scattering. The reactive scattering is initiated by a plane wave packet, describing the A+BC reagents in center-of-mass scattering coordinates, and is detected by projecting onto a series of AC+B (or AB+C) plane wave ``probe'' packets. The plane wave packets are localized at the closest distance from the scattering center at which the interaction potential can be neglected. The time evolution of the initial plane wave packet provides a clear visualization of the scattering into space of the reaction products. The projection onto the probe packets yields the time-independent, state-to-state scattering amplitude, and hence the differential cross section. We explain how best to implement the PWP approach in a numerical computation, and illustrate this with a detailed application to the H+D2 reaction.

Althorpe, Stuart C.

2004-07-01

240

Kinematically complete experiments for positron-impact ionization of helium atoms at the NEPOMUC facility  

NASA Astrophysics Data System (ADS)

Positron impact ionization of helium is studied with fully resolved momentum vectors of all continuum particles. An imaging multi-particle momentum spectrometer (reaction microscope) detecting all final state particles over the full solid angle was applied. This apparatus was connected to the NEPOMUC facility delivering intense positron beams tuneable over a large energy range with good beam quality. At 80 eV impact energy about 5000 triple coincidence events were collected. Cross sections as function of the longitudinal particle momentum show strong differences compared to respective electron impact ionization data most likely originating from the reversed post collision interaction in both cases. Calculations using the 3 Coulomb wavefunction method show clear discrepancies from the experimental results.

Pflüger, T.; Holzwarth, M.; Senftleben, A.; Ren, X.; Dorn, A.; Ullrich, J.; Hargreaves, L. R.; Lohmann, B.; Slaughter, D. S.; Sullivan, J. P.; Lower, J. C.; Buckman, S. J.

2011-01-01

241

Semiclassical method for calculating the energetic values of helium, lithium and beryllium atoms  

NASA Astrophysics Data System (ADS)

In previous papers we have presented a wave model for conservative bound systems resulted from the equivalency between the Schrödinger and wave equations. We proved that the normal curves of the characteristic surface of the wave equation, denoted by C curves, are solutions of the Hamilton-Jacobi equation, written for the same system, and correspond to the same constants of motion as those resulting from the Schrödinger equation. In this paper we present a method for computing the energetic values of conservative bound systems which is based on the properties of the C curves. The method is applied to the 1 s 2 state of helium, 1 s 22 s and 1 s 22 p states of lithium and 1 s 22 s 2 state of beryllium. Our theoretical values are compared with experimental data taken from well-known books. The relative error of our method is less than 5 x 10?3.

Popa, A.

2008-10-01

242

Helium Self-Oscillating Magnetometer Utilizing Optical Pumping of He4 Atoms.  

National Technical Information Service (NTIS)

Quantum magnetometers with optical pumping of alkaline metal pairs and metastable atoms of He4 find increasingly wide application in measuring various parameters of the geomagnetic field. These magnetometers can be constructed on a circuit with an automat...

R. A. Zhitnikov P. P. Kuleshov N. A. Dovator V. A. Azin

1974-01-01

243

Element-, time- and spatially-resolved images of scattered and recoiled atoms  

NASA Astrophysics Data System (ADS)

Element-specific, time- and spatially-resolved images of keV scattered and recoiled atomic ions plus fast atoms are exploited as a new technique of scattering and recoiling imaging spectrometry (SARIS). SARIS, an outgrowth of time-of-flight scattering and recoiling spectrometry (TOF-SARS), uses a large position-sensitive microchannel plate and TOF methods to capture images of energetic atoms which are scattered and recoiled from surfaces using a pulsed keV ion beam. The atoms are dispersed according to their velocities as a function of projectile/target atom masses and deflection angles. The spatial distributions of these atoms are captured by the MCP in time-resolved frames as short as 10 ns. Classical ion trajectory simulations provide a good description of the interactions, allowing direct simulation and interpretation of the experimental images. The images combine atomic scale microscopy and spatial averaging since they are created from a macroscopic surface area but they are directly related to the atomic arrangement of the surface at the sub-nanoscale level; the accuracy for measurement of interatomic spacings is expected to be better than 0.01 Å. Example data is presented for Pt{111}and Au{110}.

Kim, C.; Hoefner, C.; Bykov, V.; Rabalais, J. W.

244

Experimental visualization of scattering at defects in electronic transport through a single atomic junction  

NASA Astrophysics Data System (ADS)

For electronic transport at the nanoscale, coherent scattering at defects plays an important role. Therefore, the capability of visualizing the influence of defects on the conductivity of single atomic junctions may benefit the development of future nano-electronics. Here, we report imaging the coherent scattering from a defect with well-controlled geometry by quantum point contact microscopy recently developed by us. An ˜10% modulation in transport conductance of a single atomic junction is observed, with a phase shift of nearly ? compared to the tunneling conductance. With the well-defined scattering geometry, we performed a theoretical calculation of the conductance and found the result consistent with the experiment.

Zhang, Yong-hui; Wahl, Peter; Kern, Klaus

2013-05-01

245

The Scattering of Gas Atoms from Solid Surfaces  

ERIC Educational Resources Information Center

Traditional undergraduate courses in gas kinetic theory encourage the view that in all collisions between a gas atom and a surface, the angle of incidence of the gas atom equals its angle of reflection. This article illustrates and explains the incorrectness in assuming specular reflection and zero dwell time. (Author/MA)

Walton, Alan J.

1977-01-01

246

Two-atom model in enhanced ion backscattering near 180/sup 0/ scattering angles  

SciTech Connect

The recent discovery by Pronko, Appleton, Holland, and Wilson of an unusual enhancement of the yield of ions backscattered through angles close to 180/sup 0/ from the near surface regions of solids is investigated using a two-atom scattering model. The model predicts an enhancement effect in amorphous solids whose physical origin arises from the tolerance of path for those ions whose inward and outward trajectories lie in the vicinity of the critical impact parameter. Predictions are given of the dependence of the yield enhancement on the following parameters: ion energy, backscattering depth, exit angle, scattering potential, atomic numbers of projectile and target, and atomic density of target.

Oen, O.S.

1981-06-01

247

Creation, destruction, and transfer of atomic multipole moments by electron scattering: Quantum-mechanical treatment  

NASA Astrophysics Data System (ADS)

Using the wave-packet propagation method of Rodberg and Thaler and the density matrix method of Fano and Blum, we have defined by completely quantum-mechanical methods the cross sections for the creation, destruction, and transfer of atomic multipole moments by both elastic and inelastic scattering of electrons by atomic targets. All cross sections obtained quantum mechanically, except for the coherence transfer cross sections, agree in form with those obtained semiclassically by Fujimoto and co-workers. We also used the converged close-coupling (CCC) method to calculate numerically some of the above cross sections for selected transitions in electron scattering from hydrogen and barium atoms.

Csanak, G.; Kilcrease, D. P.; Fursa, D. V.; Bray, I.

2008-12-01

248

Cavity-Enhanced Light Scattering in Optical Lattices to Probe Atomic Quantum Statistics  

SciTech Connect

Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.

Mekhov, Igor B. [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria); V. A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg (Russian Federation); Maschler, Christoph; Ritsch, Helmut [Institut fuer Theoretische Physik, Universitaet Innsbruck, Innsbruck (Austria)

2007-03-09

249

Quantitative Surface Atomic Structure Analysis by Low-Energy Ion Scattering Spectroscopy (ISS)  

NASA Astrophysics Data System (ADS)

Surface atomic structure analysis by low-energy ion scattering spectroscopy (ISS) is reviewed, with particular emphasis on quantitative surface atomic structure analysis by ISS. The important differences between ISS and Rutherford backscattering spectroscopy (RBS), some basic characteristics of ISS, a special type of ISS called impact-collision ion scattering spectroscopy (ICISS), and the general features of the shadow cone in the energy range of ISS are discussed as a basis for the description of particular examples of ISS studies which follow. The examples are mainly concerned with the analysis of the atomic arrangement, defect structure, thermal vibration, and electron spatial distribution of the (001) and (111) surfaces of TiC.

Aono, Masakazu; Souda, Ryutaro

1985-10-01

250

Spectral theory of quantum memory and entanglement via Raman scattering of light by an atomic ensemble  

Microsoft Academic Search

We discuss theoretically quantum interface between light and a spin polarized\\u000aensemble of atoms with the spin >= 1 based on an off-resonant Raman scattering.\\u000aWe present the spectral theory of the light-atoms interaction and show how\\u000aparticular spectral modes of quantum light couple to spatial modes of the\\u000aextended atomic ensemble. We show how this interaction can be used

O. S. Mishina; D. V. Kupriyanov; J. H. Muller; E. S. Polzik

2007-01-01

251

Macroscopic scattering of cracks initiated at single impurity atoms  

NASA Astrophysics Data System (ADS)

Brittle crystals, such as coloured gems, have long been known to cleave with atomically smooth fracture surfaces, despite being impurity laden, suggesting that isolated atomic impurities do not generally cause cracks to deflect. Whether cracks can ever deviate when hitting an atomic defect, and if so how they can go straight in real brittle crystals, which always contain many such defects, is still an open question. Here we carry out multiscale molecular dynamics simulations and high-resolution experiments on boron-doped silicon, revealing that cracks can be deflected by individual boron atoms. The process, however, requires a characteristic minimum time, which must be less than the time spent by the crack front at the impurity site. Deflection therefore occurs at low crack speeds, leading to surface ridges which intensify when the boron-dopage level is increased, whereas fast-moving cracks are dynamically steered away from being deflected, yielding smooth cleavage surfaces.

Kermode, J. R.; Ben-Bashat, L.; Atrash, F.; Cilliers, J. J.; Sherman, D.; de Vita, A.

2013-09-01

252

Elastic scattering of electrons on Ne atoms at intermediate energies  

NASA Astrophysics Data System (ADS)

In this work, we present a theoretical study on electron scattering by Ne in the intermediate- and high-energy range. More specifically, we report calculated differential cross sections for electron scattering by Ne in the 20-500 eV range by the Schwinger multichannel method using plane waves as a trial basis set. To include exchange plus polarization effects, we used the Born-Ochkur model and the Buckingham potential, respectively. The comparison of our calculated results with experimental data and recent theoretical studies (Jablonski et al 2004 J. Phys. Chem. Ref. Data 33 409) is encouraging.

Lino, Jorge L. S.

2010-03-01

253

Atom Probe Field Ion Microscope Study of the Range and Diffusivity of Helium in Tungsten.  

National Technical Information Service (NTIS)

A time-of-flight (TOF) atom-probe field-ion microscope (FIM) specifically designed for the study of defects in metals is described. With this automated system 600 TOF min exp -1 can be recorded and analyzed. Performance tests of the instrument demonstrate...

A. Wagner

1978-01-01

254

Energy Levels in Helium and Neon Atoms by an Electron-Impact Method.  

ERIC Educational Resources Information Center

Electronic energy levels in noble gas atoms may be determined with a simple teaching apparatus incorporating a resonance potentials tube in which the electron beam intensity is held constant. The resulting spectra are little inferior to those obtained by more elaborate electron-impact methods and complement optical emission spectra. (Author/SK)

Taylor, N.; And Others

1981-01-01

255

Compton scattering of an X-ray photon by an open-shell atom  

SciTech Connect

A nonrelativistic quantum theory for the nonresonant Compton scattering of an X-ray photon by a free many-electron atom with an open shell in the ground state has been constructed in the single-configuration Hartree-Fock approximation outside the impulse approximation widely used in the literature. The transition to an atom with closed shells reproduces the results obtained previously in [6, 7]. The results of a test calculation for atoms with open (Ti, Fe) and closed (Zn) 3d core shells are presented. The effects of the radial relaxation of one-electron states in the field of core vacancies have been taken into account. The results of the calculation agree well with the experimental results [15, 16]. It has been established that the results of the impulse approximation in the investigated X-ray photon energy ranges disagree with those of our theory not only quantitatively but also qualitatively. In particular, the impulse approximation near the elastic (Thomson and Rayleigh) scattering line leads to a gross overestimation of the contributions from the deep atomic shells involved in the inelastic photon scattering only virtually to the scattering probability. The presented theory is general in character and its applicability to a particular element of the Mendeleev table with an open core shell or to a many-electron atomic ion is limited only by the requirement that the nonrelativistic Hartree-Fock approximation be properly used in describing the scattering-state wave functions.

Hopersky, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinsky, A. M. [Rostov State University of Transport Communication (Russian Federation)

2012-09-15

256

Compton scattering of an X-ray photon by an open-shell atom  

NASA Astrophysics Data System (ADS)

A nonrelativistic quantum theory for the nonresonant Compton scattering of an X-ray photon by a free many-electron atom with an open shell in the ground state has been constructed in the single-configuration Hartree-Fock approximation outside the impulse approximation widely used in the literature. The transition to an atom with closed shells reproduces the results obtained previously in [6, 7]. The results of a test calculation for atoms with open (Ti, Fe) and closed (Zn) 3 d core shells are presented. The effects of the radial relaxation of one-electron states in the field of core vacancies have been taken into account. The results of the calculation agree well with the experimental results [15, 16]. It has been established that the results of the impulse approximation in the investigated X-ray photon energy ranges disagree with those of our theory not only quantitatively but also qualitatively. In particular, the impulse approximation near the elastic (Thomson and Rayleigh) scattering line leads to a gross overestimation of the contributions from the deep atomic shells involved in the inelastic photon scattering only virtually to the scattering probability. The presented theory is general in character and its applicability to a particular element of the Mendeleev table with an open core shell or to a many-electron atomic ion is limited only by the requirement that the nonrelativistic Hartree-Fock approximation be properly used in describing the scattering-state wave functions.

Hopersky, A. N.; Nadolinsky, A. M.

2012-09-01

257

Scattering amplitude of ultracold atoms near the p-wave magnetic Feshbach resonance  

SciTech Connect

Most of the current theories on the p-wave superfluid in cold atomic gases are based on the effective-range theory for the two-body scattering, where the low-energy p-wave scattering amplitude f{sub 1}(k) is given by f{sub 1}(k)=-1/[ik+1/(Vk{sup 2})+1/R]. Here k is the incident momentum, V and R are the k-independent scattering volume and effective range, respectively. However, due to the long-range nature of the van der Waals interaction between two colliding ultracold atoms, the p-wave scattering amplitude of the two atoms is not described by the effective-range theory [J. Math. Phys. 4, 54 (1963); Phys. Rev. A 58, 4222 (1998)]. In this paper we provide an explicit calculation for the p-wave scattering of two ultracold atoms near the p-wave magnetic Feshbach resonance. We show that in this case the low-energy p-wave scattering amplitude f{sub 1}(k)=-1/[ik+1/(V{sup eff}k{sup 2})+1/(S{sup eff}k)+1/R{sup eff}] where V{sup eff}, S{sup eff}, and R{sup eff} are k-dependent parameters. Based on this result, we identify sufficient conditions for the effective-range theory to be a good approximation of the exact scattering amplitude. Using these conditions we show that the effective-range theory is a good approximation for the p-wave scattering in the ultracold gases of {sup 6}Li and {sup 40}K when the scattering volume is enhanced by the resonance.

Zhang Peng [Exploratory Research for Advanced Technology, Macroscopic Quantum Project, Japan Science and Technology, Tokyo 113-8656 (Japan); Department of Physics, Renmin University of China, Beijing 100872 (China); Naidon, Pascal [Exploratory Research for Advanced Technology, Macroscopic Quantum Project, Japan Science and Technology, Tokyo 113-8656 (Japan); Ueda, Masahito [Exploratory Research for Advanced Technology, Macroscopic Quantum Project, Japan Science and Technology, Tokyo 113-8656 (Japan); Department of Physics, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan)

2010-12-15

258

Atom probe field ion microscope study of the range and diffusivity of helium in tungsten  

Microsoft Academic Search

A time-of-flight (TOF) atom-probe field-ion microscope (FIM) specifically designed for the study of defects in metals is described. With this automated system 600 TOF min⁻¹ can be recorded and analyzed. Performance tests of the instrument demonstrated that (1) the seven isotopes of molybdenum and the five isotopes of tungsten can be clearly resolved; and (2) the concentration and spatial distribution

1978-01-01

259

Observation of a Feshbach Resonance in Cold Atom Scattering  

NASA Astrophysics Data System (ADS)

We probe s-wave collisions of laser-cooled 85Rb\\( f = 2,mf = -2\\) atoms with Zeeman-resolved photoassociation spectroscopy. We observe that these collisions exhibit a magnetically tunable Feshbach resonance, and determine that this resonance tunes to zero energy at a magnetic field of 164+/-7 G. This result indicates that the self-interaction energy of an 85Rb Bose-Einstein condensate can be magnetically tuned. We also demonstrate that Zeeman-resolved photoassociation spectroscopy provides a useful new tool for the study of ultracold atomic collisions.

Courteille, Ph.; Freeland, R. S.; Heinzen, D. J.; van Abeelen, F. A.; Verhaar, B. J.

1998-07-01

260

He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth. Progress report, May 1, 1992--April 30, 1993  

SciTech Connect

Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.

Not Available

1992-11-01

261

Scattering of helium nozzle beams from LiF/001/ and NaCl/001/ crystal surfaces. I - Elastic and inelastic transitions  

NASA Technical Reports Server (NTRS)

Nozzle-type atomic beams and time-of-flight detection methods are employed in studies of the scattering of thermal-energy He-4 atoms from LiF (001) and NaCl (001) surfaces under conditions where diffraction is observed and where substantial inelastic scattering occurs. Intensity and speed-distribution measurements are obtained for the portion of the scattering within the plane of incidence. For these measurements, incident-beam orientation with respect to target (polar angle and azimuth), incident-beam de Broglie wavelength (0.38-0.60 A), and crystal temperature (300-1000 K) are varied. For LiF, the measured intensity distributions exhibit sharp peaks comprised essentially of elastically scattered atoms and corresponding to up to third-order diffraction, inelastic scattering in the form of local dispersion about each of the elastic peaks, and a component of nominally diffuse scattering distributed below and between the peaks. For NaCl, the same general types of scattering are observed, with elastic scattering less prevalent, intensity peaks not as sharp, and dispersions of inelastic scattering harder to resolve.

Bledsoe, J. R.; Fisher, S. S.

1974-01-01

262

Collective atomic recoil in a moving Bose-Einstein condensate: From superradiance to Bragg scattering  

NASA Astrophysics Data System (ADS)

We present the results of an experiment on light scattering from an elongated Bose-Einstein condensate (BEC) interacting with a far-off-resonant pump laser. By collective atomic recoil lasing (CARL) a coherent superposition of two atomic wave packets with different momenta is created. Varying the intensity of a weak counterpropagating laser beam we observe the transition from the pure superradiant regime to the Bragg scattering regime, where Rabi oscillations in a two-level system are observed. The process is limited by the decoherence between the two atomic wave packets. In the superradiant regime the experiment gives evidence of a contribution to decoherence which depends on the initial velocity of the condensate. The system is described by the CARL-BEC model, which is a generalization of the Gross-Pitaevskii model to include the self-consistent evolution of the scattered field and a phase-diffusion decoherence process, which accounts for the observed damping.

Fallani, L.; Fort, C.; Piovella, N.; Cola, M.; Cataliotti, F. S.; Inguscio, M.; Bonifacio, R.

2005-03-01

263

Precision measurement of laser RF double resonance spectra with an effective compensation of residual magnetic field. For nuclear laser spectroscopy of RI atoms in superfluid helium  

NASA Astrophysics Data System (ADS)

We have been developing a novel laser spectroscopy method-"OROCHI" for radioisotopes trapped in superfluid helium. This new method is expected to determine nuclear spins and moments of exotic nuclei by precise measurement of Zeeman and hyperfine splitting of atoms using laser double resonance method. Its feasibility has been confirmed by means of a series of experiments with various stable atoms in superfluid helium, while the accuracy of experimental results is found strongly affected by external magnetic field. In order to obtain reliable and accurate results for atomic spectra with "OROCHI" method, based on laser RF double resonance spectroscopy of on-line experiment, we performed off-line test experiments for Rb in helium buffer gas. In this test experiment, we used three mutually orthogonal coils to effectively compensate for laboratory residual magnetic field and subsequently observed precise laser RF double resonance spectra of atoms which affords us accurate nuclear spin value. By comparison of those results, we could make clear the effect of residual magnetic field on experimental results. The details of "OROCHI" method and test experiments are presented.

Yang, X. F.; Furukawa, T.; Fujita, T.; Imamura, K.; Matsuo, Y.

2014-06-01

264

Helium Cryostat with Liquid Hydrogen Target for Experiments on Polarization Measurement in PO Scattering at Small Momentum Transfers.  

National Technical Information Service (NTIS)

The work describes a liquid hydrogen target with closed capacity and a helium cryostat for cooling the target. Helium is supplied to a coupling encompassing the side walls of the target via thin tubes (dia 3 mm) from the cryostat installed at 1 m from the...

A. M. Gordeev V. I. Martynov B. V. Morozov V. M. Nesterov I. I. Pershin

1977-01-01

265

Cross sections for scattering of deuterium mesic atoms on deuterium nuclei  

Microsoft Academic Search

Cross sections have been calculated for elastic scattering of deuterium mesic atoms in ortho and para states on deuterium nuclei in the 0-50 eV energy range; cross sections for spin-flip have also been calculated. The calculations have been performed in the adiabatic representation where the initial problem of slow collisions in a three-body system is reduced to the multichannel scattering

V. S. Melezhik; J. Wozniak

1986-01-01

266

Theory of resonance scattering and absorption of strong coherent radiation by thermally relaxing multilevel atomic systems  

Microsoft Academic Search

The resonant response of a multilevel atomic system to strong coherent radiation is analyzed using an extension of the methods of time-independent scattering theory, adapted to the density-matrix formalism in order to include thermal bath effects. General steady-state expressions are derived for self-attenuation and resonance scattering rates in strong saturating fields, as functions of the coupling strengths, relaxation parameters, and

Abraham Ben-Reuven; Yitzhak Rabin

1979-01-01

267

Analytic description of atomic interaction at ultracold temperatures. II. Scattering around a magnetic Feshbach resonance  

SciTech Connect

Starting from a multichannel quantum-defect theory, we derive analytic descriptions of a magnetic Feshbach resonance in an arbitrary partial wave l and the atomic interactions around it. An analytic formula, applicable to both broad and narrow resonances of arbitrary l, is presented for ultracold atomic scattering around a Feshbach resonance. Other related issues addressed include (a) the parametrization of a magnetic Feshbach resonance of arbitrary l, (b) rigorous definitions of ''broad'' and ''narrow'' resonances of arbitrary l and their different scattering characteristics, and (c) the tuning of the effective range and the generalized effective range by a magnetic field.

Gao Bo [Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP), Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States); Department of Physics and Astronomy, Mailstop 111, University of Toledo, Toledo, Ohio 43606 (United States)

2011-08-15

268

Impact of anisotropic atomic motions in proteins on powder-averaged incoherent neutron scattering intensities  

NASA Astrophysics Data System (ADS)

This paper addresses the question to which extent anisotropic atomic motions in proteins impact angular-averaged incoherent neutron scattering intensities, which are typically recorded for powder samples. For this purpose, the relevant correlation functions are represented as multipole series in which each term corresponds to a different degree of intrinsic motional anisotropy. The approach is illustrated by a simple analytical model and by a simulation-based example for lysozyme, considering in both cases the elastic incoherent structure factor. The second example shows that the motional anisotropy of the protein atoms is considerable and contributes significantly to the scattering intensity.

Kneller, Gerald R.; Chevrot, Guillaume

2012-12-01

269

Impact of anisotropic atomic motions in proteins on powder-averaged incoherent neutron scattering intensities  

SciTech Connect

This paper addresses the question to which extent anisotropic atomic motions in proteins impact angular-averaged incoherent neutron scattering intensities, which are typically recorded for powder samples. For this purpose, the relevant correlation functions are represented as multipole series in which each term corresponds to a different degree of intrinsic motional anisotropy. The approach is illustrated by a simple analytical model and by a simulation-based example for lysozyme, considering in both cases the elastic incoherent structure factor. The second example shows that the motional anisotropy of the protein atoms is considerable and contributes significantly to the scattering intensity.

Kneller, Gerald R. [Centre de Biophys. Moleculaire, CNRS, Rue Charles Sadron, 45071 Orleans (France); Synchrotron Soleil, L'Orme de Merisiers, 91192 Gif-sur-Yvette (France); Universite d'Orleans, Chateau de la Source-Av. du Parc Floral, 45067 Orleans (France); Chevrot, Guillaume [Centre de Biophys. Moleculaire, CNRS, Rue Charles Sadron, 45071 Orleans (France); Synchrotron Soleil, L'Orme de Merisiers, 91192 Gif-sur-Yvette (France)

2012-12-14

270

Light Scattering for Thermometry of Fermionic Atoms in an Optical Lattice  

SciTech Connect

We propose a method of using off-resonant light scattering to measure the temperature of fermionic atoms tightly confined in a two-dimensional optical-lattice potential. We show that fluctuations of the intensity in the far-field diffraction pattern arising from thermal correlations of the atoms can be accurately detected above the shot noise by collecting photons scattered in a forward direction, with the diffraction maxima blocked. The sensitivity of this method of thermometry is enhanced by an additional harmonic trapping potential.

Ruostekoski, J. [School of Mathematics, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Foot, C. J.; Deb, A. B. [Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU (United Kingdom)

2009-10-23

271

Positron scattering from hydrogen atom with screened Coulomb potentials  

NASA Astrophysics Data System (ADS)

Elastic positron-hydrogen collisions with screened Coulomb potentials have been investigated using a second-order distorted wave Born approximation in the momentum space. Two types of potentials have been considered, namely, static screened Coulomb potential and exponential cosine-screened Coulomb potential. Using a simple variationally determined hydrogenic wave function it has been possible to obtain the scattering amplitude in a closed form. A detailed study has been made on the differential and total cross sections in the energy range 20-300 eV.

Ghoshal, Arijit; Nayek, Sujay; Kamali, M. Z. M.; Ratnavelu, K.

2014-03-01

272

Measurement of effective atomic number of gunshot residues using scattering of gamma rays  

NASA Astrophysics Data System (ADS)

Better understanding of gunshot residues and the major elemental composition would be valuable to forensic scientists for their analysis work and interpretation of results. In the present work, the effective atomic numbers of gunshot residues (cartridge case, bullet core, bullet jacket and gunpowder) were analyzed using energy dispersive X-ray analysis (EDX). The scattering of 59.54 keV gamma rays is studied using a high-resolution HPGe detector. The experiment is performed on various elements with atomic number in the 4?Z?82. The intensity ratio of coherent to Compton scattered peaks, corrected for photo-peak efficiency of gamma detector and absorption of photons in the sample and air, is plotted as a function of atomic number and constituted a best-fit-curve. From this fit-curve, the respective effective atomic numbers of gunshot residues are determined.

Y?lmaz, Demet; Tur?ucu, Ahmet; Uzuno?lu, Zeynep; Korucu, Demet

2014-09-01

273

Accurate Kohn-Sham potential for the 1s2s S-3 state of the helium atom: Tests of the locality and the ionization-potential theorems  

Microsoft Academic Search

The local Kohn-Sham potential is constructed for the 1s2s S-3 state of the helium atom, using the procedure proposed by van Leeuwen and Baerends (Phys. Rev. A, 49, 2138 (1994)) and the many-body electron density, obtained from the pair-correlation program of Salomonson and Oster (Phys. Rev. A, 40, 5559 (1989)). The Kohn-Sham orbitals reproduce the many-body density very accurately, demonstrating

Sten Salomonson; F. Moller; Ingvar Lindgren

2005-01-01

274

Construction of accurate Kohn-Sham potentials for the lowest states of the helium atom: Accurate test of the ionization-potential theorem  

Microsoft Academic Search

Accurate local Kohn-Sham potentials have been constructed for the ground 1s21S state and, in particular, for the lowest triplet 1s2s3S state of the helium atom, using electron densities from many-body calculations and the procedure of van Leeuwen and Baerends. The resulting Kohn-Sham orbitals reproduce the many-body densities very accurately; furthermore, we have demonstrated that the negative of the energy eigenvalue

I. Lindgren; S. Salomonson; F. Möller

2005-01-01

275

Relativistic atomic form factors and photon coherent scattering cross sections  

Microsoft Academic Search

Tabulations are presented of relativistic Hartree-Fock atomic form factors F (x,Z), for values of x (=sin(&Vthgr;\\/2)\\/? from 0.01 to 109 A??1, for all elements Z=1 to 100. For Z=1, F (x,Z) is given by the exact expression of Pirenne. For Z=2 to 98, x=0.01 to 2.0 A??1, the tabulated values are those of Cromer and Waber given in the InternationalTablesforX?RayCrystallography

J. H. Hubbell

1979-01-01

276

Crossed-molecular-beams reactive scattering of oxygen atoms  

SciTech Connect

The reactions of O(/sup 3/P) with six prototypical unsaturated hydrocarbons, and the reaction of O(/sup 1/D) with HD, have been studied in high-resolution crossed-molecular-beams scattering experiments with mass-spectrometric detection. The observed laboratory-product angular and velocity distributions unambiguously identify parent-daughter ion pairs, distinguish different neutral sources of the same ion, and have been used to identify the primary products of the reactions. The derived center-of-mass product angular and translational energy distributions have been used to elucidate the detailed reaction dynamics. These results demonstrate that O(/sup 3/P)-unsaturated hydrocarbon chemistry is dominated by single bond cleavages, leading to radical products exclusively.

Baseman, R.J.

1982-11-01

277

Positron scattering from hydrogen atom embedded in weakly coupled plasma  

SciTech Connect

The positron-hydrogen collision problem in weakly coupled plasma environment has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. A simple variational hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s{yields}1s and 2s{yields}2s elastic collisions, 1s{yields}2s excitation, positronium formation, elastic proton-positronium collisions, have been reported. Furthermore, a detailed study has been made on differential and total cross sections of the above processes in the energy range 13.6-350 eV of the incident positron.

Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal (India); Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Kamali, M. Z. M. [Centre for Foundation Studies in Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)

2013-01-15

278

Anomalous attenuation at low temperatures in high-intensity helium beam sources  

NASA Astrophysics Data System (ADS)

High-intensity supersonic helium beam sources are a critical component in modern thermal energy helium atom scattering apparatuses. In common with sources developed elsewhere, we have observed beam attenuation at low temperature as the helium flow through the nozzle is increased. A detailed analysis of the measurements demonstrates that direct backscattering in the nozzle-skimmer region is likely to be the major attenuation source. A numerical model, which describes the principle sources of scattering in the region between source and skimmer, is shown to provide a good description of the experimental data for a range of flow conditions and for stagnation temperatures between 37 and 300 K. The model includes partial accommodation of atoms scattered from surfaces of the skimmer and chamber, together with a realistic scattering potential. We use the model to predict the effect of various geometric alterations, aimed at improving the ultimate beam intensity.

Hedgeland, H.; Jardine, A. P.; Allison, W.; Ellis, J.

2005-12-01

279

Anomalous attenuation at low temperatures in high-intensity helium beam sources  

SciTech Connect

High-intensity supersonic helium beam sources are a critical component in modern thermal energy helium atom scattering apparatuses. In common with sources developed elsewhere, we have observed beam attenuation at low temperature as the helium flow through the nozzle is increased. A detailed analysis of the measurements demonstrates that direct backscattering in the nozzle-skimmer region is likely to be the major attenuation source. A numerical model, which describes the principle sources of scattering in the region between source and skimmer, is shown to provide a good description of the experimental data for a range of flow conditions and for stagnation temperatures between 37 and 300 K. The model includes partial accommodation of atoms scattered from surfaces of the skimmer and chamber, together with a realistic scattering potential. We use the model to predict the effect of various geometric alterations, aimed at improving the ultimate beam intensity.

Hedgeland, H.; Jardine, A.P.; Allison, W.; Ellis, J. [Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE (United Kingdom)

2005-12-15

280

Elastic and Inelastic Scattering of Positrons by Potassium Atoms  

NASA Astrophysics Data System (ADS)

The investigations of the elastic and inelastic collisions of positrons with potassium atoms, K (1s2, 2s2, 2p6, 3s2, 3p6, 4s), are presented. The potassium target atoms are described using Clementi-Roetti wavefunctions within the framework of the one-valence-electron model. The total cross-sections which correspond to eight partial cross-sections are calculated at 34 values of the incident energy k21 (2.5 eV <= k12<= 100 eV) using the coupled-static approximation. The resulting total elastic, ground- and excited-positronium formation cross-sections are compared with experimental results and those calculated by other authors. In the vicinity of 6 eV, and consistent with the measurements of Parikh et al.,2 our total cross-section displays a pronounced peak. We support the conclusion of McAlinden et al.15 and Hewitt et al.14 that above about 4 eV, positronium formation is mainly into excited states. Good agreement is obtained with the total cross-section measurements of Kwan et al.1 and Parikh et al.2 Positronium formation is not important above about 50 eV.

El-Bakry, Salah Yaseen

281

Coulomb excitation of helium atoms in collisions with highly charged ions  

NASA Astrophysics Data System (ADS)

Collisional excitation of He atoms by 65 and 80 MeV 40Arq+ ions (q = 6,13,14) was investigated by measuring the intensities Iicons/Journals/Common/lambda" ALT="lambda" ALIGN="MIDDLE"/>(Fz) of He I spectral lines at 401 nm and 447 nm as functions of an electric field -30 < Fz < +30 kV cm-1 applied parallel and antiparallel to the ion beam. Well resolved signals of singlet-triplet anticrossings 0953-4075/32/23/309/img1" ALT="(img) with n = 4 and 5 were measured for both field directions in addition to smooth intensity variations of the 0953-4075/32/23/309/img2" ALT="(img) lines with n = 7 and 5. The asymmetric signal structure indicates a highly coherent excitation of states with different angular momenta. For comparison, some supplementary measurements of I447 for proton impact are also reported. The results are discussed within the framework of saddle dynamics and the Paul-trap model. They confirm the Janev-Presnyakov scaling law valid for electric dipole Coulomb excitation, according to which the excitation process is essentially determined by the scaled energies E0 = Eion/(Aicons/Journals/Common/cdot" ALT="cdot" ALIGN="TOP"/> q) of the projectile.

Tschersich, M.; Drozdowski, R.; Busch, M.; Skogvall, B.; von Oppen, G.

1999-12-01

282

New method of evaluation for interatomic interaction potential in LEIS with large-angle scattering using the two-atom scattering model  

NASA Astrophysics Data System (ADS)

The interaction potential between an incident ion and a target atom in impact-collision ion scattering spectroscopy (ICISS), which is a specialization of low energy ion scattering (LEIS) and its variants, i.e. ICISS with detection of neutrals (NICISS), coaxial ICISS (CAICISS) and impact-collision atom scattering spectroscopy with detection of neutrals (NICASS), has been evaluated by the new method using the dependence of the total scattering angle on the impact parameter for the first collision in the numerical calculations based on the two-atom scattering model (TWASM). From the comparison of determined values of scaling factor for the Firsov screening length by three-dimensional computer simulations with calculated ones by TWASM, it became obviously that the interatomic potentials for the various combinations of an incident ion and a target atom in LEIS are suitably given by the Moliere potential with the reduced Firsov screening length employing the scaling factor obtained in TWASM calculations.

Takeuchi, Wataru; Matsuda, Naoki

2008-03-01

283

Diffraction of fast atoms and molecules during grazing scattering from surfaces  

NASA Astrophysics Data System (ADS)

Grazing scattering of light atoms and small molecules with energies up to several keV from atomically clean and flat surfaces along low-indexed directions gives rise to diffraction phenomena. The potential of this new method of Fast Atom Diffraction (FAD) as surface analytical tool is discussed. We show that, despite substantial decoherence due to thermal vibrations, nuclear energy loss, and, especially, excitations of the electronic system, FAD is not limited to insulator or semiconductor surfaces. Detailed studies of the geometric structure of insulator surfaces and superstructures on metal surfaces performed using FAD as an efficient virtually non-destructive method are presented.

Schüller, A.; Busch, M.; Seifert, J.; Wethekam, S.; Winter, H.

2009-11-01

284

Scattering of atomic dark-bright solitons from narrow impurities  

NASA Astrophysics Data System (ADS)

In this work, we examine the collision of an atomic dark-bright soliton, in a two-component Bose-Einstein condensate, with a Gaussian barrier or well. Our study has both an experimental component and a theoretical/computational one. First, we present the results of an experiment, illustrating the classical particle phenomenology (transmission or reflection) in the case of an equal barrier in both components. Then, motivated by the experimental observations, we perform systematic simulations considering not only the case of equal heights of a barrier (or a well), but also the considerably more complex setting, where the potential affects only one of the two components. We systematically classify the ensuing cases within a two-parameter diagram of potential amplitudes in the two components, and provide intuitive explanations for the resulting observations, as well as of their variations as the strength of the potential changes.

Álvarez, A.; Cuevas, J.; Romero, F. R.; Hamner, C.; Chang, J. J.; Engels, P.; Kevrekidis, P. G.; Frantzeskakis, D. J.

2013-03-01

285

Electron screening in low energy scattering of muonic hydrogen on hydrogen atoms  

Microsoft Academic Search

Electron screening corrections to the cross sections for low energy scattering of muonic hydrogen on hydrogen atoms are calculated. It is shown that the presence of the electron influences considerably the elastic cross sections at collision energies below 1 eV. This influence is relatively small for the spin-flip and isotopic exchange processes.

A. Adamczak; V. S. Melezhik; L. I. Menshikov

1986-01-01

286

Diffraction and vibrational dynamics of large clusters from He atom scattering  

Microsoft Academic Search

The vibrational dynamics of large Arn clusters from n=30 to n=4500 is investigated by measuring the energy loss of He atoms in a high resolution scattering experiment. The clusters are generated by adiabatic expansion through conical nozzles and contain a distribution of cluster sizes. The He supersonic nozzle beam provides a resolution of better than 1 meV. The results are

Udo Buck; Reinhard Krohne; Jörg Siebers

1993-01-01

287

THE SCATTERING OF A POTASSIUM ATOMIC BEAM BY A CROSSED BEAM OF BROMINE MOLECULES  

Microsoft Academic Search

A study was made of the scattering of crossed molecular beams for the ; determinntion of information on intermolecular forces and chemical reaction cross ; sections. A high resolution molecular beam apparatus was constructed to study ; the interaction of a monoenergetic beam of potassium atoms with a crossed beam of ; bromine molecules. The device incorporates resistance heated ovens,

1960-01-01

288

On neutrino-atom scattering in searches for neutrino magnetic moments  

Microsoft Academic Search

In the experimental searches for neutrino magnetic moments using germanium detectors one studies the ionization channel in the neutrino-atom scattering. We find that the so-called stepping approximation to the neutrino-impact ionization is exact in the semiclassical limit, and that the deviations from this approximation are very small.

Konstantin A. Kouzakov; Alexander I. Studenikin; Mikhail B. Voloshin

2011-01-01

289

On neutrino-atom scattering in searches for neutrino magnetic moments  

NASA Astrophysics Data System (ADS)

In the experimental searches for neutrino magnetic moments using germanium detectors one studies the ionization channel in the neutrino-atom scattering. We find that the so-called stepping approximation to the neutrino-impact ionization is exact in the semiclassical limit, and that the deviations from this approximation are very small.

Kouzakov, Konstantin A.; Studenikin, Alexander I.; Voloshin, Mikhail B.

2012-08-01

290

Molecular beam studies of hot atom chemical reactions: Reactive scattering of energetic deuterium atoms  

SciTech Connect

A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H/sub 2/ /minus/> DH + H and the substitution reaction D + C/sub 2/H/sub 2/ /minus/> C/sub 2/HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible. 18 refs., 9 figs.

Continetti, R.E.; Balko, B.A.; Lee, Y.T.

1989-02-01

291

Impact Collision Ion Scattering Spectroscopy Applied to the Determination of Atomic Surface Structure  

NASA Astrophysics Data System (ADS)

The technique of impact collision ion scattering spectroscopy (ICISS) was used to investigate the atomic structure and low energy ion scattering dynamics from various surfaces. A new formalism for calculating the three-dimensional cross section for an ion to scatter sequentially and classically from two atoms has been developed. This method can be used to assist in the interpretation of ICISS data in terms of quantitative surface-structure models. Shadowing and blocking effects for energetic ions scattering from more than one atom are shown to be special cases of rainbow scattering. Even at keV energies and above, the cross section at the critical angle for scattering must be evaluated by quantum or semi-classical means to avoid the singularity in the classically calculated cross sections. In an ICISS investigation of the Ag(110) surface, a surface flux peak analysis demonstrated that the surface was not a complete monolayer, but rather contained 10-15% random vacancies. Subsurface Li^+ scattering results confirmed the oscillatory relaxation of the first two atomic layers of the surface, with Delta_{12} = -7.5% and Delta_{23} = 4.0%. Modeling of the neutralization mechanism for the He^+ scattering gave a best fit time-dependent Auger neutralization time constant of 0.84 +/- 0.08 fs. A neutralization study of 5 keV He^+ ions scattered from Au adatoms on the Si(111)- sqrt{3} x sqrt {3}-Au surface showed the He^+ ICISS data contained false shadowing features that were actually the result of local neutralization effects. Good agreement was obtained for a radially dependent ion-atom neutralization theory with rate R = Aexp (-ar) , where A and a are 15.5 fs^{ -1} and 1.94 A^{-1} , respectively. A detailed examination of the Si(111)- sqrt{3} x sqrt{3 })-Ag surface was also made. The 5 keV Li ^+ ICISS data gave evidence for Ag island formation at single monolayer coverages of silver, while the LEED, AES and LEIS data showed that at relatively high coverages of Ag (35 ML) small areas of sqrt {3} x sqrt{3} character were still present. Nine structurally different models of the sqrt{3} surface were tested and compared to the experimental ICISS results, with only the honeycomb-chained-trimer and missing-top-layer models found to be consistent with the Li^+ ICISS results.

Daley, Richard Stephen

1990-08-01

292

Circularly Polarized Laser Field-Induced Rescattering Plateaus in Electron-Atom Scattering  

NASA Astrophysics Data System (ADS)

Using effective range theory within a quasienergy state approach, we extend our recent analysis of the energy spectrum of electrons scattered from atoms in the presence of an intense, elliptically polarized laser field [1] to the case of atoms supporting negative ions having weakly bound p-electrons. Numerical results for e-H and e-F scattering are presented. In both cases there are two (i.e., low- and high-energy) plateau structures in the electron spectrum for any laser polarization, including for the case of circular polarization. The high-energy plateau is shown to originate from rescattering effects, thus providing the first example of the importance of recattering in the case of circular laser polarization. Basic equations of the rescattering scenario are deduced from our ab initio quantum results for the scattering amplitude in the quasiclassical limit. [1] A.V. Flegel et al., Phys. Lett. A 334, 197 (2005); J. Phys. B 38, L27 (2005).

Starace, Anthony F.; Flegel, A. V.

2005-05-01

293

Collisional lasing on a self-terminating transition 2?1Po1 — 2?1S0 in helium atom  

NASA Astrophysics Data System (ADS)

Lasing on a self-terminating transition 2?1Po1 — 2?1S0 (? = 2.058 ?m) in helium atom is studied for a single- and double-pulse operation regimes under electron beam pumping in pure helium and its mixtures with H2, N2, O2, CO2, H2O, NH3, and N2O. In pure helium, the maximal pulse duration is ~50 ns, which agrees with the calculated value. Recovery of lasing in the second pulse is observed at a time delay between the pulses of longer than 1.25 ?s. In adding CO2, N2O, NH3, and H2O, the relaxation rate for population of the metastable state He(2?1S0) increases, which makes the delay, needed for recovering lasing, shorter up to pulse merging in the case of H2O. At the exciting pulse base-level duration of 1.2 ?s, in mixtures of helium with NH3 and H2O, laser pulses with a duration of ~0.8 ?s are observed, which testifies that collisional quasi-cw lasing occurs. Mechanisms of collisional lasing are discussed.

Bel'skaya, E. V.; Bokhan, P. A.; Zakrevskii, D. E.; Lavrukhin, M. A.

2012-02-01

294

Self-trapping of helium in metals  

Microsoft Academic Search

Atomistic calculations are presented which demonstrate that helium atoms in a metal lattice are able to cluster with each other, producing vacancies and nearby self-interstitial defects. Even a small number of helium atoms is found to be sufficient to create these large distortions. As few as five interstitial helium atoms can spontaneously produce a lattice vacancy and nearby self-interstitial. An

W. D. Wilson; C. L. Bisson; M. I. Baskes

1981-01-01

295

Highly accurate analysis of the rotationally excited 2 1P (L = 1) and 2 3P (L = 1) states in helium atoms  

NASA Astrophysics Data System (ADS)

The rotationally excited 2 1P (L = 1) and 2 3P (L = 1) states in the inftyHe, 3He and 3He helium atoms are considered by using our multi-box variational procedure (Frolov 2001 Phys. Rev. E 64 036704). In particular, the total non-relativistic energies of these states for the inftyHe atom have been determined to very high accuracy. These energies are -2.123 843 086 498 101 357 17 au (2 1P state) and -2.133 164 190 779 283 204 14 au (2 3P state). A number of bound state properties for these two states in the inftyHe atom are also presented. The total energies of the 2 1P (L = 1) and 2 3P (L = 1) states in 3He and 4He have been determined. Some astrophysical applications of the rotationally excited 2 1P (L = 1) and 2 3P (L = 1) states in the helium atoms are briefly discussed.

Frolov, Alexei M.

2003-07-01

296

Cross sections for inelastic scattering of electrons by atoms: selected topics related to electron microscopy  

SciTech Connect

We begin with a resume of the Bethe theory, which provides a general framework for discussing the inelastic scattering of fast electrons and leads to powerful criteria for judging the reliability of cross-section data. The central notion of the theory is the generalized oscillator strength as a function of both the energy transfer and the momentum transfer, and is the only non-trivial factor in the inelastic-scattering cross section. Although the Bethe theory was initially conceived for free atoms, its basic ideas apply to solids, with suitable generalizations; in this respect, the notion of the dielectric response function is the most fundamental. Topics selected for discussion include the generalized oscillator strengths for the K-shell and L-shell ionization for all atoms with Z less than or equal to 30, evaluated by use of the Hartree-Slater potential. As a function of the energy transfer, the generalized oscillator strength most often shows a non-monotonic structure near the K-shell and L-shell thresholds, which has been interpreted as manifestations of electron-wave propagation through atomic fields. For molecules and solids, there are additional structures due to the scattering of ejected electrons by the fields of other atoms.

Inokuti, M.; Manson, S.T.

1982-01-01

297

Collective Atomic Recoil Lasing and Superradiant Rayleigh Scattering in a high-Q ring cavity  

NASA Astrophysics Data System (ADS)

Cold atoms in optical high-Q cavities are an ideal model system for long-range interacting particles. The position of two arbitrary atoms is, independent on their distance, coupled by the back-scattering of photons within the cavity. This mutual coupling can lead to collective instability and self-organization of a cloud of cold atoms interacting with the cavity fields. This phenomenon (CARL, i.e. Collective Atomic Recoil Lasing) has been discussed theoretically for years, but was observed only recently in our lab. The CARL-effect is closely linked to superradiant Rayleigh scattering, which has been intensely studied with Bose-Einstein condensates in free space. By adding a resonator the coherence time of the system, in which the instability occurs, can be strongly enhanced. This enables us to observe cavity-enhanced superradiance with both Bose-Einstein condensates and thermal clouds and allows us to close the discussion about the role of quantum statistics in superradiant scattering.

Slama, Sebastian; Krenz, Gordon; Bux, Simone; Zimmermann, Claus; Courteille, Philippe W.

2008-01-01

298

An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements  

NASA Technical Reports Server (NTRS)

A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.

Ross, H. Richard

1993-01-01

299

Collective Rayleigh scattering from dielectric particles: A classical theory of the Collective Atomic Recoil Laser  

NASA Astrophysics Data System (ADS)

A classical theory of Rayleigh scattering of electromagnetic radiation by dielectric particles is presented, in which the particles may interact cooperatively via common pump and probe radiation fields. The collective nature of the process is manifest both in the exponential growth of the bunching of the particles at the radiation wavelength to form a particle grating, and in the exponential growth of the counterpropagating probe radiation intensity. We call this `Collective Rayleigh Scattering'. This process arises from a fully classical description of the Collective Atomic Recoil Laser (CARL) with linear dielectric particles.

McNeil, B. W. J.; Robb, G. R. M.

1998-03-01

300

Neutrino Scattering on Atomic Electrons in Searches for the Neutrino Magnetic Moment  

SciTech Connect

The scattering of a neutrino on atomic electrons is considered in the situation where the energy transferred to the electrons is comparable to the characteristic atomic energies, as relevant to the current experimental search for the neutrino magnetic moment. The process is induced by the standard electroweak interaction as well as by the possible neutrino magnetic moment. Quantum-mechanical sum rules are derived for the inclusive cross section at a fixed energy deposited in the atomic system, and it is shown that the differential over the energy transfer cross section is given, modulo very small corrections, by the same expression as for free electrons, once all possible final states of the electronic system are taken into account. Thus, the atomic effects effectively cancel in the inclusive process.

Voloshin, M. B. [William I. Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455 (United States) and Institute of Theoretical and Experimental Physics, Moscow, 117218 (Russian Federation)

2010-11-12

301

Atom-dimer scattering in a three-component Fermi gas.  

PubMed

Ultracold gases of three distinguishable particles with large scattering lengths are expected to show rich few-body physics related to the Efimov effect. We have created three different mixtures of ultracold 6Li atoms and weakly bound 6Li2 dimers consisting of atoms in three different hyperfine states and studied their inelastic decay via atom-dimer collisions. We have found resonant enhancement of the decay due to the crossing of Efimov-like trimer states with the atom-dimer continuum in one mixture as well as minima of the decay in another mixture, which we interpret as a suppression of exchange reactions of the type |12+|3?|23+|1. Such a suppression is caused by interference between different decay paths and demonstrates the possibility of using Efimov physics to control the rate constants for molecular exchange reactions in the ultracold regime. PMID:20867517

Lompe, T; Ottenstein, T B; Serwane, F; Viering, K; Wenz, A N; Zürn, G; Jochim, S

2010-09-01

302

Spectral theory of quantum memory and entanglement via Raman scattering of light by an atomic ensemble  

NASA Astrophysics Data System (ADS)

We discuss theoretically quantum interface between light and a spin polarized ensemble of atoms with the spin ?1 based on an off-resonant Raman scattering. We present the spectral theory of the light atom interaction and show how particular spectral modes of quantum light couple to spatial modes of the extended atomic ensemble. We show how this interaction can be used for quantum memory storage and retrieval and for deterministic entanglement protocols. The proposed protocols are attractive due to their simplicity since they involve just a single pass of light through atoms without the need for elaborate pulse shaping or quantum feedback. As a practically relevant example we consider the interaction of a light pulse with hyperfine components of D1 line of Rb87 . The quality of the proposed protocols is verified via analytical and numerical analysis.

Mishina, O. S.; Kupriyanov, D. V.; Müller, J. H.; Polzik, E. S.

2007-04-01

303

An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis.  

PubMed

The crystal structure of thin films grown by atomic layer deposition (ALD) will determine important performance properties such as conductivity, breakdown voltage, and catalytic activity. We report the design of an atomic layer deposition chamber for in situ x-ray analysis that can be used to monitor changes to the crystal structural during ALD. The application of the chamber is demonstrated for Pt ALD on amorphous SiO2 and SrTiO3 (001) using synchrotron-based high resolution x-ray diffraction, grazing incidence x-ray diffraction, and grazing incidence small angle scattering. PMID:24880424

Geyer, Scott M; Methaapanon, Rungthiwa; Johnson, Richard W; Kim, Woo-Hee; Van Campen, Douglas G; Metha, Apurva; Bent, Stacey F

2014-05-01

304

An atomic layer deposition chamber for in situ x-ray diffraction and scattering analysis  

NASA Astrophysics Data System (ADS)

The crystal structure of thin films grown by atomic layer deposition (ALD) will determine important performance properties such as conductivity, breakdown voltage, and catalytic activity. We report the design of an atomic layer deposition chamber for in situ x-ray analysis that can be used to monitor changes to the crystal structural during ALD. The application of the chamber is demonstrated for Pt ALD on amorphous SiO2 and SrTiO3 (001) using synchrotron-based high resolution x-ray diffraction, grazing incidence x-ray diffraction, and grazing incidence small angle scattering.

Geyer, Scott M.; Methaapanon, Rungthiwa; Johnson, Richard W.; Kim, Woo-Hee; Van Campen, Douglas G.; Metha, Apurva; Bent, Stacey F.

2014-05-01

305

Measurements of ultra-low-energy electron scattering cross sections of atoms and molecules  

NASA Astrophysics Data System (ADS)

A new experimental technique for the total cross section measurements of ultra-low energy electron collisions with atoms and molecules utilizing the synchrotron radiation is presented. The technique employs a combination of the penetrating field technique and the threshold photoionization of rare gas atoms using the synchrotron radiation as an electron source in order to produce a high resolution electron beam at very low energy. Absolute total cross sections for electron scattering from He, Ne, Ar, Kr, and Xe in the energy region from extremely low electron energy to 20 eV are presented.

Kitajima, M.; Shigemura, K.; Kurokawa, M.; Odagiri, T.; Kato, H.; Hoshino, M.; Tanaka, H.; Ito, K.

2014-03-01

306

QED effects in scattering processes involving atomic bound states: Radiative recombination  

NASA Astrophysics Data System (ADS)

The standard perturbative expansion of the S matrix cannot generally be used in the treatment of atomic scattering processes, involving atomic bound states, due to the special type of singularity that can appear here. It is demonstrated in the present paper that as a consequence of the optical theorem for free particles the effective Hamiltonian is closely related to the total cross section, a relation that is valid also when bound states are present. This implies that methods designed for structure calculations also can be used in dynamical processes. We have found that the covariant-evolution-operator technique that we have developed for structure calculations is here particularly useful. This is a consequence of the fact that the regular part of this operator (the Green's operator), running over all times, is essentially equal to the effective Hamiltonian and therefore directly related to the scattering cross section. In this paper the procedure is demonstrated for the case of radiative recombination.

Lindgren, Ingvar; Salomonson, Sten; Holmberg, Johan

2014-06-01

307

Atomic Optics in Low Energy Ion Scattering and Surface Imaging by SARIC.  

NASA Astrophysics Data System (ADS)

Well ordered structures of crystalline surfaces act like nature's smallest lenses, i. e. atomic lenses, when a monoenergetic beam of noble gas ions interacts with the crystal in the low keV energy range. These can be either magnifying or focusing lenses, constituting a basis for a new area of atomic optics. A new experimental approach based on this phenomenon, Scattering And Recoiling Imaging Spectrometry (SARIS), allows some surface structural features to be magnified in real space as high as 10^8 times. In order to elucidate surface structure from SARIS images, a new computer code based on the binary collision approximation, called Scattering And Recoiling Imaging Code (SARIC), was developed and successfully tested. The basics of SARIS and the details of SARIC will be discussed. SARIC simulated images of (001), (011), and (111) planes of some fcc metals will be presented.

Bykov, V.; Marton, D.; Rabalais, J. W.

1997-03-01

308

Analytic description of elastic electron-atom scattering in an elliptically polarized laser field  

NASA Astrophysics Data System (ADS)

An analytic description of laser-assisted electron-atom scattering (LAES) in an elliptically polarized field is presented using time-dependent effective range (TDER) theory to treat both electron-laser and electron-atom interactions nonperturbatively. Closed-form formulas describing plateau features in LAES spectra are derived quantum mechanically in the low-frequency limit. These formulas provide an analytic explanation for key features of the LAES differential cross section. For the low-energy region of the LAES spectrum, our result generalizes the Kroll-Watson formula to the case of elliptic polarization. For the high-energy (rescattering) plateau in the LAES spectrum, our result generalizes prior results for a linearly polarized field valid for the high-energy end of the rescattering plateau [Flegel , J. Phys. BJPAPEH0953-407510.1088/0953-4075/42/24/241002 42, 241002 (2009)] and confirms the factorization of the LAES cross section into three factors: two field-free elastic electron-atom scattering cross sections (with laser-modified momenta) and a laser field-dependent factor (insensitive to the scattering potential) describing the laser-driven motion of the electron in the elliptically polarized field. We present also approximate analytic expressions for the exact TDER LAES amplitude that are valid over the entire rescattering plateau and reduce to the three-factor form in the plateau cutoff region. The theory is illustrated for the cases of e-H scattering in a CO2-laser field and e-F scattering in a midinfrared laser field of wavelength ?=3.5?m, for which the analytic results are shown to be in good agreement with exact numerical TDER results.

Flegel, A. V.; Frolov, M. V.; Manakov, N. L.; Starace, Anthony F.; Zheltukhin, A. N.

2013-01-01

309

Self-trapping of helium in metals  

Microsoft Academic Search

Atomistic calculations are presented which demonstrate that helium atoms in a metal lattice are able to cluster with each other, producing vacancies and nearby self-interstitial defects. Even a small number of helium atoms is found to be sufficient to create these large distortions. As few as five interstitial helium can spontaneously produce a lattice vacancy and nearby self-interstitial. An eight-helium-atom

W. D. Wilson; C. L. Bisson; M. I. Baskes

1981-01-01

310

Simultaneous characterization of protein coated iron oxide nanoparticles with nuclear inelastic scattering and atomic force microscopy  

NASA Astrophysics Data System (ADS)

Bovine serum albumin coated magnetic iron oxide nanoparticles (IONPs), which were synthesized using a co-precipitation method with 57Fe have been subject to a combined study using atomic force microscopy (AFM) and nuclear inelastic scattering (NIS). The obtained partial density of vibrational states (pDOS) shows evidence for lattice stiffening and a pronounced mode at 23 meV compared to thin film magnetite at room temperature.

Marx, J.; Huang, H.; Faus, I.; Rackwitz, S.; Wolny, J. A.; Schlage, K.; Ulber, R.; Wille, H.-C.; Schünemann, V.

2014-04-01

311

Extended wave packet dynamics; exact solution for collinear atom, diatomic molecule scattering  

NASA Astrophysics Data System (ADS)

The semiclassical wave packet dynamics method of Heller is extended to provide a formally exact theory of quantum mechanical motion for multidimensional anharmonic systems by introducing a complete, orthonormal, time-dependent basis of generalized oscillator functions. The exact wavefunction is expressed in terms of this basis and the expansions are shown to develop according to linear, coupled first-order differential equations. Application to collinear inelastic atom-diatomic molecule scattering demonstrates the feasibility and convergence of the new method.

Coalson, R. D.; Karplus, M.

1982-08-01

312

X-ray resonant Raman scattering from noble gas atoms and beyond  

NASA Astrophysics Data System (ADS)

We discuss general characteristics of the resonant X-ray scattering and briefly illustrate its applications in atomic, molecular and solid state physics by a few selected examples. The Ljubljana high resolution spectrometer set-up is presented, which was recently employed at ELETTRA and ESRF synchrotron beamlines to study X-ray emission of inner-shell excited states of xenon and argon, and of simple sulfur containing molecules and solid compounds.

Žitnik, M.; Kav?i?, M.; Bu?ar, K.; Miheli?, A.

2009-01-01

313

On neutrino-atom scattering in searches for neutrino magnetic moments  

Microsoft Academic Search

In the experimental searches for neutrino magnetic moments using germanium\\u000adetectors one studies the ionization channel in the neutrino-atom scattering.\\u000aWe find that the so-called stepping approximation to the neutrino-impact\\u000aionization is exact in the semiclassical limit, and that the deviations from\\u000athis approximation are very small.

Konstantin A. Kouzakov; Alexander I. Studenikin; Mikhail B. Voloshin

2011-01-01

314

Applicability of modified effective-range theory to positron-atom and positron-molecule scattering  

SciTech Connect

We analyze low-energy scattering of positrons on Ar atoms and N{sub 2} molecules using the modified effective-range theory (MERT) developed by O'Malley, et al. [J. Math. Phys. 2, 491 (1961)]. We use the formulation of MERT based on exact solutions of the Schroedinger equation with polarization potential rather than low-energy expansions of phase shifts into momentum series. We show that MERT describes the experimental data well, provided that effective-range expansion is performed both for s- and p-wave scattering, which dominate in the considered regime of positron energies (0.4-2 eV). We estimate the values of the s-wave scattering length and the effective range for e{sup +}-Ar and e{sup +}-N{sub 2} collisions.

Idziaszek, Zbigniew; Karwasz, Grzegorz [CNR-INFM BEC Center, I-38050 Povo (Italy) and Centrum Fizyki Teoretycznej, Polska Akademia Nauk, 02-668 Warsaw (Poland); Instytut Fizyki, Uniwersytet Mikolaja Kopernika, 87-100 Torun (Poland)

2006-06-15

315

Search for inelastic electrons scattered off ions in energetic ion-atom collisions  

NASA Astrophysics Data System (ADS)

The collision of target electrons with ionic projectiles, in highly asymmetric ion-atom collisions, can be simulated within the impulse approximation (IA) by a beam of electrons scattering off the projectile ion, with a collision energy broadened by the momentum distribution (Compton profile) of the target. This description works particularly well for 180° elastic scattering of target electrons off the ion (Phys. Rev. A 41 (1990) 4816 [1]) appearing in the laboratory as the well known binary encounter electron peak. Inelastic processes due to target-electron-projectile-electron interactions (e-e) such as e-e excitation (Phys. Rev. Lett. 62 (1989) 2261 [2]) and e-e ionization (Phys. Rev. Lett. 63 (1990) 1938; J. Phys. B 24 (1991) 977; Phys. Rev. A 46 (1992) 1374; Phys. Rev. Lett. 69 (1992) 3033, 72 (1994) 3170, 72 (1994) 3166 [3-8]) are also well documented. However, for these processes, the target electron undergoing inelastic scattering has never been explicitly identified and measured in ion-atom collisions. A simple theoretical Born-IA treatment gives the expected double differential cross sections and their angular distributions for H-like ions in collision with H 2 targets. The viability of observing these effects in ion-atom collisions by electron spectroscopy is investigated.

Zouros, T. J. M.; Liao, C.; Hagmann, S.; Toth, G.; Montenegro, E. C.; Richard, P.; Benis, E. P.

1995-05-01

316

Oxygen adsorption on GaAs(0 0 1) surface by edge-effect rainbow enhancement in ion scattering using the three-atom scattering model  

NASA Astrophysics Data System (ADS)

The backscattered intensity for a triple-scattering sequence in which the second target atom is lighter than the projectile has been calculated using the three-atom scattering model (THASM). The numerical calculations are performed for the case of 12 keV Ar + ions incident along the [1 1 0] direction of a GaAs(0 0 1) surface. An edge-effect rainbow singularity that drastically enhances the yield of backscattered intensity results from the forward scattering of argon by oxygen adsorbed on the GaAs(0 0 1) surface. This classical resonance can be employed for the determination of position of oxygen adsorbed on the GaAs(0 0 1) surface with high sensitivity. From the comparison of THASM results with TOF-ICISS data, it was found that the oxygen atoms are adsorbed in twofold hollow sites 0.50 Å below surface gallium atoms along the [1 1 0] azimuth.

Takeuchi, Wataru; Yamamura, Yasunori

1999-06-01

317

The Distribution of Angular Correlation in Two-Electron Atoms. I. The 2(1)S State of Helium.  

National Technical Information Service (NTIS)

Calculations of the distribution of angular correlation in the 2(1)S state of helium were made for the case of t = 0. The nodal region in the wave function has a marked effect upon angular correlation in that it changes the angular interaction from repuls...

J. P. Tatum

1968-01-01

318

Rutherford backscattering oscillation in scanning helium-ion microscopy  

NASA Astrophysics Data System (ADS)

Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He+) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He+ beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the ``Z2-oscillations'' of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets.

Kostinski, Sarah; Yao, Nan

2011-03-01

319

Inversionless generation of radiation in stimulated Raman and hyper-Raman scattering at allowed transitions in atoms  

Microsoft Academic Search

The theory of stimulated Raman and hyper-Raman scattering involving resonance transitions to the ground states of atoms is\\u000a presented, where the atoms are modeled by the three-level cascade quantum system. The possibility of efficient inversionless\\u000a generation of radiation is shown for all three transitions participating in the stimulated Raman scattering and for the two\\u000a electric-dipole allowed transitions in the hyper-Raman

V. P. Kochanov

2009-01-01

320

Effect of electron correlation on high-order-harmonic generation of helium atoms in intense laser fields: Time-dependent generalized pseudospectral approach in hyperspherical coordinates  

SciTech Connect

We present a time-dependent generalized pseudospectral (TDGPS) approach in hyperspherical coordinates for fully ab initio nonperturbative treatment of multiphoton dynamics of atomic systems in intense laser fields. The procedure is applied to the investigation of high-order-harmonic generation (HHG) of helium atoms in ultrashort laser pulses at a KrF wavelength of 248.6 nm. The six-dimensional coupled hyperspherical-adiabatic-channel equations are discretized and solved efficiently and accurately by means of the TDGPS method. The effects of electron correlation and doubly excited states on HHG are explored in detail. A HHG peak with Fano line profile is identified which can be attributed to a broad resonance of doubly excited states. Comparison of the HHG spectra of the ab initio two-electron and the single-active-electron model calculations is also presented.

Guan Xiaoxu; Chu, S.-I [Department of Chemistry, University of Kansas, and Kansas Center for Advanced Scientific Computing, Lawrence, Kansas 66045 (United States); Tong, X.-M. [Institute of Materials Science, Graduate School of Pure and Applied Science, and Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan)

2006-02-15

321

Mechanism map for nucleation and growth of helium bubbles in metals  

Microsoft Academic Search

The total free energy of a system containing helium bubbles and point defects (vacancies, helium and self-interstitial atoms) was evaluated and activation barrier for forming a helium bubble was derived, where the effect of helium on helium bubble formation is clearly shown. The rates of inflow to a helium bubble and outflow from a helium bubble were evaluated for vacancies,

Kazunori Morishita; Ryuichiro Sugano

2006-01-01

322

Quantum fluid dynamics based current-density functional study of a helium atom in a strong time-dependent magnetic field  

NASA Astrophysics Data System (ADS)

Evolution of the helium atom in a strong time-dependent (TD) magnetic field ( B) of strength up to 1011 G is investigated through a quantum fluid dynamics (QFD) based current-density functional theory (CDFT). The TD-QFD-CDFT computations are performed through numerical solution of a single generalized nonlinear Schrödinger equation employing vector exchange-correlation potentials and scalar exchange-correlation density functionals that depend both on the electronic charge-density and the current-density. The results are compared with that obtained from a B-TD-QFD-DFT approach (based on conventional TD-DFT) under similar numerical constraints but employing only scalar exchange-correlation potential dependent on electronic charge-density only. The B-TD-QFD-DFT approach, at a particular TD magnetic field-strength, yields electronic charge- and current-densities as well as exchange-correlation potential resembling with that obtained from the time-independent studies involving static (time-independent) magnetic fields. However, TD-QFD-CDFT electronic charge- and current-densities along with the exchange-correlation potential and energy differ significantly from that obtained using B-TD-QFD-DFT approach, particularly at field-strengths >109 G, representing dynamical effects of a TD field. The work concludes that when a helium atom is subjected to a strong TD magnetic field of order >109 G, the conventional TD-DFT based approach differs "dynamically" from the CDFT based approach under similar computational constraints.

Vikas, Hash(0x125f4490)

2011-02-01

323

Change in total angular momentum within the z 3° titanium excited state induced by collisions with ground-state argon, neon, and helium atoms  

NASA Astrophysics Data System (ADS)

Collisions that produce a change in the total angular momentum and quenching processes involving the triplet z 3° titanium excited level and noble gases have been studied by laser perturbation and time-resolved spectroscopy. Titanium atoms are produced in a hollow-cathode discharge, and the analysis of resonance and sensitized fluorescence light decays enable us to determine total-angular-momentum-changing (J-changing) and quenching cross sections induced by collisions with helium, neon, and argon atoms. The thermally averaged J-changing cross section (z 3F ° i-->z 3F ° j) in units of 10-16 cm2 are ?¯4-->2=1.7+/-0.5, 0.7+/-0.06, 3.1+/-1 ?¯4-->3=11+/-2, 1.4+/-0.1, 11+/-1 ?¯3-->2=7+/-2, 2.2+/-0.3, 14+/-2, respectively, for helium, neon, and argon colliding partners. As for alkali-metal-noble-gas collisions, a pronounced minimum of the J-changing cross sections is obtained for the titanium (z 3F °)-neon collisions. Radiative destruction probabilities of the z 3F ° j (j=4,3,2) titanium sublevels have been measured also, and good agreement with accepted values is found.

Dezert, D.; Quichaud, V.; Degout, D.; Catherinot, A.

1986-12-01

324

Three-dimensional N-atom model for computer simulation of impact-collision ion scattering spectroscopy  

NASA Astrophysics Data System (ADS)

A new method for a computer simulation of impact-collision ion scattering spectroscopy (ICISS), a three-dimensional N-atom (3DNA) model, has been developed as an extension of the three-dimensional three-atom (3D3A) model [W. Hayami, R. Souda, T. Aizawa, Y. Ishizawa, Surf. Sci. 303 (1994) 247]. This 3DNA model can include arbitrary number of atoms, and the scattering cross-section of the system at an arbitrary scattering angle is analytically calculated as a function of impact parameter only, so that the computational time is as short as that of the 3D3A model. As an example, an ICISS spectrum of a four-atom system has been calculated, showing a different critical angle from the 3D3A model when two shadowcones overlap on the target atom.

Hayami, Wataru; Aizawa, Takashi; Asari, Eiji; Souda, Ryutaro

2000-02-01

325

All-atom ensemble modeling to analyze small angle X-ray scattering of glycosylated proteins  

PubMed Central

Summary The flexible and heterogeneous nature of carbohydrate chains often renders glycoproteins refractory to traditional structure determination methods. Small Angle X-ray scattering (SAXS) can be a useful tool for obtaining structural information of these systems. All-atom modeling of glycoproteins with flexible glycan chains was applied to interpret the solution SAXS data for a set of glycoproteins. For simpler systems (single glycan, with a well defined protein structure), all-atom modeling generates models in excellent agreement with the scattering pattern, and reveals the approximate spatial occupancy of the glycan chain in solution. For more complex systems (several glycan chains, or unknown protein substructure), the approach can still provide insightful models, though the orientations of glycans become poorly determined. Ab initio shape reconstructions appear to capture the global morphology of glycoproteins, but in most cases offer little information about glycan spatial occupancy. The all-atom modeling methodology is available as a webserver at http://modbase.compbio.ucsf.edu/allosmod-foxs.

Guttman, Miklos; Weinkam, Patrick; Sali, Andrej; Lee, Kelly K.

2013-01-01

326

Atomic Force Microscopy and Light Scattering of Small Unilamellar Actin-Containing Liposomes  

PubMed Central

Three-dimensional networks of filamentous actin (F-actin) encapsulated inside phosphatidylcholine liposomes are currently being used in an effort to model the cytoskeleton and plasma membrane of eukaryotic cells. In this article, unilamellar lipid vesicles consisting of egg yolk-derived phosphatidylcholine encapsulating monomeric actin (G-actin) were made via extrusion in low ionic strength buffer (G-buffer). Vesicle shape and structure in these dispersions was studied using a combination of fluid-tapping atomic force microscopy, and multiangle static light scattering. After subjecting the liposome dispersion to high ionic strength polymerization buffer (F-buffer) containing K+ ions, atomic force microscopy imaging and light scattering of these liposomes indicated the formation of specialized structures, including an overall liposome structure transformation from spherical to torus, disk-shaped geometries and tubular assemblies. Several atomic force microscopy control measurements were made to ascertain that the specialized structures formed were not due to free G-actin and F-actin self-assembling on the sample surface, plain liposomes exposed to G- and F-buffer, or liposomes encapsulating G-actin. Liposomes encapsulating G-actin assumed mostly thin disk shapes and some large irregularly shaped aggregates. In contrast, liposomes encapsulating polymerized actin assumed mostly torus or disk shapes along with some high aspect ratio tubular structures.

Palmer, Andre F.; Wingert, Philip; Nickels, Jonathan

2003-01-01

327

Scattering properties of ground-state spin-polarized atomic hydrogen  

NASA Astrophysics Data System (ADS)

In this paper, the scattering properties of ground-state spin-polarized atomic hydrogen (H?) are studied at 0 K using the Lippmann-Schwinger formalism. The total, diffusion and viscosity cross sections, as well as the S-wave scattering length, are calculated. The S-wave scattering cross section is found to be the most significant partial wave contributing to the total cross section at low energy. The contribution of the higher angular momentum waves, especially the D-wave (?=2), to the scattering increases with increasing relative momentum k. Our calculations are performed for three triplet-state potentials: Morse-type, Silvera and Born-Oppenheimer potentials. It is also noted that as k?0, the results of the Morse potential are larger than those of the Silvera and Born-Oppenheimer potentials. This is because of the exponential tail of the Morse potential which falls off more rapidly than the r-6 behavior of the Silvera and Born-Oppenheimer potentials. Also, the Morse potential is relatively shallower than the other two potentials. For high k, the Morse cross sections approach the corresponding Silvera cross sections. This is because these triplet-state potentials have almost the same short-range part. The total cross sections reflect the quantum oscillations arising from the diffraction caused by the repulsive short-range part of the potential. Our results are consistent with those obtained by other methods.

Joudeh, B. R.

2013-07-01

328

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth  

SciTech Connect

Investigations in this laboratory have focused on the surface structure and dynamics of ionic insulators and on epitaxial growth onto alkali halide crystals. In the later the homoepitaxial growth of NaCl/NaCl(001) and the heteroepitaxial growth of KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been studied by monitoring the specular He scattering as a function of the coverage and by measuring the angular and energy distributions of the scattered He atoms. These data provide information on the surface structure, defect densities, island sizes and surface strain during the layer-by-layer growth. The temperature dependence of these measurements also provides information on the mobilities of the admolecules. He atom scattering is unique among surface probes because the low-energy, inert atoms are sensitive only to the electronic structure of the topmost surface layer and are equally applicable to all crystalline materials. It is proposed for the next year to exploit further the variety of combinations possible with the alkali halides in order to carry out a definitive study of epitaxial growth in the ionic insulators. The work completed so far, including measurements of the Bragg diffraction and surface dispersion at various stages of growth, appears to be exceptionally rich in detail, which is particularly promising for theoretical modeling. In addition, because epitaxial growth conditions over a wide range of lattice mismatches is possible with these materials, size effects in growth processes can be explored in great depth. Further, as some of the alkali halides have the CsCl structure instead of the NaCl structure, we can investigate the effects of the heteroepitaxy with materials having different lattice preferences. Finally, by using co-deposition of different alkali halides, one can investigate the formation and stability of alloys and even alkali halide superlattices.

Not Available

1992-01-01

329

Atomic-scale dynamics inside living cells explored by neutron scattering  

PubMed Central

Single-particle neutron spectroscopy has contributed important experimental data on molecular dynamics in biological systems. The technique provides information on atomic and molecular motions in macromolecules on the picosecond to the nanosecond time scale, which are essential to biological function. Here, we report on recent neutron measurements performed directly in living cells by using isotope labelling to explore the dynamics of specific cellular components. The paper proposes an integrated view of results on atomic-scale cell water dynamics, internal and global macromolecular motions and solvent isotope effect on macromolecular dynamics. The work established the specific usefulness of the neutron scattering technique to get insight into biologically relevant dynamical features, in particular through comparative measurements. The method developed can now be applied to look for dynamical signatures related to cell characteristics in many different cell types and organelles.

Jasnin, Marion

2009-01-01

330

Absolute Measurements of Total Cross Sections for the Scattering of Low-Energy Electrons by Atomic and Molecular Oxygen  

Microsoft Academic Search

The atom-beam recoil technique has been used to measure absolute total cross sections for the scattering of electrons by atomic and molecular oxygen at 22 energies between 0.5 and 11.3 eV, with additional data obtained up to 100 eV. In this method, a modulated electron beam cross-fires an atom beam, whose attenuation at the modulation frequency is observed. A mechanical

Gabriel Sunshine; Bertrand B. Aubrey; Benjamin Bederson

1967-01-01

331

Elastic Electron Scattering by Laser-Excited (sup 138)Ba (...6s6p (sup 1)P(sub 1)) Atoms  

NASA Technical Reports Server (NTRS)

The result of a joint experimental and theoretical study concerning elastic electron scattering by laser-excited (sup 138)Ba (...6s6p (sup 1)P(sub 1)) atoms are presented. From these studies, we extracted differential scattering cross sections (DCS's) and collision parameters for elastic scattering by the coherently prepared (sup 1)P(sub 1) atoms.

Csanak, G.

1997-01-01

332

X-ray radiation from nonlinear Thomson scattering of an intense femtosecond laser on relativistic electrons in a helium plasma.  

PubMed

We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a(0). This radiative process is dominant for a(0) greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma. PMID:14611585

Ta Phuoc, K; Rousse, A; Pittman, M; Rousseau, J P; Malka, V; Fritzler, S; Umstadter, D; Hulin, D

2003-11-01

333

State-Selective and Total Single-Capture Cross Sections for Fast Collisions of Multiply Charged Ions with Helium Atoms  

NASA Astrophysics Data System (ADS)

The four-body boundary corrected first Born approximation (CB1-4B) is used to calculate the single electron capture cross sections for collisions between fully stripped ions (He2+, Be4+, B5+ and C6+) and helium target at intermediate and high impact energies. The main goal of this study is to assess the usefulness of the CB1-4B method at intermediate and high impact energies for these collisions. Detailed comparisons with the measurements are carried out and the obtained theoretical cross sections are in reasonable agreement with the available experimental data.

Man?ev, Ivan; Milojevi?, Nenad; Belki?, Dževad

2013-11-01

334

Ejection of quasi-free-electron pairs from the helium-atom ground state by single-photon absorption.  

PubMed

We investigate the single-photon double ionization of helium at photon energies of 440 and 800 eV. We observe doubly charged ions with close to zero momentum corresponding to electrons emitted back to back with equal energy. These slow ions are the unique fingerprint of an elusive quasifree photon double ionization mechanism predicted by Amusia et al. nearly four decades ago [J. Phys. B 8, 1248 (1975)]. It results from the nondipole part of the electromagnetic interaction. Our experimental data are supported by calculations performed using the convergent close-coupling and time-dependent close-coupling methods. PMID:23862999

Schöffler, M S; Stuck, C; Waitz, M; Trinter, F; Jahnke, T; Lenz, U; Jones, M; Belkacem, A; Landers, A L; Pindzola, M S; Cocke, C L; Colgan, J; Kheifets, A; Bray, I; Schmidt-Böcking, H; Dörner, R; Weber, Th

2013-07-01

335

ASPIN: An all spin scattering code for atom molecule rovibrationally inelastic cross sections  

NASA Astrophysics Data System (ADS)

We present in this work a new computational code for the quantum calculation of integral cross sections for atom-molecule (linear) scattering processes. The atom is taken to be structureless while the molecule can be in its singlet, doublet, or triplet spin states and can be treated as either a rigid rotor or a rovibrational target. All the relevant state-to-state integral cross sections, and their sums over final states, can be calculated with the present code, for which we also describe in detail the various component routines. Program summaryProgram title: ASPIN Catalogue identifier: AEBO_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBO_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 99 596 No. of bytes in distributed program, including test data, etc.: 1 267 615 Distribution format: tar.gz Programming language: Fortran/MPI Computer: AMD OPTERON COMPUTING SYSTEMS, model TYAN GX28 (B2882) Operating system: SuSE LINUX Professional 9 RAM: 128 GB Classification: 2.6 External routines: LAPACK/BLAS Nature of problem: Scattering of a diatomic molecule in its ?1, ?2, or ?3 spin states with an atom in its S1 state. Partial and integral cross sections. Solution method: The coupled channel equations that describe the scattering process are solved through the propagation of the reactance K matrix employing a modification of the Variable Phase Method [1-3]. Restrictions: Depending on the vib-rotational base used the problem may or may not fit into available RAM memory because all the runtime relevant quantities are stored on RAM memory instead of on disk. Additional comments: Both serial and parallel implementations of the program are provided. The CPC Librarian was not able to successfully run the parallel version. Running time: For simple and converged calculations a usual running time is in the order of a few minutes in the computer mentioned above, being shorter for the singlet and longer for the triplet. References: [1] F. Calogero, Variable Phase Approach to Potential Scattering, New York, 1967. [2] A. Degasperis, Il Nuovo Cimento 34 (1964) 1667. [3] C. Zemach, Il Nuovo Cimento 33 (1964) 939.

López-Durán, D.; Bodo, E.; Gianturco, F. A.

2008-12-01

336

Time of Flight, Low Energy and Impact Collision Ion Scattering Spectroscopies Applied to the Study of Atomic Surfaces.  

NASA Astrophysics Data System (ADS)

An apparatus was built to perform Time of Flight Low Energy Ion Scattering (LEIS) Spectroscopies and implemented to study the neutralization of Ne^+ scattered from Ag. Both 5 and 10 keV Ne^+ scattered from Ag(001) displayed considerable path dependent neutralization while that of Na^+ was negligible. A study of sqrt {3} x sqrt{3} Ag/Si(111) surfaces showed that the neutralization probability for 5 keV Ne^+ scattered from Ag at a nominal angle of 135^circ is dependent on the density of Ag atoms present in the epitaxial monolayer. The neutralization probability of normal incidence 1-11 keV Ne^+ scattered along a (110) azimuth of Ag(001) was exponentially dependent on the primary ion energy. A computer algorithm was developed to transform the raw time of flight distributions to energy distributions without knowing the actual energies of the scattered ions. A computational study of a previously collected Impact Collision Ion Scattering Spectroscopy (ICISS) scan showed that the Cu(110) 2 x 1 - O reconstruction was best described by a missing row model. The missing rows refer to the alternating (001) rows of copper atoms which are absent when Cu(110) reconstructs. Correlated triple scattering (CTS), in which an ion can interact with the shadowing atom of a two atom target both before and after the backscattering interaction, was examined for scattering near 180^circ and 135^circ. The CTS is much more sensitive to changes in the scattering geometry than scattering involving only two interactions making it a potentially powerful tool for surface analysis. LEIS and ICISS were used to study a disordered Au/GaAs(001) surface. For depositions on room temperature GaAs(001), shadowing of Au by substrate atoms at low scattering angles showed that Au penetrated an estimated two to three atomic planes below the GaAs surface. A combination of LEIS and ICISS experiments were used to monitor the evolution of the Au/GaAs surface morphology as a function of annealing temperature. The thin Au films deposited on GaAs were sensitive to bombardment by low energy (5 keV) He ions. Fluences as low as 10^{15} ions cm^{-2} caused enhanced diffusion of the Au into the GaAs substrate.

Charatan, Robert Morris

337

Computing many-body wave functions with guaranteed precision: The first-order Møller-Plesset wave function for the ground state of helium atom  

NASA Astrophysics Data System (ADS)

We present an approach to compute accurate correlation energies for atoms and molecules using an adaptive discontinuous spectral-element multiresolution representation for the two-electron wave function. Because of the exponential storage complexity of the spectral-element representation with the number of dimensions, a brute-force computation of two-electron (six-dimensional) wave functions with high precision was not practical. To overcome the key storage bottlenecks we utilized (1) a low-rank tensor approximation (specifically, the singular value decomposition) to compress the wave function, and (2) explicitly correlated R12-type terms in the wave function to regularize the Coulomb electron-electron singularities of the Hamiltonian. All operations necessary to solve the Schrödinger equation were expressed so that the reconstruction of the full-rank form of the wave function is never necessary. Numerical performance of the method was highlighted by computing the first-order Møller-Plesset wave function of a helium atom. The computed second-order Møller-Plesset energy is precise to ~2 microhartrees, which is at the precision limit of the existing general atomic-orbital-based approaches. Our approach does not assume special geometric symmetries, hence application to molecules is straightforward.

Bischoff, Florian A.; Harrison, Robert J.; Valeev, Edward F.

2012-09-01

338

Solutions of the Schrödinger equations for lithium and excited helium (2 1S) atoms with a correlation-function hyperspherical harmonic and generalized Laguerre-function expansion method  

NASA Astrophysics Data System (ADS)

By introducing a simple spatially symmetric correlation function, we have modified a hyperspherical harmonic and generalized Laguerre function (HHGLF) into a correlation function HHGLF (CFHHGLF) expansion method and used it to solve directly the Schrödinger equations of ground-state lithium and excited helium (2 1S) atoms. In such a scheme, the wave function of the lithium atom is decomposed into the product of a correlation function X (X=exp[-Z(r1+r2+ra)]), and a wave function ? expanded in the same way as in the HHGLF method. The eigenenergy can be calculated explicitly by solving a simple secular equation. We have obtained a ground-state eigenenergy which is much better than the Hartree-Fock in precision and approaches the experimental value. The result indicates that it is possible to generalize the hyperspherical harmonic method to a four-body atomic system more successfully. In addition, the exact eigenenergy of the excited He (2 1S) has also been obtained with the CFHHGLF method with X=exp[-2(r1+r2)].

Wang, Yixuan; Deng, Conghao; Feng, Dacheng

1995-01-01

339

Continuous-flow determination of aqueous sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry with gas-phase sample introduction  

NASA Astrophysics Data System (ADS)

A simple continuous-flow generation of volatile hydrogen sulfide and sulfur dioxide by acidification of aqueous sulfide and sulfite ions, respectively, is described for the determination of low concentrations of sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the MIP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Sulfur atomic emission lines at 180.73, 182.04 and 217.05 nm have been selected as the analytical lines. Of the various acids examined, 1.0 M hydrochloric acid is the most favorable for both the generation of hydrogen sulfide from sulfide ions and sulfur dioxide from sulfite ions. Either generated hydrogen sulfide or sulfur dioxide is separated from the solution in a simple gas-liquid separator and swept into the helium stream of a microwave-induced plasma for analysis. The best attainable detection limits (3 ? criterion) for sulfur at 180.73 nm were 0.13 and 1.28 ng ml -1 for the generation of hydrogen sulfide and sulfur dioxide, respectively, with the corresponding background equivalent concentrations of 20.9 and 62.2 ng ml -1 in sulfur concentration. The typical analytical working graphs obtained under the optimized experimental conditions were rectilinear over approximately four orders of magnitude in sulfur concentration. The present method has been successfully applied to the recovery test of the sulfide spiked to waste water samples and to the determination of sulfite in some samples of commercially available wine.

Nakahara, Taketoshi; Mori, Toshio; Morimoto, Satoru; Ishikawa, Hiroshi

1995-06-01

340

Spin-dependent electron-atom scattering: What can be learned from the simplest systems  

SciTech Connect

Bederson first summarized the requirements of the {open_quotes}complete{close_quotes} scattering experiment, in which the magnitudes and phases of all scattering amplitudes would be determined as functions of both scattering angle and energy of the collision partners. Ever since, both theorists and experimentalists have been devising more intricate and illuminating combinations of polarized projectiles and spin- and angular momentum-oriented targets, and ever more novel techniques for increasing the resolution, if you will, of spin and angular momentum transferred during the collision. The {open_quotes}complete{close_quotes} experiment has yet to be performed, but great progress has been made, particularly for relatively simple targets such as sodium and cesium. For these hydrogen-like systems, the number of parameters needed to define the {open_quotes}complete{close_quotes} experiment is at a manageable minimum, but the alkalis` greater nuclear charge increases the impact of spin-dependent forces, such as the spin-orbit interaction. Thus the possibility of obtaining useful insight from calculations or measurements is maximized. This talk will focus, for these two atoms, on selected theoretical and experimental results for spin-dependent effects, such as the {open_quotes}fine-structure{close_quotes} effect, that do not require the use of polarized electrons; for spin-dependent effects such as the pure exchange interaction, that do require the use of polarized electrons; and, for cesium, results that begin to elucidate effects in the scattering process that do not emerge until one steps beyond the constraints of the non-relativistic Schrodinger equation.

Norcross, D.W.

1993-05-01

341

Interferences of real trajectories and the emergence of quantum features in electron-atom scattering in a strong laser field  

NASA Astrophysics Data System (ADS)

Using the example of electron-atom scattering in a strong laser field, it is shown that the oscillatory structure of the scattered electron spectrum can be explained as a consequence of the interference of the real electron trajectories in terms of Feynman’s path integral. While in previous work on quantum-orbit theory the complex solutions of the saddle-point equations were considered, we show here that for the electron-atom scattering with much simpler real solutions a satisfactory agreement with the strong-field-approximation results can be achieved. Real solutions are applicable both for the direct (low-energy) and the rescattering (high-energy) plateau in the scattered electron spectrum. In between the plateaus and beyond the rescattering cutoff good results can be obtained using the complex (quantum) solutions and the uniform approximation. The interference of real solutions is related to the recent attosecond double-slit experiment in time.

?erki?, A.; Miloševi?, D. B.

2006-03-01

342

Interferences of real trajectories and the emergence of quantum features in electron-atom scattering in a strong laser field  

SciTech Connect

Using the example of electron-atom scattering in a strong laser field, it is shown that the oscillatory structure of the scattered electron spectrum can be explained as a consequence of the interference of the real electron trajectories in terms of Feynman's path integral. While in previous work on quantum-orbit theory the complex solutions of the saddle-point equations were considered, we show here that for the electron-atom scattering with much simpler real solutions a satisfactory agreement with the strong-field-approximation results can be achieved. Real solutions are applicable both for the direct (low-energy) and the rescattering (high-energy) plateau in the scattered electron spectrum. In between the plateaus and beyond the rescattering cutoff good results can be obtained using the complex (quantum) solutions and the uniform approximation. The interference of real solutions is related to the recent attosecond double-slit experiment in time.

Cerkic, A. [Federal Meteorological Institute, Bardakcije 12, 71000 Sarajevo (Bosnia and Herzegowina); Milosevic, D. B. [Faculty of Science, University of Sarajevo, Zmaja od Bosne 35, 71000 Sarajevo (Bosnia and Herzegowina); Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin (Germany)

2006-03-15

343

Interferences of real trajectories and the emergence of quantum features in electron-atom scattering in a strong laser field  

Microsoft Academic Search

Using the example of electron-atom scattering in a strong laser field, it is shown that the oscillatory structure of the scattered electron spectrum can be explained as a consequence of the interference of the real electron trajectories in terms of Feynman's path integral. While in previous work on quantum-orbit theory the complex solutions of the saddle-point equations were considered, we

A. Cerkic; D. B. Milosevic

2006-01-01

344

Measurements of differential cross sections for elastic electron scattering and electronic excitation of silver and lead atoms  

NASA Astrophysics Data System (ADS)

This paper presents absolute differential cross sections (DCSs) and integrated cross sections (ICSs) for both elastic and inelastic electron scattering by lead and silver atoms in the energy range from 10 to 100 eV. The DCSs were measured as a function of scattering angle. Scattering angles are from 1° to 150° for the excitations of the unresolved 4d105p 2P1/2, 3/2 silver line and 6p7s 3P0,1 lead line, while for the elastic scattering they span from 10° to 150°. The measurements utilize crossed beam technique with effusive atomic beam being perpendicularly crossed by electron beam. Monoenergetic electron beam is obtained by means of hemispherical selector and it is focused by cylindrical electrostatic lenses while effusive atomic beam is formed by heating of Knudsen type oven. Absolute values for the resonance states are obtained by normalization of relative differential cross sections to the optical oscillator strengths, while the absolute values for the elastic scattering are obtained from the intensity ratios at particular scattering angles. Obtained absolute DCSs were extrapolated to 0° and 180° and numerically integrated to yield integral, momentum transfer and viscosity cross sections. The experimental results have been compared with the corresponding calculations.

Toši?, S. D.

2012-11-01

345

The smoothing kinetics of Ag(1 1 0) studied by thermal energy He atom scattering  

NASA Astrophysics Data System (ADS)

The smoothening process of nanometer-scale ripples grown on the (1 1 0) surface of silver is investigated using thermal energy He atom scattering. Morphological equilibration the corrugated surface is followed in real time in the temperature range between 205 and 230 K. The mean ripple wavelength, ?, is observed to increase during surface recovery. To take this effect into account the decay time is assumed to scale as ?3. Within this approximation the ripple amplitude is observed to decay linearly with time. The activation energy of the mechanism driving surface relaxation is estimated as (0.46 ± 0.02) eV. The underlying rate limiting process, i.e. adatom detachment from the open <0 0 1> step edges is evidenced.

Pedemonte, L.; Bracco, G.; Boragno, C.; Buatier de Mongeot, F.; Valbusa, U.

2004-09-01

346

Atomic mass dependence of hadron production in semi-inclusive deep inelastic lepton-nucleus scattering  

NASA Astrophysics Data System (ADS)

Hadron production in lepton-nucleus deep inelastic scattering is studied in a quark energy loss model. The leading-order computations for hadron multiplicity ratios are presented and compared with the selected HERMES pions production data with the quark hadronization occurring outside the nucleus by means of the hadron formation time. It is found that the obtained energy loss per unit length is 0.440±0.013 GeV/fm for an outgoing quark by the global fit. It is confirmed that the atomic mass number dependence of hadron attenuation is theoretically and experimentally in good agreement with the A2/3 power law for quark hadronization occurring outside the nucleus.

Song, Li-Hua; Liu, Na; Duan, Chun-Gui

2013-08-01

347

Applications of Quantum Theory of Atomic and Molecular Scattering to Problems in Hypersonic Flow  

NASA Technical Reports Server (NTRS)

The general status of a grant to investigate the applications of quantum theory in atomic and molecular scattering problems in hypersonic flow is summarized. Abstracts of five articles and eleven full-length articles published or submitted for publication are included as attachments. The following topics are addressed in these articles: fragmentation of heavy ions (HZE particles); parameterization of absorption cross sections; light ion transport; emission of light fragments as an indicator of equilibrated populations; quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen; evaluation of NUCFRG2, the semi-empirical nuclear fragmentation database; investigation of the single- and double-ionization of He by proton and anti-proton collisions; Bose-Einstein condensation of nuclei; and a liquid drop model in HZE particle fragmentation by hydrogen.

Malik, F. Bary

1995-01-01

348

Total cross sections for positrons scattered elastically from helium based on new measurements of total ionization cross sections  

NASA Technical Reports Server (NTRS)

An improved technique is presented for employing the 2.3m spectrometer to measure total ionization cross sections, Q sub ion, for positrons incident on He. The new ionization cross section agree with the values reported earlier. Estimates are also presented of total elastic scattering cross section, Q sub el, obtained by subtracting from total scattering cross sections, Q sub tot, reported in the literature, the Q sub ion and Q sub Ps (total positronium formation cross sections) and total excitation cross sections, Q sub ex, published by another researcher. The Q sub ion and Q sub el measured with the 3m high resolution time-of-flight spectrometer for 54.9eV positrons are in accord with the results from the 2.3m spectrometer. The ionization cross sections are in fair agreement with theory tending for the most part to be higher, especially at 76.3 and 88.5eV. The elastic cross section agree quite well with theory to the vicinity of 50eV, but at 60eV and above the experimental elastic cross sections climb to and remain at about 0.30 pi a sub o sq while the theoretical values steadily decrease.

Diana, L. M.; Chaplin, R. L.; Brooks, D. L.; Adams, J. T.; Reyna, L. K.

1990-01-01

349

Three-dimensional three-atom model for computer simulation of impact-collision ion scattering spectroscopy  

NASA Astrophysics Data System (ADS)

A new model for computer simulation of impact-collision ion scattering spectroscopy (ICISS) has been developed. By this model, the scattering cross section of the three target atoms arbitrarily placed in the three-dimensional space can be calculated. This made it possible to interpret ICISS data including shadowing and blocking effects from out-of-plane scattering. The method is also effective in the case that the scattering angle is not 180°. As an example, ICISS data of the NbC(111) surface along the [1¯10] azimuth have been analysed. The result of the calculation is in a good agreement with the experimental data. The computational time is sufficiently short, so this method is useful for a quantitative analysis of ICISS data with arbitrary scattering angle and azimuth.

Hayami, Wataru; Souda, Ryutaro; Aizawa, Takashi; Ishizawa, Yoshio

1994-02-01

350

ARTICLES: Electron stimulated Raman scattering and four-wave interaction in barium atomic vapor pumped by tunable ultrashort light pulses  

Microsoft Academic Search

A phosphate neodymium glass laser emitting picosecond pulses tunable in the 1.05-1.07 mu range was developed to study nonlinear optical processes in atomic barium vapor. Its temporal characteristics were investigated using a modified second harmonic beam method. Electron stimulated Raman scattering and four-photon parametric conversion in atomic barium vapor were used to obtain efficient conversion of the third harmonic of

S. O. Sapondzhyan; D. G. Sarkisyan; G. A. Torosyan

1985-01-01

351

Electron stimulated Raman scattering and four-wave interaction in barium atomic vapor pumped by tunable ultrashort light pulses  

Microsoft Academic Search

A phosphate neodymium glass laser emitting picosecond pulses tunable in the 1.05–1.07 ? range was developed to study nonlinear optical processes in atomic barium vapor. Its temporal characteristics were investigated using a modified second harmonic beam method. Electron stimulated Raman scattering and four-photon parametric conversion in atomic barium vapor were used to obtain efficient conversion of the third harmonic of

S O Sapondzhyan; D G Sarkisyan; G A Torosyan

1985-01-01

352

Laser-Induced Optical Pumping Measurements of Cross Section for Fine- and Hyperfine-Structure Transitions in Sodium Induced by Collisions with Helium and Argon Atoms  

NASA Technical Reports Server (NTRS)

Optical pumping of the ground states of sodium can radically alter the shape of the laser-induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections lor DELTA.F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), DELTA.F cross sections. The hyperfine cross sections measured using this method, which to our knowledge is novel, are compared with cross sections for transitions involving polarized magnetic substates m(sub F) measured previously using polarization sensitive absorption. Also, fine-structure transition cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.

Dobson, Chris C.; Sung, C. C.

1999-01-01

353

Comparison between Laser Thomson Scattering and Spectroscopic Measurements in Low Temperature Helium Plasmas in Divertor/Edge Simulator MAP-II  

NASA Astrophysics Data System (ADS)

Electron temperature and density measurements of low temperature Helium plasmas are performed in the divertor/edge plasma simulator MAP-II, by means of Laser Thomson Scattering (using a ND:YAG Laser, a double monochromator and an ICCD detector) and optical emission spectroscopy (using a spectrometer and a CCD detector). The recent upgrades of our LTS system (reduction of the level of stray light and reduction of the band width of the notch filter) allowed the measurement of temperatures as low as 0.1 eV and the investigation of Electron Ion Recombination (EIR) processes in He plasma. Spatial profiles of electron temperature and density along the plasma column have been taken moving the plasma recombination front across the measurement point by controlling the gas pressure from 80 to about 145 mTorr. A comparison between LTS results and spectroscopic analysis based on a He I CR model including radiation trapping is shown in order to confirm the consistency of the diagnostics. CR model results, obtained fitting the excited state populations with principal quantum number n = 3,4, are consistent with those from LTS. The discrepancies are found to be attributable to the mixing of the ionization and recombination regimes over the line of sight of the optics.

Scotti, Filippo; Kado, Shinichiro; Okamoto, Atsushi; Shikama, Taiichi; Kuwahara, Yosuke; Kurihara, Kiminori; Chung, Kyu-Sun; Tanaka, Satoru

354

Scattering of electron vortex beams on a magnetic crystal: Towards atomic-resolution magnetic measurements  

NASA Astrophysics Data System (ADS)

Use of electron vortex beams (EVB), that is, convergent electron beams carrying an orbital angular momentum (OAM), is a novel development in the field of transmission electron microscopy. They should allow measurement of element-specific magnetic properties of thin crystals using electron magnetic circular dichroism (EMCD)—a phenomenon similar to the x-ray magnetic circular dichroism. Recently, it has been shown computationally that EVBs can detect magnetic signal in a scanning mode only at atomic resolution. In this follow-up work, we explore in detail the elastic and inelastic scattering properties of EVBs on crystals, as a function of beam diameter, initial OAM, acceleration voltage, and beam displacement from an atomic column. We suggest that for a 10-nm layer of bcc iron oriented along (001) zone axis, an optimal configuration for a detection of EMCD is an EVB with OAM of 1? and a full width at half maximum diffraction-limited beam diameter of 1.6 Å, acceleration voltage 200 kV, and an annular detector with inner and outer radii of 7 and 44 mrad, respectively.

Rusz, Ján; Bhowmick, Somnath; Eriksson, Mattias; Karlsson, Nikolaj

2014-04-01

355

Small-angle x-ray scattering measurements of the microstructure of liquid helium mixtures adsorbed in aerogel  

SciTech Connect

Small-angle x-ray scattering (SAXS) was used to measure the microstructure of isotopic mixtures of {sup 3}He and {sup 4}He adsorbed into silica aerogels as a function of temperature and {sup 3}He concentration. The SAXS measurements could be well described by the formation of a nearly pure film of {sup 4}He which separates from the bulk mixture onto the aerogel strands and which thickens with decreasing temperature. Previous observations of a superfluid {sup 3}He-rich phase are consistent with superfluidity existing within this film phase. Observed differences between different density aerogels are explained in terms of the depletion of {sup 4}He from the bulk mixture due to film formation.

Lurio, L. B.; Mulders, N.; Paetkau, M.; Chan, M. H. W.; Mochrie, S. G. J. [Department of Physics, Northern Illinois University, DeKalb, Illinois 60115 (United States); Department of Physics, University of Delaware, Newark, Delaware 19716 (United States); Department of Physics and Astronomy, Okanagan College, British Columbia V1Y4X8 (Canada); Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Department of Physics, Yale University, New Haven, Connecticut 06511 (United States)

2007-07-15

356

Helium production in natural gas reservoirs  

Microsoft Academic Search

About 11,000 published natural gas analyses of helium are used in the estimation of the average global scale accumulation and concentration of radiogenic helium in sediments. Simple lognormal statistics is employed to derive a net accumulation rate between 1†105 to 6.7†105 helium atoms per cubic meter of reservoir rock per second. This acccumulation rate permitted to infer an average helium

E. B. Pereira; J. A. S. Adams

1982-01-01

357

Helium production in natural gas reservoirs  

Microsoft Academic Search

About 11,000 published natural gas analyses of helium are used in the estimation of the average global scale accumulation and concentration of radiogenic helium in sediments. Simple lognormal statistics is employed to derive a net accumulation rate between 1dagger10⁵ to 6.7dagger10⁵ helium atoms per cubic meter of reservoir rock per second. This acccumulation rate permitted to infer an average helium

E. B. Pereira; J. A. S. Adams

1982-01-01

358

Low photon scattering rates and large optical depths of atoms in donut modes of hollow core optical fibers  

NASA Astrophysics Data System (ADS)

We have guided cold rubidium atoms in blue-detuned hollow optical modes of a hollow fiber. These higher order modes allow large optical depth, low scattering rates, and efficient use of guide laser power. Atoms are transported through a 3-cm-long hollow fiber with a 100 micron diameter using the first three optical modes of the fiber. We compare guiding properties in the red-detuned, fundamental HE11 mode with the blue-detuned TE01 (first order) and HE12 (second order) modes. Using guide laser powers below 50 mW and detunings below 1.5 nm, we have directly measured recoil scattering rates in the three different guides and found that atoms in the HE12 mode typically have a 10x lower recoil scattering rate compared to the red-detuned HE11 mode for equal guide peak intensity. Furthermore, we have observed optical depths of ˜20 for the blue-detuned guides with recoil scattering rates below 10 Hz. We will discuss our ongoing experiments using the atoms in these guides. This work supported by the Office of Naval Research and the Defense Advanced Research Projects Agency.

Pechkis, Joseph A.; Fatemi, Fredrik K.

2012-06-01

359

Exploring local atomic arrangements in amorphous and metastable phase change materials with x-ray and neutron total scattering  

Microsoft Academic Search

Very little experimental work has conclusively explored the structural transformation between the amorphous and metastable crystalline phases of phase change chalcogenides. A recent flurry of theoretical work has supported likely mechanisms for the phase transition process in Ge-Sb-Te (GST) compositions and invigorated efforts at probing local atomic arrangements experimentally. The pair distribution function (PDF) formalism of total scattering data provides

Katharine Page; Luc Daemen; Thomas Proffen

2010-01-01

360

Low-energy electron-impact ionization of the helium atom using the multiconfiguration Hartree-Fock method  

SciTech Connect

We have extended the multiconfiguration Hartree-Fock method for electron-impact ionization of atoms to investigate the effects of polarization and electron correlation of the target in the initial state. As a test case, the method is applied to calculate triple differential cross sections for electron-impact ionization of He atom at an excess energy of 2 eV for the coplanar {theta}{sub 12}={pi} geometry for equal and unequal energies of two final-state outgoing electrons. To determine the effects of electron correlation between the two outgoing electrons in the final state, the variationally determined screening potential approximation is used. It is found that target correlation in the initial state has smaller effect on the triple differential cross section but the polarization of the target by the incident electron has considerable effect on the triple differential cross section at low incident energy. The results are compared with absolute measurement and other available theoretical results.

Saha, Hari P. [Physics Department, University of Central Florida, Orlando, Florida 32816 (United States)

2010-10-15

361

Surface Phonon Dispersion Curves of Rubidium Chloride, Potassium Bromide, Rubidium Bromide and Sodium Iodide Studied by Inelastic Helium Atom Scattering  

Microsoft Academic Search

The alkali halide surfaces were the first for which full surface phonon dispersion curves were measured. Most of the early work was mainly concerned with the low-energy modes for the lighter alkali halides, such as LiF and NaF, and a full survey of a more representative sampling of these crystals was never made. A recent theoretical calculation has also suggested

Gung Chern

1989-01-01

362

Measurements of scattering processes in negative ion: Atom collisions. Technical progress report, 1 September 1991--31 December 1994  

SciTech Connect

This report describes the progress made on the research objectives during the past three years of the grant. This research project is designed to study various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets in the intermediate energy region. These processes include: elastic scattering, single- and double-electron detachment, and target excitation/ionization. For the elastic and target inelastic processes where H{sup {minus}} is scattered intact, the experimental technique of Ion Energy-Loss Spectroscopy (IELS) will be employed to identify the final target state(s). In most of the above processes, cross sections are unknown both experimentally and theoretically. The measurements will provide total cross sections (TCS) initially, and once the angular positioning apparatus is installed, will provide angular differential cross sections (ADCS).

Kvale, T.J.

1994-09-27

363

ELSEPA—Dirac partial-wave calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules  

NASA Astrophysics Data System (ADS)

The FORTRAN 77 code system ELSEPA for the calculation of elastic scattering of electrons and positrons by atoms, positive ions and molecules is presented. These codes perform relativistic (Dirac) partial-wave calculations for scattering by a local central interaction potential V(r). For atoms and ions, the static-field approximation is adopted, with the potential set equal to the electrostatic interaction energy between the projectile and the target, plus an approximate local exchange interaction when the projectile is an electron. For projectiles with kinetic energies up to 10 keV, the potential may optionally include a semiempirical correlation-polarization potential to describe the effect of the target charge polarizability. Also, for projectiles with energies less than 1 MeV, an imaginary absorptive potential can be introduced to account for the depletion of the projectile wave function caused by open inelastic channels. Molecular cross sections are calculated by means of a single-scattering independent-atom approximation in which the electron density of a bound atom is approximated by that of the free neutral atom. Elastic scattering by individual atoms in solids is described by means of a muffin-tin model potential. Partial-wave calculations are feasible on modest personal computers for energies up to about 5 MeV. The ELSEPA code also implements approximate factorization methods that allow the fast calculation of elastic cross sections for much higher energies. The interaction model adopted in the calculations is defined by the user by combining the different options offered by the code. The nuclear charge distribution can be selected among four analytical models (point nucleus, uniformly charged sphere, Fermi's distribution and Helm's uniform-uniform distribution). The atomic electron density is handled in numerical form. The distribution package includes data files with electronic densities of neutral atoms of the elements hydrogen to lawrencium ( Z=1-103) obtained from multiconfiguration Dirac-Fock self-consistent calculations. For comparison purposes, three simple analytical approximations to the electron density of neutral atoms (corresponding to the Thomas-Fermi, the Thomas-Fermi-Dirac and the Dirac-Hartree-Fock-Slater models) are also included. For calculations of elastic scattering by ions, the electron density should be provided by the user. The exchange potential for electron scattering can be selected among three different analytical approximations (Thomas-Fermi, Furness-McCarthy, Riley-Truhlar). The offered options for the correlation-polarization potential are based on the empirical Buckingham potential. The imaginary absorption potential is calculated from the local-density approximation proposed by Salvat [Phys. Rev. A 68 (2003) 012708]. Program summaryTitle of program:ELSEPA Catalogue identifier: ADUS Program summary URL:http://cpc.cs.qub.ac.uk/cpc/summaries/ADUS Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland License provisions: none Computer for which the program is designed and others in which it is operable: Any computer with a FORTRAN 77 compiler Operating systems under which the program has been tested: Windows XP, Windows 2000, Debian GNU/Linux 3.0r0 (sarge) Compilers:Compaq Visual Fortran v6.5 (Windows); GNU FORTRAN, g77 (Windows and Linux) Programming language used: FORTRAN 77 No. of bits in a word: 32 Memory required to execute with typical data: 0.6 Mb No. of lines in distributed program, including test data, etc.:135 489 No. of bytes in distributed program, including test data, etc.: 1 280 006 Distribution format: tar.gz Keywords: Dirac partial-wave analysis, electron elastic scattering, positron elastic scattering, differential cross sections, momentum transfer cross sections, transport cross sections, scattering amplitudes, spin polarization, scattering by complex potentials, high-energy atomic screening functions Nature of the physical problem: The code calculates differential cross sections, total cross sections and transport cross sections for

Salvat, Francesc; Jablonski, Aleksander; Powell, Cedric J.

2005-01-01

364

Excitations of light atoms during nuclear reactions with fast neutrons  

SciTech Connect

The probabilities of various excitations or ionization processes are determined in a number of light atoms during elastic and nonelastic neutron-nucleus scattering. In particular, we have evaluated the final-state probabilities in the cases of elastic scattering of fast neutrons at the hydrogen and helium atoms. Atomic excitation or ionization probabilities have been determined numerically for the neon atom. This study is an important step in our understanding of numerous optical phenomena which can be observed when an intense flux of fast neutrons propagates in a dense medium.

Talman, James D.; Frolov, Alexei M. [Department of Applied Mathematics and Centre for Chemical Physics, University of Western Ontario, London, Ontario, N6A 5B7 (Canada)

2006-03-15

365

Quantum effects in the collective light scattering by coherent atomic recoil in a Bose-Einstein condensate  

NASA Astrophysics Data System (ADS)

We extend the semiclassical model of the collective atomic recoil laser (CARL) to include the quantum mechanical description of the center-of-mass motion of the atoms in a Bose-Einstein condensate (BEC). We show that when the average atomic momentum is less than the recoil momentum ? q?, the CARL equations reduce to the Maxwell-Bloch equations for two momentum levels. In the conservative regime (no radiation losses), the quantum model depends on a single collective parameter, ?, that can be interpreted as the average number of photons scattered per atom in the classical limit. When ??1, the semiclassical CARL regime is recovered, with many momentum levels populated at saturation. On the contrary, when ??1, the average momentum oscillates between zero and ? q?, and a periodic train of 2 ? hyperbolic secant pulses is emitted. In the dissipative regime (large radiation losses) and in a suitable quantum limit, a sequential superfluorescence scattering occurs, in which after each process atoms emit a ? hyperbolic secant pulse and populate a lower momentum state. These results describe the regular arrangement of the momentum pattern observed in recent experiments of superradiant Rayleigh scattering from a BEC.

Piovella, N.; Gatelli, M.; Bonifacio, R.

2001-07-01

366

Possibility of giant enhancement of low-frequency non-resonant Rayleigh scattering by atomic systems within dense plasmas  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate the possibility of electron density-induced giant growth of non-resonant Rayleigh scattering of electromagnetic radiation (in the low-frequency limit) by atomic systems within dense plasmas. Non-relativistic quantum mechanical calculation is performed under electric dipole approximation, for elastic scattering of radiation by the ground states 1s of plasma-embedded hydrogen-like atomic ions treated within the framework of the ion-sphere model. The results indicate giant enhancement of the non-resonant (photon frequency ? being much smaller than the lowest resonance frequency ?1s-2p) Rayleigh cross-section by an order of magnitude, at (atomic system-specific) high enough plasma electron densities under present consideration. The Z-8-scaling of the non-resonant Rayleigh cross-section in free and isolated H-isoelectronic sequence of ions is shown to be broken in dense plasma environments.

Basu, Joyee; Ray, Debasis

2014-03-01

367

Elastic scattering and the associated anomalous dispersion in the atomic region 13 <= Z <= 82 at 30.85 keV  

Microsoft Academic Search

We have measured the differential elastic scattering cross sections in the atomic region 13 ? Z ? 82 using nearly monoenergetic unpolarised Cs K? (30.85 keV) radiation at a scattering angle of 90. Experimental elastic scattering cross sections are compared with the theoretical estimates based on form factor formalisms (relativistic, non-relativistic and relativistic modified form factors). Good agreement is observed

D. V. Rao; R. Cesareo; G. E. Gigante

1997-01-01

368

Decomposition of experimentally determined atomic (e,2e) ionization measurements  

Microsoft Academic Search

A set of previously measured helium (e,2e) coincidence ionization differential cross sections obtained over an exceptionally wide range of outgoing electron angles has been decomposed into tensorial angular components. A technique has been used which is familar in nuclear physics for the analysis of cascade decay correlations but which does not appear to have been applied previously to atomic scattering

A. J. Murray; F. H. Read; N. J. Bowring

1994-01-01

369

SCATTERING OF HIGH-VELOCITY NEUTRAL PARTICLES. XII. HeCHâ He CFâ. CHâ-CHâ AND CFâ-CFâ INTERACTIONS  

Microsoft Academic Search

Collision cross sections were measured for helium atoms with energies ; between 500 and 2100 ev, scattered in room temperature CHâ and CFâ. ; The results were analyzed to obthin the average potential between a helium atom ; and a CHâ molecule, STAV(r)!\\/sub Av\\/ = 602\\/r\\/sup 9.4\\/³ev, for r ; between 1.92 and 2.37 A, and the average potential between

I. Amdur; M. S. Longmire; E. A. Mason

1961-01-01

370

RNA and Its Ionic Cloud: Solution Scattering Experiments and Atomically Detailed Simulations  

PubMed Central

RNA molecules play critical roles in many cellular processes. Traditionally viewed as genetic messengers, RNA molecules were recently discovered to have diverse functions related to gene regulation and expression. RNA also has great potential as a therapeutic and a tool for further investigation of gene regulation. Metal ions are an integral part of RNA structure and should be considered in any experimental or theoretical study of RNA. Here, we report a multidisciplinary approach that combines anomalous small-angle x-ray scattering and molecular-dynamics (MD) simulations with explicit solvent and ions around RNA. From experiment and simulation results, we find excellent agreement in the number and distribution of excess monovalent and divalent ions around a short RNA duplex. Although similar agreement can be obtained from a continuum description of the solvent and mobile ions (by solving the Poisson-Boltzmann equation and accounting for finite ion size), the use of MD is easily extended to flexible RNA systems with thermal fluctuations. Therefore, we also model a short RNA pseudoknot and find good agreement between the MD results and the experimentally derived solution structures. Surprisingly, both deviate from crystal structure predictions. These favorable comparisons of experiment and simulations encourage work on RNA in all-atom dynamic models.

Kirmizialtin, Serdal; Pabit, Suzette A.; Meisburger, Steve P.; Pollack, Lois; Elber, Ron

2012-01-01

371

Atomic vibrations in iron nanoclusters : nuclear resonant inelastic x-ray scattering and molecular dynamics simulations.  

SciTech Connect

The lattice vibrational dynamics of supported, self-assembled, isolated {sup 57}Fe nanoclusters was studied by nuclear resonant inelastic x-ray scattering and molecular dynamics calculations. The morphological and structural properties and the chemical state of the experimental nanoclusters were investigated by atomic force microscopy, high resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. The measured and calculated vibrational densities of states (VDOSs) reveal an enhancement of the low- and high-energy phonon modes and provide experimental and theoretical proof of non-Debye-like behavior in the low-energy region of the VDOS. Experimentally, this effect was found to depend on the nature of the surface shell (oxide or carbide) of the core/shell nanoclusters. According to the calculations for supported isolated pure Fe nanoclusters, the non-Debye-like behavior appears not only in the surface shell but also in the bcc-Fe core of the nanocluster due to the hybridization of surface and bulk modes.

Cuenya, B. R.; Naitabdi, A.; Croy, J.; Sturhahn, W.; Zhao, J. Y.; Alp, E. E.; Meyer, R.; Sudfeld, D.; Schuster, E.; Keune, W.; X-Ray Science Division; Univ. of Central Florida; Univ. Duisburg-Essen

2007-11-01

372

Large-scale pseudostate calculations for electron scattering from neon atoms  

NASA Astrophysics Data System (ADS)

We report large-scale R-matrix (close-coupling) with pseudostates calculations for electron scattering from Ne atoms. The present calculations were performed in the nonrelativistic LS-coupling approximation with a recently developed parallel version of our suite of B-spline R-matrix codes. The principal goal was to generate converged (with the number of states in the close-coupling expansion) results for angle-integrated elastic, ionization, and total cross sections. The cross sections for excitation, which are also required for the latter, are generated in this nonrelativistic model as the sum for all terms. The close-coupling expansion used in this work includes 679 target states, with the lowest-lying 55 states representing the Ne bound spectrum and the remaining 624 states representing the ionization continuum. Our results are in close agreement with available experimental data for the elastic and total cross sections over the wide range of electron energies between 0.1 and 200 eV. With the pseudostate approach, we also obtain accurate cross sections for ionization from both the ground and the metastable states of neon. Our results confirm the very strong influence of coupling to the target continuum on theoretical predictions for excitation cross sections in Ne at intermediate energies, an effect that was previously reported by Ballance and Griffin [J. Phys. BJPAPEH0953-407510.1088/0953-4075/37/14/008 37, 2943 (2004)].

Zatsarinny, Oleg; Bartschat, Klaus

2012-06-01

373

BKLT equations for reactive scattering. I. Theory and application to three finite mass atom systems  

SciTech Connect

The BKLT equations for reactive scattering are considered in detail, both from a formal and computational point of view. The equations are very attractive because they do not require any matching of wave functions. It is shown how these equations may be solved for a general collinear three-finite mass atom system. Special care is taken to treat subleties in the theory arising from restrictions on the ranges of the vibrational coordinate of the various diatoms due to the skewing angle being less than 90/sup 0/. In addition, the structure of the equations is explored in detail since this has significance for their optimum solution. It is found that the structure of the equations for asymmetric systems leads to important redutions in the size of the matrix which must be inverted within the present, nonpropagative method. Other solution methods are also discussed to some extent. Finally, the method is illustrated by an application to the H+H/sub 2/ exchange reaction with the Porter--Karplus potential surface. The results obtained agree well with those obtained earlier by Diestler using a close coupling, propagation procedure.

Shima, Y.; Kouri, D.J.; Baer, M.

1983-06-01

374

Energy deposition by electrons in superfluid helium  

NASA Astrophysics Data System (ADS)

Measurements have been performed on the energy deposition of single monoenergetic electrons stopped in superfluid 4He at low temperatures. The passage of the charged particle through the helium generates excited He 2 dimers. The radiative decay of these dimers results in scintillation light in the extreme ultraviolet. The charged particle also generates a distribution of quasiparticles in the liquid. A single quasiparticle can eject a single helium atom from the bulk in a process known as quantum evaporation. Both the scintillation light and the ejected atoms from quantum evaporation were measured calorimetrically using a thin- film, superconducting transition-edge sensor evaporated on a sapphire wafer. The wafer was mounted above the liquid surface. The two signal components are separated by using the differences in their times-of-flight. Both components of the signal were measured using various source positions and liquid levels with respect to the wafer. Measurements of the energy deposition of 364 keV electrons in a prototype cell of 5 liters are presented. An energetic electron stopped in liquid helium, will emit 35% of its energy into 4? sr in the form of scintillation light. In addition, ~3% of the energy of the electron will be deposited on the wafers in the form of evaporated helium atoms. The evaporation signal will be contained within a cone of ~30° with respect to the position of the event. The variation of the evaporation signal with respect to both liquid level and source position lead to the conclusion that the quasiparticle distribution generated in the liquid follows the density of states and, are thus, primarily rotons. In addition, it is concluded that the evaporation signal is primarily due to R+ rotons away from the roton minimum, which implies that rotons near the minimum have a low probability of causing quantum evaporation. The processes involved are being studied for use in HERON, a proposed detector of low-energy solar neutrinos that will use as a target material, 10 tons of liquid helium. The HERON detector is intended to detect pp and 7Be neutrinos from the sun in real time with an energy threshold of approximately 50 keV. The recoil energy of electrons resulting from the elastic scattering of neutrinos would be measured with calorimetric wafers above the free surface of the liquid at 40 mK. An explanation of the physical processes which contribute to the signal as well as the viability of a HERON type neutrino detector are discussed.

Adams, Joseph Simmons

2001-09-01

375

Critical Landau Velocity in Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concept can still be applied to nanometer-scale, finite size helium systems. To this end, atoms and molecules embedded in helium nanodroplets of various sizes are accelerated out of the droplets by means of optical excitation, and the speed distributions of the ejected particles are determined. The measurements reveal the existence of a critical velocity in these systems, even for nanodroplets consisting of only a thousand helium atoms. Accompanying theoretical simulations based on a time-dependent density functional description of the helium confirm and further elucidate this experimental finding.

Brauer, Nils B.; Smolarek, Szymon; Loginov, Evgeniy; Mateo, David; Hernando, Alberto; Pi, Marti; Barranco, Manuel; Buma, Wybren J.; Drabbels, Marcel

2013-10-01

376

The atomic scale structure of CXV carbon: wide-angle x-ray scattering and modeling studies  

NASA Astrophysics Data System (ADS)

The disordered structure of commercially available CXV activated carbon produced from finely powdered wood-based carbon has been studied using the wide-angle x-ray scattering technique, molecular dynamics and density functional theory simulations. The x-ray scattering data has been converted to the real space representation in the form of the pair correlation function via the Fourier transform. Geometry optimizations using classical molecular dynamics based on the reactive empirical bond order potential and density functional theory at the B3LYP/6-31g* level have been performed to generate nanoscale models of CXV carbon consistent with the experimental data. The final model of the structure comprises four chain-like and buckled graphitic layers containing a small percentage of four-fold coordinated atoms (sp3 defects) in each layer. The presence of non-hexagonal rings in the atomic arrangement has been also considered.

Hawelek, L.; Brodka, A.; Dore, J. C.; Honkimaki, V.; Burian, A.

2013-11-01

377

Scattering-theoretical investigation of the vibrational excitation of atomic molecules at collision energies above 15 eV  

Microsoft Academic Search

The collision induced vibrational excitation of atomic molecules was studied. Three-dimensional calculations were made by the quantum mechanic breathing sphere approximation. An extensive systematic calculation of integral vibrationally inelastic scattering cross sections of different collision systems was made using the close coupling method. Feshbach resonances were identified for the system H-ion\\/CO using model calculations. A rainbow structure was found by

G. Drolshagen

1982-01-01

378

A MATLAB-based finite-element visualization of quantum reactive scattering. I. Collinear atom-diatom reactions.  

PubMed

We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H2), a heavy-light-light reaction (F+H2), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM. PMID:25028010

Warehime, Mick; Alexander, Millard H

2014-07-14

379

Low energy ion and atom scattering spectroscopy for surface structural analysis of single metal and insulator crystals  

NASA Astrophysics Data System (ADS)

Applications of low energy ion scattering and low energy atom scattering spectroscopy have been described. Time of flight impact-collision ion scattering (TOF-ICISS) has been used to investigate the heteroepitaxial growth of 3 ML of FCC elements on Ni(1 1 1) and Cu(1 1 1) over a wide temperature range from 300 K through 700 K. There were two different types of epitaxial growth; FCC(1 1 1)[1 1 2¯]//Sub(1 1 1)[1 1 2¯] and FCC(1 1 1)[1¯ 1¯ 2]//Sub(1 1 1)[1 1 2¯]. FCC represents Au, Ag, Pb, Pd and Sub represents Ni or Cu. Relative amounts of these two growth modes show oscillatory dependence on the substrate temperature during deposition. However, it is not understood the physics behind this behavior. TOF-ICISS is quite useful to know the surface structure of epitaxy. A low energy Ne atom scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. It has a potential for insulator surface structural analysis.

Umezawa, K.

2008-04-01

380

Paramagnetic Attraction of Impurity-Helium Solids  

NASA Technical Reports Server (NTRS)

Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

2003-01-01

381

The Formation Energies and Binding Energies of Helium Vacancy Cluster: Comparative Study in Ni and Pd  

NASA Astrophysics Data System (ADS)

Molecular dynamics calculations are performed to calculate the formation energy for helium in Ni-vacancy and Pd-vacancy clusters. The binding energies of helium and metal self-interstitial atoms (SIA) to the helium-vacancy cluster are also determined. The comparison of these energies indicates that helium to vacancy ratio (He/V) for helium in Pd is much higher.

Yang, Jianyu; Ao, Bingyun; Hu, Wangyu; Wang, Xiaolin

2006-01-01

382

Antiprotonic helium atomcules  

NASA Astrophysics Data System (ADS)

About 3% of antiprotons (bar{p}) stopped in helium are long-lived with microsecond lifetimes, against picoseconds in all other materials. This unusual longevity has been ascribed to the trapping of bar{p} on metastable bound states in bar{p}He+ helium atom-molecules thus named atomcules. Apart from their unique dual structure investigated by laser spectroscopy - a near-circular quasi-classical Rydberg atom with l n - 1 37 or a special diatomic molecule with a negatively charged bar{p} nucleus in high rotational state with J = l - the chemical physics aspects of their interaction with other atoms or molecules constitute an interesting topic for molecular physics. While atomcules may resist to million collisions in helium, molecular contaminants such as H2 are likely to destroy them in a single one, down to very low temperatures. In the Born-Oppenheimer framework, we interpret the molecular interaction obtained by ab initio quantum chemical calculations in terms of classical reactive channels, with activation barriers accounting for the experiments carried out in He and H2. From classical trajectory Monte Carlo simulations, we show that the thermalization stage strongly quenches initial populations, thus reduced to a recovered 3 % trapping fraction. This work illustrates the pertinence of chemical physics concepts to the study of exotic processes involving antimatter. New insights into the physico-chemistry of cold interstellar radicals are anticipated.

Sauge, Sébastien

2012-10-01

383

Spin-dependent electron-atom scattering: What can be learned from the simplest systems  

Microsoft Academic Search

Bederson first summarized the requirements of the {open_quotes}complete{close_quotes} scattering experiment, in which the magnitudes and phases of all scattering amplitudes would be determined as functions of both scattering angle and energy of the collision partners. Ever since, both theorists and experimentalists have been devising more intricate and illuminating combinations of polarized projectiles and spin- and angular momentum-oriented targets, and ever

Norcross

1993-01-01

384

Electron scattering in hot-dense plasmas  

NASA Astrophysics Data System (ADS)

Hot-dense plasmas have direct industrial applications in inertial confinement fusion. We have used the convergent close-coupling (CCC) method to investigate electron scattering off hydrogen and helium atoms in a hot-dense weakly coupled (Debye) plasma. The Yukawa-type Debye-Hückel potential has been used to describe the plasma screening effects. Integrated excitation, total ionization and total cross sections have been calculated over a broad range of energies and various Debye lengths, D.

Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor

2012-11-01

385

Atomic-resolution structural information from scattering experiments on macromolecules in solution.  

PubMed

The pair-distance distribution function (PDDF) contains all structural information probed in an elastic scattering experiment of macromolecular solutions. However, in small-angle x-ray scattering (SAXS) or small-angle neutron scattering (SANS) experiments only their Fourier transform is measured over a restricted range of scattering angles. We therefore developed a mathematically simple and computationally efficient method to calculate the PDDFs as well as accurate scattering intensities from molecular dynamics simulations. The calculated solution scattering intensities are in excellent agreement with SAXS and wide-angle x-ray scattering (WAXS) experiments for a series of proteins. The corresponding PDDFs are remarkably rich in features reporting on the detailed protein structure. Using an inverse Fourier transform method, most of these features can be recovered if scattering intensities are measured up to a momentum transfer of q?2-3Å(-1). Our results establish that high-precision solution scattering experiments utilizing x-ray free-electron lasers and third generation synchrotron sources can resolve subnanometer structural detail, well beyond size, shape, and fold. PMID:23767571

Köfinger, Jürgen; Hummer, Gerhard

2013-05-01

386

Atomic-resolution structural information from scattering experiments on macromolecules in solution  

NASA Astrophysics Data System (ADS)

The pair-distance distribution function (PDDF) contains all structural information probed in an elastic scattering experiment of macromolecular solutions. However, in small-angle x-ray scattering (SAXS) or small-angle neutron scattering (SANS) experiments only their Fourier transform is measured over a restricted range of scattering angles. We therefore developed a mathematically simple and computationally efficient method to calculate the PDDFs as well as accurate scattering intensities from molecular dynamics simulations. The calculated solution scattering intensities are in excellent agreement with SAXS and wide-angle x-ray scattering (WAXS) experiments for a series of proteins. The corresponding PDDFs are remarkably rich in features reporting on the detailed protein structure. Using an inverse Fourier transform method, most of these features can be recovered if scattering intensities are measured up to a momentum transfer of q?2-3Å-1. Our results establish that high-precision solution scattering experiments utilizing x-ray free-electron lasers and third generation synchrotron sources can resolve subnanometer structural detail, well beyond size, shape, and fold.

Köfinger, Jürgen; Hummer, Gerhard

2013-05-01

387

Mechanism map for nucleation and growth of helium bubbles in metals  

NASA Astrophysics Data System (ADS)

The total free energy of a system containing helium bubbles and point defects (vacancies, helium and self-interstitial atoms) was evaluated and activation barrier for forming a helium bubble was derived, where the effect of helium on helium bubble formation is clearly shown. The rates of inflow to a helium bubble and outflow from a helium bubble were evaluated for vacancies, helium and self-interstitial atoms at the equilibrium and irradiation conditions to understand the mechanism of nucleation and growth of helium bubbles. It indicates that both the thermal emissions of helium and self-interstitial atoms may competitively occur at the irradiation condition from relatively small helium bubbles with high helium pressure.

Morishita, Kazunori; Sugano, Ryuichiro

2006-07-01

388

Simultaneous detection of surface coverage and structure of krypton films on gold by helium atom diffraction and quartz crystal microbalance techniques  

SciTech Connect

We describe a quartz crystal microbalance setup that can be operated at low temperatures in ultra high vacuum with gold electrode surfaces acting as substrate surface for helium diffraction measurements. By simultaneous measurement of helium specular reflection intensity from the electrode surface and resonance frequency shift of the crystal during film adsorption, helium diffraction data can be correlated to film thickness. In addition, effects of interfacial viscosity on the helium diffraction pattern could be observed. To this end, first, flat gold films on AT cut quartz crystals were prepared which yield high enough helium specular reflection intensity. Then the crystals were mounted in the helium diffractometer sample holder and driven by means of a frequency modulation driving setup. Different crystal geometries were tested to obtain the best quality factor and preliminary measurements were performed on Kr films on gold surfaces. While the crystal structure and coverage of krypton films as a function of substrate temperature could successfully be determined, no depinning effects could be observed.

Danisman, M. Fatih; Oezkan, Berrin [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)

2011-11-15

389

Atomic oxygen effects on thin film space coatings studied by spectroscopic ellipsometry, atomic force microscopy, and laser light scattering  

NASA Technical Reports Server (NTRS)

The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.

Synowicki, R. A.; Hale, Jeffrey S.; Woollam, John A.

1992-01-01

390

Systematic Pseudomagnetic Measurements of the Spin-Dependent Scattering Length of Slow Neutrons with Atomic Nuclei  

NASA Astrophysics Data System (ADS)

The magnitude and the sign of spin-dependent scattering lengths of slow neutrons by nuclei of Li7, Al27, Sc45, Zr91, Nb93, La139, and Ta181 have been determined by measuring the dependence of the precession angle of the neutron spins on the nuclear polarization of the scattering target.

Roubeau, P.; Abragam, A.; Bacchella, G. L.; Glättli, H.; Malinovski, A.; Meriel, P.; Piesvaux, J.; Pinot, M.

1974-07-01

391

Magnesium cluster film synthesis by helium nanodroplets.  

PubMed

Atomic and molecular clusters are a unique class of substances with properties that differ greatly from those of the bulk or single atoms due to changes in surface to volume ratio and finite size effects. Here, we demonstrate the ability to create cluster matter films using helium droplet mediated cluster assembly and deposition, a recently developed methodology that condenses atoms or molecules within liquid helium droplets and then gently deposits them onto a surface. In this work, we examine magnesium nanocluster films, which exhibit growth behavior comparable to low-energy cluster beam methods, and demonstrate physical properties and morphology dependent on helium droplet size. PMID:23927262

Emery, Samuel B; Rider, Keith B; Little, Brian K; Schrand, Amanda M; Lindsay, C Michael

2013-08-01

392

Production of a Biomimetic Fe(I)-S Phase on Pyrite by Atomic-Hydrogen Beam-Surface Reactive Scattering  

PubMed Central

Molecular beam-surface scattering and X-ray absorption spectroscopic experiments were employed to study the reaction of deuterium atoms with a pyrite, FeS2 (100), surface and to investigate the electronic and geometric structures of the resulting Fe-S phases. Incident D atoms, produced by a radio frequency plasma and expanded in an effusive beam, were directed at a pyrite surface held at various temperatures from ambient up to 200 °C. During exposure to the D-atom beam, D2S products were released with a thermal distribution of molecular speeds, indicating that the D atoms likely reacted in thermal equilibrium with the surface. The yield of D2S from the surface decreased approximately exponentially with exposure duration, suggesting that the surface accessible sulfur atoms were depleted, thus leaving an iron-rich surface. This conclusion is consistent with X-ray absorption measurements of the exposed surfaces, which indicated the formation of a layered structure, with elemental iron as the outermost layer on top of a formally Fe(I)-S phase as an intermediate layer and a formally Fe(II)-S2 bulk pyrite layer at lower depths. The reduced Fe(I)-S phase is particularly remarkable because of its similarity to the catalytically active sites of small molecule metalloenzymes, such as FeFe-hydrogenases and MoFe-nitrogenases.

Che, Li; Gardenghi, David J.; Szilagyi, Robert K.; Minton, Timothy K.

2011-01-01

393

Resolution and transfer width of thermal energy atomic scattering from solid surfaces (TEAS)  

NASA Astrophysics Data System (ADS)

The resolution of TEAS has been investigated as a function of energy spread of atomic beam. The model calculations have been executed within the framework of time dependent Schrödinger equation. The energy spread of realistic atomic beam has been taken into account by a wave-packet. The wave-packet describes the atomic beam as an ensemble of independent particles by quantum mechanics. Taking ideally periodic surface the resolution of diffraction peaks increases when the energy spread is decreased. This fact underlines the higher efficiency of the supersonic atomic source than the effusive atomic source. Furthermore the transfer width of experimental equipment increases—when the atomic beam monochromaticity is also increased—according to the concept of the transfer width. The relation between the transfer width and the size of the period of the surface topography significantly determines the resolution of the diffraction pattern.

Varga, G.

1999-04-01

394

Solid Helium.  

National Technical Information Service (NTIS)

Although the zero-point energy dominates the properties of the solid helium isotopes at low densities, more and more experimental evidence is accumulating to show that, except perhaps at a few singular points or limited regions of very low density, the th...

J. S. Dugdale

1964-01-01

395

Energy-related atomic and molecular structure and scattering studies. Annual progress report, July 1, 1980-June 30, 1981  

SciTech Connect

The basic goals of this program concern the experimental determination of properties of atoms and molecules and molecular clusters that are important in a wide range of energy-related processes, in particular, measurements of polarizabilities of highly polar molecules and their polymers, and of a number of important atomic elements distributed through the periodic table, as well as of the scattering of low-energy electrons by these same systems. The most significant scientific accomplishment of the program during the past year has been the completion of measurements of the dc electric dipole polarizabilities of a number of alkali halide dimers ((KCl)/sub 2/, (RbCl)/sub 2/, (CsCl)/sub 2/, (KF)/sub 2/, and (CsF)/sub 2/). An experiment was completed to measure the total cross sections for the scattering of low-energy electrons by atomic lithium, a very significant experimental test of a relatively simple, many-body system, which is amenable to elaborate computational determination.

Bederson, B.

1981-02-01

396

On the inversion of the atomic beam scattering data in the Eikonal approximation  

NASA Astrophysics Data System (ADS)

The inversion method of Celli, Garcia and Rieder requires some a-priori knowledge about the phases of the dominant scattering amplitudes. A perturbational method will be introduced here which is evaluated in the Eikonal approximation, but can in principle be extended to the Helmholtz equation. It is based on the observation that the expansion coefficients PG( n) of the scattering intensities with respect to ki, the incident wave vector, are functions of the corrugation amplitudes and phase differences and fulfill certain sum rules. If these coefficients are determined by several measurements with varying scattering parameters, then the lowest PG( n) for n = 2,3.4 are sufficient for finding the essentially unique surface profile function. As an example, simulated surface domain structure scattering data will be inverted.

Schlup, W. A.

1989-04-01

397

Application of the semiclassical perturbation (SCP) approximation to diffraction and rotationally inelastic scattering of atoms and molecules from surfaces  

SciTech Connect

The semiclassical perturbation (SCP) approximation of Miller and Smith (Phys. Rev. A 17, 17 (1978)) is applied to the scattering of atoms and molecules from crystal surfaces. Specifically, diffraction of He from LiF, and diffraction and rotationally inelastic scattering of H/sub 2/ from LiF are treated, and the SCP model is seen to agree well with earlier coupled-channel and quantum sudden calculations. These tests of the SCP model are all for ''soft'' interaction potentials, e.g., of the Lennard-Jones Devonshire variety, but it is also shown that the model behaves correctly in the limit of an impulsive hard-wall potential function. The SCP picture thus appears to have a wide range of validity for describing the dynamics of gas-surface collisions.

Hubbard, L.M.; Miller, W.H.

1983-02-15

398

A study of pseudoresonances in the application of the Schwinger variational principle to electron scattering from atomic hydrogen  

NASA Technical Reports Server (NTRS)

The Schwinger variational principle is applied to s-wave electron-hydrogen atom scattering. Computationally, consistent with a recent paper by Apagyi et al. (1988), there are pseudoresonances at the static exchange level of approximation, but not at the static level. The T-matrix as well as the K-matrix version of the Schwinger principle is used with a real Slater basis, and the same results are obtained in both. The origin of the pseudoresonances from singularities in the separable potential that is effectively employed in the Lippman-Schwinger equation from which the Schwinger variational principle can be derived. The determination of the pseudoresonance parameters from the separable potential is computationally inexpensive and may be used to predict the pseudoresonance parameters for the scattering calculations so as to avoid them.

Weatherford, Charles A.; Odom, Gregory; Tucker, Roy

1989-01-01

399

Energy-related atomic and molecular structure and scattering studies. Annual progress report, July 1, 1979-June 30, 1980  

SciTech Connect

The basic goals of this program concern the experimental determination of properties of atoms and simple molecules that are important in a wide range of energy-related processes. In particular we have initiated measurements of polarizabilities of highly polar molecules and dimers, and of a number of atoms distributed through the periodic table, and, of the scattering of low energy electrons by highly polar molecules. For this latter series of measurements an entirely new apparatus has been designed and its external components have been completed. A new electron optics assembly has also been designed and is currently under construction. Details of all these projects are presented; analysis and data of the polarizability measurements are also given.

Bederson, B.

1980-03-01

400

Interaction potentials for multi-electron atoms in front of a LiF (0 0 1) surface from rainbow scattering  

NASA Astrophysics Data System (ADS)

Pairwise interaction potentials for multi-electron atoms moving in front of a LiF (0 0 1) surface are investigated theoretically and experimentally. From angular distributions of fast He, N, S, Cl and Kr atoms grazingly scattered under axial surface channeling conditions, rainbow angles are experimentally determined for a wide range of energies for the motion normal to the surface plane. These angles are used as a benchmark to probe the pairwise potential model. In the simulations the scattering process is described by means of the surface eikonal approximation, while the atom-surface interaction is derived by adding binary interatomic potentials that include the proper asymptotic limit.

Gravielle, M. S.; Miraglia, J. E.; Schüller, A.; Winter, H.

2013-12-01

401

Determination of the electronic structure of atoms and molecules in the ground state: Measurement of molecular hydrogen by high-resolution x-ray scattering  

NASA Astrophysics Data System (ADS)

The high-resolution x-ray-scattering technique is used to study the elastic scattering of atoms and molecules in the gas phase. The elastic squared form factor, which is the square of the Fourier transformation of the electron density distribution in position space and reveals the pure electronic structure of atoms and molecules in the ground state, of molecular hydrogen is measured at an incident photon energy of about 9889 eV and an energy resolution of about 70 meV. Although it is generally thought that the x-ray-scattering technique is identical to high-energy electron scattering, at least for elastic scattering these two techniques have an apparent difference, i.e., the pure electronic structure of a molecule in the ground state can be determined by x-ray scattering while it cannot be obtained by the high-energy electron impact method due to the interference between the scattering of separate nuclei and of the electrons in the target. The present experimental results match the theoretical calculations very well, which demonstrates that high-resolution x-ray scattering is a powerful tool to study the electronic structure of atoms and molecules in the ground state.

Liu, Ya-Wei; Mei, Xiao-Xun; Kang, Xu; Yang, Ke; Xu, Wei-Qing; Peng, Yi-Geng; Hiraoka, Nozomu; Tsuei, Ku-Ding; Zhang, Peng-Fei; Zhu, Lin-Fan

2014-01-01

402

The surface morphology of a growing crystal studied by thermal energy atom scattering (TEAS)  

NASA Astrophysics Data System (ADS)

The growth of a Cu(100) surface from its vapour has been investigated by TEAS for different surface temperatures. The specularly reflected intensity of the growing surface shows temporal oscillations for in-phase and out-of-phase scattering conditions. In-phase data have been analyzed in terms of the, diffuse scattering from the surface steps whereas out-of-phase oscillations in terms of a kinematical and purely elastic description of the scattering from a random distribution of terraces. In both cases the temporal evolution of the step concentration of the growing crystal was obtained. Also, the surface diffusion coefficient of Cu adatoms was directly estimated from the experiments resulting in a preexponential of 1.4×10 -4cm 2s -1 and an activation energy of 0.40 eV.

De Miguel, J. J.; Sánchez, A.; Cebollada, A.; Gallego, J. M.; Ferrón, J.; Ferrer, S.

1987-10-01

403

Optimized Helium-Brayton Power Conversion for Fusion Energy Systems  

Microsoft Academic Search

This paper presents an overview and a few point designs for multiple-reheat helium Brayton cycle power conversion systems using molten salts (or liquid metals or direct helium cooling). All designs are derived from the General Atomics GT-MHR power conversion unit (PCU). The important role of compact, offset fin heat exchangers for heat transfer to the power cycle helium, and the

Zhao Haihua; Grant Fukuda; Ryan P. Abbott; Per F. Peterson

2005-01-01

404

One-photon scattering by an atomic chain in a two-mode resonator: cyclic conditions  

PubMed Central

In this work, a chain of N identical two-level atoms coupled with a quantized electromagnetic field, initially prepared via a single-photon Fock state, is investigated. The N-particle state amplitude of the system is calculated for several space configurations of the atoms in the Weisskopf-Wigner approximation. It was shown that the space configuration of an atomic chain, the total number of atoms, and even the available volume for the field modes define the behavior of the system state amplitude with time. Applying the condition of ‘cyclic bonds’, presented in this work, to the elaborated theory allows to describe the system time evolution, practically, for any space configuration.

2014-01-01

405

One-photon scattering by an atomic chain in a two-mode resonator: cyclic conditions  

NASA Astrophysics Data System (ADS)

In this work, a chain of N identical two-level atoms coupled with a quantized electromagnetic field, initially prepared via a single-photon Fock state, is investigated. The N-particle state amplitude of the system is calculated for several space configurations of the atoms in the Weisskopf-Wigner approximation. It was shown that the space configuration of an atomic chain, the total number of atoms, and even the available volume for the field modes define the behavior of the system state amplitude with time. Applying the condition of `cyclic bonds', presented in this work, to the elaborated theory allows to describe the system time evolution, practically, for any space configuration.

Sizhuk, Andrii S.; Yezhov, Stanislav M.

2014-05-01

406

One-photon scattering by an atomic chain in a two-mode resonator: cyclic conditions.  

PubMed

In this work, a chain of N identical two-level atoms coupled with a quantized electromagnetic field, initially prepared via a single-photon Fock state, is investigated. The N-particle state amplitude of the system is calculated for several space configurations of the atoms in the Weisskopf-Wigner approximation. It was shown that the space configuration of an atomic chain, the total number of atoms, and even the available volume for the field modes define the behavior of the system state amplitude with time. Applying the condition of 'cyclic bonds', presented in this work, to the elaborated theory allows to describe the system time evolution, practically, for any space configuration. PMID:24860278

Sizhuk, Andrii S; Yezhov, Stanislav M

2014-01-01

407

Positron scattering by atomic hydrogen using optical potentials and with positronium formation  

NASA Technical Reports Server (NTRS)

The scattering is considered of positrons by H(ls) in a two-state model which incorporates optical potentials. The model explicitly describes elastic scattering, i.e., positron + H(ls) yields positron + H(ls) and Ps(ls) yields Ps(ls) + p. The inelastic processes positron + H(ls) yields positron + H* Ps(ls) + p yields Ps* + p where * stands for a state other than ls, are implicitly taken into account through the optical potentials, which also allow for polarization of H(ls) and Ps(ls).

Walters, H. R. J.

1990-01-01

408

Adiabatic Dynamics of Periodic Waves in Bose-Einstein Condensates with Time Dependent Atomic Scattering Length  

Microsoft Academic Search

Evolution of periodic matter waves in one-dimensional Bose-Einstein condensates with time-dependent scattering length is described. It is shown that variation of the effective nonlinearity is a powerful tool for controlled generation of bright and dark solitons starting with periodic waves.

F. Kh. Abdullaev; A. M. Kamchatnov; V. V. Konotop; V. A. Brazhnyi

2003-01-01

409

Adiabatic Dynamics of Periodic Waves in Bose-Einstein Condensates with Time Dependent Atomic Scattering Length  

Microsoft Academic Search

Evolution of periodic matter waves in one-dimensional Bose-Einstein\\u000acondensates with time dependent scattering length is described. It is shown\\u000athat variation of the effective nonlinearity is a powerful tool for controlled\\u000ageneration of bright and dark solitons starting with periodic waves.

F. Kh; A. M. Kamchatnov; V. V. Konotop; V. A. Brazhnyi

2003-01-01

410

Effect of inelastic scattering on the resonance line shapes in He-graphite  

SciTech Connect

Recent experiments on the scattering of low-energy neutral helium beams from the basal surface of graphite have produced detailed spectra with prominent resonant features characteristic of physisorption of the incident atoms. Elastic calculations of the expected angular spectra show only qualitative agreement, with large discrepancies in both the overall scattered intensity and the widths and, in some cases, the signatures of the resonances. By consistently including a Debye-Waller factor to account for inelastic processes in scattering from the strongly repulsive part of the atom-surface potential, we obtain calculated spectra in very good agreement with observation, except near grazing incidence.

Hutchison, J.S.

1980-12-15

411

Combined inelastic neutron scattering and solid-state DFT study of dynamics of hydrogen atoms in trioctahedral 1 M phlogopite  

NASA Astrophysics Data System (ADS)

Inelastic neutron scattering (INS) was used to study the vibrational dynamics of the hydrogen atoms in natural trioctahedral phlogopite, K0.93Na0.03(Mg2.47Fe0.22Al0.16Fe0.04Tl0.06)[Si2.84Al1.16]O10OH1.71F0.28Cl0.01, within the 50-1,000 cm-1 energy range. The INS spectra collected using direct geometry spectrometer SEQUOIA (ORNL) were interpreted by means of the solid-state DFT calculations covering both normal mode analysis and molecular dynamics. To optimize the structure and to calculate the vibrational modes under harmonic approximation, both a hybrid PBE0 and the AM05 functional were used, while the molecular dynamics calculations (60 ps/1 fs) were performed only with the computationally less-demanding AM05 functional. The main contributions to the dominant band within ~750-550 cm-1 are symmetric and antisymmetric Mg-O-H bending modes, overlapping with the skeletal stretching and bending modes causing weaker secondary movements of H atoms of inner hydroxyl groups. Signatures of the Mg-O-H bending modes appear down to ~400 cm-1, where a region of octahedra deformation modes starts. These deformations cause just shallow movements of the hydrogen atoms and are mirrored by the modes with close vibrational energies. The region from ~330 cm-1 down to the low-energy end of the spectrum portrays induced vibrations of the H atoms caused by deformation of individual polyhedra, translational vibrations of the parts of the 2:1 layer relative one to another, and librational and translational vibrations of the layer. The main difference between the INS spectrum of dioctahedral Al-muscovite and trioctahedral Mg-phlogopite is that the Mg-O-H modes are all assigned to in-plane vibrations of the respective hydrogen atoms.

Smr?ok, L'ubomír; Kolesnikov, Alexander I.; Rieder, Milan

2012-10-01

412

Bichromatic Slowing of Metastable Helium  

NASA Astrophysics Data System (ADS)

This dissertation describes experiments to develop and realize an atomic decelerator (or "slower") for metastable helium using the optical bichromatic force (BCF). The research comprises two subtopics---using the bichromatic force at very large detunings, and developing a chirped BCF slower. There is experimental evidence that as bichromatic detunings approach 300 times the natural linewidth, the BCF breaks down. The likely cause is that large Doppler frequency shifts from the rapid deceleration result in cumulative dephasing of the Rabi cycling of the atom. To circumvent this and other problems, we have developed an alternate slower design in which the center frequency of a narrow BCF force profile is swept to stay resonant with the atoms as they are slowed. Results from a first-generation experiment show atomic slowing larger than has previously been possible with a large fixed detuning. Additional refinements will allow the design to be scaled up enough to slow metastable helium atoms to magneto-optical trapping velocities, with a brightness comparable to modern Zeeman slowers, but in a much smaller and considerably simplified configuration. I close with a discussion of prospects for direct laser slowing of molecules using the BCF. An estimate for CaF shows that a buffer-gas cooled beam can be slowed to rest, and proof-of-principle experiments in atomic helium yield very promising results.

Chieda, Michael Andrew

413

Intense-field scattering and capture of an electron by a model atom  

SciTech Connect

We have solved numerically the time-dependent Schroedinger equation for an electron in a superstrong laser field while it undergoes a collision with a model one-dimensional hydrogen atom. We show that a certain fraction of the electron can be trapped by the atom in superstrong fields. This trapped portion has a dichotomous spatial probability distribution, corresponding to an effective excitation of Kramers-Henneberger field-dressed states, which is quite resistant against subsequent detachment. By varying the incoming electron's kinetic energy these states can be selectively excited.

Grobe, R.; Eberly, J.H. (Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States))

1993-01-01

414

Dynamics of hydrogen atoms in superoxide dismutase by quasielastic neutron scattering.  

PubMed Central

The low energy dynamic of the enzyme Cu,Zn superoxide dismutase have been investigated by means of quasielastic neutron scattering in the temperature range 4-320 K. Below 200 K the scattering is purely elastic, while above this temperature a pronounced decrease in the elastic intensity is observed, together with the onset of a small quasielastic component. This behavior is similar to that previously observed in other more flexible globular proteins, and can be attributed to transitions between slightly different conformational substates of the protein tertiary structure. The presence of only a small quasielastic component, whose intensity is < or = 25% of the total spectrum, is related to the high structural rigidity of this protein.

Andreani, C; Filabozzi, A; Menzinger, F; Desideri, A; Deriu, A; Di Cola, D

1995-01-01

415

Relativistic distorted-wave calculation of inelastic electron-alkali atom scattering  

Microsoft Academic Search

The relativistic distorted-wave method was used to perform calculations for electron impact excitation of the first (n${\\\\rm p}) {}^2{\\\\rm P}_{1\\/2,3\\/2}$levels of Na, K and Rb at incident electron energies in the range 20-200 eV. Scattering parameters presented include differential and integrated cross sections, differential and integrated Stokes parameters, generalized STU-parameters and various collisional alignment and orientation parameters. Comparisons with experiment

V. Zeman; R. P. McEachran; A. D. Stauffer

1998-01-01

416

Resonances in the total cross section for scattering of electrons by atomic oxygen  

Microsoft Academic Search

In Radiological and Environmental Research Division annual report: ; radiation physics, July 1972--June 1973. By using an electron-scattering ; technique, two new resonant states of O⁻ were located at 8.80 eV and 14.06 ; eV. In addition, the existence of four other resonances previously observed in ; ion-neutral collision experiments was verified. An electron configuration 2p\\/sup ; 3\\/(⁴S)3s²(⁴S) has been

D. Spence; W. A. Chupka

1973-01-01

417

On the accuracy of the 'decoupled l-dominant' approximation for atom-molecule scattering  

Microsoft Academic Search

Cross sections for rotational excitation and spectral pressure broadening of HD, HCl, CO, and HCN due to collisions with low energy He atoms have been computed within the 'decoupled l-dominant' (DLD) approximation and are compared with accurate close coupling results and also with two similar approximations, the effective potential of Rabitz and the coupled states of McGuire and Kouri. DLD

Sheldon Green

1976-01-01

418

Rainbow structure and g-u-interference effects in the elastic scattering of low energy protons on deuterium and hydrogen atoms  

Microsoft Academic Search

Elastic differential cross sections for the scattering of low energy protons (Ec.m.=11-142 eV) on H and D atoms have been obtained. The curves exhibit clearly rainbow structure, g-u oscillations and a type of rapid interference, if coherent scattering of both sigmag and sigmau potential curves is taken into account. For comparison, partial wave calculations have been performed using WKB phases

A. Ding; J. Karlau; J. Weise

1976-01-01

419

Effect of quenching in resonant coherent excitation of hydrogen atoms scattered from LiF surfaces  

SciTech Connect

In this paper we analyze theoretically the 'signal background' observed in experimental studies of the radiative decay of hydrogen atoms following resonant coherent excitation (RCE) in grazing collisions with a LiF surface. The radiation intensity is evaluated by treating the RCE within a time-dependent (classical-trajectory) quantal approach, and by assuming that the excited electronic states are quenched whenever the atom-surface distance drops below a certain ''switching distance.'' Associating the mechanism of excited-state quenching with the charge transfer to the LiF conduction band we show that the hereto unexplained signal background can be attributed to the dependence of the switching distance on the incident energy.

Lugovskoy, A.V.; Bray, I. [Centre for Atomic, Molecular and Surface Physics, School of Mathematical and Physical Sciences, Murdoch University, Perth 6150 (Australia)

2003-03-01

420

Resonance enhancement of relativistic effects for the scattering of very slow electrons by heavy atoms  

SciTech Connect

Polarization of scattered electrons is enhanced up to 1 near {ital p}- and {ital d}-wave resonances or weakly bound negative-ion energy levels ({vert bar}{ital E}{vert bar}{approx lt}0.1 eV, {ital v}{sup 2}/{ital c}{sup 2}{approx lt}10{sup {minus}6}). We consider as examples Ra and Ba. We also note that the cross section for Ra is very large ({gt}10{sup 11} b at electron energy {similar to}10{sup {minus}2} eV).

Dzuba, V.A. (Institute of Nuclear Physics, Novosibirsk 630090 (U.S.S.R.)); Flambaum, V.V. (Institute of Nuclear Physics, Novosibirsk 630090, U.S.S.R. and Joint Institute for Laboratory Astrophysics (University of Colorado) National Institute of Standards and Technology, Boulder, Colorado (USA)); Sushkov, O.P. (Institute of Nuclear Physics, Novosibirsk 630090 (U.S.S.R.))

1991-10-01

421

X-ray scattering for the atomic structure of a barium-induced Si(111)-3 × 2 surface  

NASA Astrophysics Data System (ADS)

We have investigated the atomic arrangement of a barium (Ba)-induced Si(111)-3×2 surface by using surface-sensitive synchrotron X-ray scattering. In-plane fractional-order reflections obtained from three rotational domains of 3×1 symmetry have been used to examine several competing structural models including the honeycomb-chain-channel (HCC) and the double-?-bonded chain (D?C) models. By fitting two different data sets, both the goodness-of-the fits ?2 and the residuum R-factor strongly favor the HCC over the D?C model. We conclude that a Ba-paired HCC structure with a 1/3 monolayer of Ba coverage best describes the Ba-induced 3×2 surface with a Ba-Ba interatomic spacing d = 1.93 Å.

Kim, N. D.; Kang, T. S.; Je, J. H.; Kim, H. J.; Noh, D. Y.; Chung, J. W.

2008-04-01

422

CCMR: Characterization of Organic semiconductor thin films: In situ synchrotron x-ray scattering and ex situ atomic force microscopy  

NSDL National Science Digital Library

Our group studies the growth of organic semiconductor thin films, to better understand the connection between thin film morphology, crystal structure, and electronic device properties. Conventionally, thin films of organic semiconductors are deposited using thermal evaporation. However, the use of supersonic molecular beams to deposit thin films allows the incident kinetic energy of the organic semiconductor to be tuned in the range of 4-16 eV. The organic semiconductor thin films are characterized using in situ real time synchrotron x-ray scattering, and ex situ atomic force microscopy (AFM). My research experience this summer primarily consisted of analyzing x-ray data and studying the morphology of the thin films deposited on various dielectrics (self-assembled monolayers, SAMs) of varying chain length using AFM.

Greer, Douglas

2009-08-15

423

Stability of Helium Clusters during Displacement Cascades  

SciTech Connect

The interaction of displacement cascades with helium-vacancy clusters is investigated using molecular dynamics simulations. The He-vacancy clusters initially consist of 20 vacancies with a Helium-to-vacancy ratio ranging from 0.2 to 3. The primary knock-on atom (PKA) energy, Ep, varies from 2 keV to 10 keV, and the PKA direction is chosen such that a displacement cascade is able to directly interact with a helium-vacancy cluster. The simulation results show that the effect of displacement cascades on a helium-vacancy cluster strongly depends on both the helium-to-vacancy ratio and the PKA energy. For the same PKA energy, the size of helium-vacancy clusters increases with the He/V ratio, but for the same ratio, the cluster size changes more significantly with increasing PKA energy. It has been observed that the He-vacancy clusters can be dissolved when the He/V ratio less than 1, but they are able to re-nucleate during the thermal spike phase, forming small He-V nuclei. When the He/V ratio is larger than 1, the He-V clusters can absorb a number of vacancies produced by displacement cascades, forming larger He-V clusters. These results are discussed in terms of PKA energy, helium-to-vacancy ratio, number of vacancies produced by cascades, and mobility of helium atoms.

Yang, Li; Zu, Xiaotao T.; Xiao, H. Y.; Gao, Fei; Heinisch, Howard L.; Kurtz, Richard J.; Wang, Zhiguo; Liu, K. Z.

2007-02-01

424

Integral cross sections for electron scattering by ground-state Ba atoms  

NASA Astrophysics Data System (ADS)

We have used the convergent close-coupling method and a unitarized first-order many-body theory to calculate integral cross sections for elastic scattering and momentum transfer, for excitation of the 5d2 1S, 6s6p 1P1, 6s7p 1P1, 6s8p 1P1, 6s5d 1D2, 5d2 1D2, 6s6d 1D2, 6p5d 1F3, 6s4f 1F3, 6p5d 1D2, 6s6p 3P0,1,2, 6s5d 3D1,2,3, and 6p5d 3D2 states, for ionization and for total scattering by electron impact on the ground state of barium at incident electron energies from 1 to 1000 eV. These results and all available experimental data have been combined to produce a recommended set of integral cross sections.

Fursa, D. V.; Trajmar, S.; Bray, I.; Kanik, I.; Csanak, G.; Clark, R. E. H.; Abdallah, J., Jr.

1999-12-01

425

?-connectin studies by small-angle x-ray scattering and single-molecule force spectroscopy by atomic force microscopy  

NASA Astrophysics Data System (ADS)

The three-dimensional structure and the mechanical properties of a ?-connectin fragment from human cardiac muscle, belonging to the I band, from I27 to I34, were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I27-I34 fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described.

Marchetti, S.; Sbrana, F.; Toscano, A.; Fratini, E.; Carlà, M.; Vassalli, M.; Tiribilli, B.; Pacini, A.; Gambi, C. M. C.

2011-05-01

426

Effective Field Theory for Atom-Molecule Systems III: Dynamic Effects of a Feshbach Resonance on Bragg scattering from a Bose-Einstein Condensate  

Microsoft Academic Search

We present a theoretical model for Bragg scattering from a Bose-Einstein condensate (BEC) in the vicinity of a magnetic Feshbach resonance, using a two c-field formalism, one c-field for the atom and the other for a molecule formed of two atoms. We use this model to numerically simulate a recent experiment [S. B. Papp et al., Phys. Rev. Lett., 101(13):135301,

Catarina E. Sahlberg; R. J. Ballagh; C. W. Gardiner

2011-01-01

427

Electronically stimulated Raman scattering and four-photon parametric interaction in barium atom vapor under pumping by tunable ultrashort light pulses  

Microsoft Academic Search

A phosphate neodymium glass laser has been developed to study nonlinear optical processes in barium atom vapor. The temporal characteristics of barium atom vapor were investigated experimentally using the modified second-harmonic beam method. Electronically stimulated Raman scattering and four-photon parametric interaction were used to convert laser pulses into Stokes and anti-Stokes waves. The wavelengths of the Stokes and anti-Stokes waves

S. O. Sapondzhian; D. G. Sarkisian; G. A. Torosian

1985-01-01

428

Complex angular momentum analysis of low-energy electron elastic scattering from lanthanide atoms  

SciTech Connect

Electron attachment to the lanthanide and Hf atoms resulting in the formation of stable excited lanthanide and Hf anions as Regge resonances is explored in the near-threshold electron impact energy region, E<1.0 eV. The investigation uses the recent Regge-pole methodology wherein is embedded the electron-electron correlations together with a Thomas-Fermi-type model potential incorporating the crucial core-polarization interaction. The near-threshold electron elastic total cross sections (TCSs) for the lanthanide and Hf atoms are found to be characterized by extremely narrow resonances whose energy positions are identified with the binding energies (BEs) of the resultant anions formed during the collision as Regge resonances. The extracted BEs for excited lanthanide anions are contrasted with those of the most recently calculated electron affinities (ground state BEs). We conclude that the BEs for the Pr{sup -}, Tb{sup -}, Dy{sup -}, Ho{sup -}, Er{sup -}, and Tm{sup -} anions of O'Malley and Beck [Phys. Rev. A 79, 012511 (2009)] are not identifiable with the electron affinities as claimed. Formation of bound excited anions is identified in the elastic TCSs of all the lanthanide atoms including Hf, except Eu and Gd. The imaginary part of the complex angular momentum L, ImL is used to distinguish between the shape resonances and the bound excited negative ions. These results challenge both experimentalists and theoreticians alike since the excited anions are very weakly bound, but mostly tenuously bound (BEs<0.1 eV). Shape resonances and Ramsauer-Townsend minima are also presented.

Felfli, Z.; Msezane, A. Z. [Department of Physics and Centre for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, Georgia 30314 (United States); Sokolovski, D. [School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN (United Kingdom); Department of Chemical Physics, University of the Basque Country, Leioa (Spain)

2010-04-15

429

Collisions of excited alkali atoms with O2. II. Reactive scattering  

Microsoft Academic Search

Inelastic and reactive channels in excited Na atom\\/ O2 molecule collisions have been included into a single model based on multiple crossings between curves of the Na(n,l)–O2, Na+–O?2 (X 2&Pgr;g), and Na+–O?2 (A 2&Pgr;u) systems. Additionally, estimation is provided of the excited ion pair surface Na+–O?2 (A2&Pgr;u) in collinear geometry. This paper is essentially concerned with the reaction of Na(4D)

J. M. Mestdagh; D. Paillard; J. Berlande

1988-01-01

430

Note: Mechanical etching of atomic force microscope tip and microsphere attachment for thermal radiation scattering enhancement.  

PubMed

This Note describes a mechanical etching technique which can be used to prepare silicon tips used in atomic force microscopy apparatus. For such devices, dedicated tips with specific shapes are now commonly used to probe surfaces. Yet, the control of the tip morphology where characteristic scales are lower than 1 ?m remains a real challenge. Here, we detail a controlled etching process of AFM probes apex allowing micrometer-sized sphere attachment. The technique used and influent parameters are discussed and SEM images of the achieved tips are given. Deceptive problems and drawbacks that might occur during the process are also covered. PMID:24387482

Brissinger, D; Parent, G; Lacroix, D

2013-12-01

431

Note: Mechanical etching of atomic force microscope tip and microsphere attachment for thermal radiation scattering enhancement  

NASA Astrophysics Data System (ADS)

This Note describes a mechanical etching technique which can be used to prepare silicon tips used in atomic force microscopy apparatus. For such devices, dedicated tips with specific shapes are now commonly used to probe surfaces. Yet, the control of the tip morphology where characteristic scales are lower than 1 ?m remains a real challenge. Here, we detail a controlled etching process of AFM probes apex allowing micrometer-sized sphere attachment. The technique used and influent parameters are discussed and SEM images of the achieved tips are given. Deceptive problems and drawbacks that might occur during the process are also covered.

Brissinger, D.; Parent, G.; Lacroix, D.

2013-12-01

432