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1

Helium Atom Scattering from Isolated Adsorbates and Ordered Adsorbate Layers.  

NASA Astrophysics Data System (ADS)

The results of two experiments on the scattering of thermal energy helium atoms from metal surfaces with adsorbed atoms or molecules are reported. In the first experiment, measurements were made on the scattering from low coverages of adsorbed CO molecules on the Au(111) surface. The measured total and differential scattering cross sections for an isolated adsorbed CO molecule are in good agreement with a proposed model of the scattering interaction based on the gas phase He-CO interaction potential, and are dominated by a long-range attractive interaction. A binding energy of 0.4eV/molecule and a sticking coefficient of 2 times 10^{-6} are determined for the CO-Au(111) system. In the second experiment, measurements were made on the scattering from several ordered carbon overlayers on the W(100) surface. Helium scattering was used to characterize the high temperature oxidation of the saturated W(100)-(5 x 1)C surface, which repeatably produced the lower coverage c(2 x 2) carbon overlayer before the onset of tungsten oxide formation. Diffraction from the c(2 x 2) and (5 x 1) overlayers is analyzed to give an approximate topography of the outer surface layer at the dilute surface charge density probed by a low energy helium atom. Strong first order scattering observed from the (5 x 1) overlayer indicates that the surface topography is highly corrugated and more complicated than a simple distorted hexagonal overlayer. Helium diffraction peak splittings were observed from a stepped c(2 x 2) carbide structure during extensive oxidation of the W(100) surface. Consideration of the transfer width of the apparatus shows that the observed splittings cannot arise as first order diffraction from a laterally periodic array of steps with a large superperiod. The qualitative features of the splittings can be explained using a simple two level surface model, with no lateral order in the step distribution that joins the two levels.

Elliott, Gregory Stuart

1988-06-01

2

Helium atom scattering investigation of the Sb(111) surface  

NASA Astrophysics Data System (ADS)

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 Å of the remaining terraces.

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

2013-10-01

3

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

2013-08-23

4

Selective detection of metastable helium atoms by elastic scattering collisions  

NASA Astrophysics Data System (ADS)

A method for efficient and selective detection of 21S and 23S metastable He atoms is presented. Elastic collisions with Ar atoms in a diffuse gas spatially separate these 2S atoms from the copropagating UV photons that are inherently present in metastable beams. The deflected 2S atoms are detected on a large-solid-angle Faraday cup. A He discharge lamp can selectively quench 21S atoms, and optical pumping together with a Stern-Gerlach magnet can selectively remove 23S atoms. As a result, we are able to efficiently detect either 21S or 23S atoms (or both) without a UV background.

Kato, K.; Fitzakerley, D. W.; George, M. C.; Vutha, A. C.; Weel, M.; Storry, C. H.; Kirchner, T.; Hessels, E. A.

2012-07-01

5

Observation of jump diffusion of isolated sodium atoms on a Cu(001) surface by helium atom scattering  

Microsoft Academic Search

The diffusion of sodium adatoms on a Cu(001) surface has been studied with quasielastic helium atom scattering. A jump mechanism was found with activation energy 51 meV, jump length 2.56 Å, and jump attempt frequency nu0 0.53 THz. The adatom vibrational frequency parallel to the surface is measured to be 1.23 THz. The data are interpreted with the aid of

J. Ellis; J. P. Toennies

1993-01-01

6

Surface-phonon dispersion curves of KBr(001) via helium-atom scattering: Comparison with calculations  

SciTech Connect

A helium-atom surface-scattering instrument, employing a time-of-flighttechnique to observe inelastically scattered He atoms, has been used to measurethe surface-phonon dispersion curves of the KBr(001) surface. Data werecollected in the two high-symmetry directions, <100> and<110>, over the entire Brillouin zone for a target temperatureof /similar to/115 K and incident He wave vector /ital k//sub /ital i//approx.7A/sup /minus/1/. The results show important differences from sometheoretical predictions of shell-model calculations that use parametersobtained by fitting bulk dispersion curves. In addition, the measured surfacedispersion curves of KBr and of RbCl (reported previously) deviate from''mirror-symmetry'' behavior, unlike their bulk dispersion curves.

Chern, G.; Skofronick, J. G.; Brug, W. P.; Safron, S. A.

1989-06-15

7

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

8

The surface phase diagram of Li/Cu(001) explored by helium atom scattering  

NASA Astrophysics Data System (ADS)

We use helium atom scattering to investigate the structures formed by Li adsorption onto Cu(001) in the 0-2 ML regime. Submonolayer growth at 180 K proceeds through a sequence of ordered overlayers, including a c(2 × 2) structure at 0.5 ML and a series of 'ladder' superlattices around 0.6 ML. Beyond 1 ML, incommensurate, three-dimensional Li islands develop. A quantum close-coupled scattering analysis is performed to study the empirical He-surface potential of the structurally heterogeneous ladder structures. Good agreement with the measured distribution of diffracted intensity is obtained by describing the He-ladder interaction potential as the summation of only six one-dimensional Fourier components. The fitted potential indicates a remarkably flat surface that is punctuated by substantial, striped protrusions in the electron density. The result is consistent with the formation of one-dimensional Li wires, indicating an inhomogeneous metallization process.

Huang, Congcong; MacLaren, D. A.; Bacon, R. T.; Allison, W.

2011-09-01

9

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

PubMed

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. PMID:22354901

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

2012-03-14

10

ATOMIC AND MOLECULAR PHYSICS: Coupled-Channels Optical Calculation for Electron Scattering from Metastable Helium  

NASA Astrophysics Data System (ADS)

Coupled-channels optical calculations for total and resonance excitation integral cross sections for electron scattering on the metastable level 21,3 S of helium are presented. The results are in agreement with other theoretical and experimental data.

Wang, Yuan-Cheng; Zhou, Ya-Jun; Cheng, Yong-Jun; Ma, Jia

2009-08-01

11

Remark on polarization effects in small angle electron scattering by helium atoms in a CO2 laser field  

NASA Astrophysics Data System (ADS)

Referring to recent experiments by Wallbank and Holmes [Phys. Rev. A 48 (1993) R2515; J. Phys. B 27 (1994) 1221] on small angle, low energy electron scattering by helium atoms in a CO2 laser field, we investigate the possible influence of laser-induced target polarization and statistical fluctuations of the laser light on the observed non-linear cross section data.

Varró, S.; Ehlotzky, F.

1995-02-01

12

Surface Structure of Lithium Doped Potassium Tantalate (KLT) using Helium Atom Scattering.  

SciTech Connect

The structures of the (001) surface of potassium tantalate doped with nominally 2, 4 and 7% lithium have been investigated using high resolution helium atom scattering. The surfaces were prepared by cleaving single crystal samples in situ under UHV conditions. Diraction measurements in the region around the He specular re ection angle soon after cleaving yielded specular peaks initially with broad shoulders. However, over a period of about an hour, the widths of these specular peaks decreased markedly as the shoulders diminished into the background. Drift spectra measurements of the stabilized surfaces revealed that the step heights separating surface terraces were predominantly multiples of the cubic unit cell dimension, about 4A, rather than multiples of a half unit cell, 2A, expected from the cleaving of these crystals. Together these results suggest that after cleaving these surfaces are rapidly modied by migration of ions to the surface from the near-surface. Further, half-order diraction peaks were observed in the <100> azimuth a short time after cleaving samples at room temperature, indicating that domains with (21) structure had formed.

Fatema, Rifat [Florida State University; Van Winkle, David [Florida State University; Skofronick, J. G. [Florida State University; Sanfron, Sanford a [Department of Chemistry and Biochemistry, Florida State University; Flaherty, F. A. [Valdosta State University, Valdosta, GA; Boatner, Lynn A [ORNL

2013-01-01

13

Compton-scattering studies on the helium atom beyond the impulse approximation  

SciTech Connect

A series expansion of the Born propagator allows one to represent successive corrections to the impulse approximation and exhibits their relative dependence in momentum transfer k and the Compton (target-structure) parameter q. The proposed treatment provides a physical interpretation of the observed Compton defects. It is shown here to be in close agreement with high-energy-electron-impact spectroscopy measurements obtained for helium atoms.

Tavard, C.; Dal Cappello, M.C.; Gasser, F.; Dal Cappello, C.; Wellenstein, H.F.

1983-01-01

14

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

15

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

16

Helium atom scattering study of the interaction of water with the BaF2(111) surface.  

PubMed

The interaction of water with the BaF2(111) single crystal surface is investigated using the helium atom scattering technique. It is found that H2O forms a long-range ordered two-dimensional (2D) phase with (1 x 1) translational symmetry already after an exposure of 3 L (1 L=10(-6) Torr s) at temperatures below 150 K. The activation energy for desorption of the saturated 2D phase, which is assigned to a bilayer, is estimated to be 46+/-2 kJ mol(-1), corresponding to a desorption temperature of 165 K. The desorption of multilayers was observed at 150 K, consistent with a binding energy of 42+/-2 kJ mol(-1). Before completion and after desorption of the saturated 2D phase, a superstructure consistent with a disordered (square root of 3 x square root of 3)R30 degrees lattice has been observed, which is attributed to the first layer of water with a coverage of one molecule per surface unit cell, in accordance with recent theoretical studies. Desorption of this phase is observed at temperatures above 200 K, consistent with an unexpectedly strong bonding of the molecules to the substrate. PMID:17614580

Vogt, Jochen

2007-06-28

17

Enhanced creation of dispersive monolayer phonons in XePt(111) by inelastic helium atom scattering at low energies.  

PubMed

Conditions likely to lead to enhanced inelastic atomic scattering that creates shear horizontal (SH) and longitudinal acoustic (LA) monolayer phonons are identified, specifically examining the inelastic scattering of (4)He atoms by a monolayer solid of XePt(111) at incident energies of 2-25 meV. There is strong inelastic scattering for both dispersive phonon branches (SH and LA) of the monolayer at incident energies below 8 meV. Several improvements enable more complete wave packet calculations of the inelastic scattering than in previous work. Long propagation times are made feasible by adding an absorbing potential at large distance. The times now extend to beyond 100 ps and enable a clarification of processes involving transient trapping of the He atoms. The wave packet is made more monochromatic by significantly increasing the spatial width of the initial Gaussian shape. The narrower energy distribution in the incident beam then enables a demonstration of strong energy dependence of the scattering over a scale of less than 0.3 meV. PMID:18052447

Hansen, F Y; Bruch, L W

2007-11-28

18

Precision spectroscopy of the helium atom.  

SciTech Connect

Persistent efforts in both theory and experiment have yielded increasingly precise understanding of the helium atom. Because of its simplicity, the helium atom has long been a testing ground for relativistic and quantum electrodynamic effects in few-body atomic systems theoretically and experimentally. Comparison between theory and experiment of the helium spectroscopy in 1s2p{sup 3}P{sub J} can potentially extract a very precise value of the fine structure constant a. The helium atom can also be used to explore exotic nuclear structures. In this paper, we provide a brief review of the recent advances in precision calculations and measurements of the helium atom.

Hu, S.-M.; Lu, Z.-T.; Yan, Z.-C.; Physics; Univ. of Science and Technology of China; Univ. of Chicago; Univ. of New Brunswick

2009-06-01

19

Helium Atom Scattering from KTa0:7Nb0:3O3 (001): Anomalous Surface reflectivity with varying surface temperature and helium wave vector  

SciTech Connect

Helium atom diraction experiments have been carried out on the (001) surface of KTaO3 doped with 30% Nb. The surfaces were produced by cleaving single crystals of the material in situ. After the samples were thermally cycled, the angular distributions measured in the <100> azimuth, but not those in the <110> azimuth, revealed half-order diraction peaks. These indicate the formation of small (21) surface domains. The scans of the specular and Bragg diraction peak intensities as the sample temperatures were varied from about 325K to 60-80K and back to 325K showed large hysteresis particularly in the <100> azimuth. In addition, these scans showed a distinct intensity dip at about 85K, which is far removed from any bulk phase transition temperature of this material. Most curious, the specular re ectivity of the surface was found to be a strong function of the He wavevector, decreasing rapidly as the wavevector was varied above or below an optimum value.

Fatema, Rifat [Florida State University; Trelenberg, T. W. [Florida State University; Van Winkle, David [Florida State University; Skofronick, J. G. [Florida State University; Safron, Sanford A. [Florida State University; Flaherty, F. A. [Valdosta State University, Valdosta, GA; Boatner, Lynn A [ORNL

2011-01-01

20

Atom lithography with metastable helium  

NASA Astrophysics Data System (ADS)

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* 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 ?=1083 nm light was used to channel and focus the He* atoms into lines separated by ?/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

2010-02-01

21

Investigation of epitaxial growth via high-resolution helium atom scattering: KBr onto RbCl(001)  

SciTech Connect

High-resolution He atom scattering experiments have been employed to study the growth of KBr onto a cleaved RbCl(001) surface in the temperatures range [approximately]180--220 K. Three kinds of measurements were carried out: deposition curves (specular intensity vs deposition time), angular distribution (total scattering intensity vs incident angle), and time-of-flight spectra. The oscillations in the deposition curves show the characteristic behavior of layer-by-layer growth. However, the analysis of the data indicates that the step height of the first layer is different from that of subsequent layers, 3.71 [angstrom] compared with 3.32 [angstrom] expected from the bulk lattice spacing. The results also suggest that the growth mode in this temperature range is to form numerous small islands initially which then merge together with continued deposition. At the same time the defect density is very low for the first monolayer, but it increases with the number of layers grown. Analysis of the time-of-flight spectra for the one monolayer film yields surface phonon dispersion branches consisting of the Rayleigh wave, a longitudinal resonance, and a surface optical mode lying in the gap between the bulk optical and acoustic bands. The Rayleigh wave appears very nearly the same as that for cleaved RbCl and KBr(001) surfaces (very similar to each other); the other branches are significantly softened. 54 refs., 12 figs.

Safron, S.A.; Duan, J.; Bishop, G.G.; Gillman, E.S.; Skofronick, J.G. (Florida State Univ., Tallahassee (United States))

1993-03-04

22

Helium inductively coupled plasmas for atomic spectrometry  

Microsoft Academic Search

Annular helium inductively coupled plasmas (ICPs) operated at atmospheric pressure have been developed for atomic spectrometry. Compared to the conventional argon ICP, the helium plasma exhibited superior detection power for the determination of nonmetals by atomic emission spectrometry and mass spectrometry. In general, both the emission background and the mass spectral background for the He ICP were simpler than those

Chan

1989-01-01

23

Inelastic Scattering of Electrons by Helium.  

National Technical Information Service (NTIS)

Bethe-Goldstone continuum equations for the scattering of electrons from helium are solved variationally in the energy range between the n = 2 and n = 3 thresholds. Polarization and correlation effects are included in the calculations by allowing for virt...

R. S. Oberoi R. K. Nesbet

1973-01-01

24

COMMENT: `Small angle scattering of slow electrons by helium atoms in a ? laser field: a collective model' by S Varró and F Ehlotzky  

NASA Astrophysics Data System (ADS)

Varró and Ehlotzky (1995) have employed an effective laser-induced polarizability to explain the breakdown of the Kroll - Watson approximation observed for small-angle electron - helium scattering in a laser field. Their derivation omits a cancelling electronic contribution so that the coherent polarization potential they introduce is much too weak to explain the breakdown.

Dickinson, Alan S.

1996-04-01

25

Calculation of electron-helium scattering  

Microsoft Academic Search

We present the convergent close-coupling theory for the calculation of electron-helium scattering. We demonstrate its applicability at a range of projectile energies of 1.5 to 500 eV to scattering from the ground state to n<=3 states. Generally, good agreement with experiment is obtained with the available differential, integrated, ionization, and total cross sections, as well as with the electron-impact coherence

Dmitry V. Fursa; Igor Bray

1995-01-01

26

Low-energy scattering of muonic hydrogen on helium and lithium nuclei  

Microsoft Academic Search

The energy dependence of the formation rates of the hydrogen-helium and hydrogen-lithium mesomolecules and the elasic cross sections for the scattering of muonic hydrogen on helium and lithium are calculated. The Ramsauer-Townsend effect is predicted for the elastic scattering. The elastic cross section for the t-mu atom attains the magnitude of the atomic dimensions. The electron screening effect is shown

A. V. Kravtsov; A. I. Mikhailov; N. P. Popov

1986-01-01

27

Electron-helium scattering in Debye plasmas  

SciTech Connect

Electron-helium scattering in weakly coupled hot-dense (Debye) plasma has been investigated using the convergent close-coupling method. The Yukawa-type Debye-Hueckel potential has been used to describe plasma Coulomb screening effects. Benchmark results are presented for momentum transfer cross sections, excitation, ionization, and total cross sections for scattering from the ground and metastable states of helium. Calculations cover the entire energy range up to 1000 eV for the no screening case and various Debye lengths (5-100 a{sub 0}). We find that as the screening interaction increases, the excitation and total cross sections decrease, while the total ionization cross sections increase.

Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor [ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia); Janev, R. K. [Macedonian Academy of Sciences and Arts, P.O. Box 428, 1000 Skopje (Macedonia, The Former Yugoslav Republic of)

2011-11-15

28

Neutral atom lithography with metastable helium  

NASA Astrophysics Data System (ADS)

In this dissertation we describe our performance of resist assisted neutral atom lithography using a bright beam of metastable 23S1 Helium (He*). Metastable Helium atoms have 20 eV of internal energy making them easy to detect and able to destroy a resist. The He* is produced by a reverse flow DC discharge source and then collimated with the bichromatic force, followed by three optical molasses velocity compression stages. The atoms in the resulting beam have a mean longitudinal velocity of 1125 m/s and a divergence of 1.1 mrad. The typical beam flux is 2 x 109 atoms/mm2s through a 0.1mm diameter aperture 70 cm away from the source. The internal energy of the atoms damages the molecules of a self assembled monolayer (SAM) of nonanethiol. The undisturbed SAM protects a 200 A layer of gold that has been evaporated onto a prepared Silicon wafer from a wet chemical etch. Two methods are used to pattern the He* atoms before they destroy the SAM. First, a Nickel micro mesh was used to protect the SAM. These experiments established an appropriate dosage and etch time for patterning. The samples were analyzed with an atomic force microscope and found to have an edge resolution of 63 nm. Then, patterning was accomplished using the dipole force the atoms experience while traversing a standing wave of lambda = 1083nm light tuned 500MHz below the 23S 1 ? 23P2 transition. Depending on the intensity of the light, the He* atoms are focused or channeled into lines separated by lambda/2. The lines 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 x 10 3 lines of length 5500lambda. These results agree with our numerical simulations of the experiment.

Allred, Claire Shean

29

(Helium atom surface scattering apparatus for studies of crystalline surface dynamics): Progress report covering the period from May 1, 1985 to April 30, 1988  

SciTech Connect

The primary goal of this grant was the construction of a state-of-the-art He atom-surface spectroscopy (HASS) scattering instrument which would be capable of determining both the structure and the dynamics of metal, insulator and semiconductor surfaces. The essence of the method is the measurement of the elastic and inelastic scattering of He atoms from the crystal surface as a function of angle and energy gains or losses. The time period for the construction was projected to be approximately three years, after which a program of studies on the surface dynamics of various crystal surfaces would be started. The project was begun on May 1, 1985, and this report covers the progress from inception to present. In what follows, we will show that the construction is very nearly complete, the nozzle beam has been characterized, both before and after scattering from a LiF crystal surface, and angular distributions from this surface have also been taken. They show, in addition to the specular and Bragg peaks, fine structure between the peaks due to various inelastic collision processes which have previously been reported in the literature. Our current efforts are to measure the inelastic processes by time-of-flight methods so as to repeat the previous surface dispersion measurements. 9 refs.

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

1987-01-01

30

Nature of excited helium atoms in liquid helium: a theoretical model  

Microsoft Academic Search

A model is developed in which excited helium atoms in liquid helium may exist in stable cavities of diameter 10 A and larger. A repulsive effective interaction between the excited atom and the remaining atoms in the ground state is responsible for cavity formation. The equilibrium shape of the cavity is determined by minimizing the total energy, which is the

A. P. Hickman; W. Steets

1975-01-01

31

Implantation of neutral atoms into liquid helium by laser sputtering  

Microsoft Academic Search

We have developed a new method for producing a high density of neutral atoms in liquid helium; laser sputtering within liquid helium. When we irradiate samples immersed in liquid helium with a pulsed laser, a large number of clusters are introduced into the liquid. When we further irradiate these clusters with an additional pulse laser, the clusters are sputtered and

A. Fujisaki; K. Sano; T. Kinoshita; Y. Takahashi; T. Yabuzaki

1993-01-01

32

Nondispersive Two-Electron Wave Packets in a Helium Atom  

NASA Astrophysics Data System (ADS)

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

2005-09-01

33

Semiclassical theory of the helium atomic spectrum  

SciTech Connect

A semiclassical theory of the excitations of two-electron atoms is developed, based on the collective coordinate method and the 1/N expansion, and its application to the s-state helium spectrum is considered. The leading approximation, where quantum fluctuations due to the kinetic term are quenched, while attendant effects are accommodated by an effective potential, provides an inset to delineate spontaneous symmetry rearrangement of the system. The cumulative spectral content of the fragmentation or single-particle regime and the affiliated electron regime as reflected by the doubly excited states, is a Rydberg series within a Rydberg series. The collective regime promotes novel molecular features, such as vibrational s states, due to the underlying geometrical configurations of the affiliated electrons. The work also touches on issues such as quantum defect theory, topological quantization, and rotational effects.

van der Merwe, P.d.T.

1984-12-20

34

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

35

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

36

Energy Relaxation of Helium Atoms in Astrophysical Gases  

NASA Astrophysics Data System (ADS)

We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular- and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy- and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.

Lewkow, N. R.; Kharchenko, V.; Zhang, P.

2012-09-01

37

ENERGY RELAXATION OF HELIUM ATOMS IN ASTROPHYSICAL GASES  

SciTech Connect

We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular- and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy- and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.

Lewkow, N. R.; Kharchenko, V. [Department of Physics, University of Connecticut, Storrs, CT 06269 (United States); Zhang, P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2012-09-01

38

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

39

Scattering models for ultracold atoms  

NASA Astrophysics Data System (ADS)

We present a review of scattering models that can be used to describe the low-energy behavior of identical bosonic atoms. In the simplest models, the only degrees of freedom are atoms in the same spin state. More elaborate models have other degrees of freedom, such as atoms in other spin states or diatomic molecules. The parameters of the scattering models are specified by giving the S-wave phase shifts for scattering of atoms in the spin state of primary interest. The models are formulated as local quantum field theories and the renormalization of their coupling constants is determined. Some of the parameters can be constrained by renormalizability or by the absence of negative-norm states. The Green's functions that describe the evolution of two-atom states are determined analytically. They are used to determine the T-matrix elements for atom-atom scattering and the binding energies of diatomic molecules. The scattering models all exhibit universal behavior as the scattering length in a specific spin state becomes large.

Braaten, Eric; Kusunoki, Masaoki; Zhang, Dongqing

2008-07-01

40

Scattering models for ultracold atoms  

SciTech Connect

We present a review of scattering models that can be used to describe the low-energy behavior of identical bosonic atoms. In the simplest models, the only degrees of freedom are atoms in the same spin state. More elaborate models have other degrees of freedom, such as atoms in other spin states or diatomic molecules. The parameters of the scattering models are specified by giving the S-wave phase shifts for scattering of atoms in the spin state of primary interest. The models are formulated as local quantum field theories and the renormalization of their coupling constants is determined. Some of the parameters can be constrained by renormalizability or by the absence of negative-norm states. The Green's functions that describe the evolution of two-atom states are determined analytically. They are used to determine the T-matrix elements for atom-atom scattering and the binding energies of diatomic molecules. The scattering models all exhibit universal behavior as the scattering length in a specific spin state becomes large.

Braaten, Eric [Department of Physics, Ohio State University, 191 W Woodruff Avenue, Columbus, OH 43210 (United States)], E-mail: braaten@mps.ohio-state.edu; Kusunoki, Masaoki [Department of Physics, University of Arizona, Tucson, AZ 85721 (United States)], E-mail: masa@mps.ohio-state.edu; Zhang Dongqing [Department of Physics, The Ohio State University, 191 W Woodruff Avenue, Columbus, OH 43210 (United States)], E-mail: zhangdq@mps.ohio-state.edu

2008-07-15

41

Neutron scattering study of elementary excitations in liquid helium-3  

Microsoft Academic Search

The neutron inelastic scattering function of liquid helium-3 at 0.015 K has been measured for wave vectors in the range 0.8 A⁻¹< or =q< or =2.2 A⁻¹. For q<1.4 A⁻¹, the scattering function contains two peaks. The peak at lower energy is due to spin-fluctuation scattering in the particle-hole region while the peak at higher energy is identified to be

K. Skold; C. A. Pelizzari; R. Kleb; G. E. Ostrowski

1976-01-01

42

Dispersion coefficients for interactions between helium atoms in Debye plasmas  

SciTech Connect

Effect of Debye plasmas on the dispersion coefficients C{sub 8}, C{sub 10}, and C{sub 12} for interactions between atoms has been investigated using highly accurate correlated exponential basis functions. In the free-atom case, the dispersion C{sub 12} coefficient and the hexadecapole polarizability for helium are reported. The dispersion coefficients, hexadecapole polarizability, and 1s5g {sup 1}G{sup e} state energy of helium for different screening parameters are also reported.

Kar, Sabyasachi [Center for Theoretical Atomic and Molecular Physics, The Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China); Ho, Y. K. [Institute of Atomic and Molecular Sciences, Academia Sinica, Post Office Box 23-166, Taipei, Taiwan 106 (China)

2010-06-15

43

Nuclear polarizability of helium isotopes in atomic transitions  

SciTech Connect

We estimate the nuclear polarizability correction to atomic transition frequencies in various helium isotopes. This effect is non-negligible for high precision tests of quantum electrodynamics or accurate determination of the nuclear charge radius from spectroscopic measurements in helium atoms and ions; in particular it amounts to 28(3) kHz for 1S-2S transition in {sup 4}He{sup +}.

Pachucki, K. [Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Moro, A. M. [Departamento de FAMN, Universidad de Sevilla, Apartado 1065, 41080 Sevilla (Spain)

2007-03-15

44

Atomic resonance and scattering  

SciTech Connect

Experiments were conducted in the following areas: mapping of energy levels of a Rydberg lithium atom in a strong magnetic field in the vicinity of a crossing between levels from different principle quantum numbers, electrodynamics in a cavity, resonance enhanced multiphoton ionization, velocity dependence of rotational rainbow structure in Na2-Ar, high precision mass measurement on single ions using cyclotron resonance, low temperature energy transfer, trapping of neutral atoms, and vibrationally inelastic collisions.

Kleppner, D.; Pritchard, D.E.; Ahmad-Bitar, R.; Ducas, T.; Kelleher, D.; Ligare, M.; Lyyra, A.M.; Moskowitz, P.; Saenger, K.L.; Smith, N.

1984-01-01

45

Observing Superradiant Decay of Excited-State Helium Atoms Inside Helium Plasma  

NASA Astrophysics Data System (ADS)

Using femtosecond transient absorption spectroscopy on excited-state helium atoms in a plasma created through optical field ionization, we measured the decay of 2S3-2P3 excitation with sub-ps temporal resolution. The population evolution shows that initial decay is significantly faster than the electron-atom collisions and three orders of magnitude faster than the single atom spontaneous decay rate. This indicates on superradiant coherent behavior of the atomic system inside the plasma.

Xia, Hui; Svidzinsky, Anatoly A.; Yuan, Luqi; Lu, Chao; Suckewer, Szymon; Scully, Marlan O.

2012-08-01

46

Convergent close-coupling calculations of positron scattering on metastable helium  

SciTech Connect

The convergent close-coupling method has been applied to positron scattering on a helium atom in the 2 {sup 3}S metastable state. For this system the positronium (Ps) formation channel is open even at zero scattering energy making the inclusion of the Ps channels especially important. Spin algebra is presented for the general case of arbitrary spins. A proof is given of the often-used assumption about the relationship between the amplitudes for ortho-positronium and para-positronium formation. The cross sections for scattering from 2 {sup 3}S are shown to be significantly larger than those obtained for the ground state.

Utamuratov, R.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.; Stelbovics, A. T. [ARC Centre for Antimatter-Matter Studies, Department of Applied Physics, Curtin University, Perth 6152 (Australia)

2010-10-15

47

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

48

Elastic Electron Scattering from Tritium and Helium3  

Microsoft Academic Search

The mirror nuclei of tritium and helium-3 have been studied by the method of elastic electron scattering. Absolute cross sections have been measured for incident electron energies in the range 110-680 MeV at scattering angles lying between 40 and 135° in this energy range. The data have been interpreted in a straightforward manner and form factors are given for the

H. Collard; R. Hofstadter; E. B. Hughes; A. Johansson; M. R. Yearian; R. B. Day; R. T. Wagner

1965-01-01

49

Linewidths in bound state resonances for helium scattering from Si(111)-(1 × 1)H.  

PubMed

Helium-3 spin-echo measurements of resonant scattering from the Si(111)-(1 × 1)H surface, in the energy range 4-14 meV, are presented. The measurements have high energy resolution yet they reveal bound state resonance features with uniformly broad linewidths. We show that exact quantum mechanical calculations of the elastic scattering, using the existing potential for the helium/Si(111)-(1 × 1)H interaction, cannot reproduce the linewidths seen in the experiment. Further calculations rule out inelastic and other mechanisms that might give rise to losses from the elastic scattering channels. We show that corrugation in the attractive part of the atom-surface potential is the most likely origin of the experimental lineshapes. PMID:21828452

Tuddenham, F E; Hedgeland, H; Knowling, J; Jardine, A P; Maclaren, D A; Alexandrowicz, G; Ellis, J; Allison, W

2009-06-11

50

Electron-Helium Atom Collisions in the Presence of a Bichromatic Laser Field  

NASA Astrophysics Data System (ADS)

The differential cross section (DCS) for electron-helium atom collisions in the presence of a bichromatic CO2 laser field is investigated as a function of the scattering angle ? by employing first-Born approximation (FBA) with a simple screening electric potential. We discuss in detail the influence of the scattering geometry, the photon energy and the number of photons exchanged on the DCSs. These illustrate that the three factors have important effects on the elastic scattering and the screening electric potential is effective.

Zhu, Zun-Lue; Liang, Ming-Chao; Sun, Jin-Feng

2008-08-01

51

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

52

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

53

Spectroscopy of barium atoms in liquid and solid helium matrices  

SciTech Connect

We present an exhaustive overview of optical absorption and laser-induced fluorescence lines of Ba atoms in liquid and solid helium matrices in visible and near-infrared spectral ranges. Due to the increased density of isolated atoms, we have found a large number of spectral lines that were not observed in condensed helium matrices before. We have also measured the lifetimes of metastable states. The lowest {sup 3}D{sub 1} metastable state has lifetime of 2.6 s and can be used as an intermediate state in two-step excitations of high-lying states. Various matrix-induced radiationless population transfer channels have been identified.

Lebedev, V.; Moroshkin, P.; Weis, A. [Departement de Physique, Universite de Fribourg, Chemin du Musee 3, CH-1700 Fribourg (Switzerland)

2011-08-15

54

Using Uncertainty Principle to Find the Ground-State Energy of the Helium and a Helium-like Hookean Atom  

ERIC Educational Resources Information Center

|In this paper, we accurately estimate the ground-state energy and the atomic radius of the helium atom and a helium-like Hookean atom by employing the uncertainty principle in conjunction with the variational approach. We show that with the use of the uncertainty principle, electrons are found to be spread over a radial region, giving an electron…

Harbola, Varun

2011-01-01

55

Resonance studies of H atoms interacting with liquid helium surfaces. Annual summary report  

SciTech Connect

Techniques developed by this investigator for studying the hyperfine resonance of gaseous atomic hydrogen in storage bulbs under liquid helium will be extended downwards in temperature to 0.5 K, in order to study the interactions of H atoms with superfluid liquid helium surfaces and with each other while adsorbed on the liquid helium surfaces. A liquid helium temperature state-selected H atom beam will be developed and used to study the feasibility of hydrogen maser oscillation at liquid helium temperatures.

Crampton, S.B.

1980-10-01

56

High-energy electron-helium scattering in a Nd:YAG laser field  

SciTech Connect

We report measurements of the scattering of electrons by helium atoms in the presence of 1.17 eV photons from a Nd:YAG laser. The incident energy of the electrons was in the range 50-350 eV, and the polarization of the laser was arranged to be parallel to electrons scattered through 135 deg. Energy-shifted peaks corresponding both to one- and two-photon emission were observed. Calculations using the Kroll-Watson approximation are perfectly consistent with the data.

Harak, B. A. de [Physics Department, Illinois Wesleyan University, P.O. Box 2900, Bloomington, Illinois 61702-2900 (United States); Ladino, L.; MacAdam, K. B.; Martin, N. L. S. [Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055 (United States)

2011-02-15

57

Electron-helium free-free scattering in the presence of a laser field  

NASA Astrophysics Data System (ADS)

We report measurements of the scattering of electrons by helium atoms in the presence of 1.17 eV photons from a Nd:YAG laser. The incident energy of the electrons was in the range 50 - 350 eV and the polarization of the laser was arranged to be parallel to the scattered electrons. Energy-shifted peaks corresponding both to one- and two-photon emission were observed. Calculations using the Kroll-Watson approximation are perfectly consistent with the data.

deHarak, B. A.; Ladino, L.; MacAdam, K. B.; Martin, N. L. S.

2012-11-01

58

Atomic impact experiments with free helium-3 and helium-4 clusters  

Microsoft Academic Search

Free helium clusters with of the order of 103 to 107 atoms have been predicted to reach final temperatures of about 0.4 K in the case of4He, and of 0.15 K in the case of3He. In the first case, the clusters have to be expected to be superfluid, in the latter case to be normalfluid. Impact experiments with cesium atoms,

Jürgen Gspann

1995-01-01

59

The Helium Atom and Isoelectronic Ions in Two Dimensions  

ERIC Educational Resources Information Center

|The energy levels of the helium atom and isoelectronic ions in two dimensions are considered. The difficulties encountered in the analytical evaluation of the perturbative and variational expressions for the ground state, promote an interesting factorization of the inter-electronic interaction, leading to simple expressions for the energy. This…

Patil, S. H.

2008-01-01

60

Analysis of helium-ion scattering with a desktop computer  

Microsoft Academic Search

This paper describes a program written in an enhanced BASIC language for a desktop computer, for simulating the energy spectra of high-energy helium ions scattered into two concurrent detectors (backward and glancing). The program is designed for 512-channel spectra from samples containing up to 8 elements and 55 user-defined layers. The program is intended to meet the needs of analyses

J. W. Butler

1986-01-01

61

ATOMIC AND MOLECULAR PHYSICS: Influence of Isotope Substitution Helium Atom on Partial Cross Sections in He-HF Collisions  

NASA Astrophysics Data System (ADS)

Close-coupling equation and anisotropic potential developed in our previous research are applied to HF-3He (4He, 6He, 8He, 10He) collision system, and partial cross sections (PCSs) at the incident energy of 40 meV are calculated. By analyzing the differences of these PCSs, change rules of PCSs with the increase of partial wave number, and with the change of the mass of isotope substitution helium atom are obtained. The results show that excitation PCSs converge faster than elastic PCSs for collision energy and each of systems considered here. Also excitation PCSs converge more rapidly for high-excited states. Tail effect is present only in elastic scattering and low-excited states but not in high-excited states. With the increase of the mass of isotope substitution helium atom, converging speed of elastic, total inelastic, and state-to-state excitation PCS slows down, and the maxima of these PCSs undergoes a regular change.

Yu, Chun-Ri; Zhang, Jie; Chen, Li; Jiang, Gui-Sheng; Huang, Guo-Dong

2009-11-01

62

Electron Ejection from an Atomically Clean Tungsten Surface by Helium and Neon Metastable Atoms  

Microsoft Academic Search

The absolute electron yield gammam of helium and neon metastable atoms incident on an atomically clean polycrystalline tungsten surface has been determined. The value of gammam for helium excited by 28-volt electrons is 0.306+\\/-0.025, where 1S0 and 3S1 yields are equal within an experimental error of 20%; the value of gammam for neon is 0.215+\\/-0.020. The contribution of each of

D. A. Maclennan

1966-01-01

63

Ultrafast probing of ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets  

SciTech Connect

The ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets are studied with time-resolved extreme ultraviolet ion imaging spectroscopy. At excitation energies of 23.6 {+-} 0.2 eV, Rydberg atoms in n= 3 and n= 4 states are ejected on different time scales and with significantly different kinetic energy distributions. Specifically, n= 3 Rydberg atoms are ejected with kinetic energies as high as 0.85 eV, but their appearance is delayed by approximately 200 fs. In contrast, n= 4 Rydberg atoms appear within the time resolution of the experiment with considerably lower kinetic energies. Major features in the Rydberg atom kinetic energy distributions for both principal quantum numbers can be described within a simple elastic scattering model of localized perturbed atomic Rydberg atoms that are expelled from the droplet due to their repulsive interaction with the surrounding helium bath. Time-dependent kinetic energy distributions of He{sub 2}{sup +} and He{sub 3}{sup +} ions are presented that support the formation of molecular ions in an indirect droplet ionization process and the ejection of neutral Rydberg dimers on a similar time scale as the n= 3 Rydberg atoms.

Buenermann, Oliver; Kornilov, Oleg; Neumark, Daniel M. [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Haxton, Daniel J.; Gessner, Oliver [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Leone, Stephen R. [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States)

2012-12-07

64

Quantum Solvation of Carbonyl Sulfide with Helium Atoms  

Microsoft Academic Search

High-resolution infrared and microwave spectra of HeN-carbonyl sulfide (HeN-OCS) clusters with N ranging from 2 to 8 have been detected and unambiguously assigned. The spectra show the formation of a solvation layer beginning with an equatorial ``donut'' of five helium atoms around the OCS molecule. The cluster moment of inertia increases as a function of N and overshoots the liquid

Jian Tang; Yunjie Xu; A. R. W. McKellar; Wolfgang Jäger

2002-01-01

65

Electron and positron atomic elastic scattering cross sections  

NASA Astrophysics Data System (ADS)

A method was developed to calculate the total and differential elastic-scattering cross sections for incident electrons and positrons in the energy range from 0.01eV to 1MeV for atoms of /Z=1-100. For electrons, hydrogen, helium, nitrogen, oxygen, krypton, and xenon, and for positrons, helium, neon, and argon atoms were considered for comparison with experimental data. First, the variationally optimized atomic static potentials were calculated for each atom by solving the Dirac equations for bound electron states. Second, the Dirac equations for a free electron or positron are solved for an atom using the previously calculated static potential accomplished (in the case of electrons) by ``adjusted'' Hara's exchange potential for a free-state particle. Additional to the exchange effects, the charge cloud polarization effects are considered applying the correlation-polarization potential of O'Connell and Lane (with correction of Padial and Norcross) for incident electrons, and of Jain for incident positrons. The total, cutoff and differential elastic-scattering cross sections are calculated for incident electrons and positrons with the help of the relativistic partial wave analysis. The solid state effects for scattering in solids are described by means of a muffin-tin model, i.e. the potentials of neighboring atoms are superpositioned in such a way that the resulting potential and its derivative are zero in the middle distance between the atoms. The potential of isolated atom is calculated up to the radius at which the long-range polarization potential becomes a value of -10-8.

Stepanek, Jiri

2003-02-01

66

Experimental study of {mu}-atomic and {mu}-molecular processes in pure helium and deuterium-helium mixtures  

SciTech Connect

We present experimental results of {mu}-atomic and {mu}-molecular processes induced by negative muons in pure helium and helium-deuterium mixtures. The experiment was performed at the Paul Scherrer Institute (Switzerland). We measured relative intensities of muonic x-ray K series transitions in ({mu}{sup 3,4}He){sup *} atoms in pure helium as well as in helium-deuterium mixtures. The d{mu}{sup 3}He radiative decay probabilities for two different helium densities in D{sub 2}+{sup 3}He mixture were also determined. Finally, the q{sub 1s}{sup He} probability for a d{mu} atom formed in an excited state to reach the ground state was measured and compared with theoretical calculations using a simple cascade model.

Bystritsky, V.M.; Boreiko, V.F.; Gerasimov, V.V.; Pavlov, V.N.; Sandukovsky, V.G.; Stolupin, V.A.; Volnykh, V.P. [Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Czaplinski, W.; Popov, N.P.; Wozniak, J. [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, PL-30059 Cracow (Poland); Filipowicz, M. [AGH University of Science and Technology, Faculty of Fuels and Energy, PL-30059 Cracow (Poland); Huot, O.; Knowles, P.E.; Schaller, L.A.; Schneuwly, H. [Department of Physics, University of Fribourg, CH-1700 Fribourg (Switzerland); Mulhauser, F. [University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2005-03-01

67

Helium-atom-scattering study of multiphonon processes on LiF(001){l_angle}100{r_angle} with temperature variation for specular and off-specular angles  

SciTech Connect

High-resolution inelastic He-atom-scattering experiments, employing a time-of-flight energy resolution technique, have been carried out on LiF(001){l_angle}100{r_angle} for a wide range of temperatures and for several different incident beam angles. A quantum-mechanical multiphonon theory is used to explain the observed inelastic background. Numerical calculations based on the theory produce good agreement with experiment.

Bishop, G.G.; Gillman, E.S.; Baker, J.; Hernandez, J.J.; Safron, S.A.; Skofronick, J.G. [Department of Physics, Department of Chemistry, and Center for Materials Science Research and Development (MARTECH), Florida State University, Tallahassee, Florida 32306 (United States); Weera, S.M.; Manson, J.R. [Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (United States)

1995-11-01

68

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

69

Study of the stabilization and recombination of nitrogen atoms in impurity-helium condensates  

Microsoft Academic Search

The stabilization and recombination of nitrogen atoms N(4S) in nitrogen-helium and nitrogen–neon-helium condensates obtained by the injection of impurity particles from a gas discharge into bulk superfluid helium are investigated by the EPR method. It is established that the stabilized nitrogen atoms reside inside and on the surface of impurity clusters forming a porous structure in the bulk superfluid helium.

R. E. Boltnev; I. N. Krushinskaya; A. A. Pelmenev; E. A. Popov; D. Yu. Stolyarov; V. V. Khmelenko

2005-01-01

70

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

71

Ionization of helium atoms under the effect of the antineutrino magnetic moment  

SciTech Connect

Differential cross sections for inelastic antineutrino interaction with a helium atom are calculated. It is shown that, in the energy-transfer range extending up to 1 keV, the cross sections in question are considerably enhanced in the electromagnetic-interaction channel in relation to the cross sections for elastic scattering on a free electron. Absolute cross-section values are of interest in searches for the antineutrino magnetic moment, provided that its value in Bohr magneton units falls within the range (10{sup -13}-10{sup -12}){sub Micro-Sign B}.

Martemyanov, V. P., E-mail: vpmar@kiae.ru; Tsinoev, V. G. [Russian Research Centre Kurchatov Institute (Russian Federation)

2011-12-15

72

Collisions with Laser-Cooled, Metastable Helium Atoms  

NASA Astrophysics Data System (ADS)

Laser manipulation techniques have been used to create a bright beam of metastable He(2^3S) atoms which is used, amongst other things, as a source of cold atoms for loading a 3-D magneto-optical trap of He(2^3S). The trapped atoms provide an ideal vehicle for collision studies including atom-atom and electron-atom collisions, both with and without resonant, or near-resonant laser fields present. This talk will review the motivation for such studies and discuss the techniques which we use to create a cold ( 300 mK), dense ( 10^8 atoms/cc) cloud of trapped, excited He atoms. Experimental results for total electron scattering cross sections from He(2^3S) at energies between 5 and 100 eV will be presented, as will results of scattering from He(2^3P) atoms, formed in the trap by optical pumping of the 2^3S atoms at 1083 nm.

Buckman, Stephen J.

2003-10-01

73

Coherently enhanced Raman scattering in atomic vapor  

SciTech Connect

We present a scheme to obtain the coherently enhanced Raman scattering in atomic vapor which is induced by a spin wave initially written by a weak write laser. The enhancement of Raman scattering is dependent on the number and the spatial distribution of the flipped atoms generated by the weak write laser. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy because of its simplicity.

Yuan Chunhua; Chen, L. Q.; Jing, Jietai; Zhang, Weiping [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Ou, Z. Y. [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Department of Physics, Indiana University-Purdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202 (United States)

2010-07-15

74

Parametric Amplification of Scattered Atom Pairs  

Microsoft Academic Search

We have observed parametric generation and amplification of ultracold atom pairs. A Rb87 Bose-Einstein condensate was loaded into a one-dimensional optical lattice with quasimomentum k0 and spontaneously scattered into two final states with quasimomenta k1 and k2. Furthermore, when a seed of atoms was first created with quasimomentum k1 we observed parametric amplification of scattered atoms pairs in states k1

Gretchen K. Campbell; Jongchul Mun; Micah Boyd; Erik W. Streed; Wolfgang Ketterle; David E. Pritchard

2006-01-01

75

High precision calculation of helium and atom energy levels  

SciTech Connect

This work is concerned with the high-presicion calculation of the energies of the gound and excited states of the helium atom (or other light helium-like ions) to match the recent advances in experimental laser spectroscopic studies of transitions between these states with a precision of better than 10{sup {minus}4} cm{sup {minus}1}. At this level of accuracy it is essential to include mass-polarization effects through 2nd order, relativistic effects properly scaled by appropriate powers of the reduced mass, and quantum electrodynamic (QED) effects. In recent work on excited states of helium we have attained this level of accuracy for all the non-QED effects. Our results are in good agreement with those obtained independently by G. W. F. Drake. We are proceeding with a high-precision evaluation of the Bethe logarithm, which is the principal source of uncertainty in the theoretically determined QED effects. The refinement of these calculations at the 10{sup {minus}5} cm{sup {minus}1} level and beyond is expectd to stimulate further advances both theoretical and experimental, both in the calculations of 0({alpha}{sup 4}) Rydberg relativistic and QED effects and in the high-precision measurement of transition wavelengths.

Baker, J.; Hill, R.N.; Morgan, J.D. III (Department of Physics, University of Delaware, Newark, DE 19716 (USA))

1989-06-15

76

Scattering of photons from atomic electrons  

SciTech Connect

Validity of simpler approaches for elastic and inelastic photon scattering by atoms and ions is assessed by comparison with second-order S-matrix predictions. A simple scheme for elastic scattering based on angle-independent anomalous scattering factors has been found to give useful predictions near and below photoeffect thresholds. In inelastic scattering, major deviations are found from A{sup 2}-based calculations. Extension of free-atom and free-ion cross sections to the dense plasma regime is discussed. 20 refs., 6 figs.

Pratt, R.H.; Zhou, B.; Bergstrom, P.M. Jr. (Pittsburgh Univ., PA (USA). Dept. of Physics and Astronomy); Kissel, L. (Pittsburgh Univ., PA (USA). Dept. of Physics and Astronomy Sandia National Labs., Albuquerque, NM (USA)); Pisk, K.; Suric, T. (Institut Rudjer Boskovic, Zagreb (Yugoslavia))

1990-01-01

77

Pressure dependent line shifts of atoms in superfluid helium  

NASA Astrophysics Data System (ADS)

Defect atoms and ions in superfluid helium open the possibility to study the nature of the defect with respect to its environment. Depending on the electronic structure and charge of the foreign particles two forms of defects are built: so-called "bubbles" and "snowballs"(B. Tabbert, H. Günther and G. zu Putlitz, J. Low. Temp. Phys.) 109, 653 (1997). Defect ions are produced by laser sputtering, they can recombine with electrons from a field emission tip(I. Baumann, M. Foerste, K. Layer, G. zu Putlitz, B. Tabbert and C. Zühlke, J. Low. Temp. Phys.) 110, 213 (1998). The spectral lines observed are shifted and broadened compared to the free atomic transitions. The radius and the shape of the defect structure are supposed to be pressure dependent. Consequently we employ a pressure cell which allows for the spectroscopic measurements up to external pressures of 40 bar. Since liquid helium solidifies above 25 bar a study of the phase transition from the liquid to the solid can be made.

Putlitz, Gisbert Zu; Baumann, I.; Foerste, M.; Jungmann, K.; Tabbert, B.; Wiebe, J.; Zühlke, C.

1998-05-01

78

Transition wavelengths for helium atom in weakly coupled hot plasmas  

NASA Astrophysics Data System (ADS)

We have investigated the effect of surrounding plasmas on several singly excited and doubly excited meta-stable bound states of helium atom using highly correlated basis functions for singly excited S, P, D states and CI-type basis functions for doubly excited meta-stable D states. Plasma effect is taken care of by using a screened Coulomb (Yukawa) potential obtained from the Debye model that admits a variety of plasma conditions, and such a model plays an important role in plasma spectroscopy. The wavelengths for transitions from the 1snp 1P° (n=2,3)?1s21Se, 1snp 3P° (n=2,3)?1s2s 3Se, 2pnp 1Pe (n=3,4)?1s2p 1P°, 2pnp 3Pe (n=2,3)?1s2p 3P°, 2pnd 1D° (n=3,4)?1s3d 1De, 2pnd 3D° (n=3,4)?1s3d 3De, 2p3p 1Pe?2pnd 1D° (n=3,4), 2pnd 1D°(n=3, 4)?2p4p 1Pe, 2pnp 3Pe (n=2,3)?2p3d 3D°, and 2pnp 3Pe (n=2,3)?2p4d 3D° of helium atom in plasmas for various Debye lengths are reported.

Kar, Sabyasachi; Ho, Y. K.

2007-09-01

79

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

80

Photoionization Spectroscopy of Isolated cr Atoms in Ultracold Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Recently we succeeded in doping Cr atoms to He nanodroplets (HeN) at 0.4 Kand carried out resonance ionization mass spectroscopy (RIMS). Here we present resonant two-photon ionization (R2PI) measurements in the wavelength range from 350 to 361 nm (27700 - 28600 cm-1, 3.43 - 3.54 eV). As one of several possible ionization pathways we allocate a first excitation step to the y7Po ? a7S3 transition, happening inside the HeN. Due to the interaction with the surrounding He this excitation appears broadened in the spectra and gives the possibility to obtain detailed information about the perturbation upon electronic excitation of the Cr atom in HeN. Subsequently, the dopant atom leaves the HeN and is ionized in the gas phase where discrete free atom autoionization levels are populated leading to additional sharp spectral features. Future investigations with two photon two color ionization and selective electron energy ionization as well as quantum chemistry calculations will be discussed. M. Ratschek, M. Koch, and W. E. Ernst, J. Chem. Phys., in press (2012) 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.

Kautsch, Andreas; Hasewend, Matthias; Ratschek, Martin; Koch, Markus; Ernst, Wolfgang E.

2012-06-01

81

Rotational spectroscopic investigation of carbonyl sulfide solvated with helium atoms  

NASA Astrophysics Data System (ADS)

Rotational spectra of small- to medium-sized HeN-OCS clusters with N from 2 to 8 were investigated using a pulsed molecular beam Fourier transform microwave spectrometer and a microwave-microwave double resonance spectrometer. Spectra of five to eight isotopomers were measured for each HeN-OCS cluster. Nuclear quadrupole hyperfine structures were observed for 33S and 17O containing isotopomers. The isotopic data, together with the microwave-microwave double resonance experiments, were used to establish unambiguous assignments for these clusters. The assignment of N, the number of solvating helium atoms in a particular cluster, was supported by the observed intensity change under different backing pressure and nozzle cooling conditions and in particular by the systematic infrared vibrational band shifts from the concurrent infrared study. This sequence of clusters contains some of the largest clusters that have thus far been investigated with high-resolution spectroscopic techniques. This study provides detailed and important information for the understanding of the quantum solvation process of dopant molecules in helium nanodroplets.

Xu, Yunjie; Jäger, Wolfgang

2003-09-01

82

Scattering of electrons by hydrogen atoms  

SciTech Connect

The cross sections for elastic scattering and for excitation of hydrogen atoms by electron impact are calculated for energies in the range from 10.2 to 12.1 eV. The calculations are made variationally. A pseudostate expansion is employed to represent the target atom. Energies and widths of resonances are obtained. Results are compared with experiment.

Callaway, J.

1982-07-01

83

Using uncertainty principle to find the ground-state energy of the helium and a helium-like Hookean atom  

NASA Astrophysics Data System (ADS)

In this paper, we accurately estimate the ground-state energy and the atomic radius of the helium atom and a helium-like Hookean atom by employing the uncertainty principle in conjunction with the variational approach. We show that with the use of the uncertainty principle, electrons are found to be spread over a radial region, giving an electron cloud. Our calculation also shows how the Coulomb interaction between electrons affects their distribution. This leads to a physical picture of how electrons are located with respect to each other in these atoms. Finally, we also obtain through our calculations a general formula for the estimate of ground-state energy and radius of two electron atoms and ions with atomic number Z.

Harbola, Varun

2011-11-01

84

Efimov physics in atom-dimer scattering of Li atoms  

Microsoft Academic Search

Li atoms in the three lowest hyperfine states display universal properties when the S-wave scattering length between each pair of states is large. Recent experiments reported four pronounced features arising from Efimov physics in the atom-dimer relaxation rate, namely two resonances and two local minima. We use the universal effective-field theory to calculate the atom-dimer relaxation rate at zero temperature.

H.-W. Hammer; Daekyoung Kang; Lucas Platter

2010-01-01

85

Electron-Atom Shadow Scattering  

Microsoft Academic Search

The elastic small-angle scattering of 15- to 25-keV electrons by He, Ne, and Ar shows a rapid increase towards decreasing scattering angles superimposed with a diffraction pattern. The observed excess of the elastic differential cross section as compared with the Born cross section is due to the coupling to the inelastic channels. It may be also explained as a diffraction

Jürgen Geiger; Dagoberto Morón-León

1979-01-01

86

Symmetric And Non-Symmetric Muonic Helium Atoms Studies  

SciTech Connect

The ground state hyperfine structure and other properties are calculated for muonic helium atoms ({sup 3}He{sup +2}{mu}{sup -}e{sup -} or {sup 4}He{sup +2}{mu}{sup -}e{sup -}) with the use of some local properties of the wave functions in the domains where two particles are close to each other or far away. Simple wave functions incorporating these properties with one variational parameter is developed. The calculated values for hyperfine structure, energy and average interparticle distances in ground state are compared with the correlation function hyper-spherical harmonic method and multibox variational approach. The obtained results are very close to the values calculated by mentioned methods, giving strong indications that the proposed wave functions provide relatively accurate values.

Mohammadi, S. [Physics Department, Payame Noor University, Mashad 91735 (Iran, Islamic Republic of)

2011-10-28

87

Diffraction electron-atom scattering in an intense low-frequency laser field  

NASA Astrophysics Data System (ADS)

An explanation of discrepancies between predictions of the Kroll-Watson theory and cross sections measured in the Wallbank-Holmes experiments on electron-atom scattering in the presence of a powerful low-frequency laser field is presented. Our model calculations for helium and argon as target atoms come out to be in good agreement with experimental results; i.e., obtained cross sections are by many orders of magnitude larger than those predicted by the Kroll-Watson theory. A mechanism responsible for such a substantial increase of the calculated cross sections is found to be due to the diffraction scattering of electrons by atomic obstacles.

Jaro?, A.; Kami?ski, J. Z.

1997-12-01

88

Dynamic polarizabilities of rare-earth-metal atoms and dispersion coefficients for their interaction with helium atoms  

SciTech Connect

The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms are calculated with time-dependent density functional theory. The frequency-dependent polarizabilities at imaginary frequencies are used to determine the isotropic and orientation-dependent van der Waals coefficients for the interactions of the rare-earth-metal atoms with helium atoms. The static polarizabilities are compared with other theoretical values and with experimental results. The agreement is satisfactory in most cases but there are some exceptions where the discrepancy between theory and experiment is significant. The derived isotropic van der Waals coefficients range between 37 and 50 E{sub H}a{sub 0}{sup 6} and the orientation-dependent coefficients between 2 and -1 E{sub H}a{sub 0}{sup 6}. Thus the ratio of elastic to inelastic scattering cross sections is expected to be substantial and any one of the rare-earth-metal atoms is an excellent candidate for trapping and cooling in a He gas.

Chu, Xi; Dalgarno, Alexander; Groenenboom, Gerrit C. [Department of Chemistry, University of Montana, Missoula, Montana 59812 (United States); ITAMP, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States); Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525ED, Nijmegen (Netherlands)

2007-03-15

89

Semiempirical potentials for positron scattering by atoms  

SciTech Connect

We report calculations of differential and integral cross sections for positron scattering by noble gas and alkaline-earth atoms within the same methodology. The scattering potentials are constructed by scaling adiabatic potentials so that their minima coincide with the covalent radii of the target atoms. Elastic differential and integral cross sections are calculated for Ne, Ar, Be, and Mg, and the results are very close to experimental and best theoretical data. Particularly, elastic differential cross sections for Be and Mg at low energies are reported.

Assafrao, Denise; Walters, H. R. J.; Arretche, Felipe; Dutra, Adriano; Mohallem, J. R. [Departamento de Fisica, Universidade Federal do Espirito Santo, 29075-910, Vitoria, ES (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen's University, Belfast, BT7 1NN (United Kingdom); Departamento de Fisica, Universidade do Estado de Santa Catarina, 89223-100, Joinville, SC (Brazil); Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, PO Box 702, 30123-970, Belo Horizonte, MG (Brazil)

2011-08-15

90

Parametric Amplification of Scattered Atom Pairs  

NASA Astrophysics Data System (ADS)

We have observed parametric generation and amplification of ultracold atom pairs. A ^87Rb Bose-Einstein condensate was loaded into a one-dimensional optical lattice with quasimomentum k0 and spontaneously scattered into two final states with quasimomenta k1 and k2 . Furthermore, when a seed of atoms was first created with quasimomentum k1 we observed parametric amplification of scattered atoms pairs in states k1 and k2 when the phase-matching condition was fulfilled. This process is analogous to optical parametric generation (OPG) and amplification (OPA) of photons and could be used to efficiently create entangled pairs of atoms. Furthermore, these results could explain the dynamic instability of condensates in moving lattices observed in recent experiments.

Campbell, Gretchen K.; Mun, Jongchul; Boyd, Micah; Streed, Erik W.; Ketterle, Wolfgang; Pritchard, David E.

2006-05-01

91

Focusing a helium atom beam using a quantum-reflection mirror  

NASA Astrophysics Data System (ADS)

We demonstrate one-dimensional (1D) focusing of a thermal helium atom beam by quantum reflection from a cylindrical concave quartz mirror at near-grazing incidence. The smallest width of the focus achieved is 1.8 ?m, essentially limited by spherical aberration. The various effects that contribute to the finite focal width have been investigated. We propose to apply near-grazing reflection from two concave elliptical mirrors in a Kirkpatrick-Baez arrangement for two-dimensional (2D) focusing of a helium atom beam, paving the way for a helium atom microprobe.

Schewe, H. Christian; Zhao, Bum Suk; Meijer, Gerard; Schöllkopf, Wieland

2009-11-01

92

J-matrix calculation of electron-helium S-wave scattering. II. Single ionization and single excitation  

NASA Astrophysics Data System (ADS)

In the preceding paper [Konovalov , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.032707 84, 032707 (2011)] we used the J-matrix (JM) method to solve the S-wave e-He scattering problem within the frozen-core model of helium. In the present work we go beyond the frozen-core model and adopt a general configuration-interaction description of helium (within the S-wave model). As a result a more accurate description of the helium target states is achieved that allowed us to obtain highly accurate numerical solutions of the e-He scattering problem for the elastic, 21,3S, 31,3S excitation and total ionization cross sections. The JM results are confirmed by the corresponding convergent-close-coupling (CCC) calculations. At energies above the ionization threshold some minor pseudoresonances are still evident in both the JM and CCC results despite the large bases used. The pseudoresonances are nearly completely eliminated by averaging a number of JM calculations creating a challenging benchmark for any current or future ab initio electron-atom scattering methods.

Konovalov, Dmitry A.; Fursa, Dmitry V.; Bray, Igor

2012-11-01

93

Formation of long-lived gas-phase antiprotonic helium atoms and quenching by H2  

Microsoft Academic Search

IN 1964 Condo1 suggested that the decay characteristics of negative (pi- and K-) mesons in helium bubble chambers could be explained by the capture of these particles in large-angular-momentum meta-stable orbitals of exotic helium atoms. Russell2 predicted that similar \\

T. Yamazaki; E. Widmann; R. S. Hayano; M. Iwasaki; S. N. Nakamura; K. Shigaki; F. J. Hartmann; H. Daniel; T. von Egidy; P. Hofmann; Y.-S. Kim; J. Eades

1993-01-01

94

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

95

Shift and broadening of resonance lines of antiprotonic helium atoms in liquid 4He  

NASA Astrophysics Data System (ADS)

The shift and broadening of the resonance lines in the spectrum of antiprotonic helium atoms p¯He+ located in fluid and superfluid 4He have been estimated. The contributions to the shift and broadening from collective degrees of freedom in liquid 4He have been evaluated using the phenomenological response function. The shift due to collisions of p¯He+ with 4He atoms has been calculated in the quasistatic limit using the experimental pair-correlation function. It has been shown that an implanted p¯He+ atom establishes a good probe of liquid-helium properties, since this atom practically does not change the target structure.

Adamczak, Andrzej; Bakalov, Dimitar

2013-10-01

96

Classical theory of the chaotic ionization of highly excited helium atoms  

NASA Astrophysics Data System (ADS)

In this paper, we introduce a classical model for the behavior of the outer electron of a Rydberg helium atom in both static and time-dependent electric fields; we contrast the behavior of this dynamical system with the behavior of the classical model for highly excited hydrogen atoms in similar fields; and we show that these classical models recover many features of the system that would seem to be purely quantal in origin. Perhaps the most surprising of these is the apparent presence of ``classical avoided crossings'' in the Stark energy level structure of the classical helium model. Finally, we compare the behavior of our helium model to experimental data obtained by Koch, Mariani, and co-workers in their investigations of the ionization of highly excited helium atoms in a microwave field, and we note the agreement between experiment and theory.

Sanders, M. M.; Jensen, R. V.

1996-08-01

97

Electron mobility on the surface of liquid Helium: influence of surface level atoms and depopulation of lowest subbands  

SciTech Connect

The temperature dependence of electron mobility is examined. We calculate the contribution to the electron scattering rate from the surface level atoms (SLAs), proposed in [10]. This contribution is substantial at low temperatures T < 0.5, when the He vapor concentration is exponentially small. We also study the effect of depopulation of the lowest energy subband, which leads to an increase in the electron mobility at high temperature. The results explain certain long-standing discrepancies between the existing theory and experiment on electron mobility on the surface of liquid helium.

Grigoriev, P. D., E-mail: grigorev@itp.ac.ru; Dyugaev, A. M. [Landau Institute for Theoretical Physics (Russian Federation); Lebedeva, E. V. [Institute of Solid State Physics (Russian Federation)

2008-02-15

98

Electron and positron scattering from atoms  

SciTech Connect

Four distinct projects carried out are discussed. First, differential and integrated cross sections for the elastic scattering of low- and intermediate-energy (3-300 eV) positrons and electrons by argon atoms are calculated. Higher transport cross sections, representing moments of 1 - (cos theta)/sup n/, for these systems are also obtained for n = 1-4. Model potentials are used to represent the interactions between positrons or electrons and argon atoms. For each impact energy, the phase shifts of the lower partial waves are obtained exactly by numerical integration of the radial equation. Second, closed form expressions for the contributions of higher partial waves (2 ell > n-3) to the elastic scattering amplitude for various long range interactions, which fall off as r/sup -n/ as r ..-->.. infinity, are obtained for n ranging from 3 to 8. Third, the differential and total cross sections for the formation of positronium in its ground state from Li and Na atoms by the impact of intermediate-energy positrons are calculated in the first Born and the distorted wave Born approximations. Finally, formation of positronium (Ps) in different states by the impact of intermediate energy (20-500 eV) positrons on atomic hydrogen are calculated using the first Born approximation (FBA) and the distorted-wave Born approximation.

Nahar, S.N.

1987-01-01

99

Implantation of atoms into liquid helium for the purpose of impurity spectroscopy  

Microsoft Academic Search

Ca+, Sr+, and Ba+ ions are immersed in liquid He II and neutralized in the liquid subsequently by electrons produced by the ``tip-discharge'' method. Strong recombination light emission serves as detector for the production of these atoms in liquid helium. Laser-excited fluorescence spectroscopy of Ca, Sr and Ba atoms in the liquid can be a tool to study the environment

H. Bauer; M. Beau; A. Bernhardt; B. Friedl; H. J. Reyher

1989-01-01

100

Inelastic scattering of atoms in a double well  

SciTech Connect

We study a mixture of two light spin-1/2 fermionic atoms and two heavy atoms in a double-well potential. Inelastic scattering processes between both atomic species excite the heavy atoms and renormalize the tunneling rate and the interaction of the light atoms (polaron effect). The effective interaction of the light atoms changes its sign and becomes attractive for strong inelastic scattering. This is accompanied by a crossing of the energy levels from singly occupied sites at weak inelastic scattering to a doubly occupied and an empty site for stronger inelastic scattering. We are able to identify the polaron effect and the level crossing in the quantum dynamics.

Annibale, E. S. [Instituto de Fisica, Universidade de Sao Paulo, 05508-090, Sao Paulo (Brazil); Institut fuer Physik, Universitaet Augsburg, D-86135, Augsburg (Germany); Fialko, O. [Institut fuer Physik, Universitaet Augsburg, D-86135, Augsburg (Germany); Centre for Theoretical Chemistry and Physics, Massey University (Albany Campus), Private Bag 102904, North Shore MSC, Auckland 0745 (New Zealand); Ziegler, K. [Institut fuer Physik, Universitaet Augsburg, D-86135, Augsburg (Germany)

2011-04-15

101

Atomic alkali-metal gas cells at liquid-helium temperatures: Loading by light-induced atom desorption  

Microsoft Academic Search

We have studied the loading of gaseous alkali-metal atoms into glass cells held at about 2 K by light-induced atom desorption (LIAD). In LIAD loading, the cell containing dense helium gas and a small amount of alkali metal is irradiated with cw laser light. This technique has two unique features to be investigated: alkali-metal atoms are desorbed, even by weak

A. Hatakeyama; K. Enomoto; N. Sugimoto; T. Yabuzaki

2002-01-01

102

Dynamic polarizabilities of rare-earth-metal atoms and dispersion coefficients for their interaction with helium atoms  

Microsoft Academic Search

The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms are calculated with time-dependent density functional theory. The frequency-dependent polarizabilities at imaginary frequencies are used to determine the isotropic and orientation-dependent van der Waals coefficients for the interactions of the rare-earth-metal atoms with helium atoms. The static polarizabilities are compared with other theoretical values and with experimental results. The agreement

Xi Chu; Alexander Dalgarno; Gerrit C. Groenenboom

2007-01-01

103

Elastic Scattering of Lithium Ions in Helium and Hydrogen  

Microsoft Academic Search

The cross sections for elastic scattering of 50- to 800-eV Li+ ions in He and in H2 have been measured using a method in which the energy-loss spectrum of the ions is observed as a function of the scattering path length. The experimental procedure yields directly the cross section for scattering outside a given angle which ranges from 10° to

F. J. Zehr; H. W. Berry

1967-01-01

104

Collisional lasing on a self-terminating transition of a helium atom  

SciTech Connect

Laser on a self-contained transition of a helium atom is studied under excitation of the helium mixture with molecular gases by single long-duration (up to 700ns) or double nanosecond pulses. In He - H{sub 2}O and He - NH{sub 3} mixtures, no limitations were found on the pulse repetition rate and the laser pulse duration obtained was equal to that of the pump pulse. (lasers and amplifiers)

Bel'skaya, E V; Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

2011-01-24

105

Collisions with Laser-Cooled, Metastable Helium Atoms  

Microsoft Academic Search

Laser manipulation techniques have been used to create a bright beam of metastable He(2^3S) atoms which is used, amongst other things, as a source of cold atoms for loading a 3-D magneto-optical trap of He(2^3S). The trapped atoms provide an ideal vehicle for collision studies including atom-atom and electron-atom collisions, both with and without resonant, or near-resonant laser fields present.

Stephen J. Buckman

2003-01-01

106

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

107

Atom-interferometric studies of light scattering  

NASA Astrophysics Data System (ADS)

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?k at t=2T . Matter wave interference is associated with the formation of a density grating with period ?/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-?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 ?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 ?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.; Yavin, I.; Kumarakrishnan, A.

2009-07-01

108

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

109

The Effects of the Pauli Exclusion Principle in Determining the Ionization Energies of the Helium Atom and Helium-Like Ions  

ERIC Educational Resources Information Center

|For helium and helium-like ions, we have examined the differences between the values of the ionization energies as calculated from the Bohr theory and those measured in experiments. We find that these differences vary linearly with the atomic number of the system. Using this result, we show how the Bohr model for single-electron systems may be…

Deeney, F. A.; O'Leary, J. P.

2012-01-01

110

ELECTRON-ATOM SCATTERING AND NUCLEON-NUCLEUS SCATTERING--AN ANALOGY  

Microsoft Academic Search

An analogy is drawn between low-energy nucleonnucleus scattering and low-; energy electron-atom scattering. Proper scaling indicates that the Ramsauer ; resonances ln electron scattering are analogous to the size'' resonances of ; nucleon scattering. Total cross sections, angular distributions, and spin ; polarizations are calculated. An imaginary potential is introduced, and its ; consequences for direct electron-atom interactions are discussed.

1962-01-01

111

Crucial electronic contributions to measures of surface diffusion by He atom scattering  

NASA Astrophysics Data System (ADS)

We examine theoretically recent He atom scattering measurements of Na/Cu(001), identifying a nontrivial relation between the dynamics of the electron distribution and that of the Na ions. The magnitude of the calculated variations in the charge density, and their dependence on the local density of adsorbates, account for the correlated three-dimensional (3D) motion experimentally observed. The results of this study further highlight the sensitivity of helium scattering to the electron distribution of the sample and point out the role of electronic contributions in high-resolution measures of surface dynamics.

Fratesi, Guido; Alexandrowicz, Gil; Trioni, Mario Italo; Brivio, Gian Paolo; Allison, William

2008-06-01

112

Submonolayer alloying of copper on vicinal platinum: A combined atom and ion scattering study  

SciTech Connect

We present a combined helium atom scattering (HAS) and medium energy ion scattering (MEIS) study to provide a detailed description of sub-monolayer growth of copper on vicinal platinum. Initial growth is epitaxial but induces a small relaxation in the substrate. A strong temperature dependence of growth is observed and MEIS indicates the formation of a thin (two-layer) alloy between 450 K and 500 K. In-situ HAS measurements allow for the direct observation of alloying and reveal that it occurs in two unusually sharp phase transitions. Both HAS and MEIS indicate the onset of bulk alloying and dissolution of copper at surface temperatures above 600 K.

MacLaren, D.A.; Bacon, R.T.; Allison, W.; O'Connor, D.J.; Dastoor, P.C.; Noakes, T.C.Q.; Bailey, P. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); School of Mathematical and Physical Sciences, University of Newcastle, Callaghan, New South Wales 2308 (Australia); CCLRC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD (United Kingdom)

2004-09-15

113

Phonon-roton scattering and kinetic coefficients in helium II  

SciTech Connect

Significant factors in the scattering of an energetic phonon by a roton are the inelasticity of the process and the form of the dispersion curve E(P) for rotons, and these factors should be taken into account. We propose a simple method for calculating the scattering cross section based on a dependence E(P) outside the framework of the standard parabolic Landau approximation. The scattering cross section for this process and the phonon contributions to the viscoity and thermal conductivity coefficients are found. The expressions are in good agreement with experiment, without the use of any adjustable parameters.

Khalatnikov, I.M.; Matveev, Y.A.

1983-04-01

114

Electron and Positron Scattering from Atoms.  

NASA Astrophysics Data System (ADS)

Four distinct projects are carried out for the Ph.D. dissertation. In the first project, differential and integrated cross sections for the elastic scattering of low- and intermediate -energy (3 - 300 eV) positrons and electrons by argon atoms are calculated. Higher transport cross sections, representing moments of 1 - (cos(theta))('n), for these systems are also obtained for n = 1 - 4. Model potentials are used to represent the interactions between positrons or electrons and argon atoms. For each impact energy, the phase shifts of the lower partial waves are obtained exactly by numerical integration of the radial equation. The Born approximation is used to obtain the contribution of the higher partial waves to the scattering amplitude. In the second project, closed form expressions for the contri- butions of higher partial waves (2L > n - 3) to the elastic scattering amplitude for various long range interactions, which fall off as r('-n) as r (--->) (INFIN), are obtained for n ranging from 3 to 8. In the third project, the differential and total cross sections for the formation of positronium in its ground state from Li and Na atoms by the impact of intermediate -energy positrons are calculated in the first Born and the distorted wave Born approximations. Hellmann type pseudopotentials are used to represent the alkali ion cores. The difference in the use of pseudopotentials and the static potential for the core representation for evaluating various rearrangement cross sections is discussed. As a continuation of the previous project, the formation of positronium (Ps) in different states by the impact of intermediate energy (20 - 500 eV) positrons on atomic hydrogen are calculated using the first Born approximation (FBA) and the distorted wave Born approximation (DWBA). Differential and integrated cross sections for the formation of Ps(1s), Ps(2s), Ps(2p(,0)) and Ps(2p(,1)) have been evaluated individually and 1/n('3) behavior for charge transfer cross sections is used for n (GREATERTHEQ) 3 to obtain the total cross section for positronium formation. The present results for positronium (1s) formation cross sections are in agreement with the results of some other available investigations. An application of the DWBA to compute the cross section for the formation of hydrogen in its ground state by the impact of intermediate energy (50 - 250 keV) protons on hydrogen atoms has also been made.

Nahar, Sultana Nurun

115

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

116

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

117

Diffraction electron-atom scattering in an intense low-frequency laser field  

SciTech Connect

An explanation of discrepancies between predictions of the Kroll-Watson theory and cross sections measured in the Wallbank-Holmes experiments on electron-atom scattering in the presence of a powerful low-frequency laser field is presented. Our model calculations for helium and argon as target atoms come out to be in good agreement with experimental results; i.e., obtained cross sections are by many orders of magnitude larger than those predicted by the Kroll-Watson theory. A mechanism responsible for such a substantial increase of the calculated cross sections is found to be due to the diffraction scattering of electrons by atomic obstacles. {copyright} {ital 1997} {ital The American Physical Society}

Jaron, A.; Kaminski, J.Z. [Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warszawa (Poland)

1997-12-01

118

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`.

119

Polarization Control in Two-Color Above-Threshold Ionization of Atomic Helium  

Microsoft Academic Search

Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In the photoelectron spectrum, lines associated with direct ionization and above-threshold ionization show strong variations of their amplitudes as a function of both the intensity of the optical dressing field and the relative

M. Meyer; D. Cubaynes; D. Glijer; J. Dardis; P. Hayden; P. Hough; V. Richardson; E. T. Kennedy; J. T. Costello; P. Radcliffe; S. Düsterer; A. Azima; W. B. Li; H. Redlin; J. Feldhaus; R. Taïeb; A. Maquet; A. N. Grum-Grzhimailo; E. V. Gryzlova; S. I. Strakhova

2008-01-01

120

Excited Muonic Atom Scattering: New Adiabatic Approach  

NASA Astrophysics Data System (ADS)

Two adiabatic approaches: Born-Oppenheimer (BO) [1, 2] and hyperradial adiabatic (HA) [3] are frequently used for (x?) n (n?2) muonic atom scattering. In both cases the Coriolis coupling operator has the same form and is treated within the close-coupling scheme. Recently, we have developed a symmetry-adapted version of the HA approach [4] (SAHA) in which Coriolis couplings are calculated as the “fast” component of the dynamics. In SAHA the adiabatic problem should be solved for any pair of the total angular momentum J and total parity p repeatedly but the number of adiabatic states (and the number of channels in the close-coupling calculations) is reduced by J-factor.

Matveenko, A. V.

2001-12-01

121

Quantitative Theory for Electron-Atom Scattering  

NASA Astrophysics Data System (ADS)

The aim of this work is to develop a general approach to electron and photon impact ionization. This approach should *be non-perturbative, *not be restricted to simple systems, *be straightforward to systematically improve, *be computationally efficient, *treat symmetric problems symmetrically. R operator formalism The concept of an R-matrix has been extended to a general coordinate hyperspace by the introduction of an R-operator, [1]. We have developed an approach to electron-atom scattering within the context of the R-operator formalism. Results will be presented for the Temkin-Poet problem [2, 3] as well as for e-H collisions. [1] R. K. Nesbet, Phys. Rev. B, 30, 4230, 1984 [2] A.Temkin, Phys. Rev. A, 126, 130, 1962 [3] R. Poet, J. Phys. B, 13,2995,1980

Whelan, Colm T.; Nesbet, Robert K.; Martinez, Jason.

2006-05-01

122

On soft collisions of fast highly-charged ions with hydrogen and helium atoms  

Microsoft Academic Search

Ionization of hydrogen and helium atoms in small momentum transfer collisions with fast highly-charged ions is considered for the range of parameters 0953-4075\\/29\\/22\\/019\\/img1, 0953-4075\\/29\\/22\\/019\\/img2 (Z and v are the ion charge and velocity, respectively, and 0953-4075\\/29\\/22\\/019\\/img3 is the characteristic velocity of the electron in the atom ground state). Analytical expressions have been derived for single and double differential cross sections

A. B. Voitkiv

1996-01-01

123

Conductivity Measurement of Helium Surface Electrons in the Coexistence of Adsorbed 2D Atomic Hydrogen Gas  

NASA Astrophysics Data System (ADS)

Cold hydrogen atoms (H) are adsorbed on liquid helium surface to form two-dimensional (2D) quantum gas. Because of the boson nature of H atoms, when 2D H gas is cold and dense enough, it is expected to exhibit a transition to superfluid phase by Kosterlitz-Thouless mechanism. In order to sense the state of 2D H gas, we used helium surface electrons as a probe. Since the conductivity of surface electrons is sensitively influenced by collisions with its environment, such as He vapor atoms and ripplons, it is expected to detect the existence of H atoms on the same surface. We prepared a 2D mixture gas of H and electrons on a helium surface and measured the conductivity of the electrons. Strong magnetic field was applied to avoid chemical processes: electron attachment on H atom and H-H recombination. We employed pulse excited edge-magnetoplasmon (EMP) technique for the conductivity measurement. We show EMP spectrum under the influence of H atoms and discuss the potentiality of surface electrons for probing states of adsorbed 2D H gas.

Arai, T.; Yamanaka, S.; Yayama, H.; Fukuda, A.; Sawada, A.

2009-02-01

124

Quantum transmission of atoms through a slab of superfluid helium.  

PubMed

We describe a measurement of the transmission probability of 4He atoms through a freely suspended slab of superfluid 4He at low temperatures. In our experiment the slab is realized by using an array of parallel cylindrical holes of diameter 51 microm in a glass disc of thickness 190 microm. By controlling the chemical potential, the holes can be made to fill or empty with liquid, and the surface curvature varied. We have measured the transmission of atom beams, generated by a thin-film heater and detected with a sensitive bolometer, through this structure. The results show that the dominant transmission channel is atom-R+ roton-atom with a probability p approximately 0.12 and that R+ rotons can undergo total internal reflection at the free liquid surfaces. PMID:14525250

Williams, C D H; Wyatt, A F G

2003-08-18

125

Low-energy scattering of antihydrogen by helium and molecular hydrogen  

SciTech Connect

In this paper, we describe in detail calculations that we have carried out of cross sections for rearrangement processes in very low-energy helium+antihydrogen (H-bar) scattering that result in He{sup +}p-bar+Ps or Hep-bar+e{sup +} or {alpha}p-bar+Ps{sup -}. The interaction between the leptons is taken into account very accurately. Results are presented for all three processes. A description is also given of a preliminary calculation of elastic and antiproton annihilation cross sections for very low-energy H{sub 2}+H-bar scattering.

Armour, E. A. G.; Todd, A. C.; Liu, Y.; Gregory, M. R. [School of Mathematical Sciences, Nottingham University, Nottingham NG7 2RD (United Kingdom); Jonsell, S. [Department of Physics, University of Wales Swansea, Swansea SA2 8PP (United Kingdom); Plummer, M. [CLRC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)

2008-08-08

126

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

NASA Astrophysics Data System (ADS)

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.

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

1992-10-01

127

Study of Rayleigh scattering for visualization of helium-air mixing at Mach 6  

NASA Astrophysics Data System (ADS)

Using an ArF excimer laser, planar Rayleigh scattering measurements were performed to investigate helium mixing into air at supersonic speeds. These experiments were conducted in the Mach 6, high-Reynolds-number facility at NASA Langley Research Center. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment was demonstrated. The qualitative agreement between the averaged Rayleigh results and the reduced mean-mass-densities obtained from probe measurements substantiate that careful application of the technique, even in the presence of clusters, can give very useful results. It was also demonstrated that planar, quantitative measurements can be made in the absence of clusters.

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

128

THERMAL SCATTERING OF ATOMS BY HOMONUCLEAR DIATOMIC MOLECULES  

Microsoft Academic Search

The formal theory of scattering by a rigid rotator is applied to the ; problem of the rotational excitation and elastic scattering of homonuclear ; diatomic molecules by atoms. A statistical theory is employed to analyze the ; effects of the strong coupling that occurs between the different scattering ; channels. Numerical results are presented for the collision of argon

R. B. Bernstein; A. Dalgarno; H. Massey; I. C. Percival

1963-01-01

129

Exploiting Universality in Atoms with Large Scattering Lengths  

SciTech Connect

The focus of this research project was atoms with scattering lengths that are large compared to the range of their interactions and which therefore exhibit universal behavior at sufficiently low energies. Recent dramatic advances in cooling atoms and in manipulating their scattering lengths have made this phenomenon of practical importance for controlling ultracold atoms and molecules. This research project was aimed at developing a systematically improvable method for calculating few-body observables for atoms with large scattering lengths starting from the universal results as a first approximation. Significant progress towards this goal was made during the five years of the project.

Braaten, Eric

2012-05-31

130

ATOMIC AND MOLECULAR PHYSICS: Calculation of Energy and Other Properties of Muonic Helium Atom Using Boundary Conditions of Wave Function  

NASA Astrophysics Data System (ADS)

The properties of muonic helium atom (4He+2?-e-) in ground state are considered. In this work, the energy and average distance between particles have been obtained using a wave function, which satisfies boundary conditions. It is shown that the obtained energy are very close to the values calculated by others. But the small differences of the expectation values of r2n are due to the incorporated boundary conditions in proposed wave function and are expected.

Rezaei, B.

2010-09-01

131

Measurements of the density of metastable helium atoms in dielectric barrier discharges  

NASA Astrophysics Data System (ADS)

Measurements of the density of metastable helium atoms in dielectric barrier discharges operating in glow discharge mode are reported. The measurements were made in two systems using three different approaches. One DBD was created in air with helium flowing in the inter-electrode gap, in the other the DBD was in a vacuum chamber in static pure helium with some impurities present. In the first system a multi-pass absorption technique at 388.865 nm was used, the lack of any absorption signal over a path length of 25 cm indicated an upper limit of the metastable density in this system of 2x10^10 cm-3 [1]. In the second system the time dependence of the helium metastable density using laser collisional-induced fluorescence established that the maximum density in this system was in the range 0.5 to 2.5 x10^10 cm-3 and from the time dependence the metastable density at the next breakdown was estimated to be about 10^4. When the glass plates in the latter system were replaced by optical quality quartz, helium metastable absorption can be seen as an optogalvanic effect on the measured discharge current, indicating a higher metastable density in this case. [1]G Nersisyan, T Morrow, WG Graham Appl. Phys. Lett. 85, 1487 (2004).

El-Astal, Ali; Nersisyan, Gagik; Morrow, Tom; Graham, William

2006-10-01

132

Light scattering by ultracold atoms in an optical lattice  

NASA Astrophysics Data System (ADS)

We investigate theoretically light scattering of photons by ultracold atoms in an optical lattice in the linear regime. A full quantum theory for the atom-photon interactions is developed as a function of the atomic state in the lattice along the Mott-insulator-superfluid phase transition, and the photonic-scattering cross section is evaluated as a function of the energy and of the direction of emission. The predictions of this theory are compared with the theoretical results of a recent work on Bragg scattering in time-of-flight measurements [A.M. Rey , Phys. Rev. A 72, 023407 (2005)]. We show that, when performing Bragg spectroscopy with light scattering, the photon recoil gives rise to an additional atomic site-to-site hopping, which can interfere with ordinary tunneling of matter waves and can significantly affect the photonic-scattering cross section.

Rist, Stefan; Menotti, Chiara; Morigi, Giovanna

2010-01-01

133

Inelastic scattering of hydroxyl radicals with helium and argon by velocity-map imaging  

NASA Astrophysics Data System (ADS)

The hydroxyl radical (OH) is one of the most interesting molecules in molecular dynamics. In particular, inelastic collisions of free radicals such as OH are profoundly important in environments ranging from combustion to astrochemistry. However, measuring the velocities of OH molecules in specific internal quantum states has proven to be very difficult. A method that can provide this important information is velocity-map imaging. Although this technique is very widely applicable in principle, it does require a sensitive and selective laser-ionization scheme. Here we show that, under the right conditions, velocity-map imaging can be applied to the study of the inelastic scattering of OH using crossed-molecular-beam methods. We measure fully quantum-state-specified product angular distributions for OH collisions with helium and argon. The agreement between exact close-coupling quantum scattering calculations on ab initio potential energy surfaces and experimental data is generally very satisfactory, except for scattering in the most forward directions.

Sarma, Gautam; Marinakis, Sarantos; Ter Meulen, J. J.; Parker, David H.; McKendrick, Kenneth G.

2012-12-01

134

Helium ion Measurements From the Arecibo Incoherent Scatter Radar and the DMSP Satelites  

NASA Astrophysics Data System (ADS)

Data from the Arecibo incoherent scatter radar (ISR) and the DMSP-F13 (Defense Meteorological Satellite Program) satellite are presented and compared. Observations from periods exhibiting the He+ layering phenomenon are analyzed. Historically, there has been little attempt to compare data from the two sources due to difficulties in combining ground-based and space-based studies; also, only recently have light ion concentration measurements from Arecibo been possible in the topside ionosphere up to 2000 km altitude. The results presented show favorable comparison between the two data sources, giving users increased levels of confidence in the observations. Regions where the helium ions are of comparable concentration to the major ions (O+ and H+) are apparent in the data, serving to reinforce the view that the helium ion should not be regarded as a minor ion under all conditions.

Wilford, C. R.; Moffett, R. J.; Gonzalez, S. A.; Venkatraman, S.

2003-12-01

135

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

136

Elastic Positronium-Atom Scattering Using the Stochastic Variational Method  

SciTech Connect

The stochastic variational method is used in conjunction with stabilization ideas to compute the low energy phase shifts and scattering lengths for positronium-atom scattering. Results are obtained for the Ps-H, Ps-Li{sup +} , Ps-He, and Ps-Ps systems. The Ps-H scattering lengths are probably accurate to better than 5% and are the most accurate so far computed. The results for Ps-Li{sup +} and Ps-Ps scattering represent the first published scattering lengths for these systems. The positive scattering length for completely spin-aligned {sup 3}Ps- {sup 3}Ps scattering, namely 2.95a{sub 0} , is particularly significant since it demonstrates the feasibility of forming a stable Bose-Einstein condensate of {sup 3}Ps atoms.

Ivanov, I. A.; Mitroy, J.; Varga, K.

2001-08-06

137

Bremsstrahlung of polarized positrons scattered off atoms  

NASA Astrophysics Data System (ADS)

The leading-order positron-atom bremsstrahlung is investigated within the rigorous relativistic approach based on the partial-wave representation of the Dirac wave functions in the external atomic field. Approximating the atomic target by an effective local potential, we calculate the Stokes parameters of the emitted photon for different polarizations of the initial positron. The results for positron-atom bremsstrahlung are compared with analogous data for the electron-atom bremsstrahlung.

Yerokhin, V. A.; Surzhykov, A.; Märtin, R.; Tashenov, S.; Weber, G.

2013-09-01

138

Absolute Density Measurement of Metal Atoms by Laser Resonance Scattering with the Aid of Rayleigh Scattering  

Microsoft Academic Search

The absolute density of metal atoms such as iron and aluminium atoms, the knowledge of which is urgently needed for study of the high temperature plasma-wall interaction, was measured by the laser resonance scattering method within an accuracy of 50%. The calibration of the optical system was performed by using the Rayleigh scattering from argon gas at sub-atmospheric pressure, and

Makoto Hamamoto; Mitsuo Maeda; Katsunori Muraoka; Masanori Akazaki

1981-01-01

139

Negative ion productions in high velocity collision between small carbon clusters and Helium atom target  

NASA Astrophysics Data System (ADS)

We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

M, Chabot; K, Béroff; T, Pino; G, Féraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier

2012-11-01

140

Photoabsorption and Compton scattering in ionization of helium at high photon energies  

SciTech Connect

Production of singly and doubly charged helium ions by impact of keV photons is studied. The ratio R{sub ph} = {sigma}{sub ph}{sup ++}/{sigma}{sub ph}{sup +} for photoabsorption is calculated in the photon-energy range 2--18 keV using correlated initial- and final- state wave functions. Extrapolation towards asymptotic photon energies yields R{sub ph}({omega} {yields} {infinity}) = 1.66% in agreement with previous predictions. Ionization due to Compton scattering, which becomes comparable to photoabsorption above {omega} {approximately} 3 keV, is discussed.

Andersson, L.R.; Burgdoerfer, J. [Oak Ridge National Lab., TN (United States)]|[Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy

1993-10-01

141

Eikonal Theory of Intermediate-Energy Electron-Atom Scattering.  

National Technical Information Service (NTIS)

An eikonal theory of elastic electron-atom scattering in the region of intermediate energies is proposed. In addition tot the effects of the static and polarization potentials, the leading absorption corrections, using the equivalent-potential method are ...

C. J. Joachain M. H. Mittleman

1971-01-01

142

Determination of the surface corrugation amplitude from classical atom scattering.  

PubMed

The energy landscape of an atomic or molecular projectile interacting with a surface is often described in terms of a corrugation function that gives the classical turning point as a function of position vector parallel to the surface. It is shown here that the relative height variation of the corrugation function for scattering of atoms under classical conditions can be determined by a measurement of the maximum intensity in energy-resolved scattering spectra as a function of surface temperature. This is demonstrated by developing a semiclassical quantum theory of atomic scattering from corrugated surfaces and then extending the theory to the classical limit of large incident energies and high surface temperatures. Comparisons of calculations with available data for Ar atom scattering determine the corrugation amplitude for a molten In surface to be about 29% of the mean interparticle spacing in the bulk liquid. PMID:23006264

Hayes, W W; Manson, J R

2012-08-10

143

Study of formation of hydrogen atoms in grazing surface scattering  

NASA Astrophysics Data System (ADS)

We have studied the formation of hydrogen atoms in grazing collisions of 25 keV protons with a clean and atomically flat Fe(110)-surface. Application of an electric field directed normal to the polar plane of scattering allows to separate the angular distributions of scattered projectiles leaving the surface to be separated into neutral hydrogen atoms and protons. We detect a small angular shift between the two distributions, which is attributed to the effect of the image potential on the trajectory of the protons. Since the image interaction is affected to a large extent by charge exchange during the scattering event, the analysis of data allows important information on the mechanisms of formation of hydrogen atoms in ion-surface scattering to be deduced.

Winter, H.; Leuker, J.

1992-10-01

144

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

145

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

146

Quasi-elastic electron scattering from atoms and molecules  

Microsoft Academic Search

Over the past four years we have measured quasi-elastic electron scattering spectra from molecules and atoms at large momentum transfer (100° angle, 2.25keV incident energy, ?20a.u.). The peak positions agree completely with those predicted by classical conservation of momentum and energy, assuming the electron scatters from each atom independently. However the peak intensities do not agree with expectations, particularly for

A. P. Hitchcock; G. Cooper; R. A. Bonham; C. A. Chatzidimitriou-Dreismann

2010-01-01

147

Positron-rubidium atom scattering at intermediate and high energies  

NASA Astrophysics Data System (ADS)

In this work, the coupled-channel optical method (CCOM) is implemented in a study of positron-rubidium (Rb) scattering at intermediate and high energies. The CCOM provides a realistic calculation for positron-atom scattering where the ab-initio optical potential accounts for the omitted continuum effect in the scattering system. The integral, positronium (Ps) formation and total cross sections are compared to experimental and other theoretical data where available.

Chin, J. H.; Ratnavelu, K.; Zhou, Y.

2012-03-01

148

Scattering of low-energy electrons by helium in a CO2 laser field  

NASA Astrophysics Data System (ADS)

The scattering of low-energy electrons by helium in the presence of a CO2 laser field is studied using the R-matrix Floquet theory. Two target states are retained in the calculations, the 1S ground state and a 1Po pseudostate optimized to describe the polarizability of the target. Differential cross sections for elastic scattering with net absorption/emission of up to two photons are calculated for collision energies between 1 eV and 8 eV and over a range of intensities from 107 W cm-2 up to 108 W cm-2. Various geometries are considered, including those in which the incident electron beam is not parallel to the laser polarization axis. The results are compared with those of Wallbank and Holmes (2001 Can. J. Phys. 79 1237), and are found to be several orders of magnitude smaller.

Dunseath, K. M.; Terao-Dunseath, M.

2004-03-01

149

Stark recurrence spectroscopy of Rydberg helium and argon atoms: The convergence of quantum and classical mechanics  

NASA Astrophysics Data System (ADS)

In the present experimental and theoretical dissertation, we study the quantum photoabsorption spectrum of Rydberg states of helium and argon in a strong electric field, and the classical closed orbit spectral counterpart, the recurrence spectrum. Connections between classical and quantum descriptions are investigated. We present a complete experimental scaled energy absorption spectra for m = 0 and 1 singlet and triplet helium atoms, over a scaled energy range epsilon = -2.0 to -3.5 and principle quantum number range n = 15 to 25. Agreement with semiclassical theory is excellent. Also, we present experimental results for the many electron Rydberg atom argon, with core angular momentum state J = 3/2, for epsilon = -2.0 to -3.5 and for n = 15 to 25. Measurements of anomalous long-lived states above the classical ionization threshold in m = 1 singlet helium are presented and we show that hydrogenic theory is not valid in this case. We describe a calculation for all the primitive orbits for m = 1 hydrogen, in the range epsilon = -2.0 to -1.8, and find a simple way to calculate the initial launching radius. Measured trajectories show very good agreement with computed classical trajectories. Also, we present a simple formula to calculate the scaled action with respect to the scaled energy that agrees well with observation. Finally, the importance of the primitive orbit and its repetitions in the recurrence map is examined.

Flores-Rueda, Heric

150

Estimate of surfon evaporation time from the liquid helium surface due to the scattering on ripplons  

NASA Astrophysics Data System (ADS)

Recently a new type of surface excitations, surfons, has been proposed. Phenomenologically, these excitations can be interpreted as atoms on a surface quantum level. They explain the strong temperature dependence of surface tension coefficient of liquid helium. In the present work we studied theoretically the interaction of these excitations with ripplons, the quanta of surface waves. The lifetime of surfons due to the absorption of a ripplon and subsequent evaporation from the surface was estimated. The obtained surfon lifetime considerably exceeds the inverse surfon energy, substantiating the treatment of surfons as quasiparticles.

Grigoriev, A. D.; Grigoriev, P. D.; Dyugaev, A. M.; Krutov, A. F.

2012-11-01

151

High-resolution infrared spectra of carbonyl sulfide solvated with helium atoms  

NASA Astrophysics Data System (ADS)

Infrared spectra of HeN-OCS clusters with N up to about 20 have been studied in the 2062 cm-1 region of the O-C stretching vibration using a tunable diode laser spectrometer to probe pulsed supersonic expansions from moderately high-pressure (<35 atm) cooled (>-60 °C) jet sources. Resolved rotation-vibration transitions have been assigned for the clusters with N=2-8, and these assignments have been confirmed in detail by observations of the corresponding pure rotational transitions in the microwave region. The vibrational frequencies (band origins) were observed to move to higher frequencies (blueshift) for N=2-5, continuing the shift previously observed for the binary complex, He-OCS. Then, for N=6-8, the vibrational frequency moves back in the direction of lower frequencies (redshift), leading towards the limiting redshift previously observed in larger helium nanodroplets with N~103-104. These vibrational shifts are consistent with a model in which the first five helium atoms fill a ``ring'' around the ``equator'' of the OCS molecule, with the subsequent heliums then taking positions closer to the ends. The cluster rotational constants decrease monotonically (increasing rotational moments of inertia) for N=1-8, falling below the value previously observed for the ``free'' rotation of OCS in helium nanodroplets. Strong, sharp spectral lines from clusters in the size range N~9-20 were also observed, but not assigned. This difficulty in extending the analysis for N>8 may be related to the onset of partially free internal rotation of the OCS within the helium cluster, which in turn has interesting implications for the nature of superfluid-type behavior in this finite scale system.

Tang, Jian; McKellar, A. R. W.

2003-09-01

152

Mesoscopic entanglement of atomic ensembles through nonresonant stimulated Raman scattering  

Microsoft Academic Search

We propose a scheme of generating and verifying mesoscopic-level entanglement between two atomic ensembles using nonresonant stimulated Raman scattering. Entanglement can be generated by direct detection or balanced homodyne detection of the Stokes fields from the two cells after they interfere on a beam splitter. The entanglement of the collective atomic fields can be transferred to the anti-Stokes fields in

Wenhai Ji; Chunbai Wu; S. J. van Enk; M. G. Raymer

2007-01-01

153

Modeling of atom-diatom scattering. Technical report  

SciTech Connect

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 several atom-diatom scattering systems. Two scattering systems, in particular, that were successfully modeled and compared to measurements were Ar-KBr and Ar-CsF. The IA model provided an explanation for the rapid deactivation evident in the Ar-KBr system. Experimental results in the Ar-CsF experiment that could not be explained by conventional models were also successfully modeled using the IA. Results fit the experimental observations.

Sindoni, J.M.

1992-05-30

154

Coherent scattering by a spherical medium of resonant atoms  

SciTech Connect

We consider the problem of coherent resonant scattering of electromagnetic waves by a spherical medium of two-level atoms. The frequency dependence of the scattering amplitudes and cross sections reveals a complex structure of narrow peaks and dips. We relate these scattering resonances to the cooperative emission resonances characteristic of a sphere. We find the scattering to show considerable interference between the electric and magnetic multipole contributions, particularly in the lower multipole orders. This interference tends to enhance anisotropies in the differential scattering cross section even for small spheres. For such spheres, the peak values of the resonant contributions of the low-order multipoles to the total scattering cross section can increase with multipole order, in contrast to the usual decrease seen in nonresonant scattering.

Prasad, Sudhakar; Glauber, Roy J. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 (United States); Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)

2011-06-15

155

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

156

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

PubMed

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. PMID:17139089

Petrova, Tatiana; Ginell, Stephan; Mitschler, Andre; Hazemann, Isabelle; Schneider, Thomas; Cousido, Alexandra; Lunin, Vladimir Y; Joachimiak, Andrzej; Podjarny, Alberto

2006-11-23

157

Scattering properties of weakly bound dimers of fermionic atoms  

SciTech Connect

We consider weakly bound diatomic molecules (dimers) formed in a two-component atomic Fermi gas with a large positive scattering length for the interspecies interaction. We develop a theoretical approach for calculating atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic collisional relaxation of the molecules into deep bound states. This approach is based on the single-channel zero-range approximation, and we find that it is applicable in the vicinity of a wide two-body Feshbach resonance. Our results draw prospects for various interesting manipulations of weakly bound dimers of fermionic atoms.

Petrov, D.S. [ITAMP, Harvard-Smithsonian Center for Astrophysics, and Harvard-MIT Center for Ultracold Atoms, Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Salomon, C. [Laboratoire Kastler-Brossel, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France); Shlyapnikov, G.V. [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Laboratoire Physique Theorique et Modeles Statistique, Universite Paris Sud, Batiment 100, 91405 Orsay (France); Van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65/67, 1018 XE Amsterdam (Netherlands)

2005-01-01

158

A discrete variable representation for electron-hydrogen atom scattering  

SciTech Connect

A discrete variable representation (DVR) suitable for treating the quantum scattering of a low energy electron from a hydrogen atom is presented. The benefits of DVR techniques (e.g. the removal of the requirement of calculating multidimensional potential energy matrix elements and the availability of iterative sparse matrix diagonalization/inversion algorithms) have for many years been applied successfully to studies of quantum molecular scattering. Unfortunately, the presence of a Coulomb singularity at the electrically unshielded center of a hydrogen atom requires high radial grid point densities in this region of the scattering coordinate, while the presence of finite kinetic energy in the asymptotic scattering electron also requires a sufficiently large radial grid point density at moderate distances from the nucleus. The constraints imposed by these two length scales have made application of current DVR methods to this scattering event difficult.

Gaucher, L.F.

1994-08-01

159

Eletron-helium laser-assisted free-free scattering with variable laser polarization  

NASA Astrophysics Data System (ADS)

We report a series of experiments that examine electron-helium scattering in the presence of an Nd:YAG laser field of 1.17 eV photons. In previous experimentsootnotetextB. A. deHarak, L. Ladino, K. B. MacAdam and N. L. S. Martin, Phys. Rev. A 83, (2011) 022706. we examined the range of incident electron energies from 50 eV to 350 eV, and found the results to be in good agreement with the Kroll-Watson approximation (KWA).ootnotetextN. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804 (1973) In these experiments the laser polarization was fixed relative to the scattering plane. Experiments are now being carried out where, at each electron energy, the direction of the polarization is varied within a plane perpendicular to the scattering plane. Of particular interest is the case where the polarization is perpendicular to the scattering plane for which the KWA predicts vanishing cross section. Other workers have found that the KWA tends to be inaccurate for those cases when it predicts small cross sections.ootnotetextM. O. Musa, A. MacDonald, L. Tidswell, J. Holmes, and B. Wallbank, J. Phys. B, 43 (17):175201, 2010.

Deharak, B. A.; Nosarzewski, Benjamin; Siavashpouri, Mahsa; Martin, N. L. S.

2012-06-01

160

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

161

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

162

Influence of an External Electric Field on Thermal Collisions Between Circular Rydberg-State Atoms and Ground-State Helium.  

National Technical Information Service (NTIS)

The influence of an external electric field on thermal collisions between a sodium atom excited in a ''circular'' Rydberg state and a ground-state helium atom is studied numerically within the framework of the impulse approximation. The effect of the fiel...

E. Prunele

1986-01-01

163

Metastable helium Bose-Einstein condensate with a large number of atoms  

SciTech Connect

We have produced a Bose-Einstein condensate of metastable helium ({sup 4}He*) containing over 1.5x10{sup 7} atoms, which is a factor of 25 higher than previously achieved. The improved starting conditions for evaporative cooling are obtained by applying one-dimensional Doppler cooling inside a magnetic trap. The same technique is successfully used to cool the spin-polarized fermionic isotope ({sup 3}He*), for which thermalizing collisions are highly suppressed. Our detection techniques include absorption imaging, time-of-flight measurements on a microchannel plate detector, and ion counting to monitor the formation and decay of the condensate.

Tychkov, A. S.; Jeltes, T.; McNamara, J. M.; Tol, P. J. J.; Herschbach, N.; Hogervorst, W.; Vassen, W. [Laser Centre Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands)

2006-03-15

164

Theory of evaporative cooling with energy-dependent elastic scattering cross section and application to metastable helium  

SciTech Connect

The kinetic theory of evaporative cooling developed by Luiten et al. [Phys. Rev. A 53, 381 (1996)] is extended to include the dependence of the elastic scattering cross section on collision energy. We introduce a simple approximation by which the transition range between the low-temperature limit and the unitarity limit is described as well. Applying the modified theory to our measurements on evaporative cooling of metastable helium, we find a scattering length a=10(5) nm.

Tol, Paul J.J.; Hogervorst, Wim; Vassen, Wim [Laser Centre Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands)

2004-07-01

165

Anomalous scattering effects in elastic photon-atom scattering from biomedically important elements  

Microsoft Academic Search

In a variety of biomedical applications it has been demonstrated that elastic photon-atom scattering can be important. These include: solving for the crystal structure of a macromolecule, imaging, and radiation dose calculations. To the extent that scattering is significant, it is important to remember that there are a number of effects which go beyond the form-factor approximation. In this paper,

D. A Bradley; S. C Roy; Lynn Kissel; R. H Pratt

1999-01-01

166

Electron-helium free-free scattering in the presence of a laser field  

NASA Astrophysics Data System (ADS)

We report a series of experiments that examine electron-helium scattering in the presence of an Nd:YAG laser field of 1.17 eV photons. The goal of these experiments is to span the range of incident electron energies from 50 eV to 350 eV, and compare the results to the Kroll-Watson approximationootnotetextN. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804 (1973) (KWA) calculations. Effects of an intense laser field on the elastic scattering of electrons from argon were first reported by Andrick in 1976ootnotetextD. Andrick and L. Langhans, J. Phys. B 9, L459 (1976). In general, KWA calculations have been adequate to describe experimental results where the photon energy is significantly less than the incident electron energy -- a major exception being the case of small scattering angles where large discrepencies have been notedootnotetexte.g., B. Wallbank and J. K. Holmes, Phys. Rev. A 48, R2515 (1973). Our experiments test the KWA over a range of electron incident energies that has not been previously investigated.

Deharak, B. A.; Ladino, L.; Martin, N. L. S.

2010-03-01

167

Electron-helium scattering in the presence of a laser field at moderate incident energies  

NASA Astrophysics Data System (ADS)

We have begun to perform a series of experiments that examine electron-helium scattering in the presence of an Nd:YAG laser field. The goal of these experiments is to span the range of incident electron energies from 50 eV to 250 eV, and compare the results to Kroll-Watson approximationfootnotetextN. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804 (1973) (KWA) calculations. Effects of an intense laser field on the elastic scattering of electrons from argon were first reported by Andrick in 1976.footnotetextD. Andrick and L. Langhans, J. Phys. B 9, L459 (1976) In general, KWA calculations have been adequate to describe experimental results where the photon energy is significantly less than the incident electron energy -- a major exception being the case of small scattering angles where large discrepencies have been noted.footnotetexte.g., B. Wallbank and J. K. Holmes, Phys. Rev. A 48, R2515 (1973) Our experiments will test the KWA over a range of electron incident energies that has not been previously investigated.

Deharak, Bruno; Ladino, Luis; Martin, Nicholas

2009-10-01

168

Convergent J-matrix Calculation of the Differential Cross-Sections for Electron-Helium Scattering.  

NASA Astrophysics Data System (ADS)

Despite the fact that J-matrix method was proposed over 20 years ago by Heller and Yamani(Heller E.J. and Yamani H.A. Phys. Rev A 9) 1201 (1974), numerically converged practical applications have only recently been reported by Konovalov and McCarthy(Konovalov D.A. and McCarthy I.E. J. Phys. B 27) L407-L412 and L741-L747 (1994). Here we report a detailed investigation of the J-matrix method for electron-helium scattering. Particular attention will be paid to the description of the initial target states and their influence on the final result. J-matrix results will be compared with other recent theoretical results and experimental data.

Kravtsov, V. D.; Madison, D. H.; Konovalov, D. A.

1996-05-01

169

Calculation of electron-helium scattering at 40 eV  

SciTech Connect

We apply the convergent close-coupling (CCC) method to calculation of 40-eV electrons scattering on the ground state of helium. We present the differential cross sections up to the [ital n][le]3 levels, as well as the electron-impact coherence parameters for the 3 [sup 1][ital D] state. We find our results to be in excellent agreement with the measurements. It is shown that at this energy treating the target continuum has a large effect on the presented results, and for this reason the CCC theory is the only one that is able to obtain agreement with experiment. Integrated, total ionization, and total cross sections are also presented, and are found to be in excellent agreement with experiment.

Bray, I.; Fursa, D.V.; McCarthy, I.E. (Electronic Structure of Materials Centre, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide 5001 (Australia))

1995-01-01

170

Exotic atoms, K-nucleus scattering and hypernuclei  

SciTech Connect

Recent progress in exotic atom physics, kaon-nucleus scattering, and hypernuclear physics is reviewed. Specific problems discussed include searches for muon-nucleon interactions beyond QED, a comparison of data and recent calculation of K/sup + -/ + /sup 12/C elastic and inelastic scattering, as well as recent studies of ..sigma.. and ..lambda.. hypernuclei including new data on the level structure of /sup 13/C/..lambda...

Barnes, P. D.

1981-01-01

171

Feshbach resonances in ultracold atom-diatom scattering  

SciTech Connect

Quantum-mechanical scattering calculations of Feshbach resonances arising from van der Waals molecule formation are used to determine vibrational and rotational predissociation lifetimes. A multichannel effective range theory is used to establish the relationship between predissociation and the zero-temperature limit of collisional quenching for resonances lying close to the thresholds for dissociation. The elastic scattering Feshbach resonances may be measurable in ultracold atom-molecule experiments. {copyright} {ital 1998} {ital The American Physical Society}

Forrey, R.C.; Balakrishnan, N.; Kharchenko, V.; Dalgarno, A. [Institute for Theoretical Atomic and Molecular Physics, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)

1998-10-01

172

Theoretical studies on tunneling ionizations of helium atom in intense laser fields.  

PubMed

Our generalized Keldysh theory is applied to the simplest many-electron atom, helium atom. For the single ionization (He-->He(+)+e) we derive a compact rate formula, which does not contain any series summation or integral and thus is as simple as the Ammosov-Delone-Krainov ionization rates. In addition to its simplicity, our formula can explicitly show the wavelength dependence. Furthermore a simple form of the angular distribution of the photoelectron is available. Our compact formula agrees well with both the exact numerical calculations [A. Scrinzi et al., Phys. Rev. Lett. 83, 706 (1999)] and experimental data [B. Walker et al., Phys. Rev. Lett. 73, 1227 (1994)] in the intensity range of I<5x10(15) Wcm(2). In higher intensity regions, we suggest to utilize another simple formula which is valid in the tunneling limit. PMID:16626192

Nagaya, K; Mishima, K; Hayashi, M; Lin, S H

2006-04-14

173

Wave functions and two-electron probability distributions of the Hooke's-law atom and helium  

SciTech Connect

The Hooke's-law atom (hookium) provides an exactly soluble model for a two-electron atom in which the nuclear-electron Coulombic attraction has been replaced by a harmonic one. Starting from the known exact position-space wave function for the ground state of hookium, we present the momentum-space wave function. We also look at the intracules, two-electron probability distributions, for hookium in position, momentum, and phase space. These are compared with the Hartree-Fock results and the Coulomb holes (the difference between the exact and Hartree-Fock intracules) in position, momentum, and phase space are examined. We then compare these results with analogous results for the ground state of helium using a simple, explicitly correlated wave function.

O'Neill, Darragh P.; Gill, Peter M. W. [School of Chemistry, University of Nottingham, Nottingham NG7 2RD, (United Kingdom)

2003-08-01

174

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

175

Continuum-Coupling in Electron-Atom scattering  

SciTech Connect

High quality fundamental atomic data provide the foundation of accurate collisional-radiative models of laboratory and astrophysical plasmas. In the SciDAC (Scientific Discovery through Advanced Computing) project entitled 'Terascale Computational Atomic Physics for the Edge Region in Controlled Fusion Plasmas', we employ an integrated approach from the calculation of basic atomic data to the modeling necessary for the interpretation of controlled nuclear fusion experiments. For example, helium electron-impact excitation results support helium puff experiments on the MAST (Mega Ampere Spherical Tokamak) at Culham to diagnose the radial variation in plasma density and temperature. Similarly, electron-impact excitation/ionization work for isonuclear beryllium will prove vital if beryllium is adopted as a surface material for the plasma-facing walls for ITER. Here we will discuss some examples of electron-impact excitation and ionization, where the effects of coupling to and between the target continuum states are large, and advanced close-coupling methods are required in order to generate data of sufficient accuracy.

Ballance, C.P.; Griffin, D.C. [Department of Physics, Rollins College, Winter Park, FL 32789 (United States); Badnell, N.R. [Department of Physics, University of Strathclyde, Glasgow, UK G4 0NG (United Kingdom); Loch, S.D.; Pindzola, M.S. [Department of Physics, Auburn University, Alabama, AL 36849 (United States)

2004-10-20

176

Rubidium Atoms on Helium Droplets: Analysis of AN Exotic Rydberg Complex  

NASA Astrophysics Data System (ADS)

Rubidium atoms on the surface of superfluid helium droplets have been excited into Rydberg states. The excitation spectrum of the Rb-He_N system has been recorded from the 5^2D state manifold up to the ionization threshold by resonant three-photon-ionization time-of-flight spectroscopy. The observation of droplet size dependent shifts of excited states with respect to bare atom states is explained by a decreased quantum defect and a lowered ionization threshold. Within the scope of a Rydberg model we demonstrate that quantum defects and ionization thresholds are constant for each specific Rydberg series, which confirms the Rydberg character of excited Rubidium states on helium droplets. A set of six Rydberg series could be identified. Individual Rydberg states are observed with effective principle quantum numbers up to n* ? 19 and l ? 3, for which the expectation value of the electron orbital radius is about ten times larger than the droplet radius. M. Theisen, F. Lackner, G. Krois, and W.E. Ernst, J. Phys. Chem. Lett., 2, 2778-2782 (2011) F. Lackner, G. Krois, M. Theisen, M. Koch, and W.E. Ernst, Phys. Chem. Chem. Phys., 13, 18781-18788 (2011) J.E. Murphy, J.M. Berg, A.J. Merer, N.A. Harris, and R.W. Field, Phys. Rev. Lett. 65, 1861 (1990)

Lackner, Florian; Krois, Günter; Koch, Markus; Ernst, Wolfgang E.

2012-06-01

177

Electronic Debye-Waller effect in atom-surface scattering  

SciTech Connect

The reduction of the specular-beam intensity in the scattering of thermalized He atoms from densely packed surfaces of metals is investigated in terms of nonadiabatic multiple excitation of low-energy surface electronic density fluctuations. Their effect on the atom-scattering spectra is studied within the time-dependent approach developed by Doniach and Mueller-Hartmann, Rama- krishnan, and Toulouse to treat localized perturbations in metals. This mechanism may explain the peculiar coexistence of the unitarity defect with the absence of diffractive peaks as reported recently for the system He/Cu(100).

Crljen, Z.; Gumhalter, B.

1984-06-15

178

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

179

Mesoscopic entanglement of atomic ensembles through nonresonant stimulated Raman scattering  

Microsoft Academic Search

We propose a scheme of generating and verifying mesoscopic-level entanglement\\u000abetween two atomic ensembles using non-resonant stimulated Raman scattering.\\u000aEntanglement can be generated by direct detection or balanced homodyne\\u000adetection of the Stokes fields from the two cells, after they interfere on a\\u000abeam splitter. The entanglement of the collective atomic fields can be\\u000atransferred to the anti-Stokes fields in

Wenhai Ji; Chunbai Wu; S. J. van Enk; M. G. Raymer

2007-01-01

180

Ramsauer-Townsend effect in muonic atom scattering  

SciTech Connect

We present the final results of an experimental study of {mu}d and {mu}t atom scattering in solid hydrogen cooled to 3 K. Strong effects resulting from the Ramsauer-Townsend effect have been observed in the TRIUMF experiment E742 where muons were stopped in thin frozen layers of hydrogen. The measured Ramsauer-Townsend minimum energy for both {mu}d and {mu}t atoms and the minimum cross section are in agreement with theory.

Mulhauser, F.; Huot, O.; Jacot-Guillarmod, R.; Knowles, P. E.; Schaller, L. A. [Department of Physics, University of Fribourg, CH-1700 Fribourg (Switzerland); Adamczak, A. [Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Cracow (Poland); Beer, G. A. [Department of Physics and Astronomy, University of Victoria, Victoria, V8W 2Y2 (Canada); Bystritsky, V. M.; Stolupin, V. A. [Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation); Filipowicz, M. [Faculty of Fuels and Energy, AGH University of Science and Technology, PL-30059 Cracow (Poland); Fujiwara, M. C.; Marshall, G. M.; Olin, A.; Porcelli, T. A. [TRIUMF, Vancouver, V6T 2A3 (Canada); Huber, T. M. [Gustavus Adolphus College, St. Peter, Minnesota 56082 (United States); Kammel, P. [University of California, Berkeley, California 94720 (United States); Kim, S. K. [Physics Department, Jeonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of); Kunselman, A. R. [University of Wyoming Physics, Laramie, Wyoming 82071-3905 (United States); Petitjean, C. [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Wozniak, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, PL-30059 Cracow (Poland)] (and others)

2006-03-15

181

Stimulated Raman scattering in atomic ensembles: Toward quantum state entanglement  

Microsoft Academic Search

Entanglement generation and verification are essential steps to achieve long-distance quantum communication with atomic ensembles according to some protocols. In this dissertation, new schemes for generating quantum state entanglement between two atomic ensembles by stimulated Raman scattering are proposed and analyzed under various practical factors such as linear dispersion, readout losses, and detector noise. In the photon-number-state entanglement scheme, new

Wenhai Ji

2007-01-01

182

Role of core-scattered closed orbits in nonhydrogenic atoms  

Microsoft Academic Search

While both diamagnetic and Stark spectra of hydrogen can be analyzed accurately in terms of classical orbits, in nonhydrogenic atoms the multielectron core induces additional spectral modulations that cannot be analyzed reliably in terms of standard periodic orbit-type theories. However, by extending closed-orbit theory to include core-scattered waves consistently, both diamagnetic and Stark photoabsorption spectra of nonhy- drogenic Rydberg atoms

P. A. Dando; T. S. Monteiro; D. Delande; K. T. Taylor

1996-01-01

183

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

184

Stimulated Raman scattering in atomic ensembles: Toward quantum state entanglement  

NASA Astrophysics Data System (ADS)

Entanglement generation and verification are essential steps to achieve long-distance quantum communication with atomic ensembles according to some protocols. In this dissertation, new schemes for generating quantum state entanglement between two atomic ensembles by stimulated Raman scattering are proposed and analyzed under various practical factors such as linear dispersion, readout losses, and detector noise. In the photon-number-state entanglement scheme, new regimes of discrete-variable entanglement are found to be achievable at microscopic and mesoscopic excitation levels. In the field-quadrature-amplitude entanglement scheme, the inequality of quadrature variance satisfies the entanglement criteria for bipartite Gaussian state entanglement, even at low readout efficiency. Significant progress towards the experimental generation of such entanglement is reported. Population transfer between the atomic ground states is a prerequisite step to prepare the gain medium for stimulated Raman scattering. The high transfer efficiency is achieved through broadband optical pumping. The Stokes and time-delayed anti-Stokes scattering are observed, which is a primary step to verify the quantum memory effect in the atomic vapor. The photon statistics of the Stokes field is measured with a photon-number detection system operating at below the shot-noise level. The pulse energy dependence of Stokes fields on several practical factors is explored. Some new features and phenomena of stimulated Raman scattering in rubidium vapor are observed and analyzed. The simultaneous generation of Stokes and anti-Stokes scattering is observed in the cooperative Raman scattering process, in which only a single strong pump field is present. An enhanced Raman scattering process is also observed, in which the Stokes signal generated by the time-delayed second pump is enhanced by the presence of the first pump when the two pumps are in the Stokes pump frequency range. In addition, we observe very large pulse delay during propagation through 85Rb cell, and we explain it with a theoretical linear dispersion model.

Ji, Wenhai

185

Enhancement of motional entanglement of cold atoms by pairwise scattering of photons  

Microsoft Academic Search

The mechanism of pairwise scattering of photons with cold atoms is investigated. We show that considerable motional correlation can be established between atoms during the scattering process, which can effectively squeeze the scattering spectrum and can be utilized to produce highly entangled atomic wave packet. Under certain conditions, the atomic momentum entanglement can be efficiently enhanced beyond the 1 entanglement

Rui Guo; Xiaoji Zhou; Xuzong Chen

2008-01-01

186

Efimov physics in atom-dimer scattering of Li6 atoms  

Microsoft Academic Search

Li6 atoms in the three lowest hyperfine states display universal properties when the S-wave scattering length between each pair of states is large. Recent experiments reported four pronounced features arising from Efimov physics in the atom-dimer relaxation rate, namely two resonances and two local minima. We use the universal effective-field theory to calculate the atom-dimer relaxation rate at zero temperature.

H.-W. Hammer; Daekyoung Kang; Lucas Platter

2010-01-01

187

Efimov Physics in Atom-Dimer Scattering of Lithium6 Atoms  

Microsoft Academic Search

Lithium-6 atoms in the three lowest hyperfine states display universal\\u000aproperties when the S-wave scattering length between each pair of states is\\u000alarge. Recent experiments reported four pronounced features arising from Efimov\\u000aphysics in the atom-dimer relaxation rate, namely two resonances and two local\\u000aminima. We use the universal effective field theory to calculate the atom-dimer\\u000arelaxation rate at zero

H.-W. Hammer; Daekyoung Kang; Lucas Platter

2010-01-01

188

Effective atomic number in the Rayleigh to Compton scattering ratio  

NASA Astrophysics Data System (ADS)

Detection and counting X-ray photons scattered by the Rayleigh and Compton processes enable matter to be characterized locally. A theoretical relation was first established which simulates the result of a Rayleigh to Compton ratio measurement. It can thus be shown that a correct choice of scattering angle and photon energy enables a result to be obtained which is almost independent of X-ray attenuation inside the sample. With this condition, the Rayleigh to Compton scattering ratio depends only on the mixture under study and provides a local measurement of certain complicated functions of the atomic number Z and of the weight percentage of the different elements which constitute the compound. This function is usually called the ``effective atomic number'', Zeff. Different methods of calculation of Zeff are found in the literature, four of them, those used most frequently, were tested. There is no unique relation between the computed Zeff and 80 experimental results performed on aqueous solutions with different concentrations of eight elements, having Z values ranging from 13 to 64. This observation led us to the conclusion that any effective atomic number is valid only for given experimental conditions. Finally, a new method of calculating Zeff was developed for the Rayleigh to Compton scattering ratio, which is applicable for any material, scattering angle or photon energy.

Duvauchelle, P.; Peix, G.; Babot, D.

189

X-ray-photon scattering by an excited atom  

NASA Astrophysics Data System (ADS)

The existence of resonances in a double differential cross section of anomalous inelastic scattering of an x-ray photon by an excited atom at the attosecond time scale of the photon-electron contact interaction is theoretically predicted. These resonances realize unusual types of the excited atom vacancy decay channels. The subject of investigation is the atom of Be, excited to a discrete spectrum state via the 1s?np, n?2 channel. Experimental realization of the theoretically predicted quantum effect may provide a new method for increasing the energy of photons generated by an x-ray free electron laser.

Hopersky, Alexey N.; Nadolinsky, Alexey M.; Novikov, Sergey A.

2013-09-01

190

Resonant inelastic x-ray scattering from molecules and atoms  

SciTech Connect

X-ray fluorescence spectroscopy is one of the most powerful methods for the understanding of the electronic structure of matter. We report here on fluorescence experiments in the 2 to 6 keV photon energy range using tunable synchrotron radiation and the resulting experimental programs on resonant inelastic scattering in atoms and on polarization measurements in resonant molecular excitations.

Arp, U.; Deslattes, R.D. [National Institute of Standards and Technology, Gaithersburg, MD (United States); Miyano, K.E. [Brooklyn College, Brooklyn, NY (United States); Southworth, S.H. [and others

1995-12-31

191

Density matrices of the excited H (n = 2 and 3) atoms formed in 25--100-keV proton-helium charge-transfer collisions  

SciTech Connect

We present ab initio calculations for the differential and integrated (over impact parameters) density matrices of the excited hydrogen atoms (n = 2 and 3 manifolds) formed in 25--100-keV proton-helium charge-transfer collisions. The transition amplitudes for excited states are determined in a modified two-center atomic-orbital-expansion approach within the close-coupling treatment. The target helium atom is described in a one-electron picture. The calculated partial (nlm) and total charge-transfer cross sections are in good agreement with earlier theoretical and experimental data in this energy range. From the scattering amplitudes, the integrated density matrix and its various first-order moments for the n = 3 manifold are compared with recent measurements. From the three-dimensional charge-density plots, it is illustrated that the captured electron lags behind the projectile in the present energy range. From the impact-parameter-dependent density-matrix analysis, an approximate ''classical'' picture of the captured electron is presented.

Jain, A.; Lin, C.D.; Fritsch, W.

1987-09-01

192

Inelastic scattering of electrons by black hole atoms  

NASA Astrophysics Data System (ADS)

Electron-impact inelastic scattering processes involving black hole atoms are calculated by direct solution of the general relativistic Klein-Gordon equation. In Eddington-Finkelstein coordinates for the space-time metric, the Hamiltonian is non-singular, complex and non- Hermitian. Bound states of an electron and a black hole with a mass of 3.8 × 1012 kg and 3.8 × 1013 kg are found by matrix diagonalization of the time-independent Klein-Gordon equation. Absorption effects on inelastic scattering of electrons by a black hole atom are investigated by comparing solutions of the time-dependent Klein-Gordon equation with and without general relativistic corrections to the Newtonian gravitational potential. As the black hole becomes more massive, the absorption effects on the inelastic scattering become more pronounced.

Pindzola, M. S.

2009-05-01

193

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

194

Photon scattering from strongly driven atomic ensembles  

SciTech Connect

The second-order correlation function for light emitted from a strongly and near-resonantly driven dilute cloud of atoms is discussed. Because of the strong driving, the fluorescence spectrum separates into distinct peaks, for which the spectral properties can be defined individually. It is shown that the second-order correlations for various combinations of photons from different spectral lines exhibit bunching together with super-Poissonian or sub-Poissonian photon statistics, tunable by the choice of the detector positions. Additionally, a Cauchy-Schwarz inequality is violated for photons emitted from particular spectral bands. The emitted light intensity is proportional to the square of the number of particles, and thus can potentially be intense. Three different averaging procedures to model ensemble disorder are compared.

Jin Luling [Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Department of Physics, Northwest University, Xi'an 710069, Shaanxi (China); Evers, Joerg; Macovei, Mihai [Max-Planck Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)

2011-10-15

195

Collisional perturbation of states in atomic ytterbium by helium and neon  

SciTech Connect

Results of an investigation of collisional deexcitation of the metastable 6s6p&hthinsp;{sup 3}P{sub 0} state in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching cross sections to be {sigma}{sub He}{lt}13{times}10{sup {minus}22}&hthinsp;cm{sup 2} and {sigma}{sub Ne}{lt}8{times}10{sup {minus}22}&hthinsp;cm{sup 2}. The small cross sections may allow an ytterbium parity nonconservation experiment to be performed in a vapor cell. We have also measured the pressure broadening and shift of the 6s6p&hthinsp;{sup 3}P{sub 0}{r_arrow}6s7s&hthinsp;{sup 3}S{sub 1} and 6s{sup 2}&hthinsp;{sup 1}S{sub 0}{r_arrow}6s6p&hthinsp;{sup 3}P{sub 1} transitions by helium and neon. {copyright} {ital 1999} {ital The American Physical Society}

Kimball, D.F.; Clyde, D.; Budker, D.; Freedman, S.J.; Rochester, S.; Stalnaker, J.E. [Physics Department, University of California at Berkeley, Berkeley, California 94720-7300 (United States); Budker, D.; Freedman, S.J. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); DeMille, D. [Physics Department, Yale University, New Haven, Connecticut 06520 (United States); Zolotorev, M. [Center for Beam Physics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

1999-08-01

196

Diffusion coefficient of krypton atoms in helium gas at low and moderate temperatures  

NASA Astrophysics Data System (ADS)

In the present work, using the Chapman-Enskog method for dilute gases, the diffusion coefficients of ground krypton atoms in a very weakly ionized helium buffer gas are revisited. The calculations are carried out quantum mechanically in the range of low and moderate temperatures. The 1 ?+ potential-energy curve via which Kr approaches He is constructed from the most recent ab initio energy points. The reliable data points used in the construction are smoothly connected to adequate long- and short-range forms. The calculations of the classical second virial coefficients and the Boyle temperature of the helium-krypton mixture are also discussed. These coefficients and their variations in terms of temperature are analysed by adopting the constructed HeKr potential and the Lennard-Jones form that fits it. The diffusion and elastic cross sections are also explored and the resonance features they exhibit are closely examined. The variation law of the diffusion coefficients with temperature is determined for typical values of density and pressure. The coefficients show excellent agreement with the available experimental data; the discrepancies do not exceed 5%.

Bouazza, M. T.; Bouledroua, M.

197

Single-electron capture from helium-like atomic systems by bare projectiles  

NASA Astrophysics Data System (ADS)

The continuum-distorted-wave Born-initial-state (CDW-BIS) approximation for the description of single-electron capture from helium-like atomic systems by completely stripped projectiles is presented. The theoretical total cross-sections for charge exchange in ?-He and p-Li+ collisions are reported in the energy range 50 2000 keV/amu. We also report the results obtained by means of the continuum-distorted-wave Born-final-state (CDW-BFS) approximation. Detailed computations for differential cross-sections are performed for p-He collisions at 500 and 200 keV. A comparison between the four-body one-channel distorted-wave approximation and three-body distorted-wave (CDW-3B) approximation is made for differential cross-sections at 200 keV. The validity of our findings is critically assessed in comparison with the available experimental data.

Mancev, I.

2005-01-01

198

Polarization Control in Two-Color Above-Threshold Ionization of Atomic Helium  

SciTech Connect

Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In the photoelectron spectrum, lines associated with direct ionization and above-threshold ionization show strong variations of their amplitudes as a function of both the intensity of the optical dressing field and the relative orientation of the linear polarization vectors of the two fields. The polarization dependence provides direct insight into the symmetry of the outgoing electrons in above-threshold ionization. In the high field regime, the monochromaticity of the XUV radiation enables the unperturbed observation of nonlinear processes in the optical field.

Meyer, M.; Cubaynes, D.; Glijer, D. [LIXAM, UMR 8624, CNRS-Universite Paris Sud, Batiment 350, 91405 Orsay Cedex (France); Dardis, J.; Hayden, P.; Hough, P.; Richardson, V.; Kennedy, E. T.; Costello, J. T. [National Center for Plasma Science and Technology and School of Physical Sciences, Dublin City University, Dublin (Ireland); Radcliffe, P.; Duesterer, S.; Azima, A.; Li, W. B.; Redlin, H.; Feldhaus, J. [HASYLAB at DESY, Notkestr. 85, D-22607 Hamburg (Germany); Taieeb, R.; Maquet, A. [UPMC, Universite Paris 06, CNRS, UMR 7614, LCPMR, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Grum-Grzhimailo, A. N.; Gryzlova, E. V.; Strakhova, S. I. [Institute of Nuclear Physics, Moscow State University, Moscow 119991 (Russian Federation)

2008-11-07

199

Polarization control in two-color above-threshold ionization of atomic helium.  

PubMed

Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In the photoelectron spectrum, lines associated with direct ionization and above-threshold ionization show strong variations of their amplitudes as a function of both the intensity of the optical dressing field and the relative orientation of the linear polarization vectors of the two fields. The polarization dependence provides direct insight into the symmetry of the outgoing electrons in above-threshold ionization. In the high field regime, the monochromaticity of the XUV radiation enables the unperturbed observation of nonlinear processes in the optical field. PMID:19113264

Meyer, M; Cubaynes, D; Glijer, D; Dardis, J; Hayden, P; Hough, P; Richardson, V; Kennedy, E T; Costello, J T; Radcliffe, P; Düsterer, S; Azima, A; Li, W B; Redlin, H; Feldhaus, J; Taïeb, R; Maquet, A; Grum-Grzhimailo, A N; Gryzlova, E V; Strakhova, S I

2008-11-07

200

Role of electron wavepacket interference in the optical response of helium atoms  

NASA Astrophysics Data System (ADS)

Attosecond control of the optical response of helium atoms to extreme ultraviolet radiation in the presence of moderately strong infrared laser light has been recently demonstrated both by employing attosecond pulse trains (APTs) and single attosecond pulses. In the case of APTs the interference between different transiently bound electron wavepackets excited by consecutive attosecond light bursts in the train was indicated as the predominant mechanism leading to the control. We studied the same physical system with transient absorption spectroscopy using elliptically polarized infrared pulses or APTs with a varying number of pulses down to a single pulse. Our new results are not consistent with this kind of wavepacket interference being the dominant mechanism and show that its role in the control over the photoabsorption probability has to be rediscussed.

Lucchini, Matteo; Herrmann, Jens; Ludwig, André; Locher, Reto; Sabbar, Mazyar; Gallmann, Lukas; Keller, Ursula

2013-10-01

201

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

202

High resolution infrared spectra of a carbon dioxide molecule solvated with helium atoms  

NASA Astrophysics Data System (ADS)

Infrared spectra of HeN-CO2 clusters with N up to about 20 have been studied in the region of the CO2 ?3 fundamental band (~2350 cm-1) using a tunable diode laser spectrometer and pulsed supersonic jet source with cooled (>-150 °C) pinhole or slit nozzles and high backing pressures (<40 atm). Compared to previous studies of HeN-OCS and -N2O clusters, the higher symmetry of CO2 results in simpler spectra but less information content. Discrete rotation-vibration transitions have been assigned for N=3-17, and their analysis yields the variation of the vibrational band origin and B rotational constant over this size range. The band origin variation is similar to HeN-OCS, with an initial blueshift up to N=5, followed by a monotonic redshift, consistent with a model where the first five He atoms fill a ring around the equator of the molecule, forcing subsequent He atom density to locate closer to the ends. The B value initially drops as expected for a normal molecule, reaching a minimum for N=5. Its subsequent rise for N=6 to 11 can be interpreted as the transition from a normal (though floppy) molecule to a quantum solvation regime, where the CO2 molecule starts to rotate separately from the He atoms. For N>13, the B value becomes approximately constant with a value about 17% larger than that measured in much larger helium nanodroplets.

Tang, Jian; McKellar, A. R. W.

2004-07-01

203

Blackbody-induced decay, excitation and ionization rates for Rydberg states in hydrogen and helium atoms  

NASA Astrophysics Data System (ADS)

New features of the blackbody-induced radiation processes on Rydberg atoms were discovered on the basis of numerical data for the blackbody-induced decay Pdnl(T), excitation Penl(T) and ionization Pionnl(T) rates of nS, nP and nD Rydberg states calculated together with the spontaneous decay rates Pspnl in neutral hydrogen, and singlet and triplet helium atoms for some values of the principal quantum number n from 10 to 500 at temperatures from T = 100 K to 2000 K. The fractional rates Rd(e, ion)nl(T) = Pnld(e, ion)(T)/Pspnl equal to the ratio of the induced decay (excitation, ionization) rates to the rate of spontaneous decay were determined as functions of T and n in every series of states with a given angular momentum l = 0, 1, 2. The calculated data reveal an essential difference between the asymptotic dependence of the ionization rate Pionnl(T) and the rates of decay and excitation Pd(e)nl(T)~T/n2. The departures appear in each Rydberg series for n > 100 and introduce appreciable corrections to the formula of Cooke and Gallagher. Two different approximation formulae are proposed on the basis of the numerical data, one for Rd(e)nl(T) and another one for Rionnl(T), which reproduce the calculated values in wide ranges of principal quantum number from n = 10 to 1000 and temperatures between T = 100 K and T = 2000 K with an accuracy of 2% or better. Modified Fues' model potential approach was used for calculating matrix elements of bound-bound and bound-free radiation transitions in helium.

Glukhov, I. L.; Nekipelov, E. A.; Ovsiannikov, V. D.

2010-06-01

204

Spin Ordering on the Niobium OXIDE(100) Surface Measured by Elastic Metastable Helium Scattering.  

NASA Astrophysics Data System (ADS)

Magnetic insulating solids show a rich variety of electron spin ordering configurations due to the existence of several competing magnetic coupling mechanisms. Calculations indicate that spin ordering on the 2-dimensional surface of a solid may differ from the 3-dimensional bulk spin arrangement. However, the lack of suitable experimental probes has greatly limited the study of spin ordering on solid surfaces. In this thesis, I present a novel experimental technique that is capable of measuring surface long-range spin ordering using elastic scattering of metastable He 2^3S atoms (ESMA). I also present results from the first application of this technique, the determination of the spin ordering on a NiO(100) surface. ESMA is based on the spin dependent de-excitation probability of the He 2^3S atoms (He*) at a magnetic surface. The electronic metastable 2^3S state of He is very long lived in vacuum, but on impact with a surface a large fraction of the metastable atoms de-excite to the electronic ground state. However, on an insulating surface with localized spins, the local nature of the atom-surface interaction together with Auger selection rules will prevent the de -excitation of a He* atom with a spin orientation parallel to the local surface electron spin. Thus, a periodic arrangement of the local surface moments leads to a periodic modulation of the elastically scattered He* beam which is manifested in the corresponding diffraction pattern. Application of this technique to the NiO(100) surface reveals a spin structure that is quite different from the bulk anti-ferromagnetic arrangement. The data suggests the presence of a frozen spin wave arrangement on the surface, where the surface spin ordering has acquired a longer super-periodicity in a high symmetry direction, due to a spatial precession of the spins around the spin directions defined by the bulk ordering. In order to better understand these results, I have developed a model of the scattering process that includes the effect of a spatially modulated attenuation of the metastable He* beam due to the spin dependent de-excitation probability of the He* atoms. The results show good qualitative agreement with the NiO(100) data, and demonstrate that a small spatial modulation of the de-excitation probability over the surface will give rise to corresponding diffraction peaks.

Swan, Anna K.

205

Spin asymmetry in elastic scattering of electrons by hydrogen atoms  

SciTech Connect

We have performed calculations of the spin asymmetry in elastic scattering of electrons by hydrogen atoms using an optical potential appraoch. An 18-state basis set is employed. The scattering calculations are carried out explicitly for the channels corresponding to the lowest six states. The effects of other channels are included via a second-order optical potential. The present values of the asymmetry at 90/sup 0/ are in agreement with the recent experimental values of Fletcher et al. and resolve the discrepancy between theory and experiment which they reported in the intermediate-energy region.

Oza, D.H.; Callaway, J.

1985-10-01

206

Optical-potential model for electron-atom scattering  

SciTech Connect

It is proposed that the addition of a matrix optical potential to a close-coupling calculation should lead to improved results in studies of electron-atom scattering. This procedure is described with use of a pseudostate expansion to evaluate the optical potential. The integro-differential equations are solved by a linear-algebraic method. As a test case, applications are made to electron-hydrogen scattering, and the results are compared with those obtained by other calculational procedures, and with experiment.

Callaway, J.; Oza, D.H.

1985-11-01

207

Cs atoms on helium nanodroplets and the immersion of Cs{sup +} into the nanodroplet  

SciTech Connect

We report the non-desorption of cesium (Cs) atoms on the surface of helium nanodroplets (He{sub N}) in their 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state upon photo-excitation as well as the immersion of Cs{sup +} into the He{sub N} upon photo-ionization via the 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state. Cesium atoms on the surface of helium nanodroplets are excited with a laser to the 6{sup 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{sub N} is excited with photon energies close to the atomic D{sub 1}-line, which implies an attractive character of the excited state system (Cs*-He{sub 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{sub N} in a pseudo-diatomic model. Calculated Franck-Condon factors for emission from the 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) to the 6{sup 2}S{sub 1/2} ({sup 2}{Sigma}{sub 1/2}) state help to explain the experimental data. The stability of the Cs*-He{sub N} system allows to form Cs{sup +} snowballs in the He{sub N}, where we use the non-desorbing 6{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 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{sup 2}P{sub 1/2} ({sup 2}{Pi}{sub 1/2}) state gives rise to a very high yield of immersed Cs{sup +} in contrast to an ionization scheme via the 6{sup 2}P{sub 3/2} ({sup 2}{Pi}{sub 3/2}) state. When resonant two-photon ionization is applied to cesium dimers on He droplets, Cs{sub 2}{sup +}-He{sub N} aggregates are observed in time-of-flight mass spectra.

Theisen, Moritz; Lackner, Florian; Ernst, Wolfgang E. [Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria)

2011-08-21

208

J-matrix calculation of electron-helium S-wave scattering  

SciTech Connect

The J-matrix approach to electron-atom scattering is revised by merging it with the Fano's multiconfiguration interaction matrix elements [U. Fano, Phys. Rev. 140, A67 (1965)]. The revised method is then applied to the S-wave model of the e-He scattering problem demonstrating remarkable computational efficiency and accuracy. In particular, the method is in complete agreement with the convergent-close-coupling elastic, 2{sup 1,3}S excitation and single ionization cross sections for impact energies in the range 0.1-1000 eV. The S-wave resonance structures in the elastic and 2{sup 1,3}S excitation cross sections are highlighted.

Konovalov, D. A.; Fursa, D. V.; Bray, I. [Discipline of Information Technology, School of Business, James Cook University, Townsville, Queensland 4811 (Australia); ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, Western Australia 6845 (Australia)

2011-09-15

209

Scattering approach to dispersive atom-surface interactions  

SciTech Connect

We develop the scattering approach for the dispersive force on a ground state atom on top of a corrugated surface. We present explicit results to first order in the corrugation amplitude. A variety of analytical results are derived in different limiting cases, including the van der Waals and Casimir-Polder regimes. We compute numerically the exact first-order dispersive potential for arbitrary separation distances and corrugation wavelengths, for a Rubidium atom on top of a silicon or gold corrugated surface. We consider in detail the correction to the proximity force approximation, and present a very simple approximation algorithm for computing the potential.

Dalvit, Diego [Los Alamos National Laboratory; Messina, Riccardo [LAB KASTLER BROSSEL; Maia Neto, Paulo [INSTITUTO DE FISICA UFRJ; Lambrecht, Astrid [LAB KASTLER BROSSEL; Reynaud, Serge [LAB KASTLER BROSSEL

2009-01-01

210

Neutral atom lithography using the 389 nm transition in metastable helium  

NASA Astrophysics Data System (ADS)

Resist based neutral atom lithography with metastable 23 S1 Helium (He*) has been used to produce small structures in both gold and palladium. A beam of He* from a reverse flow, DC discharge source is collimated by the bichromatic optical force followed by three optical molasses velocity compression stages. The He* beam then crosses a region where a mechanical or optical mask creates the desired pattern. In the first experiments, a self assembled monolayer (SAM) of nonanethiol is grown on a gold coated silicon wafer and then exposed to the bright, collimated beam of He* after a nickel micro mesh mask. The mesh protects parts of the SAM from the 20 eV of internal energy deposited by the impact of a He* atom onto the sample surface. The pattern of the mesh is transferred into the ˜200 A gold layer with a standard selective etch that removes the gold from under the damaged SAM molecules. The samples were analyzed with an Atomic Force Microscope and Scanning Electron Microscope. The second set of experiments were performed using an optical mask to pattern a gold coated silicon wafer. In the optical mask, the He* atoms experience the dipole force while traversing a standing light wave of lambda1 = 1083 nm light tuned 490 MHz above the 23S1 ? 23P2 transition or, in separate experiments, lambda 2 = 389 nm light tuned 80 MHz below the 23S1 ? 33P2 transition. Using the optical masks, He* can be focused or channeled into parallel lines separated by lambda/2 by varying the intensity of the standing light wave. The small structures created by the 389 nm optical mask began approaching the gold surface granularity. A ˜ 200A layer of palladium on silicon was chosen as the palladium granularity is much smaller and the SAM of nonanethiol will still form on the surface. Experiments using a nickel micro mesh as a mechanical mask have demonstrated similar features to those in gold.

Reeves, Jason

211

Inelastic Scattering of Electrons by Black Hole Atoms  

NASA Astrophysics Data System (ADS)

Electron-impact inelastic scattering processes involving black hole atoms are calculated by direct solution of the general relativistic Klein-Gordon equation. In Eddington-Finkelstein coordinates for the space-time metric, the Hamiltonian is non-singular, complex, and non-Hermitian. Bound states of electrons and black holes with masses ranging from 3.8 x 10^12 kg to 7.6 x 10^13 kg are found by matrix solution of the time-independent Klein-Gordon equation. Absorption effects on inelastic scattering of electrons by black hole atoms are investigated by comparing solutions of the time-dependent Klein-Gordon equation with and without general relativistic corrections to the Newtonian gravitational potential.

Pindzola, M. S.; Robicheaux, F.

2009-05-01

212

Rayleigh scattering from excited states of atoms and ions  

SciTech Connect

Elastic photon scattering from the ground state and various excited states of carbon atoms and ions has been investigated, using the S-matrix formalism, for incident photon energies ranging from 100 eV to 10 keV, contrasting the results obtained for different configurations. The excited states considered include hollow-atom states, where one or more inner shells are completely vacated. Ionic cases are considered as a limit of excitation. Results demonstrate how cross sections for different excited states group together according to shared properties of the configurations, such as the number of K electrons. Cross sections may exhibit deep dips below the K edge, depending on the occupation of the subshells corresponding to the strongest transitions. Scattering from excited states can have significantly larger cross sections than scattering from the ground state, particularly just below the K resonance region, and therefore it needs to be considered in situations where there is a large population of these excited states. Results are interpreted in terms of form-factor arguments and the qualitative behavior of individual subshell amplitudes. The angular dependence of cross sections can be understood in terms of angle-dependent form factors and anomalous scattering factors, taken to be angle independent. Cases are identified for which excited-state total integrated cross sections are much larger than the corresponding cross sections for scattering from the ground state. Our main results use an averaging over magnetic substates at the level of the amplitude, exact only for fully filled subshells, but generally appropriate for the carbon case considered, which simplifies the discussion and explains most of the general features. We also present results for a hollow lithium atom with and without this approximation to illustrate the differences that can arise in certain circumstances. (c) 2000 The American Physical Society.

Carney, J. P. J. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Pratt, R. H. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Kissel, Lynn [Physics and Space Technology, Lawrence Livermore National Laboratory, Livermore, California 94551-0808 (United States); Roy, S. C. [Department of Physics, Bose Institute, Calcutta 700009, West Bengal, (India); Sen Gupta, S. K. [University Science Instrumentation Centre, North Bengal University, Darjeeling 734430, (India)

2000-05-01

213

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

214

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

215

Measurements of scattering processes in negative ion-atom collisions  

SciTech Connect

This Technical Progress Report describes the progress made on the research objectives during the past twelve months. This research project is designed to provide measurements of various scattering processes which occur in H{sup {minus}} collisions with atomic (specifically, noble gas and atomic hydrogen) targets at intermediate energies. 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 in progress will provide either experimentally-determined cross sections or set upper limits to those cross sections. In either case, these measurements will be stringent tests of our understanding in energetic negative ion-atom collisions. This series of experiments required the construction of a new facility and the initial ion beam was accelerated through the apparatus in April 1991.

Kvale, T.J.

1992-01-01

216

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

217

Control of atomic dynamics in laser-assisted electron-atom scattering through the driving-laser ellipticity  

NASA Astrophysics Data System (ADS)

Orders of magnitude increases of the cross sections are predicted for laser-assisted low-energy electron-atom scattering (accompanied by absorption of laser photons) as the laser ellipticity is increased. These ellipticity-controlled enhancements are manifestations of the field-free electron-atom scattering dynamics, such as the Ramsauer-Townsend effect in low-energy elastic electron-atom scattering. The strong sensitivity of laser-assisted scattering cross sections to this dynamics and the laser ellipticity is illustrated for e-Ne and e-Ar scattering in both midinfrared (?=3.5?m) and CO2 (?=10.6?m) laser fields of moderate intensities.

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

2013-03-01

218

Cooperative scattering and radiation pressure force in dense atomic clouds  

SciTech Connect

Atomic clouds prepared in ''timed Dicke'' states, i.e. states where the phase of the oscillating atomic dipole moments linearly varies along one direction of space, are efficient sources of superradiant light emission [Scully et al., Phys. Rev. Lett. 96, 010501 (2006)]. Here, we show that, in contrast to previous assertions, timed Dicke states are not the states automatically generated by incident laser light. In reality, the atoms act back on the driving field because of the finite refraction of the cloud. This leads to nonuniform phase shifts, which, at higher optical densities, dramatically alter the cooperative scattering properties, as we show by explicit calculation of macroscopic observables, such as the radiation pressure force.

Bachelard, R. [University of Nova Gorica, School of Applied Sciences, Vipavska 11c SI-5270 Ajdovscina (Slovenia); Piovella, N. [Dipartimento di Fisica, Universita Degli Studi di Milano, Via Celoria 16, I-20133 Milano (Italy); Courteille, Ph. W. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, 13560-970 Sao Carlos, SP (Brazil)

2011-07-15

219

Mesoscopic entanglement of atomic ensembles through nonresonant stimulated Raman scattering  

SciTech Connect

We propose a scheme of generating and verifying mesoscopic-level entanglement between two atomic ensembles using nonresonant stimulated Raman scattering. Entanglement can be generated by direct detection or balanced homodyne detection of the Stokes fields from the two cells after they interfere on a beam splitter. The entanglement of the collective atomic fields can be transferred to the anti-Stokes fields in a readout process. By measuring the operator moments of the anti-Stokes fields, we can verify the presence of entanglement. We model the effects of practical factors such as Stokes-field detector quantum efficiency and additive thermal noise in the entanglement generating process, and anti-Stokes-field losses in the entanglement verification process, and find achievable regimes in which entanglement can be verified at the levels of tens to hundreds of atomic excitations in the ensembles.

Ji, Wenhai; Wu, Chunbai; Enk, S. J. van; Raymer, M. G. [Oregon Center for Optics and Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States)

2007-05-15

220

Esr Spectra of Alkali-Metal Atoms on Helium Nanodroplets: a Theoretical Model for the Prediction of Helium Induced Hyperfine Structure Shifts  

NASA Astrophysics Data System (ADS)

We predict He-droplet-induced changes of the isotropic HFS constant a_{HFS} of the alkali-metal atoms M = Li, Na, K and Rb on the basis of a model description. Optically detected electron spin resonance spectroscopy has allowed high resolution measurements that show the influence of the helium droplet and its size on the unpaired electron spin density at the alkali nucleus. Our theoretical approach to describe this dependence is based on a combination of two well established techniques: Results of relativistic coupled-cluster calculations on the alkali-He dimers (energy and HFS constant as functions of the binding length) are mapped onto the doped-droplet-situation with the help of helium-density functional theory. We simulate doped droplets He_{N} with N ranging from 50 to 10000, using the diatomic alkali-He-potential energy curves as input. From the obtained density profiles we evaluate average distances between the dopant atom and its direct helium neighborhood. The distances are then set in relation to the variation of the HFS constant with binding length in the simplified alkali-He-dimer model picture. This method yields reliable relative shifts but involves a systematic absolute error. Hence, the absolute values of the shifts are tied to one experimentally determined HFS constant for ^{85}Rb-He_{N = 2000}. With this parameter choice we obtain results in good agreement with the available experimental data for Rb and K^{a,b} confirming the predicted 1/N trend of the functional dependence^{c}. M. Koch, G. Auböck, C. Callegari, and W. E. Ernst, Phys. Rev. Lett. 103, 035302-1-4 (2009) M. Koch, C. Callegari, and W. E. Ernst, Mol. Phys. 108 (7), 1005-1011 (2010) A. W. Hauser, T. Gruber, M. Filatov, and W. E. Ernst, ChemPhysChem (2013) online DOI: 10.1002/cphc.201200697

Hauser, Reas W.; Filatov, Michael; Ernst, Wolfgang E.

2013-06-01

221

Scattering of Low-Energy Electrons by Excited Sodium Atoms Using a Photon and Electron Atomic Beam Recoil Technique  

Microsoft Academic Search

A new method for measuring cross sections for the scattering of electrons by laser-excited atoms is described. It is a generalization of the atomic-beam recoil technique, taking advantage of the recoil of atoms during resonant photon interactions to spatially separate excited from nonexcited atoms. A preliminary value for the total cross section for the scattering of electrons by the 32P32(mF=3)

N. D. Bhaskar; B. Jaduszliwer; B. Bederson

1977-01-01

222

Scattering of an ultrashort electromagnetic radiation pulse by an atom in a broad spectral range  

SciTech Connect

The scattering of an ultrashort electromagnetic pulse by atomic particles is described using a consistent quantum-mechanical approach taking into account excitation of a target and nondipole electromagnetic interaction, which is valid in a broad spectral range. This approach is applied to the scattering of single- and few-cycle pulses by a multielectron atom and a hydrogen atom. Scattering spectra are obtained for ultrashort pulses of different durations. The relative contribution of 'elastic' scattering of a single-cycle pulse by a hydrogen atom is studied in the high-frequency limit as a function of the carrier frequency and scattering angle.

Astapenko, V. A., E-mail: astval@mail.ru [Moscow Institute of Physics and Technology (Russian Federation)

2011-02-15

223

Positronium - hydrogen atom scattering using the static exchange model  

NASA Astrophysics Data System (ADS)

Scattering of positronium atoms by hydrogen atoms has been investigated using the static exchange model and the first Born approximation (FBA) using only the exchange interaction. The FBA elastic total cross section at very low energy is very close to the estimated value of Massey and Mohr in the zero energy limit. We report total elastic, differential and quenching cross sections using the static exchange model for the energy range 0.068 - 100 eV. The present static exchange results are found to differ from the corresponding results of Fraser. The ratio of the quenching to total elastic cross section approaches the value 0.25 with increasing energy as predicted by Massey and Mohr.

Ray, H.; Ghosh, A. S.

1996-11-01

224

Fast atom diffraction for multi-electronic atoms scattered from a LiF surface  

NASA Astrophysics Data System (ADS)

In this work we investigate experimentally and theoretically angular distributions of swift multi-electronic atoms after colliding with a LiF(001) surface under axial surface channeling conditions. We use the surface eikonal approximation to describe the quantum interference of scattered projectiles. The atom-surface interaction is represented by means of a pairwise additive potential that includes the contribution of the projectile polarization. The aim is to use the experimental spectra to test the range of validity of the proposed potential model.

Gravielle, M. S.; Schüller, A.; Winter, H.; Miraglia, J. E.

2012-11-01

225

Measurements of cross sections for positrons scattered by Cs atoms^*  

NASA Astrophysics Data System (ADS)

We report our most recent measurements of total and positronium (Ps) formation cross sections (Q_Ps's) for positrons scattered by Cs atoms. These results are found to be in reasonable agreement with the theoretical calculations by Kernoghan et al.^1 The total cross sections and the upper limit on the Q_Ps's are measured using a beam transmission technique. The lower limit on the Q_Ps's and an additional contribution from ortho-Ps decay are measured by detecting two coincident ? rays in different energy windows. We are also making first estimates of Cs excitation cross sections. These results are obtained from the analysis of the energy spectrum of positrons that have passed through the scattering region. We resolve the fraction of positrons that have lost energy due to the excitation of Cs atoms. ^*Research supported by NSF Grant PHY 99-88093. ^1 A.A. Kernoghan, M.T. McAlinden, H.R.J. Walters, J. Phys. B 29, 3971 (1996).

Surdutovich, E.; Kauppila, W. E.; Miller, E. G.; Price, K. A.; Stein, T. S.

2004-05-01

226

Many-electron scattering applied to atomic point contacts.  

PubMed

Electron transport in a strong coupling regime is investigated by applying the many-electron correlated scattering (MECS) method to an atomic point contact model. Comparing the theoretical calculations to the quantum of conductance obtained experimentally for these systems allows for the error associated with the numerical implementation of the MECS method to be estimated and attributed to different components of the calculations. Errors associated with implementing the scattering boundary conditions and determination of the applied voltage in a finite explicit electrode model are assessed, and as well the impact on the basis set description on predicting the conductance is examined in this weakly correlated limit. The MECS calculation for the atomic point contact results in a conductance of 0.6G(0), in reasonable agreement with measurements for gold point contacts where approximately the conductance quantum G(0) is obtained. The analysis indicates the error attributable to numerical approximations and the explicit electrode model introduced in the calculations should not exceed 40% of the total conductance, whereas the effect of electron-electron correlations, even in this weakly correlated regime, can result in as much as a 30% change in the predicted conductance. PMID:22369783

McDermott, Shane; Greer, J C

2012-02-28

227

Measurements of cross-sections for positrons and electrons scattered by Cs atoms  

NASA Astrophysics Data System (ADS)

Total scattering cross-sections have been measured for 1-60 eV positrons and 6-200 eV electrons scattered by Cs atoms using a beam-transmission technique with a heated scattering cell. For 0.5-25 eV positron scattering we have measured both upper and lower limits on positronium formation cross-sections.

Surdutovich, E.; Kauppila, W. E.; Kwan, C. K.; Miller, E. G.; Parikh, S. P.; Price, K. A.; Stein, T. S.

2004-07-01

228

Efimov physics in atom-dimer scattering of {sup 6}Li atoms  

SciTech Connect

{sup 6}Li atoms in the three lowest hyperfine states display universal properties when the S-wave scattering length between each pair of states is large. Recent experiments reported four pronounced features arising from Efimov physics in the atom-dimer relaxation rate, namely two resonances and two local minima. We use the universal effective-field theory to calculate the atom-dimer relaxation rate at zero temperature. Our results describe the four features qualitatively and imply there is a hidden local minimum. In the vicinity of the resonance at 685 G, we perform a finite temperature calculation which improves the agreement of theory and experiment. We conclude that finite temperature effects cannot be neglected in the analysis of the experimental data.

Hammer, H.-W. [Helmholtz-Institut fuer Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universitaet Bonn, D-53115 Bonn (Germany); Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195 (United States); Kang, Daekyoung [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States); Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195 (United States); Platter, Lucas [Institute for Nuclear Theory, University of Washington, Seattle, Washington 98195 (United States)

2010-08-15

229

Efimov physics in atom-dimer scattering of Li6 atoms  

NASA Astrophysics Data System (ADS)

Li6 atoms in the three lowest hyperfine states display universal properties when the S-wave scattering length between each pair of states is large. Recent experiments reported four pronounced features arising from Efimov physics in the atom-dimer relaxation rate, namely two resonances and two local minima. We use the universal effective-field theory to calculate the atom-dimer relaxation rate at zero temperature. Our results describe the four features qualitatively and imply there is a hidden local minimum. In the vicinity of the resonance at 685 G, we perform a finite temperature calculation which improves the agreement of theory and experiment. We conclude that finite temperature effects cannot be neglected in the analysis of the experimental data.

Hammer, H.-W.; Kang, Daekyoung; Platter, Lucas

2010-08-01

230

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

231

Single-photon ionization of helium from 4.5 to 12 keV by Compton scattering and the photoelectric effect  

NASA Astrophysics Data System (ADS)

We have measured the ratio of the cross sections for double-to-single ionization in helium for several monoenergetic photon energies between 4.5 and 12 keV using time-of-flight ion charge state spectroscopy. In this energy range, both the photoelectric effect and inelastic (Compton) scattering contribute significantly to the total cross section. The ionization states caused by Compton scattering were distinguished from those caused by the photoelectric effect by the different recoil energies of the helium ion associated with the two processes. The ratios of the double-to-single ionization cross sections of helium for the photoelectric effect (Rp) and for Compton scattering (Rc) are given, and compared with previous measurements and theoretical calculations. The measured value for Rc at 12 keV is (1.21+/-0.27)%, which agrees well with the theoretical calculations of Andersson and Burgdörfer [Phys. Rev. A 50, R2810 (1994)].

Morgan, D. V.; Bartlett, R. J.

1999-05-01

232

Time-domain perspective on Autler-Townes splitting in attosecond transient absorption of laser-dressed helium atoms  

NASA Astrophysics Data System (ADS)

We present a theoretical study of the delay-dependent Autler-Townes (AT) splitting in transient absorption spectroscopy of an isolated attosecond pulse in helium atoms subject to a delayed infrared (IR) pulse. We concentrate on cases in which the IR pulse is resonant with the helium 1s2p-1s2s transition and provide a time-domain perspective of the dynamics in the delay-dependent pump-probe system. We identify several interesting delay-dependent features in the transient absorption spectrum such as AT splitting, oscillation between absorption and emission at the resonant absorption frequency, and sub-IR-cycles oscillations. We then explain the origins of these features in the time domain in terms of a strongly driven two-level system, in the language of population transfer and coherent control.

Wu, Mengxi; Chen, Shaohao; Gaarde, Mette B.; Schafer, Kenneth J.

2013-10-01

233

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH(3)-Si(111) and CD(3)-Si(111) surfaces.  

PubMed

The surface structure and vibrational dynamics of CH(3)-Si(111) and CD(3)-Si(111) surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited a lattice constant of 3.82 A?, in accordance with the spacing of the silicon underlayer. The excellent quality of the observed diffraction patterns, along with minimal diffuse background, indicated a high degree of long-range ordering and a low defect density for this interface. The vibrational dynamics were investigated by measurement of the Debye-Waller attenuation of the elastic diffraction peaks as the surface temperature was increased. The angular dependence of the specular (?(i)=?(f)) decay revealed perpendicular mean-square displacements of 1.0×10(-5)?A?(2)?K(-1) for the CH(3)-Si(111) surface and 1.2×10(-5)?A?(2)?K(-1) for the CD(3)-Si(111) surface, and a He-surface attractive well depth of ?7?meV. The effective surface Debye temperatures were calculated to be 983 K for the CH(3)-Si(111) surface and 824 K for the CD(3)-Si(111) surface. These relatively large Debye temperatures suggest that collisional energy accommodation at the surface occurs primarily through the Si-C local molecular modes. The parallel mean-square displacements were 7.1×10(-4) and 7.2×10(-4)?A?(2)?K(-1) for the CH(3)-Si(111) and CD(3)-Si(111) surfaces, respectively. The observed increase in thermal motion is consistent with the interaction between the helium atoms and Si-CH(3) bending modes. These experiments have thus yielded detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces. PMID:20849184

Becker, James S; Brown, Ryan D; Johansson, Erik; Lewis, Nathan S; Sibener, S J

2010-09-14

234

High-lying resonances in positron scattering by the helium ion below the Ps(n=3) threshold  

NASA Astrophysics Data System (ADS)

Ever since Bhatia and Drachman [1] reported two S-wave resonances in positron scattering by a helium ion, there has been considerable interest in and sometimes controversial on the investigation of the resonances in such a system [2]. In the present work, we apply the method of complex-coordinate rotation to investigate resonances in positron scattering by helium ions. Highly correlated Hylleraas functions are used to calculate resonances for high-angular-momentum states up to L=9. We will report the results for high-lying resonances below Ps(n=3) threshold. A comparison will be made with the available results in the literature. [1] A. K. Bhatia and R. J. Drachman, Phys. Rev. A 42, 5117 (1990) [2] Y. K. Ho, Phys. Rev. A 53, 3165 (1996); A. Igarashi and I. Shimamura, Phys. Rev. A 56, 4733 (1997); Y. K. Ho and Z.-C. Yan, Phys. Rev. A 66, 062705 (2002); A. Igarashi and I. Shimamura, Phys. Rev. A 70, 012706 (2004); N. Yamanaka, et al. Phys. Rev. A 70, 062701 (2004)

Yan, Z.-C.; Ho, Y. K.

2005-05-01

235

Contribution of light-by-light scattering to energy levels of light muonic atoms  

NASA Astrophysics Data System (ADS)

The complete contribution of diagrams with the light-by-light scattering to the Lamb shift is found for muonic hydrogen, deuterium and helium ion. The results are obtained in the static-muon approximation and a part of the paper is devoted to the verification of this approximation and analysis of its uncertainty.

Karshenboim, S. G.; Korzinin, E. Yu.; Ivanov, V. G.; Shelyuto, V. A.

2010-07-01

236

Quantitative Local Atomic Displacements from Huang Scattering Normalized by Thermal Diffuse Scattering  

NASA Astrophysics Data System (ADS)

The three-dimensional (3-D) pattern of atomic displacements at the core of a small defect or defect cluster embedded in a bulk crystal is possible to measure in principle, but difficult to obtain in practice, especially if quantitative displacements are desired. Here, it is demonstrated that a least-squares fit to the single-crystal X-ray Huang-scattering distribution surrounding an intense Bragg peak is a practical means of obtaining quantitative displacements when thermal diffuse scattering is used as an internal intensity standard. After fitting a model based on local Kanzaki forces embedded within an elastic continuum, the use of finite-defect and point-defect methods of computing and interpreting the pattern of local displacements are compared and contrasted. To make the analysis general with regard to both crystal symmetry and defect symmetry, numerical Fourier transforms are employed rather than pursuing analytical expressions for the displacements.

Campbell, Branton J.

2010-05-01

237

Laser assisted electron-atom scattering in critical geometries  

NASA Astrophysics Data System (ADS)

We investigate the scattering of electrons off of neutral targets in the presence of a linearly polarized, low frequency laser field. The laser has large enough extent for the wavefunction to be treated in the Floquet expansion. The scattering geometries of interest are small angles where momentum transfer is nearly perpendicular to the field, and the Kroll Watson approximation breaks down. We use the eigenchannel R matrix method to solve the Schr"odinger equation, employing Hamiltonians in both the length and the velocity gauges in different regions. The target atom is represented by a model potential including a screened coulomb term near the origin and a longer range induced dipole interaction. The short range reaction matrix in the Kramers-Henneberger (acceleration) representation is found by matching the velocity gauge R matrix to spherical Gordon-Volkov states, and from this the cross section is derived. Experiments have shown emission and absorption cross sections at small angles to be much higher than the approximation predicts, and we hope to gain insight into the cause of this phenomenon.

Morrison, Nathan; Greene, Chris H.

2012-06-01

238

Time-Dependent Approach to Electron--Atom Scattering.  

NASA Astrophysics Data System (ADS)

The B-spline method [1] was used to represent the Hamiltonian describing the interaction of a projectile and a target on a discrete lattice. The time-dependent Schrödinger equation was then solved by explicit integration using different time propagation schemes, such as Taylor expansion and the ``leap-frog'' method [2]. In order to assess the accuracy and efficiency of the different approaches, the method was tested for several one-dimensional model problems, such as scattering of a Gaussian wavepacket from various arrangements of steps and barriers. The program is currently being applied to the two-dimensional Temkin-Poet model of electron scattering from atomic hydrogen [3]. The most recent results for excitation and ionization cross sections will be presented at the conference and compared with other theoretical work. 1. A.S. Umar, J. Wu, M.R. Strayer and C. Bottcher, J. Comp. Phys. 93, 1. 426 (1991) 2. W.H. Press, S.A. Teucholsky, V.T. Vetterling, and B.P. Flannery, 2. Numerical Recipes (Cambridge University Press, New York 1992) 3. A. Temkin, Phys. Rev. A 126, 130 (1962)

Krilov, Goran

1997-04-01

239

Quantum dynamics of an excited alkali atom in a noble gas cluster: lithium attached to a helium cluster.  

PubMed

An alkali atom-noble gas cluster system is considered as a model for solvation effects in optical spectra, within a quantum-classical description based on the density operator of a many-atom system and its partial Wigner transform. This leads to an eikonal-time-dependent molecular orbital treatment suitable for a time-dependent description of the coupling of light emission and atom dynamics in terms of the time-dependent electric dipole of the whole system. As an application, we consider an optically excited lithium atom as the dopant in a helium cluster at 0.5 K. We describe the motions of the excited Li atom interacting with a cluster of He atoms and calculate the time-dependent electric dipole of the Li-He(99) system during the dynamics. The electronic Hamiltonian is taken as a sum of three-body Li-He diatomic potentials including electronic polarization and repulsion, with l-dependent atomic pseudopotentials for Li and He, while we use a modified pair potential for He-He. The calculations involve the coupling of 12 quantum states with 300 classical degrees of freedom. We present results for the dynamics and spectra of a Li atom interacting with a model cluster surface of He atoms and also interacting with a droplet of He. We have found that the Li atom is attracted or repulsed from the He surface, depending on the orientation of its 2p orbitals. The spectra and dynamics of Li inside and at the surface of a cluster are found to be strongly dependent on its electronic states, its velocity direction, and whether light is present during emission or not. PMID:18163688

Pacheco, Alexander B; Thorndyke, Brian; Reyes, Andrés; Micha, David A

2007-12-28

240

Chaos in Atomic Physics  

NASA Astrophysics Data System (ADS)

Preface; 1. Introduction; 2. Chaos: tools and concepts; 3. Chaos in classical mechanics; 4. Chaos in quantum mechanics; 5. The kicked rotor: paradigm of chaos; 6. Microwave-driven surface state electrons; 7. The hydrogen atom in a strong magnetic field; 8. The kicked hydrogen atom; 9. Chaotic scattering with CsI molecules; 10. The helium atom; 11. Chaos in atomic physics: state of the art and research directions; References; Index.

Blümel, R.; Reinhardt, W. P.

2005-08-01

241

Three-Body Recombination of {sup 6}Li Atoms with Large Negative Scattering Lengths  

SciTech Connect

The three-body recombination rate at threshold for distinguishable atoms with large negative pair scattering lengths is calculated in the zero-range approximation. The only parameters in this limit are the 3 scattering lengths and the Efimov parameter, which can be complex-valued. We provide semianalytic expressions for the cases of 2 or 3 equal scattering lengths, and we obtain numerical results for the general case of 3 different scattering lengths. Our general result is applied to the three lowest hyperfine states of {sup 6}Li atoms. Comparisons with recent experiments provide indications of loss features associated with Efimov trimers near the 3-atom threshold.

Braaten, Eric; Kang, Daekyoung; Platter, Lucas [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States); Hammer, H.-W. [Helmholtz-Institut fuer Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universitaet Bonn, 53115 Bonn (Germany)

2009-08-14

242

Correlation-enhanced phase-sensitive Raman scattering in atomic vapors  

NASA Astrophysics Data System (ADS)

We theoretically propose a method to enhance Raman scattering by injecting a seeded light field which is correlated with the initially prepared atomic spin wave. Such a light-atom correlation leads to an interference in the Raman scattering. The interference is sensitive to the relative phase between the seeded light field and initially prepared atomic spin wave. For constructive interference, the Raman scattering is greatly enhanced. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics, and optical metrology due to its simplicity.

Yuan, Chun-Hua; Chen, L. Q.; Ou, Z. Y.; Zhang, Weiping

2013-05-01

243

Three-body recombination of 6Li atoms with large negative scattering lengths.  

PubMed

The three-body recombination rate at threshold for distinguishable atoms with large negative pair scattering lengths is calculated in the zero-range approximation. The only parameters in this limit are the 3 scattering lengths and the Efimov parameter, which can be complex-valued. We provide semianalytic expressions for the cases of 2 or 3 equal scattering lengths, and we obtain numerical results for the general case of 3 different scattering lengths. Our general result is applied to the three lowest hyperfine states of 6Li atoms. Comparisons with recent experiments provide indications of loss features associated with Efimov trimers near the 3-atom threshold. PMID:19792641

Braaten, Eric; Hammer, H-W; Kang, Daekyoung; Platter, Lucas

2009-08-13

244

Three-Body Recombination of Li6 Atoms with Large Negative Scattering Lengths  

NASA Astrophysics Data System (ADS)

The three-body recombination rate at threshold for distinguishable atoms with large negative pair scattering lengths is calculated in the zero-range approximation. The only parameters in this limit are the 3 scattering lengths and the Efimov parameter, which can be complex-valued. We provide semianalytic expressions for the cases of 2 or 3 equal scattering lengths, and we obtain numerical results for the general case of 3 different scattering lengths. Our general result is applied to the three lowest hyperfine states of Li6 atoms. Comparisons with recent experiments provide indications of loss features associated with Efimov trimers near the 3-atom threshold.

Braaten, Eric; Hammer, H.-W.; Kang, Daekyoung; Platter, Lucas

2009-08-01

245

Coherent effects in the incoherent channel of resonant radiation scattering from excited atoms  

SciTech Connect

Scattering of a resonance electromagnetic field from excited atoms cannot be described by the semiclassical theory of radiation operating with nonquantized electromagnetic fields. Field quantization effects are manifested in this case on the macroscopic level and lead to evolution of statistical properties of radiation in the course of scattering. It is found that a combined process coupling elastic scattering from an atom and induced emission from the same atom, which cannot be studied by the methods of the standard perturbation theory, plays a significant role in this effect. The process of combined scattering in extended media exhibits coherent properties that cannot be described by the standard refractive index.

Veklenko, B. A., E-mail: veklenkoba@yandex.ru [Moscow Power Engineering Institute (Technical University) (Russian Federation)

2011-05-15

246

Light scattering from ultracold atomic gases in optical lattices at finite temperature  

SciTech Connect

We study light scattering from atoms in optical lattices at finite temperature. We examine the light scattered by fermions in the noninteracting regime and by bosons in the superfluid and Mott insulating regimes. We extend previous theoretical studies to include the full band structure of the optical lattice. We find that light scattering that excites atoms out of the lowest band leads to an increase in light scattering away from the classical diffraction peaks and is largely temperature independent. This additional light scattering leads to lower efficiency of temperature measurements based on photon counting.

Douglas, James S. [Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Burnett, Keith [University of Sheffield, Western Bank, Sheffield S10 2TN (United Kingdom)

2011-09-15

247

Effective-range corrections to three-body recombination for atoms with large scattering length  

NASA Astrophysics Data System (ADS)

Few-body systems with large scattering length a have universal properties that do not depend on the details of their interactions at short distances. The rate constant for three-body recombination of bosonic atoms of mass m into a shallow dimer scales as ?a4/m times a log-periodic function of the scattering length. We calculate the leading and subleading corrections to the rate constant, which are due to the effective range of the atoms, and study the correlation between the rate constant and the atom-dimer scattering length. Our results are applied to He4 atoms as a test case.

Hammer, H.-W.; Lähde, Timo A.; Platter, L.

2007-03-01

248

Semiclassical explanation of the generalized Ramsauer-Townsend minima in electron-atom scattering  

SciTech Connect

The generalized Ramsauer-Townsend minima which occur, at certain scattering angles, in the intensity of electrons elastically scattered by atoms have been a subject of interest in atomic physics for over sixty years. While quantum mechanical calculations predict these minima with great accuracy, no clear, simple, intuitively appealing description of the underlying scattering processes has been given. It is shown here for the first time that simple semiclassical calculations provide such a description.

Egelhoff, W.F. Jr. (National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States))

1993-11-01

249

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

250

Attosecond-resolved evolution of a laser-dressed helium atom: interfering excitation paths and quantum phases.  

PubMed

Using high-order harmonic attosecond pulse trains, we investigate the photoionization dynamics and transient electronic structure of a helium atom in the presence of moderately strong (?10(12)??W?cm(-2)) femtosecond laser pulses. We observe quantum interferences between photoexcitation paths from the ground state to different laser-dressed Floquet state components. As the intensity ramps on femtosecond time scales, we observe switching between ionization channels mediated by different atomic resonances. Using precision measurements of ion yields and photoelectron distributions, the quantum phase difference between interfering paths is extracted for each ionization channel and compared with simulations. Our results elucidate photoionization mechanisms in strong fields and open the doors for photoabsorption or photoionization control schemes. PMID:23003031

Shivaram, Niranjan; Timmers, Henry; Tong, Xiao-Min; Sandhu, Arvinder

2012-05-09

251

Calculations of D-wave bound states and resonance states of the screened helium atom using correlated exponential wave functions  

NASA Astrophysics Data System (ADS)

We have investigated the effects of screened Coulomb (Yukawa) potentials on the bound 1,3D states and the doubly excited 1,3 De resonance states of helium atom using highly correlated exponential basis functions. The Density of resonance states are calculated using stabilization method. Highly correlated exponential basis functions are used to consider the correlation effect between the charged particles. A total of 18 resonances (nine each for 1 De and 3 De states) below the n = 2 He + threshold has been calculated. For each spin states, this includes four members in the 2pnp series, three members in the 2snd series, and two members in 2pnf series. The resonance energies and widths for various screening parameters ranging from infinity to a small value for these 1,3 De resonance states are reported along with the bound-excited 1s3d 1,3 D state energies. Overall behavior of the spectral profile of 1s3d 1D state of helium atom due to electron-electron and electron-nucleus screening are also presented. Accurate resonance energies and widths are also reported for He in vacuum.

Kar, Sabyasachi; Ho, Y. K.

252

Elastic Scattering of Electrons by P Orbital - 3(2)(3\\/2) Sodium Atoms  

Microsoft Academic Search

An electron and photon atomic-recoil technique has been used to study collisions of electrons by laser -excited sodium atoms in the 3^2 P_ {3\\/2},F = 3 state. The experiment was performed in a crossed-beam apparatus in which observation of the scattering is made on the recoiled atom, rather than on the scattered electron. In contrast to the conventional crossed-beam technique,

Ming Zuo

1989-01-01

253

Chaotic scattering from hydrogen atoms in a circularly polarized laser field  

NASA Astrophysics Data System (ADS)

We investigate the classical dynamics of a hydrogen atom in a circularly polarized laser beam with finite radius. The spatial cutoff for the laser field allows us to use scattering processes to examine the laser-atom dynamics. We find that for certain field parameters, the delay times, the angular momentum, and the distance of closest approach of the scattered electron exhibit fractal behavior. This fractal behavior is a signature of chaos in the dynamics of the atom-field system.

Okon, Elias; Parker, William; Chism, Will; Reichl, Linda E.

2002-11-01

254

Absorption and emission of radiation during electron excitation of the 2 1S and 2 1P states of helium  

Microsoft Academic Search

We are reporting electron spectra resulting from the inelastic scattering of 45-eV electrons from helium atoms through a scattering angle of 12° in the presence of an intense carbon dioxide laser. The spectra presented are in the region of the 2 1S and 2 1P states of helium. These data show additional structure when the laser is present at scattered

B. Wallbank; J. K. Holmes; A. Weingartshofer

1989-01-01

255

Measurement of angular distribution of incoherently scattered gamma rays from atoms  

Microsoft Academic Search

There has been comparatively little experimental investigation on the whole-atom incoherent scattering of photons in the x-ray and gamma-ray regions. A rigorous theoretical treatment of this type of scattering has not yet yielded enough results and the incoherent scattering function approach is taken to calculate the incoherent scattering cross section. Recently, Cromer and Mann calculated using SCF Hartree-Fock wave functions

B. Sinha; N. Chaudhuri

1977-01-01

256

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

257

Exact quantum scattering calculations of transport properties: CH2(X~3B1, a~1A1)-helium  

NASA Astrophysics Data System (ADS)

Transport properties for collisions of methylene, in both its ground X~3B1 and low-lying a~1A1 electronic states, with helium have been computed using recently computed high-quality ab initio potential energy surfaces (PESs). Because of the difference in the orbital occupancy of the two electronic states, the anisotropies of the PESs are quite different. The CH2(a~)-He PES is very anisotropic because of the strong interaction of the electrons on the helium atom with the unoccupied CH2 orbital perpendicular to the molecular plane, while the anisotropy of the CH2(X~)-He PES is significantly less since this orbital is singly occupied in this case. To investigate the importance of the anisotropy on the transport properties, calculations were performed with the full potential and with the spherical average of the potential for both electronic states. Significant differences (over 20% for the a~ state at the highest temperatures considered) in the computed transport properties were found.

Dagdigian, Paul J.; Alexander, Millard H.

2013-04-01

258

Exact quantum scattering calculations of transport properties: CH2(X?3B1, a?1A1)-helium.  

PubMed

Transport properties for collisions of methylene, in both its ground X?(3)B1 and low-lying a?(1)A1 electronic states, with helium have been computed using recently computed high-quality ab initio potential energy surfaces (PESs). Because of the difference in the orbital occupancy of the two electronic states, the anisotropies of the PESs are quite different. The CH2(a?)-He PES is very anisotropic because of the strong interaction of the electrons on the helium atom with the unoccupied CH2 orbital perpendicular to the molecular plane, while the anisotropy of the CH2(X?)-He PES is significantly less since this orbital is singly occupied in this case. To investigate the importance of the anisotropy on the transport properties, calculations were performed with the full potential and with the spherical average of the potential for both electronic states. Significant differences (over 20% for the a? state at the highest temperatures considered) in the computed transport properties were found. PMID:23635136

Dagdigian, Paul J; Alexander, Millard H

2013-04-28

259

Total scattering cross sections and interatomic potentials for neutral hydrogen and helium on some noble gases  

SciTech Connect

Measurements of energy-dependent scattering cross sections for 30 to 1800 eV D incident on He, Ne, Ar, and Kr, and for 40 to 850 eV He incident on He, Ar, and Kr are presented. They are determined by using the charge-exchange efflux from the Princeton Large Torus tokamak as a source of D or He. These neutrals are passed through a gas-filled scattering cell and detected by a time-of-flight spectrometer. The cross section for scattering greater than the effective angle of the apparatus (approx. =20 mrad) is found by measuring the energy-dependent attenuation of D or He as a function of pressure in the scattering cell. The interatomic potential is extracted from the data.

Ruzic, D.N.; Cohen, S.A.

1985-04-01

260

Coherent control calculations for helium atom in short and intensive XUV laser pulses  

Microsoft Academic Search

Coherent control calculations are presented for helium. With the help of a genetic algorithm (GA) phase-modulated extreme ultra violet (XUV) laser pulses were controlled to maximize or minimize the non-resonant two-photon 1s1s --> 1s3s excitation. Linearly polarized laser pulses were chosen at the frequency of 0.4 a.u. with a duration of about 15 fs and 1014 Wcm-2 peak intensity. We

I. F. Barna

2005-01-01

261

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

262

On the Calculation of Total Electron Inelastic Scattering Cross Sections for Neutral Atoms in the KeV Energy Range.  

National Technical Information Service (NTIS)

The total inelastic cross sections for electron scattering from neutral atoms are calculated by integrating the Morse inelastic intensity over all scattering angles using the Waller-Hartree values of the inelastic scattering factors given by Tavard. (Auth...

R. A. Bonham E. W. Ng

1969-01-01

263

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

264

Partial Atomic and Ionic Stopping Powers of Gaseous Hydrogen for Helium and Hydrogen Beams  

Microsoft Academic Search

The partial stopping power of a target material for an ion or an atom is the energy lost per target particle per cm2 in all types of collisions in which the ion or the atom is the projectile, with the exception of those collisions in which the projectile leaves with its charge changed. Partial atomic stopping powers of target gases

J. Cuevas; M. Garcia-Munoz; P. Torres; S. K. Allison

1964-01-01

265

Three-body Recombination of Fermionic Atoms with Large Scattering Lengths  

NASA Astrophysics Data System (ADS)

The 3-body recombination rate at threshold for fermions with three spin states and large scattering lengths is calculated in the zero-range approximation. The only parameters in this limit are the three scattering lengths and the Efimov parameter, which can be complex valued. Semi-analytic results are obtained for the cases of negative scattering lengths, two of which are equal. The general result is applied to the three lowest hyperfine states of Lithium-6 atoms in regions of the magnetic field in which the three scattering lengths are all large and negative. Comparisons with recent experiments provide indications of loss features associated with Efimov trimers near the 3-atom threshold.

Kang, Daekyoung; Braaten, Eric; Hammer, Hans-Werner; Platter, Lucas

2009-05-01

266

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

267

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

268

Coherent control calculations for helium atom in short and intensive XUV laser pulses  

Microsoft Academic Search

Coherent control calculations are presented for helium.\\u000aWith the help of a genetic algorithm (GA) phase-modulated extreme\\u000aultra violet (XUV) laser pulses were controlled to \\u000amaximize or minimize the non-resonant two-photon 1s1s ?\\u000a1s3s excitation.\\u000aLinearly polarized laser pulses were chosen at the frequency of 0.4 a.u.\\u000awith a duration of about 15 fs and 1014 Wcm-2 peak intensity.\\u000aWe verified the theory

I. F. Barna

2005-01-01

269

Differential Elastic Scattering Cross Sections for 54.9EV Positrons Incident on Helium.  

National Technical Information Service (NTIS)

Absolute differential elastic scattering cross sections measured with the 3-m, high resolution, time-of-flight spectrometer are presented for 54.9eV positrons incident on He. Five point moving average differential cross sections are plotted against averag...

R. L. Chaplin L. M. Diana D. L. Brooks

1990-01-01

270

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

271

Energy-dependent photoelectron angular distributions of two-color two-photon above threshold ionization of atomic helium  

SciTech Connect

Energy-dependent photoelectron angular distributions from two-color two-photon above threshold ionizations are investigated to determine the partial-wave characteristics of free-free electronic transitions in helium. Sideband photoelectron energies ranging from 0.18 to 13.0 eV are measured with different wavelengths of the perturbative infrared dressing field as well as different individually selected high-order harmonics. Using the experimentally measured cross-section ratios and anisotropy parameters together with analytical expressions derived from second-order perturbation theory, the partial-wave branching fractions going to the S and D waves in the positive and negative sidebands are determined as a function of photoelectron kinetic energy. The results provide a sensitive test for theoretical models of two-color two-photon above threshold ionization in atoms and molecules.

Haber, Louis H.; Doughty, Benjamin; Leone, Stephen R. [Departments of Chemistry and Physics, and Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)

2011-07-15

272

Raman scattering of atoms from a quasicondensate in a perturbative regime  

NASA Astrophysics Data System (ADS)

Using the perturbative approach, it is demonstrated that the widths of the density and second-order correlation function of atoms scattered from a quasicondensate in a Raman process are sensitive to the phase fluctuations induced by the nonzero temperature of the mother cloud. It is also shown how these widths evolve during expansion of the halo of scattered atoms. It is also argued that if the Raman scattering is preceded by expansion of the mother cloud, the density of atoms widens substantially, while the second-order correlation function remains practically unchanged. These results are useful for planning future Raman scattering experiments and indicate the degree of spatial resolution of atom-position measurements necessary to detect the temperature dependence of the quasicondensate. All the calculations are performed using experimental parameters of a metastable 4He* quasicondensate of the Palaiseau group.

Wasak, T.; Chwede?czuk, J.; Zi?, P.; Trippenbach, M.

2012-10-01

273

X-ray atomic scattering factors of low-Z ions with a core hole  

SciTech Connect

Short and intense x-ray pulses may be used for atomic-resolution diffraction imaging of single biological molecules. One of the dominant damage mechanisms is atomic ionization, resulting in a large fraction of atoms with core holes. We calculated the atomic scattering factor of atoms with atomic charge numbers between 3 and 10 in different ionization states with and without a core hole. Our results show that orbital occupation and the change of the orbitals upon core ionization (core relaxation) have a significant impact on the diffraction pattern.

Hau-Riege, Stefan P. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)

2007-10-15

274

Atom interferometric studies of light scattering - A new technique for measuring atomic recoil  

NASA Astrophysics Data System (ADS)

This dissertation presents two techniques for measuring the atomic recoil frequency, oq, using a single-state atom interferometer that utilizes a dilute cloud of laser-cooled 85Rb atoms. An important motivation for these measurements is that o q, which is related to the ratio of Planck's constant and the atomic mass of rubidium hmRb , can be used to infer the atomic fine structure constant, alpha. The two techniques presented here involve time domain measurements carried out with standing-wave laser fields that manipulate atoms in the same atomic ground state and exploit the wave nature of cold atoms. The first technique uses two off-resonant standing-wave pulses to interfere momentum states so that the recoil frequency can be determined. However, to model the signal shape it is necessary to include effects of spontaneous emission during the interaction with light and the spatial profile of the laser beam. The second technique provides a robust alternative approach for measuring the recoil frequency because the signal shape is considerably simpler and can be modeled easily. We report measurements of atomic recoil using both techniques that are precise to ˜ 1 part per million. The precision was limited mainly by the time scale of the experiment (˜ 20 ms) due to the presence of magnetic field gradients. The dissertation also discusses recent improvements that have extended the time scale to the transit time limit for cold atoms. This is the time of travel of cold atoms through the region of interaction defined by the laser beams. The interferometer uses two standing-wave pulses separated by time T to put the atoms in a superposition of momentum states. Interference between momentum states produce a density grating echo signal at time 2 T. The echo time, 2T, corresponds to the time at which the Doppler phases of the momentum states associated with all atoms in the sample cancel. The echo technique is, therefore, a general method to overcome the effect of the velocity distribution of the sample. The amplitude of the echo signal is related to the contrast of the density grating and is periodic in T. The first technique exploits this dependence to measure oq. To carry out the measurement of oq using the first technique, it is necessary to understand the effects of spontaneous emission and the spatial profile of the laser beam. We find that spontaneous emission influences both the shape of the echo signal and its periodic T dependent amplitude in a manner consistent with theoretical predictions. The results show that the T dependent signal is related to the effective radiative decay rate of the excited state. We also present results that test theoretical predictions for several properties of the echo formation, such as the variation in momentum transfer due to the change in the angle between the traveling-wave components of the excitation pulses, strength of the atom-field interaction, and the effect of spatial profile of the excitation beams. We have also demonstrated a considerable improvement in the signal-to-noise ratio of the echo signal by using intensity detection with a photomultiplier tube in place of heterodyne detection. We have also used this interferometer to investigate the effect of light scattering due to an additional standing wave pulse applied at t = 2T -- deltaT. In this case, the grating contrast can be fully recovered if deltaT is an integral multiple of the recoil period Tr = pi/o q. Measuring the revival in contrast over the time scale of the experiment has resulted in the development of the second technique to measure oq. The contrast is accurately described by a coherence function which is the Fourier transform of the momentum distribution produced by the additional standing wave pulse. The effects of spontaneous emission and spatial profile of the laser beam are only to modify the Fourier coefficients used to fit the data and, therefore, no prior knowledge of these parameters is required, ensuring that the technique is both simple and robust. We also show that coherence functions can be used to make

Beattie, Scott

275

Confined quantum systems: a comparison of the spectral properties of the two-electron quantum dot, the negative hydrogen ion and the helium atom  

Microsoft Academic Search

The spectrum, the electron density distribution and the character of three two-electron quantum systems, namely the two-electron quantum dot, the negative hydrogen ion and the helium atom, confined by an anisotropic harmonic oscillator potential, have been studied for different confinement strengths, omega, by using the quantum chemical configuration interaction (CI) method employing a Cartesian anisotropic Gaussian basis set supplemented by

T. Sako; G. H. F. Diercksen

2003-01-01

276

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

277

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

NASA Astrophysics Data System (ADS)

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.; Nadolinsky, A. M.; Ikoeva, K. Kh.; Khoroshavina, O. A.

2011-11-01

278

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

279

Surface phonon dispersion curves via thermal energy atom scattering: He atoms on RbCl(001) surface  

SciTech Connect

A thermal energy atom scattering instrument, employing a time-of-flight technique to observe inelastically scattered He atoms, has been used to measure the surface phonon dispersion curves of the RbCl(001) surface. Data were collected over the entire Brillouin zone for a target temperature of 115 K and incident He wave vector of k/sub i/ approx. =7 A/sup -1/. The results for the <100> and <110> high-symmetry directions are in good agreement with theoretical predictions based on a slab dynamics model calculation. Relaxation effects of the surface are negligible for this crystal.

Chern, G.; Brug, W.P.; Safron, S.A.; Skofronick, J.G.

1989-05-01

280

HIPPO: A supersonic helium jet gas target for nuclear astrophysics  

NASA Astrophysics Data System (ADS)

A high density supersonic helium jet gas target has been developed for the newly installed St. George Recoil Mass Separator, at the Nuclear Science Laboratory, University of Notre Dame. The jet's properties for both helium and nitrogen have been studied by means of elastic scattering and energy loss experiments. The helium jet's full width at half maximum was found to be 2.1 mm, assuming axially symmetric gas expansion with a maximum target thickness of (2.67±0.16)×1017 atoms/cm2 at 1500 mbar of inlet pressure, and well confined within the jet region.

Kontos, Antonios; Schürmann, Daniel; Akers, Charles; Couder, Manoel; Görres, Joachim; Robertson, Daniel; Stech, Ed; Talwar, Rashi; Wiescher, Michael

2012-02-01

281

Positronium scattering from closed-shell atoms and ions  

NASA Astrophysics Data System (ADS)

The scattering of orthopositronium from He, Ne, Ar, Li+, Na+, and K+ is investigated with the fixed-core stochastic variational method. The scattering length for Ps-He scattering was 1.57a0, a value consistent with the threshold cross sections derived from three positron lifetime experiments. The scattering lengths for the Ps-Ne and Ps-Ar systems were 1.55a0 and 1.79a0, respectively. That there was only a 15% variation among the scattering lengths is compatible with the experiment of Coleman et al. [J. Phys. B 27, 981 (1994)], who found the low-energy cross sections for He, Ne, and Ar to be about the same size. The scattering lengths for Ps scattering from Li+, Na+, and K+ were 12.9a0, 28.5a0, and -1.9a0. The relatively small magnitude of the Ps-K+ scattering length strongly supports previous suggestions that the Ps-K+ system does not support a bound state. The annihilation parameter 1Zeff has also been computed as part of the analysis. The present values of 1Zeff are about 2.5-3 times smaller than the accepted experimental values since short-range electron-positron correlations were not taken into consideration when the annihilation matrix element was evaluated.

Mitroy, J.; Ivanov, I. A.

2002-01-01

282

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

Microsoft Academic Search

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

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

1995-01-01

283

SCATTERING OF MEDIUM-FAST ELECTRONS ON PLASTICS WITH EMBEDDED HEAVY METAL ATOMS  

Microsoft Academic Search

Scattering was observed of 70-kev electrons by Collodium foils ; containing elements of high atomic number (lead). The contents of lead are ; determined and the kind of distribution of lead in the foil is described. The ; differential cross section as a fanction of the angle of scattering approximates ; the cross section calculated by Sherman with lower contents

1962-01-01

284

Three-Body Recombination of Li Atoms with Large Negative Scattering Lengths  

Microsoft Academic Search

The three-body recombination rate at threshold for distinguishable atoms with large negative pair scattering lengths is calculated in the zero-range approximation. The only parameters in this limit are the 3 scattering lengths and the Efimov parameter, which can be complex-valued. We provide semianalytic expressions for the cases of 2 or 3 equal scattering lengths, and we obtain numerical results for

Eric Braaten; Daekyoung Kang; Lucas Platter; H.-W. Hammer

2009-01-01

285

Three-Body Recombination of Li6 Atoms with Large Negative Scattering Lengths  

Microsoft Academic Search

The three-body recombination rate at threshold for distinguishable atoms with large negative pair scattering lengths is calculated in the zero-range approximation. The only parameters in this limit are the 3 scattering lengths and the Efimov parameter, which can be complex-valued. We provide semianalytic expressions for the cases of 2 or 3 equal scattering lengths, and we obtain numerical results for

Eric Braaten; H.-W. Hammer; Daekyoung Kang; Lucas Platter

2009-01-01

286

Complete Breakup of the Helium Atom by Proton and Antiproton Impact  

SciTech Connect

We present a fully ab initio, nonperturbative, time-dependent approach to describe single and double ionization of helium by proton and antiproton impact. The problem is discretized by a flexible finite-element discrete-variable representation on the radial grid. Good agreement with the most recent experimental data for absolute angle-integrated cross sections is obtained for projectile energies between 3 keV and 6 MeV. Also, angle-differential cross sections for two-electron ejection are predicted for a proton impact energy of 6 MeV. The time evaluation of the ionization process is portrayed by displaying the electron density as a function of the projectile location.

Guan Xiaoxu; Bartschat, Klaus [Department of Physics and Astronomy, Drake University, Des Moines, Iowa 50311 (United States)

2009-11-20

287

Wave functions and two-electron probability distributions of the Hooke's-law atom and helium  

Microsoft Academic Search

The Hooke's-law atom (hookium) provides an exactly soluble model for a two-electron atom in which the nuclear-electron Coulombic attraction has been replaced by a harmonic one. Starting from the known exact position-space wave function for the ground state of hookium, we present the momentum-space wave function. We also look at the intracules, two-electron probability distributions, for hookium in position, momentum,

Darragh P. ONeill; Peter M. W. Gill

2003-01-01

288

Experimental-theoretical comparisons of 11S-->31P differential magnetic sublevel cross sections for electron-helium scattering at 80 and 100 eV  

Microsoft Academic Search

Experimental normalized absolute differential cross sections (DCS) for the excitation 11S to 31P in helium are reported at incident electron energies of 80 and 100 eV, and at scattering angles between 7 degrees and 135 degrees . The measurements are combined with results of recent electron-photon coincidence studies, and absolute DCS for the excitation of the magnetic sublevels 31P0 and

A. Chutjian

1976-01-01

289

Measurement of the surface dynamics of RbCl(001) via high resolution He atom scattering  

SciTech Connect

High resolution He atom scattering experiments have been carried out on the cleaved RbCl(001) surface in the [l angle]100[r angle] direction. For most of the experiments reported here the incident He atom wave vector [ital k][sub [ital i

Bishop, G.G.; Duan, J.; Gillman, E.S.; Safron, S.A.; Skofronick, J.G. (Departments of Physics and Chemistry and the Materials Research and Technology Center, The Florida State University, Tallahassee, Florida 32306 (United States))

1993-07-01

290

Positive effect of scattering strength of a microtoroidal cavity on atomic entanglement evolution  

Microsoft Academic Search

We show that the rough surface of a microtoroidal cavity (scattering strength) can play a constructive role by studying the entanglement of two atoms surrounding the cavity. Analytical results show that appropriate surface roughness can enhance the atomic entanglement. In particular, the rough surface can also compensate for the loss of maximal entanglement during the evolution caused by cavity leakage

Jin Jiasen; Yu Changshui; Pei Pei; Song Heshan

2010-01-01

291

Coverage-dependent quantum versus classical scattering of thermal neon atoms from Li/Cu(100)  

NASA Astrophysics Data System (ADS)

We show that subtle variations in surface structure can enhance quantum scattering and quench atom-surface energy transfer. The scattering of thermal energy neon atoms from a lithium overlayer on a copper substrate switches between a classical regime, dominated by multiphonon interactions, and a quantum regime, dominated by elastic diffraction. The transition is achieved by simple tailoring of the lithium coverage and quantum scattering dominates only in the narrow coverage range of ?=0.3-0.6 ML. The results are described qualitatively using a modified Debye-Waller model that incorporates an approximate quantum treatment of the adsorbate-substrate vibration.

MacLaren, D. A.; Huang, C.; Levi, A. C.; Allison, W.

2008-09-01

292

EUV resonance radiation from helium atoms and ions in the geocorona  

Microsoft Academic Search

We computed the emission of He 584-A and He + 304-A radiation from the geocorona, assuming resonance scattering of solar radiation. Comparison of these calculations with recent rocket experiments shows that (o,) the Jacchia 1970 He model gives the observed variation of 584 A with altitude and solar zenith angle, but large discrepancies are evident in the absolute value of

R. R. Meier; C. S. Weller

1972-01-01

293

Spin-dependent deep inelastic positron scattering from a polarized helium-3 internal gas target  

NASA Astrophysics Data System (ADS)

This thesis presents the first results from the HERMES experiment, using the data taken in 1995. In this year the HERMES experiment was successfully commissioned and data were taken on the deep inelastic scattering asymmetry of positrons from polarized 3He. The author's main involvement was with the design and construction of the metastability exchange optically pumped 3He gas target and the analysis of the inclusive as well as the semi-inclusive asymmetries. The thesis is divided into five chapters. The first chapter presents an overview of the physics goals pursued by the HERMES experiment. In the second chapter the HERA accelerator facility and the HERMES detector are described. The third chapter goes into the details of the target construction and operation. The fourth chapter explains particular aspects of the analysis of the data, especially the data quality criteria. In the last chapter the results of the analysis of the inclusive scattering data are presented. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

de Schepper, Dirk

294

Comparison of the electron density measurements using Thomson scattering and emission spectroscopy for laser induced breakdown in one atmosphere of helium  

SciTech Connect

Thomson scattering from laser-induced plasma in atmospheric helium was used to obtain temporally and spatially resolved electron temperature and density profiles. Electron density measurements at 5 {mu}s after breakdown are compared with those derived from the separation of the allowed and forbidden components of the 447.1 nm He I line. Plasma is created using 9 ns, 140 mJ pulses from Nd:YAG laser at 1064 nm. Electron densities of {approx}5 x 10{sup 16 }cm{sup -3} are in good agreement with Thomson scattering measurements, benchmarking this emission line as a useful diagnostic for high density plasmas.

Nedanovska, E.; Nersisyan, G.; Lewis, C. L. S.; Riley, D.; Graham, W. G. [Department of Physics and Astronomy, Centre for Plasma Physics, Queen's University Belfast, BT71NN (United Kingdom); Morgan, T. J.; Huewel, L. [Department of Physics, Wesleyan University, Middletown, Connecticut 06459 (United States)

2011-12-26

295

Interaction potentials for fast atoms in front of Al surfaces probed by rainbow scattering  

NASA Astrophysics Data System (ADS)

Rainbow scattering for grazing-angle incidence of atoms at surfaces along low-indexed channeling directions provides a sensitive probe of quasistatic atom-surface potentials. The dependence of the rainbow angle on the kinetic energy for the projectile motion perpendicular to the surface, E? , varies with the electronic structure of the projectile as well as the crystallographic face of the aluminum surface. Comparison between experiment and classical Monte Carlo trajectory simulations demonstrates that the superposition of binary atom-atom potentials fails to adequately represent the equipotential surfaces. Ab initio atom-surface potentials based on density-functional theory are required to reach satisfactory agreement with experiment.

Tiwald, P.; Schüller, A.; Winter, H.; Tökesi, K.; Aigner, F.; Gräfe, S.; Lemell, C.; Burgdörfer, J.

2010-09-01

296

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

297

Comparison of Electron Elastic-Scattering Cross Sections Calculated from Two Commonly Used Atomic Potentials  

Microsoft Academic Search

We have analyzed differential cross sections (DCSs) for the elastic scattering of electrons by neutral atoms that have been derived from two commonly used atomic potentials: the Thomas–Fermi–Dirac (TFD) potential and the Dirac–Hartree–Fock (DHF) potential. DCSs from the latter potential are believed to be more accurate. We compared DCSs for six atoms (H, Al, Ni, Ag, Au, and Cm) at

A. Jablonski; F. Salvat; C. J. Powell

2004-01-01

298

Calculation of Charge Exchange in Potassium Ions/atoms Scattered from Metal Surfaces  

NASA Astrophysics Data System (ADS)

The charge-exchange processes of K ions/atoms scattered from metal surface are discussed in terms of the time-dependent Newns-Anderson quantum model with intra-atomic Coulomb interaction. The final charge-states distribution is calculated as a function of work function of the surfaces. The calculated results are compared with the experimental data. Furthermore, the probabilities of charge states of the moving K ions/atoms approaching to and leaving from the surface are demonstrated.

Pan, Limin; Wang, Yansen; Huang, Fayang; Tang, Jiayong; Yang, Fujia

299

Interatomic potentials from rainbow scattering of keV noble gas atoms under axial surface channeling  

NASA Astrophysics Data System (ADS)

For grazing scattering of keV Ne and Ar atoms from a Ag(1 1 1) and a Cu(1 1 1) surface under axial surface channeling conditions we observe well defined peaks in the angular distributions for scattered projectiles. These peaks can be attributed to “rainbow-scattering” and are closely related to the geometry of potential energy surfaces which can be approximated by the superposition of continuum potentials along strings of atoms in the surface plane. The dependence of rainbow angles on the scattering geometry provides stringent tests on the scattering potentials. From classical trajectory calculations based on universal (ZBL), adjusted Moliere (O’Connor and Biersack), and individual interatomic potentials we obtain corresponding rainbow angles for comparison with the experimental data. We find good overall agreement with the experiments for a description of trajectories based on adjusted Moliere and individual potentials, whereas the agreement is poorer for potentials with ZBL screening.

Schüller, A.; Wethekam, S.; Mertens, A.; Maass, K.; Winter, H.; Gärtner, K.

2005-04-01

300

Quasiparticles in Raman scattering of an electromagnetic wave by an atomic condensate  

SciTech Connect

Raman scattering of an intense electromagnetic wave by a free atomic Bose condensate is considered. In a system of atoms and photons, a subsystem is separated whose dynamics can be naturally described in terms of quasiparticles: quasi-atoms and quasi-photons. The dispersion laws of quasiparticles are interrupted by the instability interval. The introduction of quasiparticles within this interval is impossible, while dispersion laws that are continued formally acquire imaginary components. The dynamic scattering model is generalized by including dissipative annihilation processes of scattered photons and uncondensed atoms. A stationary solution of the corresponding quantum control equation is found, allowing the calculation of momentum distributions of real particles and quasiparticles. The outlook for the experimental detection of quasiparticles is discussed.

Il'ichev, L. V., E-mail: leonid@iae.nsk.su [Novosibirsk State University (Russian Federation)

2011-02-15

301

Effective-range corrections to three-body recombination for atoms with large scattering length  

SciTech Connect

Few-body systems with large scattering length a have universal properties that do not depend on the details of their interactions at short distances. The rate constant for three-body recombination of bosonic atoms of mass m into a shallow dimer scales as ({Dirac_h}/2{pi})a{sup 4}/m times a log-periodic function of the scattering length. We calculate the leading and subleading corrections to the rate constant, which are due to the effective range of the atoms, and study the correlation between the rate constant and the atom-dimer scattering length. Our results are applied to {sup 4}He atoms as a test case.

Hammer, H.-W.; Laehde, Timo A.; Platter, L. [Helmholtz-Institut fuer Strahlen- und Kernphysik (Theorie), Universitaet Bonn, 53115 Bonn (Germany); Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States); Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States)

2007-03-15

302

Multiple scattering of light in cold atomic clouds in a magnetic field  

NASA Astrophysics Data System (ADS)

Starting from a microscopic theory for atomic scatterers, we describe the scattering of light by a single atom and study the coherent propagation of light in a cold atomic cloud in the presence of a magnetic field B in the mesoscopic regime. Nonpertubative expressions in B are given for the magneto-optical effects and optical anisotropy. We then consider the multiple-scattering regime and address the fate of the coherent-backscattering (CBS) effect. We show that, for atoms with nonzero spin in their ground state, the CBS interference contrast can be increased compared to its value when B=0, a result at variance with classical samples. We validate our theoretical results by a quantitative comparison with experimental data.

Sigwarth, Olivier; Labeyrie, Guillaume; Delande, Dominique; Miniatura, Christian

2013-09-01

303

The electron-pair density of atomic systems. Rigorous bounds and application to helium  

Microsoft Academic Search

Firstly, the monotonicity properties of the electron-pair densityI(u) of atomic systems are investigated. Leth(u) denote the spherically-averaged electron-pair density of an arbitraryN-electron system, which essentially coincides withI(u) in the case of atoms. It is found that the interelectronic functiong?(u)=h(u)\\/u?, ??0, is not only monotonically decreasing from the origin for ???1=max{uh?(u)\\/h(u)} but it also has the property of convexity for ???2,

J. S. Dehesa; J. C. Angulo; Toshikatsu Koga

1992-01-01

304

Elastic light scattering by the atoms of a Bose gas confined in a parabolic trap  

SciTech Connect

It is shown that the emergence of a condensate fraction in a gas confined in a trap leads to a sharp increase in the intensity of elastic scattering (scattering not accompanied by a change in the quantum numbers describing the motion of gas atoms in the trap) of light. Under typical experimental conditions, this intensity may be thousands of times greater than the intensity of inelastic scattering, which is hardly affected by the condensate. The angular distribution of elastic scattering of light allows one to determine the size of the condensate, and its intensity makes it possible to determine the number of particles trapped in the condensate.

Alekseev, V. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)], E-mail: valeks@sci.lebedev.ru

2008-09-15

305

Multimode entanglement of light and atomic ensembles via off-resonant coherent forward scattering  

SciTech Connect

Quantum theoretical treatment of coherent forward scattering of light in a polarized atomic ensemble with an arbitrary angular momentum is developed. We consider coherent forward scattering of a weak radiation field interacting with a realistic multilevel atomic transition. Based on the concept of an effective Hamiltonian and on the Heisenberg formalism, we discuss the coupled dynamics of the quantum fluctuations of the polarization Stokes components of propagating light and of the collective spin fluctuations of the scattering atoms. We show that in the process of coherent forward scattering, this dynamics can be described in terms of a polariton-type spin wave created in the atomic sample. Our work presents a general example of an entangling process in the system of collective quantum states of light and atomic angular momenta, previously considered only for the case of spin-(1/2) atoms. We use the developed general formalism to test the applicability of the spin-(1/2) approximation for modeling the quantum nondemolishing measurement of atoms with a higher angular momentum.

Kupriyanov, D.V.; Mishina, O.S.; Sokolov, I.M.; Julsgaard, B.; Polzik, E.S. [Department of Theoretical Physics, State Polytechnic University, 195251 St. Petersburg (Russian Federation); QUANTOP-Danish Quantum Optics Center, Niels Bohr Institute, 2100 Copenhagen (Denmark)

2005-03-01

306

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

307

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

308

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

309

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

310

Proton Scattering from Polarized HELIUM-3 in the Energy Range from 20 TO 35 Mev.  

NASA Astrophysics Data System (ADS)

The ('3)He analyzing powers have been measured at the forward angles ((LESSTHEQ) 100(DEGREES)) and at energies of 25, 30, 32.5, and 35 MeV. A polarized ('3)He target has been built using optical pumping with ('4)He -discharge lamps. An improved version of the equations describing the balance between polarizing and depolarizing processes was developed. Polarization through excitation of alternative transitions is discussed. Among the depolarizing processes, especially the reabsorption of pumping light is considered. The experience with the polarized target in nuclear scattering experiments is described. Single energy phase shift analyses have been made using the available precise data at seven energies between 19.5 and 35 MeV. Real phases up to L = 4, imaginary phases up to L = 3, and coupling between channels with J = 1 and 2 were allowed in the analysis. Singlet and triplet waves of the same angular momentum have considerable mixing, which reaches a maximum at 31 and 28 MeV for channels with respectively J('(pi)) = 1('-) and 2('+). Mixing angles for tensor coupling were always found to be close to zero. Several ambiguities in previous phase shift analyses are clarified. Also, the real phases have a smoother energy dependence than was found before. No significant excursions in the imaginary phases could be detected.

Verheijen, Peter Joannes Theodorus

311

Multiphonon scattering of thermal energy He atoms from the LiF(001) surface  

SciTech Connect

Results from the scattering of nearly monoenergetic ([Delta][ital E]/[ital E][approx]2%) thermal energy He atoms from the LiF(001) surface are presented and discussed with particular emphasis on multiphonon interactions. These experiments represent the next step in a series of experiments exploring the multiphonon scattering of He from alkali halides in that previous work [G. G. Bishop [ital et] [ital al]., Phys. Rev. B [bold 47], 3966 (1993)] has now been extended to include nonspecular angles. The LiF surface was prepared as in the previous experiments by cleaving the crystal in air and cleaning it by sublimation in the ultrahigh vacuum system. The measurements consist of time-of-flight spectra of the scattered He atoms taken for a number of incident angles as a function of the surface temperature ranging from 290 to 720 K and for He incident wave vectors ranging from 7 to 11 A[sup [minus]1]. Analysis of the data was carried out using a theoretical model developed by Manson [Phys. Rev. B [bold 43], 6924 (1991)], which allows the determination of the interaction potential between the incident atoms and the LiF surface by isolating the scattering form factor. The good representation of the multiphonon scattering found from the model allows this background to be subtracted from the time-of-flight spectra to enhance the single-phonon He atom scattering signal, which in turn permits improved surface phonon dispersion measurements and interpretation.

Bishop, G.G.; Gillman, E.S.; Hernandez, J.J.; Baker, J.; Skofronick, J.G.; Safron, S.A. (Department of Physics, Department of Chemistry, and Center for Materials Research and Technology, Florida State University, Tallahassee, Florida 32306 (United States))

1994-07-01

312

Atomic scattering factors for K-shell and L-shell ionization by fast electrons  

PubMed

Atomic scattering factors have been calculated for K-shell ionization for elements in the range Z = 6 (carbon) to Z = 50 (tin) and for L-shell ionization in the range Z = 20 (calcium) to Z = 60 (neodymium). The calculations are based on relativistic Hartree-Fock wave functions for the atomic bound states and Hartree-Slater wave functions for the continuum wave functions. The results are presented in tabular form such that accurate values of the scattering factors can be obtained by cubic spline interpolation for incident electron energies between 50 and 400 keV and for scattering vectors with magnitude s = sin straight theta / lambda up to 2.5 A(-1) (2straight theta is the scattering angle and lambda the wavelength of the incident electrons). A separate parameterization of the form factors is given for 2.5 atomic scattering factors in an exponential form has been obtained by fitting the calculated form factors in the region s scattering factors are suitable for the calculation of ionization cross sections for use in atom location by channelling-enhanced microanalysis (ALCHEMI). PMID:10967525

Oxley; Allen

2000-09-01

313

Deactivation of xenon atoms in the 6s resonant state in collisions with xenon and helium atoms  

SciTech Connect

The absorption probing method was used to investigate collisional deactivation of the 6s[3/2]{sub 1}{sup 0}({sup 3}P{sub 1}) state of the xenon atom in high-pressure He - Xe mixtures with a low xenon concentration. Measurements were made of the rate constants of the following plasma-chemical reactions: Xe* + Xe + He {yields} Xe{sub 2}* + He [(2.1 {+-} 0.2) x 10{sup -32} cm{sup 6}s{sup -1}], Xe* + 2He {yields} HeXe* + He (less than 10{sup -35} cm{sup 6}s{sup -1}), and Xe* + He {yields} products + He (less than 3 x 10{sup -15} cm{sup 3}s{sup -1}). (active media)

Zayarnyi, D A; Semenova, Ludmila V; Ustinovskii, N N; Kholin, I V; Chugunov, A Yu [P.N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

1999-02-28

314

Deactivation of the xenon atom in the 6s metastable state in collisions with xenon and helium atoms  

SciTech Connect

The absorption probing method was used to investigate collisional deactivation of the metastable 6s[3/2]{sub 2}{sup 0}({sup 3}P{sub 2}) state of the xenon atom in high-pressure He - Xe mixtures with a low xenon concentration. Measurements were made of the rate constants of the plasma-chemical reactions Xe*+Xe+He {yields} Xe{sub 2}*+He [(1.7 {+-}0.2) x10{sup -32} cm{sup 6} s{sup -1}], Xe*+2He{yields} HeXe*+He (less than 3 x 10{sup -35} cm{sup 6} s{sup -1}), and Xe*+He{yields} products+He (less than 10{sup -15} cm{sup 3} s{sup -1}). (active media)

Zayarnyi, D A; Semenova, Ludmila V; Ustinovskii, N N; Kholin, I V; Chugunov, A Yu [P.N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

1998-03-31

315

Helium microwave induced plasma atomic emission detection for liquid chromatography utilizing a moving band interface  

Microsoft Academic Search

A moving band interface is used to separate HPLC solvent from analyte before introduction into a microwave-induced plasma atomic emission detector. Spectral scans indicate that all detectable solvent is removed prior to analyte introduction. Analyte memory effects are not detectable. Chlorine element selective detection limits are 140,410, 220, and 770 pg\\/s for 9-chlorofluorene, p-chlorobiphenyl, 4-chlorobenzophenone, and [alpha],[alpha]'-dichloro-o-xylene, respectively. If the

Peter B. Mason; Liming. Zhang; Jon W. Carnahan; Randall E. Winans

1993-01-01

316

Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion.  

PubMed

The superradiant Rayleigh scattering using a pump laser incident along the short axis of a Bose-Einstein condensate with a density distortion is studied, where the distortion is formed by shocking the condensate utilizing the residual magnetic force after the switching-off of the trapping potential. We find that very small variation of the atomic density distribution would induce remarkable asymmetrically populated scattering modes by the matter-wave superradiance with long time pulse. The optical field in the diluter region of the atomic cloud is more greatly amplified, which is not an ordinary mode amplification with the previous cognition. Our numerical simulations with the density envelop distortion are consistent with the experimental results. This supplies a useful method to reflect the geometric symmetries of the atomic density profile by the superradiance scattering. PMID:23787626

Wang, Zhongkai; Niu, Linxiao; Zhang, Peng; Wen, Mingxuan; Fang, Zhen; Chen, Xuzong; Zhou, Xiaoji

2013-06-17

317

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

SciTech Connect

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.; Inguscio, M. [INFM and European Laboratory for Non-Linear Spectroscopy (LENS), via Nello Carrara 1, I-50019 Sesto Fiorentino, Florence (Italy); Dipartimento di Fisica, Universita di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Florence (Italy); Piovella, N.; Cola, M.; Bonifacio, R. [INFM and European Laboratory for Non-Linear Spectroscopy (LENS), via Nello Carrara 1, I-50019 Sesto Fiorentino, Florence (Italy); Dipartimento di Fisica, Universita degli Studi di Milano, via Celoria 16, I-20133 Milan (Italy); Cataliotti, F. S. [INFM and European Laboratory for Non-Linear Spectroscopy (LENS), via Nello Carrara 1, I-50019 Sesto Fiorentino, Florence (Italy); INFM-MATIS, Scuola Superiore di Catania, Dipartimento di Fisica, Universita di Catania, via Santa Sofia 64, I-95124 Catania (Italy)

2005-03-01

318

A spectroscopic determination of scattering lengths for sodium atom collisions  

Microsoft Academic Search

The authors report a preliminary value for the zero magnetic field Na ²S (f = 1, m = -1) + Na ²S (f = 1, m = -1) scattering length, a{sub 1.-1}. This parameter describes the low-energy elastic two-body processes in a dilute gas of composite bosons and determines, to a large extent, the macroscopic wavefunction of a Bose condensate

Eite Tiesinga; Carl J. Williams; Paul S. Julienne; Kevin M. Jones; Paul D. Lett; W. D. Phillips

1996-01-01

319

Characterization of near-infrared nonmetal atomic emission from an atmospheric helium microwave-induced plasma using a Fourier transform spectrophotometer  

SciTech Connect

A new approach for using Fourier transform spectroscopy (FTS) for the detection of atomic emission from an atmospheric helium plasma has been developed and the results obtained are described. Among the different types of plasma source available, the atmospheric pressure microwave helium plasma appears to be an efficient excitation source for the determination of nonmetal species. The more complete microwave plasma emission spectra of Cl, Br, I, S, O, P, C, N, and He in the near-infrared region were obtained and their corrected relative emission intensities are reported. This makes qualitative identification simple, and aids in the quantitative analysis of atomic species. The accuracy of the emission wavelengths obtained with the Fourier transform spectrophotometer was excellent and the resolution provided by the FTS allowed certain adjacent emission lines to be adequate for analytical applications.

Hubert, J.; Van Tra, H.; Chi Tran, K.; Baudais, F.L.

1986-08-01

320

Sensitive polarization dependence for helium Rydberg atoms driven by strong microwave fields  

SciTech Connect

The authors prepare n{sup 3}S He Rydberg atoms with selected values n {ge} 25 in a fast beam using CO{sub 2} lasers and double-resonance excitation. They then fly through a TE{sub 121} mode cavity, exposing them to a half-sine pulse (about 350 field osc.) of 9.904 GHz electric field whose polarization can be varied; linear (LP), elliptical (EP), and circular (CP). Making EP close to LP can lead to substantial changes in microwave-power-dependent transitions to nearby bound states. In at least one case, a sharp dip in the LP signal is transformed by EP into a pattern reminiscent of Stueckelberg oscillations, previously observed with LP at higher frequencies. Calculations suggest that pulse-shape-induced dynamics at Floquet avoided-crossing(s) explain the LP behavior. Changing the field to EP clearly must modify this behavior. The authors will discuss this kind of data as well as the polarization dependence of microwave ionization of n{sup 3}S He Rydberg atoms.

Zelazny, S.A.; Bellermann, M.R.W.; Smith, L.L.; Koch, P.M.

1996-05-01

321

Low energy electron scattering from atoms: Search for nanocatalysts  

NASA Astrophysics Data System (ADS)

Manipulating the structure and the dynamics of metallic nanoparticles, attractive due to their optical, electronic and magnetic properties, including applications in catalysis, requires a fundamental understanding of the dynamic processes at the atomic level. The fundamental mechanism of catalysis at the atomic scale has already been proposed and demonstrated in Au, Pd and Au-Pd catalysis of H2O2 through the scrutiny of low energy electron elastic total cross sections (TCSs) [1]. The use of mixed precious metal catalysts can produce even higher activities compared to Au alone [2]. Here the interplay between negative ion resonances and Ramsauer-Townsend minima that characterize low energy electron TCSs for Au is identified as the fundamental signature of nanoscale catalysts. Calculated electron elastic TCSs for Ag, Pt, Pd, Ru and Y atoms are presented as illustrations. The recent complex angular momentum methodology is used for the calculations [3]. It is concluded that these atoms are suitable candidates for nanocatalysts individually or in combinations. [4pt] [1] A.Z. Msezane et al, J. Phys. B 43, 201001 (2010); EurophysicsNews 6, 11 (2010) [0pt] [2] D.T. Thompson, Nano Today 2, 40 (2007) [0pt] [3] D. Sokolovski et al, Phys. Rev. A 76, 012705 (2007)

Msezane, A. Z.; Felfli, Z.; Sokolovski, D.

2011-06-01

322

Effective-range corrections to three-body recombination for atoms with large scattering length  

Microsoft Academic Search

Few-body systems with large scattering length a have universal properties that do not depend on the details of their interactions at short distances. The rate constant for three-body recombination of bosonic atoms of mass m into a shallow dimer scales as ℏa4\\/m times a log-periodic function of the scattering length. We calculate the leading and subleading corrections to the rate

H.-W. Hammer; Timo A. Lähde; L. Platter

2007-01-01

323

Effective-range corrections to three-body recombination for atoms with large scattering length  

Microsoft Academic Search

Few-body systems with large scattering length a have universal properties that do not depend on the details of their interactions at short distances. The rate constant for three-body recombination of bosonic atoms of mass m into a shallow dimer scales as (\\/2)a\\/m times a log-periodic function of the scattering length. We calculate the leading and subleading corrections to the rate

L. Platter; Timo A. Laehde; H.-W. Hammer

2007-01-01

324

Spin-orbit corrections of order malpha6 to the fine structure of the (37,35) state in the H4ep¯ antiprotonic helium atom  

Microsoft Academic Search

Precise numerical calculation of radiofrequency intervals between hyperfine sublevels of the (37,35) state of the antiprotonic helium-4 atom is presented. Theoretical consideration includes the QED corrections of order malpha6 to the electron spin-orbit interaction. Only the leading order contribution in the electron-to-antiproton and electron-to- alpha particle mass ratios is considered, so the alpha particle and antiproton are treated nonrelativistically. The

Vladimir I. Korobov; Zhen-Xiang Zhong

2009-01-01

325

Spin-orbit corrections of order m to the fine structure of the (37,35) state in the He p antiprotonic helium atom  

Microsoft Academic Search

Precise numerical calculation of radiofrequency intervals between hyperfine sublevels of the (37,35) state of the antiprotonic helium-4 atom is presented. Theoretical consideration includes the QED corrections of order m to the electron spin-orbit interaction. Only the leading order contribution in the electron-to-antiproton and electron-to- particle mass ratios is considered, so the particle and antiproton are treated nonrelativistically. The effective Hamiltonian

Zhong Zhenxiang; Vladimir I. Korobov

2009-01-01

326

Matter-Wave Scattering from Ultracold Atoms in an Optical Lattice  

SciTech Connect

We study matter-wave scattering from an ultracold, many-body atomic system trapped in an optical lattice. The angular cross section of the target lattice for a matter wave is determined and is demonstrated to have a strong dependence on the many-body phase, superfluid, or Mott insulator. Analytical approaches are employed deep in the superfluid and Mott-insulator regimes, while intermediate points in the phase transition are treated numerically. Matter-wave scattering offers a convenient method for nondestructively probing the quantum many-body phase transition of atoms in an optical lattice.

Sanders, Scott N. [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Harvard University, Cambridge, Massachusetts 02138 (United States); Mintert, Florian [Albert-Ludwigs-Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg (Germany); Heller, Eric J. [Harvard University, Cambridge, Massachusetts 02138 (United States)

2010-07-16

327

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

328

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

329

Resonance inelastic scattering of an x-ray photon by the xenon atom  

NASA Astrophysics Data System (ADS)

The effect of many-particle and relativistic effects on the absolute values and the shape of the doubly differential cross section of resonance inelastic scattering of a linearly polarized x-ray photon by the free xenon atom in the energy region of the K ionization threshold is studied theoretically. The evolution of the spatially extended structure of the scattering cross section in the K?,? structure of the x-ray emission spectrum of the xenon atom is demonstrated. The calculations were performed in the dipole approximation for the anomalous dispersion part of the total amplitude of probability of inelastic scattering and in the impulse approximation for the contact part of this amplitude. The radial relaxation of electronic shells, the spin-orbit splitting, the double excitation/ionization of the ground atomic state, as well as the Auger and radiative decays of the atomic core vacancies being formed were taken into account. In constructing the probability amplitude of the process, the relativistic effects were taken into account as a passage from the nonrelativistic Hartree-Fock wave functions to the relativistic Dirac-Hartree-Fock wave functions of the one-particle scattering states and as the passage (for the radiative transition amplitudes) to the relativistic form of the operator of the photon-atom interaction. The calculation results are predictive in character and, at the incident photon energy 34.42 keV, agree well with the results of the synchrotron experiment.

Khoperski?, A. N.; Nadolinski?, A. M.; Yavna, V. A.; Kasprzhitski?, A. S.

2007-11-01

330

Low-energy positron scattering on atoms and molecules  

NASA Astrophysics Data System (ADS)

We report total cross sections (TCS) measurements for positron scattering on N2, Ar, He and three cyclic hydrocarbons. The data have been obtained with a new linear low-energy spectrometer at Trento University. Both nitrogen and argon total cross sections shows a flat part in TCS from few eV up to the positronium formation thresholds. For cyclocarbons he has found very high values of the TCS in low energy range. Modeling using effective range theory is performed for benzene and cyclohexane. In He results we found some resonant structures indicating formation of virtual positronium.

Karwasz, G.; Pliszka, D.; Zecca, A.

2005-06-01

331

Differential cross sections for positron scattering from alkali atoms  

SciTech Connect

Close-coupling calculations for differential cross sections for elastic and inelastic positron-alkali scattering at incident energies between 1 eV and 100 eV will be presented. Particular emphasis is placed on excitation of the resonant (ns){sup 2}S {yields} (np){sup 2}P{sup o} and the optically forbidden (ns){sup 2}S {yields} (n{prime}d){sup 2}D transitions. The results will be compared with first order DWBA calculations to assess the importance of channel coupling in the theoretical description of these collision processes.

DeVries, K.M.; Bartschat, K.; McEachran, R.P. [and others

1993-05-01

332

Rayleigh scattering from a trapped bose condensate and the corresponding recoil atom velocity distribution  

SciTech Connect

An approach has been developed that allows the Rayleigh scattering cross section to be calculated with allowance for the quantum character of motion of the center of mass of the trapped scattering particles. The shape of the line of light scattering from a Bose condensate in a parabolic trap has been studied. A shift of the scattering line center is equal to the recoil shift, while the line width depends on the chemical potential of the Bose gas and on the relaxation time of the velocity of the above-condensate recoil particles. A velocity distribution function in the beam of recoil atoms formed in the course of induced Rayleigh scattering is determined. It is shown that, under the typical experimental conditions, the characteristic width {delta}v/v of the recoil velocity distribution in this beam is on the order of 10{sup -3} at a velocity v on the order of several centimeters per second.

Alekseev, V. A. [Russian Academy of Sciences, Lebedev Institute of Physics (Russian Federation)], E-mail: valeks@sci.lebedev.ru

2007-03-15

333

UPPER-ATMOSPHERE HELIUM IONS  

Microsoft Academic Search

An experimental measurement of the ion concentration in the upper ; ionosphere is examined in light of a suggestion that helium is an important ; constituent of the high atmosphere. An isothermal region of helium ions at l600 ; deg K is found above approximately 1200 km. Consideration of the loss mechanism ; for helium ions by ion-atom interchange with

W. B. Hanson

1962-01-01

334

Classical Helium Model  

NSDL National Science Digital Library

The EJS Classical Helium Model is an example of a three-body problem that is similar to the gravitational three-body problem of a heavy sun and two light planets. The important difference is that the helium atom's two electrons repel one another, unlike the planetary case where the intraplanetary interaction is attractive. The EJS Classical Helium Model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_mech_orbits_ClassicalHelium.jar file will run the program if Java is installed.

Christian, Wolfgang

2009-03-14

335

Collisional lasing on a self-terminating transition 2{sup 1}P{sup o}{sub 1} - 2{sup 1}S{sub 0} in helium atom  

SciTech Connect

Lasing on a self-terminating transition 2{sup 1}P{sup o}{sub 1} - 2{sup 1}S{sub 0} ({lambda} = 2.058 {mu}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 H{sub 2}, N{sub 2}, O{sub 2}, CO{sub 2}, H{sub 2}O, NH{sub 3}, and N{sub 2}O. In pure helium, the maximal pulse duration is {approx}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 {mu}s. In adding CO{sub 2}, N{sub 2}O, NH{sub 3}, and H{sub 2}O, the relaxation rate for population of the metastable state He(2{sup 1}S{sub 0}) increases, which makes the delay, needed for recovering lasing, shorter up to pulse merging in the case of H{sub 2}O. At the exciting pulse base-level duration of 1.2 {mu}s, in mixtures of helium with NH{sub 3} and H{sub 2}O, laser pulses with a duration of {approx}0.8 {mu}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 [A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

2012-02-28

336

Positron scattering from hydrogen atom embedded in weakly coupled plasma  

NASA Astrophysics Data System (ADS)

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++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. 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; Kamali, M. Z. M.; Ratnavelu, K.

2013-01-01

337

The use of electron scattering for studying atomic momentum distributions: The case of graphite and diamond  

NASA Astrophysics Data System (ADS)

The momentum distributions of C atoms in polycrystalline diamond (produced by chemical vapor deposition) and in highly oriented pyrolitic graphite (HOPG) are studied by scattering of 40 keV electrons at 135°. By measuring the Doppler broadening of the energy of the elastically scattered electrons, we resolve a Compton profile of the motion of the C atoms. The aim of the present work is to resolve long-standing disagreements between the calculated kinetic energies of carbon atoms in HOPG and in diamond films and the measured ones, obtained both by neutron Compton scattering (NCS) and by nuclear resonance photon scattering (NRPS). The anisotropy of the momentum distribution in HOPG was measured by rotating the HOPG sample relative to the electron beam. The obtained kinetic energies for the motion component along, and perpendicular to, the graphite planes were somewhat higher than those obtained from the most recent NCS data of HOPG. Monte Carlo simulations indicate that multiple scattering adds about 2% to the obtained kinetic energies. The presence of different isotopes in carbon affects the measurement at a 1% level. After correcting for these contributions, the kinetic energies are 3%-6% larger than the most recent NCS results for HOPG, but 15%-25% smaller than the NRPS results. For diamond, the corrected direction-averaged kinetic energy is ~ 6% larger than the calculated value. This compares favorably to the ~25% discrepancy between theory and both the NCS and NRPS results for diamond.

Vos, M.; Moreh, R.; T?Kési, K.

2011-07-01

338

Thickness-dependent interfacial coulomb scattering in atomically thin field-effect transistors.  

PubMed

Two-dimensional semiconductors are structurally ideal channel materials for the ultimate atomic electronics after silicon era. A long-standing puzzle is the low carrier mobility (?) in them as compared with corresponding bulk structures, which constitutes the main hurdle for realizing high-performance devices. To address this issue, we perform a combined experimental and theoretical study on atomically thin MoS2 field effect transistors with varying the number of MoS2 layers (NLs). Experimentally, an intimate ?-NL relation is observed with a 10-fold degradation in ? for extremely thinned monolayer channels. To accurately describe the carrier scattering process and shed light on the origin of the thinning-induced mobility degradation, a generalized Coulomb scattering model is developed with strictly considering device configurative conditions, that is, asymmetric dielectric environments and lopsided carrier distribution. We reveal that the carrier scattering from interfacial Coulomb impurities (e.g., chemical residues, gaseous adsorbates, and surface dangling bonds) is greatly intensified in extremely thinned channels, resulting from shortened interaction distance between impurities and carriers. Such a pronounced factor may surpass lattice phonons and serve as dominant scatterers. This understanding offers new insight into the thickness induced scattering intensity, highlights the critical role of surface quality in electrical transport, and would lead to rational performance improvement strategies for future atomic electronics. PMID:23862641

Li, Song-Lin; Wakabayashi, Katsunori; Xu, Yong; Nakaharai, Shu; Komatsu, Katsuyoshi; Li, Wen-Wu; Lin, Yen-Fu; Aparecido-Ferreira, Alex; Tsukagoshi, Kazuhito

2013-07-22

339

Excitation and ionisation of the positronium atom in positronium-hydrogen molecule scattering  

NASA Astrophysics Data System (ADS)

We investigate discrete and continuum excitation of the Ps atom in Ps-H2 scattering in the framework of the first Born approximation (FBA) using direct interactions. We report target elastic total cross sections as well as angle integrated cross sections for the discrete and continuum excitations of the Ps atom in the energy range 7-150 eV. The continuum excitation of the Ps atom is identified as the channel responsible for the experimental peak observed by Garner and Laricchia [Proc. Positron Workshop '95, Can. J. Phys., in press].

Biswas, P. K.; Ghosh, A. S.

1996-02-01

340

Spin-Polarization in the Elastic Scattering of Electrons by One-Electron Atoms.  

National Technical Information Service (NTIS)

An analysis of spin-polarization in low energy elastic scattering of electrons by one electron s-state atoms is carried out allowing both for electron exchange and relativistic effects. First the collision matrix is written in terms of the asymptotic form...

P. G. Burke J. F. B. Mitchell

1973-01-01

341

The Coherent Scattering of gamma -rays by K Electrons in Heavy Atoms. I. Method  

Microsoft Academic Search

A method for evaluating transition amplitudes for bound electrons in second order in the effects of the radiation field is outlined. An example of the type of problem concerned is the coherent scattering of gamma -rays by the K electrons in heavy atoms. The static field in which the electron moves is taken into account exactly; no expansion is made

G. E. Brown; R. E. Peierls; J. B. Woodward

1954-01-01

342

Critical Assessment of the Polarized-Orbital Method in Atomic Scattering  

Microsoft Academic Search

The method of polarized orbitals used in calculating electron-atom scattering amplitudes has two obvious flaws: the wave function is discontinuous, and the method is not variationally based. These are corrected in a somewhat arbitrary manner, and it is found that the results then depend upon a parameter of the theory sufficiently strongly that there are serious doubts about the predictive

Marvin H. Mittleman; Jerry L. Peacher

1968-01-01

343

Resonant scattering of an X-ray photon by a heavy atom  

SciTech Connect

The influence of many-body and relativistic effects on the absolute values and shape of the double differential cross section for the resonant scattering of a linearly polarized X-ray photon by a free xenon atom near the K-shell ionization threshold has been theoretically analyzed. The evolution of the spatially extended structure of the scattering cross section to the K{sub {alpha}}{sub ,{beta}} structure of the X-ray spectrum of the xenon atom emission has been demonstrated. The calculations have been performed in the dipole approximation for the anomalous dispersion component of the total inelastic scattering amplitude and in the impulse approximation for the contact component of this amplitude. The contribution of the Rayleigh (elastic) scattering component is taken into account using the methods developed in Hopersky et al., J. Phys. B 30, 5131 (1997). The effects of the radial relaxation of the electron shells, spin-orbit splitting, double excitation/ionization of the atomic ground state, as well as the Auger and radiative decays of the produced main vacancies, are considered. Using the results obtained by Tulkki, Phys. Rev. A 32, 3153 (1985) and Biggs et al., At. Data Nucl. Data Tables 16, 201 (1975), the nonrelativistic Hartree-Fock wavefunctions are changed to the relativistic Dirac-Hartree-Fock wavefunctions of the single-particle scattering states when constructing the process probability amplitude. The calculations are predicting and are in good agreement with the synchrotron experiment on the measurement of the absolute values and shape of the double differential cross section for the resonant scattering of an X-ray photon by a free xenon atom reported by Czerwinski et al., Z. Phys. A 322, 183 (1985)

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

2007-10-15

344

Resonant scattering of an X-ray photon by a heavy atom  

NASA Astrophysics Data System (ADS)

The influence of many-body and relativistic effects on the absolute values and shape of the double differential cross section for the resonant scattering of a linearly polarized X-ray photon by a free xenon atom near the K-shell ionization threshold has been theoretically analyzed. The evolution of the spatially extended structure of the scattering cross section to the K ?, ? structure of the X-ray spectrum of the xenon atom emission has been demonstrated. The calculations have been performed in the dipole approximation for the anomalous dispersion component of the total inelastic scattering amplitude and in the impulse approximation for the contact component of this amplitude. The contribution of the Rayleigh (elastic) scattering component is taken into account using the methods developed in Hopersky et al., J. Phys. B 30, 5131 (1997). The effects of the radial relaxation of the electron shells, spin-orbit splitting, double excitation/ionization of the atomic ground state, as well as the Auger and radiative decays of the produced main vacancies, are considered. Using the results obtained by Tulkki, Phys. Rev. A 32, 3153 (1985) and Biggs et al., At. Data Nucl. Data Tables 16, 201 (1975), the nonrelativistic Hartree-Fock wavefunctions are changed to the relativistic Dirac-Hartree-Fock wavefunctions of the single-particle scattering states when constructing the process probability amplitude. The calculations are predicting and are in good agreement with the synchrotron experiment on the measurement of the absolute values and shape of the double differential cross section for the resonant scattering of an X-ray photon by a free xenon atom reported by Czerwinski et al., Z. Phys. A 322, 183 (1985).

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

2007-10-01

345

A New Three-Body Wavefunction for Continuum Atomic Scattering  

NASA Astrophysics Data System (ADS)

We present here a new three-body wavefuction which is a product of phfive kinematically coupled Coulomb waves. The ``KC5C'' wavefunction is valid to second order and satisfies all asymptotic boundary conditions of the Schrödinger equation. The model couples the pheffective potential with the kinetic energy and allows me to retain the exact three-body Hamiltonian. In this way a symmetric and complete description of the local momenta arises naturally. The strength of the new model is illustrated by showing that it contains the appropriate two-body coalesence, reproduces the results of BBK(M. Brauner phet. al.), J. Phys. B 22, 2265(1989). for the electron ionization of hydrogen, and retains the results of the AM(E. O. Alt and A. M. Mukhamedzhanov, Phys. Rev. A 47), 2004(1993). model while providing a much clearer physical and mathematical formulation of the phlocal momenta. With this new framework, it is easy to see why the paradigm 3C wavefunction is so successful. We show that the contribution of the phlocal momenta are small at high energies and identically zero for all energies over a family of curves - the shape of which is determined by the TDCS scattering angles.

Schillaci, M. J.; Lieber, M.

1998-05-01

346

Reactive scattering of a supersonic fluorine atom beam: F I2  

NASA Astrophysics Data System (ADS)

Reactive scattering of F atoms with I2 molecules has been studied at an initial translational energy E ˜ 20 kJ mol-1 using a supersonic beam of F atoms seeded in Ne buffer gas. The differential reaction cross section is found to be almost symmetrical about centre-of-mass scattering angle ? = 90° but with a minor additional component to the scattering in the forward hemisphere with very low product translational energy. Kinematic analysis of previous measurements at an initial translational energy E ˜ 40 kJ mol-1 using a supersonic beam of F atoms seeded in He buffer gas has been refined and shows increased scattering which is peaked quite sharply in the backward direction. These features are in accord with the predictions of a recent quasiclassical trajectory study which shows that migratory dynamics are followed by approximately half of all reactive trajectories with scattering favouring the backward hemisphere while nonmigratory trajectories favour scattering into the forward hemisphere. Migratory trajectories are promoted by the accessibility of a second potential energy well in the IFI configuration in addition to the well in the FII configuration which is accessed initially on the F + I2 potential energy surface. The F + I2 reactive scattering is similar to that of O + I2 which suggests that migratory trajectories may also occur for the O + I2 reaction with access to a well in the IOI configuration on the singlet potential energy surface following initial access of reactants to a well in the OII configuration on the triplet potential energy surface.

Firth, N. C.; Keane, N. W.; Smith, D. J.; Grice, R.

347

Scattering of He atoms from KCN(001): Analysis of the energy exchange  

SciTech Connect

High-resolution inelastic He-atom surface scattering experiments have been carried out on an {ital in} {ital situ} cleaved KCN(001) molecular crystal surface in the temperature range of 40{lt}{ital T}{lt}334 K covering the temperature range of the two known bulk phase transitions at 168 and 83 K. No Bragg diffraction peaks other than the specular beam are observed over the entire temperature range. The scattering intensity is primarily composed of inelastic multiphonon processes along with some diffuse elastic-scattering contributions, the latter of which increases in magnitude with decreasing temperature while the former decreases in intensity with decreasing temperature. A theoretical model developed for explaining the multiphonon-scattering process gives very good quantitative agreement with the data.

Weera, S.M.; Manson, J.R. [Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (United States); Baker, J.; Gillman, E.S.; Hernandez, J.J.; Bishop, G.G.; Safron, S.A.; Skofronick, J.G. [Departments of Physics and Chemistry and Center for Materials Research Technology, Florida State University, Tallahassee, Florida 32306 (United States)

1995-11-15

348

Investigations of Silk Fibers Using X-Ray Scattering and Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

Silk fibers from the cocoon of Bombyx mori and the dragline of Nephila clavipes have been investigated by small angle x-ray scattering (SAXS) and atomic force microscopy (AFM). The large scale morphology of these silks have minimum scattering dimensions, and correlation length on the order of 150-300 nm. Several types of AFM measurements on peeled and abraided silk samples have revealed dimensions in agreement with SAXS results. Further agreemeent has been found through the incorporation of discrete Fourier transform theory on AFM topographic information as compared to SAXS patterns. This incorporation allows the materials scientist a way of visualizing the relationship between a material and its resulting scattering function. All of these studies yield a more complete view of the silk morphology and give a new method of model building from scattering experiments.

Miller, Lance D.; Putthanarat, Sirina; Eby, Ronald K.; Adams, W. W.; Liu, G. F.

1998-03-01

349

Spacelab 2 measurement of the solar coronal helium abundance  

NASA Astrophysics Data System (ADS)

The abundance of helium relative to hydrogen has been measured with the 'Coronal Helium Abundance Spacelab Experiment' (CHASE) from the space shuttle Challenger in 1985. Previous solar measurements have proved difficult due to the temperature-sensitivity of the electron excitation rates for the observed lines. In this approach, scattered Lyman Alpha radiation of helium and hydrogen formed in the corona were measured with a grazing-incidence spectrometer and compared with the intensity of the illuminating flux from the solar chromosphere. The abundance ratio by number of atoms was found to be 0.070 with an uncertainty of 0.011. Scattered light in the telescope is the main source of error.

Gabriel, A. H.; Culhane, J. L.; Patchett, B. E.; Breeveld, E. R.; Lang, J.; Parkinson, J. H.; Payne, J.; Norman, K.

1995-07-01

350

Energy transfer in O collisions with He isotopes and Helium escape from Mars  

NASA Astrophysics Data System (ADS)

Accurate data on energy-transfer collisions between hot oxygen atoms and the atmospheric helium gas on Mars, are reported. Anisotropic cross sections for elastic collisions of O(3P) and O(1D) atoms with helium gas have been calculated quantum mechanically and found to be surprisingly similar. Cross sections, computed for collisions with both helium isotopes, 3He and 4He, have been used to construct the kernel of the Boltzmann equation describing the energy relaxation of hot oxygen atoms. Computed rates of energy transfer in O+He collisions have been used to evaluate the flux of He atoms escaping from the Mars atmosphere. Atmospheric layers mostly responsible for production of the He escape flux are identified. Our results demonstrate that strong angular anisotropy of scattering cross sections increases the collisional ejection of light atoms and is critical in the evaluation of He escape from Mars, Venus and Earth.

Bovino, S.; Zhang, P.; Gianturco, F. A.; Dalgarno, A.; Kharchenko, V.

2011-01-01

351

Formation of cations and anions upon electron interaction with (doped) helium droplets  

NASA Astrophysics Data System (ADS)

Superfluid helium droplets have provided a new perspective for studying electron induced chemistry at extremely low temperatures. Helium droplets represent an ideal environment for the formation of novel and exotic agglomerates of atoms and molecules. Mass spectrometry can be used to detect the resulting ions formed upon electron ionization and electron attachment to doped droplets. In the case of electron ionization a helium atom of the droplet is ionized initially and after few resonant charge transfer reactions between helium atoms the charge finally localises on the dopant. An alternative process is Penning ionization of the dopant, where the scattered electron first electronically excites a helium atom on the surface of the droplet. The attachment of a low energy electron leads to formation of an electron bubble inside the droplet which decays by autodetachment or localization on a dopant, if present in the droplet. In the present minireview a general overview about the field of electron scattering with doped helium droplets is given and a presentation of important recent results related to these electron collision studies is given as well.

Denifl, S.

2013-10-01

352

Theoretical Studies of Energy and Momentum Exchange in Atomic and Molecular Scattering from Surfaces  

SciTech Connect

The contributions that we have made during the grant period of DE-FG02-98ER45704 can be placed into six different categories: (1) advances in the Theory of Molecule-Surface Scattering, (2) advances in the Theory of Atom-Surface Scattering, (3) utilization of scattering theory to Extract Physical Information about Surfaces, (4) Gas-Surface Interactions, (5) Ion Scattering from surfaces and (6) Scanning Tunneling Microscopy (STM). These six topics are discussed below as individual listings under the title 'IV. Detailed description of research accomplishments'. These advances show that we have made significant progress on several scientific problems in atomic and molecular surface scattering during the course of this grant as well as contributions to other areas. It is also noted that this work, although fundamentally theoretical, is marked by its strong motivation to explain current experimental measurements. This was an important secondary goal in the proposed work. We have developed theory that is useful to experimentalists in the explanation and analysis of their experimental data.

Joseph R. Manson

2005-06-30

353

Energy loss of 100-keV hydrogen atoms during grazing scattering from Cu(111)  

SciTech Connect

The energy loss of 100-keV hydrogen atoms scattered under a grazing angle of incidence from a clean and flat Cu(111) surface is studied in coincidence with the number of emitted electrons. From the dependence of the energy loss on the angle of incidence we deduce the position dependent stopping power which shows the same functional dependence but a factor of about 2 higher values than recent calculations. From the number of emitted electrons related to a specific energy loss we reveal processes related to electron emission as dominant channel for energy dissipation of scattered projectiles.

Lederer, S.; Winter, H. [Institut fuer Physik, Humboldt Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin-Adlershof (Germany)

2006-05-15

354

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

355

Confined quantum systems: a comparison of the spectral properties of the two-electron quantum dot, the negative hydrogen ion and the helium atom  

NASA Astrophysics Data System (ADS)

The spectrum, the electron density distribution and the character of three two-electron quantum systems, namely the two-electron quantum dot, the negative hydrogen ion and the helium atom, confined by an anisotropic harmonic oscillator potential, have been studied for different confinement strengths, omega, by using the quantum chemical configuration interaction (CI) method employing a Cartesian anisotropic Gaussian basis set supplemented by a quantum chemical standard Cartesian Gaussian basis set, respectively, and a full CI wavefunction. Energy level diagrams and electron density distributions are displayed for low lying electronic singlet states and selected confinement parameters. The results for the three confined quantum systems are compared with each other: in general, the absolute energies of the states and the interval between states increase with increasing confinement, omega. The ordering of states may vary for different values of omega. The shape of the electron density distribution differs among the three systems. Its size increases in the order He < H- < two-electron quantum dot. Electron distributions in prolate type confinement are stretched along the z axis, while those in oblate type are compressed with respect to this axis. The CI wavefunction of most of the low lying states for the helium atom and the negative hydrogen ion is dominated by one configuration, while some of the CI wavefunctions corresponding to states of the two-electron quantum dot have more than one leading configuration. The ground state CI wavefunctions of the negative hydrogen ion and the helium atom confined in a spherical potential are dominated by harmonic oscillator functions up to 82.4 and 47.1%, respectively, for the smallest confinement of omega = 0.1. These values increase to 98.8 and 89.0%, respectively, for omega = 0.5.

Sako, T.; Diercksen, G. H. F.

2003-05-01

356

Absorption and emission of radiation during electron excitation of the 2 sup 1 S and 2 sup 1 P states of helium  

SciTech Connect

We are reporting electron spectra resulting from the inelastic scattering of 45-eV electrons from helium atoms through a scattering angle of 12{degree} in the presence of an intense carbon dioxide laser. The spectra presented are in the region of the 2 {sup 1}S and 2 {sup 1}P states of helium. These data show additional structure when the laser is present at scattered electron energies which correspond to an increase or decrease in electron kinetic energy of the equivalent of one laser quantum. These measurements demonstrate the simultaneous electron-photon excitation of an atom at high incident-electron energies.

Wallbank, B.; Holmes, J.K.; Weingartshofer, A. (Department of Physics, St. Francis Xavier University, Antigonish, Nova Scotia, Canada B2G1C0 (CA))

1989-11-01

357

Scattering of Stark-decelerated OH radicals with rare-gas atoms  

NASA Astrophysics Data System (ADS)

We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH (X2?3/2, J = 3 / 2, f) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D2 as a function of the collision energy between ~70 cm-1 and 400 cm-1. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by coupled channel scattering calculations based on accurate ab initio potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom, G. Meijer, Science 313, 1617 (2006)], Ar [L. Scharfenberg, J. K?os, P.J. Dagdigian, M.H. Alexander, G. Meijer, S.Y.T. van de Meerakker, Phys. Chem. Chem. Phys. 12, 10660 (2010)], He, and D2 [M. Kirste, L. Scharfenberg, J. K?os, F. Lique, M.H. Alexander, G. Meijer, S.Y.T. van de Meerakker, Phys. Rev. A 82, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.

Scharfenberg, L.; Gubbels, K. B.; Kirste, M.; Groenenboom, G. C.; van der Avoird, A.; Meijer, G.; van de Meerakker, S. Y. T.

2011-11-01

358

Hyperfine structure of the excited state 1s1/2(e)2s1/2(?) of the muonic helium atom  

NASA Astrophysics Data System (ADS)

The recoil, vacuum polarization, and electron vertex corrections of first and second orders in the fine structure constant ? and the ratio of electron to muon and electron to ?-particle masses are calculated for the hyperfine splitting of the 1s1/2(e)2s1/2(?) state of muonic helium atom (?e24He) on the basis of perturbation theory. We obtain a total result for the muonically excited state hyperfine splitting ??hfs=4295.66 MHz, which improves previous calculations, taking additional corrections into account, and a more accurate treatment of the electron vertex contribution.

Krutov, A. A.; Martynenko, A. P.

2012-11-01

359

Fission-fusion correlations for swelling and microstructure in stainless steels: effect of the helium-to-displacement-per-atom ratio  

SciTech Connect

The initial irradiated structural materials data base for fusion applications will be developed in fission reactors. Hence, this data may need to be adjusted using physically-based procedures to represent behavior in fusion environments, viz. - fission-fusion correlations. Such correlation should reflect a sound mechanistic understanding, and be verified in facilities which most closely simulate fusion conditions. In this paper we review the effects of only one of a number of potentially significant damage variables, the helium to displacement per atom ratio, on microstructural evolution in austenitic stainless steels. Dual-ion and helium preinjection data are analyzed to provide mechanistic guidance; these results appear to be qualitatively consistent with a more detailed comparison made between fast (EBR-II) and mixed (HFIR) spectrum neutron data for a single heat of 20% cold-worked 316 stainless steel. These two fission environments bound fusion (He/dpa ratios. A model calibrated to the fission reactor data is used to extrapolate to fusion conditions. Both the theory and broad empirical observation suggest that helium to dpa ratios have both a qualitative and quantitative influence on microstructural evolution; and that the very high and low ratios found in HFIR and EBR-II may not result in behavior which brackets intermediate fusion conditions.

Odette, G.R.; Maziaz, P.J.; Spitznagel, J.A.

1981-01-01

360

Diffraction of swift atoms after grazing scattering from metal surfaces: N/Ag(111) system  

SciTech Connect

Diffraction patterns produced by grazing scattering of fast N atoms from a Ag(111) surface are investigated by employing the surface eikonal approximation. This method is a distorted-wave theory that takes into account the coherent addition of contributions coming from different projectile paths. In the model the projectile-surface potential is obtained from an accurate density-functional theory calculation. The dependence of the scattered projectile spectra on impact energy and incidence channel is analyzed, and possible incident direction and energy range for the observation of the interference patterns are predicted. In addition, it is found that as a result of the high reactivity of N atoms, asymmetries of the surface potential might be detected through their effects on diffraction patterns.

Gravielle, M. S. [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA) and Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Bocan, G. A. [Centro Atomico Bariloche, Comision Nacional de Energia Atomica, and Consejo Nacional de Investigaciones Cientificas y Tecnicas, S.C. de Bariloche, Rio Negro (Argentina); Diez Muino, R. [Donostia International Physics Center (DIPC) and Centro de Fisica de Materiales CSIC-UPV/EHU, San Sebastian (Spain)

2010-11-15

361

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

362

Absolute electron-scattering total cross section measurements for noble gas atoms and diatomic molecules  

Microsoft Academic Search

Absolute electron-scattering total cross sections for noble gas atoms (He, Ne, Ar, Kr, and Xe) and H2, N2, CO, NO, and O2 molecules have been measured at impact energies between 0.5 and 250 eV by the linear transmission method with the same experimental set-up for all the investigated targets. Generally, our total cross sections have been found to be in

Czeslaw Szmytkowski; Krzysztof Maciag; Grzegorz Karwasz

1996-01-01

363

Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length  

SciTech Connect

We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by modulating the atomic scattering length via a Feshbach resonance. Excitation occurs at various modulation frequencies, and resonances located at the natural quadrupole frequency of the condensate and at the first harmonic are observed. We also investigate the amplitude of the excited mode as a function of modulation depth. Numerical simulations based on a variational calculation agree with our experimental results and provide insight into the observed behavior.

Pollack, S. E.; Dries, D.; Hulet, R. G.; Magalhaes, K. M. F.; Henn, E. A. L.; Ramos, E. R. F.; Caracanhas, M. A.; Bagnato, V. S. [Department of Physics and Astronomy and Rice Quantum Institute, Rice University, Houston, Texas 77005 (United States); Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, 13560-970 Sao Carlos-SP (Brazil)

2010-05-15

364

Effective-range corrections to three-body recombination for atoms with large scattering length  

Microsoft Academic Search

Few-body systems with large scattering length a have universal properties\\u000athat do not depend on the details of their interactions at short distances. The\\u000arate constant for three-body recombination of bosonic atoms of mass m into a\\u000ashallow dimer scales as \\\\hbar a^4\\/m times a log-periodic function of the\\u000ascattering length. We calculate the leading and subleading corrections to the

H.-W. Hammer; Timo A. Lahde; L. Platter

2007-01-01

365

Exchange amplitudes and forward dispersion relations for electron-atomic hydrogen scattering  

Microsoft Academic Search

The analytic properties of the forward elastic exchange amplitude g(E) are studied as a function of the incident electron energy E for electron scattering by atomic hydrogen. The authors first prove that the bound-state of gB2(E), the second Born contribution to g(E), has an infinite number of singularities due to the analytic structure of the off-shell first-order exchange matrix element.

F. W. Byron Jr.; C. J. Joachain

1978-01-01

366

Photon antibunching upon scattering by an atomic Bose-Einstein condensate  

SciTech Connect

Antibunching of photodetections from different modes is shown to arise when two quantized light modes are scattered by an atomic Bose-Einstein condensate. This effect appears because of the uncertainty in the position of the condensate wave function relative to the optical lattice formed by the light beams. It is shown how the information contained in the history of photodetections leads to a spatial localization of the condensate wave function.

Ilichev, L. V., E-mail: leonid@iae.nsk.su; Chapovsky, P. L. [Russian Academy of Sciences, Siberian Branch, Institute of Automation and Electrometry (Russian Federation)

2010-05-15

367

Study of effective atomic number of breast tissues determined using the elastic to inelastic scattering ratio  

NASA Astrophysics Data System (ADS)

In this work we have measured Compton and Rayleigh scattering radiation from normal (adipose and fibroglandular), benign (fibroadenoma) and malignant (ductal carcinoma) breast tissues using a monoenergetic beam of 17.44 keV and a scattering angle of 90° (x=0.99 Å?1). A practical method using the area of Rayleigh and Compton scattering was used for determining the effective atomic number (Zeff) of the samples, being validated through measurements of several reference materials. The results show that there are differences in the distributions of Zeff of breast tissues, which are mainly related to the elemental composition of carbon (Z=6) and oxygen (Z=8) of each tissue type. The results suggest that is possible to use the method to characterize the breast tissues permitting study histological features of the breast tissues related to their elemental composition.

Antoniassi, M.; Conceição, A. L. C.; Poletti, M. E.

2011-10-01

368

Semiclassical description of the small angle differential cross section for elastic atom—atom scattering  

NASA Astrophysics Data System (ADS)

The scattering amplitude is investigated for small angles ?* ? 8.5, with ?* = ?/? o a reduced scattering angle. The scaling angle is ? o = (4?/ k2Q3) 1/2, with k the wavenumber and Q3 the total cross section due to the attractive branch of the intermolecular potential. Both pure inverse power potentials and realistic intermolecular potentials are investigated. The method used is a least-square curve fit of the real and imaginary parts of quantum-mechanically calculated scattering amplitudes f(?) with suitable model functions. The shape of these model functions is partially based on the classical and semiclassical results for small angle scattering. For the shape of the attractive contribution to the differential cross section ? 3(?) in the case of an inverse power potential we give a new model function that describe the quantum oscillations (diffraction) modulating the classical result ? e1(?) HE for the differential cross section in the high energy approximation, i.e. the approximation of a straight line trajectory. The first order correction on this straight line approximation is also derived and incorporated in our model function. For s = 6 and 2.5 ? ?* ? 8.5 we find a description of ? 3(?)/? e1(?) HE with a rms deviation of 2.3 × 10 -3. For the shape of the differential cross section at small angles we give a second, new semi-empirical model functions, ? 3(?)/? 3(0) = [1 -1 c1 sin ( c2?* 2) + c3?* 2] -(3 + 1)/3, with s the power of the potential. The asymptotic behaviour of this function for ?* ? 1 and ?* ? is in good agreement with the corresponding semiclassical and classical results. For s = 6 the parameters are c1 = 3.75, c2 = 0.556, and c3 = 2.94, resulting in a description of ? 3(?)/? 3(0) with a rms deviation of 0.9 × 10 -3 for ?* ? 4.0. A simple and accurate model function for the phase angle ? a(?) = arg( f(?)) enables us to include the glory behaviour in the case of a realistic intermolecular potential. For the analysis of the differential cross section of a realistic potential a suitable model function for the glory contribution is added, resulting in a description of ?(?)/?(0) with a rms deviation of 3 × 10 -3 for ?* ? 4.0. A universal set of parameters is presented that can be used for predicting the differential cross section for a realistic intermolecular potential. It is also shown that the velocity dependency of the attractive and the glory contribution to the imaginary part of the scattering amplitude for ?* = 0, i.e. the total cross section, can be effectively used for predicting the small angle behaviour of the differential cross section.

Beijerinck, H. C. W.; van der Kam, P. M. A.; Thijssen, W. J. G.; Verster, N. F.

1980-01-01

369

Elastic electron scattering from the antimony atom in the spin-polarized optical potential approach  

NASA Astrophysics Data System (ADS)

This is the first theoretical study of elastic scattering of electrons on antimony atoms in a broad range of low and intermediate collision energies from 0.1 eV to 1 keV. A complex optical potential (OP) in the spin-polarized approximation is used for the calculation of differential (DCSs) and integral scattering cross sections as well as a spin exchange asymmetry parameter. It is shown that for this atom the spin dependence of not only exchange interaction, but also polarization interaction should be taken into account at the asymmetry calculation. Two types of absorption potential are used: a non-empirical potential within the quasi-free electron scattering approximation and a McCarthy-type empirical potential. The calculations are also performed without taking account of absorption effects, i.e. in the approximation of solely the parameter-free real part of the OP. Characteristics of the antimony atom and spin correlation-polarization potentials are found using the local spin density approximation. Energy and angular positions of 11 critical minima in the DCSs are found. The highest energy minimum among them is located at [663.2 eV; 132.02°]. In the angular vicinities of the critical minima, spin polarization parameters, the Sherman function S(?) and the U(?) function are calculated. The present DCSs and S(?) are compared with other available theoretical and experimental data.

Kelemen, V. I.; Remeta, E. Yu

2010-12-01

370

Electron scattering from cold atoms - Design and operation of the AC driven Magneto Optical Trap (AC-MOT)  

NASA Astrophysics Data System (ADS)

Electron scattering from cold atoms provides significant advantages compared to collisions with atoms emanating from a hot effusive source. Here we describe a new type of cold atom trap (the AC-MOT) that allows measurements from cold and trapped atoms at low impact energies, by eliminating the MOT magnetic fields very rapidly. The design and operation of the AC-MOT will be described, together with results from experiments that have been performed.

Harvey, Matthew; Murray, Andrew; Agomuo, John

2012-11-01

371

A Measurement of the Nuclear Magnetic Moment of the Helium3 Atom in Terms of that of the Proton  

Microsoft Academic Search

We have measured the ratio of the NMR spin precession frequencies of optically pumped low pressure helium-3 and of protons in water, using free induction decay. This was done by direct substitution in a flux density of 0,1 T of samples in an accurately spherical 25 mm diameter sample cell, without removing the sample cell from the magnet. The water

J L Flowers; B W Petley; M G Richards

1993-01-01

372

Scattering angle-integrated (total) and magnetic sublevel cross-sections and degree of linear polarization for electron and proton induced excitation [HeI (1 snp) 1P 0 ( n=2–5)] of helium  

Microsoft Academic Search

Experimental scattering-angle-integrated (total) cross-sections ??, (scattering) angle-integrated magnetic sublevel cross-sections ??ML, and degree of linear polarization data have been measured in the extreme ultraviolet (EUV) wavelength region following decay of HeI (1snp)1P0 (n=2–5) states induced by electron and proton impact on a neutral helium target. These measurements are compared with a first Born approach as well as more sophisticated theoretical

H. Merabet; R. Bruch; J. Hanni; M. Bailey; A. L. Godunov; J. H. McGuire; D. V. Fursa; I. Bray; K. Bartschat; H. C. Tseng; C.-D. Lin

2003-01-01

373

Mobility of electrons in a quasi-one-dimensional conducting channel on the liquid-helium surface  

Microsoft Academic Search

The mobility of electrons in a quasi-one-dimensional channel on the surface of liquid helium is studied theoretically at temperatures lower than 1.5 K. The influence on the mobility due to the electron-ripplon interaction and to the electron scattering from helium atoms in the vapor phase is investigated. The nonmonotonic temperature dependence of the mobility below 0.5 K is attributed to

Sviatoslav S. Sokolov; Guo-Qiang Hai; Nelson Studart

1995-01-01

374

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Photoionisation of a helium atom involving autoionisation states coupled by a circularly polarised laser field  

NASA Astrophysics Data System (ADS)

The rotating wave approximation is used to obtain parametric expressions for the resonance cross section for the atomic ground state ionisation by linearly polarised probe radiation in the vicinity of an autoionisation state coupled resonantly to another autoionisation state through circularly polarised laser radiation. Calculations are made for the 2s2p 1P and 2s3d 1D states of the helium atom. It is shown that the structure of the photoionisation cross-section spectrum formed for circularly polarised laser radiation differs qualitatively from the structure formed in the case of linear polarisation. The dependence of this structure on the intensity and frequency of laser radiation and the direction of polarisation of the probe radiation is studied.

Gryzlova, E. V.; Magunov, A. I.; Rotter, I.; Strakhova, S. I.

2005-01-01

375

Crucial electronic contributions to measures of surface diffusion by He atom scattering  

NASA Astrophysics Data System (ADS)

In a He atom scattering (HAS) experiment, the position and motion of atoms or molecules at a surface is inferred indirectly, through the electron distribution at the sample surface. Nevertheless, surface diffusion measurements are typically analyzed assuming that the electron distribution simply follows the position of the surface atoms. We have examined theoretically recent HAS measurements of Na/Cu(001), identifying a non trivial relation between the dynamics of the electron distribution and that of the Na ions. The magnitude of the calculated variations in the charge density, and their dependence on the local density of adsorbates, account for the correlated 3D motion experimentally observed. The results of this study further highlight the sensitivity of HAS to the electron distribution of the sample and point out the role of electronic contributions in high-resolution measures of surface dynamics.

Fratesi, Guido; Alexandrowicz, Gil; Italo Trioni, Mario; Brivio, Gian Paolo; Allison, William

2008-03-01

376

Changes in the Atomic Structure through Glass Transition Observed by X-Ray Scattering  

SciTech Connect

The glass transition involves a minor change in the internal energy, and yet the physical and mechanical properties of a glass change dramatically. In order to determine the evolution of the atomic structure through the glass transition, we employed in-situ synchrotron X-ray scattering measurements as a function of temperature on a model material: Zr-Cu-Al metallic glass. We found that the thermal expansion at the atomic level is smaller than the macroscopic thermal expansion, and significantly increases above the glass transition temperature. The observed changes in the pair-distribution function (PDF) are explained in terms of the fluctuations in the local atomic volume and their change through the glass transition.

Egami, Takeshi [ORNL

2012-01-01

377

Quantum trajectories in elastic atom-surface scattering: threshold and selective adsorption resonances.  

PubMed

The elastic resonant scattering of He atoms off the Cu(117) surface is fully described with the formalism of quantum trajectories provided by Bohmian mechanics. Within this theory of quantum motion, the concept of trapping is widely studied and discussed. Classically, atoms undergo impulsive collisions with the surface, and then the trapped motion takes place covering at least two consecutive unit cells. However, from a Bohmian viewpoint, atom trajectories can smoothly adjust to the equipotential energy surface profile in a sort of sliding motion; thus the trapping process could eventually occur within one single unit cell. In particular, both threshold and selective adsorption resonances are explained by means of this quantum trapping considering different space and time scales. Furthermore, a mapping between each region of the (initial) incoming plane wave and the different parts of the diffraction and resonance patterns can be easily established, an important issue only provided by a quantum trajectory formalism. PMID:15638686

Sanz, A S; Miret-Artés, S

2005-01-01

378

Electron scattering by atomic hydrogen: elastic and inelastic phenomena at 13.9 to 200 eV.  

National Technical Information Service (NTIS)

A six state coupled-channel optical potential method for electron-atom scattering is applied to electron-hydrogen scattering at energies of 13.87, 16.46, 19.58, 35, 40, 54.4, 100, and 200 eV. The n = 1, 2, and 3 channels are coupled explicitly whereas the...

I. Bray D. A. Konovalov I. E. McCarthy

1991-01-01

379

On mechanism of low-energy heavy ions scattering on a target surface with small atomic mass  

Microsoft Academic Search

In the present work, an experimental study of low-energy (E0=20–500 eV) heavy Cs+ ions scattering on target surfaces with small atomic masses (Al, Si, Ni) has been performed for more accurate definition of mechanism of scattering and evaluation of an opportunity for use of heavy ions scattering as a tool of surface layer analysis. It is shown that the dependence

F. F Umarov; N. N Bazarbaev; L. B Kudryashova; N. M Krylov

2002-01-01

380

On mechanism of low-energy heavy ions scattering on a target surface with small atomic mass  

Microsoft Academic Search

In the present work, an experimental study of low-energy (E0=20-500 eV) heavy Cs+ ions scattering on target surfaces with small atomic masses (Al, Si, Ni) has been performed for more accurate definition of mechanism of scattering and evaluation of an opportunity for use of heavy ions scattering as a tool of surface layer analysis. It is shown that the dependence

F. F. Umarov; N. N. Bazarbaev; L. B. Kudryashova; N. M. Krylov

2002-01-01

381

2-Dimentional Islanding and Sublimation of Dodecane on a Au(111) Surface: An Investigation using Helium Atom Reflectivity  

Microsoft Academic Search

Dodecane is deposited at sub-monolayer coverages onto a Au(111) surface, and the 2-dimensional gas crystallizes into islands, which can again sublimate to a 2-dimensional gas at higher substrate temperatures. We observe island formation and subsequent sublimation, using low energy helium reflectivity. When the dodecane molecules are deposited onto the gold surface, the specular intensity decreases as a result of loss

Timothy Arlen; Craig Webster; Peter Schwartz

2005-01-01

382

The mobility of potassium ions in helium  

NASA Astrophysics Data System (ADS)

The mobility of 0953-4075/29/10/006/img5 ions in helium has been measured at 76.8 K and E/N values up to 15 Td, and at room temperature up to 300 Td. The experimental scatter is of the order of 0.1 - 0.2%. The experimental mobilities are compared with values calculated from a new and accurate ab initio potential (Røeggen et al 1996). The agreement between experimental and theoretical values is significantly better than in earlier studies of this ion - atom system, but some unexplained discrepancies of the order of 1% still exist.

Skullerud, H. R.; Elford, M. T.; Røeggen, I.

1996-05-01

383

Near-threshold emission of electrons during grazing scattering of keV Ne atoms from an Al(111) surface  

SciTech Connect

The number of electrons emitted during grazing scattering of Ne atoms with kilo-electron-volt energies from an Al(111) surface is recorded in coincidence with the energy loss of scattered projectiles. Irrespective of the total projectile energies used, we observe a pronounced increase of total electron emission yields when the energy for motion normal to the surface exceeds about 25 eV. Based on energy loss spectra and classical computer simulations of projectile trajectories we attribute electron emission under these scattering conditions to a promotion mechanism in binary collisions between Ne and Al target atoms resulting in single and double excitations of projectiles.

Matulevich, Y.; Lederer, S.; Winter, H. [Institut fuer Physik, Humboldt Universitaet zu Berlin, Brook-Taylor-Str. 6, D-12489 Berlin (Germany)

2005-01-15

384

Convergent perturbative solution to the attractive corrugated hard wall model of atom--surface scattering  

SciTech Connect

The attractive corrugated wall model of atom--surface scattering is solved by an expansion method. The approach is similar to a Born expansion; however, projection operators must be introduced in order to obtain a convergent series near resonances. Diffraction intensities are calculated for He--LiF(001) and He--NaF(001) scattering. Good agreement with experimental intensities is obtained when the series is taken to convergence. In some cases (He--NaF) this requires calculation to as high as 12th order in the expansion parameter. At this order as many as 169 channels are included in the calculation. Preliminary estimates for the values for v/sub 01/ and v/sub 11/ for the He--NaF system have been found by comparison of theoretical and experimental intensities.

Wolfe-Brannon, K.; Weare, J.H.

1982-07-01

385

Theory of negative-ion conversion of neutral atoms in grazing scattering from alkali halide surfaces  

NASA Astrophysics Data System (ADS)

The theoretical approach proposed by Borisov et al. [Phys. Rev. Lett. 77, 1893 (1996)] to treat negative-ion conversion of neutral atoms at ionic crystal surfaces is described in detail. Due to the localization of the valence-band electrons at the anionic sites of the crystal, the conversion process is viewed as a result of successive binary collisions between the projectile and the negatively charged sites at the surface. Parameter-free calculations of F- formation in grazing scattering from LiF(100) and KI(100) are performed using a model in which all sites of the crystal lattice but one, the active site, are represented by eventually polarizable point charges. Parallel velocity thresholds for negative-ion formation, relative efficiency of the negative-ion formation for LiF and KI crystals, and dependences of this efficiency on the scattering angle correspond well to the experimental results.

Borisov, A. G.; Sidis, V.

1997-10-01

386

Positron and electron scattering on atoms and molecules-modified effective range theory revisited  

NASA Astrophysics Data System (ADS)

New experiments on the very low-energy electron and positron scattering allow to verify the old question on applicability of modified effective range theory (MERT). We perform it using an analytical solution of the Schrödinger equation with the long-range polarization potential. In this work two atomic (He, Ar) and molecular (H2, CH4) target are studied using this approach. Total cross sections were used for obtaining parameters characterizing the scattering phase shifts related to the short-range interaction potential; differential cross sections were used for comparison. Differently from previous works, we conclude that MERT with few (2-3) partial waves applies very well up to energies of few eV in all four targets studied. For positrons, reliable experimental data indicate occurrence of zeros in the s-wave phase shifts for all four targets. This should be recognized as Ramsauer-Townsend minima.

Fedus, K.; Idziaszek, Z.; Karwasz, G. P.

2013-10-01

387

Quantum trajectories in atom-surface scattering with single adsorbates: the role of quantum vortices.  

PubMed

In this work, a full quantum study of the scattering of He atoms off single CO molecules, adsorbed onto the Pt(111) surface, is presented within the formalism of quantum trajectories provided by Bohmian mechanics. By means of this theory, it is shown that the underlying dynamics is strongly dominated by the existence of a transient vortitial trapping with measurable effects on the whole diffraction pattern. This kind of trapping emphasizes the key role played by quantum vortices in this scattering. Moreover, an analysis of the surface rainbow effect caused by the local corrugation that the CO molecule induces on the surface, and its manifestation in the corresponding intensity pattern, is also presented and discussed. PMID:15267811

Sanz, A S; Borondo, F; Miret-Artés, S

2004-05-01

388

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

389

Quantum scattering of distinguishable bosons using an ultracold-atom collider  

SciTech Connect

We describe an implementation of a magnetic collider for investigating cold collisions between ultracold atomic clouds in different spin states, and we use this to study scattering involving both even- and odd-order partial waves. Our method relies on the axial asymmetry of a double-well magnetic trap to selectively prepare the spin state in each cloud. We measure the energy dependence of s, p, and d partial-wave phase shifts in collisions up to 300 {mu}K between {sup 87}Rb atoms in the 5S{sub 1/2},F=1,m{sub F}=-1 and 5S{sub 1/2},F=2,m{sub F}=1 states.

Mellish, Angela S.; Wilson, Andrew C. [Department of Physics, University of Otago, Dunedin (New Zealand); Kjaergaard, Niels [Department of Physics, University of Otago, Dunedin (New Zealand); Niels Bohr Institute, University of Copenhagen, Copenhagen (Denmark); QUANTOP, Danish National Research Foundation Center for Quantum Optics, Copenhagen (Denmark); Julienne, Paul S. [National Institute of Standards and Technology, 100 Bureau Drive, Stop 8423, Gaithersburg, Maryland 20899-8423 (United States)

2007-02-15

390

Static atomic displacements in Cu&barbelow;-Mn measured with diffuse x-ray scattering  

NASA Astrophysics Data System (ADS)

Diffuse x-ray scattering of a Cu- 17.2at.% Mn single crystal, which was aged at 483 K for 2 weeks, was taken at three energies, namely, 6526, 8969, and 8909 eV, which were suited for an evaluation by the 3? technique. The values of the species-dependent static atomic displacements closely agree with those of a Georgopoulos-Cohen evaluation, which also uses the three data sets. Nearest-neighbor displacements are dominant and with ˜0.038Å largest among Cu-Mn pairs. A tendency is noted for lattice expansion between those elements (equal or unequal pairs) that are preferred in site occupancy over a random arrangement because of local atomic order.

Schönfeld, B.; Roelofs, H.; Kostorz, G.; Robertson, J. L.; Zschack, P.; Ice, G. E.

2008-04-01

391

PROPERTIES OF THE DIFFUSE NEUTRAL HELIUM IN THE INNER HELIOSPHERE  

SciTech Connect

Sensitive SOLARC imaging spectropolarimetric observations from Haleakala reveal a diffuse coronal surface brightness in the He I 1083 nm line. A series of observations suggests that this signal originates from an 'inner source' of neutral helium atoms in the solar corona. Here, we explore the possibility that this cold coronal component originates from helium ions that are neutralized by the near-Sun dust and subsequently excited to the metastable 1s2s {sup 3} S state, which then scatters photons from the solar disk. This picture suggests a deficit of coronal dust inside about 2-4 R{sub sun} in order to account for both the flat radial brightness distribution and the small velocity line width of the observations. We find a strong correlation between the polarized He brightness and coronal white light brightness that supports the argument that electronic collisional excitation of the metastable helium triplet level is responsible for our polarization signal.

Moise, E.; Raymond, J.; Kuhn, J. R. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)

2010-10-20

392

Plasma screening effects on the Ramsauer minima for the polarization electron-atom scattering in weakly coupled plasmas  

NASA Astrophysics Data System (ADS)

The plasma screening effects on the Ramsauer phenomena for the polarization electron-atom scattering in weakly coupled plasmas are investigated by using the phase theory. The Fermi pseudopotential and Buckingham potential are employed to obtain the scattering phase shift and scattering cross section as functions of the scattering length, polarizability, collision energy, and Debye radius. It is shown that the Ramsauer energy for the Ramsauer minimum is found to be increased with decreasing Debye radius. It is also found that the plasma screening effect enhances the Ramsauer minimum of the electron-atom scattering cross section below the Ramsauer energy. However, the plasma screening effect suppresses the Ramsauer minimum above the Ramsauer energy.

Na, Sang-Chul; Jung, Young-Dae

2010-03-01

393

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

2013-07-02

394

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

395

Laser-assisted electron - atom resonance scattering and laser-induced resonance interference  

NASA Astrophysics Data System (ADS)

The weak-field soft-photon theory for free - free transitions is generalized to include atomic potentials which support resonances. The present formulation is not restricted by geometrical constraints. In particular, it may be applied in situations where the laser polarization is perpendicular to the electron momentum transfer. In this special geometry, former theories have predicted that laser-assisted electron - atom scattering resonances should appear as pure Breit - Wigner peaks on a vanishingly small background. The present theory includes higher-order terms and shows that the background amplitude may compete with the resonance part to produce characteristic Fano-type resonance signals. Considering tunable radiation fields it is shown that the laser may induce resonance-interference effects. The shapes of overlapping resonances are in general determined by an interplay between resonance scattering amplitudes and a laser-controlled contrast parameter. Characteristic spectral features in the laser-induced overlap between fine-structure components are uniquely related to the distinctly different interference properties of direct and spin-flip amplitudes.

Bojer Madsen, Lars; Taulbjerg, Knud

1997-03-01

396

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. 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

397

A quantum mechanical theory for the scattering of low-energy atoms from incommensurate crystal surface layers  

SciTech Connect

This dissertation reports a new theory for the scattering of low energy atoms off crystal surfaces. First, existence of the Moller wave operators is proven for the general case of inelastic scattering from both ordered and disordered crystal slabs. Next, a general time-independent inelastic scattering theory is developed, based on the use of the integral form of the Lippmann-Schwinger equation. This theory is then specialized to elastic scattering from crystal monolayers with multiple commensurate or incommensurate surface periodicities, and a practical numerical implementation of the elastic theory is developed. Finally, extensive validation of the scattering theory and its numerical implementation is presented, including a successful comparison to experimental results from the scattering of He from LiF(001).

Prentice, J.K.

1992-01-01

398

Scattering of electrons by atomic hydrogen at intermediate energies: Elastic scattering and n = 2 excitation from 12 to 54 eV  

SciTech Connect

Cross sections for elastic scattering and excitation of the n = 2 states of atomic hydrogen by electrons are computed for incident energies in the range from 12 to 54 eV. The calculations are based primarily on an 11-state expansion including seven pseudostates. Pseudothresholds and pseudoresonances are suppressed by appropriate averaging.

Callaway, J.

1985-08-01

399

Negative ion resonance measurements in the autoionizing region of helium measured across the complete angular scattering range (0°-180°)  

NASA Astrophysics Data System (ADS)

Excitation function measurements for the decay of the 2s22p 2P and 2s2p2 2D triply excited negative ion resonances in helium to singly excited n = 2 states have been measured. These excitation functions have been determined across the complete angular range (0-180°) using a magnetic angle changer with a soft-iron core. The convergent close-coupling method has been used to calculate the cross sections, with the underlying complexity of the problem not yet being able to be fully resolved. Agreement between the present experimental data and previous experimental data is good, with these excitation functions confirming the presence of an unusual (2s22p)2P resonance behaviour in the 21S channel at 90°, where this would not usually be expected. Resonance energy and width values have been obtained, with a mean energy for the (2s22p)2P resonance of 57.20 ± 0.08 eV and a mean width of 73 ± 20 meV, and a mean energy of the (2s2p2)2D resonance of 58.30 ± 0.08 eV and a mean width of 59 ± 27 meV. Resonant cross section and ?2 values have been calculated across the angular range for the first time, providing angular distribution data on decay propensities for both resonances.

Ward, R.; Cubric, D.; Bowring, N.; King, G. C.; Read, F. H.; Fursa, D. V.; Bray, I.

2013-02-01

400

Photoabsorption profile and satellite features of the potassium 4s?4p transition perturbed by ground-state helium atoms  

NASA Astrophysics Data System (ADS)

Quantal calculations are performed to determine the absorption profile of the broadened potassium resonance line 4p?4s in its far wings provoked by helium perturbers. First, the X2?+, A2?, and B2?+ potentials, as well as the transition dipole moments, are carefully computed through ab initio methods, based on state-averaged complete active space self-consistent field multireference configuration interaction (SA-CASSCF-MRCI) calculations involving the Davidson and basis-set superposition error (BSSE) corrections. The data are then used to generate the KHe photoabsorption spectra and to examine their behavior with temperature. The theoretical profile is dominated by the free-free transitions and exhibits, in the vicinity of the wavelength position of 693 nm, a satellite peak in the blue wing attributed to the B?X transitions. The results are compared with previous theoretical and experimental investigations and, in general, good agreement is found.

Boutarfa, H.; Alioua, K.; Bouledroua, M.; Allouche, A.-R.; Aubert-Frécon, M.

2012-11-01

401

ATOMIC AND MOLECULAR PHYSICS: The effect of dynamical screening on helium (e, 2e) fully differential cross-sections  

NASA Astrophysics Data System (ADS)

This paper presents the fully differential cross sections (FDCS) for 102eV electron impact single ionization of helium for both the coplanar and perpendicular plane asymmetric geometries within the framework of dynamically screened three-Coulomb-wave theory. Comparisons are made with the experimental data and those of the three-Coulomb wave function model and second-order distorted-wave Born method. The angular distribution and relative heights of the present FDCS is found to be in very good agreement with the experimental data in the perpendicular plane geometry. It is shown that dynamical screening effects are significant in this geometry. Three-body coupling is expected to be weak in the coplanar geometry, although the precise absolute value of the cross section is still sensitive to the interaction details.

Sun, Shi-Yan; Jia, Xiang-Fu; Miao, Xiang-Yang; Zhang, Jun-Feng; Xie, Yi; Li, Xiong-Wei; Shi, Wen-Qiang

2009-07-01

402

Back-scattered detection provides atomic-scale localization precision, stability, and registration in 3D.  

PubMed

State-of-the-art microscopy techniques (e.g., atomic force microscopy, scanning-tunneling microscopy, and optical tweezers) are sensitive to atomic-scale (100 pm) displacements. Yet, sample drift limits the ultimate potential of many of these techniques. We demonstrate a general solution for sample control in 3D using back-scattered detection (BSD) in both air and water. BSD off a silicon disk fabricated on a cover slip enabled 19 pm lateral localization precision (Deltaf = 0.1-50 Hz) with low crosstalk between axes (atomic-scale stabilization (88, 79, and 98 pm, in x, y, and z, respectively; Deltaf = 0.1-50 Hz) and registration ( approximately 50 pm (rms), N = 14, Deltat = 90 s) of a sample in 3D that allows for stabilized scanning with uniform steps using low laser power (1 mW). Thus, BSD provides a precise method to locally measure and thereby actively control sample position for diverse applications, especially those with limited optical access such as scanning probe microscopy, and magnetic tweezers. PMID:19550612

Carter, Ashley R; King, Gavin M; Perkins, Thomas T

2007-10-01

403

Hartree-Fock Values of Coupling Constants, Polarizabilities, Susceptibilities and Radii for the Neutral Atoms, Helium to Nobelium  

Microsoft Academic Search

Presented here are the values, obtained with Hartree-Fock functions, for ; the spin --orbit, magnetic-dipole, and electric-quadrupole coupling constants, ; electric-dipole polarizabilities, magnetic excited states of the neutral atoms ; from He to No. (auth);

S. Fraga; J. Karwowski; K. M. S. Saxena

1973-01-01

404

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

405

LETTER TO THE EDITOR: Possible role of double scattering in electron - atom scattering in a laser field  

NASA Astrophysics Data System (ADS)

By considering observations of double-scattering effects in the excitation of the 0953-4075/29/22/004/img5 level of He, gas density values are estimated for the laser-assisted elastic scattering experiments of Wallbank and Holmes (1993, 1994a, b) for which the Kroll - Watson approximation appears to fail. Using comparable densities for He and lower densities for Ar, and assuming the Kroll - Watson approximation for single-scattering events, differential cross sections are calculated including double scattering for laser-assisted scattering for a range of energies and scattering angles. Comparison with the observed values shows that double-scattering effects can give a semi-quantitative explanation of the apparent breakdown of the Kroll - Watson approximation in both He and Ar.

Rabadán, I.; Méndez, L.; Dickinson, A. S.

1996-11-01

406

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

407

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

NASA Astrophysics Data System (ADS)

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 the validity of the Kohn-Sham model and the locality theorem in this case. The ionization-potential theorem, stating that the Kohn-Sham energy eigenvalue of the outermost electron orbital agrees with the negative of the corresponding many-body ionization energy (including electronic relaxation), is verified in this case to nine digits. A Kohn-Sham potential is also constructed to reproduce the Hartree-Fock density of the same state, and the Kohn-Sham 2s eigenvalue is then found to agree with the same accuracy with the corresponding Hartree-Fock eigenvalue. This is consistent with the fact that in this model the energy eigenvalue equals the negative of the ionization energy without relaxation due to Koopmans' theorem. Related calculations have been performed previously, particularly for atomic and molecular ground states, but none of matching accuracy. In the computations presented here there is no conflict between the locality of the Kohn-Sham potential and the exclusion principle, as claimed by Nesbet (Phys. Rev. A, 58, R12 (1998)).

Salomonson, S.; Moller, F.; Lindgren, I.

2005-01-01

408

Stokes parameters of resonance lines scattered by a moving, magnetic medium. Theory of the two-level atom  

NASA Astrophysics Data System (ADS)

The aim of the present work is to present theoretical results on the Stokes parameters of a resonance spectral line, scattered by moving atoms (or ions) in the presence of a local magnetic field. We assume that the scattered line is sensitive to the Hanle effect due to the magnetic field and also to Doppler redistribution due to the atomic motions. The present theory is developed for a two-level atom, in the framework of the density matrix formalism Blum (1981). Analogous results given in Sahal-Bréchot et al. (1986) for the magnetic-field effect alone, and in Sahal-Bréchot et al. (\\cite{Sahal98}) for the velocity-field effect alone, can be obtained from our theory by cancelling in the equations, respectively, the velocity field or the magnetic field. The results of our theory are general and can be used for astrophysical studies concerning the Hanle effect and the Doppler redistribution effect on the linear polarization parameters of the scattered radiation. They can be used particularly to interpret linear polarization of coronal spectral lines to get a complete determination of vectorial quantities such as the coronal magnetic field and the solar wind velocity field vectors. As an application, the atomic velocity field distribution is supposed to be Maxwellian with a drift velocity field vector. This latter describes the macroscopic motion of the scattering atoms. In the solar corona, it can be assimilated into the solar wind velocity field vector.

Raouafi, N.-E.

2002-05-01

409

Detecting antiferromagnetism of atoms in an optical lattice via optical Bragg scattering  

NASA Astrophysics Data System (ADS)

Antiferromagnetism of ultracold fermions in an optical lattice can be detected by Bragg diffraction of light, in analogy to the diffraction of neutrons from solid-state materials. A finite sublattice magnetization will lead to a Bragg peak from the ((1)/(2)(1)/(2)(1)/(2)) crystal plane with an intensity depending on details of the atomic states, the frequency and polarization of the probe beam, the direction and magnitude of the sublattice magnetization, and the finite optical density of the sample. Accounting for these effects we make quantitative predictions about the scattering intensity and find that with experimentally feasible parameters the signal can be readily measured with a CCD camera or a photodiode and used to detect antiferromagnetic order.

Corcovilos, T. A.; Baur, S. K.; Hitchcock, J. M.; Mueller, E. J.; Hulet, R. G.

2010-01-01

410

The s-wave ?d scattering length from ?d atom using effective field theory  

NASA Astrophysics Data System (ADS)

The ?-d atom strong energy-level shift in the 1s state is derived by using the effective field theory. Taking into account the large value of radius of pionic deuterium and short radius of strong interaction between pion and deuteron we have considered deuteron as a particle described by a vector field. Pion is described by a scalar field. To obtain non-relativistic Hamiltonian for ?d system Foldy-Wouthuysen transformation has been derived for the vector field. The strong interaction between pion and deuteron has been taken of zero-range. We have found the Deser type formula for relation between the strong energy-level shift and the s-wave ?d scattering length.

Irgaziev, B. F.; Fayzullaev, B. A.

411

Doubly differential spectra of scattered protons in ionization of atomic hydrogen  

SciTech Connect

We have measured and calculated doubly differential cross sections for ionization of atomic hydrogen using 75-keV proton impact for fixed projectile energy losses as a function of scattering angle. This collision system represents a pure three-body system and thus offers an accurate test of the theoretical description of the few-body dynamics without any complications presented by electron correlation in many-electron targets. Comparison between experiment and several theoretical models reveals that the projectile-target nucleus interaction is best described by the operator of a second-order term of the transition amplitude. Higher-order contributions in the projectile-electron interaction, on the other hand, are more appropriately accounted for in the final-state wave function.

Schulz, M.; Laforge, A. C.; Egodapitiya, K. N.; Alexander, J. S. [Department of Physics and LAMOR, Missouri University of Science and Technology, Rolla, Missouri 65409 (United States); Hasan, A. [Department of Physics, UAE University, Post Office Box 17551, Alain, Abu Dhabi (United Arab Emirates); Ciappina, M. F. [Institute of High Performance Computing, 1 Fusionopolis Way, 16-16, Connexis 138632 (Singapore); Roy, A. C. [School of Mathematical Sciences, Ramakrishna Mission, Vivekananda University, Belur Math 711202 (India); Dey, R. [Max Planck Institut fuer Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching (Germany); Samolov, A.; Godunov, A. L. [Department of Physics, Old Dominion University, Norfolk, Virginia 23529 (United States)

2010-05-15

412

Detecting antiferromagnetism of atoms in an optical lattice via optical Bragg scattering  

SciTech Connect

Antiferromagnetism of ultracold fermions in an optical lattice can be detected by Bragg diffraction of light, in analogy to the diffraction of neutrons from solid-state materials. A finite sublattice magnetization will lead to a Bragg peak from the ((1/2)(1/2)(1/2)) crystal plane with an intensity depending on details of the atomic states, the frequency and polarization of the probe beam, the direction and magnitude of the sublattice magnetization, and the finite optical density of the sample. Accounting for these effects we make quantitative predictions about the scattering intensity and find that with experimentally feasible parameters the signal can be readily measured with a CCD camera or a photodiode and used to detect antiferromagnetic order.

Corcovilos, T. A.; Hitchcock, J. M.; Hulet, R. G. [Department of Physics and Astronomy, and Rice Quantum Institute, Rice University, Houston, Texas 77005 (United States); Baur, S. K.; Mueller, E. J. [Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853 (United States)

2010-01-15

413

Time-dependent approach to transport and scattering in atomic and mesoscopic physics  

SciTech Connect

Transport and scattering phenomena in open quantum-systems with a continuous energy spectrum are conveniently solved using the time-dependent Schroedinger equation. In the time-dependent picture, the evolution of an initially localized wave-packet reveals the eigenstates and eigenvalues of the system under consideration. We discuss applications of the wave-packet method in atomic, molecular, and mesoscopic systems and point out specific advantages of the time-dependent approach. In connection with the familiar initial value formulation of classical mechanics, an intuitive interpretation of transport emerges. For interacting many-particle systems, we discuss the efficient calculation of the self-consistent classical transport in the presence of a magnetic field.

Kramer, Tobias [Institut fuer Theoretische Physik, Universitaet Regensburg, 93040 Regensburg (Germany)

2011-03-21

414

Total cross sections for electrons scattering from simple molecules containing the larger atom sulfur at 30 5000eV  

Microsoft Academic Search

A complex optical model potential modified by the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds, is employed to calculate the total cross sections for electrons scattering from simple molecules (SO2, H2S, OCS, CS2 and SO3) containing the larger atom, sulfur, at 30-5000eV by using the additivity rule model at Hartree-Fock level. The quantitative

De-Heng Shi; Yu-Fang Liu; Jin-Feng Sun; Xiang-Dong Yang; Zun-Lue Zhu

2005-01-01

415

Measurements of total and positronium formation cross sections for positrons scattered by Cs atoms^*  

NASA Astrophysics Data System (ADS)

Total cross sections for positrons scattered by Cs atoms have been measured from 1 to 60 eV using a beam-transmission technique and are in reasonable agreement shape-wise with the theoretical calculations by Kernoghan et al.^1, but are about 25% smaller. Both upper and lower limits on positronium (Ps) formation cross sections (Q_ Ps's) have been measured from 0.5 to 25 eV. The upper limit measured using a beam-transmission technique is in reasonable agreement with the theoretical results^1 above 5 eV. A lower limit is obtained by detecting two 511 keV gamma rays in coincidence which are produced by para-Ps decays and by ortho-Ps interactions with the walls of the scattering cell. Our lower limits are in reasonable agreement shape-wise with the theoretical predictions^1, but are significantly lower. We also measure and analyze a 2 of 3? signal by detecting coincident gamma rays in the energy range 300-460 keV produced by ortho-Ps decays. This contribution may eventually allow us to measure the total Q_Ps. ^*Research supported by NSF Grant PHY 99-88093. ^1 A.A. Kernoghan, M.T. McAlinden, H.R.J. Walters, J. Phys. B 29, 3971 (1996).

Surdutovich, E.; Kauppila, W. E.; Miller, E. G.; Price, K.; Stein, T. S.

2003-05-01

416

Assessment of General Atomics accelerator transmutation of waste concept based on gas-turbine-modular helium cooled reactor technology  

Microsoft Academic Search

An assessment has been performed for an Accelerator Transmutation of Waste (ATW) concept based on the use of the high temperature gas reactor technology. The concept has been proposed by General Atomics for the ATW system. The assessment was jointly conducted at Argonne National Laboratory (ANL) and Los Alamos national laboratory to assess and to define the potential candidates for

Y. Gohar; T. A. Taiwo; J. E. Cahalan; P. J. Finck

2001-01-01

417

Helium cryogenics  

Microsoft Academic Search

The goal of this work is to bridge the gap between physics and engineering aspects of helium fluids to encourage their use and enhance their usefulness in low-temperature systems. Topics covered include thermodynamic laws, electrical and thermal conductivities, spin systems, virial expansion, liquid He I, transport properties, density of helium as a quantum fluid, vortices and turbulence in He II,

Van Sciver

1986-01-01

418

Comparison of Theoretical Doubly Differential Cross Sections for Atomic Compton Scattering with Experimantal Data  

NASA Astrophysics Data System (ADS)

Doubly differential cross sections (DDCS) for inelastic photon atom scattering that result in the ejection of a single electron are calculated for selected atoms at various incident photon energies using three different theories. One theory utilizes the relativistic second order S-matrix formalism, the other two are the relativistic and nonrelativistic impulse approximation (RIA and NRIA). All three calculations are done within the independent particle approximation (IPA). DDCS for Copper K-shell ionization with incident photon energy E_in=60 keV, obtained from S-matrix theory, were found to be in good agreement with the experimental values of J. Laukkanen et. al. [1] for all final electron energies. Agreement was better than with RIA and NRIA calculations. Good agreement has also been found for K-shell DDCS with the experimental results of Thanomngam et. al. [2] for Ta and Pb at 320 kev and for Ta at 662 keV. However the DDCS reported for Pb at 662 kev were at least an order of magnitude greater than our theoretical results. We note that such results for Pb at 662 keV, appear to be inconsistent with the earlier singly differential cross sections of Wolf et. al. [3]. In comparisons between S-matrix, RIA and NRIA DDCS for several atoms, it was found that NRIA results were in better agreement with S-matrix and experimental than RIA for the low final photon energy side of the Compton peak. 1. J. Laukkanen, K. Hamalainen and S. Manninen, J. Phys. Condensed Matter 8 2153 (1996). 2. P. Thanomngam and P. N. Johnston, Poster presented at ISRP-9 (2003), submitted for publication in Rad. Phys. And Chem. 3. W. Wolf, H. E. Wolf, L. f. S. Coelho, S. deBarrus, and J. Eichler, Phys. Rev. A 40 3543 (1991).

Lajohn, L. A.; Pratt, R. H.

2004-05-01

419

Opto-mechanical estimation of micro-trap with cold atoms via nonlinear stimulated Raman scattering spectrum  

NASA Astrophysics Data System (ADS)

High-gain resonant nonlinear Raman spectrum on trapped cold atoms within a high-finesse optical cavity is simply explained under a nonlinear opto-mechanical mechanism, and a proposal using it to detect frequency of micro-trap is presented. The enhancement of this scattering spectrum is due to a coherent Raman conversion between two different cavity modes mediated by collective vibrations of atoms with nonlinear opto-mechanical couplings. The physical conditions of this technique are roughly estimated on Rubidium atoms, and a simple quantum analysis as well as a multi-body semiclassical simulation on this nonlinear Raman spectrum is conducted.

Zhang, Lin

2013-05-01

420

Scattering of electrons by atomic hydrogen at intermediate energies: Total cross section from 12 to 54 eV  

SciTech Connect

The total cross section for electrons scattered by ground-state hydrogen atoms has been calculated for incident energies from 12 to 54 eV. The calculations are based primarily on an 11-state expansion including seven pseudostates. The cross section for all inelastic processes is also reported.

Callaway, J.; Oza, D.H.

1986-08-01

421

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

422

FAST TRACK COMMUNICATION: Analytic description of the high-energy plateau in laser-assisted electron-atom scattering  

Microsoft Academic Search

A closed-form analytic formula describing plateau features in laser-assisted electron-atom scattering (LAES) is derived quantum mechanically in the low-frequency limit. The presented formula confirms the classical rescattering scenario for LAES and provides an analytic explanation for oscillatory structures in the high-energy part of LAES spectra.

A. V. Flegel; M. V. Frolov; N. L. Manakov; A. N. Zheltukhin

2009-01-01

423

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

424

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

425

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

NASA Astrophysics Data System (ADS)

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 of the outermost electron orbital agrees with the corresponding ionization energy with extreme accuracy. The procedure is also applied to the Hartree-Fock density of the 1s2s3S state, and the Kohn-Sham eigenvalue of the 2s orbital is found to agree very well with the corresponding Hartree-Fock eigenvalue, which is the negative of the ionization energy in this model due to Koopmans' theorem. The results clearly demonstrate that there is no conflict between the locality of the Kohn-Sham potential and the exclusion principle, as claimed by Nesbet. Content:text/plain; charset="UTF-8"

Lindgren, I.; Salomonson, S.; Möller, F.

426

Helium cryogenics  

SciTech Connect

The goal of this work is to bridge the gap between physics and engineering aspects of helium fluids to encourage their use and enhance their usefulness in low-temperature systems. Topics covered include thermodynamic laws, electrical and thermal conductivities, spin systems, virial expansion, liquid He I, transport properties, density of helium as a quantum fluid, vortices and turbulence in He II, Kapitza conductance, acoustic mismatch theory, nucleate boiling heta transfer, surface effects, general considerations of internal flow, ideal liquefaction, stirling cycle, and the helium-3 isotope.

Van Sciver, S.W.

1986-01-01

427

Electron Attachment Reaction Rates in 2D Atomic Hydrogen-Electron Mixed System on Liquid Helium Surface  

SciTech Connect

We have measured the temperature dependence of the electron attachment reaction rate of atomic hydrogen (H) on a liquid 4He surface in applied magnetic fields of 0-5 T at 0.2-0.6 K. The measured surface state electron (SSE) losses are faster at lower temperatures for a given magnetic field. This behavior can be qualitatively understood, since the surface coverage of adsorbed H is large at low temperature and the collisions between H and SSE are frequent. However, the reaction is faster than expected based on the collision frequency argument. The measured reaction rate coefficient Ke is strongly temperature dependent. We observe that, as the temperature is lowered, Ke increases by several orders of magnitude. This indicates that some additional effect enhances electron attachment at low temperature. We discuss a possible reaction mechanism between H and SSE.

Arai, Toshikazu [LTM Center, Kyoto University, Kitashirakawa-Oiwakecho, Kyoto 606-8502 (Japan); Mitsui, Tomoyuki; Yayama, Hideki [Department of Physics, Kyushu University, 4-2-1 Ropponmatsu, Fukuoka 810-8560 (Japan)

2006-09-07

428

Helium cryopumping  

Microsoft Academic Search

Dependences of sticking coefficient on amount of the absorbed helium and a sorbent temperature and dependences of critical and limiting sorption capacities on a sorbent temperature have been obtained.

L. S. Gurevich; V. V. Petrovsky; A. V. Pustovoit

1990-01-01

429

Fully relativistic R-matrix study of the interaction between a slow electron and atomic iodine: Scattering and photodetachment  

SciTech Connect

An 11-state close-coupling calculation for the interaction between a slow electron and atomic iodine is carried out using the fully relativistic R-matrix method. The cross sections are presented for the photodetachment of a negative atomic iodine ion and for electron scattering by neutral atomic iodine from the threshold to 8 eV. The electron affinity for negative iodine is obtained as 2.958 eV. For the photodetachment process, we get fairly good agreement with experimental results for the distinct spin-orbit split between the 5p{sub 3/2} and 5p{sub 1/2} thresholds due to the relativistic effect as well as for the cross sections near the thresholds. The electron scattering cross sections display energy dependence similar to that for electron scattering by heavy rare-gas atoms, i.e., a Ramsauer-Townsend minimum well at a lower energy and a broad peak after the well.

Wu Jianhua; Yuan Jianmin [Department of Physics, National University of Defense Technology, Changsha 410073 (China)

2007-08-15

430

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

431

Surface dynamics of NaCl(001) by inelastic He atom scattering  

SciTech Connect

The relatively simple structure of alkali halide crystals has made these materials the paradigm for the understanding of the dynamics of ionic insulators. We have employed a time-of-flight (TOF) technique to determine the energy loss/gain due to single phonon creation/annihilation events in the scattering of He atoms from the NaCl(001) surface. From these data the surface dispersion curves over the {bar {Gamma}}{ital {bar M}} region of the surface Brillouin zone have been constructed. The results compare favorably with both the slab dynamics and the Green's function calculations reported for this crystal, and with previous measurements in the {l angle}100{r angle} direction. Of particular interest, we report the first evidence for the crossing mode in the {l angle}100{r angle} direction, which had been predicted for NaCl. Additionally, we have employed the TOF technique to examine the Debye-Waller attenuation of the {ital elastic} (specular) intensity and the relative height of an {ital inelastic} multiphonon foot'' at the base of the specular beam as a function of the crystal surface temperature (120--670 K).

Safron, S.A.; Brug, W.P.; Chern, G.; Duan, J.; Skofronick, J.G. (Departments of Chemistry, The Florida State University, Tallahassee, FL (USA) Department of Physics, The Florida State University, Tallahassee, FL (USA) MARTECH, The Florida State University, Tallahassee, FL (USA)); Manson, J.R. (Department of Physics and Astronomy, Clemson University, Clemson, SC (USA))

1990-05-01

432

Surface phonon modes of the NaI(001) crystal surface by inelastic He atom scattering  

SciTech Connect

The present theoretical treatment of the surface dynamics of ionic insulators employs the shell model with parameters obtained from bulk materials. The approach has been generally very successful in comparisons with experiment. However, most of the experimental surface dynamics work has been on the low-mass alkali halides with very little effort on higher energy modes or on the heavier alkali halides, where effects from relaxation might be important. The work of this paper explores these latter two conditions. Inelastic scattering of He atoms from the {l angle}110{r angle}NaI(001) surface has been used to obtain the acoustic {ital S}{sub 1} Rayleigh mode, the {ital S}{sub 6} longitudinal mode, and the {ital S}{sub 8} crossing mode, however, no gap {ital S}{sub 4} optical mode was seen. The results compare favorably with reported theoretical models employing both slab calculations and the Green's function method thus indicating that bulk parameters and the shell model go a long way in explaining most of the observations.

Brug, W.P.; Chern, G.; Duan, J.; Safron, S.A.; Skofronick, J.G. (MARTECH, The Florida State University, Tallahassee, FL (USA) Department of Physics, The Florida State University, Tallahassee, FL (USA) Department of Chemistry, The Florida State University, Tallahassee, FL (USA)); Benedek, G. (Dipartimento di Fisica dell' Universita', Via Celoria 16, I-20133, Milano (Italy))

1990-05-01

433

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

434

Laser-assisted elastic electron-atom collisions  

Microsoft Academic Search

We report experimental measurements of electron spectra resulting from the scattering of 9.5-eV electrons by helium atoms through an angle of 9° in the presence of a high-intensity (~108 W cm-2) CO2 laser. The intensities of the additional peaks which occur separated from the elastic scattering peak by multiples of the photon energy in the presence of the laser are

B. Wallbank; J. K. Holmes

1993-01-01

435

Comment on ``Suppression of inelastic bound-state resonance effects by the dimensionality of an atom-surface scattering event''  

NASA Astrophysics Data System (ADS)

The bound-state-plus-two-phonon resonances in scattering of atoms by surface phonons including phonon-assisted parallel momentum transfer are reconsidered using improved energy resolution and the phonon state basis. Our results agree qualitatively concerning the general dimensional trends but differ in physical conclusions. (1) The peak height of resonances above the exponentiated Born approximation) is two to four times bigger in our results. (2) Besides the peaks in the Debye Waller factor (DWF) we consider the corresponding dips in inelastic scattering intensities. In contrast to the peaks in the DWF these dips may be observable for He and will be so for Ne.

Brenig, W.

2007-01-01

436

Experimental studies on kaonic atoms at DA{Phi}NE  

SciTech Connect

We have measured the K-series x-rays of kaonic hydrogen atoms to determine the strong-interaction energy-level shift and width of the 1s atomic state with significant improvements over the previous experiments. The measurement offers a unique possibility to precisely determine the complex K{sup -}p S-wave scattering length. We have also measured kaonic x-ray spectra with several gaseous targets : deuterium, helium-3 and helium-4. In this paper, we present an overview of this experiment and preliminary spectra of those kaonic x-rays.

Okada, S.; Bazzi, M.; Berucci, C.; Bragadireanu, A. M.; Clozza, A.; Corradi, G.; Curceanu, C.; D'Uffizi, A.; Guaraldo, C.; Iliescu, M.; Sandri, P. Levi; Lucherini, V.; Pietreanu, D.; Piscicchia, K.; Lener, M. Poli; Rizzo, A.; Vidal, A. Romero; Sbardella, E.; Scordo, A.; Sirghi, D. L. [INFN, Laboratori Nazionali di Frascati, Frascati, Roma (Italy)

2011-10-21

437

Phonon--phonon interactions in liquid helium  

Microsoft Academic Search

This is a short review of recent experimental and theoretical studies of phonon interactions in superfluid helium. Phonon--phonon scattering in helium is strongly influenced by the conservation laws and by the peculiarities of the phonon dispersion relation. Theory predicts that because of these factors the spontaneous decay rate varies dramatically with phonon energy, and experiments have confirmed this prediction. The

Humphrey Maris

1977-01-01

438

Cryosorption of helium on argon frost TFTR (Tokamak Fusion Test Reactor) neutral beamlines  

Microsoft Academic Search

Helium pumping on argon frost has been investigated on TFTR neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are 25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, > 20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a two-fold

J. H. Kamperschroer; M. B. Cropper; H. F. Dylla; V. Garzotto; L. E. Dudek; L. R. Grisham; G. D. Martin; T. E. OConnor; T. N. Stevenson; A. von Halle

1989-01-01

439

Cryosorption of helium on argon frost in Tokamak Fusion Test Reactor neutral beamlines  

Microsoft Academic Search

Helium pumping on argon frost has been investigated on Tokamak Fusion Test Reactor (TFTR) neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are {similar to}25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, <20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential

J. H. Kamperschroer; M. B. Cropper; H. F. Dylla; V. Garzotto; L. E. Dudek; L. R. Grisham; G. D. Martin; T. E. O'Connor; T. N. Stevenson; A. von Halle; M. D. Williams; J. Kim

1990-01-01

440

Elastic scattering of 200 keV electrons in elemental solids: experimental observation of atomic-number-dependent oscillatory behavior.  

PubMed

Mean free path of elastic electron scattering ?(el) has been measured with a 200 keV transmission electron microscope for a wide range of stable elemental solids. An oscillating behavior versus atomic number Z has been revealed, such that, within one row of the periodic table, ?(el) exhibits minimum (maximum) for elements with completed (empty) outer d shells. These ?(el)(Z) oscillations are attributed to Z dependence of the atomic density, and their importance for the interpretation of electron microscope images is demonstrated. PMID:21825363

Iakoubovskii, Konstantin; Mitsuishi, Kazutaka

2009-03-20