Angular Dependence of the Scattering of Metastable Helium Atoms in Helium and Neon
H. L. Richards; E. E. Muschlitz Jr.
1964-01-01
A molecular beam method has been used to perform scattering experiments with an atomic beam of metastable helium atoms in helium and neon. The atomic beam, in which some of the atoms had been excited by electron impact, was passed through a scattering chamber containing gas at low pressures and subsequently detected by electron ejection from gold surfaces. The 21S
Cohen-Tannoudj, Claude
Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances-polarized metastable helium atoms. The precise value of Eb2 that we obtain can also be used to check the predictions a new measurement of the s-wave scattering length a of spin-polarized helium atoms in the 2 3S1
Scattering length of the helium-atom-helium-dimer collision
Elena A. Kolganova; Alexander K. Motovilov; Werner Sandhas
2004-01-01
We present our recent results on the scattering length of ⁴He-⁴He collisions. These investigations are based on the hard-core version of the Faddeev differential equations. As compared to our previous calculations of the same quantity, a much more refined grid is employed, providing an improvement of about 10%. Our results are compared with other ab initio and model calculations.
Manson, Joseph R.
Helium atom scattering from isolated CO molecules on copper(001) A. P. Graham, F. Hofmann, and J. P 1996! Angular distributions have been measured for helium atoms scattering from isolated CO molecules with difficulties. Helium atom scattering ~HAS!, on the other hand, can, at least for simple systems, also detect
Manson, Joseph R.
Helium atom scattering from isolated CO molecules on copper(001) A. P. Graham, F. Hofmann, and J. P 1996 Angular distributions have been measured for helium atoms scattering from isolated CO molecules with difficulties. Helium atom scattering HAS , on the other hand, can, at least for simple systems, also detect
Helium-atom scattering investigation of facetting of the Al stepped (332) surface
B. J. Hinch; A. Lock; H. H. Madden; J. P. Toennies; G. Witte
1990-01-01
Helium-atom scattering has been used to study the facetting of an aluminum crystal that was cut at an angle of 10.0 from the (111) face to produce a (332) periodically stepped surface. After initial surface preparation of repeated sputtering and annealing cycles, the diffraction peak structures indicated strong facetting. Data collected for a wide range of initial He-atom wave vectors
Unveiling mode-selected electron-phonon interactions in metal films by helium atom scattering.
Benedek, G; Bernasconi, M; Bohnen, K-P; Campi, D; Chulkov, E V; Echenique, P M; Heid, R; Sklyadneva, I Yu; Toennies, J P
2014-04-28
The quasi two-dimensional electron gas on a metal film can transmit to the surface even minute mechanical disturbances occurring in the depth, thus allowing the gentlest of all surface probes, helium atoms, to perceive the vibrations of the deepest atoms via the induced surface-charge density oscillations. A density functional perturbation theory (DFPT) and a helium atom scattering study of the phonon dispersion curves in lead films of up to 7 mono-layers on a copper substrate show that: (a) the electron-phonon interaction is responsible for the coupling of He atoms to in-depth phonon modes; and (b) the inelastic HAS intensity from a given phonon mode is proportional to its electron-phonon coupling. The direct determination of mode-selected electron-phonon coupling strengths has great relevance for understanding superconductivity in thin films and two-dimensional systems. PMID:24473191
Self-consistent theory of helium atom scattering by a thermally excited monolayer solid
NASA Astrophysics Data System (ADS)
Bruch, L. W.; Hansen, F. Y.
2015-03-01
The inelastic scattering of a helium atom beam by an incommensurate monolayer solid of Xe/Pt(111) for incident energies in the range 4 -16 meV and monolayer temperatures of 25 - 75 K is evaluated self-consistently (SC) in the one-phonon approximation. The target is very corrugated and the final scattering state comprises strong diffraction and inelastic terms. At 50 and 75 K, the atom energy gain (phonon annihilation) processes have strength comparable to the energy loss (phonon creation) processes; there are pervasive and large departures from expectations based on weak-coupling detailed balance ratios. The SC results are compared to experimental data and to results from a simpler non-self-consistent approximation (NSC) that relies on harmonic approximations to the Debye-Waller attenuations of elastic and inelastic strengths. There are major differences in the trends seen in the SC and NSC results.
A. Herzenberg; H. S. M. Lau
1968-01-01
The elastic scattering of electrons is calculated with a Hylleraas product wave function for the target atom and with neglect of polarization. A narrow resonance is found at an incident kinetic energy of 4.2 eV, provided that the exchange operator is changed slightly, from the value corresponding to the no-polarization approximation, by multiplying by a constant factor differing from unity
The surface phase diagram of Li/Cu(001) explored by helium atom scattering.
Huang, Congcong; MacLaren, D A; Bacon, R T; Allison, W
2011-09-01
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. PMID:21775801
Vibrational dynamics and surface structure of Bi(111) from helium atom scattering measurements
NASA Astrophysics Data System (ADS)
Mayrhofer-Reinhartshuber, M.; Tamtgl, A.; Kraus, P.; Rieder, K. H.; Ernst, W. E.
2012-03-01
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.
O. I. Kartavtsev
1995-07-22
Metastable antiprotonic helium atoms $^{3,4}\\! H\\! e\\bar pe$ have been discovered recently in experiments of the delayed annihilation of antiprotons in helium media. These exotic atoms survive for an enormous time (about tens of microseconds) and carry the extremely large total angular momentum $L\\sim 30-40$. The theoretical treatment of the intrinsic properties of antiprotonic helium atoms, their formation and collisions with atoms and molecules is discussed.
NASA Astrophysics Data System (ADS)
Wang, Yuan-Cheng; Zhou, Ya-Jun; Cheng, Yong-Jun; Ma, Jia
2009-08-01
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.
Hansen, F. Y. [Department of Chemistry, Technical University of Denmark, IK-207-DTU, DK-2800 Lyngby (Denmark); Bruch, L. W. [Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, Wisconsin 53706 (United States); Dammann, B. [Department of Informatics and Mathematical Modeling, Technical University of Denmark, 321-DTU, DK 2800 Lyngby (Denmark)
2013-03-14
Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated by propagating a wavepacket and including the effect of a feedback of the inelastic wave onto the diffracted wave, which represents a coherent re-absorption of the created phonons. Parameters are chosen to be representative of an observed p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/NaCl(001) and a conjectured p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/KCl(001). For the latter, there are cases where part of the incident beam is trapped in the interlayer region for times exceeding 50 ps, depending on the spacing between the monolayer and the substrate and on the angle of incidence. The feedback effect is large for cases of strong transient trapping.
Kim, J; Portier, M; Dugu, J; Leduc, M; Cohen-Tannoudji, Claude
2005-01-01
We observe light-induced frequency shifts in one-color photoassociative spectra of magnetically trapped $^4$He$^*$ atoms in the metastable $2^3S_1$ state. A pair of ultracold spin-polarized $2^3S_1$ helium atoms is excited into a molecular bound state in the purely long range $0_u^+$ potential connected to the $2^3S_1 - 2^3P_0$ asymptote. The shift arises from the optical coupling of the molecular excited bound state with the scattering states and the bound states of two colliding $2^3S_1$ atoms. A linear dependence of frequency-shifts is found as a function of the PA laser intensity and measured for several ro-vibrational levels in the $0^+_u$ potential. Comparison with a theoretical analysis provides a good indication for the s-wave scattering length $a$ of the quintet ($^5\\Sigma_g^+$) potential, 6.6 nm $< a <$ 7.7 nm, which is significantly lower than previous results obtained by non-spectroscopic methods.
Helium Atom Scattering from C2H6, F2HCCH3, F3CCH2F and C2F6 in Crossed Molecular Beams
NASA Astrophysics Data System (ADS)
Hammer, Markus; Seidel, Wolfhart
1997-10-01
Rotationally unresolved differential cross sections were measured in crossed molecular beam experiments by scattering Helium atoms from Ethane, 1,1-Difluoroethane, 1,1,1,2-Tetrafluoroethane and Hexafluoroethane. The damping of observed diffraction oscillations was used to extract anisotropic interaction potentials for these scattering systems applying the infinite order sudden approximation (IOSA). Binary macroscopic parameters such as second heterogeneous virial coefficients and the coefficients of diffusion and viscosity were computed from these potentials and compared to results from macroscopic experiments.
Approximating the Helium Wavefunction in Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
DiRienzi, Joseph; Drachman, Richard J.
2003-01-01
In the Kohn variational treatment of the positronium- hydrogen scattering problem the scattering wave function is approximated by an expansion in some appropriate basis set, but the target and projectile wave functions are known exactly. In the positronium-helium case, however, a difficulty immediately arises in that the wave function of the helium target atom is not known exactly, and there are several ways to deal with the associated eigenvalue in formulating the variational scattering equations to be solved. In this work we will use the Kohn variational principle in the static exchange approximation to d e t e e the zero-energy scattering length for the Ps-He system, using a suite of approximate target functions. The results we obtain will be compared with each other and with corresponding values found by other approximation techniques.
Safron, S.A.; Skofronick, J.G.
1997-07-01
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.
NASA Astrophysics Data System (ADS)
Kedziera, Dariusz; Mentel, ?ukasz; ?uchowski, Piotr S.; Knoop, Steven
2015-06-01
We have obtained accurate ab initio +4? quartet potentials for the diatomic metastable triplet helium+alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections CCSD(T) calculations and accurate calculations of the long-range C6 coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that result in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium+alkali-metal mixture experiments.
Dariusz K?dziera; ?ukasz Mentel; Piotr S. ?uchowski; Steven Knoop
2015-06-26
We have obtained accurate ab initio quartet potentials for the diatomic metastable triplet helium + alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections [CCSD(T)] calculations and accurate calculations of the long-range $C_6$ coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that results in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium + alkali-metal mixture experiments.
NASA Astrophysics Data System (ADS)
Yarevsky, E.; Yakovlev, S. L.; Larson, ; Elander, N.
2015-06-01
The study of scattering processes in few body systems is a difficult problem especially if long range interactions are involved. In order to solve such problems, we develop here a potential-splitting approach for three-body systems. This approach is based on splitting the reaction potential into a finite range core part and a long range tail part. The solution to the Schrdinger equation for the long range tail Hamiltonian is found analytically, and used as an incoming wave in the three body scattering problem. This reformulation of the scattering problem makes it suitable for treatment by the exterior complex scaling technique in the sense that the problem after the complex dilation is reduced to a boundary value problem with zero boundary conditions. We illustrate the method with calculations on the electron scattering off the hydrogen atom and the positive helium ion in the frame of the TemkinPoet model.
Ultracold collisions of metastable helium atoms
Leo, P J; Whittingham, I B; Babb, J F
2001-01-01
We report scattering lengths for the singlet Sigma g +, triplet Sigma u + and quintet Sigma g + adiabatic molecular potentials relevant to collisions of two metastable (n=2 triplet S) helium atoms as a function of the uncertainty in these potentials. These scattering lengths can be used to calculate elastic cross sections and inelastic rates of experimental interest at temperatures where the Wigner threshold approximation is valid. Importantly, we show that the scattering length of the quintet Sigma g + potential, crucial to the experimental attainment of Bose-Einstein condensation in a gas of spin-polarized metastable atoms, can be obtained from a measurement of the total elastic cross section in an unpolarized gas.
Precision spectroscopy 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
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.
The Ionization of Helium by Neutral Helium Atoms
Frank Horton; Dorothy M. Millest
1946-01-01
A method is described for investigating the ionization produced in helium by collisions between quasi-stationary atoms-that is, atoms possessing only thermal velocities-and a beam of neutral helium atoms with kinetic energy less than 100 eV. Ionization is shown to begin when the kinetic energy of the bombarding atoms is twice as great as the minimum kinetic energy which electrons must
Atom lithography with metastable helium
Allred, Claire S.; Reeves, Jason; Corder, Christopher; Metcalf, Harold [Physics and Astronomy, Stony Brook University, Stony Brook. New York 11794-3800 (United States)
2010-02-15
A bright metastable helium (He*) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He* atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He{sup *} was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of {lambda}=1083 nm light was used to channel and focus the He* atoms into lines separated by {lambda}/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.
NASA Technical Reports Server (NTRS)
Newman, J. H.; Smith, K. A.; Stebbings, R. F.; Chen, Y. S.
1985-01-01
This paper reports the first results of an experimental program established to provide cross section data for use in modeling various atmospheric processes. Absolute cross sections, differential in the scattering angle, have been measured for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2 at laboratory scattering angles between 0.1 deg and 5 deg. The results are the sums of cross sections for elastic and inelastic scattering of helium atoms; charged collision products are not detected. Integration of the differential cross section data yields integral cross sections consistent with measurements by other workers. The apparatus employs a position-sensitive detector for both primary and scattered particles and uses a short target cell with a large exit aperture to ensure a simple and well-defined apparatus geometry.
NASA Astrophysics Data System (ADS)
Graham, A. P.; Hinch, B. J.; Kochanski, G. P.; McCash, E. M.; Allison, W.
1994-11-01
The incommensurate 53 structure, which is formed when silicon is deposited on copper(001) via a saturation exposure to silane at 420 K, has been examined with helium-atom scattering and scanning tunneling microscopy. The surface was found to be a two-dimensional copper-silicon alloy having large domains of a near perfect hexagonal structure with Cu2Si stoichiometry. The surface layer displays a rotation of one surface-lattice vector with respect to the substrate of 4.4, and a high-order commensuration along the other surface-lattice vector, without rotation. The overlayer exhibited unequal densities of the four possible domains and it appears that the long-range order is influenced by the presence of steps on the copper(001) surface. The overall atomic density in the surface layer is 27.6% higher than on the unreconstructed surface. The driving force for the formation of the sheared hexagonal structure is believed to be the need to increase surface coordination and density together with a strongly directional in-plane bonding between Cu and Si atoms.
Flaherty, F. A.; Trelenberg, T. W.; Li, J. A.; Fatema, R.; Skofronick, J. G.; Van Winkle, D. H.; Safron, S. A.; Boatner, L. A.
2015-07-01
The structure and dynamics of cleaved (001) surfaces of potassium tantalates doped with niobium, KTa1-xNbxO? (KTN), with x ranging from 0% to 30%, were measured by helium atom scattering (HAS). Through HAS time-of-flight (TOF) experiments, a dispersionless branch (Einstein phonon branch) with energy of 13-14 meV was observed across the surface Brillouin zone in all samples. When this observation is combined with the results from earlier experimental and theoretical studies on these materials, a consistent picture of the stable surface structure emerges: After cleaving the single-crystal sample, the surface should be composed of equal areas of KO and TaO?/NbO? terraces.moreThe data, however, suggest that K? and O? ions migrate from the bulk to the surface, forming a charged KO lattice that is neutralized primarily by additional K? ions bridging pairs of surface oxygens. This structural and dynamic modification at the (001) surface of KTN appears due to its formally charged KO(-1) and TaO?/NbO?(+1) layers and avoids a polar catastrophe. This behavior is contrasted with the (001) surface behavior of the fluoride perovskite KMnF? with its electrically neutral KF and MnF? layers.less
NASA Astrophysics Data System (ADS)
Skofronick, J. G.; Toennies, J. P.; Traeger, F.; Weiss, H.
2000-03-01
Helium atom scattering has been used to probe the surface dynamical character of N2 grown by isothermal adsorption at partial pressures of about 2.5\\cdot 10-8 mbar at temperatures held in the range of 11 to 12 K onto an in situ cleaved MgO(100) substrate. The scattering chamber base pressure during the measurements was in the mid 10-11 mbar range. N2 coverages of a full monolayer and submonolayer were studied. With the full monolayer and with an incident beam of 28.8 meV, two Einstein type modes were observed at 13 meV and 6.7 meV. The latter was a parallel vibration as judged by the intensity increase toward the zone boundary. The 13 meV mode favors parallel polarization, however, the intensity was weaker and the argument is not so clear; it could be an overtone of the 6.7 meV mode. With an incident beam energy of 18.8 meV, a third mode at 3.5 meV was seen, with uncertain character. For submonolayer coverage, three modes were observed: one at 2.8 meV (a rotational mode), a weak 5.6 meV mode and a mode at 8 meV. The latter mode decreased in energy with increased coverage becoming the 6.7 meV mode of the full monolayer. The modes were identified by observing the frequency change with different isotopes of N_2.
Average-Atom Thomson Scattering
Johnson, Walter R.
Average-Atom Thomson Scattering Applications Xray Scattering from Warm Dense Matter Thomson Scattering in the Average-Atom Approximation W. R. Johnson, Notre Dame Collaborators: Joe Nilsen & K. T. Cheng, LLNL July 10, 2012 Atomic Physics Seminar Xray Scattering #12;Average-Atom Thomson Scattering
Electron scattering in helium for Monte Carlo simulations
Khrabrov, Alexander V.; Kaganovich, Igor D. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
2012-09-15
An analytical approximation for differential cross-section of electron scattering on helium atoms is introduced. It is intended for Monte Carlo simulations, which, instead of angular distributions based on experimental data (or on first-principle calculations), usually rely on approximations that are accurate yet numerically efficient. The approximation is based on the screened-Coulomb differential cross-section with energy-dependent screening. For helium, a two-pole approximation of the screening parameter is found to be highly accurate over a wide range of energies.
NASA Astrophysics Data System (ADS)
Kraus, Patrick; Mayrhofer-Reinhartshuber, Michael; Gsweiner, Christian; Apolloner, Florian; Miret-Arts, Salvador; Ernst, Wolfgang E.
2014-12-01
The exact elastic close-coupling formalism is used to compare the performance of several interaction potentials suggested in literature for describing the measured elastic diffraction peak intensities in helium scattering experiments. The coupling parameters have been analytically calculated for the corrugated Morse potential on a hexagonal surface structure and adapted for usage with similar interaction potentials. The potentials used have been fitted to previously known bound state energies complemented by two additional levels which are found by improving energy resolution. It is established that the shifted Morse potential reproduces the experimental He-Sb(111) bound state more closely than the other considered potential shapes. The performance of several interaction potentials in describing the elastic scattering intensities is presented and discussed. Morse and Morse-related potentials provide the best compromise for the description of elastic scattering intensities. The different effects of the potential shape were determined by comparing the calculated scattering intensities.
Average-Atom Thomson Scattering
Johnson, Walter R.
Average-Atom Thomson Scattering Applications Xray Scattering from WDM Thomson Scattering in the Average-Atom Approximation W. R. Johnson, Notre Dame Collaborators: Joe Nilsen & K. T. Cheng, LLNL Computational Challenges in WDM PLWS-4 Xray Scattering #12;Average-Atom Thomson Scattering Applications Outline
Long range forces between atomic impurities in liquid helium
Long range forces between atomic impurities in liquid helium J. Dupont-Roc Laboratoire Kastler in a polarizable medium. We show that atomic impurities in liquid helium may indeed realize repulsive forces embedded in liquid helium, super uid or not. Solid helium have also been used. Successful theoretical
Variational calculation of antiprotonic helium atoms
O. I. Kartavtsev
1995-12-21
A few per cent fraction of antiprotons stopped in helium survives for an enormous time (up to tens of microseconds) in comparison with the usual lifetime ($10^{-12}s$) of these particles in matter. The explanation is that antiprotons are captured in the metastable antiprotonic helium atoms $^{3,4}\\! H\\! e\\bar pe$ carrying an extremely large total angular momentum $L\\sim 30-40$. Initial populations, level lifetimes and very precise values of the transition energies were obtained in experiments on the resonant laser--induced annihilation. Analogous long-lived systems were observed in experiments with negative kaons and pions. The purpose of this report is to present the results of calculation of eigenenergies, radiative transition rates, energy-level splitting due to relativistic interactions and Auger decay rates of antiprotonic helium atoms within the variational approach.
Classical Helium Atom with Radiation Reaction G. Camelio,1
Carati, Andrea
Classical Helium Atom with Radiation Reaction G. Camelio,1 A. Carati,2 and L. Galgani2 1) Universit November 2011) We study a classical model of Helium atom in which, in addition to the Coulomb forces be singular with respect to that of Lebesgue. PACS numbers: 05.45.-a, 41.60.-m Keywords: classical Helium atom
Light scattering by a liquid-gas helium spray
NASA Astrophysics Data System (ADS)
Ladam, Y.; Wolf, P.-E.; Thibault, P.; Puech, L.
2001-05-01
Light scattering by liquid helium droplets or gaseous helium bubbles is strongly forward. This has two direct experimental consequences: rare scatterers are very bright in a narrow (ll 5^{circ}) angular region in the forward direction; and even in the presence of multiple scattering the intensity collected at large angles is linear in the concentration of scatterers. These properties are explained, and the second one is illustrated with a liquid-gas helium spray.
Interaction of Helium Rydberg State Atoms with Superfluid Helium
NASA Astrophysics Data System (ADS)
Fiedler, Steven L.; Eloranta, Jussi
2014-03-01
The pair potentials between ground state helium and Rydberg He atoms are calculated by the full configuration interaction electronic structure method for both the electronic singlet and the triplet manifolds. The obtained pair potentials are validated against existing experimental molecular and atomic data. Most states show remarkable energy barriers at long distances ( ), which can effectively stabilize He against the formation of He at low nuclear kinetic energies. Bosonic density functional theory calculations, based on the calculated pair potential data, indicate that the triplet ground state He reside in spherical bubbles in superfluid helium with a barycenter radius of 6.1 at the liquid saturated vapor pressure. The pressure dependency of the relative He absorption line blue shift in the liquid was obtained through both the statistical line broadening theory as well as the dynamic adiabatic following method. The pronounced difference between the results from the static and dynamic models is attributed to the dynamic Jahn-Teller effect that takes places in the electronically excited state within the dephasing time of 150 fs. Transient non-thermalized liquid surroundings near He may contribute to an artificial reduction in the absorption line blue shift by up to 30 cm.
Elastic and inelastic scattering of He atoms from Bi(111)
NASA Astrophysics Data System (ADS)
Tamtgl, A.; Mayrhofer-Reinhartshuber, M.; Balak, N.; Ernst, W. E.; Rieder, K. H.
2010-08-01
Elastic and inelastic scattering of helium atoms has been used to study the Bi(111) surface. Sharp diffraction peaks are found with results in excellent agreement with previous structure determinations of the Bi(111) surface. The rather large first order peaks with respect to the zero order peak indicate a stronger surface corrugation than observed in helium scattering from other metallic surfaces. Time-of-flight spectra of scattered He atoms clearly reveal two inelastic scattering maxima, which allow a first report on phonon creation and annihilation events on the Bi(111) surface. An estimate of the group velocity shows that the phonon creation peak is likely to correspond to a Rayleigh mode.
NSDL National Science Digital Library
From the Lawrence Berkeley Laboratory's Center for X-Ray Optics, these "atomic scattering factors are based upon photoabsorption measurements of elements in their elemental state." These easy-to-use tables allow users to search out atomic scattering factor data by element and look up the x-ray properties of elements, the index of refraction for a compound material, the x-ray attenuation length of a solid, the x-ray transmission of a solid or a gas, and more. Most of the tables are accessed by way of an online query form with variables such as material, density, and photon energy range entered by the user. Most outputs come in plot form for quick viewing, or results may be retrieved as a text or postscript file for use with a personal plotting software.
N. C. Pyper; D. W. Essex; Colm T. Whelan
2001-01-01
The energy of the He 1s ? 1s2p(P) transition for helium atoms in liquid helium, solid helium and helium bubbles in metals is greater than for free helium atoms by an amount known as the energy shift. The energy shift is calculated by combining the results of ab-initio self-consistent field electronic structure calculations with corrections to account for the effects
Helium in confinement: the filling A Neutron Scattering investigation.
Glyde, Henry R.
Helium in confinement: the filling parameter. A Neutron Scattering investigation. Francesco Albergamo Institut Laue-Langevin, France Helium in confinement: the filling parameter. p.1/13 #12;outline introduction and motivation Helium in confinement: the filling parameter. p.2/13 #12;outline introduction
Searching for dark matter with helium atom
Imre Ferenc Barna
2006-08-10
With the help of the boost operator we can model the interaction between a weakly interacting particle(WIMP) of dark matter(DAMA) and an atomic nuclei. Via this "kick" we calculate the total electronic excitation cross section of the helium atom. The bound spectrum of He is calculated through a diagonalization process with a configuration interaction (CI) wavefunction built up from Slater orbitals. All together 19 singly- and doubly-excited atomic sates were taken with total angular momenta of L=0,1 and 2. Our calculation may give a rude estimation about the magnitude of the total excitation cross section which could be measured in later scintillator experiments. The upper limit of the excitation cross section is $9.7\\cdot 10^{-8}$ barn.
Metastable Aluminum Atoms Floating on the Surface of Helium Nanodroplets
NASA Astrophysics Data System (ADS)
Jeffs, Jay; Besley, Nicholas A.; Stace, Anthony J.; Sarma, Gautam; Cunningham, Ethan M.; Boatwright, Adrian; Yang, Shengfu; Ellis, Andrew M.
2015-06-01
Metal atoms have proved to be sensitive probes of the properties of superfluid helium nanodroplets. To date, all experiments on the doping of helium droplets have concentrated on the attachment of metal atoms in their ground electronic states. Here we report the first examples of metal atoms in excited states becoming attached to helium nanodroplets. The atoms in question are aluminum, and they have been generated by laser ablation in a metastable quartet state, which attaches to and remains on the surface of helium droplets. Evidence for a surface location comes from electronic spectra, which consist of very narrow absorption profiles that show very small spectral shifts. Supporting ab initio calculations show there to be an energy incentive for a metastable Al atom to remain on the surface of a helium droplet rather than move to the interior. The results suggest that helium droplets may provide a method for the capture and transport of metastable excited atomic and molecular species.
Classical Helium Atom with Radiation Reaction
G. Camelio; A. Carati; L. Galgani
2011-11-24
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.
Potential scattering in atomic physics
P. G. Burke; Robert St John
1977-01-01
An in-depth examination of potential field scattering of particles is presented with particular reference to elastic electron scattering by an ion or a neutral atom. Included are scattering by a short-range, Coulomb, and spin--orbit potentials, and by one-electron atoms, low energy effective-range theory, bound states and resonances, variational methods and bound principles, integral equation methods and the Born approximation, and
The scattering of low energy positrons by helium
NASA Technical Reports Server (NTRS)
Humberston, J. W.
1973-01-01
Kohn's variational method is used to calculate the positron-helium scattering length and low energy S-wave phase shifts for a quite realistic Hylleraas type of helium function containing an electron-electron correlation term. The zero energy wavefunction is used to calculate the value of the annihilation rate parameter Z sub eff. All the results are significantly different from those for Drachman's helium model B, but are in better agreement with the available experimental data.
Single-electron capture by hydrogen atoms and helium ions from helium atoms
Mancev, I. [Department of Physics, University of Nis, P.O. Box 91, 18001 Nis (Yugoslavia)
1996-07-01
The four-body corrected first Born approximation is used to investigate the single-electron transfer in fast collisions of hydrogenlike projectiles with helium atoms. The initial state of the target active electron is described by a Roothan-Hartree-Fock wave function. For an illustration, total cross sections are computed for electron capture from the ground state of He by fast H atom and He{sup +} ion. The theoretical results are in good agreement with available experimental data. {copyright} {ital 1996 The American Physical Society.}
Helium nanobubble release from Pd surface: An atomic simulation
Wang, Liang; Hu, Wangyu; Deng, Huiqiu; Xiao, Shifang; Yang, Jianyu; Gao, Fei; Heinisch, Howard L.; Hu, Shilin
2011-02-14
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.
Mechanodynamic diffusion of helium atoms into porous copper
NASA Astrophysics Data System (ADS)
Klyavin, O. V.; Nikolaev, V. I.; Smirnov, B. I.; Khabarin, S. V.; Chernov, Yu. M.; Shpe?zman, V. V.
2008-05-01
Mechanodynamic penetration of helium atoms into porous copper compressively strained at 4.2 K is studied. Porous copper is obtained by vaporizing zinc out of brass in vacuum at a temperature of 800C for 8 h. The number of helium atoms which penetrated into the sample increased monotonically with strain to reach 2.9 1016 atoms/cm2 at ? = 42%. This amount of helium is two and even more orders of magnitude larger than that obtained from the data available thus far on mechanodynamic penetration of atoms of an external medium into crystalline and amorphous materials under strain. The relations obtained suggest that specific types of helium traps determine the kinetics of mechanodynamic diffusion of helium into solids.
V. M. Bystritsky; V. F. Boreiko; M. Filipowicz; V. V. Gerasimov; O. Huot; P. E. Knowles; F. Mulhauser; V. N. Pavlov; N. P. Popov; L. A. Schaller; H. Schneuwly; V. G. Sandukovsky; V. A. Stolupin; V. P. Volnykh; J. Wozniak
2003-01-01
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 muonic x--ray $K$ series transitions relative intensities in $(\\\\mu{}^{3,4}\\\\mathrm{He})^*$ atoms in pure helium as well as in helium--deuterium mixture. The muon stopping powers ratio between helium and deuterium atoms
Retardation Effects in Very Low-Energy Helium-Helium Scattering
John Konrady; Joseph Sucher
1972-01-01
The elastic differential and total helium-helium scattering cross sections are computed at very low energies. Retardation effects, which are accurately taken into account by using the arc tangent approximation to the Casimir-Polder potential, are shown to contribute several percent to the cross sections.
Atomic origins of solid helium bubbles in tungsten
NASA Astrophysics Data System (ADS)
Xia, Min; Guo, Hong-Yan; Dai, Yong; Yan, Qing-Zhi; Guo, Li-Ping; Li, Tie-Cheng; Qiao, Yi; Ge, Chang-Chun
2014-12-01
Solid helium bubbles were directly observed in the helium ion implanted tungsten (W), by different transmission electron microscopy (TEM) techniques at room temperature. The diameters of these solid helium bubbles range from 1 nm to 8 nm in diameter with the mean bubble size about 3 nm. The selected area electron diffraction (SAED) and fast Fourier transform (FFT) images revealed that solid helium bubbles possess body-centered cubic (bcc) structure with a lattice constant of 0.447 nm. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images further confirmed the existence of helium bubble in tungsten. The present findings provide an atomic level view of the microstructure evolution of helium in the materials, and revealed the existence of solid helium bubbles in materials.
NASA Astrophysics Data System (ADS)
Skofronick, J. G.; Toennies, J. P.; Traeger, F.; Weiss, H.
2001-03-01
Helium atom scattering has been used to probe the surface structure and dynamical character of H_2, p-H_2, HD and D2 molecules grown by isothermal adsorption at partial pressures in the 10-7 - 10-5 mbar range onto an in situ cleaved MgO(100) substrate held at temperatures between 7-12 K. The background pressure was in the mid 10-11 mbar range. A first and second adsorbed layer of hydrogen were observed. In the first, the sequence c(2x2), c(4x2) and c(6x2), as mentioned in the literature, was measured while in the second layer, the structure was not so clear. The surface dynamics for the c(4x2) showed a single mode at 9-10 meV in the [100] direction, but in the [110] direction two Einstein modes at about 10.5 and 8.5 meV were observed and a third mode (with dispersion) which ranged from 2 to 6 meV was also measured. The c(6x2) surface dynamics was similar to c(4x2). The second layer had a single Einstein surface mode very near 5 meV. The dispersive mode is believed associated with parallel oscillations along the long edge of the cell and the dispersionless modes from parallel and perpendicular oscillations along the short length of the elementary cell.
V. M. Bystritsky; V. F. Boreiko; W. Czaplinski; M. Filipowicz; V. V. Gerasimov; O. Huot; P. E. Knowles; F. Mulhauser; V. N. Pavlov; N. P. Popov; L. A. Schaller; H. Schneuwly; V. G. Sandukovsky; V. A. Stolupin; V. P. Volnykh; J. Wozniak
2005-01-01
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 (muHe3,4)* atoms in pure helium as well as in helium-deuterium mixtures. The dmuHe3 radiative decay probabilities for two
Positron-alkali atom scattering
NASA Technical Reports Server (NTRS)
Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.
1990-01-01
Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.
Varun Harbola
2011-01-01
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
Atomic interactions between plutonium and helium.
Valone, S. M. (Steven M.); Baskes, M. I. (Michael I.); Martin, R. L. (Richard L.)
2002-01-01
An essential issue in gallium (Ga)-stabilized fcc-phase plutonium ({delta}-Pu) is the formation of helium (He) voids and bubbles emanating from the radiolytic decay of the Pu. The rate of formation of He voids and bubbles is related to the He-defect formation energies and their associated migration barriers. The size and shape distributions of the bubbles are coupled to these critical migration processes. The values of the defect formation energies, internal pressure, and migration barriers can be estimated from atomistic calculations. Complicating this picture is the destruction of He-filled voids and bubbles by subsequent radiolytic decay events. The present study concerns the construction of the necessary potential energy surfaces for the Pu-He and He-He interactions within the modified embedded atom method (MEAM). Once fully tested, the potentials will be used to estimate the He-defect formation energies and barriers to the migration of these defects for both interstitial and substitutional He on an fcc Pu lattice. The He-He interactions are modeled from ab initio electronic structure calculations for the He{sub 2} dimer and the equilateral He, trimer. The experimental data and the electronic structure calculations on He{sub 2} agree very well. These data were fit to a Rose function fn{sub R}(x) = A P({alpha}x) exp(-{alpha}x), where P is a polynomial, x = R/R{sub 0}-1, R is the bond length, and R{sub 0} is its equilibrium value. The fits are very satisfactory. Both linear (P = 1+{alpha}x, zeroth-order Rose) and rational (P = 1+{alpha}x+a{sub 3} ({alpha}x){sup 3}/(1+x) first-order Rose) polynomials in the Rose function were tried. The more flexible rational form does improve the fit, but only marginally. Only the linear form was used thereafter. The resulting MEAM potential was used to predict the behavior of the linear trimer and the fcc cold compression curve. The results are shown in Fig. 2 and appear to be satisfactory. The compression regions of the curves are of particular interest for several reasons. First, an octahedral interstitial He atom in anfcc Pu lattice with a lattice constant of 4.64 {angstrom} has a nearest Pu neighbor distance of 2.32 {angstrom}. This distance is in the compressive region of the potential energy curve. Second, the compressive region will partially determine the internal pressure of He-filled voids and bubbles. Third, the shape of the He-filled voids will be influenced by the compression region of the potential. The Pu-He interactions are also modeled from ab initio electronic structure calculations, this time only for the PuHe dimer. The lowest-energy spin state of the dimer appears to be the S=7/2 state with a 'Stuttgart small-core RECP/6-31 g' basis. Two electronic structure methods were tried which would bound the extremes of the Pu-He interaction. One was the local density approximation (LDA), which tends to overestimate binding strength. It gives a well depth of 0.08 eV and a bond length of 3.6 {angstrom}. The other used the Becke-3-Lee-Yang-Parr (B3LYP) exchange-correlation energy functional, which tends to underestimate binding strength. It predicts no binding at any separation. For purposes of fitting to the Rose functional form, a well depth of 0.03 eV and bond length of 4.8 {angstrom} was used. The bond length exceeds the cutoff distance that will be used in future simulations to limit the maximum range of the atomic interactions and is effectively purely repulsive. Furthermore, the dimer information is sufficient to determine the painvise part of the Pu-He MEAM potential, but not the effective electron density that determines the many-body part of the potential, the embedding functions F{sub He} and F{sub Pu} in Fig. 3. The effective electron density, as well as determining which of the two dimer curves (LDA or B3LYP) is preferable, will be decided by comparing simulation results to known information about He bubble formation rates at elevated temperatures and estimates of Me bubble sizes. Initial simulations suggest that an interstitial He defect, based on either the LDA
Spectroscopy of barium atoms in liquid and solid helium matrices
Lebedev, V.; Moroshkin, P.; Weis, A. [Departement de Physique, Universite de Fribourg, Chemin du Musee 3, CH-1700 Fribourg (Switzerland)
2011-08-15
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.
Inelastic multiphonon helium scattering from a stepped Ni(977) surface
Daniel J. Gaspar; Aubrey T. Hanbicki; S. J. Sibener
1998-01-01
The multiphonon energy exchange between a neutral He atom and a stepped Ni(977) surface has been measured in order to examine how the presence of a regular array of atomic-scale steps on a surface modifies energy exchange in the classical multiphonon scattering regime. At elevated substrate temperatures, we compare the multiphonon scattering with the predictions of a classical theory that
Spectra of helium clusters with up to six atoms using soft-core potentials
Gattobigio, M. [Universite de Nice-Sophia Antipolis, Institut Non-Lineaire de Nice, CNRS, 1361 route des Lucioles, F-06560 Valbonne (France); Kievsky, A.; Viviani, M. [Istituto Nazionale di Fisica Nucleare, Largo Pontecorvo 3, I-56100 Pisa (Italy)
2011-11-15
In this paper, we investigate small clusters of helium atoms using the hyperspherical harmonic basis. We consider systems with A=2,3,4,5,6 atoms with an interparticle potential which does not present a strong repulsion at short distances. We use an attractive Gaussian potential that reproduces the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the widely used He-He interactions, the Aziz and Slaman potential, called LM2M2. In systems with more than two atoms, we consider a repulsive three-body force that, by construction, reproduces the trimer binding energy of the LM2M2 potential. With this model, consisting of the sum of a two- and three-body potential, we have calculated the spectrum of clusters formed by four, five, and six helium atoms. We have found that these systems present two bound states, one deep and one shallow, close to the threshold fixed by the energy of the (A-1)-atom system. Universal relations between the energies of the excited state of the A-atom system and the ground-state energy of the (A-1)-atom system are extracted, as well as the ratio between the ground state of the A-atom system and the ground-state energy of the trimer.
Spectra of helium clusters with up to six atoms using soft core potentials
M. Gattobigio; A. Kievsky; M. Viviani
2011-12-01
In this work we investigate small clusters of helium atoms using the hyperspherical harmonic basis. We consider systems with $A=2,3,4,5,6$ atoms with an inter-particle potential which does not present a strong repulsion at short distances. We use an attractive gaussian potential that reproduces the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the widely used He-He interactions, the LM2M2 potential. In systems with more than two atoms we consider a repulsive three-body force that, by construction, reproduces the trimer binding energy of the LM2M2 potential. With this model, consisting in the sum of a two- and three-body potential, we have calculated the spectrum of clusters formed by four, five and six helium atoms. We have found that these systems present two bound states, one deep and one shallow close to the threshold fixed by the energy of the $(A-1)$-atom system. Universal relations between the energies of the excited state of the $A$-atom system and the ground state energy of the $(A-1)$-atom system are extracted as well as the ratio between the ground state of the $A$-atom system and the ground state energy of the trimer.
Imprints from the solar cycle on the helium atom and helium pickup ion distributions
D. Rucinski; M. Bzowski; H. J. Fahr
2003-01-01
Neutral interstellar helium atoms penetrate into the solar system almost unaffected by gas-plasma interactions in the heliospheric interface region, and thus can be considered as carriers of original information on the basic parameters (like density, temperature, bulk velocity) of the Very Local Interstellar Medium (VLISM). Such information can nowadays be derived from analysis of data obtained from different experimental methods:
Atomic impact experiments with free helium-3 and helium-4 clusters
Jrgen Gspann
1995-01-01
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,
Interaction potential between a helium atom and metal surfaces
NASA Technical Reports Server (NTRS)
Takada, Y.; Kohn, W.
1985-01-01
By employing an S-matrix theory for evanescent waves, the repulsive potential between a helium atom and corrugated metal surfaces has been calculated. P-wave interactions and intra-atomic correlation effects were found to be very important. The corrugation part of the interaction potential is much weaker than predicted by the effective-medium theory. Application to Cu, Ni, and Ag (110) surfaces gives good agreement with experiment without any adjustable parameters.
Photoionization of atoms and molecules. [of hydrogen, helium, and xenon
NASA Technical Reports Server (NTRS)
Samson, J. A. R.
1976-01-01
A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.
Energy of Interaction between a Hydrogen Atom and a Helium Atom
E. A. Mason; J. Ross; P. N. Schatz
1956-01-01
The potential energy of interaction between a hydrogen atom and a helium atom has been calculated as a function of separation distance by standard quantum mechanical variation procedures. The approximate molecular wave functions used contained both homopolar and ionic contributions, and were constructed from 1s hydrogen-like atomic wave functions. All integrals involved have been evaluated accurately. The results are in
Cohen-Tannoudj, Claude
Giant Helium Dimers Produced by Photoassociation of Ultracold Metastable Atoms J. Leonard,* M long-range helium dimers by photoassociation of metastable helium atoms in a magnetically trapped in the metastable 23S1 (He) state absorb laser light tuned close to the 23S1 23P0 (D0) atomic line at 1083 nm
NASA Astrophysics Data System (ADS)
Yu, Chun-Ri; Zhang, Jie; Chen, Li; Jiang, Gui-Sheng; Huang, Guo-Dong
2009-11-01
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.
Simulations of the effect of final state interactions on the scattering reponses of helium droplets
Yang, Jian
1996-01-01
We study the effect of final state interactions (FSI) on the scattering responses of Helium droplets. By computing the s-wave component of the one-body density matrix of a Helium droplet, we find strong similarity between bulk Helium and Helium...
Simulations of the effect of final state interactions on the scattering reponses of helium droplets
Yang, Jian
1996-01-01
We study the effect of final state interactions (FSI) on the scattering responses of Helium droplets. By computing the s-wave component of the one-body density matrix of a Helium droplet, we find strong similarity between bulk Helium and Helium...
A. A. Zakharenko
2007-01-01
The experimental results of creating bulk elementary excitations (BEEs) in isotopically pure liquid helium-II by helium atomic beams at low temperatures ? 60 mK are presented. In the present experiment, BEE signals generated by He-atomic beams incident on the liquid free surface were detected by a bolometer positioned in the liquid helium-II. Some detected signals were very weak and depended
Scattering lengths for spin-polarized metastable helium-3 and helium-4
A. S. Dickinson; F. X. Gada; T. Leininger
2004-01-01
Upper and lower bounds are estimated for the scattering length, a, for the various isotopes of spin-polarized metastable helium. From a previous study involving various large basis sets and two ab initio approaches, and paying special attention to combine them with the accurate long-range potential, we get, for 4He*-4He* collisions (in Bohr) 152 < 4-4a < 230 and for 3He*-3He*
Inelastic Multiphonon Helium Scattering from a Stepped Ni(977) Surface
Daniel J. Gaspar; Aubrey T. Hanbicki; Steven J. Sibener
1998-01-01
This experiment examines how the presence of a regular array of atomic-scale steps on a surface modifies energy exchange in the inelastic multiphonon scattering regime. We have measured the multiphonon energy exchange between a neutral He atom beam and a stepped Ni(977) surface with scattering kinematics chosen to be both in- and out-of-phase with respect to the terraces. As the
NASA Astrophysics Data System (ADS)
Chu, Xi; Dalgarno, Alexander; Groenenboom, Gerrit C.
2007-03-01
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 EHa06 and the orientation-dependent coefficients between 2 and -1 EHa06 . 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.
Resonance Phenomena in Large-Angle Helium Ion-Helium Atom Collisions
F. P. Ziemba; E. Everhart
1959-01-01
When He\\/sup +\\/ ions are scattered from He atoms at kev energies, a small ; fraction of thesc collisions results in large-angle scattering of the incident ; particle. Particles from He\\/sup +\\/-He collisions were analyzed to determine the ; fractions which were neutral and doubly ionized. These data are shown ; graphically. (A.C.);
Quantum solvation of carbonyl sulfide with helium atoms.
Tang, Jian; Xu, Yunjie; McKellar, A R W; Jger, Wolfgang
2002-09-20
High-resolution infrared and microwave spectra of He(N)-carbonyl sulfide (He(N)-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 droplet limit for N > 5, implying that even atoms in the first solvation shell are decoupled from the OCS rotation in helium nanodroplets. To the extent that this is due to superfluidity, the results directly explore the microscopic evolution of a phenomenon that is formally macroscopic in nature. PMID:12242436
Zeeman deceleration of electron-impact-excited metastable helium atoms
NASA Astrophysics Data System (ADS)
Dulitz, Katrin; Tauschinsky, Atreju; Softley, Timothy P.
2015-03-01
We present experimental results that demonstratefor the first timethe Zeeman deceleration of helium atoms in the metastable 23S1 state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m s?1 to a final velocity of 370 m s?1. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Metastable helium is efficiently generated even in a mixture of other noble gases that have much lower excitation energies. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.
Lamb Shift in the Metastable States of the Helium Atom
Kiu S. Suh; M. H. Zaidi
1966-01-01
The radiative corrections of order alpha^3 rydbergs are evaluated for the ionization energy of the metastable states 21,3S, of the helium atom. In the calculation of the average excitation energy k_0, the main contribution comes from the transition to (ms, np) and (ms, ? p) states. The oscillator strengths for transitions to (1s, ? p), (2s, ? p) and (3s,
Spectroscopy of Lithium Atoms and Molecules on Helium Nanodroplets
2013-01-01
We report on the spectroscopic investigation of lithium atoms and lithium dimers in their triplet manifold on the surface of helium nanodroplets (HeN). We present the excitation spectrum of the 3p ? 2s and 3d ? 2s two-photon transitions for single Li atoms on HeN. The atoms are excited from the 2S(?) ground state into ?, ?, and ? pseudodiatomic molecular substates. Excitation spectra are recorded by resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) mass spectroscopy, which allows an investigation of the exciplex (Li*Hem, m = 13) formation process in the LiHeN system. Electronic states are shifted and broadened with respect to free atom states, which is explained within the pseudodiatomic model. The assignment is assisted by theoretical calculations, which are based on the OrsayTrento density functional where the interaction between the helium droplet and the lithium atom is introduced by a pairwise additive approach. When a droplet is doped with more than one alkali atom, the fragility of the alkaliHeN systems leads preferably to the formation of high-spin molecules on the droplets. We use this property of helium nanodroplets for the preparation of Li dimers in their triplet ground state (13?u+). The excitation spectrum of the 23?g(?? = 011) ? 13?u+(?? = 0) transition is presented. The interaction between the molecule and the droplet manifests in a broadening of the transitions with a characteristic asymmetric form. The broadening extends to the blue side of each vibronic level, which is caused by the simultaneous excitation of the molecule and vibrations of the droplet (phonons). The two isotopes of Li form 6Li2 and 7Li2 as well as isotope mixed 6Li7Li molecules on the droplet surface. By using REMPI-TOF mass spectroscopy, isotope-dependent effects could be studied. PMID:23895106
Atomic masses of tritium and helium-3.
Myers, E G; Wagner, A; Kracke, H; Wesson, B A
2015-01-01
By measuring the cyclotron frequency ratios of (3)He(+) to HD(+) and T(+) to HD(+), and using HD(+) as a mass reference, we obtain new atomic masses for (3)He and T. Our results are M[(3)He]=3.016?029?322?43(19)??u and M[T]=3.016?049?281?78(19)??u, where the uncertainty includes an uncertainty of 0.12 nu in the mass reference. Allowing for cancellation of common systematic errors, we find the Q value for tritium ? decay to be (M[T]-M[(3)He])c(2)=18?592.01(7)??eV. This allows an improved test of systematics in measurements of tritium ? decay that set limits on neutrino mass. PMID:25615466
Atomic Masses of Tritium and Helium-3
NASA Astrophysics Data System (ADS)
Myers, E. G.; Wagner, A.; Kracke, H.; Wesson, B. A.
2015-01-01
By measuring the cyclotron frequency ratios of 3He+ to HD+ and T+ to HD+ , and using HD+ as a mass reference, we obtain new atomic masses for 3He and T. Our results are M [3He]=3.016 029 322 43 (19 ) u and M [T ]=3.016 049 281 78 (19 ) u , where the uncertainty includes an uncertainty of 0.12 nu in the mass reference. Allowing for cancellation of common systematic errors, we find the Q value for tritium ? decay to be (M [T ]-M [3He])c2=18 592.01 (7 ) eV . This allows an improved test of systematics in measurements of tritium ? decay that set limits on neutrino mass.
Robert Hellmann; Eckard Bich; Eckhard Vogel
2007-01-01
A heliumhelium interatomic potential energy curve was determined from quantum-mechanical ab initio calculations. Very large atom-centred basis sets including a newly developed d-aug-cc-pV8Z basis set supplemented with bond functions and ab initio methods up to full CI were applied. The aug-cc-pV7Z basis set of Gdanitz (J. Chem. Phys. 113, 5145 (2000)) was modified to be more consistent with the aug-cc-pV5Z
Slow atom scattering from magnetic media
NASA Astrophysics Data System (ADS)
Roach, Timothy; Candee, Katelyn; Moran, Kevin; Richardson, Craig
2013-05-01
The use of magnetic field gradients to manipulate atomic motion has a long history, using a variety of field sources: permanent- and electro-magnet, time- and space-dependent, on macro- and micro-scopic scales. We use a curved sub-micron patterned permanent magnet made from recording media to scatter slow atoms arriving at near normal incidence. The atomic waves are expected to be both diffracted and focused. A cloud of Rb atoms from a MOT is released to fall ~10cm to the magnetic surface and the atoms are probed with laser light after the interaction. Preliminary measurements of the scattered atoms will be presented.
A four-body approach to electron-impact single ionization of helium atoms
NASA Astrophysics Data System (ADS)
Ghanbari-Adivi, Ebrahim; Abdollahi-Tadi, Rayhaneh
2013-12-01
A four-body approach based on the three-Coulomb distorted wave (3CDW) model is applied to study of the electron-impact single ionization of helium atoms. Triply differential cross sections (TDCS) are calculated for different values of the incident and ejection energies and various amounts of the scattering angles. The ejection angular distribution of the TDCS in general exhibits two peaks, binary and recoil peaks. The obtained results are compared with the available experimental data as well as other theoretical predictions. The comparison shows a good agreement between the present calculations and the measurements. Also, the obtained results are compatible with the other theories.
Probing helium interfaces with light scattering : from fluid mechanics to statistical physics
Pierre-Etienne Wolf; Fabien Bonnet; Sylvain Perraud; Laurent Puech; Bernard Rousset; Pierre Thibault
2008-07-10
We have investigated the formation of helium droplets in two physical situations. In the first one, droplets are atomised from superfluid or normal liquid by a fast helium vapour flow. In the second, droplets of normal liquid are formed inside porous glasses during the process of helium condensation. The context, aims, and results of these experiments are reviewed, with focus on the specificity of light scattering by helium. In particular, we discuss how, for different reasons, the closeness to unity of the index of refraction of helium allows in both cases to minimise the problem of multiple scattering and obtain results which it would not be possible to get using other fluids.
Probing helium interfaces with light scattering: From fluid mechanics to statistical physics
NASA Astrophysics Data System (ADS)
Wolf, P. E.; Bonnet, F.; Guyon, L.; Lambert, T.; Perraud, S.; Puech, L.; Rousset, B.; Thibault, P.
2009-02-01
We have investigated the formation of helium droplets in two physical situations. In the first one, droplets are atomised from superfluid or normal liquid by a fast helium vapour flow. In the second, droplets of normal liquid are formed inside porous glasses during the process of helium condensation. The context, aims, and results of these experiments are reviewed, with focus on the specificity of light scattering by helium. In particular, we discuss how, for different reasons, the closeness to unity of the index of refraction of helium allows in both cases to minimise the problem of multiple scattering and obtain results which it would not be possible to get using other fluids.
Spectral line shifts of alkali atoms in liquid helium: a relativistic density functional approach
J. Anton; P. K. Mukherjee; B. Fricke; S. Fritzsche
2007-01-01
Excitation line shifts of the principal resonance transitions in alkali atoms sodium and cesium embedded inside the liquid helium environment have been calculated using four-component relativistic density functional theory. The effect of the liquid helium environment is assumed to be represented by a cluster of 14 atoms surrounding the central alkali atom. The estimated blue shift of the principal resonance
Population dynamics of microwave driven helium Rydberg atoms
NASA Astrophysics Data System (ADS)
Zelazny, Stephen Andrew
2000-11-01
The transition probability of helium Rydberg atoms out of their initially prepared 283S atomic state upon exposure to a pulse of microwave field is studied. Experimental measurements and theoretical models focus on the situation where the microwave pulse consists of two phase-coherent, linearly-polarized fields. A fast beam of n = 283S Helium Rydberg atoms is prepared via double-resonance excitation using CO2 lasers. Interaction with the pulse of microwaves consisting of two phase-locked frequencies occurs in a double-ridged waveguide operating in single mode from below 5 to above 18 GHz. The phase-coherent bichromatic microwave field is produced by filtered selection, separate amplification and post-filtering, and, finally, recombination of harmonics produced by driving a comb generator with a synthesized ? s = 1 GHz signal. The selected harmonics 5 <= p,q <= 18 (giving frequencies ?1 = p? s and ?2 = q? s), their individual amplitudes, and the relative phase ? are all easily varied. The measured transition probability shows structure most sensitive to the relative phase when p:q = 1:2, 2:1 and 3:1; the case p:q = 2:3 is insensitive to relative phase. Experimental results for the p:q = 3:1 case with ? 1 = 18 GHz and ?2 = 6 GHz show Stueckelberg oscillations with characteristics, i.e. fringe contrast and fringe period, sensitive to the phase. Models of the atom's dynamics are built upon energy levels computed with the Floquet method; the models reproduce the observed Stueckelberg oscillations. Association of the model results with the experimental measurements provides a means of obtaining an absolute calibration of the relative phase between ? 1 and ?2. A discussion of the role of broadband noise from the traveling wave tube amplifiers (TWTAs) and how it influences the level of agreement between model and experiment is included. Some experimental measurements of helium Rydberg atoms exposed to a microwave field of elliptical polarization (linear (LP) to circular (CP), and many intermediate values) are presented in an Appendix of this work. The dynamics of the atoms exposed to a pulse of a CP field show Stueckelberg oscillations. A model built upon a rotating frame calculation computed on a basis of atomic states requires inclusion of the magnetic fine structure interaction to reproduce the observed dynamics.
Entanglement in helium atom confined in an impenetrable cavity
Przemyslaw Koscik; Jayanta K. Saha
2015-05-24
We explore ground-state entanglement properties of helium atom confined at the center of an impenetrable spherical cavity of varying radius by using explicitly correlated Hylleraas-type basis set. Results for the dependencies of the von Neumann and linear entanglement entropic measures on the cavity radius are discussed in details. Some highly accurate numerical results for the von Neumann and linear entropy are reported for the first time. It is found that the transition to the strong confinement regime is manifested by the entropies as an appearance of the inflection points on their variations.
Spindependent deep inelastic positron scattering from a polarized helium3 internal gas target
Spindependent deep inelastic positron scattering from a polarized helium3 internal gas target positron scattering from a polarized helium3 internal gas target by Dirk De Schepper Submitted was with the design and construction of the metastability exchange optically pumped 3 He gas target and the analysis
NASA Astrophysics Data System (ADS)
Khmelenko, V. V.; Mao, S.; Meraki, A.; Wilde, S. C.; McColgan, P. T.; Pelmenev, A. A.; Boltnev, R. E.; Lee, D. M.
2014-12-01
We describe a method for creating a high flux beam of cold atoms and molecules. By using this beam method, spectroscopic studies of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures were performed. The cooling by helium vapor of a helium jet containing trace amounts of oxygen after passing through a radiofrequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increased efficiency of energy transfer from metastable helium atoms and molecules to the atomic oxygen in the cold dense helium vapor. The effect might find application for the detection of small quantities of impurities in helium gas as well as possible laser action.
Luminescence of oxygen atoms stimulated by metastable helium at cryogenic temperatures.
Khmelenko, V V; Mao, S; Meraki, A; Wilde, S C; McColgan, P; Pelmenev, A A; Boltnev, R E; Lee, D M
2013-11-01
We present investigations of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures. The cooling of a helium jet containing trace amounts of oxygen after passing through a radio frequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increasing efficiency of energy transfer from metastable helium atoms and molecules to oxygen impurities in the cold dense helium vapor. This effect might find an application for the detection of small quantities of the impurities in helium gas. PMID:24237513
Zeeman deceleration of electron-impact-excited metastable helium atoms
Dulitz, Katrin; Softley, Timothy P
2015-01-01
We present experimental results that demonstrate - for the first time - the Zeeman deceleration of helium atoms in the metastable 2^3S_1state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m/s to a final velocity of 370 m/s. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.
Binding of two helium atoms in confined geometries
Kilic, S. [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik] [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik; [Univ. of Split (Croatia). Faculty of Natural Sciences; Krotscheck, E.; Zillich, R. [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik] [Johannes Kepler Univ., Linz (Austria). Inst. fuer Theoretische Physik
1999-08-01
The authors carry out a comprehensive study of the binding of two helium atoms in unrestricted and, in particular, in restricted geometries in both two and three dimensions. Besides the well known binding of the {sup 4}He dimer in unrestricted geometry in two and three dimensions, the authors also find weakly bound states of the {sup 3}He-{sup 4}He molecule and the {sup 3}He dimer in 2 dimensions. Furthermore, any combination of two {sup 4}He or {sup 3}He atoms can form a molecule if their motion is sufficiently confined. The calculations are carried out by numerically solving the Schroedinger equation as well as by constructing a suitable variational wave function.
Re-examination of a Simplified Model for Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
DiRienzi, Joseph; Drachman, Richard J.
2003-01-01
Using a local effective potential to account for electron exchange, R J Drachman and S K Houston analyzed the zero-energy scattering of ortho-positronium by helium atoms in 1970. The idea was to use the existing static-exchange results to fit the parameters of the local potential and then to use the potential in a variational target-elastic calculation. The results were remarkably good, both for the scattering length and the annihilation parameter. Recently, however, a rigorous target-elastic calculation by Blackwood et al disagreed so strongly with these old results that we have undertaken a re-examination. We find that one of the apparently trivial assumptions of the local potential method is much more important than previously believed.
Re-Examination of a Simplified Model for Positronium-Helium Scattering
NASA Technical Reports Server (NTRS)
Drachman, Richard J.; DiRienzi, Joseph
2003-01-01
Using a local effective potential to account for electron exchange, R J Drachman and S K Houston analyzed the zero-energy scattering of ortho-positronium by helium atoms in 1970. The idea was to use the existing static-exchange results to fit the parameters of the local potential and then to use the potential in a variational target-elastic calculation. The results were remarkably good, both for the scattering length and the annihilation parameter. Recently, however, a rigorous target-elastic calculation by Blackwood et al disagreed so strongly with these old results that we have undertaken a re-examination. We find that the assumption made in the earlier work, that the direct potential is negligible compared with the exchange potential, is not quantitatively correct. But the original idea that omission of the direct potential might compensate approximately for the omission of the van der Waals potential still seems reasonable.
Alkali-Metal Atoms as Spin Labels on Helium Nanodroplets
NASA Astrophysics Data System (ADS)
Koch, Markus; Ratschek, Martin; Callegari, Carlo; Ernst, Wolfgang E.
2010-06-01
We have recently achieved electron spin resonance (ESR) of single alkali-metal atoms isolated on helium (He) nanodroplets A two-laser pump/probe setup for optically detected magnetic resonance is applied, which is based on magnetic circular dichroism to selectively address spin states. The influence of the helium droplet on the alkali-metal valence-electron wave function is directly noticeable as a shift of the ESR transitions with respect to that of free atoms. This perturbation depends on the size of the droplets and can be modeled with an increase of the hyperfine constant, that is an increase of the Fermi contact interaction. After careful characterization of the Rb--He-droplet system the method is being developed into a more universal diagnostic tool to study spin dynamics. ESR silent species located inside the droplet can be investigated by utilizing the surface Rb atom as spin label, and the droplet size is a convenient handle to control the distance between the two. In case of species with a nuclear spin (e.g., 129Xe) spin exchange between the optically pumped Rb atom and the nuclear spin can be studied. We are also extending our method to study magnetically active materials of technological importance, such as Cr, Cu, and small clusters thereof, and we strive to present the first results at the meeting. M. Koch, G. Aubck, C. Callegari, and W.E. Ernst, Phys. Rev. Lett. 103, 035302 (2009) M. Koch, J. Lanzersdorfer, C. Callegari, J.S. Muenter, and W.E. Ernst, J. Phys. Chem. A 113, 13347 (2009) M. Koch, C. Callegari, and W.E. Ernst, Mol. Phys., in press.
Positronium-atom scattering at low energies
NASA Astrophysics Data System (ADS)
Fabrikant, I. I.; Gribakin, G. F.
2014-11-01
A pseudopotential for positronium-atom interaction, based on electron-atom and positron-atom phase shifts, is constructed, and the phase shifts for Ps-Kr and Ps-Ar scattering are calculated. This approach allows us to extend the Ps-atom cross sections, obtained previously in the impulse approximation [I. I. Fabrikant and G. F. Gribakin, Phys. Rev. Lett. 112, 243201 (2014), 10.1103/PhysRevLett.112.243201], to energies below the Ps ionization threshold. Although experimental data are not available in this low-energy region, our results describe well the tendency of the measured cross sections to drop with decreasing velocity at v <1 a.u. Our results show that the effect of the Ps-atom van der Waals interaction is weak compared to the polarization interaction in electron-atom and positron-atom scattering. As a result, the Ps scattering length for both Ar and Kr is positive, and the Ramsauer-Townsend minimum is not observed for Ps scattering from these targets. This makes Ps scattering quite different from electron scattering in the low-energy region, in contrast to the intermediate energy range from the Ps ionization threshold up to v 2 a.u., where the two are similar.
Sibener, S.J.
2010-01-01
F. 0( D,) Production When dilute oxygen-helium gas mixturesoxygen-helium mixture for maximizing Of D ) production. D Ihelium mixtures (12S torr total pressure, 145 watts I The genera and have observed atomic hydrogen production.
Theoretical survey on positronium formation and ionisation in positron atom scattering
NASA Technical Reports Server (NTRS)
Basu, Madhumita; Ghosh, A. S.
1990-01-01
The recent theoretical studies are surveyed and reported on the formation of exotic atoms in positron-hydrogen, positron-helium and positron-lithium scattering specially at intermediate energy region. The ionizations of these targets by positron impact was also considered. Theoretical predictions for both the processes are compared with existing measured values.
A novel spacetime concept for describing electronic motion within a helium atom
Kunming Xu
2007-01-01
Euclidean space and linear algebra do not characterize dynamic electronic orbitals satisfactorily for even the motion of both electrons in an inert helium atom cannot be defined in reasonable details. Here the author puts forward a novel two-dimensional spacetime model from scratch in the context of defining both electrons in a helium atom. Space and time are treated as two
LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon
Budker, Dmitry
LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon D, CA 94720 Results of an investigation of collisional de-excitation of the metastable 6s6p 3 P0 state in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching
Angular-momentum effects in atom-atom scattering
A. Russek; D. B. Jr. Kimball; M. J. Cavagnero
1981-01-01
Physical effects associated with change in angular momentum (in particular, s ..-->.. p transitions) caused by collision-induced excitation at a level crossing in kilovolt-energy ion-atom or atom-atom scattering are investigated. The component of angular momentum involved in this effect is that perpendicular to the plane of collision. The excitation of p states (..delta..L\\/sub perpendicular\\/=-1) and p\\/sub +\\/ states (..delta..L\\/sub perpendicular\\/=+1)
Angular-momentum effects in atom-atom scattering
A. Russek; D. B. Kimball Jr.; M. J. Cavagnero
1981-01-01
Physical effects associated with change in angular momentum (in particular, s-->p transitions) caused by collision-induced excitation at a level crossing in kilovolt-energy ion-atom or atom-atom scattering are investigated. The component of angular momentum involved in this effect is that perpendicular to the plane of collision. The excitation of p- states (DeltaL?=-1) and p+ states (DeltaL?=+1) can be distinguished experimentally by
Scattering lengths for spin-polarized metastable helium-3 and helium-4
NASA Astrophysics Data System (ADS)
Dickinson, A. S.; Gada, F. X.; Leininger, T.
2004-02-01
Upper and lower bounds are estimated for the scattering length, a, for the various isotopes of spin-polarized metastable helium. From a previous study involving various large basis sets and two ab initio approaches, and paying special attention to combine them with the accurate long-range potential, we get, for 4He*-4He* collisions (in Bohr) 152 < 4-4a < 230 and for 3He*-3He* collisions 94 < 3-3a < 113, while a surprising result arises for mixed collisions, 3He*-4He*, 3-4a < -488 and 3-4a > 865. Indeed, the scattering length for this species is very close to the divergence occurring at the binding of a 14th vibrational level. Within these limits, our approach suggests that the values for 4-4a and 3-3a are closer to their upper bounds than to their lower bounds, and that the value for 3-4a is negative and very large (>500) in magnitude. Sympathetic cooling could therefore be very efficient for the mixed species. Cooling-rate coefficients are also evaluated: they are large, of order 10-9 cm3 s-1 at mK temperatures for all combinations.
Toward improved photon-atom scattering predictions
NASA Astrophysics Data System (ADS)
Kissel, Lynn
1994-10-01
Photon-atom scattering is important in a variety of applications, but scattering from a composite system depends on the accurate characterization of the scattering from an isolated atom or ion. We have been examining the validity of simpler approximations of elastic scattering in the light of second-order S-matrix theory. Partitioning the many-body amplitude into Rayleigh and Delbrueck components, processes beyond photoionization contribute. Subtracted cross sections for bound-bound atomic transitions, bound pair annihilation, and bound pair production are required in anomalous scattering factors for: (1) convergence of the dispersion integral; (2) agreement with predictions of the more sophisticated S-matrix approach; (3) satisfying the Thomas-Reiche-Kuhn sum rule. New accurate tabulations of anomalous scattering factors have been prepared for all Z, for energies 0-10,000 keV, within the independent particle approximation (IPA) using a Dirac-Slater model of the atom. Separately, experimental atomic photoabsorption threshold information has been used to modify these IPA predictions for improved comparison with experiment.
Toward improved photon-atom scattering predictions
NASA Astrophysics Data System (ADS)
Kissel, Lynn
1995-05-01
Photon-atom scattering is important in a variety of applications, but scattering from a composite system depends on the accurate characterization of the scattering from an isolated atom or ion. We have been examining the validity of simpler approximations of elastic scattering in the light of second-order S-matrix theory. Partitioning the many-body amplitude into Rayleigh and Delbrck components, processes beyond photoionization contribute. Subtracted cross sections for bound-bound atomic transitions and bound pair annihilation are required in anomalous scattering factors for: (1) convergence of the dispersion integral; (2) agreement with predictions of the more sophisticated S-matrix approach; (3) satisfying the Thomas-Reiche-Kuhn sum rule. New accurate tabulations of anomalous scattering factors have been prepared for all Z, for energies 0-10 000 keV, within the independent particle approximation (IPA) using a Dirac-Slater model of the atom. Separately, experimental atomic photoabsorption threshold information has been used to modify these IPA predictions for improved comparison with experiment.
Resonances of the helium atom in a strong magnetic field
NASA Astrophysics Data System (ADS)
Lhr, Armin; Al-Hujaj, Omar-Alexander; Schmelcher, Peter
2007-01-01
We present an investigation of the resonances of a doubly excited helium atom in a strong magnetic field covering the regime B=0-100a.u. A full-interaction approach which is based on an anisotropic Gaussian basis set of one-particle functions being nonlinearly optimized for each field strength is employed. Accurate results for a total of 17 resonances below the threshold consisting of He+ in the N=2 state are reported in this work. This includes states with total magnetic quantum numbers M=0,-1,-2 and even z parity. The corresponding binding energies are compared to approximate energies of two-particle configurations consisting of two hydrogenlike electrons in the strong-field regime, thereby providing an understanding of the behavior of the energies of the resonances with varying field strength.
Double Photoionization of helium atom using Screening Potential Approach
NASA Astrophysics Data System (ADS)
Saha, Haripada
2014-05-01
The triple differential cross section for double Photoionization of helium atom will be investigated using our recently extended MCHF method. It is well known that electron correlation effects in both the initial and the final states are very important. To incorporate these effects we will use the multi-configuration Hartree-Fock method to account for electron correlation in the initial state. The electron correlation in the final state will be taken into account using the angle-dependent screening potential approximation. The triple differential cross section (TDCS) will be calculated for 20 eV photon energy, which has experimental results. Our results will be compared with available experimental and the theoretical observations.
Symmetric And Non-Symmetric Muonic Helium Atoms Studies
Mohammadi, S. [Physics Department, Payame Noor University, Mashad 91735 (Iran, Islamic Republic of)
2011-10-28
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.
Chu, Xi
Polarizabilities of Sc and Ti atoms and dispersion coefficients for their interaction with helium 2005 The dynamic scalar and tensor polarizabilities of Sc and Ti are computed with time dispersion interac- tions in ScHe and TiHe. We find C6,0 ScHe =30.00, C6,2 ScHe =-1.63, C6,0 TiHe =28
Galgani, Luigi
Classical Helium Atom with Radiation Reaction G. Camelio Universit`a degli Studi di Milano, Corso: November 24, 2011) Abstract We study a classical model of Helium atom in which, in addition to the Coulomb (see for example Refs. 18), in this paper we take into account, for the case of the Helium atom
X-ray observation of a helium atom and placing a nitrogen atom inside He@C60 and He@C70
NASA Astrophysics Data System (ADS)
Morinaka, Yuta; Sato, Satoru; Wakamiya, Atsushi; Nikawa, Hidefumi; Mizorogi, Naomi; Tanabe, Fumiyuki; Murata, Michihisa; Komatsu, Koichi; Furukawa, Ko; Kato, Tatsuhisa; Nagase, Shigeru; Akasaka, Takeshi; Murata, Yasujiro
2013-03-01
Single crystal X-ray analysis has been used as a powerful method to determine the structure of molecules. However, crystallographic data containing helium has not been reported, owing to the difficulty in embedding helium into crystalline materials. Here we report the X-ray diffraction study of He@C60 and the clear observation of a single helium atom inside C60. In addition, the close packing of a helium atom and a nitrogen atom inside fullerenes is realized using two stepwise insertion techniques, that is, molecular surgery to synthesize the fullerenes encapsulating a helium atom, followed by nitrogen radio-frequency plasma methods to generate the fullerenes encapsulating both helium and nitrogen atoms. Electron spin resonance analysis reveals that the encapsulated helium atom has a small but detectable influence on the electronic properties of the highly reactive nitrogen atom coexisting inside the fullerene, suggesting the potential usage of helium for controlling electronic properties of reactive species.
Velocity-dependent total scattering cross sections for metastable helium on Kr and Xe
Hardy, K.A.; Sheldon, J.W.
1984-11-01
Single-beam attenuation measurements of velocity-dependent total scattering cross sections for the interactions of metastable helium (He() on Kr and Xe targets have been measured in the 1-- 5-km/a relative-velocity range. The results are compared with cross sections obtained by full quantum calculations for a Lennard-Jones (12-6) potential with the parameters epsilon and sigma adjusted for a best fit. The results (in atomic units) are epsilon = 3.38 x 10/sup -4/ a.u., sigma = 7.80 a.u., for the He(+Kr system and epsilon = 5.34 x 10/sup -4/ a.u. and sigma = 7.79 a.u. for the He(+Xe system.
Rioux, Frank
5 2 z 4 2 z 2 p 2 + p 4 + := Plots of the spatial and momentum radial distribution functionsHydrogen Atom and Helium Ion Spatial and Momentum Distribution Functions Illustrate, the helium ions coordinate distribution function is localized closer to the nucleus, meaning less uncertainty
Importance of considering helium excited states in He+ scattering by an aluminum surface
NASA Astrophysics Data System (ADS)
Iglesias-Garca, A.; Garca, Evelina A.; Goldberg, E. C.
2014-11-01
The He+/Al system is a very interesting projectile-surface combination which was thought initially as an example of a pure Auger neutralization mechanism. Then, because of the measured reionization explained by the antibonding interaction of the projectile state with the core target states, the resonant charge exchange with the band states was considered as another important contribution to the neutralization. Nevertheless, by only considering the neutralization to the ground state of helium, the measured ion survival probability is still overestimated. On the other hand, measurements of electron emission from an Al surface bombarded by He positive ions suggested the possibility of occupied excited states of helium due to the ion-surface collision. In this work, we also include the excited states of He within the time-dependent scattering process in which both neutralization mechanisms, resonant and Auger, are simultaneously contemplated. Our starting point is a multiorbital Anderson Hamiltonian projected over the selected space of ground and excited atomic configurations. An extra term related to the Auger mechanism is added to this Hamiltonian. A difference with previous works is that this approach includes the electron spin and, therefore, the spin fluctuation statistics in the charge-exchange process is correctly taken into account. We find a notable improvement in the agreement with the experiments and also that the interference between both mechanisms is not dramatic.
Effects of Inelastic Collisions on Transport Cross Sections for Helium Atoms
NASA Astrophysics Data System (ADS)
Phelps, A. V.
2002-10-01
We review experimental and theoretical cross sections for elastic and inelastic collisions between ground state helium atoms from 0.01 eV to 10 keV. Pure elastic scattering is calculated using potentials from thermal transport coefficients, beam attenuation data, and theory. Inelastic collisions cause rapid decreases in measured elastic differential cross sections at angle times energy products greater than 3 degree keV for collision energies above 100 eV.(R. Morgenstern et al), J. Phys. B 4, L330 (1973); M. Barat et al, J. Phys. B 6, 1206 (1973); J. C. Brenot et al, Phys. Rev A 11, 1245 (1975). At these angles, the sum of the inelastic differential cross sections is roughly half theory for elastic scattering only. The inelastic collisions extrapolate to a 40 eV threshold and significantly decrease viscosity cross sections at higher energies. The change in total cross section is small. We correct the normalization of experimental ionization and excitation to theory.(V. Kempter, in The Physics of Electronic and Atomic Collisions), ed. by J. S. Risley and R. Geballe (U. Washington, Seattle, 1975) p. 327; J. P. Gauyacq, J. Phys. B 9, 3067 (1976).
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
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.
Nanolithography with metastable helium atoms in a high-power standing-wave light field
Petra, S J H; Hogervorst, W; Vassen, W
2004-01-01
We have created periodic nanoscale structures in a gold substrate with a lithography process using metastable triplet helium atoms that damage a hydrofobic resist layer on top of the substrate. A beam of metastable helium atoms is transversely cooled and guided through an intense standing-wave light field. Compared to commonly used low-power optical masks, a high-power light field (saturation parameter of 10E7) increases the confinement of the atoms in the standing-wave considerably, and makes the alignment of the experimental setup less critical. Due to the high internal energy of the metastable helium atoms (20 eV), a dose of only one atom per resist molecule is required. With an exposure time of only eight minutes, parallel lines with a separation of 542 nm and a width of 100 nm (1/11th of the wavelength used for the optical mask) are created.
a Neutron Scattering Study of Liquid HELIUM-4.
NASA Astrophysics Data System (ADS)
Andersen, Ken Holst
Available from UMI in association with The British Library. The results of high-resolution, high-accuracy, high-precision neutron inelastic measurements on liquid ^4He are presented. In the collective excitation region, the temperature -dependence of the sharp one-phonon peak is studied and seen to exhibit a qualitative change at T_ {lambda}. The Woods-Svensson hypothesis that the scattering separates naturally into parts proportional to the macroscopic normal and superfluid densities is tested and is found to be too simplistic to describe the detailed temperature dependence. A novel theoretical approach by Glyde and Griffin is evaluated. Their formulation establishes the microscopic connection between the Bose condensate and the phonon excitations in superfluid ^4He. The present parameterisation of their model describes the qualitative temperature dependence well. At high momentum transfer we obtain estimates of the momentum distribution above and below T _lambda, by extracting the Q-dependence of the fourth central moment of the scattering. The obtained n(p) at T > T_lambda is in very good agreement with theoretical calculations. Our low-temperature momentum distribution is more sharply peaked than at high temperature, but reflects the lack of higher -order terms in the short-time expansion used for extraction of the fourth moment. Estimates of the mean kinetic energy per atom are obtained and are slightly higher than previous experimental estimates, but in agreement with theoretical calculations. From this, we evaluate the magnitude of the condensate fraction, and find n_0(T=0) = 10.3 +/- 1.0%.
Barcelona, Universitat de
The muonic helium atom as a classical three-body problem T.J.Stuchi 1 , A.C.B.Antunes 1 and M problem of the muonic helium atom, a helium atom with one of its electrons replaced by a muon. Firstly, we establish the connection of the model with the one-dimensional frozen planetary approximation of the helium
Peach, G; Beams, T J; Peach, Gillian; Whittingham, Ian B; Beams, Timothy J
2002-01-01
A novel modified oscillator method of calculating energy eigenvalues for colliding ultracold atoms tightly confined in harmonic potentials is presented and applied to trapped spin-polarized metastable helium atoms. The perturbed harmonic oscillator problem is characterized by a long asymptotic region beyond the effective range of the interatomic potential, and a very efficient method for integrating inwards through this outer region is developed. The calculated eigenvalues for states with $l=0$ agree closely with those computed directly from the radial Schr\\"{o}dinger equation for the trapped atoms using a discrete variable method, and with those computed self-consistently from an energy-dependent effective scattering length. Finally, the self-consistent method is generalized to collisions with $l \
Paris-Sud XI, Universit de
1263 Chemi-ionization reactions involving metastable helium atoms at high energy P. Pradel and J. J. Introduction. Over the last decade the chemi-ionization of atomic or molecular gases by metastable helium measured over the 15 to 1 500 eV energy interval for collisions of He 2 1S and 2 3S metastable atoms
Ground-State Entanglement Properties of Helium Atom in a Finite Spherical Cavity
NASA Astrophysics Data System (ADS)
Ko?cik, Przemys?aw; Saha, Jayanta K.
2015-05-01
The effects of the spatial confinement on the ground-state entanglement properties of the helium atom have been studied. The finite oscillator potential is used to represent the confining potential. The transition to the free atom regime and the harmonic confinement regime are discussed in detail in dependence of the control parameters of the system.
INTERACTION OF METASTABLE HELIUM ATOMS WITH A Mo [110] SURFACE. SECONDARY ELECTRON SPECTROSCOPY
Boyer, Edmond
L-339 INTERACTION OF METASTABLE HELIUM ATOMS WITH A Mo [110] SURFACE. SECONDARY ELECTRON'une neutralisation Auger. Abstract. 2014 Experimental results are given concerning the interaction of metastable. By means of a time of flight system the energy spectra of the secondary electrons due to metastable atoms
Inelastic scattering of atoms in a double well
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
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.
The role of correlation in the ground state energy of confined helium atom
Aquino, N. [Departamento de Fsica, Universidad Autnoma Metropolitana-Iztapalapa, Apartado Postal 55-534, 09340 Mxico Distrito Federal (Mexico)
2014-01-14
We analyze the ground state energy of helium atom confined by spherical impenetrable walls, and the role of the correlation energy in the total energy. The confinement of an atom in a cavity is one way in which we can model the effect of the external pressure on an atom. The calculations of energy of the system are carried out by the variational method. We find that the correlation energy remains almost constant for a range values of size of the boxes analyzed.
Excitation of helium atoms in collisions with plasma electrons in an electric field
Smirnov, B. M., E-mail: bmsmirnov@gmail.com [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)
2013-01-15
The rate constants are evaluated for excitation of helium atoms in metastable states by electron impact if ionized helium is located in an external electric field and is supported by it, such that a typical electron energy is small compared to the atomic excitation energy. Under these conditions, atomic excitation is determined both by the electron traveling in the space of electron energies toward the excitation threshold and by the subsequent atomic excitation, which is a self-consistent process because it leads to a sharp decrease in the energy distribution function of electrons, which in turn determines the excitation rate. The excitation rate constant is calculated for the regimes of low and high electron densities, and in the last case, it is small compared to the equilibrium rate constant where the Maxwell distribution function is realized including its tail. Quenching of metastable atomic states by electron impact results in excitation of higher excited states, rather than transition to the ground electron state for the electric field strengths under consideration. Therefore, at restricted electron number densities, the rate of emission of resonant photons of the wavelength 58 nm, which results from the transition from the 2{sup 1}P state of the helium atom to the ground state, is close to the excitation rate of metastable atomic states. The efficiency of atomic excitation in ionized helium, i.e., the part of energy of an electric field injected in ionized helium that is spent on atomic excitation, is evaluated. The results exhibit the importance of electron kinetics for an ionized gas located in an electric field.
Excitation of autoionizing states of helium-like ions by scattering of high-energy particles
Mikhailov, A. I.; Mikhailov, I. A.; Nefiodov, A. V., E-mail: anef@thd.pnpi.spb.ru [B. P. Konstantinov Petersburg Nuclear Physics Institute (Russian Federation); Plunien, G. [Technische Universitaet Dresden, Institut fuer Theoretische Physik (Germany)] [Technische Universitaet Dresden, Institut fuer Theoretische Physik (Germany)
2013-03-15
The cross sections for two-electron excitations of helium-like atomic systems into the autoionizing 2s{sup 2} ({sup 1}S)- and 2p{sup 2} ({sup 1}S)-states by collisions with high-energy electrons and photons are deduced. The evaluations are performed to the leading order of non-relativistic perturbation theory. The analytical formulas for cross sections are obtained in the form of universal scalings. A comparison of our theoretical predictions with available theoretical and experimental results for the helium atom is made.
Positron-Atom/Molecule Scattering Experiments
NASA Astrophysics Data System (ADS)
Stein, T. S.
1998-05-01
Recent developments in measurements of total, positronium (Ps) formation, and differential cross sections (DCS's) for positrons (1 to 300 eV) scattered by atoms (including hydrogen, alkali metals, magnesium, and inert gases) and molecules will be reviewed. Measured total and Ps formation cross sections for positron-H scattering are in very good agreement with recent calculations and are consistent with measurements and calculations of other partial cross sections for that collision system.(S. Zhou, H. Li, W.E. Kauppila, C.K. Kwan, and T.S. Stein, Phys. Rev. A 55, 361 (1997).) Ps formation is the dominant partial cross section in positron-H scattering from about 10 to 30 eV and its very important role has interesting connections to recent gamma-ray astrophysics observations. Structure observed in Ps formation cross sections measured for Ar, Kr, CO_2, and SF6 appears to be related to capture of electrons from inner subshells/orbitals of these target atoms/molecules.(W.E. Kauppila, C.K. Kwan, D. Przybyla, and T.S. Stein, XX. ICPEAC Conference Proceedings - Invited Talks - ed. F. Aumayr, G. Betz, and H.P. Winter, 1997.) Differences between various target molecules in regard to the degree of structure in measured DCS's for positron scattering suggest a possible connection between such structure and the degree of spherical symmetry of the target.(D.A. Przybyla, W. Addo-Asah, W.E. Kauppila, C.K. Kwan, and T.S. Stein, Nucl. Instr. and Meth. B, to be published.)
NASA Astrophysics Data System (ADS)
Przybytek, Micha?; Jeziorski, Bogumil
2005-10-01
We developed a series of correlation-consistent, polarized multiple zeta basis sets optimized specifically for the energy of the 2S3 state of helium atom. These basis sets were subsequently augmented with diffuse functions optimized for the van der Waals constants C6 through C14 which determine the asymptotic behavior of the second-order dispersion interaction between 2S3 helium atoms at large interatomic separation R. The resulting bases were applied to compute the Born-Oppenheimer (BO) potential for the lowest ?g+5 state of the helium dimer. The coupled cluster and the full configuration-interaction techniques were employed to account for the electron correlation effects. The cardinal number extrapolation technique was used to obtain the complete-basis-set limit V(R ) for the interaction potential and to find its lower VL(R) and upper VU(R) bounds. The resulting potentials were fitted to an analytical function containing accurate van der Waals constants C6 through C12 (including C11). We found that the complete-basis-set BO potential has a well depth De=1048.240.36cm-1. The highest rotationless vibrational level is bound by D14=90.24.7MHz, much stronger than the previous most accurate estimation of 15.2MHz. The error bounds for De and D14 were obtained using the VL(R) and VU(R) potentials. The S-wave scattering length computed using the VL(R), V(R ), and VU(R) potentials (assuming atomic masses) is aL=7.41nm, a =7.54nm, and aU=7.69nm, respectively. We also computed the adiabatic, relativistic, and quantum electrodynamics (QED) corrections to the BO potential. When these corrections are taken into account the values of D14 and of a (both computed assuming nuclear masses) are 87.46.7MHz and 7.640.20nm; the error bounds reflect now also the uncertainty of the included adiabatic, relativistic, and QED corrections. The value of the scattering length resulting from our investigation lies outside the error bounds of all experimental determinations based on the properties of Bose-Einstein condensate of spin-polarized helium atoms.
Two Electron Processes in Proton-Helium Collisions
Samuel Wright Bross
1993-01-01
Cross sections differential in projectile scattering angle for formation of hydrogen atoms have been measured utilizing recoil ion coincidence techniques in 50 to 175 keV proton-helium collisions. The experimental method allowed separation of the post collision charge states of the target atoms. With a knowledge of the amount of each helium recoil ion charge state produced at each scattering angle,
Statistical theory of electronic Raman resonance scattering by oriented atoms
J. Tulkki; T. Aberg
1980-01-01
A statistical scattering theory approach to the angular distribution and polarisation of inelastically scattered electromagnetic radiation is presented. The authors' theory, which is also applicable to fluorescence, accounts for the influence of the orientation of the target atoms on the radiation pattern of the scattered photons. Their analysis is based on a relativistic generalisation of Placzek's scattering tensor formalism (1934)
Paris-Sud XI, Universit de
L-271 Penning ionization of argon by metastable helium atoms : a study of the energy and angular of metastable helium atoms. The energy spectra of the ejected electrons are obtained at a series of angles in the range 30 to 90, and the intensities due to the different metastable states compared. LE JOURNAL DE
Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets
NASA Astrophysics Data System (ADS)
Krasnokutski, Serge A.; Huisken, Friedrich
2015-02-01
Resonant two-photon ionization (R2PI) spectroscopy has been applied to investigate the solvation of Al atoms in helium droplets. The R2PI spectra reveal vibrational progressions that can be attributed to Al-Hen vibrations. It is found that small helium droplets have very little chance to pick up an aluminum atom after collision. However, the pick-up probability increases with the size of the helium droplets. The absorption band that is measured by monitoring the ions on the mass of the Al dimer is found to be very little shifted with respect to the Al monomer band (400 cm-1). However, using the same laser wavelength, we were unable to detect any Aln photoion with n larger than two.
Wave-packet analysis of multichannel resonances in positron scattering by a helium ion
Yamanaka, Nobuhiro; Kino, Yasushi; Ichimura, Atsushi [RIKEN - Institute of Physical and Chemical Research, Wako, Saitama 351-0198 (Japan); Department of Chemistry, Tohoku University, Sendai 980-8578 (Japan); Institute of Space and Astronautical Science, JAXA, Sagamihara, Kanagawa 229-8510 (Japan)
2004-12-01
We present the wave-packet analysis for two S-wave resonances in positron scattering by a helium ion whose existence was predicted by Bhatia and Drachman but has been controversial. The evolution of the wave packet is solved to exhibit temporary formation of the quasistationary state. For both the resonances, the position and width are determined through the resulting time delays in a consideration of a multichannel nature to agree with those by previous variational eigenenergy calculations. It is further found that the lower resonance dominantly forms from, and decays into, the n=2 states of the helium ion, while the higher one the n=3 states.
Assessment of passive decay heat removal in the General Atomics Modular Helium Reactor
Cocheme, Francois Guilhem
2005-02-17
The purpose of this report is to present the results of the study and analysis of loss-of-coolant and loss-of-flow simulations performed on the Modular Helium Reactor developed by General Atomics using the thermal-hydraulics code RELAP5-3D...
Accurate Kohn-Sham potential for the S state of the helium atom: Tests
Lindgren, Ingvar
1 Accurate Kohn-Sham potential for the 1s2s 3 S state of the helium atom: Tests of the locality and the ionization-potential theorems Sten Salomonson, Fredrik M¨oller and Ingvar Lindgren Abstract: The local Kohn from the pair-correlation program of Salomonson and ¨Oster (Phys. Rev. A 40, 5559 (1989)). The Kohn
NASA Astrophysics Data System (ADS)
Imamura, Kei; Furukawa, Takeshi; Wakui, Takashi; Yang, Xiaofei; Mitsuya, Yousuke; Fujita, Tomomi; Ebara, Yuta; Hayasaka, Miki; Ichikawa, Yuichi; Shirai, Hazuki; Suzuki, Takahiro; Sato, Tomoya; Ohtomo, Yuichi; Kojima, Shuichiro; Asahi, Koichiro; Hatakeyama, Atsushi; Odashima, Hitoshi; Kobayashi, Tohru; Ueno, Hideki; Matsuo, Yukari
We have developed a new nuclear laser spectroscopy method that is named "OROCHI" (Optical RI-atom Observation in Condensed Helium as Ion-catcher). OROCHI utilizes superfluid helium both as an effective stopper of highly energetic ion beams and as a host matrix for in-situ laser spectroscopy of radioactive isotopes (RIs). Zeeman splitting energy and hyperfine splitting energy (HFS) of the atoms introduced into He II are measured to deduce nuclear spins and moments, respectively. So far, we have confirmed the feasibility of OROCHI to RIs by observing the Zeeman resonance successfully using 84-87Rb beam delivered from RIPS (RIKEN Projectile fragmentation Separator) beamline in RIBF. Recently, we have also successfully observed the HFS resonance of the injected 87Rb atoms. We report the details of the experiment.
Beams, T J; Whittingham, I B
2004-01-01
Collisions between tightly confined atoms can lead to ionization and hence to loss of atoms from the trap. We develop second-order perturbation theory for a tensorial perturbation of a spherically symmetric system and the theory is then applied to processes mediated by the spin-dipole interaction. Redistribution and loss mechanisms are studied for the case of spin-polarized metastable helium atoms and results obtained for the five lowest s states in the trap and trapping frequencies ranging from 1 kHz to 10 MHz.
Spectroscopy of antiprotonic helium atoms and its contribution to the fundamental physical constants
Hayano, Ryugo S.
2010-01-01
Antiprotonic helium atom, a metastable neutral system consisting of an antiproton, an electron and a helium nucleus, was serendipitously discovered, and has been studied at CERNs antiproton decelerator facility. Its transition frequencies have recently been measured to nine digits of precision by laser spectroscopy. By comparing these experimental results with three-body QED calculations, the antiproton-to-electron massratio was determined as 1836.152674(5). This result contributed to the CODATA recommended values of the fundamental physical constants. PMID:20075605
Excitation of Sodium Atoms Attached to Helium Nanodroplets: The 3p ? 3s Transition Revisited.
Loginov, Evgeniy; Hernando, Alberto; Beswick, J Alberto; Halberstadt, Nadine; Drabbels, Marcel
2015-06-11
The dynamics of Na atoms on the surface of helium nanodroplets following excitation via the 3p ? 3s transition has been investigated using state-specific ion-based detection of the products. Excitation of the system to the 3p (2)? states is found to lead to the desorption of both bare Na and NaHe exciplexes. The associated speed distributions point to an impulsive desorption process for Na products and a thermally driven process for the NaHe exciplexes. In contrast, excitation of the 3p (2)? state leads exclusively to the impulsive desorption of Na atoms. In this case, the desorption is accompanied by a helium-induced relaxation process, as evidenced by the large fraction of detected Na (2)P1/2 atoms. The relaxation process is thought to be related to a crossing between the (2)?1/2 and (2)? potential energy curves at large distance. PMID:25582680
Charge and radial correlations in helium and helium-like atoms
Toshikatsu Koga; Shji Aoki
1990-01-01
Summary For two-electron atoms, the method of a variable exponent, which treats the orbital exponent (or effective nuclear charge) of an electron as an explicit function of the radial coordinate of the other electron, is studied. The method is shown to improve the energy and other electronic properties remarkably. An incorporation of the variable exponent into the Kellner approximation for
NASA Astrophysics Data System (ADS)
Rezaei, B.
2010-09-01
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.
R. lvarez; M. C. Quintero; A. Rodero
2005-01-01
In this paper, the radial distributions of emissivity of the species present in the helium-nitrogen, helium-oxygen and helium-argon plasmas sustained by the axial injection torch at atmospheric pressure are studied by optical emission spectroscopy using the Abel inversion procedure. The spectrum was scanned for atomic and ionic lines together with rotational bands of neutral and ionic molecules of such species.
Excitation of lowest autoionization states in helium-like ions by photon scattering
NASA Astrophysics Data System (ADS)
Amusia, M. Ya; Mikhailov, A. I.; Mikhailov, I. A.
2001-03-01
High-frequency photon scattering by a two-electron ion with excitation of singlet autoionization states located below the first excited level of the respective one-electron ion are considered. Angular distributions of scattered photons and total cross sections are calculated for transitions to 2s2p(1P) and 2p2(1D) autoionization states (AIS) from the ground state of helium-like ions (the transitions to two lower 1S AIS were investigated earlier). In the zero approximation electrons are described by Coulomb functions and the inter-electron interaction is taken into account in the first perturbation order.
Entanglement Interferometry for Precision Measurement of Atomic Scattering Properties
Artur Widera; Olaf Mandel; Markus Greiner; Susanne Kreim; Theodor W. Hnsch; Immanuel Bloch
2004-01-01
We report on a matter wave interferometer realized with entangled pairs of trapped 87Rb atoms. Each pair of atoms is confined at a single site of an optical lattice potential. The interferometer is realized by first creating a coherent spin superposition of the two atoms and then tuning the interstate scattering length via a Feshbach resonance. The selective change of
HELIUM BACKSCATTERING FROM A RANDOMLY STEPPED SURFACE J. LAPUJOULADE and Y. LEJAY
Paris-Sud XI, Universit de
L-303 HELIUM BACKSCATTERING FROM A RANDOMLY STEPPED SURFACE J. LAPUJOULADE and Y. LEJAY Service de profil d'intensit sont en bon accord avec la macrorugosit. Abstract. 2014 The backscattering of helium to Bragg interference between helium atoms scattered by terraces separated by steps of one atom. From
Heteronuclear ionizing collisions between laser-cooled metastable helium atoms
McNamara, J M; Stas, R J W; Vassen, W
2007-01-01
We have investigated cold ionizing heteronuclear collisions in dilute mixtures of metastable (2 3S1) 3He and 4He atoms, extending our previous work on the analogous homonuclear collisions [R. J. W. Stas et al., PRA 73, 032713 (2006)]. A simple theoretical model of such collisions enables us to calculate the heteronuclear ionization rate coefficient, for our quasi-unpolarized gas, in the absence of resonant light (T = 1.2 mK): K34(th) = 2.4*10^-10 cm^3/s. This calculation is supported by a measurement of K34 using magneto-optically trapped mixtures containing about 1*10^8 atoms of each species, K34(exp) = 2.5(8)*10^-10 cm^3/s. Theory and experiment show good agreement.
Intershell correlations in Compton photon scattering by an atom
Hopersky, Alexey N.; Nadolinsky, Alexey M.; Novikov, Sergey A. [Chair of Mathematics, Rostov State University of TC, Rostov-on-Don 344038 (Russian Federation)
2010-10-15
The role of the intershell correlation effect is theoretically investigated using the example of the Ne atom in nonresonance Compton high-energy x-ray photon scattering by a free atom. The calculation results qualitatively reproduce the same results in the formalism of the generalized oscillator strength and the random phase approximation with exchange for the Compton photon and electron scattering by an atom; when the incident photon energy is 11 keV and the scattering angle is 90 deg., they correspond well with the results of the synchrotron experiment presented in the work by Jung et al. [Phys. Rev. Lett. 81, 1596 (1998)].
Excitation and Ionization-Excitation of Helium in Fast Ion-Atom Collisions
Stephan R. K. Fuelling
1991-01-01
The purpose of this work is to investigate several aspects of many-body effects in fast ion-atom collisions using the target gas helium where the projectile velocities are above the Bohr velocity. The method of high resolution extreme ultraviolet (EUV) spectroscopy has been applied in order to measure absolute state selective cross sections of emitted light from excited HeI and HeII
H. Yamaguchi; J. Eades; R. S. Hayano; M. Hori; D. Horvath; T. Ishikawa; B. Juhasz; J. Sakaguchi; H. A. Torii; E. Widmann; T. Yamazaki
2003-03-19
We have measured twelve transition frequencies of the antiprotonic helium atom (pbar-He+) with precisions of 0.1--0.2 ppm using a laser spectroscopic method. The agreement between the experiment and theories was so good that we can put a limit on the proton-antiproton mass (or charge) difference. The new limit is expected to be much smaller than the already published value, 60 ppb.
Doubly excited states of the hydrogen negative ion and helium atom in astrophysical plasmas
Jiang Pinghui [Center for Theoretical Atomic and Molecular Physics, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China); College of Electrical and Information Engineering, Heilongjiang Institute of Technology, Harbin 150050 (China); Kar, Sabyasachi; Zhou, Y. [Center for Theoretical Atomic and Molecular Physics, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China)
2013-01-15
The nonthermal effects on the doubly excited resonance states of the hydrogen negative ion and helium atom are investigated in Lorentzian astrophysical plasma environments using highly correlated Hylleraas-type wave functions in the framework of the stabilization method. Resonance parameters (resonance position and width) are reported for the first time as functions of the spectral index and plasma parameter. The screening effects are more pronounced in the stronger screening region.
Atomic delay in helium, neon, argon and krypton
NASA Astrophysics Data System (ADS)
Palatchi, Caryn; Dahlstrm, J. M.; Kheifets, A. S.; Ivanov, I. A.; Canaday, D. M.; Agostini, P.; DiMauro, L. F.
2014-12-01
Photoionization by an eXtreme UltraViolet (XUV) attosecond pulse train (APT) in the presence of an infrared pulse (RABBITT method) conveys information about the atomic photoionization delay. By taking the difference of the spectral delays between pairs of rare gases (Ar,He), (Kr,He) and (Ne,He) it is possible to eliminate in each case the larger group delay (attochirp) associated with the APT itself and obtain the Ar, Kr and Ne Wigner delays referenced to model calculations of the He delay. In this work we measure how the delays vary as a function of XUV photon energy but we cannot determine the absolute delay difference between atoms due to lack of precise knowledge of the initial conditions. The extracted delays are compared with several theoretical predictions and the results are consistent within 30 as over the energy range from 10 to 50 eV. An effective Wigner delay over all emission angles is found to be more consistent with our angle-integrated measurement near the Cooper minimum in Ar. We observe a few irregular features in the delay that may be signatures of resonances. .
Zero-energy neutron-triton and proton-Helium-3 scattering with \\eftnopi
Johannes Kirscher
2011-05-18
Model-independent constraints for the neutron-triton and proton-Helium-3 scattering lengths are calculated with a leading-order interaction derived from an effective field theory without explicit pions. Using the singlet neutron-proton scattering length, the deuteron, and the triton binding energy as input, the predictions $\\ants=9.2\\pm2.6 $fm, $\\antt=7.6\\pm1.6 $fm, $\\aphes=3.6\\pm0.32 $fm, and $\\aphet=3.1\\pm 0.23 $fm are obtained. The calculations employ the resonating group method and include the Coulomb interaction when appropriate. The theoretical uncertainty is assessed via a variation of the regulator parameter of the short-distance interaction from $400 $MeV to $1.6 $GeV. The phase-shift and scattering-length results for the proton-Helium-3 system are consistent with a recent phase shift analysis and with model calculations. For neutron-triton, the results for the scattering lengths in both singlet and triplet channels are significantly smaller than suggested by R-matrix and partial-wave-analysis extractions from data. For a better understanding of this discrepancy, the sensitivity of the low-energy four-body scattering system to variations in the neutron-neutron and proton-proton two-nucleon scattering lengths is calculated. Induced by strong charge-symmetry-breaking contact interactions, this dependence is found insignificant. In contrast, a strong correlation between the neutron-triton scattering length and the triton binding energy analogous to the Phillips line is found.
Helium in chirped laser fields as a time-asymmetric atomic switch
Kaprlov-?nsk, Petra Ruth, E-mail: kapralova@jh-inst.cas.cz [Department of Radiation and Chemical Physics, Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8 (Czech Republic); J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejkova 3, 182 23 Prague 8 (Czech Republic); Moiseyev, Nimrod, E-mail: nimrod@tx.technion.ac.il [Schulich Faculty of Chemistry and Faculty of Physics, Technion Israel Institute of Technology, Haifa 32000 (Israel)
2014-07-07
Tuning the laser parameters exceptional points in the spectrum of the dressed laser helium atom are obtained. The weak linearly polarized laser couples the ground state and the doubly excited P-states of helium. We show here that for specific chirped laser pulses that encircle an exceptional point one can get the time-asymmetric phenomenon, where for a negative chirped laser pulse the ground state is transformed into the doubly excited auto-ionization state, while for a positive chirped laser pulse the resonance state is not populated and the neutral helium atoms remains in the ground state as the laser pulse is turned off. Moreover, we show that the results are very sensitive to the closed contour we choose. This time-asymmetric state exchange phenomenon can be considered as a time-asymmetric atomic switch. The optimal time-asymmetric switch is obtained when the closed loop that encircles the exceptional point is large, while for the smallest loops, the time-asymmetric phenomenon does not take place. A systematic way for studying the effect of the chosen closed contour that encircles the exceptional point on the time-asymmetric phenomenon is proposed.
"Fast Atom Diffraction" IBA in the regime of quantum scattering
NASA Astrophysics Data System (ADS)
Winter, H.
2014-08-01
Recently, quantum effects were observed for the scattering of fast atoms from surfaces under a grazing angle of incidence. We discuss basic features of Fast Atom Diffraction (FAD) which adds a further powerful method to the established tools in ion beam analysis. Attractive features of FAD in studies on the structure of surfaces comprise negligible radiation damage, no charging effects, and an extreme sensitivity to the topmost layer of surface atoms. Scanning the quantum wavelength associated with the motion of a massive particle by the variation of its kinetic energy allows one to apply interferometric concepts to surface analysis based on the scattering of fast atoms.
NASA Astrophysics Data System (ADS)
Reininger, Charlotte; Woodfield, Kellie; Keelor, Joel D.; Kaylor, Adam; Fernndez, Facundo M.; Farnsworth, Paul B.
2014-10-01
The absolute number densities of helium atoms in the 2s 3S1 metastable state were determined in four plasma-based ambient desorption/ionization sources by atomic absorption spectroscopy. The plasmas included a high-frequency dielectric barrier discharge (HF-DBD), a low temperature plasma (LTP), and two atmospheric-pressure glow discharges, one with AC excitation and the other with DC excitation. Peak densities in the luminous plumes downstream from the discharge capillaries of the HF-DBD and the LTP were 1.39 1012 cm- 3 and 0.011 1012 cm- 3, respectively. Neither glow discharge produced a visible afterglow, and no metastable atoms were detected downstream from the capillary exits. However, densities of 0.58 1012 cm- 3 and 0.97 1012 cm- 3 were measured in the interelectrode regions of the AC and DC glow discharges, respectively. Time-resolved measurements of metastable atom densities revealed significant random variations in the timing of pulsed absorption signals with respect to the voltage waveforms applied to the discharges.
Measurement of the hyperfine splitting of 133Cs atoms in superfluid helium
NASA Astrophysics Data System (ADS)
Imamura, K.; Furukawa, T.; Yang, X. F.; Mitsuya, Y.; Fujita, T.; Hayasaka, M.; Kobayashi, T.; Hatakeyama, A.; Ueno, H.; Odashima, H.; Matsuo, Y.
2015-04-01
We have been developing a new nuclear laser spectroscopy method named "OROCHI" (Optical RI-atom Observation in Condensed Helium as Ion-catcher). OROCHI utilizes superfluid helium (He II) not only as an efficient stopping medium of highly energetic ions but also as a host matrix of in-situ atomic laser spectroscopy. Using these characteristic of He II, we produce atomic spin polarization and measure Zeeman and hyperfine structure (HFS) splitting using laser-RF (radio frequency) / MW (microwave) double resonance method. From the measured energy splittings, we can deduce nuclear spins and moments. So far, we have conducted a series of experiments using both stable (85,87Rb, 133Cs, 197Au, 107,109Ag) and unstable isotopes (84,86Rb) to confirm the feasibility of OROCHI method, especially observing Zeeman resonance and determining nuclear spins. The measurement of HFS splitting of atoms introduced into He II is indispensable to clarify the nuclear properties by deducing nuclear moments as well as the study of nuclear spins. For this purpose, we perform a precision measurement of HFS of 133Cs atoms immersed in He II using laser ablation technique. In this paper, we describe the result of the experiment.
Resonances in rotationally inelastic scattering of OH(X2?) with helium and neon.
Gubbels, Koos B; Ma, Qianli; Alexander, Millard H; Dagdigian, Paul J; Tanis, Dick; Groenenboom, Gerrit C; van der Avoird, Ad; van de Meerakker, Sebastiaan Y T
2012-04-14
We present detailed calculations on resonances in rotationally and spin-orbit inelastic scattering of OH (X(2)?, j = 3/2, F(1), f) radicals with He and Ne atoms. We calculate new ab initio potential energy surfaces for OH-He, and the cross sections derived from these surfaces compare well with the recent crossed beam scattering experiment of Kirste et al. [Phys. Rev. A 82, 042717 (2010)]. We identify both shape and Feshbach resonances in the integral and differential state-to-state scattering cross sections, and we discuss the prospects for experimentally observing scattering resonances using Stark decelerated beams of OH radicals. PMID:22502519
Volk, Alexander; Thaler, Philipp
2015-01-01
Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2. PMID:25812719
Quasi-elastic electron scattering from atoms and molecules
A. P. Hitchcock; G. Cooper; R. A. Bonham; C. A. Chatzidimitriou-Dreismann
2010-01-01
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
Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass
Hori, Masaki; Korobov, Vladimir I
2014-01-01
Metastable pionic helium ($\\pi{\\rm He}^+$) is a three-body atom composed of a helium nucleus, an electron occupying the $1s$ ground state, and a negatively charged pion $\\pi^-$ in a Rydberg state with principal- and orbital angular momentum quantum numbers of $n\\sim \\ell+1\\sim 16$. We calculate the spin-independent energies of the $\\pi{\\rm ^3He}^+$ and $\\pi{\\rm ^4He}^+$ isotopes in the region $n=15$--19. These include relativistic and quantum electrodynamics corrections of orders $R_{\\infty}\\alpha^2$ and $R_{\\infty}\\alpha^3$ in atomic units, where $R_{\\infty}$ and $\\alpha$ denote the Rydberg and fine structure constants. The fine-structure splitting due to the coupling between the electron spin and the orbital angular momentum of the $\\pi^-$, and the radiative and Auger decay rates of the states are also calculated. Some states $(n,\\ell)=(16,15)$ and $(17,16)$ retain nanosecond-scale lifetimes against $\\pi^-$ absorption into the helium nucleus. We propose to use laser pulses to induce $\\pi^-$ transitions from...
Prospects for precision measurements of atomic helium using direct frequency comb spectroscopy
Eyler, E E; Stowe, Matthew C; Thorpe, Michael J; Schibli, T R; Ye, Jun
2007-01-01
We analyze several possibilities for precisely measuring electronic transitions in atomic helium by the direct use of phase-stabilized femtosecond frequency combs. Because the comb is self-calibrating and can be shifted into the ultraviolet spectral region via harmonic generation, it offers the prospect of greatly improved accuracy for UV and far-UV transitions. To take advantage of this accuracy an ultracold helium sample is needed. For measurements of the triplet spectrum a magneto-optical trap (MOT) can be used to cool and trap metastable $2 ^3S$ state atoms. We analyze schemes for measuring the two-photon $2 ^3S \\to 4 ^3S$ interval, and for resonant two-photon excitation to high Rydberg states, $2 ^3S \\to 3 ^3P \\to n^3S,D$. We also analyze experiments on the singlet-state spectrum. To accomplish this we propose schemes for producing and trapping ultracold helium in the $1 ^1S$ or $2 ^1S$ state via intercombination transition. A particularly intriguing scenario is the possibility of direct singlet state sp...
Dynamics of entanglement between two atomic samples with spontaneous scattering
Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio [Dipartimento di Fisica 'E. R. Caianiello', Universita di Salerno, INFM-UdR di Salerno, INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via. S. Allende, I-84081 Baronissi, SA (Italy)
2004-07-01
We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement and to compare it with the predictions obtained when spontaneous scattering is neglected. We provide numerical evidence that the interferometric scheme to entangle atomic samples is only marginally affected by the presence of spontaneous scattering and should thus be robust even in more realistic situations.
Matter-wave scattering and guiding by atomic arrays
Vaishnav, J. Y. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Walls, J. D. [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States); Apratim, M. [Department of Electrical Engineering, Indian Institute of Technology, Kharagpur 721302 (India); Heller, E. J. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States)
2007-07-15
We investigate the possibility that linear arrays of atoms can guide matter waves, much as fiber optics guide light. We model the atomic line as a quasi-one-dimensional array of s-wave point scatterers embedded in two-dimensions. Our theoretical study reveals how matter-wave guiding arises from the interplay of scattering phenomena with bands and conduction along the array. We discuss the conditions under which a straight or curved array of atoms can guide a beam focused at one end of the array.
Theory of direct scattering of neutral and charged atoms
NASA Technical Reports Server (NTRS)
Franco, V.
1979-01-01
The theory for direct elastic and inelastic collisions between composite atomic systems formulated within the framework of the Glauber approximation is presented. It is shown that the phase-shift function is the sum of a point Coulomb contribution and of an expression in terms of the known electron-hydrogen-atom and proton-hydrogen-atom phase shift function. The scattering amplitude is reexpressed, the pure Coulomb scattering in the case of elastic collisions between ions is isolated, and the exact optical profile function is approximated by a first-order expansion in Glauber theory which takes into account some multiple collisions. The approximate optical profile function terms corresponding to interactions involving one and two electrons are obtained in forms of Meijer G functions and as a one-dimensional integral, and for collisions involving one or two neutral atoms, the scattering amplitude is further reduced to a simple closed-form expression.
Scattering processes in atomic physics, nuclear physics, and cosmology
NASA Astrophysics Data System (ADS)
Shchedrin, Gavriil
The universal way to probe a physical system is to scatter a particle or radiation off the system. The results of the scattering are governed by the interaction Hamiltonian of the physical system and scattered probe. An object of the investigation can be a hydrogen atom immersed in a laser field, heavy nucleus exposed to a flux of neutrons, or space-time metric perturbed by the stress-energy tensor of neutrino flux in the early Universe. This universality of scattering process designates the Scattering Matrix, defined as the unitary matrix of the overlapping in and out collision states, as the central tool in theoretical physics. In this Thesis we present our results in atomic physics, nuclear physics, and cosmology. In these branches of theoretical physics the key element that unifies all of them is the scattering matrix. Additionally, within the scope of Thesis we present underlying ideas responsible for the unification of various physical systems. Within atomic physics problems, namely the axial anomaly contribution to parity nonconservation in atoms, and two-photon resonant transition in a hydrogen atom, it was the scattering matrix which led to the Landau-Yang theorem, playing the central role in these problems. In scattering problems of cosmology and quantum optics we developed and implemented mathematical tools that allowed us to get a new point of view on the subject. Finally, in nuclear physics we were able to take advantage of the target complexity in the process of neutron scattering which led to the formulation of a new resonance width distribution for an open quantum system.
Multiple scattering and charged-particle - hydrogen-atom collisions
NASA Technical Reports Server (NTRS)
Franco, V.; Thomas, B. K.
1979-01-01
Glauber-approximation scattering amplitudes for charged-particle - hydrogen-atom elastic and inelastic collisions are derived directly in terms of the known particle-electron and particle-proton Coulomb scattering amplitudes and the known hydrogen-atom form factors. It is shown that the particle-hydrogen amplitude contains no single-scattering term. The double-scattering term is obtained as a two-dimensional integral in momentum space. It is demonstrated how the result can be used as the starting point for an alternative and relatively simple derivation, in closed form, of the Glauber particle-hydrogen scattering amplitude for transitions from the ground state to an arbitrary (nlm) state.
Charge Scattering and Mobility in Atomically Thin Semiconductors
NASA Astrophysics Data System (ADS)
Ma, Nan; Jena, Debdeep
2014-01-01
The electron transport properties of atomically thin semiconductors such as MoS2 have attracted significant recent scrutiny and controversy. In this work, the scattering mechanisms responsible for limiting the mobility of single-layer semiconductors are evaluated. The roles of individual scattering rates are tracked as the two-dimensional electron gas density is varied over orders of magnitude at various temperatures. From a comparative study of the individual scattering mechanisms, we conclude that all current reported values of mobilities in atomically thin transition-metal dichalcogenide semiconductors are limited by ionized impurity scattering. When the charged impurity densities are reduced, remote optical phonon scattering will determine the ceiling of the highest mobilities attainable in these ultrathin materials at room temperature. The intrinsic mobilities will be accessible only in clean suspended layers, as is also the case for graphene. Based on the study, we identify the best choices for surrounding dielectrics that will help attain the highest mobilities.
Millimeter-Wave Spectra of Carbon Monoxide Solvated with Helium Atoms
NASA Astrophysics Data System (ADS)
Surin, L. A.; Giesen, T. F.; Schlemmer, S.; Potapov, A. V.; Dumesh, B. S.
2009-06-01
Millimeter-wave spectra of He_N-CO (^{12}C^{16}O, ^{13}C^{16}O, ^{12}C^{18}O, ^{13}C^{18}O) clusters with N up to 10, produced in a molecular expansion, were observed using intracavity OROTRON jet spectrometer in the frequency range of 110-150 GHz. The R(0) transitions were detected, which correspond to the known b-type (K = 1 - 0) R(0) lines of the binary system, He_1-CO. Further, the a-type (K = 0 - 0) rotational transitions of He_N-CO (N = 7, 8) in the frequency range of 20-40 GHz were measured combining OROTRON spectrometer with a double resonance technique. The isotopic shifts of the cluster transitions show remarkably smooth behavior with N from 1 to 6 and become rather scattering for N ? 7. The dependence of the rotational constant (cluster moment of inertia) and of the shift of the CO fundamental vibration on the number of He atoms in cluster were obtained for He_N-CO isotopologues from the analysis of their infrared spectra and very recent microwave data for the normal He_N-^{12}C^{16}O isotopologue. This study explores the microscopic evolution of superfluidity, which becomes apparent even in such small clusters as He_4-CO. The obtained results are compared with those from recent quantum Monte-Carlo calculations. and used to further interpret recent infrared measurements of CO in helium nanodroplets. J. Tang, A. R. W. McKellar, J. Chem. Phys. 119, 763 (2003) A. R. W. McKellar, J. Chem. Phys. 121, 6868 (2004) A. R. W. McKellar, J. Chem. Phys. 125, 164328 (2006). L. A. Surin, A. V. Potapov, B. S. Dumesh, S. Schlemmer, Y. Xu, P. L. Raston, and W. Jger, Phys. Rev. Lett. 101, 233401 (2008) T. krbi?, S. Moroni, and S. Baroni, J. Phys. Chem. A 111, 7640 (2007). K. von Haeften, S. Rudolph, I. Simanovski, M. Havenith, R. E. Zillich, and K. B. Whaley, Phys. Rev. B 73, 054502 (2006).
Boyer, Edmond
ETUDE DES ATOMES METASTABLES DE L'HELIUM ET DU NEON PRESENTS DANS LES DECHARGES LUMINESCENTES A investigated metastable helium and neon atoms by means of o p t i c a l absorption. This results, supplemented a t e coefficients for the excitation and destruction of metastable atoms by electronic collisions. Nous
Energetic neutral helium atoms as a tool to study the heliosphere and the local interstellar medium
NASA Astrophysics Data System (ADS)
Swaczyna, Pawel; Grzedzielski, Stan; Bzowski, Maciej
2015-04-01
The aim of our study is to determine the utility of helium energetic neutral atoms (ENA) in the studies of the outer heliosphere, its boundary region, and the nearby interstellar medium, and to assess the requirements for future instruments to enable them to observe He ENA fluxes. Presently, studying these regions is rendered possible mostly by combining the in-situ measurements by the plasma and cosmic-ray instruments on Voyagers and the remote-sensing observations of H ENA from IBEX. Helium as the second most abundant species in the universe could potentially enable further extension of our knowledge about nearest surroundings of the Sun. We assessed the expected emission of the heliospheric He ENA and of He ENA from the nearby interstellar medium. To estimate the heliospheric emission of He ENA we used a simple model of the heliosphere and performed numerical simulations to determine the distribution of various populations of helium ions in the inner heliosphere. Based on this model, we calculated fluxes of He ENA created by charge exchange between helium ions and neutral atoms over a wide energy range from 0.5 keV/nuc up to 1 MeV/nuc. We included binary interactions between various combinations of hydrogen and helium ions and atoms. We also included the signal from the vicinity of the heliosphere produced via the secondary ENA mechanism, which is most likely the source for the observed IBEX Ribbon. The mean free path against ionization of He ENA in the local interstellar medium reaches about 8000 AU for atoms with an energy of a few keV. This is about 10 times more than the mean free path against ionization for hydrogen atoms at the same energy. Thus emission of helium ENA from hypothetic extraheliospheric sources could be detectable from larger distances than the hydrogen atoms. This could provide a novel method of sounding the sources of suprathermal ions that might operate in the surrounding of the heliosphere. The He ENA produced by charge-exchange could then be detectable by an instrument on the Earth's orbit. We found that expected fluxes of He ENA from the heliosheath are smaller by about 2-3 orders of magnitudes than the fluxes of H ENA. Thus, to observe the heliospheric He ENA emission, the future instrument with a mass spectrometer should have sensitivity at least an order of magnitude higher than IBEX. On the other hand, the "darkness" and transparency of the heliosheath in He ENA could provide opportunity to discover hypothetic extraheliospheric sources of He ENA on distances comparable with the distance to the edge of the Local Interstellar Cloud. Such sources could be even brighter than the heliospheric emission of He ENA.
Optical Pumping and Electron Spin Resonance of Single 87Rb Atoms on Helium Nanodroplets
NASA Astrophysics Data System (ADS)
Koch, Markus; Poms, Johannes; Volk, Alexander; Ernst, Wolfgang E.
2011-06-01
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. Aubck, 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
Entanglement interferometry for precision measurement of atomic scattering properties
Artur Widera; Olaf Mandel; Markus Greiner; Susanne Kreim; Theodor W. Hnsch; Immanuel Bloch
2003-10-30
We report on a two-particle matter wave interferometer realized with pairs of trapped 87Rb atoms. Each pair of atoms is confined at a single site of an optical lattice potential. The interferometer is realized by first creating a coherent spin-mixture of the two atoms and then tuning the inter-state scattering length via a Feshbach resonance. The selective change of the inter-state scattering length leads to an entanglement dynamics of the two-particle state that can be detected in a Ramsey interference experiment. This entanglement dynamics is employed for a precision measurement of atomic interaction parameters. Furthermore, the interferometer allows to separate lattice sites with one or two atoms in a non-destructive way.
Helium atom in the monochromatic electromagnetic field. A Hylleraas basis treatment
NASA Astrophysics Data System (ADS)
Ivanov, I. A.; Kheifets, A. S.
2006-05-01
We apply a non-perturbative procedure for the calculation of the total photoionization cross-section of two-electron atomic systems. The procedure is based on the Floquet-Fourier representation of the time-dependent Schrdinger equation. With the use of the Hylleraas-type basis functions, the total photoionization cross-sections obtained are within the accuracy of a fraction of a percent, which, we believe, is the most accurate estimate for the cross-sections available. The total photoionization cross-sections for neutral helium deviate notably from the benchmark experimental data [J.A.R. Samson et al., J. Phys. B 27, 887 (1994)].
Time-resolved studies on the collapse of magnesium atom foam in helium nanodroplets
Gde, S; Tiggesbumker, J; Meiwes-Broer, K -H
2012-01-01
Magnesium atoms embedded in superfluid helium nanodroplets have been identified to arrange themselves in a metastable network, refered to as foam. In order to investigate the ionization dynamics of this unique structure with respect to a possible light-induced collapse the femtosecond dual-pulse spectroscopy technique is applied. Around zero optical delay a strong feature is obtained which represents a direct probe of the foam response. We found that upon collapse, ionization is reduced. A particlar intensity ratio of the pulses allows to address either direct ionization or photoactivation of the neutral complexes, thus affecting reaction pathways. A simplified excitation scheme visualizes possible scenarios in accordance with the experimental observations.
Analytical evaluation of atomic form factors: Application to Rayleigh scattering
NASA Astrophysics Data System (ADS)
Safari, L.; Santos, J. P.; Amaro, P.; Jnkl, K.; Fratini, F.
2015-05-01
Atomic form factors are widely used for the characterization of targets and specimens, from crystallography to biology. By using recent mathematical results, here we derive an analytical expression for the atomic form factor within the independent particle model constructed from nonrelativistic screened hydrogenic wave functions. The range of validity of this analytical expression is checked by comparing the analytically obtained form factors with the ones obtained within the Hartee-Fock method. As an example, we apply our analytical expression for the atomic form factor to evaluate the differential cross section for Rayleigh scattering off neutral atoms.
NASA Technical Reports Server (NTRS)
Souder, P. A.; Casperson, D. E.; Crane, T. W.; Hughes, V. W.; Lu, D. C.; Yam, M. H.; Orth, H.; Reist, H. W.; Zu Putlitz, G.
1975-01-01
Experiments are described in which it proved possible to form the muonic helium atom by stopping polarized negative muons in a helium gas with a 2% xenon admixture at a pressure of 14 atm. The observed Larmor precession amplitudes are plotted against the gyromagnetic ratio for both muons and antimuons stopped in He + 2% Xe. In addition, a non-zero residual polarization of 0.06 plus or minus 0.01 was measured for muons stopped in pure helium gas, which corresponds to a depolarization factor of 18 plus or minus 3.
Effects of impurity atoms and molecules on the lifetime of antiprotonic helium atoms
Widmann, E.; Sugai, I.; Yamazaki, T. [Institute for Nuclear Study, University of Tokyo, 3-2-1 Midori-cho, Tanashi, Tokyo 188 (Japan)] [Institute for Nuclear Study, University of Tokyo, 3-2-1 Midori-cho, Tanashi, Tokyo 188 (Japan); Hayano, R.S.; Iwasaki, M.; Nakamura, S.N.; Tamura, H.; Ito, T.M.; Kawachi, A. [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113 (Japan)] [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113 (Japan); Nishida, N.; Higemoto, W. [Tokyo Institute of Technology, O-Okayama, Meguro-ku, Tokyo 152 (Japan)] [Tokyo Institute of Technology, O-Okayama, Meguro-ku, Tokyo 152 (Japan); Ito, Y. [Research Center for Nuclear Science and Technology, University of Tokyo, Tokai, Ibaraki 319-11 (Japan)] [Research Center for Nuclear Science and Technology, University of Tokyo, Tokai, Ibaraki 319-11 (Japan); Morita, N. [Institute for Molecular Science, Myodaiji, Okazaki 444 (Japan)] [Institute for Molecular Science, Myodaiji, Okazaki 444 (Japan); Hartmann, F.J.; Daniel, H.; von Egidy, T.; Schmid, W.; Hoffmann, J. [Physik Department, Technische Universitaet Muenchen, D-85747 Garching (Germany)] [Physik Department, Technische Universitaet Muenchen, D-85747 Garching (Germany); Eades, J. [CERN, CH-1211 Geneva 23 (Switzerland)] [CERN, CH-1211 Geneva 23 (Switzerland)
1996-05-01
Delayed annihilation time spectra (DATS) of antiprotons in room-temperature helium gas have been studied as a function of the concentration of admixed noble gases (Ne,Ar,Kr,Xe) as well as molecular gases (N{sub 2},O{sub 2},H{sub 2}) at the low-energy antiproton ring at CERN. The DATS were a superposition of two exponential components, one with a lifetime of several 100 ns and the other with a lifetime 1{endash}3 {mu}s. They showed a shorter average lifetime ({ital T}{sub av}) than DATS of pure helium. Ne, Ar, and Kr were found to affect {ital T}{sub av} only slightly even in concentrations up to 20{percent}, while Xe showed a much stronger influence. In the case of molecular gases, the presence of N{sub 2} influenced the DATS much less than O{sub 2} and H{sub 2}, which destroyed the metastability almost completely in concentrations of 100 ppm and less. The decay rate of the slow component of DATS was found to exhibit a linear relation to the number density of the admixture. From this a collisional destruction ({open_quote}{open_quote}quenching{close_quote}{close_quote}) cross section {sigma}{sub {ital q}} was extracted. No evidence for a delayed annihilation of antiprotons in pure Ne, Kr, and Xe was observed. {copyright} {ital 1996 The American Physical Society.}
Hernando, Alberto; Beswick, J Alberto; Halberstadt, Nadine
2013-12-14
The theory of photofragments angular momentum polarization is applied to the photodetachment of an electronically excited alkali atom from a helium nanocluster (N = 200). The alignment of the electronic angular momentum of the bare excited alkali atoms produced is calculated quantum mechanically by solving the excited states coupled equations with potentials determined by density functional theory (DFT). Pronounced oscillations as a function of excitation energy are predicted for the case of Na@(He)200, in marked contrast with the absorption cross-section and angular distribution of the ejected atoms which are smooth functions of the energy. These oscillations are due to quantum interference between different coherently excited photodetachment pathways. Experimentally, these oscillations should be reflected in the fluorescence polarization and polarization-resolved photoelectron yield of the ejected atoms, which are proportional to the electronic angular momentum alignment. In addition, this result is much more general than the test case of NaHe200 studied here. It should be observable for larger droplets, for higher excited electronic states, and for other alkali as well as for alkali-earth atoms. Detection of these oscillations would show that the widely used pseudo-diatomic model can be valid beyond the prediction of absorption spectra and could help in interpreting parts of the dynamics, as already hinted by some experimental results on angular anisotropy of bare alkali fragments. PMID:24329048
Bose-stimulated scattering off a cold atom trap
H. David Politzer
1996-08-28
The angle and temperature dependence of the photon scattering rate for Bose-stimulated atom recoil transitions between occupied states is compared to diffraction and incoherent Rayleigh scattering near the Bose-Einstein transition for an optically thin trap in the limit of large particle number, N. Each of these processes has a range of angles and temperatures for which it dominates over the others by a divergent factor as N->oo.
Exotic atoms, K-nucleus scattering and hypernuclei
Barnes, P. D.
1981-01-01
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...
Resonances in rotationally inelastic scattering of OH(X2?) with helium and neon
NASA Astrophysics Data System (ADS)
Gubbels, Koos B.; Ma, Qianli; Alexander, Millard H.; Dagdigian, Paul J.; Tanis, Dick; Groenenboom, Gerrit C.; van der Avoird, Ad; van de Meerakker, Sebastiaan Y. T.
2012-04-01
We present detailed calculations on resonances in rotationally and spin-orbit inelastic scattering of OH (X 2?, j = 3/2, F1, f) radicals with He and Ne atoms. We calculate new ab initio potential energy surfaces for OH-He, and the cross sections derived from these surfaces compare well with the recent crossed beam scattering experiment of Kirste et al. [Phys. Rev. A 82, 042717 (2010), 10.1103/PhysRevA.82.042717]. We identify both shape and Feshbach resonances in the integral and differential state-to-state scattering cross sections, and we discuss the prospects for experimentally observing scattering resonances using Stark decelerated beams of OH radicals.
Continuum-Coupling in Electron-Atom scattering
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
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.
Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms
Korenman, G Y
2004-01-01
Collisions of metastable antiprotonic helium with atoms of medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between antiprotonic and ordinary helium atoms. S-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F=L\\pm 1/2, J=F\\pm 1/2) of the nL level and relative angular momenta up to l=5 at the kinetic energy E<25 K. The calculated spin-flip cross sections are less than elastic ones by four orders of value in the case \\Delta J=\\pm 1, and by seven orders of value in the case \\Delta F=\\pm 1, \\Delta J=0 or \\Delta J=\\pm 2. The considered cross sections reveal a resonance behaviour at very low energy (E about 1 - 4 K depending on the model parameters). At the density N=3\\times 10^{20} cm^{-3} and T=6 K we obtain the relaxation time =160 ns, the frequency shift \\Delta\
Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms
G. Ya. Korenman; S. N. Yudin
2004-11-18
Collisions of metastable antiprotonic helium with atoms of medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between antiprotonic and ordinary helium atoms. S-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F=L\\pm 1/2, J=F\\pm 1/2) of the nL level and relative angular momenta up to l=5 at the kinetic energy E<25 K. The calculated spin-flip cross sections are less than elastic ones by four orders of value in the case \\Delta J=\\pm 1, and by seven orders of value in the case \\Delta F=\\pm 1, \\Delta J=0 or \\Delta J=\\pm 2. The considered cross sections reveal a resonance behaviour at very low energy (E about 1 - 4 K depending on the model parameters). At the density N=3\\times 10^{20} cm^{-3} and T=6 K we obtain the relaxation time =160 ns, the frequency shift \\Delta\
Scattering theory of multilevel atoms interacting with arbitrary radiation fields
Xuereb, Andr; Horak, Peter; Freegarde, Tim
2009-01-01
We present a generic transfer matrix approach for the description of the interaction of atoms possessing multiple ground state and excited state sublevels with light fields. This model allows us to treat multi-level atoms as classical scatterers in light fields modified by, in principle, arbitrarily complex optical components such as mirrors, resonators, dispersive or dichroic elements, or filters. We verify our formalism for two prototypical sub-Doppler cooling mechanisms and show that it agrees with the standard literature.
Scattering theory of multilevel atoms interacting with arbitrary radiation fields
Andr Xuereb; Peter Domokos; Peter Horak; Tim Freegarde
2009-10-05
We present a generic transfer matrix approach for the description of the interaction of atoms possessing multiple ground state and excited state sublevels with light fields. This model allows us to treat multi-level atoms as classical scatterers in light fields modified by, in principle, arbitrarily complex optical components such as mirrors, resonators, dispersive or dichroic elements, or filters. We verify our formalism for two prototypical sub-Doppler cooling mechanisms and show that it agrees with the standard literature.
Rubidium D1 and D2 atomic lines pressure broadened by ground-state helium atoms
NASA Astrophysics Data System (ADS)
Bouhadjar, F.; Alioua, K.; Bouazza, M. T.
2014-09-01
Full quantum calculations are performed to determine the spectral broadening of the rubidium D1 and D2 lines induced by collisions with helium perturbers. The potential curves of the low-lying RbHe molecular states, as well as the corresponding transition dipole moments, are generated theoretically with ab initio methods based on SA-CASSCF-MRCI calculations, including the spin-orbit effects. The absorption and emission coefficients at wavelengths lying between 650 and 950\\;nm and temperatures ranging from 100 to 3000 K are determined. The absorption profile reveals it is dominated by the free-free transitions, whereas the emission spectral shape arises from the free-free and bound-free transitions. The resulting red- and blue-wing profiles are compared with previous experimental and theoretical works.
Paul J. J. Tol; W. Hogervorst; W. Vassen
2003-12-09
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
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.
Progress on a higher precision measurement of the n =2 triplet P fine structure of atomic helium
NASA Astrophysics Data System (ADS)
Davidson, E. B.; Kato, K.; Beica, H.; George, M. C.; Vutha, A. C.; Weel, M.; Storry, C. H.; Hessels, E. A.
2013-05-01
Precision measurement of the 23P fine structure of atomic helium, when combined with precise theory, can be used to determine the value of the fine-structure constant. We report on progress towards an improved measurement using a new technique which reduces systematic effects, while improving the signal-to-noise ratio. An intense beam of 23S metastable helium atoms is created in a hollow-cathode liquid-nitrogen-cooled DC-discharge source. The atoms are laser excited to the 23P state and microwave transitions are driven between the 23P states using the Ramsey method of separated oscillatory fields (SOF). Atoms which complete the SOF sequence are shelved into the 23S m =-1 metastable state using laser transitions through the 33S state. These m =-1 atoms can be detected with high efficiency.
Experimental and theoretical study of free-free electron-helium scattering in a CO2 laser field
Paris-Sud XI, Universit de
-Francis Xavier University in Canada, using a CO2 laser and a variety of noble gas targets (see [4Experimental and theoretical study of free-free electron-helium scattering in a CO2 laser field D of a linearly polarized CO2 laser field are investigated both experimentally and theoretically. Signals
Ultra-low-temperature reactions of C(P?) atoms with benzene molecules in helium droplets.
Krasnokutski, Serge A; Huisken, Friedrich
2014-12-01
The reaction of carbon atoms with benzene has been investigated in liquid helium droplets at T = 0.37 K. We found an addition of the carbon atom to form an initial intermediate complex followed by a ring opening and the formation of a seven-membered ring. In contrast to a previous gas phase study, the reaction is frozen after these steps and the loss of hydrogen does not occur. A calorimetric technique was applied to monitor the energy balance of the reaction. It was found that more than 267 kJ mol(-1) were released in this reaction. This estimation is in line with quantum chemical calculations of the formation energy of a seven-membered carbon ring. It is suggested that reactions of this kind could be responsible for the low abundance of small polycyclic aromatic hydrocarbon molecules in the interstellar medium. We also found the formation of weakly bonded water-carbon adducts, in which the carbon atom is linked to the oxygen atom of the water molecule with a binding energy of about 33.4 kJ mol(-1). PMID:25481143
Evidence of Catalytic Production of Hot Atomic Hydrogen in RF Generated Hydrogen/Helium Plasmas
Jonathan Phillips; Chun-Ku Chen; Toshi Shiina
2005-09-14
A study of the line shapes of hydrogen Balmer series lines in RF generated low pressure H2/He plasmas produced results suggesting a catalytic process between helium and hydrogen species results in the generation of 'hot' (ca. 28 eV) atomic hydrogen. Even far from the electrodes 'hot' atomic hydrogen was predominant in H2/He plasmas. Line shapes, relative line areas of cold and hot atomic hydrogen (hot/cold>2.5), were very similar for areas between the electrodes and far from the electrodes for these plasmas. In contrast, in H2/Xe only 'warm' (<5 eV) hydrogen (warm/cold<1.0) was found between the electrodes, and only cold hydrogen away from the electrodes. Earlier postulates that preferential hydrogen line broadening in plasmas results from the acceleration of ionic hydrogen in the vicinity of electrodes, and the special charge exchange characteristics of Ar/H2+ are clearly belied by the present results that show atomic hydrogen line shape are similar for H2/He plasmas throughout the relatively large cylindrical (14 cm ID x 36 cm length) cavity.
Dynamics of entanglement between two atomic samples with spontaneous scattering
Antonio Di Lisi; Silvio De Siena; Fabrizio Illuminati
2004-01-01
We investigate the effects of spontaneous scattering on the evolution of entanglement of two atomic samples, probed by phase-shift measurements on optical beams interacting with both samples. We develop a formalism of conditional quantum evolutions and present a wave function analysis implemented in numerical simulations of the state vector dynamics. This method allows us to track the evolution of entanglement
Electron shell ionization of atoms with classical, relativistic scattering.
Ekanayake, N; Luo, S; Grugan, P D; Crosby, W B; Camilo, A D; McCowan, C V; Scalzi, R; Tramontozzi, A; Howard, L E; Wells, S J; Mancuso, C; Stanev, T; Decamp, M F; Walker, B C
2013-05-17
We investigate forward scattering of ionization from neon, argon, and xenon in ultrahigh intensities of 2 10(19) W/cm(2). Comparisons between the gases reveal the energy of the outgoing photoelectron determines its momentum, which can be scattered as far forward as 45 from the laser wave vector k(laser) for energies greater than 1 MeV. The shell structure in the atom manifests itself as modulations in the photoelectron yield and the width of the angular distributions. We arrive at an agreement with theory by using an independent electron model for the atom, a dipole approximation for the bound state interaction, and a relativistic, three-dimensional, classical radiation field including the laser magnetic field. The studies provide the atomic physics within plasmas, radiation, and particle acceleration in ultrastrong fields. PMID:25167403
Scattering of nitrogen molecules by silver atoms.
Loreau, Jrme; Zhang, Peng; Dalgarno, Alexander
2012-04-28
We present a quantal study of the rotationally elastic and inelastic scattering of Ag and N(2), with the nitrogen molecule treated as a rigid rotor. The two-dimensional potential energy surface of the AgN(2) complex is obtained ab initio by means of the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations. The global minimum is found to be located at an internuclear distance of 8.13 a(0) and an angle of 127.2. The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Ag and N(2). Elastic, excitation, and relaxation cross sections and rates are calculated for energies between 0.1 and 5000 cm(-1). The momentum transfer cross sections and rates are also computed. Finally, we compare the cross sections for Ag-N(2) and Na-N(2) to explore the possibility of using silver instead of sodium in experimental tests. PMID:22559480
Miyake, Hirokazu
We have observed Bragg scattering of photons from quantum degenerate 87Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose ...
Optically-Detected Magnetic Resonance of Alkali Atoms Isolated on Helium Nano-Droplets
NASA Astrophysics Data System (ADS)
Koch, Markus; Callegari, Carlo; Ernst, Wolfgang E.
2009-06-01
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.
K. Fukushi; S. N. Willie; R. E. Sturgeon
1993-01-01
Inorganic and organic mercury were determined by helium-microwave induced plasma-atomic emission spectrometry following cold vapor generation. Whereas only inorganic mercury was reduced by stannous ion in an acidic medium, both inorganic and organic mercury (total mercury) were reduced by stannous ion in the presence of cupric ion in a basic medium. Organic mercury was determined as the difference between total
Chuluunbaatar, O; Vinitsky, S I
2002-01-01
The uncoupled correlated variational function of the helium atom ground state declared earlier is examined in calculations of differential cross sections of fast electron impact single and double binary ionization processes. An optimal one-parametric set of orthogonal basic functions is generated to provide the considerable coincidence with the experiment and calculations with the alternative multiparametric trial wave functions.
Magee, Joseph W.
Publisher's Note: "Accurate Atomic Transition Probabilities for Hydrogen, Helium, and Lithium" J and Technology, Gaithersburg, Maryland 20899, USA Received 22 September 2009; published online 31 December 2009 published online on 24 June 2009 with incorrect breaks in the ranges in Table 14. This error resulted
Excitation of {sup 1}S and {sup 3}S Metastable Helium Atoms to Doubly Excited States
Alagia, M. [CNR-ISMN Sezione Roma, Piazzale A. Moro 5, I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy); Coreno, M. [CNR-IMIP, Montelibretti, I-00016 Roma (Italy); Farrokhpour, H.; Omidyan, R.; Tabrizchi, M. [Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Franceschi, P. [Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Tunisia) (Italy); Mihelic, A.; Zitnik, M. [Jozef Stefan Institute, P.O. Box 3000, SI-1001 Ljubljana (Slovenia); Moise, A.; Prince, K. C.; Richter, R. [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza, Trieste (Italy); Soederstroem, J. [Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden); Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Stranges, S. [Dipartimento di Chimica, Universita'La Sapienza', I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy)
2009-04-17
We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed {sup 1,3}P{sup o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s {sup 3}S{sup e}) and singlet (from 1s2s {sup 1}S{sup e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.
Helium atom in a box: Doubly excited levels within the S-wave model
Mitnik, Dario M. [Departmento de Fisica, FCEyN, Universidad de Buenos Aires (C1428EGA) Buenos Aires, Argentina and Instituto de Astronomia y Fisica del Espacio - IAFE, Casilla de Correo 67, Sucursal 28 (C1428EGA) Buenos Aires (Argentina)
2004-08-01
A complete nonperturbative close-coupling solution of the helium atom in a box problem is presented by developing two numerical techniques. The first technique is the direct solution by diagonalization of the Hamiltonian, and the second is based on a constrained relaxation of the wave functions. A Feshbach projection operator of the direct solutions to the bound-continuum subspaces allows a comparison of the low-lying autoionization levels obtained in both methods. Time-dependent propagation of these doubly excited wave functions is analyzed, allowing the calculation and the visualization of the autoionization process. In this work, results are presented for the S-wave model in which the electrons are restricted to spherical states and all angular correlations have been eliminated.
Imaging the inelastic scattering of water with helium. Comparison of experiment and theory.
Yang, Chung-Hsin; Sarma, Gautam; Ter Meulen, J J; Parker, David H; Buck, Udo; Wiesenfeld, Laurent
2010-09-16
State-to-state differential cross sections for rotationally inelastic He-H(2)O scattering have been measured at 53.3 meV (429 cm(-1)) collision energy, using the crossed molecular beam technique. The inelastic events are detected by velocity map imaging of nascent H(2)O(+) ions, which are formed by state-selective (2 + 1) resonance enhanced multiphoton ionization (REMPI) of the scattered H(2)O molecules. Raw density images are converted to flux images and the extracted differential cross sections are compared with full close-coupling calculations of state-to-state cross sections for rotational excitation based on a previously published ab initio potential. A hard-shell ellipsoid model is also employed to yield a more physical insight useful in interpreting the results. The excellent agreement of fully quantum theory and experiment found here for water collisions with helium at a collision energy relevant to that of the interstellar media place the theoretically determined potential energy surface and the collision cross sections extracted using this surface on a firmer basis. PMID:20825242
Peach, Gillian; Whittingham, Ian B.; Beams, Timothy J. [Department of Physics and Astronomy, University College London, Grower Street, London, WC1E 6BT (United Kingdom); School of Mathematical and Physical Sciences, James Cook University, Townsville, 4811 (Australia)
2004-09-01
We analyze a system of two colliding ultracold atoms under strong harmonic confinement from the viewpoint of quantum defect theory and formulate a generalized self-consistent method for determining the allowed energies. We also present two highly efficient computational methods for determining the bound state energies and eigenfunctions of such systems. The perturbed harmonic oscillator problem is characterized by a long asymptotic region beyond the effective range of the interatomic potential. The first method, which is based on quantum defect theory and is an adaptation of a technique developed by one of the authors (G.P.) for highly excited states in a modified Coulomb potential, is very efficient for integrating through this outer region. The second method is a direct numerical solution of the radial Schroedinger equation using a discrete variable representation of the kinetic energy operator and a scaled radial coordinate grid. The methods are applied to the case of trapped spin-polarized metastable helium atoms. The calculated eigenvalues agree very closely for the two methods, and with the eigenvalues computed using the generalized self-consistent method.
First ?K atom lifetime and ?K scattering length measurements
NASA Astrophysics Data System (ADS)
Adeva, B.; Afanasyev, L.; Allkofer, Y.; Amsler, C.; Anania, A.; Aogaki, S.; Benelli, A.; Brekhovskikh, V.; Cechak, T.; Chiba, M.; Chliapnikov, P.; Ciocarlan, C.; Constantinescu, S.; Doskarova, P.; Drijard, D.; Dudarev, A.; Duma, M.; Dumitriu, D.; Fluerasu, D.; Gorin, A.; Gorchakov, O.; Gritsay, K.; Guaraldo, C.; Gugiu, M.; Hansroul, M.; Hons, Z.; Horikawa, S.; Iwashita, Y.; Karpukhin, V.; Kluson, J.; Kobayashi, M.; Kruglov, V.; Kruglova, L.; Kulikov, A.; Kulish, E.; Kuptsov, A.; Lamberto, A.; Lanaro, A.; Lednicky, R.; Marias, C.; Martincik, J.; Nemenov, L.; Nikitin, M.; Okada, K.; Olchevskii, V.; Pentia, M.; Penzo, A.; Plo, M.; Ponta, T.; Prusa, P.; Rappazzo, G.; Romero Vidal, A.; Ryazantsev, A.; Rykalin, V.; Saborido, J.; Schacher, J.; Sidorov, A.; Smolik, J.; Sugimoto, S.; Takeutchi, F.; Tauscher, L.; Trojek, T.; Trusov, S.; Urban, T.; Vrba, T.; Yazkov, V.; Yoshimura, Y.; Zhabitsky, M.; Zrelov, P.
2014-07-01
The results of a search for hydrogen-like atoms consisting of ??K mesons are presented. Evidence for ?K atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic ?K pairs from their breakup in the same target (178 49) as well as in terms of produced ?K atoms (653 42). Using these results, the analysis yields a first value for the ?K atom lifetime of ? = (2.5-1.8+3.0) fs and a first measurement of the S-wave isospin-odd ?K scattering length | a0- | =1/3 |a1/2 -a3/2 | = (0.11-0.04+0.09) M?-1 (aI for isospin I).
Electron elastic scattering off a spin-polarized Cr atom
NASA Astrophysics Data System (ADS)
Dolmatov, V. K.; Amusia, M. Ya.; Chernysheva, L. V.
2014-09-01
Electron elastic scattering off a spin-polarized Cr(...3d54s1, 7S) atom is theoretically studied in the region of electron energies up to 15 eV using both a one-electron "spin-polarized" Hartree-Fock approximation and a multielectron spin-polarized random-phase approximation with exchange. It is found that scattering phase shifts of oppositely spin-polarized incoming electrons and corresponding cross sections of the scattering reactions significantly differ from each other, in general, even without accounting for spin-orbit interaction. This is shown to be associated with the presence of two semifilled 3d5 and 4s1 subshells in the Cr configuration which induce considerably different exchange in the interaction of oppositely spin-polarized incoming electrons with the atom target. The importance of electron correlation in the e-+Cr elastic-scattering process is revealed. Moreover, correlation is shown to induce strong differences between scattering of oppositely spin-polarized electrons off Cr. A physically transparent interpretation for the latter is provided.
Anomalous scattering effects in elastic photon-atom scattering from biomedically important elements
NASA Astrophysics Data System (ADS)
Bradley, D. A.; Roy, S. C.; Kissel, Lynn; Pratt, R. H.
1999-08-01
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, we discuss what is presently known about the validity of form-factor approximations for predictions of elastic photon scattering by atoms. We quantify the uncertainty in form-factor theories for sample atoms of biomedical interest, including: carbon, oxygen, aluminum, calcium, iron, iodine and lead. The importance of effects that go beyond form-factor approximation is illustrated by demonstrating that errors can be introduced in using a simple form-factor-based scaling technique using scattering factors measured at one energy to predict scattering at another energy. These anomalous dispersion have been used extensively in recent years in studying structures of biological macromolecules, either in combination with or as an alternative to isomorphous replacement techniques. We present accurate, high precision anomalous scattering factors for a range of elements commonly used in macro-molecular structure studies, tabulated on a fixed grid interval in the energy range 1- to 100 keV.
Cs atoms on helium nanodroplets and the immersion of Cs+ into the nanodroplet.
Theisen, Moritz; Lackner, Florian; Ernst, Wolfgang E
2011-08-21
We report the non-desorption of cesium (Cs) atoms on the surface of helium nanodroplets (He(N)) in their 6(2)P(1/2) ((2)?(1/2)) state upon photo-excitation as well as the immersion of Cs(+) into the He(N) upon photo-ionization via the 6(2)P(1/2) ((2)?(1/2)) state. Cesium atoms on the surface of helium nanodroplets are excited with a laser to the 6(2)P states. We compare laser-induced fluorescence (LIF) spectra with a desorption-sensitive method (Langmuir-Taylor detection) for different excitation energies. Dispersed fluorescence spectra show a broadening of the emission spectrum only when Cs-He(N) is excited with photon energies close to the atomic D(1)-line, which implies an attractive character of the excited state system (Cs?-He(N)) potential energy curve. The experimental data are compared with a calculation of the potential energy curves of the Cs atom as a function of its distance R from the center of the He(N) in a pseudo-diatomic model. Calculated Franck-Condon factors for emission from the 6(2)P(1/2) ((2)?(1/2)) to the 6(2)S(1/2) ((2)?(1/2)) state help to explain the experimental data. The stability of the Cs?-He(N) system allows to form Cs(+) snowballs in the He(N), where we use the non-desorbing 6(2)P(1/2) ((2)?(1/2)) state as a springboard for ionization in a two-step ionization scheme. Subsequent immersion of positively charged Cs ions is observed in time-of-flight mass spectra, where masses up to several thousand amu were monitored. Only ionization via the 6(2)P(1/2) ((2)?(1/2)) state gives rise to a very high yield of immersed Cs(+) in contrast to an ionization scheme via the 6(2)P(3/2) ((2)?(3/2)) state. When resonant two-photon ionization is applied to cesium dimers on He droplets, Cs(2) (+)-He(N) aggregates are observed in time-of-flight mass spectra. PMID:21861569
Cs atoms on helium nanodroplets and the immersion of Cs{sup +} into the nanodroplet
Theisen, Moritz; Lackner, Florian; Ernst, Wolfgang E. [Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz (Austria)
2011-08-21
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.
NASA Astrophysics Data System (ADS)
Krychowiak, M.; Mertens, Ph; Knig, R.; Schweer, B.; Brezinsek, S.; Schmitz, O.; Brix, M.; Samm, U.; Wolf, R.; Klinger, T.
2010-05-01
Local values of the electron density and temperature in the edge of a fusion plasma can be derived with high space and time resolution by the use of line radiation of atomic helium beams. The accuracy of this method is mainly limited by the uncertainties in the collisional-radiative (CR) model which is needed in order to obtain both plasma parameters from the measured relative intensities of atomic helium lines. Laser-induced fluorescence spectroscopy on a thermal helium beam in the edge plasma of the tokamak TEXTOR in Jlich was applied to validate the CR model of helium. By use of a high-power, pulsed laser system (a dye laser pumped by an excimer laser) several laser excitation schemes starting from the n=2 levels have been tried. The fluorescence light was observed at the laser wavelength and elsewhere in the spectrum providing information on population densities of initial levels as well as on collisional population transfer between excited levels. This paper summarises the results of the measurements, showing principal limits and possible improvements of this experimental validation method of the CR model of the diagnostic helium beam.
Recent progress in electron scattering from atoms and molecules
Brunger, M. J. [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia and Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur (Malaysia); Buckman, S. J. [Institute of Mathematical Sciences, University of Malaya, Kuala Lumpur, Malaysia and Centre for Antimatter-Matter Studies, AMPL, Australian National University, Canberra, ACT 0200 (Australia); Sullivan, J. P.; Palihawadana, P. [Centre for Antimatter-Matter Studies, AMPL, Australian National University, Canberra, ACT 0200 (Australia); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Chiari, L.; Pettifer, Z. [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Silva, G. B. da [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia and Universidade Federal de Mato Grosso, Barra do Garas, Mato Grosso (Brazil); Lopes, M. C. A. [Centre for Antimatter-Matter Studies, CAPS, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia and Departamento de Fisica, Universidade Federal de Juiz de Fora, Juiz de Fora, MG (Brazil); Duque, H. V. [Departamento de Fisica, Universidade Federal de Juiz de Fora, Juiz de Fora, MG (Brazil); Masin, Z.; Gorfinkiel, J. D. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA (United Kingdom); Garcia, G. [Instituto de Fisica Fundamental, CSIC, Madrid E-28006 (Spain); Hoshino, M.; Tanaka, H. [Department of Physics, Sophia University, Tokyo, 102-8554 (Japan); Limo-Vieira, P. [Laboratrio de Colises Atmicas e Moleculares, CEFITEC, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)
2014-03-05
We present and discuss recent results, both experimental and theoretical (where possible), for electron impact excitation of the 3s[3/2 ]{sub 1} and 3s?[1/2 ]{sub 1} electronic states in neon, elastic electron scattering from the structurally similar molecules benzene, pyrazine, and 1,4-dioxane and excitation of the electronic states of the important bio-molecule analogue ?-tetrahydrofurfuryl alcohol. While comparison between theoretical and experimental results suggests that benchmarked cross sections for electron scattering from atoms is feasible in the near-term, significant further theoretical development for electron-molecule collisions, particularly in respect to discrete excitation processes, is still required.
Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices
NASA Astrophysics Data System (ADS)
Carminati, F.-R.; Sanchez-Palencia, L.; Schiavoni, M.; Renzoni, F.; Grynberg, G.
2003-01-01
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [
Scattering approach to dispersive atom-surface interactions
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
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.
Spin Ordering on the Niobium OXIDE(100) Surface Measured by Elastic Metastable Helium Scattering.
NASA Astrophysics Data System (ADS)
Swan, Anna K.
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.
NASA Technical Reports Server (NTRS)
Fahr, H. J.; Nass, H. U.; Rucinski, D.
1984-01-01
Neutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the Sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.
NASA Astrophysics Data System (ADS)
Poms, Johannes; Hauser, Andreas W.; Ernst, Wolfgang E.
2013-06-01
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)
Scattering of cold-atom coherences by hot atoms: frequency shifts from background-gas collisions.
Gibble, Kurt
2013-05-01
Frequency shifts from background-gas collisions currently contribute significantly to the inaccuracy of atomic clocks. Because nearly all collisions with room-temperature background gases that transfer momentum eject the cold atoms from the clock, the interference between the scattered and unscattered waves in the forward direction dominates these frequency shifts. We show they are ? 10 times smaller than in room-temperature clocks and that van der Waals interactions produce the cold-atom background-gas shift. General considerations allow the loss of the Ramsey fringe amplitude to bound this frequency shift. PMID:23683186
Cooperative scattering and radiation pressure force in dense atomic clouds
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
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.
Charge Scattering and Mobility in Atomically Thin Semiconductors
NASA Astrophysics Data System (ADS)
Ma, Nan; Jena, Debdeep
2014-03-01
The electron transport properties in atomically thin semiconductors have attracted intense interest. In this work, we study the scattering mechanisms that limiting the mobility of such semiconductors. The effects of the dielectric environments are also evaluated. We find that high-K dielectrics increase the charged-impurity-limited mobility, but weaken the free-carrier screening. The strong remote optical phonon scattering from high-K dielectrics severely decrease the high-temperature mobility. From a comparative study of different scattering mechanisms, we find that all current reported measured mobilities (around 100 cm2/Vs) are dominated by charged impurity scattering. When the impurity densities are reduced, remote phonon scattering determines the room-temperature mobility upper-limits. The mobilities achieved till date are far below the intrinsic potential in these materials. The truly intrinsic mobility over 10,000 cm2/Vs at room temperature can only be achieved in ultraclean suspended samples. Among the commonly used dielectrics, AlN and BN offer the best compromise if a high mobility over 1000 cm2/Vs and a high gate capacitance are simultaneously desired, as is the case in field effect transistors.
Advances in the helium-jet coupled on-line mass separator RAMA. [Recoil Atom Mass Analyzer
D. M. Moltz; J. Aysto; M. D. Cable; R. F. Parry; P. E. Haustein; J. M. Wouters; J. Cerny
1980-01-01
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°C)
Intermediate-to high-energy positrons scattered by alkali-metal atoms David D. Reid
Wadehra, Jogindra M.
Intermediate- to high-energy positrons scattered by alkali-metal atoms David D. Reid Department cross sections for positrons scattered from alkali-metal atoms. The energy of the positrons ranges from that we recently proposed and tested for the noble-gas targets. For positronalkali-metal scattering
Observation of correlated X-ray scattering at atomic resolution.
Mendez, Derek; Lane, Thomas J; Sung, Jongmin; Sellberg, Jonas; Levard, Clment; Watkins, Herschel; Cohen, Aina E; Soltis, Michael; Sutton, Shirley; Spudich, James; Pande, Vijay; Ratner, Daniel; Doniach, Sebastian
2014-07-17
Tools to study disordered systems with local structural order, such as proteins in solution, remain limited. Such understanding is essential for e.g. rational drug design. Correlated X-ray scattering (CXS) has recently attracted new interest as a way to leverage next-generation light sources to study such disordered matter. The CXS experiment measures angular correlations of the intensity caused by the scattering of X-rays from an ensemble of identical particles, with disordered orientation and position. Averaging over 15 496 snapshot images obtained by exposing a sample of silver nanoparticles in solution to a micro-focused synchrotron radiation beam, we report on experimental efforts to obtain CXS signal from an ensemble in three dimensions. A correlation function was measured at wide angles corresponding to atomic resolution that matches theoretical predictions. These preliminary results suggest that other CXS experiments on disordered ensembles--such as proteins in solution--may be feasible in the future. PMID:24914148
Observation of correlated X-ray scattering at atomic resolution
Mendez, Derek; Lane, Thomas J.; Sung, Jongmin; Sellberg, Jonas; Levard, Clment; Watkins, Herschel; Cohen, Aina E.; Soltis, Michael; Sutton, Shirley; Spudich, James; Pande, Vijay; Ratner, Daniel; Doniach, Sebastian
2014-01-01
Tools to study disordered systems with local structural order, such as proteins in solution, remain limited. Such understanding is essential for e.g. rational drug design. Correlated X-ray scattering (CXS) has recently attracted new interest as a way to leverage next-generation light sources to study such disordered matter. The CXS experiment measures angular correlations of the intensity caused by the scattering of X-rays from an ensemble of identical particles, with disordered orientation and position. Averaging over 15 496 snapshot images obtained by exposing a sample of silver nanoparticles in solution to a micro-focused synchrotron radiation beam, we report on experimental efforts to obtain CXS signal from an ensemble in three dimensions. A correlation function was measured at wide angles corresponding to atomic resolution that matches theoretical predictions. These preliminary results suggest that other CXS experiments on disordered ensemblessuch as proteins in solutionmay be feasible in the future. PMID:24914148
Scattering of positrons and electrons by alkali atoms
NASA Technical Reports Server (NTRS)
Stein, T. S.; Kauppila, W. E.; Kwan, C. K.; Lukaszew, R. A.; Parikh, S. P.; Wan, Y. J.; Zhou, S.; Dababneh, M. S.
1990-01-01
Absolute total scattering cross sections (Q sub T's) were measured for positrons and electrons colliding with sodium, potassium, and rubidium in the 1 to 102 eV range, using the same apparatus and experimental approach (a beam transmission technique) for both projectiles. The present results for positron-sodium and -rubidium collisions represent the first Q sub T measurements reported for these collision systems. Features which distinguish the present comparisons between positron- and electron-alkali atom Q sub T's from those for other atoms and molecules (room-temperature gases) which have been used as targets for positrons and electrons are the proximity of the corresponding positron- and electron-alkali atom Q sub T's over the entire energy range of overlap, with an indication of a merging or near-merging of the corresponding positron and electron Q sub T's near (and above) the relatively low energy of about 40 eV, and a general tendency for the positron-alkali atom Q sub T's to be higher than the corresponding electron values as the projectile energy is decreased below about 40 eV.
Plasmon enhanced Raman scattering effect for an atom near a carbon nanotube
Bondarev, I. V. [North Carolina Central University, Durham, NC (United States)
2015-01-01
Quantum electrodynamics theory of the resonance Raman scattering is developed for an atom in a close proximity to a carbon nanotube. The theory predicts a dramatic enhancement of the Raman intensity in the strong atomic coupling regime to nanotube plasmon near-fields. This resonance scattering is a manifestation of the general electromagnetic surface enhanced Raman scattering effect, and can be used in designing efficient nanotube based optical sensing substrates for single atom detection, precision spontaneous emission control, and manipulation.
One-phonon transitions observed in the scattering of He atoms from a LiF/001/ surface.
NASA Technical Reports Server (NTRS)
Fisher, S. S.; Bledsoe, J. R.
1972-01-01
For the scattering of a nearly monoenergetic beam of thermal-energy He atoms from a cleaved (001)LiF crystal surface, speed distributions of the reflected atoms are measured at suitably spaced scattering angles within the plane of incidence. From the measurements, elastic and one-phonon inelastic scattering processes are identified. Elastically scattered atoms distribute themselves in a set of sharp diffraction peaks. One-phonon inelastically scattered atoms are dispersed about each diffraction peak. The most probable velocities of the inelastically scattered atoms exhibit a characteristic sawtooth variation with scattering angle which, to first approximation, corresponds to conservation of the component of atom momentum tangent to the surface.-
Scattering of high-velocity Ar atoms by CO2, OCS, and CS2
NASA Technical Reports Server (NTRS)
Amdur, I.; Peters, W. A.; Jordan, J. E.; Mason, E. A.
1976-01-01
Fast Ar beams have been scattered by room-temperature CO2, OCS, and CS2 to obtain average atom-molecule potentials. The results are consistent with other scattering measurements on similar systems, and are also in excellent agreement with available theoretical calculations based on an electron-gas model. Decomposition of the atom-molecule potentials into constituent atom-atom potentials shows that such a representation can be utilized with fair accuracy but that a definite discrepancy exists.
NASA Astrophysics Data System (ADS)
Wu, Mengxi; Chen, Shaohao; Gaarde, Mette B.; Schafer, Kenneth J.
2013-10-01
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.
Pifrader, Alexandra; Allard, Olivier; Auboeck, Gerald; Callegari, Carlo; Ernst, Wolfgang E. [Institute of Experimental Physics, TU Graz, Petersgasse 16, A-8010 Graz (Austria); Huber, Robert [Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Ancilotto, Francesco [Dipartimento di Fisica 'G. Galilei', Universita di Padova, via Marzolo 8, I-35131 Padova, Italy and CNR-IOM-Democritos, I-34014 Trieste (Italy)
2010-10-28
Alkali-metal atoms captured on the surface of superfluid helium droplets are excited to high energies ({approx_equal}3 eV) by means of pulsed lasers, and their laser-induced-fluorescence spectra are recorded. We report on the one-photon excitation of the (n+1)p(leftarrow)ns transition of K, Rb, and Cs (n=4, 5, and 6, respectively) and on the two-photon one-color excitation of the 5d(leftarrow)5s transition of Rb. Gated-photon-counting measurements are consistent with the relaxation rates of the bare atoms, hence consistent with the reasonable expectation that atoms quickly desorb from the droplet and droplet-induced relaxation need not be invoked.
Pifrader, Alexandra; Allard, Olivier; Aubck, Gerald; Callegari, Carlo; Ernst, Wolfgang E; Huber, Robert; Ancilotto, Francesco
2010-10-28
Alkali-metal atoms captured on the surface of superfluid helium droplets are excited to high energies (?3?eV) by means of pulsed lasers, and their laser-induced-fluorescence spectra are recorded. We report on the one-photon excitation of the (n+1)p?ns transition of K, Rb, and Cs (n=4, 5, and 6, respectively) and on the two-photon one-color excitation of the 5d?5s transition of Rb. Gated-photon-counting measurements are consistent with the relaxation rates of the bare atoms, hence consistent with the reasonable expectation that atoms quickly desorb from the droplet and droplet-induced relaxation need not be invoked. PMID:21033800
I. P. Bogdanova; V. D. Marusin
1973-01-01
In the collision of a metastable atom A* with atom B, whose ionization ; potential is lower than the excitation potential of the metastable atom. a ; possible ionization process of atom B (Penning process) is A* + B yields A + B\\/; sup +\\/ + e DELTA E. The effective cross section for this process was measured ; for
Pacheco, Alexander B; Thorndyke, Brian; Reyes, Andrs; Micha, David A
2007-12-28
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
NASA Astrophysics Data System (ADS)
Yang, Z. Q.; Ye, D. F.; Ding, Thomas; Pfeifer, Thomas; Fu, L. B.
2015-01-01
In the present paper, we investigate the time-resolved transient absorption spectroscopy of doubly excited states of helium atoms by solving the time-dependent two-electron Schrdinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared (IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.
Rayleigh Scattering Cross Section Redward of Ly$?$ by Atomic Hydrogen
Hee-Won Lee; Hee Il Kim
2004-02-02
We present a low energy expansion of the Kramers-Heisenberg formula for atomic hydrogen in terms of $(\\omega/\\omega_l)$, where $\\omega_l$ and $\\omega$ are the angular frequencies corresponding to the Lyman limit and the incident radiation, respectively. The leading term is proportional to $(\\omega/\\omega_l)^4$, which admits a well-known classical interpretation. With higher order terms we achieve accuracy with errors less than 4 % of the scattering cross sections in the region $\\omega/\\omega_l\\le 0.6$. In the neighboring region around Ly$\\alpha$ ($\\omega/\\omega_l >0.6$), we also present an explicit expansion of the Kramers-Heisenberg formula in terms of $\\Delta\\omega\\equiv (\\omega-\\omega_{Ly\\alpha})/\\omega_{Ly\\alpha}$. The accuracy with errors less than 4 % can be attained for $\\omega/\\omega_l \\ge 0.6$ with the expansion up to the fifth order of $\\Delta\\omega$. We expect that these formulae will be usefully applied to the radiative transfer in high neutral column density regions, including the Gunn-Peterson absorption troughs and Rayleigh scattering in the atmospheres of giants.
Quantitative Surface Atomic Structure Analysis by Low-Energy Ion Scattering Spectroscopy (ISS)
Masakazu Aono; Ryutaro Souda
1985-01-01
Surface atomic structure analysis by low-energy ion scattering spectroscopy (ISS) is reviewed, with particular emphasis on quantitative surface atomic structure analysis by ISS. The important differences between ISS and Rutherford backscattering spectroscopy (RBS), some basic characteristics of ISS, a special type of ISS called impact-collision ion scattering spectroscopy (ICISS), and the general features of the shadow cone in the energy
Inter-atomic force constants of BaF2 by diffuse neutron scattering measurement
NASA Astrophysics Data System (ADS)
Sakuma, Takashi; Makhsun, Sakai, Ryutaro; Xianglian, Takahashi, Haruyuki; Basar, Khairul; Igawa, Naoki; Danilkin, Sergey A.
2015-04-01
Diffuse neutron scattering measurement on BaF2 crystals was performed at 10 K and 295 K. Oscillatory form in the diffuse scattering intensity of BaF2 was observed at 295 K. The correlation effects among thermal displacements of F-F atoms were obtained from the analysis of oscillatory diffuse scattering intensity. The force constants among neighboring atoms in BaF2 were determined and compared to those in ionic crystals and semiconductors.
Light scattering from ultracold atomic gases in optical lattices at finite temperature
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
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.
Transverse Momentum Transfer in Atom-Light Scattering B.A. van Tiggelen,1
Paris-Sud XI, Universit de
Transverse Momentum Transfer in Atom-Light Scattering B.A. van Tiggelen,1 A. Nussle,1 and G is moving. Light scattering exchanges momentum between mat- ter and radiation, and thus induces a force on the matter. Classical light scattering is well known to be affected by a magnetic field. A specific feature
Differential elastic scattering cross sections for 54.9eV positrons incident on helium
NASA Technical Reports Server (NTRS)
Chaplin, R. L.; Diana, L. M.; Brooks, D. L.
1990-01-01
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 average scattering angles which range from 14 to 36 deg. Also the averages of five differential cross sections which have adjacent values of scattering angle are plotted versus the corresponding averages of the scattering angles. The curve fitted to these data is shaped like the theoretical curve but has its minimum and its maximum at scattering angles that are about 4 deg higher and 15 deg lower respectively than predicted by theory.
The helium trimer with soft-core potentials
A. Kievsky; E. Garrido; C. Romero-Redondo; P. Barletta
2011-01-10
The helium trimer is studied using two- and three-body soft-core potentials. Realistic helium-helium potentials present an extremely strong short-range repulsion and support a single, very shallow, bound state. The description of systems with more than two helium atoms is difficult due to the very large cancellation between kinetic and potential energy. We analyze the possibility of describing the three helium system in the ultracold regime using a gaussian representation of a widely used realistic potential, the LM2M2 interaction. However, in order to describe correctly the trimer ground state a three-body force has to be added to the gaussian interaction. With this potential model the two bound states of the trimer and the low energy scattering helium-dimer phase shifts obtained with the LM2M2 potential are well reproduced.
Exchange and polarization effects on elastic electron-atom/ion scattering
Kaganovich, Igor
Exchange and polarization effects on elastic electron-atom/ion scattering (aka. a small part approaches Needed for modeling and simulations : accurate atomic and molecular data (, d/d, , rates physics atomic physics molecular physics beam-surface interactions #12;0 ( ) ( ) ( ) ( ) e e e i i i
Safron, S.A.; Skofronick, J.G.
1994-04-01
This progress report describes work carried out in the study of surface structure and dynamics of ionic insulators, the microscopic interactions controlling epitaxial growth and the formation of overlayers, and energy exchange in multiphonon surface scattering. The approach used is to employ high resolution helium atom scattering to study the geometry and structural features of the surfaces. Experiments have been carried out on the surface dynamics of RbCl and preliminary studies done on CoO and NiO. Epitaxial growth and overlayer dynamics experiments on the systems NaCl/NaCl(001), KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been performed. They have collaborated with two theoretical groups to explore models of overlayer dynamics with which to compare and to interpret their experimental results. They have carried out extensive experiments on the multiphonon scattering of helium atoms from NaCl and, particularly, LiF. Work has begun on self-assembling organic films on gold and silver surfaces (alkyl thiols/Au(111) and Ag(111)).
Yu, Shengrui; Su, Shu; Dai, Dongxu; Yuan, Kaijun; Yang, Xueming
2015-04-21
The state-to-state dynamics of high-n Rydberg H-atom scattering with para-H2 at the collision energies of 0.45 and 1.07 eV have been studied using the H-atom Rydberg tagging time-of-flight technique. Both the inelastic scattering and reactive scattering are observed in the experimental time-of-flight spectra. The products H2(v', j' = odd) come only from reactive scattering and present clearly forward-backward asymmetric angular distributions, which differ from those of the corresponding ion-molecule reaction. The products H2(v', j' = even), however, come from both reactive scattering and inelastic scattering. Simulating the rotational distribution from reactive scattering, we found that most of the H2(v', j' = even) products come from inelastic scattering. The angular distributions of the product H2(v', j' = even) are consistent with what is predicted by the conventional textbook mechanism of inelastic scattering, and are a little different from those of the corresponding ion-molecule inelastic scattering. These results suggest that the effect of Rydberg electron could not be neglected in describing the differential cross sections of H* + para-H2 scattering. From the simulation, the branching ratios of the inelastic scattering channel were determined to be 66% and 79% at the collision energies of 0.45 and 1.07 eV, respectively. PMID:25162182
Positron scattering on helium, neon and argon above 4 eV
B. Jaduszliwer; D. A. L. Paul
1974-01-01
The authors have measured the transmission of a positron beam through helium, neon and argon gases from 4 eV up to the positronium\\u000a formation thresholds. A variable longitudinal magnetic field affects the transmission and allows some degree of phase shift\\u000a separation, analogously to the performance of an angular distribution experiment. The results for neon and argon are presented.
Can paramagnetic atoms in superfluid helium be used to search for permanent electric dipole moments?
M. Arndt; S. I. Kanorsky; A. Weis; T. W. Hnsch
1993-01-01
Large densities together with long trapping times have been observed for atoms immersed in He II. The feasibility of experiments searching for permanent electric dipole moments (PEDM) of paramagnetic atoms in He II is discussed.
{ital Ab initio} calculation for low-energy elastic scattering of electrons from sulfur atoms
Saha, H.P.; Lin, D. [Department of Physics, University of Central Florida, Orlando, Florida 32816 (United States)] [Department of Physics, University of Central Florida, Orlando, Florida 32816 (United States)
1997-09-01
The multiconfiguration Hartree-Fock method for continuum wave functions has been used to perform calculations of elastic scattering of electrons from the open-shell sulfur atom at low energies. The electron correlation and polarization of the sulfur atom by the scattered electron, which are very important in this calculation, have been taken into account very accurately {ital ab initio} through the configuration-interaction procedure by optimizing both bound and continuum orbitals simultaneously at each kinetic energy of the scattered electron. The scattering lengths, phase shifts, and differential, total and momentum-transfer cross sections for electrons elastically scattered from sulfur atoms are calculated for the impact-energy range from 0 to 27.2 eV. The wave functions computed exactly at zero energy are used to compute the scattering length. The present results are compared with other available theoretical results. {copyright} {ital 1997} {ital The American Physical Society}
Effects of cold work and niobium on the blistering of zirconium by helium atoms
NASA Astrophysics Data System (ADS)
Zee, R. H.; Watters, J. F.
1984-05-01
Zr-2.5 wt% Nb and high purity zirconium, in either the fully annealed or 40% cold-worked conditions, were irradiated with 50 keV helium ions at temperatures between 100 K and 773 K to doses up to 2 10 22 ions/m 2. Above 300 K, blisters were not observed in annealed zirconium whereas at lower temperatures, extensive surface damage was produced. In Zr-2.5 wt% Nb, blisters were found in both the annealed and cold-worked alloys at all temperatures. The blistering behaviour in zirconium is related to the trapping of the implanted helium ions and the mechanical properties of these materials. Two zirconium single crystals were irradiated at 573 K and 773 K for comparison. Extensive blistering was observed in both single crystals even though no surface damage was found in the polycrystalline material irradiated under the same conditions.
Interacting double dark resonances in a hot atomic vapor of helium
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
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.
Interacting double dark resonances in a hot atomic vapor of helium
S. Kumar; T. Lauprtre; R. Ghosh; F. Bretenaker; F. Goldfarb
2011-07-17
We experimentally and theoretically study two different tripod configurations using metastable helium ($^4$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 EIT 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.
Interacting double dark resonances in a hot atomic vapor of helium
Kumar, S; Ghosh, R; Bretenaker, F; Goldfarb, F
2011-01-01
We experimentally and theoretically study two different tripod configurations using metastable helium ($^4$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 EIT 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.
mer S?t; Adnan Kknder; Erdo?an Bykkasap
2004-01-01
We have investigated the dependence on average atomic number of coherent\\/incoherent scattering intensity ratios in molecules. A 75mCi Am-241 source is used to provide 59.5keV?-rays. Several compounds having different average atomic numbers were used as scatterers. Scattering ?-rays were counted by a Si(Li) detector (FWHM 155eV at 5.9keV). We observed an increase in the coherent\\/incoherent scattering intensity ratios with increasing
K. Birgitta Whaley
2008-01-01
Planar aromatic molecules provide strongly localizing potentials for helium that considerably modify the local superfluid properties of a solvating helium environment. I shall describe some of the effects of these interactions on the solvation structure and spectroscopy of tetracene and phthalocyanine in helium droplets, comparing results of zero and finite temperature quantum Monte Carlo simulations with experimental data. The helium
Frequency-doubled scattering of symmetry-breaking surface-state electrons on liquid Helium
Miao Zhang; Wenzhi Jia; Lianfu Wei
2013-03-18
Any systems with symmetry-breaking eigenstates can effectively radiate photons with doubled frequency of the incident light, which is known as the second harmonic generation. Here, we study the second-order nonlinear effects with the system of surface-state electrons on liquid Helium. Due to the symmetry-breaking eigenstates, we show that a Rabi oscillation between two levels of the surface-state electrons can be realized beyond the usual resonant driving. Consequently, an electromagnetic field with the doubled frequency of the applied driving could be effectively radiated. This can be regarded as a frequency-doubled fluorescence, and interestingly, it works in the unusual Terahertz range.
Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics
Igor B. Mekhov; Christoph Maschler; Helmut Ritsch
2007-10-28
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 an 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 non-demolition (QND) measurement of various atomic variables by observing light.
Elastic scattering loss of atoms from colliding bose-einstein condensate wave packets
Band; Trippenbach; Burke; Julienne
2000-06-12
Bragg diffraction of atoms by light waves can create high momentum components in a Bose-Einstein condensate. Collisions between atoms from two distinct momentum wave packets cause elastic scattering that can remove a significant fraction of atoms from the wave packets and cause the formation of a spherical shell of scattered atoms. We develop a slowly varying envelope technique that includes the effects of this loss on the condensate dynamics described by the Gross-Pitaevski equation. Three-dimensional numerical calculations are presented for two experimental situations: passage of a moving daughter condensate through a nonmoving parent condensate, and four-wave mixing of matter waves. PMID:10990970
Elastic Scattering Loss of Atoms from Colliding Bose-Einstein Condensate Wave Packets
NASA Astrophysics Data System (ADS)
Band, Y. B.; Trippenbach, Marek; Burke, J. P., Jr.; Julienne, P. S.
2000-06-01
Bragg diffraction of atoms by light waves can create high momentum components in a Bose-Einstein condensate. Collisions between atoms from two distinct momentum wave packets cause elastic scattering that can remove a significant fraction of atoms from the wave packets and cause the formation of a spherical shell of scattered atoms. We develop a slowly varying envelope technique that includes the effects of this loss on the condensate dynamics described by the Gross-Pitaevski equation. Three-dimensional numerical calculations are presented for two experimental situations: passage of a moving daughter condensate through a nonmoving parent condensate, and four-wave mixing of matter waves.
Kaganovich, Igor
(also known as Wentzel5 approximation) with energy-dependent screening can be utilized to match energies. II. WENTZEL APPROXIMATION AND THE ENERGY-DEPENDENT SCREENING PARAMETER FOR ELECTRON SCATTERING
Excitation of lower autoionization states of the helium-like ions in x-ray scattering
M. Ya. Amusia A. I. Mikhailov; I. A. Mikhailov
1999-01-01
The process of inelastic scattering of high-frequency photons leading to excitation of singlet autoionization states (AIS) with total angular momentum L = 0 located below the first excited level of the respective one-electron ion are considered. For the amplitude of the process analytical expressions are derived, which include one-dimensional integrals, the latter being evaluated numerically. The scattered photon angular distributions
Excitation of lower autoionization ? states of the helium-like ions in x-ray scattering
M. Ya Amusia; A. I. Mikhailov; I. A. Mikhailov
1999-01-01
The process of inelastic scattering of high-frequency photons leading to excitation of singlet autoionization states (AIS) with total angular momentum L = 0 located below the first excited level of the respective one-electron ion are considered. For the amplitude of the process analytical expressions are derived, which include one-dimensional integrals, the latter being evaluated numerically. The scattered photon angular distributions
Samanta, Kousik
2010-07-14
We present a complex multicon figurational self-consistent field (CMCSCF)- based approach to investigate electron{atom/molecule scattering resonances. A modifi ed second quantization algebra adapted for biorthogonal spin orbitals has been applied...
Lindgren, Ingvar
Construction of accurate Kohn-Sham potentials for the lowest states of the helium atom: Accurate Kohn-Sham potentials have been constructed for the ground 1s2 1 S state and, in particular and the procedure of van Leeuwen and Baerends (Phys. Rev. A49, 2138 (1994)). The resulting Kohn-Sham orbitals
Fukushi, K. (Kobe Univ. of Mercantile Marine (Japan)); Willie, S.N.; Sturgeon, R.E. (National Research Council of Canada, Ottawa, Ontario (Canada))
1993-02-01
Inorganic and organic mercury were determined by helium-microwave induced plasma-atomic emission spectrometry following cold vapor generation. Whereas only inorganic mercury was reduced by stannous ion in an acidic medium, both inorganic and organic mercury (total mercury) were reduced by stannous ion in the presence of cupric ion in a basic medium. Organic mercury was determined as the difference between total and inorganic mercury. Detection limits for inorganic and organic mercury were 11 and 10 pg, respectively. The accuracy of the proposed method was verified through the determination of inorganic, total and organic mercury in two marine biological standard reference materials, DORM-1 and TORT-1. 21 refs., 1 fig., 4 tabs.
Advances in the helium-jet coupled on-line mass separator RAMA. [Recoil Atom Mass Analyzer
Moltz, D M; Aysto, J; Cable, M D; Parry, R F; Haustein, P E; Wouters, J M; Cerny, J
1980-01-01
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.
NASA Astrophysics Data System (ADS)
Harries, James R.; Iwayama, Hiroshi; Nagasono, Mitsuru; Togashi, Tadashi; Yabashi, Makina; Kuma, Susumu; Nakajima, Kyo; Miyamoto, Yuki; Ohae, Chiaki; Sasao, Noboru; Shigemasa, Eiji
2015-05-01
We report the observation of superfluourescence at wavelengths (in air) of 501.6 nm, 667.8 nm, and 728.1 nm following the excitation of helium atoms with free-electron laser pulses at wavelengths of 53.7 nm (n = 3 excitation) and 52.2 nm (n = 4 excitation). The observed wavelengths of the superfluorescence pulses correspond to 1s3p1s2s, 1s3d1s2p, and 1s3s1s2p transitions. Observation of superfluorescence on these transitions implies either competing cascade decays, or direct excitation of non-dipole allowed transitions. We have studied the time structure of the emitted pulses using a streak camera, and the results cannot be explained by straightforward considerations using the usual model for two-level superfluorescence.
Debashis Das; Jon W. Carnahan
2001-01-01
The transport behavior of moderately volatile analyte in a membrane desolvation system is examined. With the goal of atomic emission determination of liquid chromatographic analytes, a tubular polytetrafluoroethylene membrane desolvator interface was used to enhance the performance of a 120W helium microwave-induced plasma atomic emission detector. To monitor organo-chlorine compounds, Cl emission was observed at 479.5nm. Membrane desolvator conditions such
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
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.
The measurement of angular differential cross sections at the SSL Atomic Scattering Facility
NASA Astrophysics Data System (ADS)
Kvale, Thomas J.
1988-12-01
The design of the SSL Atomic Scattering Facility (ASF) located at the NASA/Marshall Space Flight Center as well as some of the initial experiments to be performed with it, are covered. The goal is to develop an apparatus capable of measuring angular differential cross sections (ADCS) for the scattering of 2 to 14 eV atomic oxygen from various gaseous targets. At present little is known about atomic oxygen scattering with kinetic energies of a few eV. This apparatus is designed to increase the understanding of collisions in this energy region. Atomic oxygen scattering processes are of vital interest to NASA because the space shuttle as well as other low earth orbit satellites will be subjected to a flux of 5 eV atomic oxygen on the ram surfaces while in orbit. The primary experiments will involve the measurements of ADCS for atomic oxygen scattering from gaseous targets (in particular, molecular nitrogen). These, as well as the related initial experiments involving thermal He scattering from N2 and O2 targets will be described.
The measurement of angular differential cross sections at the SSL Atomic Scattering Facility
NASA Technical Reports Server (NTRS)
Kvale, Thomas J.
1988-01-01
The design of the SSL Atomic Scattering Facility (ASF) located at the NASA/Marshall Space Flight Center as well as some of the initial experiments to be performed with it, are covered. The goal is to develop an apparatus capable of measuring angular differential cross sections (ADCS) for the scattering of 2 to 14 eV atomic oxygen from various gaseous targets. At present little is known about atomic oxygen scattering with kinetic energies of a few eV. This apparatus is designed to increase the understanding of collisions in this energy region. Atomic oxygen scattering processes are of vital interest to NASA because the space shuttle as well as other low earth orbit satellites will be subjected to a flux of 5 eV atomic oxygen on the ram surfaces while in orbit. The primary experiments will involve the measurements of ADCS for atomic oxygen scattering from gaseous targets (in particular, molecular nitrogen). These, as well as the related initial experiments involving thermal He scattering from N2 and O2 targets will be described.
Temperature Dependence in Rainbow Scattering of Hyperthermal Ar Atoms from LiF(001)
Hayes, W W
2015-01-01
Recent experiments have reported measurements of rainbow scattering features in the angular distributions of hyperthermal Ar colliding with LiF(001) [Kondo et al., J. Chem. Phys. 122, 244713 (2005)]. A semiclassical theory of atom-surface collisions recently developed by the authors that includes multiphonon energy transfers is used to explain the temperature dependence of the measured scattered angular distribution spectra.
Spin polarisation of electrons scattered superelastically by laser-excited Na atoms
G F Hanne; C Szmytkowski; M van der Wiel
1982-01-01
The authors have measured the spin polarisation of electrons scattered superelastically from laser-excited Na atoms at a collision energy of 20 eV and a scattering angle of 30 degrees . The measured spin polarisation is 0.095+or-0.048 for scattering from the 3p2P1\\/2 excited state of Na. The polarisation changes sign if the laser is tuned to the 3p 2P3\\/2 state, as
Scattering of Polarized Protons by Polarized Helium -3 at Intermediate Energies
NASA Astrophysics Data System (ADS)
Brash, Edward James
A high pressure polarized ^3He gas target has been used to measure spin observables and absolute cross-sections for (vec p,2p) and (vec p,pn) nucleon knockout in quasielastic kinematics at 220 MeV. The leading protons were detected with the TRIUMF Medium Resolution Spectrometer and the knocked-out nucleons were detected with a recently constructed BC412 scintillator array. The neutron knockout spin observables exhibit large deviations from Plane Wave Impulse Approximation (PWIA) calculations and together with previous data at 290 MeV indicate that the discrepancy is a result of final state interactions not yet included in the calculations. At this energy, the proton knockout spin observables differ slightly from PWIA calculations, especially at low energy transfers ( omega), but this discrepancy may be resolved when recoil interactions between nucleons of the two-body recoil scattering state are included. A similar polarized ^3He target, which has been modified with an Adiabatic Spin Rotator (ASR) to produce sideways and longitudinal target polarizations, has been used to measure the absolute cross -section, sigma(theta), the in-scattering-plane observables A_{00mm }, A_{00ml}, A_{00lm}, and A _{00ll}, and the normal spin observables A_{00n0}, A_ {000n}, and A_{00nn } in ^3vec He( vec p,p) elastic scattering at energies of 200 and 500 MeV. The observables depend on linear combinations of six complex scattering amplitudes for the p-^3He system and provide a severe test of current reaction models. The in-scattering -plane observables as well as the target-related normal observables which were measured previously are all in quantitative disagreement with optical model reaction theory calculations.
Bailey, T.D.
1989-01-01
The helium microwave-induced plasma (MIP) emission excitation source is a sensitive, element selective detector for gas chromatography. Fourier transform (FT) spectrometry is a technique that allows rapid simultaneous monitoring of the full spectrum of a light source. The combination of the MIP excitation course with an FT spectrometer provides a versatile simultaneous multielement gas chromatography detector. The design and construction of a helium microwave-induced plasma/Fourier transform atomic emission detector for gas chromatography is described. Examples of the operation of this instrument are given.
Many-electron effects in anomalous elastic x-ray scattering by an atom
Khoperskii, A.N.; Yavna, V.A. [Rostov State Univ. of Means of Communications (Russian Federation)
1995-02-01
The Ne atom is used as an example to study the effect of a monopole restructuring of the electron shells in the field of a virtual vacancy and the effect of shake-up (or shake-off) processes on the differential cross section for anomalous elastic scattering of x radiation by an atom near the threshold of the atomic 1s shell. The theoretical results derived here for the region of scattering resonances are of a predictive nature. 17 refs., 2 figs., 1 tab.
Rayleigh x-ray scattering from many-electron atoms and ions
NASA Astrophysics Data System (ADS)
Surzhykov, A.; Yerokhin, V. A.; Sthlker, Th; Fritzsche, S.
2015-07-01
A theoretical analysis is presented for the elastic Rayleigh scattering of x-rays by many-electron atoms and ions. Special emphasis is placed on the angular distribution and linear polarization of the scattered photons for the case when the incident light is completely (linearly) polarized. Based on second-order perturbation theory and the independent particle approximation, we found that the Rayleigh angular distribution is strongly affected by the charge state and shell structure of the target ions or atoms. This effect can be observed experimentally at modern synchrotron facilities and might provide further insight into the structure of heavy atomic systems.
Z dependence of electron scattering by single atoms into annular dark-field detectors.
Treacy, Michael M J
2011-12-01
A simple parameterization is presented for the elastic electron scattering cross sections from single atoms into the annular dark-field (ADF) detector of a scanning transmission electron microscope (STEM). The dependence on atomic number, Z, and inner reciprocal radius of the annular detector, q(0), of the cross section ?(Z,q(0)) is expressed by the empirical relation [see formula in text] where A(q(0)) is the cross section for hydrogen (Z = 1), and the detector is assumed to have a large outer reciprocal radius. Using electron elastic scattering factors determined from relativistic Hartree-Fock simulations of the atomic electron charge density, values of the exponent n(Z,q(0)) are tabulated as a function of Z and q(0), for STEM probe sizes of 1.0 and 2.0 . Comparison with recently published experimental data for single-atom scattering [Krivanek et al. (2010). Nature 464, 571-574] suggests that experimentally measured exponent values are systematically lower than the values predicted for elastic scattering from low-Z atoms. It is proposed that this discrepancy arises from the inelastic scattering contribution to the ADF signal. A simple expression is proposed that corrects the exponent n(Z,q(0)) for inelastic scattering into the annular detector. PMID:22051035
Ab-initio calculation on elastic scattering of low energy electrons by sulfur atoms
Hari P.S.; Dong Lin [Univ. of Central Florida, Orlando, FL (United States)
1996-05-01
Accurate ab-initio calculation of scattering length, total and Momentum-transfer cross sections is performed for low-energy elastic scattering of electrons from open-shell sulfur atom. The polarization of the sulfur atoms due to the scattered electron and the electron correlation effects that are very important in the calculation are taken into account through the configuration interaction procedure using the multiconfiguration Hartree-Fock method for electron-atom scattering. The elastic differential, total elastic and momentum-transfer cross sections for low energies ranging from 0 - 27.2 eV are obtained from phase shifts for various partial waves calculated in this approximation. The present results will be compared with the available experimental and other theoretical results.
Hongwei Xiong
2011-01-03
Considerable attention has been focused on Verlinde's recent work, claiming that Newton's gravity is not a fundamental force. In a recent work (arXiv:1012.5858), we give further the logic basis and basic clues to derive the Newton's gravity, inertia law and Einstein's weak equivalence principle. In this work, we show that if the gravity is not a fundamental force, in special case, it could be repulsive when quantum wavepacket effect is considered. This quantum gravity effect leads to several physical effects: (1) It is consistent with the universe with accelerating expansion, if the gravity and quantum effect of the fluctuating 'vacuum' (dark energy) is considered. The role of the cosmological constant is naturally interpreted when the gravity and quantum effect of the whole 'vacuum' background is considered. (2) It leads to new idea about black hole information paradox, no-hair theorem and Hawking radiation. (3) With a sphere full of superfluid Helium, we propose a feasible experimental scheme to test our idea with an atom interferometer placed in the sphere. Our calculations show that the accuracy Delta g/g below 10^(-8) could be used to test our idea, which satisfies the present experimental technique of atom interferometer.
Excitation of lower autoionization states of the helium-like ions in x-ray scattering
NASA Astrophysics Data System (ADS)
Mikhailov, M. Ya. Amusia A. I.; Mikhailov, I. A.
1999-03-01
The process of inelastic scattering of high-frequency photons leading to excitation of singlet autoionization states (AIS) with total angular momentum L = 0 located below the first excited level of the respective one-electron ion are considered. For the amplitude of the process analytical expressions are derived, which include one-dimensional integrals, the latter being evaluated numerically. The scattered photon angular distributions and the absolute cross section of the considered process are obtained. The transitions into two lower AIS are investigated. The approximation is employed, in which the electrons are described by Coulomb functions, and their interaction is taken into account in the first order of the perturbation theory. The correct AIS functions of the zero approximation are used which are obtained as solutions of the secular equation.
Friction force on a vortex due to the scattering of superfluid excitations in helium II
NASA Astrophysics Data System (ADS)
Cataldo, H. M.; Jezek, D. M.
2002-05-01
The longitudinal friction acting on a vortex line in superfluid 4He is investigated within a simple model based on the analogy between such vortex dynamics and that of the quantal Brownian motion of a charged point particle in a uniform magnetic field. The scattering of superfluid quasiparticle excitations by the vortex stems from a translationally invariant interaction potential which, expanded to first order in the vortex velocity operator, gives rise to vortex transitions between nearest Landau levels. The corresponding friction coefficient is shown to be, in the limit of elastic scattering (vanishing cyclotron frequency), equivalent to that arising from the Iordanskii formula. Proposing a simple functional form for the scattering amplitude, with only one adjustable parameter whose value is set in order to get agreement to the Iordanskii result for phonons, an excellent agreement is also found with the values derived from experimental data up to temperatures about 1.5 K. Finite values of the cyclotron frequency arising from recent theories are shown to yield similar results. The incidence of vortex-induced quasiparticle transitions on the friction process is estimated to be, in the roton dominated regime, about 50% of the value of the friction coefficient, ~8% of which corresponds to roton-phonon transitions and ~42% to roton R+<-->R- ones.
EUV resonance radiation from helium atoms and ions in the geocorona
R. R. Meier; C. S. Weller
1972-01-01
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
Nonresonance Compton scattering of an X-ray photon by a Ni-like atomic ion
NASA Astrophysics Data System (ADS)
Khopersky, A. N.; Nadolinsky, A. M.; Ikoeva, K. Kh.; Khoroshavina, O. A.; Kasprzhitskii, A. S.
2012-01-01
The absolute values and the shape of the double differential cross section for nonresonance Compton scattering of an X-ray photon by an atomic ion with d symmetry in the core are studied theoretically beyond the impulse approximation for the example of the Ni-like atomic ions Zn2+, Kr8+, and Mo14+. It is established that, as the nuclear charge of an ion increases, (a) in all the scattering channels, the leading harmonics of transition to states of the continuous spectrum are concentrated and (b) the integral intensities of nonresonance Compton scattering are increasingly redistributed to the energy region of resonance Lands-berg-Mandelstam-Raman scattering between the threshold of termination of the Compton profile and the line of elastic (Thomson and Rayleigh) scattering. The calculated results are predictive in character.
Monopole electron-shell rearrangement induced by elastic scattering of a photon by an atom
Khoperskii, A.N.; Yavna, V.A.; Demekhin, V.F. [Rostov State Univ. of Communication Lines, Rostov-na-Donu (Russian Federation)
1994-12-01
The differential cross section for photon elastic near the 1s-shell threshold of the Ne atom is calculated taking into account the relaxation of the atomic core in the Hartree-Fock field of a virtual 1s vacancy. It was found that (1), in the region of scattering resonances, the relaxation effect results in the strong suppression of resonance amplitudes and in the shifts of resonance energies, as compared with the frozen-core picture; and (2), in the region of a near-threshold scattering, the relaxation effect leads to a redistribution of the scattering intensity between the short- and long-wave parts of the scattering spectrum calculated within the frozen-core approximation. The theoretical results obtained for the scattering resonances are predictive in character. 10 refs., 1 fig.
Deactivation of the xenon atom in the 6s metastable state in collisions with xenon and helium atoms
D A Zayarnyi; Ludmila V Semenova; N N Ustinovskii; I V Kholin; A Yu Chugunov
1998-01-01
The absorption probing method was used to investigate collisional deactivation of the metastable 6s[3\\/2](P) 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 Xe*+He [(1.7 {+-}0.2) x10 cm s], Xe*+2He HeXe*+He (less than 3 x 10 cm s), and Xe*+He products+He
D. A. Zayarnyi; Ludmila V. Semenova; N. N. Ustinovskii; I. V. Kholin; A. Yu Chugunov
1998-01-01
The absorption probing method was used to investigate collisional deactivation of the metastable 6s[3\\/2]20(3P2) 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 --> Xe2*+He [(1.7 0.2) 10-32 cm6 s-1], Xe*+2He--> HeXe*+He (less than 3 10-35 cm6 s-1), and Xe*+He-->
NASA Astrophysics Data System (ADS)
Hamdan, Ahmad; Margot, Jolle; Vidal, Franois; Matte, Jean-Pierre
2015-01-01
A stationary surface wave discharge is studied in helium gas at intermediate pressure. By optical emission spectroscopy, rotational temperatures derived from impurities molecular bands have been studied, as well as the excitation temperature from the Boltzmann plot method of helium lines, as a function of gas pressure, absorbed power and axial position. The rotational temperature of OH molecules is supposed to be in thermal equilibrium with the plasma gas and is used for determining its temperature. The influence of the tube diameter has also been studied; it was observed that the tubes with smaller diameter lead to higher gas temperature. By optical absorption spectroscopy, the density of metastable atoms (in 23s level) has been studied as a function of the parameters. An important dependence on the gas pressure has been observed. Indeed, a one order of magnitude reduction is obtained when the pressure increases from 5 to 50?Torr. The density of metastable atoms remains constant as a function of power and almost all along the plasma column. Finally, a collisional-radiative model was used to compare the experimental to the theoretical results of the density of metastable atoms providing at the same time estimations of the density and the temperature of the electrons as well as the density of helium (atomic and molecular) ions. Results showed a good agreement when the tube diameter is large, but for smaller tubes, the agreement was obtained only for the higher gas pressures.
Compton scattering of an X-ray photon by an open-shell atom
Hopersky, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinsky, A. M. [Rostov State University of Transport Communication (Russian Federation)
2012-09-15
A nonrelativistic quantum theory for the nonresonant Compton scattering of an X-ray photon by a free many-electron atom with an open shell in the ground state has been constructed in the single-configuration Hartree-Fock approximation outside the impulse approximation widely used in the literature. The transition to an atom with closed shells reproduces the results obtained previously in [6, 7]. The results of a test calculation for atoms with open (Ti, Fe) and closed (Zn) 3d core shells are presented. The effects of the radial relaxation of one-electron states in the field of core vacancies have been taken into account. The results of the calculation agree well with the experimental results [15, 16]. It has been established that the results of the impulse approximation in the investigated X-ray photon energy ranges disagree with those of our theory not only quantitatively but also qualitatively. In particular, the impulse approximation near the elastic (Thomson and Rayleigh) scattering line leads to a gross overestimation of the contributions from the deep atomic shells involved in the inelastic photon scattering only virtually to the scattering probability. The presented theory is general in character and its applicability to a particular element of the Mendeleev table with an open core shell or to a many-electron atomic ion is limited only by the requirement that the nonrelativistic Hartree-Fock approximation be properly used in describing the scattering-state wave functions.
Macroscopic scattering of cracks initiated at single impurity atoms
NASA Astrophysics Data System (ADS)
Kermode, J. R.; Ben-Bashat, L.; Atrash, F.; Cilliers, J. J.; Sherman, D.; de Vita, A.
2013-09-01
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.
Deactivation of the xenon atom in the 6s metastable state in collisions with xenon and helium atoms
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
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)
Adiabatic asymmetric scattering of atoms in the field of a standing wave
NASA Astrophysics Data System (ADS)
Hakobyan, M. V.; Redkov, V. M.; Ishkhanyan, A. M.
2015-06-01
A model of the asymmetric coherent scattering process (caused by initial atomic wave-packet splitting in the momentum space) taking place at the large detuning and adiabatic course of interaction for an effective two-state system interacting with a standing wave of laser radiation is discussed. We show that the same form of initial wave-packet splitting may lead to different, in general, diffraction patterns for opposite, adiabatic and resonant, regimes of the standing-wave scattering. We show that the scattering of the Gaussian wave packet in the adiabatic case presents refraction (a limiting form of the asymmetric scattering) in contrast to the bi-refringence (the limiting case of the high-order narrowed scattering) occurring in the resonant scattering.
Hubert, J.; Van Tra, H.; Chi Tran, K.; Baudais, F.L.
1986-08-01
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.
R. L. Coldwell; R. E. Lowther
1978-01-01
The fact that Monte Carlo estimates for the expectation value of the Hamiltonian have no standard deviation for exact eigenfunctions of the Hamiltonian was used to construct electronic wave functions accounting for the total correlation energy of two helium atoms separated by distances larger than 5a\\/sub B\\/ to within 5 x 10⁻⁴ Ry. The biased selection Monto Carlo method used
Taketoshi Nakahara; Toshio Mori; Satoru Morimoto; Hiroshi Ishikawa
1995-01-01
A simple continuous-flow generation of volatile hydrogen sulfide and sulfur dioxide by acidification of aqueous sulfide and sulfite ions, respectively, is described for the determination of low concentrations of sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region,
Loo
1990-01-01
The development of experimental and data analysis techniques for quantitative analysis in gas chromatography\\/low power atmospheric pressure helium microwave-induced plasma atomic emission interferometry (GC\\/HeMIPAEI) and ion cyclotron resonance mass spectroscopy (ICR\\/MS) is presented. A discussion of interferometric data analysis by discrete and fast Fourier transform (DFT and FFT, respectively) is given. Additionally, the use of two techniques (the maximum entropy
Scattering of polarized laser light by an atomic gas in free space: a QSDE approach
Luc Bouten; John K. Stockton; Gopal Sarma; Hideo Mabuchi
2007-01-30
We propose a model, based on a quantum stochastic differential equation (QSDE), to describe the scattering of polarized laser light by an atomic gas. The gauge terms in the QSDE account for the direct scattering of the laser light into different field channels. Once the model has been set, we can rigorously derive quantum filtering equations for balanced polarimetry and homodyne detection experiments, study the statistics of output processes and investigate a strong driving, weak coupling limit.
Sensitive Polarization Dependence for Helium Rydberg Atoms Driven by Strong Microwave Fields
NASA Astrophysics Data System (ADS)
Zelazny, S. A.; Bellermann, M. R. W.; Smith, L. L.; Koch, P. M.
1996-05-01
We prepare n^3S He Rydberg atoms with selected values n>=25 in a fast beam using CO2 lasers and double-resonance excitation. They then fly through a TE_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( W. van de Water et al., Phys. Rev. A 42), 572 (1990) is transformed by EP into a pattern reminiscent of Stueckelberg oscillations, previously observed with LP at higher frequencies.( S. Yoakum et al., Phys. Rev. Lett. 69), 1919 (1992) 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. We will discuss this kind of data as well as the polarization dependence of microwave ionization of n^3S He Rydberg atoms.
Sensitive polarization dependence for helium Rydberg atoms driven by strong microwave fields
Zelazny, S.A.; Bellermann, M.R.W.; Smith, L.L.; Koch, P.M.
1996-05-01
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.
s-wave scattering of a polarizable atom by an absorbing nanowire
Fink, Martin; Arnecke, Florian; Eiglsperger, Johannes; Friedrich, Harald; Madronero, Javier; Raab, Patrick [Physik Department, Technische Universitaet Muenchen, D-85747 Garching (Germany); Naranjo, Andres [Facultad de Ciencias, Universidad Nacional, Medellin (Colombia); Wirzba, Andreas [Institute for Advanced Simulation and Institut fuer Kernphysik, Forschungszentrum Juelich, D-52425 Juelich (Germany)
2010-06-15
We study the scattering of a polarizable atom by a conducting cylindrical wire with incoming boundary conditions, that is, total absorption, near the surface of the wire. Based on the explicit expression given recently [C. Eberlein and R. Zietal, Phys. Rev. A 75, 032516 (2007)] for the nonretarded atom-wire potential, we formulate a hierarchy of approximations that enables the numerical determination of this potential to any desired accuracy as economically as possible. We calculate the complex s-wave scattering length for the effectively two-dimensional atom-wire scattering problem. The scattering length a depends on the radius R of the wire and a characteristic length {beta} related to the polarizability of the atom via a simple scaling relation, a=R a{approx}({beta}/R). The 'scaled scattering length' a{approx} tends to unity in the thick-wire limit {beta}/R{yields}0, and it grows almost proportional to 1/R in the opposite thin-wire limit.
NASA Astrophysics Data System (ADS)
Kneller, Gerald R.; Chevrot, Guillaume
2012-12-01
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.
Light Scattering for Thermometry of Fermionic Atoms in an Optical Lattice
Ruostekoski, J. [School of Mathematics, University of Southampton, Southampton, SO17 1BJ (United Kingdom); Foot, C. J.; Deb, A. B. [Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU (United Kingdom)
2009-10-23
We propose a method of using off-resonant light scattering to measure the temperature of fermionic atoms tightly confined in a two-dimensional optical-lattice potential. We show that fluctuations of the intensity in the far-field diffraction pattern arising from thermal correlations of the atoms can be accurately detected above the shot noise by collecting photons scattered in a forward direction, with the diffraction maxima blocked. The sensitivity of this method of thermometry is enhanced by an additional harmonic trapping potential.
Low energy electron scattering from atoms: Search for nanocatalysts
NASA Astrophysics Data System (ADS)
Msezane, A. Z.; Felfli, Z.; Sokolovski, D.
2011-05-01
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). The use of mixed precious metal catalysts can produce even higher activities compared to Au alone. 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. It is concluded that these atoms are suitable candidates for nanocatalysts individually or in combinations. Supported by U.S. DOE, AFOSR and CAU CFNM, NSF-CREST.
Imaging nonequilibrium atomic vibrations with x-ray diffuse scattering
Trigo, M.; Chen, J.; Vishwanath, V. H.; Sheu, Y. M.; Graber, T.; Henning, R.; Reis, D. A.
2011-01-01
We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations in the lattice following ultrafast laser excitation. We present images of nonequilibrium phonons in InP and InSb throughout the Brillouin zone which remain out of equilibrium up to nanoseconds. The results are analyzed using a Born model that helps identify the phonon branches contributing to the observed features in the time-resolved diffuse scattering. In InP this analysis shows a delayed increase in the transverse-acoustic (TA) phonon population along high-symmetry directions accompanied by a decrease in the longitudinal-acoustic phonons. In InSb the increase in TA phonon population is less directional. PMID:21580798
Chen-Ting Liao; Arvinder Sandhu; Seth Camp; Kenneth J. Schafer; Mette B. Gaarde
2015-03-09
We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently to the appearance of new, narrow features in the absorption line.
State-to-state inelastic scattering of Stark-decelerated OH radicals with Ar atoms.
Scharfenberg, Ludwig; K?os, Jacek; Dagdigian, Paul J; Alexander, Millard H; Meijer, Gerard; van de Meerakker, Sebastiaan Y T
2010-09-28
The Stark deceleration method exploits the concepts of charged particle accelerator physics to produce molecular beams with a tunable velocity. These tamed molecular beams offer interesting perspectives for precise crossed beam scattering studies as a function of the collision energy. The method has advanced sufficiently to compete with state-of-the-art beam methods that are used for scattering studies throughout. This is demonstrated here for the scattering of OH radicals (X(2)Pi(3/2), J = 3/2, f) with Ar atoms, a benchmark system for the scattering of open-shell molecules with atoms. Parity-resolved integral state-to-state inelastic scattering cross sections are measured at collision energies between 80 and 800 cm(-1). The threshold behavior and collision energy dependence of 13 inelastic scattering channels is accurately determined. Excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on the most accurate ab initio OH + Ar potential energy surfaces to date. PMID:20657906
Positron scattering from hydrogen atom with screened Coulomb potentials
Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal, India and Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Nayek, Sujay [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal (India); Kamali, M. Z. M. [Centre for Foundation Studies in Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)
2014-03-05
Elastic positron-hydrogen collisions with screened Coulomb potentials have been investigated using a second-order distorted wave Born approximation in the momentum space. Two types of potentials have been considered, namely, static screened Coulomb potential and exponential cosine-screened Coulomb potential. Using a simple variationally determined hydrogenic wave function it has been possible to obtain the scattering amplitude in a closed form. A detailed study has been made on the differential and total cross sections in the energy range 20300 eV.
W. B. Hanson
1962-01-01
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
Multiphoton effects in laser-assisted ionization of a helium atom by electron impact
NASA Astrophysics Data System (ADS)
Ghosh Deb, S.; Sinha, C.
2010-11-01
The dynamics of the electron impact multiphoton ionization of a He atom in the presence of an intense laser field ( n ? _e, 2 e) is studied theoretically for laser polarization (\\vert\\vert^l) and perpendicular (bot^r) to the incident momentum. The triple differential (TDCS) as well as the double differential (DDCS) cross sections are studied for the coplanar asymmetric geometry. The results are compared with the only available kinematically complete experiment at high incident energy (1000 eV). Significant laser modification (enhancement) is noted due to multiphoton effects in the present binary and recoil peak intensities of the TDCS for both the geometries, in qualitative agreement with the experiment. In the single photon case, the net effect of the laser field is to suppress the field free (FF) TDCS as well as the DDCS in the zeroth order approximation of the ejected electron wave function (CV), while in the first order (MCV), the cross sections are found to be enhanced. The CV multiphoton cross sections obey the famous Kroll Watson (KW) sum rule while the latter does not hold good in the corresponding MCV approximation.
Manson, Joseph R.
Temperature Dependence in Atom-Surface Scattering Eli Pollak Chemical Physics Department, Weizmann measure of the temperature dependence of energy resolved atom-surface scattering spectra measured under conditions of higher translational energies, larger surface temperatures and partic- ularly for heavier mass
Kinematical rainbow and elastic focusing effects in atom-surface scattering S. Miret-Artes
Manson, Joseph R.
Kinematical rainbow and elastic focusing effects in atom-surface scattering S. Miret in elastic surface diffraction are reported. First, a kinematical rainbow KR condition, a special case of the well-known rainbow singularity, is examined and shown to be a two-dimensional counterpart of the glory
THE SCATTERING OF A POTASSIUM ATOMIC BEAM BY A CROSSED BEAM OF BROMINE MOLECULES
1960-01-01
A study was made of the scattering of crossed molecular beams for the ; determinntion of information on intermolecular forces and chemical reaction cross ; sections. A high resolution molecular beam apparatus was constructed to study ; the interaction of a monoenergetic beam of potassium atoms with a crossed beam of ; bromine molecules. The device incorporates resistance heated ovens,
Betina Giehl Zanetti-Ramos; Mauricia Beddin Fritzen-Garcia; Tnia Beatriz Creczynski-Pasa; Cristian Schweitzer De Oliveira; Andr Avelino Pasa; Valdir Soldi; Redouane Borsali
2010-01-01
The purpose of this article is to describe the use of different techniques, such as dynamic light scattering (DLS), electron microscopy (EM), and atomic force microscopy (AFM), on the characterization of particulate systems. A brief theoretical introduction for each technique is presented, including advantages and disadvantages. Micro- and nanoparticles of polyurethane were used as examples to illustrate the use of
Potentials for High-Energy Scattering from Hydrogenlike Atoms
Reading, John F.
1970-01-01
of Physics, Kent State University, Kent, Ohio 44240 (Received 15 August 1969) A general method for calculating the cross sections for single-quantum. annihilation (SQA) of positrons in various atomic shells, valid to second order in the G. Z expansion (one... that the differential cross sections are of the form 0&&(k, q) = C?&0??(k, q), where no= l+1, and k and q are the photon energy and the magnitude of momentum transfer to a nucleus, respectively. The factor C?& is evaluated in general. The SQA cross sections...
He-diamond interaction probed by atom beam scattering
Vidali, G.; Frankl, D.R.
1983-02-15
A /sup 4/He atomic beam was used to probe the He-C (diamond) interaction. Selective adsorption features have been measured and three energy levels identified: 6.4, 3.0, and 1.1 meV with a standard deviation of 0.1 meV. Diffraction patterns showed weak diffraction up to the second order; a corrugation parameter of 0.021 A was obtained with the use of a hard-wall model in the eikonal approximation. An extensive study of surface preparation was carried out and the results of /sup 4/He diffraction for different methods of surface cleaning are reported.
Vos, M; Moreh, R; Toksi, K
2011-07-14
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. PMID:21766954
NASA Astrophysics Data System (ADS)
Daley, Richard Stephen
1990-08-01
The technique of impact collision ion scattering spectroscopy (ICISS) was used to investigate the atomic structure and low energy ion scattering dynamics from various surfaces. A new formalism for calculating the three-dimensional cross section for an ion to scatter sequentially and classically from two atoms has been developed. This method can be used to assist in the interpretation of ICISS data in terms of quantitative surface-structure models. Shadowing and blocking effects for energetic ions scattering from more than one atom are shown to be special cases of rainbow scattering. Even at keV energies and above, the cross section at the critical angle for scattering must be evaluated by quantum or semi-classical means to avoid the singularity in the classically calculated cross sections. In an ICISS investigation of the Ag(110) surface, a surface flux peak analysis demonstrated that the surface was not a complete monolayer, but rather contained 10-15% random vacancies. Subsurface Li^+ scattering results confirmed the oscillatory relaxation of the first two atomic layers of the surface, with Delta_{12} = -7.5% and Delta_{23} = 4.0%. Modeling of the neutralization mechanism for the He^+ scattering gave a best fit time-dependent Auger neutralization time constant of 0.84 +/- 0.08 fs. A neutralization study of 5 keV He^+ ions scattered from Au adatoms on the Si(111)- sqrt{3} x sqrt {3}-Au surface showed the He^+ ICISS data contained false shadowing features that were actually the result of local neutralization effects. Good agreement was obtained for a radially dependent ion-atom neutralization theory with rate R = Aexp (-ar) , where A and a are 15.5 fs^{ -1} and 1.94 A^{-1} , respectively. A detailed examination of the Si(111)- sqrt{3} x sqrt{3 })-Ag surface was also made. The 5 keV Li ^+ ICISS data gave evidence for Ag island formation at single monolayer coverages of silver, while the LEED, AES and LEIS data showed that at relatively high coverages of Ag (35 ML) small areas of sqrt {3} x sqrt{3} character were still present. Nine structurally different models of the sqrt{3} surface were tested and compared to the experimental ICISS results, with only the honeycomb-chained-trimer and missing-top-layer models found to be consistent with the Li^+ ICISS results.
Elastic and Inelastic Scattering of Positrons by Potassium Atoms
NASA Astrophysics Data System (ADS)
El-Bakry, Salah Yaseen
The investigations of the elastic and inelastic collisions of positrons with potassium atoms, K (1s2, 2s2, 2p6, 3s2, 3p6, 4s), are presented. The potassium target atoms are described using Clementi-Roetti wavefunctions within the framework of the one-valence-electron model. The total cross-sections which correspond to eight partial cross-sections are calculated at 34 values of the incident energy k21 (2.5 eV <= k12<= 100 eV) using the coupled-static approximation. The resulting total elastic, ground- and excited-positronium formation cross-sections are compared with experimental results and those calculated by other authors. In the vicinity of 6 eV, and consistent with the measurements of Parikh et al.,2 our total cross-section displays a pronounced peak. We support the conclusion of McAlinden et al.15 and Hewitt et al.14 that above about 4 eV, positronium formation is mainly into excited states. Good agreement is obtained with the total cross-section measurements of Kwan et al.1 and Parikh et al.2 Positronium formation is not important above about 50 eV.
Low energy ion scattering by atomic steps on the single crystal surface
NASA Astrophysics Data System (ADS)
Dzhurakhalov, A. A.; Kutliev, U. O.; Umarov, F. F.
2004-05-01
The energy, angular distributions and trajectories of particles scattered on surfaces of Ni(100) and Cu(100), with both ideal and damaged, and semi-infinite and isolated atomic steps, have been calculated. It has been shown that from the correlation between the experimental and calculated energy distributions of the scattered particles, one may determine the spatial extension of the isolated atomic steps and the distance between them on the single crystal surface damaged by ion bombardment. The energy and angular distributions of ions dechanneled from semi-infinite steps on the GaP(100) surface have been presented. It has been shown that the dechanneling ions form the characteristic peaks in the angular and energy distributions of the scattered particles.
Helicity Resolved Raman Scattering of Atomic Layers of Transition Metal Dichalcogenides
NASA Astrophysics Data System (ADS)
Chen, Shao-Yu; Yan, Jun
2015-03-01
Semiconducting transition metal dichalcogenides (TMDCs) such as MoS2, MoSe2, WS2 and WSe2 are promising two dimensional (2D) materials for electronic and optoelectronic applications. Moreover, the unique capability to manipulate the valley degree of freedom with circularly polarized light has attracted widespread attention for potential applications in valley- and spin-tronics. In this talk we present helicity resolved Raman scattering of TMDC atomic layers. The dominant first order Raman bands, including the low energy breathing and shear modes as well as the high energy zone center optical phonons, are found to either maintain or completely switch the helicity of incident photons. This helicity selectivity due to phonon scattering is interpreted by symmetry of lattice vibrations without involving intervalley scattering. Our results provide a useful tool for characterization of TMDC atomic layers and offer new insights into the connection between photon helicity and valley polarization.
Zhou, Yun, E-mail: zhou.yun.x@gmail.com; Pollak, Eli, E-mail: eli.pollak@weizmann.ac.il [Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot (Israel)] [Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot (Israel); Miret-Arts, Salvador, E-mail: s.miret@iff.csic.es [Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 123, 28006 Madrid (Spain)] [Instituto de Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 123, 28006 Madrid (Spain)
2014-01-14
A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to soft corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.
NASA Technical Reports Server (NTRS)
Stallcop, J. R.
1974-01-01
The impact parameter method and the sudden approximation are applied to determine the total probability of inelastic rotational transitions arising from a collision of an atom and a homonuclear diatomic molecule at large impact parameters. An analytical approximation to this probability is found for conditions where the electron exchange or overlap forces dominate the scattering. An approximate upper bound to the range of impact parameters for which rotational scattering can be important is determined. In addition, an estimate of the total inelastic cross section is found at conditions for which a statistical model describes the scattering well. The results of this analysis are applied to Ar-O2 collisions and may be readily applied to other combinations of atoms and molecules.
Potentials for High-Energy Scattering from Hydrogenlike Atoms
Reading, John F.
1970-01-01
) 1646 J. F. RE ADING 1 2 1V/(r) = ?? exp(iqz) sin(2nq) dqtRl ~ lR ?rt 0 q (A2) where n = R ?r /2cZ The integral in Eq. (A2) exists for all real a. For a='0, If we write g(p)= f exp( ?r ts)d(r ) f F(e, r)d8 we note that f '/ E(8, r) d8... the diabatic ap- proximation can be relaxed by modifying V to include the effect of H, to order v . In particular in the impulse approximation, scattering is described by a static local potential Vl.(x, 8) =1/8 ?[erf(i' e+e)]/I R ?rll, where n = l R ?r t /(2...
Crossed-molecular-beams reactive scattering of oxygen atoms
Baseman, R.J.
1982-11-01
The reactions of O(/sup 3/P) with six prototypical unsaturated hydrocarbons, and the reaction of O(/sup 1/D) with HD, have been studied in high-resolution crossed-molecular-beams scattering experiments with mass-spectrometric detection. The observed laboratory-product angular and velocity distributions unambiguously identify parent-daughter ion pairs, distinguish different neutral sources of the same ion, and have been used to identify the primary products of the reactions. The derived center-of-mass product angular and translational energy distributions have been used to elucidate the detailed reaction dynamics. These results demonstrate that O(/sup 3/P)-unsaturated hydrocarbon chemistry is dominated by single bond cleavages, leading to radical products exclusively.
Positron scattering from hydrogen atom embedded in weakly coupled plasma
Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan 713 104, West Bengal (India); Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Kamali, M. Z. M. [Centre for Foundation Studies in Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)
2013-01-15
The positron-hydrogen collision problem in weakly coupled plasma environment has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. A simple variational hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s{yields}1s and 2s{yields}2s elastic collisions, 1s{yields}2s excitation, positronium formation, elastic proton-positronium collisions, have been reported. Furthermore, a detailed study has been made on differential and total cross sections of the above processes in the energy range 13.6-350 eV of the incident positron.
Near-resonance Light Scattering from a High-density, Ultracold Atomic $^{87}$Rb Gas
S. Balik; A. L. Win; M. D. Havey; I. M. Sokolov; D. V. Kupriyanov
2013-02-10
We report a combined experimental and theoretical investigation of near resonance light scattering from a high-density and ultracold atomic $^{87}$Rb gas. The atomic sample, having a peak density $\\sim 5\\cdot10^{13}$ atoms/cm$^{3}$, temperature $\\sim$ 65 $\\mu$K and initially prepared in the F = 1 lower energy $^{87}$Rb hyperfine component, is optically pumped to the higher energy F = 2 hyperfine level. Measurements are made of the transient hyperfine pumping process and of the time evolution of scattering of near resonance probe radiation on the $F = 2 \\rightarrow F' = 3$ transition. Features of the density, detuning, and temporal dependence of the signals are attributed to the high density and consequent large optical depth of the samples.
Resonant scattering of an X-ray photon by a heavy atom
Hopersky, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinsky, A. M. [Rostov State University of Transport Communication (Russian Federation)
2007-10-15
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)
Self-Consistent Model of Roton Cluster Excitations in Liquid Helium II
V. I. Kruglov; M. J. Collett
2006-05-18
We have proposed a model of roton cluster excitations in liquid helium~II based on a Schr\\"odinger-type equation with a self-consistent confining potential. We have derived an equation for the number of atoms in roton excitations, which can be treated as quantum $3{\\rm D}$ solitons, depending on vibrational quantum numbers. It is shown that the smallest roton cluster is in the symmetric vibrational quantum state and consists of 13 helium atoms. We have also used a modified Born approximation to calculate the $s$-scattering length for helium atoms. This allows us to calculate all parameters of Landau's roton excitation spectrum, in agreement to high accuracy with experimental measurements from neutron scattering.
Heinzen, Daniel J.
February 1, 1994 / Vol. 19, No. 3 / OPTICS LETTERS Spin relaxation of optically trapped atoms of optically trapped atoms that is due to light scattering from the trap laser. We observe relaxation times greater than 2 s for ground-state hyperfine-levelpopulations of 85 Rb atoms trapped in an optical dipole
Bechthold, U.; Bathelt, B.; Bohris, A.; Moshammer, R.; Schmidt-Boecking, H. [Institut fuer Kernphysik, August-Euler-Strasse 6, D-60486 Frankfurt (Germany)] [Institut fuer Kernphysik, August-Euler-Strasse 6, D-60486 Frankfurt (Germany); Bechthold, U.; Ullrich, J.; Bathelt, B.; Moshammer, R.; Kraft, G. [Gesellschaft fuer Schwerionenforschung, m.b.H., Planckstrasse 1, D-64291 Darmstadt (Germany)] [Gesellschaft fuer Schwerionenforschung, m.b.H., Planckstrasse 1, D-64291 Darmstadt (Germany); Hagmann, S.; Bhalla, C. [J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506 (United States)] [J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506 (United States); Ramm, U. [Universitaetsklinikum, ZRad, Abt. Strahlentherapie, D-60596 Frankfurt/Main (Germany)] [Universitaetsklinikum, ZRad, Abt. Strahlentherapie, D-60596 Frankfurt/Main (Germany)
1997-09-01
We present first experimental evidence for intra-atomic double scattering of binary encounter electrons produced in collisions of 5.9MeV/u U{sup 29+} with neon, xenon, and molecular gases. A broad distribution of electrons is observed at a velocity twice the velocity of the moving ion (v{sub P} ) at angles {var_theta}{sub e} up to 135{degree}. We attribute this emission pattern to well-known target binary encounter electrons around 2v{sub P} at extreme forward laboratory angles that are subsequently elastically scattered in the target nuclear potential to the large angles observed. {copyright} {ital 1997} {ital The American Physical Society}
Inokuti, M.; Manson, S.T.
1982-01-01
We begin with a resume of the Bethe theory, which provides a general framework for discussing the inelastic scattering of fast electrons and leads to powerful criteria for judging the reliability of cross-section data. The central notion of the theory is the generalized oscillator strength as a function of both the energy transfer and the momentum transfer, and is the only non-trivial factor in the inelastic-scattering cross section. Although the Bethe theory was initially conceived for free atoms, its basic ideas apply to solids, with suitable generalizations; in this respect, the notion of the dielectric response function is the most fundamental. Topics selected for discussion include the generalized oscillator strengths for the K-shell and L-shell ionization for all atoms with Z less than or equal to 30, evaluated by use of the Hartree-Slater potential. As a function of the energy transfer, the generalized oscillator strength most often shows a non-monotonic structure near the K-shell and L-shell thresholds, which has been interpreted as manifestations of electron-wave propagation through atomic fields. For molecules and solids, there are additional structures due to the scattering of ejected electrons by the fields of other atoms.
An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements
NASA Technical Reports Server (NTRS)
Ross, H. Richard
1993-01-01
A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.
Towards weighing individual atoms by high-angle scattering of electrons
Argentero, G; Kotakoski, J; Eder, F R; Meyer, J C
2015-01-01
We consider theoretically the energy loss of electrons scattered to high angles when assuming that the primary beam can be limited to a single atom. We discuss the possibility of identifying the isotopes of light elements and of extracting information about phonons in this signal. The energy loss is related to the mass of the much heavier nucleus, and is spread out due to atomic vibrations. Importantly, while the width of the broadening is much larger than the energy separation of isotopes, only the shift in the peak positions must be detected if the beam is limited to a single atom. We conclude that the experimental case will be challenging but is not excluded by the physical principles as far as considered here. Moreover, the initial experiments demonstrate the separation of gold and carbon based on a signal that is related to their mass, rather than their atomic number.
Dou, L.; Kauppila, W.E.; Kwan, C.K.; Stein, T.S.
1993-05-01
We have measured absolute values of elastic differential cross sections (DCS`s) for positron (e{sup +}) scattering by argon (8.7-300 eV), krypton (6.7-400 eV), and also neon (13.6-400 eV) using a crossed-beam experimental setup. When the DCS`s are plotted at fixed scattering angles of 30{degrees}, 60{degrees}, 90{degrees}, and 120{degrees} versus energy it has been found that well-defined resonance-like structures were found at an energy of 55-60 eV for argon and at 25 and 200 eV for krypton, with a broader structure found between 100-200 eV for neon. These observed resonance-like structures are unusual because they occur at energies well above the known inelastic thresholds for these atoms. They may represent examples of {open_quotes}coupled channel shape resonances{close_quotes}, first predicted by Higgins and Burke for e{sub +}-H scattering in the vicinity of 36 eV (width {approx} 4 eV), which occurs only when both the elastic and positronium formation scattering channels are considered together. A more recent e{sup +}-H calculation by Hewitt et al. supports the Higgins and Burke prediction. These predictions and the present observations suggest the existence of a new type of atomic scattering resonance.
Observations of resonance-like structures for positron-atom scattering at intermediate energies
Dou, L.
1993-01-01
Absolute values of elastic differential cross sections (DCS's) are measured for position (e[sup +]) scattering by argon (8.7-300 eV) krypton (6.7-400 eV) and also neon (13.6-400 eV) using a crossed-beam experimental setup. When the DCS's are plotted at fixed scattering angles of 30[degrees], 60[degrees], 90[degrees] and 120[degrees] versus energy it has been found that well-defined resonance-like structures are found at an energy of 55-60 eV for argon and at 25 and 200 eV for krypton, with a broader structure found between 100-200 eV for neon. These observed resonance-like structures are unusual because they occur at energies well above the known inelastic thresholds for these atoms. They may represent examples of [open quotes]coupled channel shape resonances[close quotes], first predicted by Higgins and Burke [1] for e[sup +]-H scattering in the vicinity of 36 eV (width [approx] 4 eV), which occurs only when both the elastic and positronium formation scattering channels are considered together. A more recent e[sup +]-H calculation by Hewitt et al. [2] supports the Higgins and Burke prediction. These predictions and the present observations suggest the existence of a new type of atomic scattering resonance.
Glyde, Henry R.
HELIUM, SOLID 1 Helium, Solid Henry R. Glyde Introduction Helium was first solidified at the famous focused on the melting curve, the specific heat, and the thermal conductivity of solid helium as a test criterion of melting does not hold in solid helium. This pioneering work up to 1957 is elegantly
Odette, G.R.; Maziaz, P.J.; Spitznagel, J.A.
1981-01-01
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.
Theory of Direct Scattering, Trapping and Desorption in Atom-Surface Collisions
Guoqing Fan; J. R. Manson
2008-04-10
When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features due to direct scattering and to trapping in the physisorption well with subsequent desorption. James Clerk Maxwell is credited with being the first to describe this situation by invoking the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that exchanges no energy and specularly reflects and another part that equilibrates or accommodates completely and then desorbs with an equilibrium distribution. In this paper a scattering theory is developed, using an iterative algorithm and classical mechanics for the collision process, that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped fraction of particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory allows a rigorous test of the Maxwell assumption and determines the conditions under which it is valid. The theory also gives quantitative explanations of recent experimental measurements which exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra.
Scattering of Stark-decelerated OH radicals with rare-gas atoms
NASA Astrophysics Data System (ADS)
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
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.
Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length
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
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.
Light scattering and localization in an ultracold and dense atomic system
I. M. Sokolov; M. D. Kupriyanova; D. V. Kupriyanov; M. D. Havey
2008-05-12
The quantum optical response of high density ultracold atomic systems is critical to a wide range of fundamentally and technically important physical processes. These include quantum image storage, optically based quantum repeaters and ultracold molecule formation. We present here a microscopic analysis of the light scattering on such a system, and we compare it with a corresponding description based on macroscopic Maxwell theory. Results are discussed in the context of the spectral resonance structure, time-dependent response, and the light localization problem.
Projectile scattering and electron-electron interaction in ion-atom collisions
NASA Astrophysics Data System (ADS)
Zapukhlyak, Myroslav; Henkel, Nils; Kirchner, Tom
2010-02-01
One- and two-electron processes involving electron transfer and excitation are considered for a few basic ion-atom collision systems at intermediate impact energies. We have used the two-center basis generator method in the framework of the independent electron model for orbital propagation and the eikonal approximation for the calculation of scattering-angle differential cross sections. Our results shed some light on the roles of the nucleus-nucleus and the electron-electron interactions in these collisions.
NASA Astrophysics Data System (ADS)
Marx, J.; Huang, H.; Faus, I.; Rackwitz, S.; Wolny, J. A.; Schlage, K.; Ulber, R.; Wille, H.-C.; Schnemann, V.
2014-04-01
Bovine serum albumin coated magnetic iron oxide nanoparticles (IONPs), which were synthesized using a co-precipitation method with 57Fe have been subject to a combined study using atomic force microscopy (AFM) and nuclear inelastic scattering (NIS). The obtained partial density of vibrational states (pDOS) shows evidence for lattice stiffening and a pronounced mode at 23 meV compared to thin film magnetite at room temperature.
Generalized Pseudo-potentials for Higher Partial Wave Scattering and Applications to Trapped Atoms
Rene Stock; Andrew Silberfarb; Ivan H. Deutsch; Eric L. Bolda
2004-01-01
We derive a generalized zero range pseudo-potential for all partial waves. Fermi's original s-wave pseudo-potential is widely used for calculating the mean field energy shift for interacting ultracold atoms. Generalizations of this pseudo-potential to p-wave scattering would be very useful, e.g., for studying ultra-cold collisions of identical Fermions. We derive a proper pseudo-potential for all higher partial waves based on
Analytic description of elastic electron-atom scattering in an elliptically polarized laser field
NASA Astrophysics Data System (ADS)
Flegel, A. V.; Frolov, M. V.; Manakov, N. L.; Starace, Anthony F.; Zheltukhin, A. N.
2013-01-01
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.
Electron-indium atom scattering and analysis of electron and optical spectra
NASA Astrophysics Data System (ADS)
Rabasovi?, Maja S.
2014-12-01
Experimental study of indium atom using electron and optical spectroscopy is presented in this paper. Both experimental techniques including experimental setups are described. Differential and integrated cross sections on elastic and inelastic electron scattering by indium atom are measured using electron spectrometer. The measurements are performed at incident electron energies of E0 = 10, 20, 40, 60, 80 and 100 eV within the large scattering angles ranging from 10 to 150 in steps of 10. The experimental results are presented and comparison with the values predicted by calculated optical potentials method is conducted, showing good agreement. The differential cross sections (DCSs) for electron-impact excitation of the resonant state 6s 2S1/2 of Indium atom are measured at small and large angles. The forward scattering function method has been used for normalizing the generalized oscillator strengths (GOS) to determine optical oscillator strength and obtaining the absolute DCS values. Optical spectrum of In I and In II lines has been acquired by a streak camera. The experimental results regarding indium lines obtained by time resolved laser induced breakdown spectroscopy (LIBS) could be useful for obtaining the important plasma parameters such as temperature, electron density as well as plasma-expansion velocity and plasma starting times.
NASA Astrophysics Data System (ADS)
Flambaum, V. V.; Kozlov, M. G.; Gribakin, G. F.
2015-05-01
In open-shell atoms and ions, processes such as photoionization, combination (Raman) scattering, electron scattering, and recombination are often mediated by many-electron compound resonances. We show that their interference (neglected in the independent-resonance approximation) leads to a coherent contribution, which determines the energy-averaged total cross sections of electron- and photon-induced reactions obtained using the optical theorem. In contrast, the partial cross sections (e.g., electron recombination or photon Raman scattering) are dominated by the stochastic contributions. Thus, the optical theorem provides a link between the stochastic and coherent contributions of the compound resonances. Similar conclusions are valid for reactions via compound states in molecules and nuclei.
Khoperskii, A. N., E-mail: hopersky_vm_1@rgups.ru; Nadolinskii, A. M.; Yavna, V. A.; Kasprzhitskii, A. S. [Rostov State University of Transport Communications (Russian Federation)
2007-04-15
The absolute value and shape of the double differential cross section of the resonance inelastic scattering of a linearly polarized photon in the ionization threshold energy range of the subvalence s shell of the free neon or argon atom are calculated in the nonrelativistic approximation for one-electron wavefunctions and in the dipole approximation for the anomalously dispersive scattering probability amplitude. The effects of radial relaxation, intershell correlations, bremsstrahlung, spin-orbit splitting, and a finite decay width of s vacancies are taken into account. The effects of radial relaxation and intershell correlations substantially affect the near-threshold scattering intensity: they decrease the contribution of the leading Compton anomalously dispersive component of the total cross section calculated in the one-electron approximation by several times. The calculation results have a predictive character.
Dimer-atom scattering between two identical fermions and a third particle
Iskin, M. [Department of Physics, Koc University, Rumelifeneri Yolu, TR-34450 Sariyer, Istanbul (Turkey)
2010-04-15
We use the diagrammatic T-matrix approach to analyze the three-body scattering problem between two identical fermions and a third particle (which could be a different species of fermion or a boson). We calculate the s-wave dimer-atom scattering length for all mass ratios, and our results exactly match the results of Petrov. In particular, we list the exact dimer-atom scattering lengths for all available two-species Fermi-Fermi and Bose-Fermi mixtures. In addition, unlike that of the equal-mass-particles case where the three-body scattering T matrix decays monotonically as a function of the outgoing momentum, we show that, after an initial rapid drop, this function changes sign and becomes negative at large momenta and then decays slowly to zero when the mass ratio of the fermions to the third particle is higher than a critical value (around 6.5). As the mass ratio gets higher, modulations of the T matrix become more apparent with multiple sign changes, related to the 'fall of a particle to the center' phenomenon and to the emergence of three-body Efimov bound states.
Howard L. Heinisch; Fei Gao; Richard J. Kurtz
2010-01-01
The interactions of He and vacancy defects with ?111? screw dislocations in alpha-Fe were modeled using molecular statics, molecular dynamics and transition state energy determinations. The formation energies and binding energies of interstitial He atoms, vacancies and Hevacancy clusters near and within dislocations in alpha-Fe were determined at various locations relative to the dislocation core. Using the dimer transition state
The Influence of Atomic Model on the Theoretical Profile of Scattering Polarization
NASA Astrophysics Data System (ADS)
Hao, LI; Zhong-quan, QU
2015-04-01
The diagnosis of solar magnetic field is a very important part in the studies of solar physics. The Stokes parameters I, Q, U, and V can give a complete description of the state of polarized light. By an inversion of the observed Stokes parameters, the information of solar magnetic field can be diagnosed. In the recent decades, the diagnosis of magnetic field is mainly based on the Zeeman effect, by which the produced line splitting is used for the diagnosis of a strong magnetic field up to several hundred Gauss. But in the solar quiet regions, there exist a large amount of weak magnetic fields with a strength less than 100 Gauss, which can be diagnosed by the Hanle effect, thus the diagnosis of weak magnetic field by the Hanle effect is one of the main topics in the diagnostics of magnetic field, and a more completely understanding for the polarization mechanism is needed. This paper focuses on the influences of atomic model on the scattering-caused line profile, and the Hanle effect when there is magnetic field existed. We adopt the neutral magnesium as a target in the study, the seven-, four-, and two-level atomic models are selected to investigate respectively the influences of these atomic models on the scattering polarization and the Hanle effect. It is found that there is a great difference between the polarization degrees produced by the two-level atomic model and multi-level ones (the seven- and four-levels). For the two-level atomic model, the b4 line is not affected by the Hanle effect of low levels, but for the multi-level atomic models, it does. Comparing the seven- and four-level atomic models, the polarization degree of spectral lines only has a small variation, and the behavior of Hanle effect is basically the same. The main conclusion of this paper is that when the linear polarization Q/I profiles of the 3 neutral magnesium b lines are used for the inversion of magnetic field, at least the four-level atomic model should be adopted. This mainly depends on the atomic level distribution in the forming region of the spectral line, the atomic levels with a greater occupation number must be considered in the study.
Oro, D.M.; Soletsky, P.A.; Zhang, X.; Dunning, F.B.; Walters, G.K. (Department of Physics and the Rice Quantum Institute, Rice University, P.O. Box 1892, Houston, Texas 77251 (United States))
1994-06-01
Measurements of ejected electron energy distributions are used in conjunction with electron spin labeling techniques to probe the mechanisms by which He(2 [sup 3][ital S]), He(2 [sup 1][ital S]), and He(2 [sup 3][ital P]) atoms are deexcited at Ar and Xe films adsorbed on a cooled Cu(100) substrate. The data for both surfaces contain features similar to those observed in gas-phase Penning ionization, indicating that ejection results, in part, from Auger deexcitation, i.e., surface Penning ionization. For Xe, however, additional features are observed that can be attributed to resonance ionization of an incident excited atom followed by neutralization of the resulting He[sup +] ion through an interaction that involves neighboring Xe atoms in the film. Indeed, the Xe data provide an exceptional example of a surface at which Auger deexcitation and resonance ionization occur in parallel with one another, with a branching ratio that changes significantly as the internal energy of the incident atoms increases. The ejected electron yield from both Ar and Xe films is substantially higher than for clean Cu(100), indicating that such films might form the basis of an efficient thermal-energy helium metastable-atom detector.
NASA Astrophysics Data System (ADS)
Nakahara, Taketoshi; Nishida, Takahiro
1998-08-01
A simple method is described for the generation of a continuous flow of volatile chlorine by the oxidation of aqueous chloride for the determination of low concentrations of chlorine by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (He MIP-AES). The chlorine atom emission line at 438.976 nm and ion emission lines at 479.454 and 481.006 nm were selected as the analytical lines of interest. Of the various oxidation reactions investigated, two analyte volatilization reactions with potassium permanganate and perbromate in combination with sulfuric acid were found to be the most appropriate for the generation of elemental chlorine. The gaseous chlorine is separated from the solution in a simple gas-liquid separator, dried with concentrated sulfuric acid and swept into the MIP with helium carrier gas for analysis. The best attainable detection limits (3 ? criterion) for chlorine at 438.976, 479.454 and 481.006 nm with the use of potassium permanganate as an oxidant were found to be 29.9, 6.8 and 12.3 ng ml -1, respectively. Typical calibration graphs obtained under the optimized experimental conditions are rectilinear over approximately three orders of magnitude of concentration. The present method has successfully been applied to the determination of chlorine as chloride in several water samples.
Kim, Tae-Kyun
1996-01-01
for the degree of MASTER OF SCIENCE August 1996 Major Subject: Mechanictd Engineering INVESTIGATION OF SONIC/SUBSONIC AIR-BLAST ATOMIZATION USING RAYLEIGH- AND MIE-SCATTERING VISUALIZATION TECHNIQUES A Thesis by TAE-KYUN KIM Submitted to Texas A...) August 1996 Major Subject: Mechanical Engineering ABSTRACT Investigation of Sonic/Subsonic Air-Blast Atomization Using Rayleigh- and Mie-Scattering Visualization Techniques. (August 1996) Tae-Kyun Kirn, B. S. , Korea Military Academy, Korea Chair...
Redistribution of light frequency by multiple scattering in a resonant atomic vapor
NASA Astrophysics Data System (ADS)
Carvalho, Joo Carlos de A.; Ori, Marcos; Chevrollier, Martine; Cavalcante, Hugo L. D. de Souza; Passerat de Silans, T.
2015-05-01
The propagation of light in a resonant atomic vapor can a priori be thought of as a multiple scattering process, in which each scattering event redistributes both the direction and the frequency of the photons. Particularly, the frequency redistribution may result in Lvy flights of photons, directly affecting the transport properties of light in a resonant atomic vapor and turning this propagation into a superdiffusion process. Here, we report on a Monte Carlo simulation developed to study the evolution of the spectrum of the light in a resonant thermal vapor. We observe the gradual change of the spectrum and its convergence towards a regime of complete frequency redistribution as the number of scattering events increases. We also analyze the probability density function of the step length of photons between emissions and reabsorptions in the vapor, which governs the statistics of the light diffusion. We observe two different regimes in the light transport: superdiffusion when the vapor is excited near the line center and normal diffusion for excitation far from the line center. The regime of complete frequency redistribution is not reached for excitation far from resonance even after many absorption and reemission cycles due to correlations between emitted and absorbed frequencies.
Eric R. Bittner; John C. Light
1994-01-01
He scattering from Xe monolayers adsorbed onto Ag substrates is studied using a quantum stochastic method. Both the He atom and the surface and bulk modes are treated quantum mechanically using a mean-field partitioning of the quantum Liouville equation. The resulting equations of motion permit the evaluation of the reduced density matrix of the He atom subsystem by averaging over
O. Ishiyama; T. Nishihara; S. Hayashi; M. Shinohara; M. Yoshimoto; T. Ohnishi; H. Koinuma; S. Nishino; J. Saraie
1997-01-01
Quantitative surface analysis includes the determination of the elemental composition and the structure of the sample under investigation. Although LEED, XPS, and SPM etc. have been used to investigate the surface structure of the materials, ambiguity remains in determining quantitatively the topmost atomic species and its alignment on an atomic scale. Therefore, we adopted coaxial impact collision ion scattering spectroscopy
R. Souda; M. Aono; C. Oshima; S. Otani; Y. Ishizawa
1983-01-01
The thermal vibration amplitude of Ti atoms in the top layer of the TiC(111) surface has been measured by a specialized technique in low-energy ion scattering spectroscopy. The root-mean-square amplitude of the surface Ti atoms is 0.076 along the surface normal at room temperature.
Ionization of He atoms during grazing scattering from a metal surface
Wethekam, S.; Winter, H. [Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Valdes, Diego; Monreal, R. C. [Departamento de Fisica Teorica de la Materia Condensada C-V, Universidad Autonoma de Madrid, E-28049 Madrid (Spain)
2009-05-15
We present a theoretical analysis of experimental data on ion fractions and polar angular distributions for He atoms and ions produced during grazing scattering of keV neutral He atoms from an atomically clean and flat Al(111) surface. The discussion focuses on the mechanism of Auger ionization for which we have recently presented the first quantitative treatment by an ab initio method [S. Wethekam, Diego Valdes, R. C. Monreal, and H. Winter, Phys. Rev. B 78, 033105 (2008)]. Auger ionization, the inverse process of Auger neutralization, is a dynamical process that converts kinetic energy from the projectile to electronic excitations. We calculate Auger ionization rates and perform molecular-dynamics and Monte Carlo simulations of trajectory and charge state of scattered projectiles. We achieve quantitative agreement with experimental ion fractions and angular distributions. This demonstrates that Auger ionization is an efficient mechanism of ionization. We also discuss the sensitivity of the results on the theoretical input used in the simulations and give an estimate on the contribution of resonant processes.
Robert Gayet; Jocelyn Hanssen; Laurent Jacqui; Alejandra Martinez; Roberto Rivarola
1996-01-01
Double electron capture by fast bare ions in helium is studied in the framework of the Four-Body Continuum Distorted Wave theory. It is shown that experimental data is well reproduced when the theoretical total cross-section include both contributions from the ground state and from the first singly excited states. In addition, cross-sections for the production of the first doubly excited
Elastic Electron Scattering by Laser-Excited (sup 138)Ba (...6s6p (sup 1)P(sub 1)) Atoms
NASA Technical Reports Server (NTRS)
Csanak, G.
1997-01-01
The result of a joint experimental and theoretical study concerning elastic electron scattering by laser-excited (sup 138)Ba (...6s6p (sup 1)P(sub 1)) atoms are presented. From these studies, we extracted differential scattering cross sections (DCS's) and collision parameters for elastic scattering by the coherently prepared (sup 1)P(sub 1) atoms.
Ordering of metal overlayers on metal substrates studied using atom beam scattering
Vidali, G.; Hutchings, C.W.; Dowben, P.A. (Physics Department, Syracuse University, Syracuse, NY (USA)); Karimi, M. (Physics Department, Alabama A M University, Normal, AL (USA)); Moses, C. (Physics Department, Utica College, Utica, NY (USA)); Foresti, M. (Dipartimento di Fisica, Universita di Campobasso, Campobasso (Italy))
1990-05-01
We will illustrate how atom beam scattering (ABS) can be used to study the growth and ordering of adsorption of Hg on Cu(001). At low coverage (less than 2% of a monolayer), we obtain that the scattering cross section of He with (adsorbed) Hg is about 50 A{sup 2}. We find that mercury forms two stable phases on Cu(001) in the temperature range between 200 and 330 K, a {ital c}(2{times}2) and a high density {ital c}(4{times}4) phase. From ABS diffraction data, we can deduce the corrugation of the surface electron charge density of the mercury layer in the two ordered phases. From the analysis of our data, we obtain a Debye temperature for the Hg overlayer of about 115 K. We will report preliminary calculations on the adsorption energy of Hg on Cu(001) and on the interaction of He with a Hg preplated Cu(001) surface.
Application of X-ray diffraction dynamics to strong anomalous scattering region of an atom
NASA Astrophysics Data System (ADS)
Zhao, Zongyan; Han, Jiahua; Zhou, Shengming; Xu, Zhangcheng; Fukamachi, Tomoe; Negishi, Riichiro; Yoshizawa, Masami; Nakajima, Tetsuo
1995-12-01
This paper gives new formulae of X-ray dynamical diffraction for a plane-parallel crystal with finite thickness. These formulae are applicable when the ratio of the two absolute values, i.e. the real part of the atomic scattering factor and the imaginary part, is arbitrary. Based on these formulae, the results calculated in both the Bragg and the Laue cases show that the formulae not only agree well with originally theoretical predictions, but also provide an incentive for cases which have not been studied.
Proton scattering by a hydrogen atom in an effectively two-body model
Pupyshev, V. V., E-mail: pupyshev@theor.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)
2013-02-15
It is assumed that the total potential of proton interaction with a hydrogen atom is the sum of the short-range nuclear soft-core Reid potential and the long-range Thomas-Fermi potential. A quantum mechanical analysis of low-energy features of the phase shift and cross section for elastic proton scattering on a hydrogen atom is given for the case of zero total angular momentum. The calculations performed in the present study within a nonlinear version of the variable-phase approach ultimately revealed that, because of a long-range character of the asymptotic behavior of the Thomas-Fermi potential, the respective cross section at low energies oscillates but has a finite number of zeros.
Generalized Pseudo-potentials for Higher Partial Wave Scattering and Applications to Trapped Atoms
NASA Astrophysics Data System (ADS)
Stock, Rene; Silberfarb, Andrew; Deutsch, Ivan H.; Bolda, Eric L.
2004-05-01
We derive a generalized zero range pseudo-potential for all partial waves. Fermi's original s-wave pseudo-potential is widely used for calculating the mean field energy shift for interacting ultracold atoms. Generalizations of this pseudo-potential to p-wave scattering would be very useful, e.g., for studying ultra-cold collisions of identical Fermions. We derive a proper pseudo-potential for all higher partial waves based on a delta-shell potential in the limit as the shell radius approaches zero, thereby taking into account the higher multipoles not captured by a delta-function at the origin. We apply this correct form to study atoms in harmonic traps interacting via short-range potentials, deriving analytic expressions for the energy eigenstates and eigenvalues.
NASA Astrophysics Data System (ADS)
Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, Mara; Alducin, Maite; Auerbach, Daniel J.
2014-08-01
Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution.
Liao, C.; Hagmann, S.; Bhalla, C.P.; Grabbe, S.R.; Cocke, C.L.; Richard, P. [J. R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506 (United States)] [J. R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506 (United States); Liao, C. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)] [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
1999-04-01
We present a method of deriving energy and angle-dependent electron-ion elastic scattering cross sections from doubly differential cross sections for electron emission in ion-atom collisions. By analyzing the laboratory frame binary encounter electron production cross sections in energetic ion-atom collisions, we derive projectile frame differential cross sections for electrons elastically scattered from highly charged projectile ions in the range between 60{degree} and 180{degree}. The elastic scattering cross sections are observed to deviate strongly from the Rutherford cross sections for electron scattering from bare nuclei. They exhibit strong Ramsauer-Townsend electron diffraction in the angular distribution of elastically scattered electrons, providing evidence for the strong role of screening played in the collision. Experimental data are compared with partial-wave calculations using the Hartree-Fock model. {copyright} {ital 1999} {ital The American Physical Society}
Taketoshi Nakahara; Takahiro Nishida
1998-01-01
A simple method is described for the generation of a continuous flow of volatile chlorine by the oxidation of aqueous chloride for the determination of low concentrations of chlorine by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (He MIP-AES). The chlorine atom emission line at 438.976nm and ion emission lines at 479.454 and 481.006nm were selected as the analytical lines
NASA Astrophysics Data System (ADS)
Lombardi, Luciano D.
The Ramsey separated oscillatory fields (SOF) technique is applied to a measurement of the helium 23P 1mJ=0-to-23P 2mJ=0, 2.291-GHz fine-structure interval. Helium is an ideal atom to study fine structure due to the long lifetime of the 23P states (98 ns) which leads to a narrow 3.25-MHz natural linewidth. The fine-structure energy splittings are also large: 2.291 GHz for the 23P1-to-23 P2 interval and 29.6 GHz for the 23 P0-to-23P1 interval. By comparison, the hydrogen n=2 fine structure has a natural linewidth of 200 MHz and an energy splitting of 10 GHz. The SOF technique can be used to narrow the linewidth for the 2.291-GHz fine-structure interval since the SOF linewidth is inversely proportional to the time separating the two oscillating fields. It is possible, using the SOF technique, to achieve subnatural linewidths, and hence greater resolution of the 2.291-GHz resonance. In addition, the use of the SOF technique involves a different set of systematics than other determinations of the helium fine structure. The goal for this measurement is to test quantum electrodynamics (QED) theory. It is important to test QED theory in a variety of different systems as this helps to test the validity of the theory and to test calculations done using the theory. The 2.291-GHz interval will test the precision of the helium fine-structure theory so that the 29.6-GHz interval, when combined with precise theory, can be used to determine a new value for the fine-structure constant. With sufficiently-precise theory, the 29.6-GHz interval measured to an accuracy of 400 Hz will yield a 6-ppb (parts per billion, parts per 109) determination of the fine-structure constant. The goal of the current SOF experiment it to measure the 2.291-GHz interval to an accuracy of 400 Hz. SOF data taken to date have already achieved a statistical uncertainty of 70 Hz. However, systematic effects are not yet understood and thus a new determination for 2.291-GHz interval at the 400-Hz level is not yet possible. Traditionally, the SOF technique is applied with two oscillating fields that are separated in space. In this experiment, however, the microwave fields are separated in time, using pulses of microwaves. These microwave pulses are phase distorted by the microwave system, leading to not-yet-fully-understood systematic shifts of the SOF linecenters.
Loo, J.F.
1990-01-01
The development of experimental and data analysis techniques for quantitative analysis in gas chromatography/low power atmospheric pressure helium microwave-induced plasma atomic emission interferometry (GC/HeMIPAEI) and ion cyclotron resonance mass spectroscopy (ICR/MS) is presented. A discussion of interferometric data analysis by discrete and fast Fourier transform (DFT and FFT, respectively) is given. Additionally, the use of two techniques (the maximum entropy method, or MEM, and linear prediction, or LP) that have shown to produce results superior to those from the FFT is shown for synthetic and experimental NMR, optical, and mass spectral data. Visual spectral comparisons, performance results as compared to known spectral parameters, and a methodology for the implementation of the linear prediction technique is given. A low-power HeMIP was constructed and used as the excitation source for an AEI detector for gas chromatography. In general, HeMIPs have the advantage of being able to excite non-metal atoms, which comprise a large fraction of the molecules used in typical organic GC analysis. Sensitivity, detection limits, their dependence on microwave power values, and elemental emission ratios are tabulated for a series of test compounds. Results show that elemental emission ratios are independent of the structure of the compound used in this study. Suggestions for further development, from the use of a concentric-flow torch and optical filters to the removal of oxygen through the use of ultra-high purity helium, are presented. Through the use of coherent pulsed excitation, electronic quadrature detection, and data analysis by linear prediction, ICR/MS relative abundance error values for the principal isotopes of krypton have been calculated to be less than 1%.
NASA Astrophysics Data System (ADS)
Nakahara, Taketoshi; Mori, Toshio; Morimoto, Satoru; Ishikawa, Hiroshi
1995-06-01
A simple continuous-flow generation of volatile hydrogen sulfide and sulfur dioxide by acidification of aqueous sulfide and sulfite ions, respectively, is described for the determination of low concentrations of sulfur by atmospheric-pressure helium microwave-induced plasma atomic emission spectrometry (MIP-AES) in the normal ultraviolet (UV) and vacuum ultraviolet (VUV) regions of the spectrum. For measuring spectral lines in the VUV region, the monochromator and the enclosed external optical path between the MIP source and the entrance slit of the monochromator have both been purged with nitrogen to minimize oxygen absorption below 190 nm. Sulfur atomic emission lines at 180.73, 182.04 and 217.05 nm have been selected as the analytical lines. Of the various acids examined, 1.0 M hydrochloric acid is the most favorable for both the generation of hydrogen sulfide from sulfide ions and sulfur dioxide from sulfite ions. Either generated hydrogen sulfide or sulfur dioxide is separated from the solution in a simple gas-liquid separator and swept into the helium stream of a microwave-induced plasma for analysis. The best attainable detection limits (3 ? criterion) for sulfur at 180.73 nm were 0.13 and 1.28 ng ml -1 for the generation of hydrogen sulfide and sulfur dioxide, respectively, with the corresponding background equivalent concentrations of 20.9 and 62.2 ng ml -1 in sulfur concentration. The typical analytical working graphs obtained under the optimized experimental conditions were rectilinear over approximately four orders of magnitude in sulfur concentration. The present method has been successfully applied to the recovery test of the sulfide spiked to waste water samples and to the determination of sulfite in some samples of commercially available wine.
Frazier
1965-01-01
This is a process of separating helium from a helium-containing natural gas. The gas is contacted within a closed vessel with a mass of small, hollow, hole-free, glass particles through which the helium selectively diffuses relative to the other components of the gas mixture. A positive helium partial-pressure differential is maintained across the glass walls of the particles with the
Requirements, possible alternatives & international NEUTRON SCATTERING
Dimeo, Robert M.
Requirements, possible alternatives & international NEUTRON SCATTERING DETECTORS for Rob Dimeo NIST neutron scattering instruments are the most demanding require background low #12;#12;The Helium-3 Supply Crisis Alternative Techniques to Helium-3 based Detectors for Neutron Scattering Applications
Circuit Quantum Electrodynamics with Electrons on Helium
Circuit Quantum Electrodynamics with Electrons on Helium A Dissertation Presented to the Faculty Fragner All rights reserved. ii #12;Abstract Circuit Quantum Electrodynamics with Electrons on Helium helium. Such a system represents a solid-state, electrical circuit analog of atomic cavity QED in which
Vogl, G.; Partyka-Jankowska, E.; ZajaPc, M.; Chumakov, A. I. [Faculty of Physics, University of Vienna, Strudlhofgasse 4, A-1090 Vienna (Austria); Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Cracow, Poland and European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, 38043 Grenoble Cedex (France); European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, 38043 Grenoble Cedex (France)
2009-09-15
We study the structure of a model surface, i.e., an Fe monolayer on W(110) by nuclear resonant scattering of x rays. We conclude that at room temperature the structure is nearly perfect, whereas when increasing the temperature up to 770 K an increasing fraction of the Fe atoms feels the appearance of defects manifested by a beat structure due to an electric field gradient. The field gradient is caused by an asymmetry of the neighborhood of part of the atoms and attributable to an increasing fraction of vacancies in the monolayer. With increasing temperature the beat structure gets smeared due to the onset of dynamics in the surface, i.e., the motion of the defects and consequently of the atoms. From the temperature dependence of the amplitude of the beat we deduce the vacancy concentration, thus the vacancy formation energy [0.17(5) eV] and from the broadening with less accuracy we deduce the vacancy migration energy [0.16(6) eV] resulting in 0.33(11) eV for the activation energy of diffusion.
Nonrelativistic quantum theory of the contact inelastic scattering of an x-ray photon by an atom
Hopersky, Alexey N.; Nadolinsky, Alexey M. [Chair of Mathematics, Rostov State University of Transport Communication, Rostov-on-Don, 344038 (Russian Federation)
2008-02-15
The nonrelativistic analytical structure of the doubly differential cross section of the contact inelastic scattering of an x-ray photon by a free atom is determined by means of the irreducible tensor operator theory outside the frame of the impulse approximation. For the neon atom in the vicinity of the 1s shell ionization threshold our theory predicts the existence of the distinct fine structure of the cross section caused by transitions of the atomic core electrons into the excited discrete spectrum states. The results of our calculations with inclusion of the effects of radial relaxation, inelastic scattering through the intermediate states, and elastic Rayleigh scattering, are predictions, while at the 22 keV incident photons they compare well with the synchrotron experiment by Jung et al. [Phys. Rev. Lett. 81, 1596 (1998)].
Giuliano Benenti; Stefano Siccardi; Giuliano Strini
2013-05-01
Using a configuration-interaction variational method, we accurately compute the reduced, single-electron von Neumann entropy for several low-energy, singlet and triplet eigenstates of helium atom. We estimate the amount of electron-electron orbital entanglement for such eigenstates and show that it decays with energy.
NASA Astrophysics Data System (ADS)
Sun, Shi-Yan; Jia, Xiang-Fu; Miao, Xiang-Yang; Zhang, Jun-Feng; Xie, Yi; Li, Xiong-Wei; Shi, Wen-Qiang
2009-07-01
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.
Helium production in natural gas reservoirs
E. B. Pereira; J. A. S. Adams
1982-01-01
About 11,000 published natural gas analyses of helium are used in the estimation of the average global scale accumulation and concentration of radiogenic helium in sediments. Simple lognormal statistics is employed to derive a net accumulation rate between 1105 to 6.7105 helium atoms per cubic meter of reservoir rock per second. This acccumulation rate permitted to infer an average helium
Helium production in natural gas reservoirs
E. B. Pereira; J. A. S. Adams
1982-01-01
About 11,000 published natural gas analyses of helium are used in the estimation of the average global scale accumulation and concentration of radiogenic helium in sediments. Simple lognormal statistics is employed to derive a net accumulation rate between 1dagger10⁵ to 6.7dagger10⁵ helium atoms per cubic meter of reservoir rock per second. This acccumulation rate permitted to infer an average helium
Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium
California at Santa Cruz, University of
Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium I. Introduction to the variational computation The Hamiltonian for the two-electron system of the helium atom is state energy of the helium atom. The ground state wave function of the helium atom is of the form: 1 2
Angular Scattering of Energetic Neutral Hydrogen Atoms off the Lunar Surface
NASA Astrophysics Data System (ADS)
Vorburger, A.; Wurz, P.; Barabash, S.; Wieser, M.; Futaana, Y.; Holmstrm, M.; Bhardwaj, A.; Dhanya, M. B.; Sridharan, R.; Asamura, K.
2012-04-01
Planetary surfaces, such as the lunar surface, which are not shielded by an atmosphere or a global magnetic field, are constantly bombarded by the surrounding plasma, e.g. by solar wind ions. When these ions hit the lunar surface, a large percentage is backscattered as energetic neutral atoms (ENAs). Measurements conducted by IBEX and Chandrayaan-1 showed that the backscatter fraction lies in the range 10-20% of the impinging solar wind ions (McComas et al., GRL 2009, Wieser et al., PSS 2009, and Rodrguez et al., PSS 2012). The energy of the backscattered ENAs is sufficiently high so that the individual trajectories can be mapped back onto the lunar surface in a straight forward manner and imaging of the surface using the ENAs is possible. To guarantee a quantitative imaging of the lunar surface, the angular distribution of the released ENAs has to be taken into account, though. It was formerly assumed that most of the impinging solar wind ions are absorbed by the lunar surface. Before CENA, no analysis of in-flight measurements concerning the angular scattering profile was available. We therefore analysed all available measurements conducted by CENA, the Chandrayaan-1 Energetic Neutral Analyzer, to derive the scattering profile of low energetic hydrogen atoms coming off the lunar surface. Our analysis shows that the angular scattering profile exhibits 4 distinct features for increasing solar zenith angle: 1) amplitude decrease, 2) increased azimuthal structure, 3) bigger ratio of sunward versus anti-sunward flux and 4) shallower polar scattering. We derived four mathematical functions, each of which describes one feature, and the product of which describes the ENA angular distribution function. The directional ENA flux can then be described as the product of the impinging solar wind flux, the reflection ratio at the sub solar point and the ENA angular distribution function. This function has been derived from lunar backscatter data, but it should be applicable to mapping of any planetary surface that is not protected by an atmosphere or a global magnetic field.
Helium in Chemically Peculiar Stars
F. Leone
1998-05-05
For the purpose of deriving the helium abundances in chemically peculiar stars, the importance of assuming a correct helium abundance has been investigated for determining the effective temperature and gravity of main sequence B-type stars, making full use of the present capability of reproducing their helium lines. Even if the flux distribution of main sequence B-type stars appears to depend only on the effective temperature for any helium abundance, the effective temperature, gravity and helium abundance have to be determined simultaneously by matching the Balmer line profiles. New MULTI NLTE calculations, performed adopting ATLAS9 model atmospheres and updated helium atomic parameters, reproduce most of the observed equivalent widths of neutral helium lines for main sequence B-type stars and they make us confident of the possibility to correctly derive the helium abundance in chemically peculiar stars. An application of previous methods to the helium rich star HD 37017 shows that helium could be stratified in the magnetic pole regions, as expected in the framework of the diffusion theory in the presence of mass loss.
K. Umezawa
2008-01-01
Applications of low energy ion scattering and low energy atom scattering spectroscopy have been described. Time of flight impact-collision ion scattering (TOF-ICISS) has been used to investigate the heteroepitaxial growth of 3ML of FCC elements on Ni(111) and Cu(111) over a wide temperature range from 300K through 700K. There were two different types of epitaxial growth; FCC(111)[112]\\/\\/Sub(111)[112] and FCC(111)[112]\\/\\/Sub(111)[112]. FCC
Horvatic, Vlasta; Mller, Saskia; Veza, Damir; Vadla, Cedomil; Franzke, Joachim
2014-01-01
The populations of the lowest excited helium states 2s 3S1, 2s 1S, 2p 3P0 J, and 2p 1P0 created in an atmospheric helium capillary dielectric barrier discharge were determined by means of optical emission spectroscopy. The emitted intensities of 388, 501, 587, and 667 nm lines were measured side-on and end-on with respect to the discharge axis. The comparison of optically thin side-on spectra with end-on spectra, which exhibited the absorption effects in the line kernels, enabled the determination of the average values of the number densities n1 in the considered He states along the plasma length L. The field of the theoretical profiles for a series of the n1L parameters pertinent to the experimental conditions was calculated for each line. By introducing the experimental data into the field of calculated curves, n1L corresponding to the particular state could be obtained. The measurements of the emission profiles were done as a function of the discharge voltage in the range covering homogeneous as well as filamentary DBD operation mode. Due to nonuniformity of the excited atom density distribution along the plasma, the values of n1 could be obtained only in the homogeneous operation mode where the nonuniformity was small. The following maximum values were found for the number densities in the investigated states: n1 av (2s 3S1) = (2.9 1.1) 1013 cm?3, n1 av (2s 1S) = (1.4 0.5) 1013 cm?3, n1 av (2p 3P0 J) = (1.1 0.4) 1013 cm?3, n1 av (2p 1P0) = (4.2 1.6) 1012 cm?3, and they represent the average populations along the plasma column in the capillary. PMID:24320177
Low-energy electron elastic scattering cross sections for excited Au and Pt atoms
NASA Astrophysics Data System (ADS)
Felfli, Zineb; Eure, Amanda R.; Msezane, Alfred Z.; Sokolovski, Dmitri
2010-05-01
Electron elastic total cross sections (TCSs) and differential cross sections (DCSs) in both impact energy and scattering angle for the excited Au and Pt atoms are calculated in the electron impact energy range 0 ? E ? 4.0 eV. The cross sections are found to be characterized by very sharp long-lived resonances whose positions are identified with the binding energies of the excited anions formed during the collisions. The recent novel Regge-pole methodology wherein is embedded through the Mulholland formula the electron-electron correlations is used together with a Thomas-Fermi type potential incorporating the crucial core-polarization interaction for the calculations of the TCSs. The DCSs are evaluated using a partial wave expansion. The Ramsauer-Townsend minima, the shape resonances and the binding energies of the excited Au - and Pt - anions are extracted from the cross sections, while the critical minima are determined from the DCSs.
Doubly differential spectra of scattered protons in ionization of atomic hydrogen
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
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.
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms.
Song, Lei; Balakrishnan, N; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C
2015-05-28
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15?000 cm(-1) based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models. PMID:26026443
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
NASA Astrophysics Data System (ADS)
Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.
2015-05-01
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm-1 based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models.
Effects of Helium on Radiation Damage Processes in Iron
Morishita, K; Wirth, B D; Diaz de la Rubia, T; Kimura, A
2001-06-02
Molecular dynamics calculations were performed to evaluate the energies of helium-related defects in ?-iron for investigation of helium behavior during irradiation. The interatomic potentials employed here were the Ackland Finnis-Sinclair N-body potential, the Wilson-Johnson potential and the ZBLBeck potential for describing interactions of Fe-Fe, Fe-He and He-He, respectively. The migration energy of interstitial helium is extremely low, indicating that an interstitial helium atom can migrate rapidly in the metal even at extremely low temperature, until the helium atom is trapped or escapes outside. One of the most efficient trapping sites for helium is a vacancy or small vacancy clusters (nanovoid). The formation energy of helium-vacancy clusters in iron was calculated as a function of the number of helium atoms and vacancies. The binding energy of an interstitial helium atom, a substitutional helium atom and a vacancy to the cluster was also determined as a function of the helium-to-vacancy ratio of the cluster. Helium is strongly bound to the helium-vacancy cluster, and it can stabilize the cluster, thereby increasing cluster lifetime by dramatically reducing thermal vacancy emission. The binding of helium and vacancies to a helium-vacancy cluster greatly depends on the helium-to-vacancy ratio of the cluster. For clusters with extremely high helium-to-vacancy ratios, it was observed that the collective motion of helium atoms produces bubble pressures large enough to spontaneously create additional vacancies and associated self-interstitial atoms at the periphery of the cluster. Finally, the possibility of athermal production of self-interstitial atom (SIA) loops (i.e., dislocation loop punching) from the cluster is discussed.
NASA Astrophysics Data System (ADS)
Pechkis, Joseph A.; Fatemi, Fredrik K.
2012-06-01
We have guided cold rubidium atoms in blue-detuned hollow optical modes of a hollow fiber. These higher order modes allow large optical depth, low scattering rates, and efficient use of guide laser power. Atoms are transported through a 3-cm-long hollow fiber with a 100 micron diameter using the first three optical modes of the fiber. We compare guiding properties in the red-detuned, fundamental HE11 mode with the blue-detuned TE01 (first order) and HE12 (second order) modes. Using guide laser powers below 50 mW and detunings below 1.5 nm, we have directly measured recoil scattering rates in the three different guides and found that atoms in the HE12 mode typically have a 10x lower recoil scattering rate compared to the red-detuned HE11 mode for equal guide peak intensity. Furthermore, we have observed optical depths of 20 for the blue-detuned guides with recoil scattering rates below 10 Hz. We will discuss our ongoing experiments using the atoms in these guides. This work supported by the Office of Naval Research and the Defense Advanced Research Projects Agency.
Omidvar
1959-01-01
The elastic scattering of electrons by atomic hydrogen including the ; effects of exchange and polarization is calculated. To include the exchange ; effect the total spin and space function of the incident and the bound electrons ; is made antisymmetric with respect to interchange of the two electrons. In this ; way an equation for the wave function of
NASA Technical Reports Server (NTRS)
Diana, L. M.; Chaplin, R. L.; Brooks, D. L.; Adams, J. T.; Reyna, L. K.
1990-01-01
An improved technique is presented for employing the 2.3m spectrometer to measure total ionization cross sections, Q sub ion, for positrons incident on He. The new ionization cross section agree with the values reported earlier. Estimates are also presented of total elastic scattering cross section, Q sub el, obtained by subtracting from total scattering cross sections, Q sub tot, reported in the literature, the Q sub ion and Q sub Ps (total positronium formation cross sections) and total excitation cross sections, Q sub ex, published by another researcher. The Q sub ion and Q sub el measured with the 3m high resolution time-of-flight spectrometer for 54.9eV positrons are in accord with the results from the 2.3m spectrometer. The ionization cross sections are in fair agreement with theory tending for the most part to be higher, especially at 76.3 and 88.5eV. The elastic cross section agree quite well with theory to the vicinity of 50eV, but at 60eV and above the experimental elastic cross sections climb to and remain at about 0.30 pi a sub o sq while the theoretical values steadily decrease.
On the Formation of (Anionic) Excited Helium Dimers in Helium Droplets
2014-01-01
Metastable atomic and molecular helium anions exhibiting high-spin quartet configurations can be produced in helium droplets via electron impact. Their lifetimes allow detection in mass spectrometric experiments. Formation of atomic helium anions comprises collision-induced excitation of ground state helium and concomitant electron capture. Yet the formation of molecular helium anions in helium droplets has been an unresolved issue. In this work, we explore the interaction of excited helium atoms exhibiting high-spin triplet configurations with ground state helium using the equation-of-motion coupled-cluster method. Transition barriers in the energetically lowest He*He and He*He interaction potentials prevent molecule formation at the extremely low temperatures present in helium droplets. In contrast, some excited states allow a barrier-free formation of molecular helium (anions). Moreover, we show that the necessary excitation energies pinpoint (higher) resonances in recently recorded mass spectra and emend the assignment of those resonances that have previously been assigned to electron-impact ionization of ground state helium necessitating subsequent double-electron capture. Embedding molecules or molecular clusters in helium droplets is a predestined experimental technique for the study of phenomena at very low temperatures. Profound knowledge about active processes in the helium environment is required for a proper assessment of experimental data. PMID:24866535
Saha, Hari P. [Physics Department, University of Central Florida, Orlando, Florida 32816 (United States)
2010-10-15
We have extended the multiconfiguration Hartree-Fock method for electron-impact ionization of atoms to investigate the effects of polarization and electron correlation of the target in the initial state. As a test case, the method is applied to calculate triple differential cross sections for electron-impact ionization of He atom at an excess energy of 2 eV for the coplanar {theta}{sub 12}={pi} geometry for equal and unequal energies of two final-state outgoing electrons. To determine the effects of electron correlation between the two outgoing electrons in the final state, the variationally determined screening potential approximation is used. It is found that target correlation in the initial state has smaller effect on the triple differential cross section but the polarization of the target by the incident electron has considerable effect on the triple differential cross section at low incident energy. The results are compared with absolute measurement and other available theoretical results.
ccsd00000660 Analysis of Photoassociation Spectra for Giant Helium Dimers.
of metastable helium atoms. The experimental spectrum obtained with the PA laser tuned closed to the 2 3 S1 $ 2 and evaporatively cooled metastable helium gas. We have thereby achieved greater state selectivity, higher density by photoas- sociation of metastable helium atoms, with the PA laser #3; Electronic address: leonard
NASA Astrophysics Data System (ADS)
Weatherford, Brandon R.; Xiong, Zhongmin; Barnat, E. V.; Kushner, Mark J.
2014-09-01
Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100-120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3 109 cm s-1, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.
NASA Astrophysics Data System (ADS)
Man?ev, I.; Milojevi?, N.; Belki?, D.
2015-03-01
The four-body boundary-corrected first Born (CB1-4B) approximation is used to compute cross sections for single electron capture from helium targets by fully stripped ions. The projectile ions are H+, He2+, Li3+, Be4+, B5+, C6+, N7+, O8+, and F9+. An extensive list of theoretical state-to-state cross sections in these collisions at energies ranging from 20 to 10 000 keV/amu is given. This list includes the state-selective cross sections Qnlm for each individual triple of the usual quantum numbers { n , l , m } of the final hydrogen-like states alongside Qnl and Qn for the pertinent sub-shells and shells where the respective summations over m and { l , m } have been carried out. The maximal value of the principal quantum number n was chosen to vary from 4 (H+) to 10 (F9+) so as to satisfy the condition n ?ZP, where ZP is the nuclear charge of the projectile. Usually, the largest cross sections stem from those values of n that match the projectile charge (n =ZP) . The total cross sections for capture summed over all the quantum numbers { n , l , m } are also tabulated. The overall goal of this study is to fill in lacunae in the existing databases of charge exchange cross sections that are needed in several inter-disciplinary fields. For example, in particle transport physics, which is of utmost importance in such emerging branches as hadron therapy, these cross sections constitute a part of the multifaceted input data for stochastic simulations of energy losses of multiply charged ions in matter, including tissue. Other significant uses of the present data are anticipated in charge exchange diagnostics within thermonuclear research project as well as in applications covering the relevant parts of plasma physics and astrophysics.
Helium Molecular Energy States as Detected by Collisions of the Second Kind in Helium
Roland Meyerott
1946-01-01
From a survey of the literature on spectra enhanced by collisions of the second kind, which take place in helium, evidence is presented for the existence in measurable concentrations of both the helium molecule-ion and the helium metastable molecule. From the intensity distribution of the enhanced spectra, the repulsive energy between two helium atoms at separations of 1.052A and 1.090A
Experimental studies on kaonic atoms at DA?NE
NASA Astrophysics Data System (ADS)
Okada, S.; Bazzi, M.; Beer, G.; Berucci, C.; Bombelli, L.; Bragadireanu, A. M.; Cargnelli, M.; Clozza, A.; Corradi, G.; Curceanu, C.; d'Uffizi, A.; Fiorini, C.; Frizzi, T.; Ghio, F.; Girolami, B.; Guaraldo, C.; Hayano, R. S.; Iliescu, M.; Ishiwatari, T.; Iwasaki, M.; Kienle, P.; Sandri, P. Levi; Longoni, A.; Lucherini, V.; Marton, J.; Pietreanu, D.; Piscicchia, K.; Lener, M. Poli; Ponta, T.; Rizzo, A.; Vidal, A. Romero; Sbardella, E.; Scordo, A.; Shi, H.; Sirghi, D. L.; Sirghi, F.; Tatsuno, H.; Tudorache, A.; Tudorache, V.; Doce, O. Vazquez; Widmann, E.; Zmeskal, J.
2011-10-01
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-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.
NASA Astrophysics Data System (ADS)
Bracco, Gianangelo; Ward, Michael D.; Scoles, Giacinto
2003-05-01
The guanidinium methanesulfonate is a layered self-assembled organic crystal which presents a bilayer structure and two different (001) planes can be exposed upon cleavage. In a previous paper we have shown that the analysis of the rate of decay in the thermal attenuation of the diffraction intensities in the scattering from the (001) surface of single crystal guanidinium methanesulfonate allows for distinguishing between the two possible (001) cleavage planes. However, since a more detailed knowledge of the He-surface interaction was lacking, in this paper we complete the investigation by studying the attractive part of the interaction potential between He and the surface terminated by methyl groups projecting outward from the hydrogen bonded sulfonate and guanidinium sheets. Four bound state levels have been determined and a well depth D=(6.70.2) meV has been estimated.
Paramagnetic Attraction of Impurity-Helium Solids
NASA Technical Reports Server (NTRS)
Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.
2003-01-01
Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.
Impact of Atomic Corrugation on Sliding Friction as Probed by QCM
Tonya Coffey; Sang Lee; Jacqueline Krim
2004-01-01
At the atomic scale, friction is believed to originate primarily via sliding induced excitation of phonons. [1] Theoretical predictions of the magnitude of phononic dissipation have been related to the atomic corrugation of the adsorbate\\/substrate potential. [2] Braun and colleagues [3] measured a corrugation of 1.9 meV for xenon on a copper(111) surface using helium atom scattering. Using the Quartz
ccsd-00000660(version1):1Oct2003 Analysis of Photoassociation Spectra for Giant Helium Dimers.
Paris-Sud XI, Universit de
dimers pro- duced by photoassociation (PA) in an ultra-cold gas of metastable helium atoms starting from a magnetically trapped and evaporatively cooled metastable helium gas. We have thereby] the observation of purely long-range helium dimers produced by photoas- sociation of metastable helium atoms
Large-scale pseudostate calculations for electron scattering from neon atoms
NASA Astrophysics Data System (ADS)
Zatsarinny, Oleg; Bartschat, Klaus
2012-06-01
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)].
RNA and Its Ionic Cloud: Solution Scattering Experiments and Atomically Detailed Simulations
Kirmizialtin, Serdal; Pabit, SuzetteA.; Meisburger, SteveP.; Pollack, Lois; Elber, Ron
2012-01-01
RNA molecules play critical roles in many cellular processes. Traditionally viewed as genetic messengers, RNA molecules were recently discovered to have diverse functions related to gene regulation and expression. RNA also has great potential as a therapeutic and a tool for further investigation of gene regulation. Metal ions are an integral part of RNA structure and should be considered in any experimental or theoretical study of RNA. Here, we report a multidisciplinary approach that combines anomalous small-angle x-ray scattering and molecular-dynamics (MD) simulations with explicit solvent and ions around RNA. From experiment and simulation results, we find excellent agreement in the number and distribution of excess monovalent and divalent ions around a short RNA duplex. Although similar agreement can be obtained from a continuum description of the solvent and mobile ions (by solving the Poisson-Boltzmann equation and accounting for finite ion size), the use of MD is easily extended to flexible RNA systems with thermal fluctuations. Therefore, we also model a short RNA pseudoknot and find good agreement between the MD results and the experimentally derived solution structures. Surprisingly, both deviate from crystal structure predictions. These favorable comparisons of experiment and simulations encourage work on RNA in all-atom dynamic models. PMID:22385853
Stillinger, Frank
effect on the ground state of the helium isoelectronic sequence David R. Herrick and Frank H. Stillinger energy of helium- like ions of arbitrary dimensionality. Dimension- ality here refers to the number) which contains some angular correlations through the interelectron separation R. %bile neither
Elastic scattering of X-rays and gamma rays by 2S electrons in ions and neutral atoms
NASA Astrophysics Data System (ADS)
Costescu, A.; Spnulescu, S.; Stoica, C.
2012-08-01
The nonrelativistic limit of Rayleigh scattering amplitude on 2s electrons of neutral and partially ionized atoms is obtained by making use of the Green Function method. The result takes into consideration the retardation, relativistic kinematics and screening effects. The spurious singularities introduced by the retardation in a nonrelativistic approach are cancelled by the relativistic kinematics. For neutral and partially ionized atoms, a screening model is considered with an effective charge obtained by fitting the Hartree-Fock charge distribution with pure Coulombian wave functions corresponding to a central potential of a nucleus with Zeff as the atomic number. The total cross section of the photoeffect on the 2s electrons is also calculated from the imaginary part of the forward scattering amplitude by means of the optical theorem. The numerical results obtained are in a good agreement (10%) with the ones obtained by Kissell for the Rayleigh amplitude and by Scofield for the Photoeffect total cross section on the 2s electrons, for atoms with atomic number 18 ? Z ? 92 and photon energies ???Zm. (?=1/137,... is the fine structure constant, m is the electron mass).
Non-resonant elastic scattering of low-energy photons by atomic sodium confined in quantum plasmas
NASA Astrophysics Data System (ADS)
Ghosh, Avijit; Ray, Debasis
2015-03-01
The non-resonant elastic scattering of low-energy photons by the bound valence electron in the ground state 3s of atomic sodium confined in quantum plasmas is investigated theoretically. The incident photon energy is assumed to be much smaller than the 3s-3p excitation energy. The alkali atom sodium is first formulated as an effective one-electron problem in which the attractive interaction between the valence electron and the atomic ion core is simulated by a spherically symmetric model potential. The Shukla-Eliasson oscillatory exponential cosine screened-Coulomb potential model is then used to mimic the effective two-body (valence-core) interaction within quantum plasmas. Non-relativistic calculations performed within the electric dipole approximation indicate that the non-resonant elastic photon scattering cross-section undergoes a dramatic growth by several orders of magnitude as the quantum wave number increases. A qualitative explanation of this phenomenon is presented. In the absence of the oscillatory cosine screening term, a similar growth is observed at larger values of the quantum wave number. Our computed relevant atomic data are in very good agreement with the experimental as well as the previous theoretical data for the zero-screening (free atom) case, and with the very limited, accurate theoretical results available for the case of exponential screened-Coulomb two-body interaction, without the cosine screening term.
Lemeshko, Mikhail; Friedrich, Bretislav [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin (Germany)
2010-08-15
We present an analytic model of the refractive index for matter waves propagating through atomic or molecular gases. The model, which combines the Wentzel-Kramers-Brillouin (WKB) treatment of the long-range attraction with the Fraunhofer model treatment of the short-range repulsion, furnishes a refractive index in compelling agreement with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)] on Li atom matter waves passing through dilute noble gases. We show that the diffractive contribution, which arises from scattering by a two-dimensional 'hard core' of the potential, is essential for obtaining a correct imaginary part of the refractive index.
Electron scattering in hot-dense plasmas
NASA Astrophysics Data System (ADS)
Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor
2012-11-01
Hot-dense plasmas have direct industrial applications in inertial confinement fusion. We have used the convergent close-coupling (CCC) method to investigate electron scattering off hydrogen and helium atoms in a hot-dense weakly coupled (Debye) plasma. The Yukawa-type Debye-Hckel potential has been used to describe the plasma screening effects. Integrated excitation, total ionization and total cross sections have been calculated over a broad range of energies and various Debye lengths, D.
J. Y. Kim; J. Y. Park; J. H. Seo; C. N. Whang; S. S. Kim; D. S. Choi; H. J. Kang; K. H. Chae
2003-01-01
The atomic structure and the saturation coverage of Cs on the Si(001)(21) surface at room temperature have been studied by coaxial impact collision ion scattering spectroscopy (CAICISS). For the atomic structure of saturated Cs\\/Si(001)(21) surface, it is found that Cs atoms occupy a single adsorption site at T3 on the Si(001) surface. The height of Cs atoms adsorbed at T3
Elastic scattering of 22.1keV photons by elements in the atomic region 12<=Z<=92
J. S. Shahi; Sanjiv Puri; D. Mehta; M. L. Garg; Nirmal Singh; P. N. Trehan
1997-01-01
Differential cross sections for the elastic scattering of 22.1-keV photons by 30 elements in the atomic region 12<=Z<=92 have been measured at an angle of 117. The measurements were performed under vacuum using Si(Li) detector and 109Cd radioisotope as photon source. The intensity of incident photons, detector efficiency, and other geometrical factors was determined by measuring the K x-ray yields
T. Nishihara; M. Shinohara; O. Ishiyama; F. Ohtani; M. Yoshimoto; T. Maeda; H. Koinuma
1996-01-01
The topmost atom of InP (001) surfaces, which were annealed at temperatures between 300 and 550?C or sputtered with 1 keV\\u000a Ar+ at 300?C in ultra high vacuum, has been directly identified by means of coaxial impact collision ion scattering spectroscopy\\u000a (CAICISS). Time-of-flight spectra of the annealed InP (001) surface exhibited both In and P peaks in both\\u000a $$[\\\\overline {\\\\text{1}}
Li, Xiaoping; Mandal, Anirban; Miliordos, Evangelos; Hunt, Katharine L C
2012-01-28
We report new ab initio results for the interaction-induced dipole moments ?? of hydrogen molecules colliding with helium atoms. These results are needed in order to calculate collision-induced absorption spectra at high temperatures; applications include modeling the radiative profiles of very cool white dwarf stars, with temperatures from 3500 K to 9000 K. We have evaluated the dipoles based on finite-field calculations, with coupled cluster methods in MOLPRO 2006 and aug-cc-pV5Z (spdfg) basis sets for both the H and He centers. We have obtained values of ?? for eight H(2) bond lengths ranging from 0.942 a.u. to 2.801 a.u., for 15 intermolecular separations R ranging from 2.0 a.u. to 10.0 a.u., and for 19 different relative orientations. In general, our values agree well with earlier ab initio results, for the geometrical configurations that are treated in common, but we have determined more points on the collision-induced dipole surface by an order of magnitude. These results make it possible to calculate transition probabilities for molecules in excited vibrational states, overtones, and rotational transitions with ?J > 4. We have cast our results in the symmetry-adapted form needed for absorption line shape calculations, by expressing ?? as a series in the spherical harmonics of the orientation angles of the intermolecular vector and of a unit vector along the H(2) bond axis. The expansion coefficients depend on the H(2) bond length and the intermolecular distance R. For large separations R, we show that the ab initio values of the leading coefficients converge to the predictions from perturbation theory, including both classical multipole polarization and dispersion effects. PMID:22299884
NASA Astrophysics Data System (ADS)
Li, Xiaoping; Mandal, Anirban; Miliordos, Evangelos; Hunt, Katharine L. C.
2012-01-01
We report new ab initio results for the interaction-induced dipole moments ?? of hydrogen molecules colliding with helium atoms. These results are needed in order to calculate collision-induced absorption spectra at high temperatures; applications include modeling the radiative profiles of very cool white dwarf stars, with temperatures from 3500 K to 9000 K. We have evaluated the dipoles based on finite-field calculations, with coupled cluster methods in MOLPRO 2006 and aug-cc-pV5Z (spdfg) basis sets for both the H and He centers. We have obtained values of ?? for eight H2 bond lengths ranging from 0.942 a.u. to 2.801 a.u., for 15 intermolecular separations R ranging from 2.0 a.u. to 10.0 a.u., and for 19 different relative orientations. In general, our values agree well with earlier ab initio results, for the geometrical configurations that are treated in common, but we have determined more points on the collision-induced dipole surface by an order of magnitude. These results make it possible to calculate transition probabilities for molecules in excited vibrational states, overtones, and rotational transitions with ?J > 4. We have cast our results in the symmetry-adapted form needed for absorption line shape calculations, by expressing ?? as a series in the spherical harmonics of the orientation angles of the intermolecular vector and of a unit vector along the H2 bond axis. The expansion coefficients depend on the H2 bond length and the intermolecular distance R. For large separations R, we show that the ab initio values of the leading coefficients converge to the predictions from perturbation theory, including both classical multipole polarization and dispersion effects.
Warehime, Mick; Alexander, Millard H
2014-07-14
We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H2), a heavy-light-light reaction (F+H2), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM. PMID:25028010
NASA Astrophysics Data System (ADS)
Warehime, Mick; Alexander, Millard H.
2014-07-01
We restate the application of the finite element method to collinear triatomic reactive scattering dynamics with a novel treatment of the scattering boundary conditions. The method provides directly the reactive scattering wave function and, subsequently, the probability current density field. Visualizing these quantities provides additional insight into the quantum dynamics of simple chemical reactions beyond simplistic one-dimensional models. Application is made here to a symmetric reaction (H+H2), a heavy-light-light reaction (F+H2), and a heavy-light-heavy reaction (F+HCl). To accompany this article, we have written a MATLAB code which is fast, simple enough to be accessible to a wide audience, as well as generally applicable to any problem that can be mapped onto a collinear atom-diatom reaction. The code and user's manual are available for download from http://www2.chem.umd.edu/groups/alexander/FEM.
Charge Density and Correlation Study of Atoms and Molecules by High-Energy Electron Scattering
Yuheng Zhang
1989-01-01
Energy resolved differential scattering cross sections of high energy electrons and small molecules were measured during the course of this study. The coherent X-ray scattering form factors, which can be derived from the electron scattering experiments, are directly related to the charge density distributions of the target molecules. The difference between the data and the calculations based on the independent
Many-Particle Effects in Resonant Inelastic Scattering of an X-ray Photon by an Atom
Hopersky, A.N.; Nadolinsky, A.M.; Yavna, V.A. [Rostov State University of Transport Communication, Rostov-on-Don, 344038 (Russian Federation)
2005-10-01
The influence of many-particle effects on the shape and values of the double differential cross section for the resonant inelastic scattering of a linearly polarized X-ray photon by a free atom near the K and KL{sub 23} ionization thresholds has been theoretically analyzed for the neon atom. The calculations have been performed using the nonrelativistic Hartree-Fock approximation for single-electron wavefunctions and the dipole approximation for the anomalous dispersion component of the cross section. The analytical structure of the contact part of the scattering cross section has been obtained beyond the dipole approximation. The effects of the radial relaxation of electron shells, spin-orbit and multiplet splitting, and configuration interaction in the doubly excited atomic states, as well as the Auger and radiative decays of the produced vacancies, are taken into account. The nature and role of the effect of correlation amplitudes, which is responsible for the appearance of the nonzero amplitudes of nonradiative transitions between intermediate and final single-electron states of the same symmetry that are obtained in different Hartree-Fock fields, have been analyzed also. The calculations are predictive and, for an incident-photon energy of 5.41 keV, agree well with experimental results for the K{alpha} X-ray emission spectrum of the neon atom.
NASA Astrophysics Data System (ADS)
Prasai, Binay; Ren, Yang; Shan, Shiyao; Zhao, Yinguang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian; Petkov, Valeri
2015-05-01
Correction for `Synthesis-atomic structure-properties relationships in metallic nanoparticles by total scattering experiments and 3D computer simulations: case of Pt-Ru nanoalloy catalysts' by Binay Prasai et al., Nanoscale, 2015, 7, 8122-8134.
Atom-surface interaction in physisorption
Vidali, G.
1982-01-01
The atom-surface interaction in physisorption was studied from both theoretical and experimental standpoints. The experimental work, i.e., atomic beam scattering of helium atoms from the diamond (111) surface, resulted in the first successful measurement of bound state resonances and diffraction patterns. From these data energy levels for the laterally-averaged He-C (diamond) potential and the modulation or corrugation of the potential on the surface were obtained. The reconstruction of the diamond (111) surface was studied using both atom beam scattering and LEED techniques. The temperature at which the reconstruction took place and the periodicity of the new surface agreed with other LEED studies. In the theoretical work values of the coefficient C/sub 3/ of the long range part of the atom-surface interaction were calculated for many systems. There values are of interest in experiments of atom beam scattering from surfaces and adsorption isotherms. A simple formula for C/sub 3/ was also obtained which permits one to obtain C/sub 3/ values using a few physical parameters. A hypothesis of universal behaviour in physical adsorption was formulated and checked with experimental data from atom beam scattering experiments. This law, analogous to corresponding states laws valid in the bulk, predicts that all atom-surface systems have a common potential when suitable reduced units are introduced. Experimental data confirm that there is a common trend, but upon closer examination, consistent differences show up for different substrates (for example, insulators vs. metals).
Zeiri, Yehuda
Photochemistry of adsorbed molecules. XV. Localized atomic scattering in the photolysis of HI/LiF(001) and HI/NaF(001) V. J. Barclay,a) W.-H. Hung,b) W. J. Keogh,c) R. Kuhnemuth, J. C. Polanyi, G have compared the ``elastic'' H atom angular-scattering, Pel , of HI ad photolyzed at 248 nm for Li
Screening Effects on Nonrelativistic Bremsstrahlung in the Scattering of Electrons by Neutral Atoms
NASA Technical Reports Server (NTRS)
Jung, Young-Dae; Lee, Kun-Sang
1995-01-01
Atomic screening effects on nonrelativistic electron-atom bremsstrahlung radiation are investigated using a simple analytic solution of the Thomas-Fermi model for many-electron atoms. The Born approximation is assumed for the initial and final states of the projectile electron. The results show that the screening effect is important in the soft radiation region and is decreasing with increasing radiation. These results help provide correct information about the behavior of bound electrons in the target atom in bremsstrahlung processes.
Danisman, M. Fatih; Oezkan, Berrin [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)
2011-11-15
We describe a quartz crystal microbalance setup that can be operated at low temperatures in ultra high vacuum with gold electrode surfaces acting as substrate surface for helium diffraction measurements. By simultaneous measurement of helium specular reflection intensity from the electrode surface and resonance frequency shift of the crystal during film adsorption, helium diffraction data can be correlated to film thickness. In addition, effects of interfacial viscosity on the helium diffraction pattern could be observed. To this end, first, flat gold films on AT cut quartz crystals were prepared which yield high enough helium specular reflection intensity. Then the crystals were mounted in the helium diffractometer sample holder and driven by means of a frequency modulation driving setup. Different crystal geometries were tested to obtain the best quality factor and preliminary measurements were performed on Kr films on gold surfaces. While the crystal structure and coverage of krypton films as a function of substrate temperature could successfully be determined, no depinning effects could be observed.
Tunable IR Lasers for Helium Optical Pumping
Padetha Tin
1990-01-01
It has been clear for a number of years that the efficiency of the optical pumping process in helium gas could be improved substantially if a tunable, intense source of radiation were available at the resonance wavelength of the helium triplet metastable atom, 1083 nm. Until recently such sources were unavailable. It was the purpose of this research to develop
Helium clusters' capture of heliophobes and strong depletion
NASA Astrophysics Data System (ADS)
Vongehr, Sascha
Mass abundance spectra of by helium clusters (HeN) captured yet heliophobe species lead to intriguing problems. To grow alkali guest clusters (Ak) with HeN hosts would enable ultra low temperature isolation spectroscopy with these for cluster science important metal nano-particles, but helium does not wet alkali atoms. It was thought impossible to grow sodium to sizes larger than the trimer Nak>3. This thesis describes the first observation of clusters Ak up to k=13 on HeN. Their surface location is proven. The clusters are Van der Waals bound; probably unsuccessful growth of metallic Ak is evaluated and alternative routes discussed. Observations have been interpreted with two mutually exclusive models---each involving a configuration HeNAk of considerable interest to cluster science. Calculations are presented that aim to resolve the issue by deriving folded statistics of capture, spin dependent desorption and evaporation of helium due to each capture event. Results are mostly exact or at least analyticity is preserved. A model applicable to most of the usually employed cells for beam scattering and pick-up is presented. They predict steady states of cluster beams that self destruct in the cloud of atoms that a beam thereby continuously replenishes. The model is applied to our setup and used to estimate whether the mechanism responsible can enhance depletion spectroscopic signals via a "Wittig-tube". Size distributions of statistical growth and decay processes are discussed and a symmetry mapping growth to decay is postulated.
Rutherford backscattering oscillation in scanning helium-ion microscopy
Kostinski, Sarah; Yao, Nan [Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544 (United States)
2011-03-15
Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He{sup +}) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He{sup +} beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the ''Z{sub 2}-oscillations'' of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets.
NASA Technical Reports Server (NTRS)
Synowicki, R. A.; Hale, Jeffrey S.; Woollam, John A.
1992-01-01
The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.
M. Aono; Y. Hou; R. Souda; C. Oshima; S. Otani; Y. Ishizawa
1983-01-01
The structure, concentration, and chemical activity of atomic vacancies at the TiC(001) surface have been directly analyzed by specialized low-energy ion-scattering spectroscopy. It has been found that carbon vacancies are formed at the surface under a certain condition, and they capture oxygen atoms into the vacancy holes exhibiting a very high activity.
Theoretical investigation of rotationally inelastic collisions of the methyl radical with helium.
Dagdigian, Paul J; Alexander, Millard H
2011-08-14
Rotationally inelastic collisions of the CH(3) molecule in its ground X(2)A(2)'' electronic state have been investigated. We have determined a potential energy surface (PES) for the interaction of rigid CH(3), frozen at its equilibrium geometry, with a helium atom, using a coupled-cluster method that includes all single and double excitations, as well as perturbative contributions of connected triple excitations [RCCSD(T)]. The anisotropy of the PES is dominated by repulsion of the helium by the hydrogen atoms. The dissociation energy D(e) was computed to equal 27.0 cm(-1). At the global minimum, the helium atom lies in the CH(3) plane between two C-H bonds at an atom-molecule separation R = 6.52 bohr. Cross sections for collision-induced rotational transitions have been determined through quantum scattering calculations for both nuclear spin modifications. Rotationally inelastic collisions can cause a change in the rotational angular momentum n and its body-frame projection k. Because of the anisotropy of the PES due to the hydrogen atoms, there is a strong propensity for ?k = 3 transitions. Thermal rate constants for state-specific total collisional removal have also been determined. PMID:21842932
The helium fine-structure controversy Ingvar Lindgren
Lindgren, Ingvar
The helium fine-structure controversy Ingvar Lindgren Physics Department, University of Gothenburg of the lowest P state of the neutral helium atom. We believe that we have found a minor error in the formulas is not known at present. 1 Introduction The fine structure of the lowest P state of neutral helium is of great
version 1.0 Hyper ne structure of muonic helium
Pachucki, Krzysztof
version 1.0 Hyper#12;ne structure of muonic helium Krzysztof Pachucki #3; Institute of Theoretical state muonic helium is calculated numer- ically using the variational approach. Comparison to former Typeset using REVT E X #3; E-mail address: krp@fuw.edu.pl 1 #12; Muonic helium is an exotic atom
Bederson, B.
1981-02-01
The basic goals of this program concern the experimental determination of properties of atoms and molecules and molecular clusters that are important in a wide range of energy-related processes, in particular, measurements of polarizabilities of highly polar molecules and their polymers, and of a number of important atomic elements distributed through the periodic table, as well as of the scattering of low-energy electrons by these same systems. The most significant scientific accomplishment of the program during the past year has been the completion of measurements of the dc electric dipole polarizabilities of a number of alkali halide dimers ((KCl)/sub 2/, (RbCl)/sub 2/, (CsCl)/sub 2/, (KF)/sub 2/, and (CsF)/sub 2/). An experiment was completed to measure the total cross sections for the scattering of low-energy electrons by atomic lithium, a very significant experimental test of a relatively simple, many-body system, which is amenable to elaborate computational determination.
Friction-Induced Energy-Loss Rainbows in Atom Surface Scattering
Jeremy M. Moix; Eli Pollak; Salvador Miret-Arts
2010-01-01
The rainbow is due to extrema of the angular deflection function of light impinging on water drops. Generically, extrema of suitably defined deflection functions lead to rainbows. These include angular and rotational rainbows in surface scattering and more. Here we introduce the concept of an ``energy-loss deflection function'' for scattering of particles from a periodic surface whose extrema lead to
Coupling between positronium formation and elastic positron-scattering channels in the rare gases
NASA Astrophysics Data System (ADS)
Jay, P. M.; Coleman, P. G.
2010-07-01
Measurements of elastic-scattering cross sections are presented for positron collisions with helium, neon, argon, krypton, and xenon around the threshold energy for positronium (Ps) formation. The elastic cross section falls slowly with increasing energy above the Ps formation threshold in helium and neon, whereas in argon, krypton, and xenon it exhibits an increase, which appears both more prominent and more sustained as the atomic number of the gas increases. It is proposed that this coupling is a result of an intermediate virtual Ps state that enhances branching into the (atom plus positron) final state.
Quasiclassical study of differential inelastic scattering of oriented Ca(4s5p,1P1) atoms on He
NASA Astrophysics Data System (ADS)
Devdariani, A.; Tchesnokov, E.; Dashevskaya, E. I.; Nikitin, E. E.
1998-06-01
A quasiclassical analysis of the differential inelastic scattering of oriented Ca(4s5p,1P1) atoms on He at a collision energy of 1 eV is presented. Inelastic channels correspond to spin-changing events populating different Zeeman sublevels of three fine-structure states of Ca(4s5p,3Pj), j=0, 1, and 2. The magnitude of the right-left scattering asymmetry in the helicopter plane is shown to depend on the locking dynamics. The relative values of different Zeeman-specific cross sections are determined by the diffraction scattering on the attractive 1? state in the entrance channels, by the Coriolis mixing between degenerate components of the repulsive 3?+ intermediate state, and by the radial coupling between 1-1 and 0--0- fine-structure components of the 3?+-3?? states in the exit channels. The predicted large right-left scattering asymmetry suggests that it can be measured experimentally.
Helicity-resolved Raman scattering of MoS?, MoSe?, WS?, and WSe? atomic layers.
Chen, Shao-Yu; Zheng, Changxi; Fuhrer, Michael S; Yan, Jun
2015-04-01
The two-fold valley degeneracy in two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) (Mo,W)(S,Se)2 is suitable for "valleytronics", the storage and manipulation of information utilizing the valley degree of freedom. The conservation of luminescent photon helicity in these 2D crystal monolayers has been widely regarded as a benchmark indicator for charge carrier valley polarization. Here we perform helicity-resolved Raman scattering of the TMDC atomic layers. In drastic contrast to luminescence, the dominant first-order zone-center Raman bands, including the low energy breathing and shear modes as well as the higher energy optical phonons, are found to either maintain or completely switch the helicity of incident photons. In addition to providing a useful tool for characterization of TMDC atomic layers, these experimental observations shed new light on the connection between photon helicity and valley polarization. PMID:25719859
Bederson, B.
1980-03-01
The basic goals of this program concern the experimental determination of properties of atoms and simple molecules that are important in a wide range of energy-related processes. In particular we have initiated measurements of polarizabilities of highly polar molecules and dimers, and of a number of atoms distributed through the periodic table, and, of the scattering of low energy electrons by highly polar molecules. For this latter series of measurements an entirely new apparatus has been designed and its external components have been completed. A new electron optics assembly has also been designed and is currently under construction. Details of all these projects are presented; analysis and data of the polarizability measurements are also given.
Scattering of He atoms from surface defects by grazing-angle diffraction beams D. Farias,2
Manson, Joseph R.
that play a large role in the way in which a surface interacts with its environment. He atom scat- tering rather large cross sections observed for He scat- tering from similar atomic species in the gas phase.1 He scat- tering from intrinsic defects such as vacancies, adatoms or steps is also large.2
ATOMIC AND MOLECULAR PHYSICS: Scattering properties of the ultracold 133Cs2 triplet state
NASA Astrophysics Data System (ADS)
Sun, Jin-Feng; Du, Bing-Ge; Zhang, Ji-Cai; Li, Wei; Zhu, Zun-Lue
2009-03-01
The elastic scattering properties of ultracold 133Cs2 triplet state are investigated in detail. We construct a potential curve of the 133Cs2 triplet state, based on the latest ab initio molecular potential data and show how the scattering parameters are obtained by using three methods: the Numerov method, the semiclassical method and the variable phase method, where the scattering lengths of the 133Cs2 triplet state, i.e. 301.79a0, 300.67a0 and 310.81a0 are obtained respectively, with a0 being the Bohr radius. We also calculate the effective range and the number of bound states for the 133Cs2 triplet state. Our results are in agreement with the recent experimental data and the theoretical calculations. This confirms that the results of the scattering properties of the ultracold 133Cs2 triplet state, calculated by using these three methods, are reliable.
NASA Astrophysics Data System (ADS)
Ma, J.; Delaire, O.; Specht, E. D.; May, A. F.; Gourdon, O.; Budai, J. D.; McGuire, M. A.; Hong, T.; Abernathy, D. L.; Ehlers, G.; Karapetrova, E.
2014-10-01
The phonon dispersions and scattering rates of the thermoelectric material Ag1-xSb1+xTe2+x(x=0,0.1,0.2) were measured with inelastic neutron scattering, as function of both temperature T and off stoichiometry x. In addition, detailed measurements of diffuse scattering were performed with both neutron and synchrotron x-ray diffraction. The results show that phonon scattering rates are large and weakly dependent on T or x, and the lattice thermal conductivity calculated from these scattering rates and group velocities is in good agreement with bulk transport measurements. We also find that the scattering rates and their temperature dependence cannot be accounted for with common models of phonon scattering by anharmonicity or point defects. The diffuse scattering measurements show a pervasive, complex signal, with several distinct components. In particular, broad superstructure reflections indicate a short-range ordering of the Ag and Sb cations on their sublattice. Single-crystal Bragg peak intensities also reveal large static atomic displacements, compatible with results from Rietveld refinement of neutron powder diffraction data. Our results indicate that a complex nanostructure, arising from multiple variants of nanoscale anisotropic superstructures of cations, and large atomic displacements, is likely responsible for the strong phonon scattering.
Nguyen, Hung T. [BioMaPS Institute for Quantitative Biology, Rutgers University, Piscataway, New Jersey 08854 (United States); Pabit, Suzette A.; Meisburger, Steve P.; Pollack, Lois [School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853 (United States); Case, David A., E-mail: case@biomaps.rutgers.edu [BioMaPS Institute for Quantitative Biology, Rutgers University, Piscataway, New Jersey 08854 (United States); Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854 (United States)
2014-12-14
A new method is introduced to compute X-ray solution scattering profiles from atomic models of macromolecules. The three-dimensional version of the Reference Interaction Site Model (RISM) from liquid-state statistical mechanics is employed to compute the solvent distribution around the solute, including both water and ions. X-ray scattering profiles are computed from this distribution together with the solute geometry. We describe an efficient procedure for performing this calculation employing a Lebedev grid for the angular averaging. The intensity profiles (which involve no adjustable parameters) match experiment and molecular dynamics simulations up to wide angle for two proteins (lysozyme and myoglobin) in water, as well as the small-angle profiles for a dozen biomolecules taken from the BioIsis.net database. The RISM model is especially well-suited for studies of nucleic acids in salt solution. Use of fiber-diffraction models for the structure of duplex DNA in solution yields close agreement with the observed scattering profiles in both the small and wide angle scattering (SAXS and WAXS) regimes. In addition, computed profiles of anomalous SAXS signals (for Rb{sup +} and Sr{sup 2+}) emphasize the ionic contribution to scattering and are in reasonable agreement with experiment. In cases where an absolute calibration of the experimental data at q = 0 is available, one can extract a count of the excess number of waters and ions; computed values depend on the closure that is assumed in the solution of the OrnsteinZernike equations, with results from the KovalenkoHirata closure being closest to experiment for the cases studied here.
Low-energy electron elastic scattering from Mn, Cu, Zn, Ni, Ag, and Cd atoms
Felfli, Z.; Msezane, A. Z. [Department of Physics and Center for Theoretical Studies of Physical Systems, Clark Atlanta University, Atlanta, Georgia 30314 (United States); Sokolovski, D. [School of Mathematics and Physics, Queen's University of Belfast, Belfast, BT7 1NN (United Kingdom); Department of Chemical Physics, University of the Basque Country, Leioa (Spain)
2011-05-15
Electron elastic total cross sections (TCSs) for ground and excited Mn, Cu, Zn, Ni, Ag, and Cd atoms have been investigated in the electron-impact energy range 0 {<=}E{<=} 1 eV. The near-threshold TCSs for both the ground and excited states of these atoms are found to be characterized by Ramsauer-Townsend minima, shape resonances, and extremely sharp resonances corresponding to the formation of stable bound negative ions. The recently developed Regge-pole methodology where the crucial electron-electron correlations are embedded is employed for the calculations. From close scrutiny of the imaginary parts of the complex angular momenta, we conclude that these atoms form stable weakly bound ground and excited negative ions as Regge resonances through slow electron collisions. The extracted electron binding energies from the elastic TCSs of these atoms are contrasted with the available experimental and theoretical values.
Dapor, M. [Ist. Trentino di Cultura, Trento (Italy)] [Ist. Trentino di Cultura, Trento (Italy); [Ist. Nazionale per la Fisica della Materia, Trento (Italy); Miotello, A. [Ist. Nazionale per la Fisica della Materia, Trento (Italy)] [Ist. Nazionale per la Fisica della Materia, Trento (Italy); [Univ. di Trento (Italy). Dipt. di Fisica
1998-05-01
The authors present tables of the differential, total, and transport cross sections for the elastic scattering of 500--4000 eV positrons by neutral atoms in the atomic number range Z = 1--92. The cross sections were computed by numerically solving the Dirac equation for a central electrostatic field up to a large radius where the atomic potential becomes negligible. The atomic potential used was Hartree-Fock for Z = 1--18 and Dirac-Hartree-Fock-Slater for Z = 19--92.
NASA Astrophysics Data System (ADS)
Smr?ok, L'ubomr; Kolesnikov, Alexander I.; Rieder, Milan
2012-10-01
Inelastic neutron scattering (INS) was used to study the vibrational dynamics of the hydrogen atoms in natural trioctahedral phlogopite, K0.93Na0.03(Mg2.47Fe0.22Al0.16Fe0.04Tl0.06)[Si2.84Al1.16]O10OH1.71F0.28Cl0.01, within the 50-1,000 cm-1 energy range. The INS spectra collected using direct geometry spectrometer SEQUOIA (ORNL) were interpreted by means of the solid-state DFT calculations covering both normal mode analysis and molecular dynamics. To optimize the structure and to calculate the vibrational modes under harmonic approximation, both a hybrid PBE0 and the AM05 functional were used, while the molecular dynamics calculations (60 ps/1 fs) were performed only with the computationally less-demanding AM05 functional. The main contributions to the dominant band within ~750-550 cm-1 are symmetric and antisymmetric Mg-O-H bending modes, overlapping with the skeletal stretching and bending modes causing weaker secondary movements of H atoms of inner hydroxyl groups. Signatures of the Mg-O-H bending modes appear down to ~400 cm-1, where a region of octahedra deformation modes starts. These deformations cause just shallow movements of the hydrogen atoms and are mirrored by the modes with close vibrational energies. The region from ~330 cm-1 down to the low-energy end of the spectrum portrays induced vibrations of the H atoms caused by deformation of individual polyhedra, translational vibrations of the parts of the 2:1 layer relative one to another, and librational and translational vibrations of the layer. The main difference between the INS spectrum of dioctahedral Al-muscovite and trioctahedral Mg-phlogopite is that the Mg-O-H modes are all assigned to in-plane vibrations of the respective hydrogen atoms.
Charged clusters in liquid helium
NASA Astrophysics Data System (ADS)
Dyugaev, A. M.; Grigor'ev, P. D.; Lebedeva, E. V.
2010-03-01
The appropriateness of the experimental study of charged clusters in liquid helium has been supported. The interaction potential of negative ions (electron bubbles) with inert clusters formed by Ne, Ar, Kr, and Xe atoms or H2 and N2 molecules has been found. Small clusters levitate at a distance of 13-16 above the negative ion. The scalings laws for the properties of charged inert clusters have been discovered and grounded; the number of quantum levels and states of such clusters has been determined. The mobility measurement of charged clusters may provide a new technique of probing the properties of impurity nanoparticles in helium.
Ko, Chung-Ting; Yang, Po-Shuan; Han, Yin-Yi; Wang, Wei-Cheng; Huang, Jhih-Jie; Lee, Yen-Hui; Tsai, Yi-Jen; Shieh, Jay; Chen, Miin-Jang
2015-07-01
Plasmonic silver nanostructures and a precise ZnO cover layer prepared by capacitively coupled plasma atomic layer deposition (ALD) were exploited to enhance the Raman scattering from nanoscale ultrathin films on a Si substrate. The plasmonic activity was supported by a nanostructured Ag (nano-Ag) layer, and a ZnO cover layer was introduced upon the nano-Ag layer to spectrally tailor the localized surface plasmon resonance to coincide with the laser excitation wavelength. Because of the optimized dielectric environment provided by the precise growth of ZnO cover layer using ALD, the intensity of Raman scattering from nanoscale ultrathin films was significantly enhanced by an additional order of magnitude, leading to the observation of the monoclinic and tetragonal phases in the nanoscale ZrO2 high-K gate dielectric as thin as ?6 nm on Si substrate. The excellent agreement between the finite-difference time-domain simulation and experimental measurement further confirms the so-called [Formula: see text] dependence of the surface-enhanced Raman scattering. This technique of plasmonic enhancement of Raman spectroscopy, assisted by the nano-Ag layer and optimized dielectric environment prepared by ALD, can be applied to characterize the structures of ultrathin films in a variety of nanoscale materials and devices, even on a Si substrate with overwhelming Raman background. PMID:26057412
NASA Astrophysics Data System (ADS)
Ko, Chung-Ting; Yang, Po-Shuan; Han, Yin-Yi; Wang, Wei-Cheng; Huang, Jhih-Jie; Lee, Yen-Hui; Tsai, Yi-Jen; Shieh, Jay; Chen, Miin-Jang
2015-07-01
Plasmonic silver nanostructures and a precise ZnO cover layer prepared by capacitively coupled plasma atomic layer deposition (ALD) were exploited to enhance the Raman scattering from nanoscale ultrathin films on a Si substrate. The plasmonic activity was supported by a nanostructured Ag (nano-Ag) layer, and a ZnO cover layer was introduced upon the nano-Ag layer to spectrally tailor the localized surface plasmon resonance to coincide with the laser excitation wavelength. Because of the optimized dielectric environment provided by the precise growth of ZnO cover layer using ALD, the intensity of Raman scattering from nanoscale ultrathin films was significantly enhanced by an additional order of magnitude, leading to the observation of the monoclinic and tetragonal phases in the nanoscale ZrO2 high-K gate dielectric as thin as ?6 nm on Si substrate. The excellent agreement between the finite-difference time-domain simulation and experimental measurement further confirms the so-called {{?ft| {\\overset{\\scriptscriptstyle\\rightharpoonup}{E}} \\right|}4} dependence of the surface-enhanced Raman scattering. This technique of plasmonic enhancement of Raman spectroscopy, assisted by the nano-Ag layer and optimized dielectric environment prepared by ALD, can be applied to characterize the structures of ultrathin films in a variety of nanoscale materials and devices, even on a Si substrate with overwhelming Raman background.
Positron scattering by atomic hydrogen using optical potentials and with positronium formation
NASA Technical Reports Server (NTRS)
Walters, H. R. J.
1990-01-01
The scattering is considered of positrons by H(ls) in a two-state model which incorporates optical potentials. The model explicitly describes elastic scattering, i.e., positron + H(ls) yields positron + H(ls) and Ps(ls) yields Ps(ls) + p. The inelastic processes positron + H(ls) yields positron + H* Ps(ls) + p yields Ps* + p where * stands for a state other than ls, are implicitly taken into account through the optical potentials, which also allow for polarization of H(ls) and Ps(ls).
Helium superfluidity. Shapes and vorticities of superfluid helium nanodroplets.
Gomez, Luis F; Ferguson, Ken R; Cryan, James P; Bacellar, Camila; Tanyag, Rico Mayro P; Jones, Curtis; Schorb, Sebastian; Anielski, Denis; Belkacem, Ali; Bernando, Charles; Boll, Rebecca; Bozek, John; Carron, Sebastian; Chen, Gang; Delmas, Tjark; Englert, Lars; Epp, Sascha W; Erk, Benjamin; Foucar, Lutz; Hartmann, Robert; Hexemer, Alexander; Huth, Martin; Kwok, Justin; Leone, Stephen R; Ma, Jonathan H S; Maia, Filipe R N C; Malmerberg, Erik; Marchesini, Stefano; Neumark, Daniel M; Poon, Billy; Prell, James; Rolles, Daniel; Rudek, Benedikt; Rudenko, Artem; Seifrid, Martin; Siefermann, Katrin R; Sturm, Felix P; Swiggers, Michele; Ullrich, Joachim; Weise, Fabian; Zwart, Petrus; Bostedt, Christoph; Gessner, Oliver; Vilesov, Andrey F
2014-08-22
Helium nanodroplets are considered ideal model systems to explore quantum hydrodynamics in self-contained, isolated superfluids. However, exploring the dynamic properties of individual droplets is experimentally challenging. In this work, we used single-shot femtosecond x-ray coherent diffractive imaging to investigate the rotation of single, isolated superfluid helium-4 droplets containing ~10(8) to 10(11) atoms. The formation of quantum vortex lattices inside the droplets is confirmed by observing characteristic Bragg patterns from xenon clusters trapped in the vortex cores. The vortex densities are up to five orders of magnitude larger than those observed in bulk liquid helium. The droplets exhibit large centrifugal deformations but retain axially symmetric shapes at angular velocities well beyond the stability range of viscous classical droplets. PMID:25146284
Konjhodzic, A.; Adamczyk, A.; Hasan, Z.; Alp, E. E.; Sturhahn, W.; Zhao, J.; Carroll, J. J.; Vagizov, F.; Univ. of Philadelphia; Youngstown State Univ.
2006-01-01
With the decrease in size of devices, rapid characterization of nano-devices is an inevitable necessity. It is shown that Moessbauer spectroscopy using synchrotron radiation from the advanced photon source provides such a tool of investigation. Results are presented and compared for conventional Moessbauer and Nuclear Forward Scattering for {sup 151}Eu-doped magnesium sulfide as an example, especially at low concentrations.
Version 1.0 # 4 Ry corrections to singlet states of helium
Pachucki, Krzysztof
Version 1.0 # 4 Ry corrections to singlet states of helium Krzysztof Pachucki # Institute Corrections of order # 4 Ry are calculated for the singlet states 1 1 S 0 and 2 1 S 0 of the helium atom frequencies between low lying levels of the helium atom. In particular theoretical predictions for the 2 1 S 0
Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium
California at Santa Cruz, University of
Physics 139B Fall 2009 The Variational Computation of the Ground State Energy of Helium I. Introduction to the variational computation The Hamiltonian for the twoelectron system of the helium atom is principle to compute the ground state energy of the helium atom. The ground state wave function
Xu Junliang; Chen Zhangjin; Lin, C. D. [Department of Physics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506 (United States); Zhou Hsiaoling [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States)
2009-05-15
We demonstrate the successful implementation of genetic algorithm for the retrieval of atomic potentials using elastic differential cross sections (DCSs) between free electrons and atomic ions for electron energies from a few to several tens of electron volts. Since the DCSs over this energy region can be extracted from laser-generated high-energy photoelectron momentum spectra, the results suggest that infrared lasers can be used to image the target structure. Extending to molecular targets, in particular, to transient molecules created by an earlier pump pulse, our results suggest that few-cycle infrared probe lasers can be used for dynamic chemical imaging with temporal resolution of a few femtoseconds.
Scattering polarization of hydrogen lines from electric-induced atomic alignment
R. Casini; R. Manso Sainz
2008-03-11
We consider a gas of hydrogen atoms illuminated by a broadband, unpolarized radiation with zero anisotropy. In the absence of external fields, the atomic J-levels are thus isotropically populated. While this condition persists in the presence of a magnetic field, we show instead that electric fields can induce the alignment of those levels. We also show that this electric alignment cannot occur in a two-term model of hydrogen (e.g., if only the Ly-alpha transition is excited), or if the level populations are distributed according to Boltzmann's law.
K. Hagita; R. L. McGreevy; T. Arai; M. Inui; K. Matsuda; K. Tamura
2010-01-01
We propose a new method for multi-scale reverse Monte Carlo (RMC) modeling of small-angle scattering data using reverse mapping from coarse-grained particles to atoms in cases where scale separation cannot be assumed. For efficient RMC analysis for small-angle scattering data, it is important to determine a large scale structure with the lowest possible computing cost. In order to find this
S. Dhar
2008-01-01
The energy spectrum of scattered particles in the K-shell ionization of medium to heavy atoms by relativistic electrons and positrons with exchange effects has been calculated for various kinematic conditions. In this calculation, the final state is described by a non-relativistic multiple-scattering wavefunction of Das and Seal (1993a Phys. Rev. A 47 2978; 1998 J. Phys. B: At. Mol. Opt.
Schafer, D.A.; Newman, J.H.; Smith, K.A.; Stebbings, R.F. (Rice Univ., Houston, TX (United States))
1987-06-01
This paper reports measurements of absolute scattering cross sections, differential in angle, for collisions of ground state oxygen atoms with He, N{sub 2}, and O{sub 2}. Data are presented for scattering of 0.5-, 1.5-, and 5.0-keV oxygen atome projectiles in the range of laboratory frame angles between 0.06{degree} and 5{degree}. These measurements provide information relevant to calculations of the aeronomic consequences of O{sup +} precipitation in the earth's upper atmosphere.
Electron-impact excitation of the 6p7s {sup 3}P{sub 1} state of Pb atom at small scattering angles
Milisavljevic, S.; Rabasovic, M. S.; Sevic, D.; Marinkovic, B. P. [Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Pejcev, V. [Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Faculty of Natural Sciences, Radoja Domanovica 12, 34000 Kragujevac (Serbia); Filipovic, D. M. [Institute of Physics, Pregrevica 118, 11080 Belgrade (Serbia); Faculty of Physics, University of Belgrade, P. O. Box 368, 11001 Belgrade (Serbia); Sharma, Lalita; Srivastava, Rajesh [Department of Physics, Indian Institute of Technology, Roorkee 247667 (India); Stauffer, A. D. [Department of Physics and Astronomy, York University, Toronto, Canada M3J 1P3 (Canada)
2007-05-15
Electron-impact excitation of the 6p7s {sup 3}P{sub 1} state of Pb atom has been investigated both experimentally and theoretically. Differential cross sections (DCSs) were measured at incident electron energies of E{sub 0}=10, 20, 40, 60, 80, and 100 eV and small scattering angles up to 10 degree sign using a crossed electron-atom beam technique. The forward scattering function method has been used for determination of the absolute generalized oscillator strengths and DCS values. Corresponding relativistic distorted wave calculations have been performed and compared with experimental results.
E. Asari; R. Souda
1999-01-01
The atomic arrangements of TiO2(110)-p(12) and p(13) surfaces were investigated using impact collision ion-scattering spectroscopy combined with computer simulation. We found that the p(12) surface has the added Ti2O3 unit rows proposed by Onishi and Iwasawa [Surf Sci. Lett. 313, L783 (1994)], but a modification is necessary, i.e., the oxygen adatoms are located along the rows of fivefold titanium atoms
Takao Ishii; Masashi Mukaida; Takaharu Nishihara; Shigeki Hayashi; Makoto Shinohara
1998-01-01
Terminating surface atoms of LiGaO2(001) substrate for GaN thin film growth have been directly identified by coaxial impact collision ion scattering spectroscopy (CAICISS). We found that the terminating atoms of the easily etched surface of the substrate are oxygen and that those of the hardly etched surface are metal (Li and Ga). The relation is explained by the surface bonding
Mitsuchika Saitoh; Fumiya Shoji; Kenjiro Oura; Teruo Hanawa
1980-01-01
Si(111)-\\\\sqrt{3}\\\\sqrt{3}-Ag surface structure has been studied by low-energy ion-scattering spectroscopy using neon ions with an energy of 500 eV, combined with LEED-AES. It has been proposed that Ag atoms giving rise to the \\\\sqrt{3} structure are slightly embedded below the outermost Si layer, including consequent displacements of the substrate Si atoms.
2014-01-01
Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium. PMID:25068008
NSDL National Science Digital Library
Greer, Douglas
2009-08-15
Our group studies the growth of organic semiconductor thin films, to better understand the connection between thin film morphology, crystal structure, and electronic device properties. Conventionally, thin films of organic semiconductors are deposited using thermal evaporation. However, the use of supersonic molecular beams to deposit thin films allows the incident kinetic energy of the organic semiconductor to be tuned in the range of 4-16 eV. The organic semiconductor thin films are characterized using in situ real time synchrotron x-ray scattering, and ex situ atomic force microscopy (AFM). My research experience this summer primarily consisted of analyzing x-ray data and studying the morphology of the thin films deposited on various dielectrics (self-assembled monolayers, SAMs) of varying chain length using AFM.
Marchetti, S; Sbrana, F; Toscano, A; Fratini, E; Carl, M; Vassalli, M; Tiribilli, B; Pacini, A; Gambi, C M C
2011-05-01
The three-dimensional structure and the mechanical properties of a ?-connectin fragment from human cardiac muscle, belonging to the I band, from I(27) to I(34), were investigated by small-angle x-ray scattering (SAXS) and single-molecule force spectroscopy (SMFS). This molecule presents an entropic elasticity behavior, associated to globular domain unfolding, that has been widely studied in the last 10 years. In addition, atomic force microscopy based SMFS experiments suggest that this molecule has an additional elastic regime, for low forces, probably associated to tertiary structure remodeling. From a structural point of view, this behavior is a mark of the fact that the eight domains in the I(27)-I(34) fragment are not independent and they organize in solution, assuming a well-defined three-dimensional structure. This hypothesis has been confirmed by SAXS scattering, both on a diluted and a concentrated sample. Two different models were used to fit the SAXS curves: one assuming a globular shape and one corresponding to an elongated conformation, both coupled with a Coulomb repulsion potential to take into account the protein-protein interaction. Due to the predominance of the structure factor, the effective shape of the protein in solution could not be clearly disclosed. By performing SMFS by atomic force microscopy, mechanical unfolding properties were investigated. Typical sawtooth profiles were obtained and the rupture force of each unfolding domain was estimated. By fitting a wormlike chain model to each peak of the sawtooth profile, the entropic elasticity of octamer was described. PMID:21728583
Photon stimulated desorption of and nuclear resonant scattering by noble gas atoms at solid surfaces
Ikeda, Akihiko
2015-01-01
When a noble gas atom approaches a solid surface, it is adsorbed via the Van der Waals force, which is called physisorption. In this thesis, several experimental results concerning physisorbed atoms at surfaces are presented. First, photon stimulated desorption of Xe atoms from a Au substrate using nano-second laser is presented. With the time-of-flight measurements, the translational temperature and the desorption yield of desorbing Xe as a function of laser fluence are obtained. It is discovered that there are non-thermal and thermal desorption pathways. It is discussed that the former path involves a transient formation of the negative ion of Xe. The desorption flux dependence of the thermal pathway is also investigated. We found that at a large desorption fluxes the desorption flow is thermalized due to the post-desorption collisions. The resultant velocity and the temperature of the flow is found to be in good agreement with the theoretical predictions based on the Knudsen layer formation. Lastly, nuclea...
NASA Astrophysics Data System (ADS)
Seelig, F. F.; Becker, G. A.
1999-12-01
Some low n1S and n3S states of the helium atom are computed with the aid of the e-e method which formulates the electronic wave function of the 2 electrons ? = e-e F, where ?=Z(r1+r2)-r12 and here Z = 2. Both the differential and the integral equation for F contain a pseudopotential ? instead of the true potential V that contrary to V is finite. For the ground state, F = 1 yields nearly the Hartree-Fock SCF accuracy, whereas a multinomial expansion in r1, r2 , r2 yields a relative error of about 10-7 . All integrals can be computed analytically and are derived from one single "parent" integral.
Sensitivity of ultracold-atom scattering experiments to variation of the fine-structure constant
Borschevsky, A.; Beloy, K. [Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand); School of Physics, University of New South Wales, Sydney 2052 (Australia); Flambaum, V. V. [School of Physics, University of New South Wales, Sydney 2052 (Australia); Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand); Schwerdtfeger, P. [Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand)
2011-05-15
We present numerical calculations for cesium and mercury to estimate the sensitivity of the scattering length to the variation of the fine-structure constant {alpha}. The method used follows the ideas of Chin and Flambaum [Phys. Rev. Lett. 96, 230801 (2006)], where the sensitivity to the variation of the electron-to-proton mass ratio {beta} was considered. We demonstrate that for heavy systems, the sensitivity to the variation of {alpha} is of the same order of magnitude as to the variation of {beta}. Near narrow Feshbach resonances, the enhancement of the sensitivity may exceed nine orders of magnitude.
Decoherence in the Diffraction of Helium at Surfaces
NASA Astrophysics Data System (ADS)
Aigner, F.; Simonovi?, N.; Solleder, B.; Burgdorfer, J.
2008-07-01
Scattering of fast neutral atoms with keV kinetic energies at alkali-halide surfaces under grazing angles displays intriguing diffraction patterns (Schuller, Wethekam and Winter 2007, Roisseau et al. 2007). In spite of the impulsive interaction with a surface at elevated temperature, which results in phonon excitation, quantum coherence evidently persists. To quantitatively study this remarkable survival of coherence, we present an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the <110> direction and compare with recent experimental diffraction data. Decoherence is analyzed employing a quantum trajectory Monte Carlo method (Minami, Reinhold and Burgdorfer 2003), calculating the ensemble average over solutions of a stochastic linear Schrodinger equation. The evolution of the atomic wavepacket is governed by a sequence of stochastic collisions and continuous propagation in the He-LiF surface potential. We find near-perfect agreement between the resulting diffraction patterns and experimental results (Schuller, Wethekam and Winter 2007) without using any adjustable parameters. The question, whether the LiF surface features ``buckling'', ! (i.e. vertical surface reconstruction where the F atoms are displaced relative to the Li atoms) has been addressed in the past (de Wette, Kress and Schroder 1985). However, experimental uncertainties were of the same order as the displacement amplitude itself. In atom-surface diffraction at a grazing angle, surface reconstruction drastically changes the diffraction patterns. By comparison of numerical and experimental results, the buckling amplitude can be determined with unprecedented accuracy.
Zagrebin, A.L.; Pavlovskaya, N.A.
1989-05-01
We have analyzed the temperature dependences of the spectral distributions of photons emitted in the processes of radiative quenching of {sup 3}{ital P}{sub 2} metastable states during thermal collisions of AR*, Kr*, and Xe* atoms with He and Ne atoms.
Confined helium on Lagrange meshes
Daniel Baye; Jrmy Dohet-Eraly
2015-06-01
The Lagrange-mesh method has the simplicity of a calculation on a mesh and can have the accuracy of a variational method. It is applied to the study of a confined helium atom. Two types of confinement are considered. Soft confinements by potentials are studied in perimetric coordinates. Hard confinement in impenetrable spherical cavities is studied in a system of rescaled perimetric coordinates varying in [0,1] intervals. Energies and mean values of the distances between electrons and between an electron and the helium nucleus are calculated. A high accuracy of 11 to 15 significant figures is obtained with small computing times. Pressures acting on the confined atom are also computed. For sphere radii smaller than 1, their relative accuracies are better than $10^{-10}$. For larger radii up to 10, they progressively decrease to $10^{-3}$, still improving the best literature results.
Confined helium on Lagrange meshes
Baye, Daniel
2015-01-01
The Lagrange-mesh method has the simplicity of a calculation on a mesh and can have the accuracy of a variational method. It is applied to the study of a confined helium atom. Two types of confinement are considered. Soft confinements by potentials are studied in perimetric coordinates. Hard confinement in impenetrable spherical cavities is studied in a system of rescaled perimetric coordinates varying in [0,1] intervals. Energies and mean values of the distances between electrons and between an electron and the helium nucleus are calculated. A high accuracy of 11 to 15 significant figures is obtained with small computing times. Pressures acting on the confined atom are also computed. For sphere radii smaller than 1, their relative accuracies are better than $10^{-10}$. For larger radii up to 10, they progressively decrease to $10^{-3}$, still improving the best literature results.
Prasai, Binay; Ren, Yang; Shan, Shiyao; Zhao, Yinguang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian; Petkov, Valeri
2015-06-14
Correction for 'Synthesis-atomic structure-properties relationships in metallic nanoparticles by total scattering experiments and 3D computer simulations: case of Pt-Ru nanoalloy catalysts' by Binay Prasai et al., Nanoscale, 2015, 7, 8122-8134. PMID:25982103
NASA Astrophysics Data System (ADS)
Jennings, Carol Ann
1995-01-01
Fourier transform surface-enhanced Raman scattering (FT-SERS) in the near-infrared and atomic force microscopy (AFM) have been used to characterize thin solid organic films. The pigments studied were phthalocyanines and perylenes which have applications as charge generation materials in organic photoreceptors. Techniques for film preparation such as Langmuir-Blodgett (LB) deposition and vacuum evaporation are discussed. The literature was reviewed for FT-Raman spectroscopy, surface-enhanced Raman spectroscopy and atomic force microscopy. A model according to Gersten and Nitzan was applied and SERS enhancement factors in the near-IR were calculated for various metal hemi-spheroids. FT-Raman spectra were presented for thin vacuum evaporated films of titanyl phthalocyanine (TiOPc) and vanadyl phthalocyanine (VOPc) prepared on glass substrates held at a range of temperatures during deposition. The frequencies were assigned and different polymorphic forms were apparent. In order to improve the signal intensity, thin films were deposited on metal substrates which produced SERS in the near-IR. The substrates selected for FT-SERS were vacuum evaporated metal island films of copper and gold of 20 nm mass thickness prepared with the glass substrate held at 200^ circC. Thin films of 3 nm mass thickness of VOPc and 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) were vacuum evaporated onto the metal island substrates and produced FT-SERS with an enhancement factor of approximately 100. Single Langmuir-Blodgett monolayers of phthalocyanines and perylenes on the metal island substrates gave FT-SERS. The FT-SERS spectra of vacuum evaporated films and LB monolayers were compared with visible laser excitation. Phthalocyanines and perylenes absorb in the visible region and produced surface-enhanced resonance Raman scattering (SERRS). The morphology and structure of single LB monolayers on mica and Si(111) wafers have been determined using atomic force microscopy. AFM results for a perylene on Si(111) showed good agreement with the orientation inferred from reflection -absorption infrared spectroscopy and transmission IR measurements.
NASA Astrophysics Data System (ADS)
Santini, Paolo; Baker, Michael; Guidi, Tatiana; Carretta, Stefano; Ollivier, Jacques; Mutka, Hannu; Guedel, Hans; Timco, Grigore; McInnes, Eric; Amoretti, Giuseppe; Winpenny, Richard
2013-03-01
Molecular nanomagnets (MNMs) have been test-beds for addressing several elusive but important phenomena in quantum dynamics, but to this point it has been impossible to determine the spin dynamics directly. We show that recently-developed inelastic-neutron-scattering instrumentation, yielding the cross-section in vast portions of reciprocal space, enables two-spin dynamical correlation functions of MNMs to be directly determined without assuming an underlying model Hamiltonian. We use the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this approach which allows us, for example, to examine how a quantum fluctuation propagates along the ring or to test the degree of validity of the Neel-vector-tunneling framework. This result opens remarkable perspectives in the understanding of the quantum dynamics in several classes of MNMs.
Shepperson, Benjamin; Liu, Jin; Ellis, Andrew M; Yang, Shengfu
2011-06-30
Electron impact ionization of helium nanodroplets containing a dopant, M, can lead to the detection of both M(+) and helium-solvated cations of the type M(+)He(n) in the gas phase. The observation of helium-doped ions, He(n)M(+), has the potential to provide information on the aftermath of the charge transfer process that leads to ion production from the helium droplet. Here we report on helium attachment to the ions from four common diatomic dopants, M = N(2), O(2), CO, and NO. For experiments carried out with droplets with an average size of 7500 helium atoms, the monomer cations show little tendency to attach and retain helium atoms on their journey out of the droplet. By way of contrast, the corresponding cluster cations, M(n)(+), where n ? 2, all show a clear affinity for helium and form He(m)M(n)(+) cluster ions. The stark difference between the monomer and cluster ions is attributed to more effective cooling of the latter in the aftermath of the ionization event. PMID:21585216
[Atomic beam studies of the interaction of hydrogen with transition metal surfaces
Not Available
1992-01-01
We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).
2D polarons in high magnetic fields on the surface of liquid helium films
NASA Astrophysics Data System (ADS)
Tress, O.; Scheuzger, P.; Mistura, G.; Penning, F. C.; Bluyssen, H.; Wyder, P.
1996-01-01
We report on measurements proving the polaronic effect in a 2D electron system prepared on helium films covering a quartz-glass substrate. In bulk systems the measured magnetoconductivity follows the extended self-consistent Born approximation (SCBA) theory up to 20 T. On films we achieved conditions at which the calculated binding energies where larger than k B T and the magnetoconductivity data could be interpreted by adding the collision frequency of the electron plus its associated dimple to the collision frequency caused by gas atom scattering.
Rotational state-changing cold collisions of hydroxyl ions with helium
Hauser, Daniel; Carelli, Fabio; Spieler, Steffen; Lakhmanskaya, Olga; Endres, Eric S; Kumar, Sunil S; Gianturco, Franco; Wester, Roland
2015-01-01
Cold molecules are important for many applications, from fundamental precision measurements, quantum information processing, quantum-controlled chemistry, to understanding the cold interstellar medium. Molecular ions are known to be cooled efficiently in sympathetic collisions with cold atoms or ions. However, little knowledge is available on the elementary cooling steps, because the determination of quantum state-to-state collision rates at low temperature is prohibitively challenging for both experiment and theory. Here we present a method to manipulate molecular quantum states by non-resonant photodetachment. Based on this we provide absolute quantum scattering rate coefficients under full quantum state control for the rotationally inelastic collision of hydroxyl anions with helium. Experiment and quantum scattering theory show excellent agreement without adjustable parameters. Very similar rate coefficients are obtained for two different isotopes, which is linked to several quantum scattering resonances a...
Theory of inelastic ion-atom scattering at low and intermediate energies
NASA Technical Reports Server (NTRS)
Schmid, G. B.; Garcia, J. D.
1977-01-01
Ab initio calculations are presented of inelastic energy loss and ionization phenomena associated with Ar(+)-Ar collisions at small distances of closest approach and for laboratory collision energies ranging from several keV to several hundred keV. Outer-shell excitations are handled statistically; inner-shell excitations are calculated from the viewpoint of quasidiabatic molecular orbital promotion. Auger electron yield, average state of ionization, and average inelastic energy loss are calculated per collision as a function of distance of closest approach of the collision partners for several laboratory collision energies. Average charge-state probabilities per collision partner are calculated as a function of the average inelastic energy loss per atom. It is shown that the structure in the data is due to the underlying structure in the inner-shell independent-electron quasimolecular promotion probabilities.
Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms.
Loreau, Jrme; Zhang, Peng; Dalgarno, Alexander
2011-11-01
A quantal study of the rotational excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN(2) complex, with the N(2) molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N(2). The total, differential, and momentum transfer cross sections for rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm(-1) and 1500 cm(-1). The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na-N(2) collisions occur in the mesosphere. PMID:22070297
Second-order Born calculation of laser-assisted single ionization of helium by electrons
NASA Astrophysics Data System (ADS)
Makhoute, Abdelkader; Ajana, Imane; Khalil, Driss; Chaddou, Souhaila
2015-06-01
The Born approximation has been extended to second-order Born amplitude in order to describe the laser-assisted single ionization of helium atom by impact of electrons. In this study, we have used a Sturmian basis expansion to perform detailed calculations of the scattering amplitudes. We discuss the influence of varying the incident energy on the angular distribution of the ejected electron. From analysis of the results, we find that second-order calculation is significantly different from the first-order calculation at low incoming energies. It means that the process of the laser-assisted single ionization of helium by slow incident electron requires a double interaction of this electron with the target.
Phase-matched emission of few high-harmonic orders from a helium gas cell
NASA Astrophysics Data System (ADS)
Teichmann, Sven; Hannaford, Peter; Van Dao, Lap
2009-04-01
We report on femtosecond-laser-based generation of a few phase-matched high-order harmonics in a helium semi-infinite gas cell. The harmonic beam consists of effectively four to six intense orders with wavelengths around 9.5 nm. By varying the effective interaction length, we observe the effects of coherence length related to plasma formation and the Gouy phase shift on the output. The atomic scattering factors for photoabsorption, the effective propagation lengths (leff,He?1 mm, leff,Ar?7.2 mm), and the energy conversion efficiencies (?He?10-7, ?Ar?510-7) are deduced for harmonic generation in helium (77th to 95th orders) and also argon (21st to 27th orders) for comparison.
Expansion coefficients of scattering parameters in quantum thermodynamic perturbation theory
Buendia, E.; Guardiola, R. (Departamento de Fisica Moderna, Universidad de Granada Granada, Spain, 18071 (ES)); De Llano, M. (Physics Department, North Dakota State University, Fargo, North Dakota 58105)
1989-07-01
We tabulate the expansion coefficients of various scattering parameters associated with several interparticle pair potentials used in the quantum thermodynamic perturbation theory of strongly coupled, many-particle substances. The expansion is in powers or the attractive part of the pair potential. The potential is divided into repulsive and attractive parts according to several methods in vogue both in classical and in quantum equation-of-state studies of condensed-matter systems. Results are reported for several interparticle potentials of helium-3 and -4 atoms, of the three electron spin-polarized isotopes of atomic hydrogen, and of the nucleon.
version 2.0 Improved result for helium 2 3
Pachucki, Krzysztof
version 2.0 Improved result for helium 2 3 S 1 ionization energy Krzysztof Pachucki #3; Institute of relativistic and quantum electrodynamic e#11;ects to order m#11; 6 on the energy of the 2 3 S 1 state in helium Typeset using REVT E X #3; E-mail address: krp@fuw.edu.pl 1 #12; The helium atom is one of the simplest
Formation of hydrogen atom in 2s state in protonsodium inelastic scattering
NASA Astrophysics Data System (ADS)
Sabbah, A. Elkilany
2015-03-01
The inelastic collision of protons with sodium atoms are treated for the first time within the framework of the coupled-static and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels (elastic and hydrogen formation in 2s state) are open. In each case, the calculations are carried out for seven values of the total angular momentum ?(0 ? ? ? 6). The target is described using the Clementi Roetti wave functions within the framework of the one valence electron model. We use LipmannSwinger equation to solve the derived equations of the problem, then apply an iterative numerical method to obtain the code of computer to calculate iterative partial cross-sections. This can be done through calculating the reactance matrix at different values of considered energies to obtain the transition matrix that gives partial and total cross sections. The present results for total hydrogen (2s state) formation cross sections are in agreement with results of other available ones in wide range of incident energy.
Aidan Kelleher
2010-10-01
Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. Of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q{sup 2} and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized {sup 3}He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. G{sup n}{sub E} was measured to be 0.0242 0.0020(stat) 0.0061(sys) and 0.0247 0.0029(stat) 0.0031(sys) at Q{sup 2} = 1.7 and 2.5 GeV{sup 2}, respectively.
B. J. Garrison; W. A. Jr. Lester
1976-01-01
A quantum mechanical scattering study is carried out to test a collisional pumping model for cooling the 6 and 2 cm doublets of interstellar formaldehyde. The Arthurs and Dalgarno formalism is extended to the collision of an s-state atom with a rigid asymmetric top molecule and applied to rotational excitation of ortho formaldehyde by helium impact. Using a previously determined
Lin, Chii-Dong
of atomic negative ions in intense laser fields XiaoXin Zhou,1,2 Zhangjin Chen,1 Toru Morishita,1,3 Anh-dimensional electron momentum distributions of atomic negative ions in an intense laser field by solving the time of atomic negative ions in the laser field. This opens up the possibility of measuring electron
Paris-Sud XI, Universit de
hal-00120114,version2-23Feb2007 Lifetime of weakly-bound dimers of ultracold metastable helium. INTRODUCTION Helium atoms 4 He in the metastable 23 S1 state are long lived (2 hours lifetime) and can- sociation, our group studied exotic molecules in which two spin-polarized metastable helium atoms are bound
Equation of state of metallic helium
Shvets, V. T., E-mail: tarval@breezein.net [Odessa State Academy of Refrigeration (Ukraine)
2013-01-15
The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters-temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.
Marchetti, S; Sbrana, F; Raccis, R; Lanzi, L; Gambi, C M C; Vassalli, M; Tiribilli, B; Pacini, A; Toscano, A
2008-02-01
In order to investigate the protein folding-unfolding process, dynamic light scattering (DLS) and atomic force microscopy (AFM) imaging were used to study two fragments of the muscle cardiac protein beta-connectin, also known as titin. Both fragments belong to the I band of the sarcomer, and they are composed of four domains from I(27) to I(30) (tetramer) and eight domains from I(27) to I(34) (octamer). DLS measurements provide the size of both fragments as a function of temperature from 20 up to 86 degrees C, and show a thermal denaturation due to temperature increase. AFM imaging of both fragments in the native state reveals a homogeneous and uniform distribution of comparable structures. The DLS and AFM techniques turn out to be complementary for size measurements of the fragments and fragment aggregates. An unexpected result is that the octamer folds into a smaller structure than the tetramer and the unfolded octamer is also smaller than the unfolded tetramer. This feature seems related to the significance of the hydrophobic interactions between domains of the fragment. The longer the fragment, the more easily the hydrophobic parts of the domains interact with each other. The fragment aggregation behavior, in particular conditions, is also revealed by both DLS and AFM as a process that is parallel to the folding-unfolding transition. PMID:18352054
NASA Technical Reports Server (NTRS)
Vidali, G.; Li, W.; Dowben, P. A.; Karimi, M.; Hutchings, C. W.; Lin, J.; Moses, C.; Ila, D.; Dalins, I.
1990-01-01
We used ABS, LEED and angle-resolved photo-electron spectroscopy (ARPES) to study bilayer films of Hg on Cu(001). In the surface temperature range of 180 to 330 K, the first Hg layer forms two ordered phases, a c(2x2) (with coverage-0.5 of Cu(001)) and a high density (partially commensurate) c(4x4) (coverage-0.62). ARPES data show that there is little or no dispersion of the 5d band of Hg. ABS data show that this layer is not flat, with in-registry Hg atoms lying about 0.15 below the not-in-registry Hg atoms. From ABS we find that the second layer forms a completely registered c(4x4) phase. From ARPES we obtain that the second layer has an electronic structure, particularly the 5d levels, characteristic of bulk mercury. Preliminary results of calculations of the structure of the bilayer are given.
Efficient magneto-optical trapping of a metastable helium gas
Dos Santos, F P; Lonard, J; Sinatra, A; Wang, J; Pavone, F S; Rasel, E; Unnikrishnan, C S; Leduc, M; Wang, Junmin
2001-01-01
This article presents a new experiment aiming at BEC of metastable helium atoms. It describes the design of a high flux discharge source of atoms and a robust laser system using a DBR diode coupled with a high power Yb doped fiber amplifier for manipulating the beam of metastable atoms. The atoms are trapped in a small quartz cell in an extreme high vacuum. The trapping design uses an additional laser (repumper) and allows the capture of a large number of metastable helium atoms (approximately $10^9$) in a geometry favorable for loading a tight magnetostatic trap.
Helium on Venus - Implications for uranium and thorium
NASA Technical Reports Server (NTRS)
Prather, M. J.; Mcelroy, M. B.
1983-01-01
Helium is removed at an average rate of 10 to the 6th atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on earth, suggesting comparable abundances of crustal uranium and thorium.
Optical Forces on Metastable Helium
NASA Astrophysics Data System (ADS)
Corder, Christopher Scott
Optical forces using lasers allow precise control over the motion of atoms. The bichromatic optical force (BF) is unique in its large magnitude and velocity range, arising from the absorption and stimulated emission processes. These properties were used to transversely collimate a beam of metastable helium (He*) using the 23S - 23P transition. The collimation created a very bright beam of He*, allowing experiments of neutral atom lithography. The He* beam was used to pattern material surfaces using a resist-based lithography technique, where the pattern was determined by either mechanical or optical masks. The optical masks produced features with a separation of half the wavelength of the light used. Patterning was successfully demonstrated with both IR and UV optical masks. The etched pattern resolution was 100 nm and limited by the material surface. Further experiments were performed studying the ability of the bichromatic force to cool. The finite velocity range of the BF allows estimation of a characteristic cooling time which is independent of the excited state lifetime, only depending on the atomic mass and optical transition energy. Past experiments, including the helium collimation used for neutral atom lithography, have demonstrated that the BF can collimate and longitudinally slow atomic beams, but required long interaction times that included many spontaneous emission (SE) events. The effect of SE can be mitigated, and is predicted to not be necessary for BF cooling. Since the BF cooling time is not related to the excited state lifetime, a transition can be chosen such that the cooling time is shorter than the SE cycle time, allowing direct laser cooling on atoms and molecules that do not have cycling transitions. Experiments using the helium 2 3S-3P transition were chosen because the BF cooling time (285 ns) is on the order of the average SE cycle time (260 ns). Numerical simulations of the experimental system were run predicting compression of the atomic velocity distribution. Our experimental results demonstrate the stimulated nature of the force through many atomic recoils from the light in less than one SE cycle time. A large range of the atomic velocity distribution is accelerated and accumulates at the velocity limit of the force. This accumulation results in an increase in the velocity space density, demonstrating cooling.
NASA Technical Reports Server (NTRS)
Cook, Joseph
1996-01-01
Proposed system recovers and stores helium gas for reuse. Maintains helium at 99.99-percent purity, preventing water vapor from atmosphere or lubricating oil from pumps from contaminating gas. System takes in gas at nearly constant low back pressure near atmospheric pressure; introduces little or no back pressure into source of helium. Concept also extended to recycling of other gases.