Fundamental Excitations of Glass Observed by Helium Atom Scattering
Manson, Joseph R.
Fundamental Excitations of Glass Observed by Helium Atom Scattering W Steurer1, A Apfolter1, M Koch. In this paper we demonstrate a new application of helium atom scattering: The investigation of amorphous solids. Introduction Helium atom scattering (HAS) is a strictly surface sensitive technique with no penetration
Atomic Form Factor and Incoherent-Scattering Function of the Helium Atom
Yong-Ki Kim; Mitio Inokuti
1968-01-01
The atomic form factor and the incoherent-scattering function of the helium atom have been calculated from several wave functions of differing accuracies. The form factor calculated from the Hartree-Fock wave function is in very close agreement with that from the 20-term Hylleraas wave function for all values of the momentum transfer. For small momentum transfers (<3 atomic units), the incoherent-scattering
Helium atom scattering investigation of the Sb(111) surface.
Mayrhofer-Reinhartshuber, M; Tamtögl, A; Kraus, P; Ernst, W E
2013-10-01
The Sb(111) surface was studied with helium atom scattering (HAS). Elastic HAS at different energies of the incident helium beam (15.3, 21.9, 28.4 meV) was applied for structural investigations. The lattice constants derived from the positions of the observed diffraction peaks up to third order were found to be in perfect agreement with previous structure determinations of Sb(111). The observed diffraction patterns with clear peaks up to second order were used to model the electronic surface corrugation with the GR method. As an estimation for the attractive part of the interaction potential a well depth of (4.0 ± 0.5) meV was found. Best fit results were obtained with a corrugation height of 12-13% of the lattice constant, which is rather large compared to other surfaces with metallic character. Intensity measurements of the specular peak as a function of incident energy were analysed to determine the distribution of terraces on the surface. The results show a quite flat Sb(111) surface and a step height of 3.81 ? of the remaining terraces. PMID:23969322
Scattering of helium atoms from rare-gas-plated graphite
Carey Schwartz
1986-01-01
Accurate close-coupling calculations are performed for helium interacting with rare-gas-plated graphite. The atom-surface potentials used in this study are based upon pairwise additivity of atom-atom interactions, and the role of three-body forces is explored. Comparison between theoretical calculations which in turn include and exclude three-body forces indicates that experimental data are sensitive to three-body forces. Further comparison between theoretical calculations
Laser-assisted inelastic scattering of electrons by helium atoms
NASA Astrophysics Data System (ADS)
Agueny, H.; Makhoute, A.; Dubois, A.; Ajana, I.; Rahali, G.
2015-07-01
The differential cross section for electron-impact excitation of helium atoms in the presence of a linearly polarized laser field is calculated. The interaction of the laser field with both the projectile electron and the target atom is treated in a fully nonperturbative way, while the electron-atom interaction is treated within the first Born approximation. We are interested in studying two cases where the photon energy of the laser field is chosen to be far from resonance and when it matches with 2 1S ?2 1P and 3 1S ?3 1P transition frequencies. The agreement between perturbative and nonperturbative results is good, except close to the resonance where the perturbative cross sections diverge while the nonperturbative ones predict no maximum of the cross sections. Another interesting effect is the presence of an avoided crossing of the Floquet pseudoenergies at resonance.
Scattering of X-ray emission lines by a helium atom
L. Vainshtein; R. Sunyaev; E. Churazov
1998-01-21
The differential cross section for scattering of the astrophysically important X-ray emission lines by a helium atom is calculated with an accuracy sufficient for astrophysical applications. For a helium atom an energy ``gap'' (due to the structure of the energy levels) is twice larger than for a hydrogen atom and the ``compton profile'' (due to broader distribution of an electron momentum) is significantly shallower. This opens principle possibility to distinguish helium and hydrogen contributions, observing scattered spectra of X-ray emission lines. With the appearance of a new generation of X-ray telescopes, combining a large effective area and an excellent energy resolution it may be possible to measure helium abundance in the molecular clouds in the Galactic Center region, in the vicinity of AGNs or on the surface of cold flaring stars.
Scattering of H(1s) off metastable helium atom at thermal energies
Sinha, Prabal K.; Ghosh, A. S. [Department of Physics, Bangabasi College, 19, Raj Kumar Chakravorty Sarani, Kolkata 700 009 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India)
2006-06-15
Quantal calculations for scattering of ground-state antihydrogen by metastable (n=2S) helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium [He(2 {sup 1}S)] target is higher than the corresponding value when the target is in the metastable triplet state [He(2 {sup 3}S)].
Spectroscopy of the phonons on noble metal surfaces using helium atomic beam scattering
NASA Astrophysics Data System (ADS)
Harten, U.
1986-02-01
Helium atomic beam scattering was used for the spectroscopy of eigenvibrations of noble metal surfaces. The experimental setup and basic observations concerning inelastic atomic beam scattering are explained. The most important result is the observation of 2 separated acoustic modes on the (111) surfaces of copper, silver, and gold. The first mode was theoretically predicted, while the second could only be reproduced in model calculations if the interatomic forces at a crystal surface were changed with respect to those in the volume. The excitation probabilities for the surface phonons are essentially determined by the interaction potential between the atoms and surface.
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
A helium atom scattering study of the structure and phonon dynamics of the ice surface
A. Glebov; A. P. Graham; A. Menzel; J. P. Toennies; P. Senet
2000-01-01
The structure and phonons of an ordered ice surface, prepared in situ under ultra high vacuum conditions, have been studied by high resolution helium atom scattering. The angular distributions are dominated by sharp hexagonal (1×1) diffraction peaks characteristic of a full bilayer terminated ice Ih crystal. Additional, very broad and weak, p(2.1×2.1) peaks may indicate the presence of small domains
Manson, Joseph R.
modes with helium atom scattering: KrÕPt,,111... Mubing Li,1 J. R. Manson,1 and A. P. Graham2, * 1; revised manuscript received 25 September 2001; published 19 April 2002 Energy resolved helium atom obtained for incident helium atom energies much greater than the fundamental S-mode energy, are modeled
NASA Astrophysics Data System (ADS)
Hansen, F. Y.; Bruch, L. W.; Dammann, B.
2013-03-01
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 × 1) commensurate monolayer solid of H2/NaCl(001) and a conjectured p(1 × 1) commensurate monolayer solid of H2/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.
Positronium formation in the n = 2 level in positron scattering from hydrogen and helium atoms
Khan, P.; Mazumdar, P.S.; Ghosh, A.S.
1985-03-01
A distorted-wave model (Phys. Rev. A 27, 1904 (1983); 28, 2180 (1983)) is applied to calculate the formation of positronium in the n = 2 states in e/sup +/ scattering from hydrogen and helium atoms. The incident wave is represented by a polarized-orbital method. The first-Born-approximation results of the 2p-excited-state capture cross section in the case of helium is reported for the first time. The first Born approximation is found to be unsuitable for prediction of the rearrangement processes. The present total (ground- and excited-state) positronium-formation cross sections have been compared with the corresponding observed values of Fornari et al. (Phys. Rev. Lett. 51, 2276 (1983)) and of Charlton et al. (J. Phys. B 16, L465 (1983)).
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.
Hansen, F. Y.; Bruch, L. W.; Dammann, B.
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.
Kais, Sabre
helium atoms M. El-Batanouny, G. Murthy, and C. R. Willis Department of Physics, Boston University atoms (He*) from surfaces of magnetic insulators to study the dynamical properties of surface electron a metastable He atom and the surface electron spins are determined by a configuration interaction calculation
Surface Structure of Lithium Doped Potassium Tantalate (KLT) using Helium Atom Scattering.
Fatema, Rifat [Florida State University; Van Winkle, David [Florida State University; Skofronick, J. G. [Florida State University; Sanfron, Sanford a [Department of Chemistry and Biochemistry, Florida State University; Flaherty, F. A. [Valdosta State University, Valdosta, GA; Boatner, Lynn A [ORNL
2013-01-01
The structures of the (001) surface of potassium tantalate doped with nominally 2, 4 and 7% lithium have been investigated using high resolution helium atom scattering. The surfaces were prepared by cleaving single crystal samples in situ under UHV conditions. Diraction measurements in the region around the He specular re ection angle soon after cleaving yielded specular peaks initially with broad shoulders. However, over a period of about an hour, the widths of these specular peaks decreased markedly as the shoulders diminished into the background. Drift spectra measurements of the stabilized surfaces revealed that the step heights separating surface terraces were predominantly multiples of the cubic unit cell dimension, about 4A, rather than multiples of a half unit cell, 2A, expected from the cleaving of these crystals. Together these results suggest that after cleaving these surfaces are rapidly modied by migration of ions to the surface from the near-surface. Further, half-order diraction peaks were observed in the <100> azimuth a short time after cleaving samples at room temperature, indicating that domains with (21) structure had formed.
NASA Astrophysics Data System (ADS)
Benedek, G.; Ellis, J.; Reichmuth, A.; Ruggerone, P.; Schief, H.; Toennies, J. P.
1992-11-01
Inelastic helium-atom scattering from epitaxial films (2-20 monolayers) of sodium on Cu(001) reveals a large number of nearly dispersionless phonon modes whose frequencies depend on the thickness and scale as the lower harmonics of an open-ended organ pipe. These data provide evidence for confined acoustic resonances, corresponding to longitudinal standing waves normal to the surface with frequencies about 20% larger than in the bulk.
Andrew P. Graham; J. Peter Toennies
1999-01-01
The lateral potential energy surface for adsorbed atoms and molecules is important for a detailed understanding of diffusion, sliding friction, catalysis, and molecular beam epitaxy. In this brief review, it is shown that the analysis of quasi-elastic helium scattering data, in addition to the complementary inelastic results for parallel translational vibrations, leads to a detailed description of the potential energy
On the Theory of the Inelastic Scattering of Electrons by Helium Atoms
W F Miller; R L Platzman
1957-01-01
The familiar relationship between the optical properties of an atom and its cross sections for inelastic electron collisions can provide a valuable criterion for the validity of such cross sections. A method of exploiting this relationship is explained and then illustrated by application to two transitions of helium (transitions to the 2 1P state, and to the ionization limit), thereby
T. S. Stein; W. E. Kauppila; V. Pol; J. H. Smart; G. Jesion
1978-01-01
Total scattering cross sections have been measured for 0.3--31 eV positrons colliding with helium atoms and for 0.25--24 eV positrons colliding with neon atoms using a beam-transmission technique. These measurements have resulted in the first direct observations of Ramsauer-Townsend effects for positrons colliding wih helium and neon, and also provide clear indications of the onset of positronium formation in each
Inelastic scattering of helium atoms from the phonons of the reconstructed Au(111) surface
NASA Astrophysics Data System (ADS)
Santoro, G.; Franchini, A.; Bortolani, V.; Harten, U.; Toennies, J. P.; Wöll, Ch.
1987-04-01
We present inelastic atom-surface phonon scattering time-of-flight spectra for the reconstructed Au(111) surface. The shapes of the spectra are compared with calculated reflection coefficients based on a simplified lattice dynamical model for the reconstructed surface. The force constants were determined from a best fit of the surface phonon dispersion curves and the lateral atom-atom interactions in the surface layer were found to be 30% of the bulk value. The theoretical spectra reproduce the overall lineshape of the experimental spectra and reveal additional features which can be attributed to the reconstruction of the surface layer with respect to the substrate.
Positron scattering from helium
NASA Astrophysics Data System (ADS)
Boadle, Roisin; Machacek, Joshua; Anderson, Emma; Caradonna, Peter; Makochekanwa, Casten; Jones, Adric; Sullivan, James; Buckman, Stephen
2012-10-01
We present new measurements of positron scattering cross sections for helium, including total scattering, total elastic and total inelastic cross sections, which have been extended up to energies of 180eV. We also present a range of low energy elastic differential cross sections. The measurements were performed using our high-resolution, Surko trap-based positron beamline with a typical energy resolution of ˜50meV. Comparisons will be made with previous experimental results and with up to date theoretical predictions.
Surface Structure of Niobium-Doped Potassium Tantalate KTa1-XNbXO3 by Helium Atom Scattering
Trelenberg, T. W. [Florida State University; Fatema, Rifat [Florida State University; Jaime, Li [Florida State University; Akhadov, E. A. [Florida State University; Van Winkle, David [Florida State University; Skofronick, J. G. [Florida State University; Safron, Sanford A. [Florida State University; Flaherty, F. A. [Valdosta State University, Valdosta, GA; Boatner, Lynn A [ORNL
2010-01-01
Helium atom scattering experiments have been carried out on the (001) surface of KTaO3 doped with 6, 10 and 15% Nb, produced by cleaving in situ single crystal samples. Several phenomena were observed through He atom diraction measurements, including metastable behavior immediately after cleaving, reconstruction of a fraction of the surface to (21) domains after thermally cycling the surface temperatures, and the distribution of step-heights of terraces at the surface as multiples of the unit cell dimension of 4 A. In addition, a large hysteresis eect was found in the in the <100> azimuth in the variation of surface re ectivity with surface temperature; a much smaller hysteresis eect was found in the <110> azimuth. The hysteresis eects appear for all Nb doping concentrations. Finally, small oscillations in the specular and Bragg diraction intensities near surface temperature 80K were also observed.
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.
K?dziera, Dariusz; ?uchowski, Piotr S; Knoop, Steven
2015-01-01
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.
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)
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.
2015-01-01
Elastic and inelastic close-coupling (CC) calculations have been used to extract information about the corrugation amplitude and the surface vibrational atomic displacement by fitting to several experimental diffraction patterns. To model the three-dimensional interaction between the He atom and the Bi(111) surface under investigation, a corrugated Morse potential has been assumed. Two different types of calculations are used to obtain theoretical diffraction intensities at three surface temperatures along the two symmetry directions. Type one consists of solving the elastic CC (eCC) and attenuating the corresponding diffraction intensities by a global Debye–Waller (DW) factor. The second one, within a unitary theory, is derived from merely solving the inelastic CC (iCC) equations, where no DW factor is necessary to include. While both methods arrive at similar predictions for the peak-to-peak corrugation value, the variance of the value obtained by the iCC method is much better. Furthermore, the more extensive calculation is better suited to model the temperature induced signal asymmetries and renders the inclusion for a second Debye temperature for the diffraction peaks futile.
NASA Astrophysics Data System (ADS)
Brown, Ryan D.; Hund, Zachary M.; Campi, Davide; O'Leary, Leslie E.; Lewis, Nathan S.; Bernasconi, M.; Benedek, G.; Sibener, S. J.
2013-04-01
The interplay of the librations of a covalently bound organic adlayer with the lattice waves of an underlying semiconductor surface was characterized using helium atom scattering in conjunction with analysis by density functional perturbation theory. The Rayleigh wave dispersion relation of CH3- and CD3-terminated Si(111) surfaces was probed across the entire surface Brillouin zone by the use of inelastic helium atom time-of-flight experiments. The experimentally determined Rayleigh wave dispersion relations were in agreement with those predicted by density functional perturbation theory. The Rayleigh wave for the CH3- and CD3-terminated Si(111) surfaces exhibited a nonsinusoidal line shape, which can be attributed to the hybridization of overlayer librations with the vibrations of the underlying substrate. This combined synthetic, experimental, and theoretical effort clearly demonstrates the impact of hybridization between librations of the overlayer and the substrate lattice waves in determining the overall vibrational band structure of this complex interface.
Brown, Ryan D; Hund, Zachary M; Campi, Davide; O'Leary, Leslie E; Lewis, Nathan S; Bernasconi, M; Benedek, G; Sibener, S J
2013-04-12
The interplay of the librations of a covalently bound organic adlayer with the lattice waves of an underlying semiconductor surface was characterized using helium atom scattering in conjunction with analysis by density functional perturbation theory. The Rayleigh wave dispersion relation of CH3- and CD3-terminated Si(111) surfaces was probed across the entire surface Brillouin zone by the use of inelastic helium atom time-of-flight experiments. The experimentally determined Rayleigh wave dispersion relations were in agreement with those predicted by density functional perturbation theory. The Rayleigh wave for the CH3- and CD3-terminated Si(111) surfaces exhibited a nonsinusoidal line shape, which can be attributed to the hybridization of overlayer librations with the vibrations of the underlying substrate. This combined synthetic, experimental, and theoretical effort clearly demonstrates the impact of hybridization between librations of the overlayer and the substrate lattice waves in determining the overall vibrational band structure of this complex interface. PMID:25167286
B. J. Hinch; C. Koziol; J. P. Toennies; G. Zhang
1989-01-01
The specular intensity of nearly mono-energetic helium atom beams (Ei=(7 20) meV) has been measured during epitaxial deposition of Pb films on Pb(111) and Cu(111) surfaces. For Pb on Pb(111) regular monotonically damped oscillations are observed indicating monolayer by monolayer growth. For Pb on Cu(111) a more complicated modulated structure was found indicating an alternation between single- and double-layer growth
NASA Technical Reports Server (NTRS)
Liu, S. M.; Knuth, E. L.
1976-01-01
Energy transfer in collisions of satellite-speed (7,000 m/sec) helium atoms with a cleaned 6061-T6 satellite-type aluminum surface was investigated using the molecular-beam technique. The amount of energy transferred was determined from the measured energy of the molecular-beam and the measured spatial and energy distributions of the reflected atoms. Spatial distributions of helium atoms scattered from a 6061-T6 aluminum surface were measured. The scattering pattern exhibits a prominent backscattering, probably due to the gross surface roughness and/or the relative lattice softness of the aluminum surface. Energy distributions of reflected helium atoms from the same surface were measured for six different incidence angles. For each incidence angle, distributions were measured at approximately sixty scattering positions. At a given scattering position, the energy spectra of the reflected helium atoms and the background gas were obtained using the retarding-field energy analyzer.
NASA Astrophysics Data System (ADS)
Yarevsky, E.; Yakovlev, S. L.; Larson, Å; 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 Schrödinger 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 Temkin–Poet model.
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.
Fatema, Rifat [Florida State University; Trelenberg, T. W. [Florida State University; Van Winkle, David [Florida State University; Skofronick, J. G. [Florida State University; Safron, Sanford A. [Florida State University; Flaherty, F. A. [Valdosta State University, Valdosta, GA; Boatner, Lynn A [ORNL
2011-01-01
Helium atom diraction experiments have been carried out on the (001) surface of KTaO3 doped with 30% Nb. The surfaces were produced by cleaving single crystals of the material in situ. After the samples were thermally cycled, the angular distributions measured in the <100> azimuth, but not those in the <110> azimuth, revealed half-order diraction peaks. These indicate the formation of small (21) surface domains. The scans of the specular and Bragg diraction peak intensities as the sample temperatures were varied from about 325K to 60-80K and back to 325K showed large hysteresis particularly in the <100> azimuth. In addition, these scans showed a distinct intensity dip at about 85K, which is far removed from any bulk phase transition temperature of this material. Most curious, the specular re ectivity of the surface was found to be a strong function of the He wavevector, decreasing rapidly as the wavevector was varied above or below an optimum value.
Atomic spectra in a helium bubble
Takashi Nakatsukasa; Kazuhiro Yabana; George F Bertsch
2002-02-01
Density functional theory (DFT) is applied to atomic spectra under perturbations of superfluid liquid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and D2 absorption lines are quite well reproduced by theory, suggesting that the DFT may be useful for describing spectral perturbations in more complex environments.
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.
Capture of slow antiprotons by helium atoms
Shevchenko, N.V. [Joint Institute for Nuclear Research, Dubna, 141980 (Russian Federation); Nuclear Physics Institute, 25068 Rez (Czech Republic); Revai, J. [Research Institute for Particle and Nuclear Physics, H-1525 Budapest, P.O.B. 49 (Hungary)
2005-10-26
A consistent quantum mechanical calculation of partial cross sections leading to different final states of antiprotonic helium atom was performed. Calculations were carried out for a wide range of antiprotonic helium states and incident energies of the antiproton below the first ionization threshold of the He atom.
Positronium formation in positron-helium scattering
Khan, P.; Ghosh, A.S.
1983-10-01
The positronium-formation cross sections in positron-helium scattering have been calculated with the use of a distorted-wave polarized-orbital method from the threshold to 100 eV. The results with and without the matrix elements involving the distorted target wave functions are found to differ appreciably. The results of the first Born approximation are not expected to be correct even at the incident-positron energy 100 eV. The measured values at 20 eV are found to be less than (1/2) of the present predicted values. The sharp rise of the formation cross section within the ore-gap region as observed by Charlton et al. has also been noticed by us. The minimum in the differential cross section has been found at all energies as in the case of hydrogen atom.
NASA Technical Reports Server (NTRS)
Liu, S. M.; Rodgers, W. E.; Knuth, E. L.
1975-01-01
Interactions of satellite-speed helium atoms with practical satellite surfaces were investigated experimentally, and spatial distributions of satellite-speed helium beams scattered from four different engineering surfaces were measured. The 7000 m/sec helium beams were produced using an arc-heated supersonic molecular beam source. The test surfaces included cleaned 6061-T6 aluminum plate, anodized aluminum foil, white paint, and quartz surfaces. Both in-plane (in the plane containing the incident beam and the surface normal) and out-of-plane spatial distributions of reflected helium atoms were measured for six different incidence angles (0, 15, 30, 45, 60, and 75 deg from the surface normal). It was found that a large fraction of the incident helium atoms were scattered back in the vicinity of the incoming beam, particularly in the case of glancing incidence angles. This unexpected scattering feature results perhaps from the gross roughness of these test surfaces. This prominent backscattering could yield drag coefficients which are higher than for surfaces with either forward-lobed or diffusive (cosine) scattering patterns.
Andrew P. Graham; Frank Hofmann; J. Peter Toennies; Gwyn P. Williams; Carol J. Hirschmugl; John Ellis
1998-01-01
Inelastic helium scattering (HAS) and infrared reflection adsorption spectroscopy (IRAS) have been used to measure the isotope shifts of the frequencies of both the parallel and perpendicular frustrated translation modes, as well as the frustrated rotation mode of CO molecules at on top sites on Cu(001). The measured isotope shifts for four different isotopomers indicates a significant rotational contribution to
NASA Astrophysics Data System (ADS)
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, KT a1 - xN bxO3 (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 Ta O2/Nb O2 terraces. The data, however, suggest that K+ and O2 - 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 Ta O2/Nb O2(+1 ) layers and avoids a "polar catastrophe." This behavior is contrasted with the (001 ) surface behavior of the fluoride perovskite KMn F3 with its electrically neutral KF and Mn F2 layers.
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.more »The data, however, suggest that K? and O²? 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
Atomic Cascade of Muonic and Pionic Helium Atoms
R. Landua; E. Klempt
1982-01-01
The cascade of muonic and pionic helium atoms in targets of arbitrary density is investigated. The calculation does not use any free parameters except for strong-interaction effects. All measured x-ray intensities are reproduced, in particular the KbetaKalpha intensity ratios in pionic helium.
A. Dalgarno; N. Lynn
1957-01-01
The available theoretical values of the oscillator strengths of dipole transitions from the ground state of helium are modified so that they satisfy four different sum rules. They are then employed to evaluate the refractive index, the Verdet constant, the diamagnetic susceptibility, the Lamb shift, the average energy loss for fast particle impact and the van der Waals interaction between
Spectral properties of endohedrally confined helium atom
NASA Astrophysics Data System (ADS)
Fang, Shuai-Shuai; Hao-Xue, Qiao
2015-08-01
Based on the B-spline basis method, the properties of the helium atom confined inside an endohedral environment, such as buckminster fullerene, are studied. In our calculations, the endohedral environment is a parabolic potential well. In this situation, the phenomenon of “mirror collapse” is exhibited for energy levels of a confined helium atom. The “giant resonance” of oscillator strength of the dipole transition emerges with the variation of depth of the confining well. The physical mechanisms of these phenomena are analyzed in this paper. Project supported by the National Natural Science Foundation of China (Grant No. 11274246.)
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.
Ground State of the Helium Atom
Toichiro Kinoshita
1957-01-01
The energy level of the ground state of atomic helium is restudied in detail. The nonrelativistic part is treated by the conventional Ritz variation technique. However, the trial functions used are more general than the ordinary Hylleraas-type functions since they contain negative power terms in addition to the positive power terms. Linear combinations of up to 39 terms are employed
Forbidden transitions in the helium atom
Grzegorz Lach; Krzysztof Pachucki
2001-01-01
Nonrelativistically forbidden, single-photon transition rates between low-lying states of the helium atom are rigorously derived within quantum electrodynamics theory. Equivalence of velocity and length gauges, including relativistic corrections is explicitly demonstrated. Numerical calculations of matrix elements are performed with the use of high-precision variational wave functions and compared to former results.
Ground State of the Helium Atom. II
Toichiro Kinoshita
1959-01-01
A further attempt is made to improve the theoretical prediction of the energy of the ground state of atomic helium. The nonrelativistic part is treated by the variational method of Stevenson and Crawford which is useful for improving the lower bound for the ground-state energy. Linear combinations of up to 80 terms of generalized Hylleraas type are employed in the
Quantum Electrodynamics of the Helium Atom
Alexander Yelkhovsky
2001-03-22
Using singlet S states of the helium atom as an example, I describe precise calculation of energy levels in few-electron atoms. In particular, a complete set of effective operators is derived which generates O(m*alpha^6) relativistic and radiative corrections to the Schr"odinger energy. Average values of these operators can be calculated using a variational Schr"odinger wave function.
Electron-helium scattering in Debye plasmas
Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor [ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia); Janev, R. K. [Macedonian Academy of Sciences and Arts, P.O. Box 428, 1000 Skopje (Macedonia, The Former Yugoslav Republic of)
2011-11-15
Electron-helium scattering in weakly coupled hot-dense (Debye) plasma has been investigated using the convergent close-coupling method. The Yukawa-type Debye-Hueckel potential has been used to describe plasma Coulomb screening effects. Benchmark results are presented for momentum transfer cross sections, excitation, ionization, and total cross sections for scattering from the ground and metastable states of helium. Calculations cover the entire energy range up to 1000 eV for the no screening case and various Debye lengths (5-100 a{sub 0}). We find that as the screening interaction increases, the excitation and total cross sections decrease, while the total ionization cross sections increase.
Absorption Studies of Helium Metastable Atoms and Molecules
A. V. Phelps
1955-01-01
The lifetimes of the metastable states of the helium atom and molecule in pure helium have been determined by using a time-sampling technique for the measurement of the time-varying optical absorption caused by the various metastables. The measured loss of helium singlet metastable atoms indicates destruction after diffusion to the wall, upon collisions with single atoms, and by conversion into
Finite element calculations for the helium atom Weiying Zheng
Zheng, Weiying
Finite element calculations for the helium atom Weiying Zheng Lung-an Ying (School of Mathematical states of the helium atom. The relative errors of our approximate energies are: O(10-8) a.u. for S states various methods to obtain high-precision energies and other expecta- tion values. Helium atom
version 1.02 Forbidden transitions in the helium atom
Pachucki, Krzysztof
version 1.02 Forbidden transitions in the helium atom Grzegorz Lach #3; and Krzysztof Pachucki Nonrelativistically forbidden, single-photon transition rates between low ly- ing states of the helium atom transitions have already been studied for many light atoms and especially for helium (for a review see [1
Droplets mediated thermal transfer from an atomized diphasic helium flow
Paris-Sud XI, Université de
Droplets mediated thermal transfer from an atomized diphasic helium flow S. Perrauda,b , L. Puecha, the superfluidity of helium may affect both the atom- ization process and the spreading of droplets on the walls. Therefore, the influence of atomization on heat transfer in a diphasic superfluid helium flow has
Rayleigh scattering of photons by helium
Chien-Ping Lin; Kwok-Tsang Cheng; W. R. Johnson
1975-01-01
We present the results of a Dirac-Hartree-Fock calculation of Rayleigh scattering from He atoms in the energy range 0-500 Ry. The second-order S matrix is used to describe the scattering; the dominant correlation corrections are extracted from the fourth-order S matrix. The scattering amplitude is decomposed into a multipole series and numerical methods are employed to study the multipole amplitudes.
Sibener, Steven
Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3Si 111 surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited is consistent with the interaction between the helium atoms and SiCH3 bending modes. These experiments have
Nature of excited helium atoms in liquid helium: a theoretical model
A. P. Hickman; W. Steets
1975-01-01
A model is developed in which excited helium atoms in liquid helium may exist in stable cavities of diameter 10 A and larger. A repulsive effective interaction between the excited atom and the remaining atoms in the ground state is responsible for cavity formation. The equilibrium shape of the cavity is determined by minimizing the total energy, which is the
Metastable Aluminum Atoms Floating on the Surface of Helium Nanodroplets.
Jeffs, Jay; Besley, Nicholas A; Stace, Anthony J; Sarma, Gautam; Cunningham, Ethan M; Boatwright, Adrian; Yang, Shengfu; Ellis, Andrew M
2015-06-12
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. PMID:26196800
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.
V. M. Bystritsky; V. F. Boreiko; \\author{W. Czapli?ski; 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. Wo?niak
2003-12-17
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 and the $d \\mu{}^3 \\mathrm{He}$ radiative decay probability of for two different helium densities in $\\mathrm{D}_2 + {}^3\\mathrm{He}$ mixture were also determined. Finally, the $\\mathrm{q}_{1s}^{\\mathrm{He}}$ probability for a $d\\mu$ atom formed in an excited state to reach the ground state was measured and compared with theoretical calculations using a simple cascade model.
Chu, Xi
Polarizabilities of Sc and Ti atoms and dispersion coefficients for their interaction with helium atoms can be cooled and trapped in a helium buffer gas. The ratio of the elastic and inelastic cross populated by the approach of the com- plex atoms and helium 3,4 . The differences are small due
Neutron Scattering on Solid Helium Three
NASA Astrophysics Data System (ADS)
Sherline, Todd E.; Adams, E. Dwight; Schöttl, Stephan; Siemensmeyer, Konrad; Boyko, Vitaly; Mat'as, Slavomir; Bat'ko, Ivan; Toader, A. M.; Schanen, R.
2002-03-01
The importance of magnetism in solid ^3He lies in the multiple exchange mechanism, which is strongly dependent on pressure, magnetic field, and temperature. Neutron scattering methods most directly determine the order parameter symmetry and magnitude of the ordered solid ^3He. A quasi-elastic scattering experiment in the paramagnetic phase will give information about the exchange parameters. However, the enormous absorption cross-section of the ^3He atoms lead to small counting rates and sample heating. This necessitates additional design considerations for the sample cell, cryostat, and spectrometer, and discussion of the design and performance of existing elements will follow. Additionally, the results of a quasi-elastic scattering experiment will be discussed.
Nuclear polarizability of helium isotopes in atomic transitions
K. Pachucki; A. M. Moro
2007-03-18
We estimate the nuclear polarizability correction to atomic transition frequencies in various helium isotopes. This effect is non-negligible for high precision tests of quantum electrodynamics or accurate determination of the nuclear charge radius from spectroscopic measurements in helium atoms and ions. In particular, it amounts to $28(3)$ kHz for 1S-2S transition in 4He+.
Martini, K.M.
1986-01-01
Structural and vibrational properties of clean and oxygen covered, single crystal Cu(100) surfaces were studied, using the technique of high resolution helium beam scattering. To carry out these investigations it was necessary to first design and build a high performance neutral atom scattering experimental setup, consisting of: (1) a high intensity, supersonic neutral atom beam source; (2) a UHV scattering chamber with sample manipulation and diagnostic facilities; (3) a novel, metastable atom detector system. Experimental results pertaining to the following are presented: (1) new information on quasi-elastic electron helium atom scattering observed in the metastable atom detector: (2) elastic He atom scattering from clean and oxygen covered Cu(100) surfaces; and (3) inelastic He atom scattering from clean Cu(100) surfaces. These experiments were performed with the detector moving in and out of the scattering plane, the latter being a novel feature of this setup. The analysis of these data gives the inherent vibrational modes of the surface. Finally, a computational investigation of the structural and dynamic properties of a model incommensurate system, the one-dimensional, finite Frenkel-Kontorova chain, is reported.
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.
Classical helium atom with radiation reaction
Camelio, G.; Carati, A.; Galgani, L.
2012-06-15
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.
ENERGY RELAXATION OF HELIUM ATOMS IN ASTROPHYSICAL GASES
Lewkow, N. R.; Kharchenko, V. [Department of Physics, University of Connecticut, Storrs, CT 06269 (United States); Zhang, P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
2012-09-01
We report accurate parameters describing energy relaxation of He atoms in atomic gases, important for astrophysics and atmospheric science. Collisional energy exchange between helium atoms and atomic constituents of the interstellar gas, heliosphere, and upper planetary atmosphere has been investigated. Energy transfer rates, number of collisions required for thermalization, energy distributions of recoil atoms, and other major parameters of energy relaxation for fast He atoms in thermal H, He, and O gases have been computed in a broad interval of energies from 10 meV to 10 keV. This energy interval is important for astrophysical applications involving the energy deposition of energetic atoms and ions into atmospheres of planets and exoplanets, atmospheric evolution, and analysis of non-equilibrium processes in the interstellar gas and heliosphere. Angular- and energy-dependent cross sections, required for an accurate description of the momentum-energy transfer, are obtained using ab initio interaction potentials and quantum mechanical calculations for scattering processes. Calculation methods used include partial wave analysis for collisional energies below 2 keV and the eikonal approximation at energies higher than 100 eV, keeping a significant energy region of overlap, 0.1-2 keV, between these two methods for their mutual verification. The partial wave method and the eikonal approximation excellently match results obtained with each other as well as experimental data, providing reliable cross sections in the astrophysically important interval of energies from 10 meV to 10 keV. Analytical formulae, interpolating obtained energy- and angular-dependent cross sections, are presented to simplify potential applications of the reported database. Thermalization of fast He atoms in the interstellar gas and energy relaxation of hot He and O atoms in the upper atmosphere of Mars are considered as illustrative examples of potential applications of the new database.
Bertsch George F.
Application of density-functional theory to line broadening: Cs atoms in liquid helium Takashi to spectral perturbations taking an example of a Cs atom surrounded by superfluid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic
Gas-Surface Energy Exchange in Collisions of Helium Atoms with Aligned Single-Walled Carbon
Maruyama, Shigeo
1 Gas-Surface Energy Exchange in Collisions of Helium Atoms with Aligned Single-Walled Carbon #12;2 ABSTRACT Since gas flows in micro/nano devices are dominated by the interaction of gas molecules accommodation of gas molecules on surfaces. The scattering of gas molecules on quartz surfaces covered with VA
Method for laser spectroscopy of metastable pionic helium atoms
NASA Astrophysics Data System (ADS)
Hori, M.; Sótér, A.; Aghai-Khozani, H.; Barna, D.; Dax, A.; Hayano, R. S.; Murakami, Y.; Yamada, H.
2015-04-01
The PiHe collaboration is currently attempting to carry out laser spectroscopy of metastable pionic helium atoms using the high-intensity ? - beam of the ring cyclotron facility of the Paul Scherrer Institute. These atoms are heretofore hypothetical three-body Coulomb systems each composed of a helium nucleus, a ? - occupying a Rydberg state, and an electron occupying the 1s ground state. We briefly review the proposed method by which we intend to detect the laser spectroscopic signal. This complements our experiments on metastable antiprotonic helium atoms at CERN.
Method for laser spectroscopy of metastable pionic helium atoms
NASA Astrophysics Data System (ADS)
Hori, M.; Sótér, A.; Aghai-Khozani, H.; Barna, D.; Dax, A.; Hayano, R. S.; Murakami, Y.; Yamada, H.
2015-08-01
The PiHe collaboration is currently attempting to carry out laser spectroscopy of metastable pionic helium atoms using the high-intensity ? - beam of the ring cyclotron facility of the Paul Scherrer Institute. These atoms are heretofore hypothetical three-body Coulomb systems each composed of a helium nucleus, a ? - occupying a Rydberg state, and an electron occupying the 1s ground state. We briefly review the proposed method by which we intend to detect the laser spectroscopic signal. This complements our experiments on metastable antiprotonic helium atoms at CERN.
Metastable helium: Atom optics with nano-grenades
Kenneth Baldwin
2005-01-01
In this, the hundredth year since Einstein first postulated the existence of photons, the successful application of wave - particle duality to matter has seen an explosion of activity in the field of atom optics and Bose - Einstein condensation (BEC). This article provides a brief introduction to atom optics, illustrated with applications taken from experiments using helium atoms in
Dispersion coefficients for interactions between helium atoms in Debye plasmas
Kar, Sabyasachi [Center for Theoretical Atomic and Molecular Physics, The Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China); Ho, Y. K. [Institute of Atomic and Molecular Sciences, Academia Sinica, Post Office Box 23-166, Taipei, Taiwan 106 (China)
2010-06-15
Effect of Debye plasmas on the dispersion coefficients C{sub 8}, C{sub 10}, and C{sub 12} for interactions between atoms has been investigated using highly accurate correlated exponential basis functions. In the free-atom case, the dispersion C{sub 12} coefficient and the hexadecapole polarizability for helium are reported. The dispersion coefficients, hexadecapole polarizability, and 1s5g {sup 1}G{sup e} state energy of helium for different screening parameters are also reported.
Nuclear polarizability of helium isotopes in atomic transitions
Pachucki, K. [Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Moro, A. M. [Departamento de FAMN, Universidad de Sevilla, Apartado 1065, 41080 Sevilla (Spain)
2007-03-15
We estimate the nuclear polarizability correction to atomic transition frequencies in various helium isotopes. This effect is non-negligible for high precision tests of quantum electrodynamics or accurate determination of the nuclear charge radius from spectroscopic measurements in helium atoms and ions; in particular it amounts to 28(3) kHz for 1S-2S transition in {sup 4}He{sup +}.
Energy--level splitting in antiprotonic helium atoms
O. I. Kartavtsev
1995-09-28
Recent experiments on the laser-induced resonant annihilation provide a precise measurement of transition energies of antiprotonic helium atoms. Relativistic corrections of an order of $\\alpha ^2$ to the pure Coulomb interaction will be taken into account in the theoretical description of energy spectra of antiprotonic helium atoms. The splitting of energy levels arising due to the spin-dependent part of the relativistic interaction is considered for a number of states of $^{3,4}\\! H\\! e\\bar pe$ systems.
Contribution of Compton scattering to the double ionization of helium
Ken-icho Hino; P. M. Jr. Bergstrom; Joseph Macek
1994-01-01
Double ionization of helium by single-photon impact is analyzed for photon energies from 4 to 12 keV. Many-body perturbation theory is applied to obtain the Compton scattering contribution to the total cross section for double ionization. Compton scattering dominates photoionization above 6 keV. Despite the differences between the two processes, the ratio of double to single ionization by Compton scattering
Charles Schwartz
1961-01-01
The calculation, first attempted by Kabir and Salpeter, of the mean excitation energy entering in the Lamb shift of the helium ground state is redone by a quite different approach. Our answer, ln[k0ry]=4.370+\\/-0.004, leaves theory and experiment on the ionization energy of helium in agreement within the experimental uncertainty of +\\/-0.15 cm-1. Incidental results are given for the electrostatic polarizability
Convergent close-coupling calculations of positron scattering on metastable helium
NASA Astrophysics Data System (ADS)
Utamuratov, R.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.; Stelbovics, A. T.
2010-10-01
The convergent close-coupling method has been applied to positron scattering on a helium atom in the 23S metastable state. For this system the positronium (Ps) formation channel is open even at zero scattering energy making the inclusion of the Ps channels especially important. Spin algebra is presented for the general case of arbitrary spins. A proof is given of the often-used assumption about the relationship between the amplitudes for ortho-positronium and para-positronium formation. The cross sections for scattering from 23S are shown to be significantly larger than those obtained for the ground state.
Dynamics of excited sodium atoms attached to helium nanodroplets.
Loginov, Evgeniy; Drabbels, Marcel
2014-04-17
The dynamics of laser-excited sodium atoms at the surface of helium nanodroplets has been investigated as a function of quantum state. For all cases, excitation of the system leads to desorption of the sodium atom from the droplet surface. The mean kinetic energy of the desorbed atoms scales linearly with excitation frequency, indicative of an impulsive desorption process. The energy partitioning between the helium and the desorbing sodium atom depends on the quantum state and appears to be related to the size and shape of the electron orbital. The speed distributions of desorbed NaHe exciplexes point toward a direct formation process of an exciplex with no internal energy. Photoelectron spectroscopy reveals an increasing importance of helium-induced relaxation with increasing quantum state, which is tentatively attributed to curve crossing between different NaHeN interaction potentials during the desorption process. PMID:24673631
Corrections to the Nonrelativistic Ground Energy of a Helium Atom
Yi-Shi Duan; Yu-Xiao Liu; Li-Jie Zhang
2005-11-20
Considering the nuclear motion, the authors give out the nonrelativistic ground energy of a helium atom by using a simple but effective variational wave function with a flexible parameter $k$. Based on this result, the relativistic and radiative corrections to the nonrelativistic Hamiltonian are discussed. The high precision value of the helium ground energy is evaluated to be -2.90338 a.u., and the relative error is 0.00034%.
Shift and broadening of resonance lines of antiprotonic helium atoms in solid helium
Adamczak, Andrzej
2014-01-01
We have estimated the shift and broadening of the resonance lines in the spectrum of antiprotonic helium atoms $\\bar{p}\\mathrm{He}^{+}$ implanted in solid helium $^4$He. The application of the response function for crystalline helium has enabled determination of the contributions from the collective degrees of freedom to the shift and broadening. It occurs that the broadening due to the collective motion is negligible compared to the natural line width. The available pair-correlation functions for crystalline $^4$He have been applied for estimating the resonance-line shift due to collisions of $\\bar{p}\\mathrm{He}^{+}$ atom with the surrounding $^4$He atoms. The dependence of the line shift, which has been calculated in the quasistatic limit, on the solid-$^4$He density is nonlinear.
Helium atom in an external electric field: Exact diagonalization
NASA Astrophysics Data System (ADS)
Antsygina, T. N.; Chishko, K. A.
2014-09-01
An exact diagonalization method is applied to solve the quantum-mechanical problem of spinless helium atom in an external electric field of arbitrary magnitude. The basis set for two-electron problem is built from different pair combinations ?nalama(?ra)?nblbmb(?rb) of orthonormalized single-particle hydrogen-like wave functions ?nml(r) belonging to any possibly bound states of the individual a- and b-electrons in the Coulomb central field renormalized by the scale parameter ? > 0. Within the selected basis the matrix elements of the total Hamiltonian allows an exact analytical representation in the form of finite numerical sums. The diagonalization procedure is performed by Jacobi algorithm for N × N square Hermitian matrix built on the basis of dimension N = 25. The systematics and the numerical values of the low-lying energy levels at zero field are in good agreement with known experimental data. The field dependences of low-lying levels (Stark effect) and polarizability in the ground state of helium atom are presented. It is shown that even extremely high external fields lead only to shifting or splitting of existing low levels, without disturbance of their systematics. Typically, no new low-energy excitation can be created under external electric field of moderate intensity. Radical reconstruction in spectrum of individual helium atoms can be expected in condensed helium phases where each atom is deeply affected by interaction fields from neighbors. This result should be taken into account at interpretation of electrodynamic experiments on superfluid helium.
Spectroscopy of Mg atoms solvated in helium nanodroplets
NASA Astrophysics Data System (ADS)
Reho, J.; Merker, U.; Radcliff, M. R.; Lehmann, K. K.; Scoles, G.
2000-05-01
We have measured the laser-induced fluorescence excitation spectra of the 3 1P10?3 1S0 transition of Mg atoms solvated in helium nanodroplets. The observed blue shifts and line broadenings mirror the shifts and broadenings observed in studies of Mg atoms solvated in bulk liquid helium. This similarity allows us to conclude that Mg atoms reside in the interior of the helium droplet. The 3 1P10?3 1S0 transition shows a splitting which we attribute to a quadrupolelike deformation of the cavity which forms around the solute atom after excitation. Temporal evolution of the fluorescence from the solvated 3 1P10 Mg yields a longer lifetime (2.39±0.05 ns) than found in vacuum (1.99±0.08 ns). This difference can be accounted for quantitatively by evaluation of the anisotropic distribution of the helium density in the neighborhood of the excited Mg atom. The question of solvation vs surface location for the guest atoms is also discussed in light of the model of Ancilotto et al. [F. Ancilotto, P. B. Lerner, and M. W. Cole, J. Low Temp. Phys. 101, 1123 (1995)], of existing metal atom-helium potential energy functions, and of our own calculations for the MgHe and CaHe ground states. While the Ancilotto model successfully predicts solvation (or lack of it) if the solvation parameter of the guest atom is not too near the threshold of 1.9, the present knowledge of the interatomic potentials is not precise enough to test the model in the neighborhood of the critical value.
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 helium atoms and U.V. photons, produced in the same source, with a clean molybdenum [110] surface of photons and metastable atoms was designed to give a beam containing no helium atoms of high kinetic energy
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.
Ground State of the Helium Atom
Charles Schwartz
1962-01-01
Following a recent attempt to analyze the rate of convergence of Rayleigh-Ritz variational calculations on the ground state of helium, we were led to re-investigate the usefulness of inserting fractional powers of the variables into the conventional Hylleraas series. The results have been very successful: With a 164-term trial function containing half-powers of the variable s=r1+r2, we have matched the
Penning ionization by metastable helium atoms
K. L. Bell; A. Dalgarno; A. E. Kingston
1968-01-01
Values of the van der Waals interaction between the 2 1S and 2 3S metastable states of helium and the systems Ne, Ar, Kr, Xe, H2, N2, O2, CH4, Li, Na, K, Rb, Cs and O are computed. The values are used to determine Penning ionization probabilities from the experimental data with results differing significantly from an earlier analysis. Estimates
Quantum Field Theory and the Helium Atom: 101 Years Later
J. Sucher
1996-12-11
Helium was first isolated on Earth in 1895, by Sir William Ramsey. One hundred and one years later, it seems like a good time to review our current theoretical understanding of the helium atom. Helium has played an important role in the development of both quantum mechanics and of quantum field theory. The early history of helium is sketched. Various aspects of the modern theory are described in some detail, including (1) the computation of fine structure to order \\alpha^2 Ry and \\alpha^3 Ry, (2) the decay of metastable states, and (3) Rydberg states and long-range forces. A brief survey is made of some of the recent work on the quantum field theory of He and He-like ions.
Spin physics with laser-pumped helium atoms
Schearer, L.D. [Univ. of Missouri, Rolla, MO (United States)
1993-05-01
With the development of new, tunable lasers at 1083 nm, direct optical pumping of the triplet metastable atoms of helium yields an almost perfectly aligned ensemble. In {sup 3}He the hyperflne interaction and collisions transfer the orientation to the groundstate nuclear spins. The optical pumping process in {sup 3}He is extraordinarily efficient- nearly 2.5 nuclei are oriented per absorbed photon at turn-on. Applications to magnetometry, the production of spin-polarized electron and ion beams, and the development of polarized neutron beams and dense targets will be discussed. The progress of the UNI-Mainz experiment to measure the electric and magnetic form factors of the neutron will be described. In this experiment the polarized {sup 3}He target is mechanically compressed to several atmospheres with minimal loss of nuclear polarization. Extension of this dense nuclear target for use as a neutron spin filter is also in progress. We will also describe the status of our experiment to observe scattering asymmetries of polarized electrons by chiral molecules. Progress on the development of a compact, moderate current, polarized e-beam will be discussed.
Spectra of helium clusters with up to six atoms using soft-core potentials
NASA Astrophysics Data System (ADS)
Gattobigio, M.; Kievsky, A.; Viviani, M.
2011-11-01
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.
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.
Decoherence due to Scattering Atoms
NASA Astrophysics Data System (ADS)
Uys, Hermann; Perreault, John; Cronin, Alex
2004-05-01
Coherent manipulation of a quantum system is difficult because of uncontrolled interactions with the system's environment. The study of decoherence so introduced is important for progress in quantum mechanical engineering, and for understanding the transition from quantum to classical behavior. We have observed loss of fringe contrast in a Mach-Zhender atom interferometer due to scattering background gas atoms and propose that this might be interpreted as quantum decoherence. Progress will be reported on the use of a general model of decoherence incorporating a semi-classical picture of atom scattering to explain the contrast loss [1]. A formal analogy is made to decoherence due to scattering photons from atoms in an interferometer [2]. [1] S.M. Tan, D.F. Waals, ``Loss of coherence in interferometry", Phys. Rev. A 47 p.4663 (1993) [2] D.A. Kokorowski, A.D. Cronin, T.D. Roberts, and D.E. Pritchard, ``From single- to multiple-photon decoherence in an atom interferometer", Phys. Rev. Lett. 86 p. 2191 (2001)
Asymptotic Double-Photoexcitation Cross Sections of the Helium Atom
T. Åberg
1970-01-01
A relative cross section for simultaneous excitation and ionization of the helium atom is derived from the sudden approximation. It is shown to agree with that obtained from the velocity form of the cross section in the Coulomb approximation. It is connected to the asymptotic cross section of Kabir and Salpeter through the cusp condition at the nucleus. An analysis
Calculation of diffusion barriers for helium atom in metals
Long De-shun; Xu Hui-zhong; Wang Yan-sen; Zhao Guo-qing; Peng Shu-ming; Zhao Peng-ji; Xu Zhi-lei
1999-01-01
The diffusion barriers for the single helium atom in 3d transition metals are systematically studied by effective medium theory without any adjustable parameters. In the calculation, the relaxiation effects of lattice are taken into account. The comparison of our calculated results with the available experimental data and other theoretical values shows good agreement.
CPT tests with antihydrogen and antiprotonic helium atoms
NASA Astrophysics Data System (ADS)
Hayano, Ryugo
2014-09-01
Recent progress of the CPT tests with antihydrogen and antiprotonic helium atoms by the ASACUSA collaboration at CERN's antiproton decelerator will be presented. The antiprotonic helium atom (antiproton+electron+helium nucleus) is a serendipitously discovered metastable three-body system, whose energy levels can now be studied by laser spectroscopy techniques to a relative precision of ~10-9. By comparing these precise experimental results with the result of three-body QED calculation, the antiproton-to-electron mass ratio was determined to a relative precision of 1 . 2 ×10-9 . While this can be used as a precise test of the CPT symmetry, CODATA instead assumed the CPT, and combined our results with the proton-to-electron mass ratio measured by the Penning trap method in their adjustment of the fundamental physical constants. In addition to the laser spectroscopy of antiprotonic helium, ASACUSA collaboration also aims at measuring the ground-state hyperfine splitting of antihydrogen using the (anti)-atomic beam method. Extraction of antihydrogen atoms from a ``cusp'' trap has so far been demonstrated. Both of these experiments will benefit from the completing of a new antiproton decelerator-cooler ring called ELENA, which is under construction at CERN.
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.
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...
Version 3.0 Nuclear polarizability of helium isotopes in atomic transitions
Pachucki, Krzysztof
Version 3.0 Nuclear polarizability of helium isotopes in atomic transitions K. Pachucki 1 and A the nuclear polarizability correction to atomic transition frequencies in various helium iso topes of the nuclear charge radius from spectroscopic measurements in helium atoms and ions, in particular it amounts
LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon
Pines, Alexander
LBNL-42730 1 Collisional Perturbation of States in Atomic Ytterbium by Helium and Neon D in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching with respect to helium (He) and neon (Ne) are measured. The 3 P0 state is populated by exciting Yb atoms from
Rioux, Frank
Hydrogen Atom and Helium Ion Spatial and Momentum Distribution Functions Illustrate for oneelectron species such as the hydrogen atom and the helium ion. The coordinate 1s wave function for the hydrogen atom (z=1) and helium ion (z=2) clearly illustrate the uncertainty principle. 0 2 4 6 r 2 1 r
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
Bound states of interacting helium atoms
Stefan V. Mashkevich; Stanislav I. Vilchynskyy
1999-11-11
We study the possibility of existence of bound states for two interacting He-4 atoms. It is shown that for some potentials, there exist not only discrete levels but also bands akin to those in the Kronig--Penney model.
Rayleigh scattering from excited atoms in plasmas
W.-G. Wrobel; K.-H. Steuer; H. Roehr
1976-01-01
Rayleigh and resonance scattering allow spatially resolved measurements of the neutral density and temperature in a plasma. While resonance scattering often is disturbed by line radiation of the plasma, this can be overcome by observation of near-resonant Rayleigh scattering. Scattering experiments were performed at the 587.6-nm helium line using a flashlamp-pumped dye laser. The spectral dependence of the Rayleigh cross
Rayleigh scattering from excited atoms in plasmas
W. Wrobel; K. Steuer; H. Roehr
1976-01-01
Rayleigh and resonance scattering allow spatially resolved measurements of the neutral density and temperature in a plasma. While resonance scattering often is disturbed by line radiation of the plasma, this can be overcome by observation of near-resonant Rayleigh scattering. We performed scattering experiments at the 587.6-nm helium line using a flashlamp-pumped dye laser. The spectral dependence of the Rayleigh cross
Semiclassical quantization of Bohr orbits in the helium atom
NASA Astrophysics Data System (ADS)
Belov, V. V.; Maksimov, V. A.
2007-05-01
We use the complex WKB-Maslov method to construct the semiclassical spectral series corresponding to the resonance Bohr orbits in the helium atom. The semiclassical energy levels represented as the Rydberg tetra series correspond to the doubly symmetrically excited states of helium-like atoms. This level series contains the Rydberg triple series reported by Richter and Wintgen in 1991, which corresponds to the Z2+e-e- configuration of electrons observed by Eichmann and his collaborators in experiments on the laser excitation of the barium atom in 1992. The lower-level extrapolation of the formula obtained for the semiclassical spectrum gives the value of the ground state energy, which differs by 6% from the experimental value obtained by Bergeson and his collaborators in 1998. We also calculate the fine structure of the semiclassical spectrum due to the spin-orbit and spin-spin interactions of electrons.
Search for Positron Bound States in the Doubly Excited Region of the Helium Atom
NASA Astrophysics Data System (ADS)
Boadle, Roisin; Machacek, Joshua; Anderson, Emma; Sullivan, James; Buckman, Stephen
2012-10-01
Positron-atom binding has been the subject of many theoretical calculations in recent years. In these systems, a positron becomes temporarily bound to the atom, either through polarisation of the electronic charge cloud or formation of positronium (an e^-e^+ pair) which is weakly bound to the atom. There is now theoretical evidence of numerous positron-atom bound states, including for the helium atom. Ground state helium is incapable of binding a positron; however, recent calculations [1] have indicated that excited metastable states and doubly excited states may do so. These bound states might be expected to manifest themselves as structure in the energy dependence of the cross sections for processes such as total scattering, positronium formation, or ionization. We have carried out an experimental search for these positronic helium states in the doubly-excited region near 58 eV, using our high-resolution, trap-based positron beam. Results from this study will be presented and their ramifications discussed. [4pt] [1] M.J. Bromley and J. Mitroy Private Communication (2012)
Buenermann, Oliver; Kornilov, Oleg; Neumark, Daniel M. [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Haxton, Daniel J.; Gessner, Oliver [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Leone, Stephen R. [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Chemistry, University of California, Berkeley, California 94720 (United States); Department of Physics, University of California, Berkeley, California 94720 (United States)
2012-12-07
The ejection dynamics of Rydberg atoms and molecular fragments from electronically excited helium nanodroplets are studied with time-resolved extreme ultraviolet ion imaging spectroscopy. At excitation energies of 23.6 {+-} 0.2 eV, Rydberg atoms in n= 3 and n= 4 states are ejected on different time scales and with significantly different kinetic energy distributions. Specifically, n= 3 Rydberg atoms are ejected with kinetic energies as high as 0.85 eV, but their appearance is delayed by approximately 200 fs. In contrast, n= 4 Rydberg atoms appear within the time resolution of the experiment with considerably lower kinetic energies. Major features in the Rydberg atom kinetic energy distributions for both principal quantum numbers can be described within a simple elastic scattering model of localized perturbed atomic Rydberg atoms that are expelled from the droplet due to their repulsive interaction with the surrounding helium bath. Time-dependent kinetic energy distributions of He{sub 2}{sup +} and He{sub 3}{sup +} ions are presented that support the formation of molecular ions in an indirect droplet ionization process and the ejection of neutral Rydberg dimers on a similar time scale as the n= 3 Rydberg atoms.
Collisions between hydrogen atoms and helium ions
NASA Technical Reports Server (NTRS)
Franco, V.
1980-01-01
By the use of a new theory developed for collisions between atomic hydrogen and arbitrary ions or atoms, the cross section for the direct excitation process He(+)(1s) + H(1s) yields He(+)(2s) + H(Sigma) in which the H atom is left in any discrete or continuum final state is calculated. The results are compared with other theories and with recent measurements for He-3(+) energies between 22 and 346 keV. The theory predicts a maximum near 84 keV, in excellent agreement with the data. Above 200 keV all theories yield cross sections which do not decrease rapidly enough with increasing energy when compared with the data.
Quantum entanglement for helium atom in the Debye plasmas
NASA Astrophysics Data System (ADS)
Lin, Yen-Chang; Fang, Te-Kuei; Ho, Yew Kam
2015-03-01
In the present work, we present an investigation on quantum entanglement of the two-electron helium atom immersed in weakly coupled Debye plasmas, modeled by the Debye-Hückel, or screened Coulomb, potential to mimic the interaction between two charged particles inside the plasma. Quantum entanglement is related to correlation effects in a multi-particle system. In a bipartite system, a measurement made on one of the two entangled particles affects the outcome of the other particle, even if such two particles are far apart. Employing wave functions constructed with configuration interaction B-spline basis, we have quantified von Neumann entropy and linear entropy for a series of He 1,3Se and 1,3Po states in plasma-embedded helium atom.
High Energy Inelastic Neutron Scattering from Helium in Vycor
NASA Astrophysics Data System (ADS)
Azuah, Richard; Pearce, Jonathan; Stirling, William; Sokol, Paul
2000-03-01
We have carried out high energy inelastic neutron scattering studies of liquid helium confined in porous vycor glass at several temperatures spanning the superfluid and normal liquid phases. These measurements provide direct information on the single particle momentum distribution; the only experimental quantity directly showing the effects of the Bose condensate. The measurements were carried out using the MARI chopper spectrometer at the ISIS spallation source. We will present values for the kinetic energy and the condensate fraction of the confined liquid and contrast these to the values measured in the bulk and for helium confined in aerogel. This work was supported by the National Science Foundation through grant DMR 9970126 and by the EPSRC.
Bound states of helium atom in dense plasmas
Sabyasachi Kar; Y. K. Ho
2006-01-01
We have obtained the bound 1s2 1S, 1s2s 1,3S, and 1s2p 1,3P states energies of helium atom in dense plasma environments in accurate variation calculations. A screened Coulomb potential to represent the Debye model is used for the interaction between the charged particles. A correlated wave function consisting of a generalized exponential expansion has been used to take care of
Bound D-states of helium atom under Debye screening
Sabyasachi Kar; Y. K. Ho
2007-01-01
We have investigated the 1snd1,3D (3 ? n ? 7) state energies of helium atom embedded in weakly coupled plasma environments using the Rayleigh-Ritz variational method. The effect of the plasma environment is taken care of using a Debye screening model. A correlated wave function involving exponential expansion has been used to represent correlation between the charge particles. The bound
Quantum Solvation of Carbonyl Sulfide with Helium Atoms
Jian Tang; Yunjie Xu; A. R. W. McKellar; Wolfgang Jäger
2002-01-01
High-resolution infrared and microwave spectra of HeN-carbonyl sulfide (HeN-OCS) clusters with N ranging from 2 to 8 have been detected and unambiguously assigned. The spectra show the formation of a solvation layer beginning with an equatorial ``donut'' of five helium atoms around the OCS molecule. The cluster moment of inertia increases as a function of N and overshoots the liquid
Ground State Hyperfine Structure of Muonic Helium Atom
A. A. Krutov; A. P. Martynenko
2008-07-21
On the basis of the perturbation theory in the fine structure constant $\\alpha$ and the ratio of the electron to muon masses we calculate one-loop vacuum polarization and electron vertex corrections and the nuclear structure corrections to the hyperfine splitting of the ground state of muonic helium atom $(\\mu e ^4_2He)$. We obtain total result for the ground state hyperfine splitting $\\Delta \
Classical limit states of the helium atom J. A. West,1,2
Stroud, Carlos R.
Classical limit states of the helium atom J. A. West,1,2 Z. D. Gaeta,1,3 and C. R. Stroud, Jr.1,2 1 for the simplest such atom, helium, this extension is nontrivial because the old quantum theory of Bohr was never wave packets are used to explore the classical limit states of helium. A class of shape
Collisional radiative model of a helium capillary glow discharge including atomic collisions
Paris-Sud XI, Université de
689 Collisional radiative model of a helium capillary glow discharge including atomic collisions G- cients of the most important elementary processes in a helium afterglow discharge (diffusion of atomic. Abstract 2014 A new collisional radiative model of helium capillary glow discharge has been developed
Spectroscopy of lithium atoms and molecules on helium nanodroplets.
Lackner, Florian; Poms, Johannes; Krois, Günter; Pototschnig, Johann V; Ernst, Wolfgang E
2013-11-21
We report on the spectroscopic investigation of lithium atoms and lithium dimers in their triplet manifold on the surface of helium nanodroplets (He(N)). We present the excitation spectrum of the 3p ? 2s and 3d ? 2s two-photon transitions for single Li atoms on He(N). 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*–He(m), m = 1–3) formation process in the Li–He(N) system. Electronic states are shifted and broadened with respect to free atom states, which is explained within the pseudodiatomic model. The assignment is assisted by theoretical calculations, which are based on the Orsay–Trento density functional where the interaction between the helium droplet and the lithium atom is introduced by a pairwise additive approach. When a droplet is doped with more than one alkali atom, the fragility of the alkali–He(N) systems leads preferably to the formation of high-spin molecules on the droplets. We use this property of helium nanodroplets for the preparation of Li dimers in their triplet ground state (13?u(+)). The excitation spectrum of the 23?g(?? = 0–11) ? 13?u(+)(?? = 0) transition is presented. The interaction between the molecule and the droplet manifests in a broadening of the transitions with a characteristic asymmetric form. The broadening extends to the blue side of each vibronic level, which is caused by the simultaneous excitation of the molecule and vibrations of the droplet (phonons). The two isotopes of Li form 6Li2 and 7Li2 as well as isotope mixed 6Li7Li molecules on the droplet surface. By using REMPI-TOF mass spectroscopy, isotope-dependent effects could be studied. 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.
Semi-Classical Description of Antiproton Capture on Atomic Helium
W. A. Beck; L. Wilets; M. A. Alberg
1993-04-15
A semi-classical, many-body atomic model incorporating a momentum-dependent Heisenberg core to stabilize atomic electrons is used to study antiproton capture on Helium. Details of the antiproton collisions leading to eventual capture are presented, including the energy and angular momentum states of incident antiprotons which result in capture via single or double electron ionization, i.e. into [He$^{++}\\,\\bar p$ or He$^{+}\\,\\bar p$], and the distribution of energy and angular momentum states following the Auger cascade. These final states are discussed in light of recently reported, anomalously long-lived antiproton states observed in liquid He.
Electron impact excitation of helium atom
NASA Astrophysics Data System (ADS)
Han, Xiao-Ying; Zeng, De-Ling; Gao, Xiang; Li, Jia-Ming
2015-08-01
A method to deal with the electron impact excitation cross sections of an atom from low to high incident energies are presented. This method combines the partial wave method and the first Born approximation (FBA), i.e., replacing the several lowest partial wave cross sections of the total cross sections within FBA by the corresponding exact partial wave cross sections. A new set of codes are developed to calculate the FBA partial wave cross sections. Using this method, the convergent e–He collision cross sections of optical-forbidden and optical-allowed transitions at low to high incident energies are obtained. The calculation results demonstrate the validity and efficiency of the method. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921501 and 2013CB922200), the National Natural Science Foundation of China (Grant Nos. 11274035, 11275029, 11328401, 11371218, 11474031, 11474032, and 11474034), and the Foundation of Development of Science and Technology of Chinese Academy of Engineering Physics (Grant Nos. 2013A0102005 and 2014A0102005).
Rayleigh Scattering at Atoms with Dynamical Nuclei
J. Froehlich; M. Griesemer; B. Schlein
2005-01-01
Scattering of photons at an atom with a dynamical nucleus is studied on the subspace of states of the system with a total energy below the threshold for ionization of the atom (Rayleigh scattering). The kinematics of the electron and the nucleus is chosen to be non-relativistic, and their spins are neglected. In a simplified model of a hydrogen atom
Absolute Cross Sections for Penning Ionization of Atomic Oxygen by Helium Metastable Atoms
T. B. Cook; W. P. West; F. B. Dunning; R. D. Rundel; R. F. Stebbings
1974-01-01
Summary. Penning ionization of atomic oxygen by helium roetastable atoms has been studied by using a crossed beams technique. Absolute cross sections are 44 and 124 for He(23S) and He(2S), respectively, at a mean energy in the center of mass frame of 0.1 eV. Penning ionization of atomic oxygen has long been recognized as an important mechanism causing
Application of density functional theory to line broadening: Cs atoms in liquid helium
Takashi Nakatsukasa; Kazuhiro Yabana; George F. Bertsch
2001-10-10
We test the applicability of density functional theory (DFT) to spectral perturbations taking an example of a Cs atom surrounded by superfluid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and D2 absorption lines are quite well reproduced by theory, suggesting that the DFT may be useful for describing spectral perturbations in more complex environments.
H. Höche; J. P. Toennies; R. Vollmer
1994-01-01
The electron-microscope surface-decoration technique and He-atom scattering (HAS) have been used to characterize the topography of NaCl(001) cleavage faces during vacuum ultraviolet (VUV) photon-stimulated desorption (PSD). The experiments were carried out at crystal temperatures below 550 K for which pure thermal desorption can be neglected. In the temperature range from T=550 to 440 K the decoration experiments reveal that PSD
Satellite drag coefficients calculated from measured distributions of reflected helium atoms
NASA Technical Reports Server (NTRS)
Liu, S.-M.; Sharma, P. K.; Knuth, E. L.
1979-01-01
The primary objectives of this study were to obtain the necessary data and develop a calculation procedure that would facilitate predicting the atmospheric-helium contribution to the drag of a satellite having a predominantly convex exterior. Molecular-beam techniques were used to measure, for several incidence angles, the spatial and energy distributions of 7000 m/s helium atoms scattered from a 6061-T6 aluminum plate and an anodized 1235-0 aluminum surface. From these measured distributions, tangential and normal momentum accommodation coefficients were calculated as functions of incidence angle. Using these calculated accommodation coefficients, one can predict drag coefficients for satellites having predominantly convex exteriors. For spherical satellites, drag coefficients of 2.64 and 2.62 were predicted for the subject surfaces.
Ionization of helium atoms under the effect of the antineutrino magnetic moment
Martemyanov, V. P. Tsinoev, V. G.
2011-12-15
Differential cross sections for inelastic antineutrino interaction with a helium atom are calculated. It is shown that, in the energy-transfer range extending up to 1 keV, the cross sections in question are considerably enhanced in the electromagnetic-interaction channel in relation to the cross sections for elastic scattering on a free electron. Absolute cross-section values are of interest in searches for the antineutrino magnetic moment, provided that its value in Bohr magneton units falls within the range (10{sup -13}-10{sup -12}){sub Micro-Sign B}.
The interaction of metastable helium atoms with alkali atoms
M.-W. Ruf; A. J. Yencha; H. Hotop
1987-01-01
Using crossed beams of ground state alkali atoms A (A = Li, Na, K, Rb, Cs) and metastable He(23S), He(21S) atoms, we have measured the energy spectra of electrons resulting in the respective Penning ionization processes at: thermal collision energies. The data are interpreted to yield the well depthDe* of the2S interaction potentials as follows: He(23S)+A:De* (A=Li)=868(20) meV;De*(Na)=740(25) meV;De*(K)=591(24) meV;De*(Rb)=546(18)
Magee, Joseph W.
Accurate Atomic Transition Probabilities for Hydrogen, Helium, and Lithium W. L. Wiese and J. R transitions; atomic transition probabilities; f values; helium; hydrogen; line strengths; lithium; oscillator September 2009 We have carried out a comprehensive tabulation of the atomic transition probabilities
Semiclassical initial value calculations of collinear helium atom
Celal Harabati; Kenneth G. Kay
2007-04-26
Semiclassical calculations using the Herman-Kluk initial value treatment are performed to determine energy eigenvalues of bound and resonance states of the collinear helium atom. Both the $eZe$ configuration (where the classical motion is fully chaotic) and the $Zee$ configuration (where the classical dynamics is nearly integrable) are treated. The classical motion is regularized to remove singularities that occur when the electrons collide with the nucleus. Very good agreement is obtained with quantum energies for bound and resonance states calculated by the complex rotation method.
Hyperfine structure of excited state of muonic helium atom
A. A. Krutov; A. P. Martynenko
2012-08-23
The recoil, vacuum polarization and electron vertex corrections of first and second orders in the fine structure constant $\\alpha$ and the ratio of electron to muon and electron to \\alpha-particle masses are calculated in the hyperfine splitting of the $1s^{(e)}_{1/2}2s^{(\\mu)}_{1/2}$ state of muonic helium atom (\\mu e ^4_2He) on the basis of a perturbation theory. We obtain total result for the muonically excited state hyperfine splitting $\\Delta \
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.
PREFACE: Atom-surface scattering Atom-surface scattering
NASA Astrophysics Data System (ADS)
Miret-Artés, Salvador
2010-08-01
It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific contributions. J R Manson, or Dick to his friends and colleagues, is one of the founding fathers, together with N Cabrera and V Celli, of the 'Theory of surface scattering and detection of surface phonons'. This is the title of the very well-known first theoretical paper by Dick published in Physical Review Letters in 1969. My first meeting with Dick was around twenty years ago in Saclay. J Lapujoulade organized a small group seminar about selective adsorption resonances in metal vicinal surfaces. We discussed this important issue in surface physics and many other things as if we had always known each other. This familiarity and warm welcome struck me from the very beginning. During the coming years, I found this to be a very attractive aspect of his personality. During my stays in Göttingen, we had the opportunity to talk widely about science and life at lunch or dinner time, walking or cycling. During these nice meetings, he showed, with humility, an impressive cultural background. It is quite clear that his personal opinions about history, religion, politics, music, etc, come from considering and analyzing them as 'open dynamical systems'. In particular, with good food and better wine in a restaurant or at home, a happy cheerful soirée is guaranteed with him, or even with only a good beer or espresso, and an interesting conversation arises naturally. He likes to listen before speaking. Probably not many people know his interest in tractors. He has an incredible collection of very old tractors at home. In one of my visits to Clemson, he showed me the collection, explaining to me in great detail, their technical properties; all of them were ready for use! We cannot imagine him without his two old-fashioned Mercedes, also in his collection. He also has technical skills in construction and music and always has time for jogging. I would finally say that he is an even-tempered person. In brief, mens sana in corpore sano 1 . Dick is a theorist bound to experimental work, extremely intuitive and very dedicated. In his long stays outside Clemson, he always visited places where experiments were being carried out. He has been, and still is, of great help to experimental PhD students, postdocs or senior scientists in providing valuable advice and suggestions towards new measurements. Plausible interpretations of their results developing theoretical models or always searching for good agreement with experiment are two constants in his daily scientific work. Experimental work is present in most of his 150 papers. One of the main theoretical challenges in this field was to develop a formalism where the plethora of experimental results reported in the literature were accommodated. His transition matrix formalism was also seminal in the field of atom-surface scattering. Elastic and inelastic (single and double phonon) contributions were determined as well as the multiphonon background. This work was preceded by a theory for diffuse inelastic scattering and a posterior contribution for multiphonon scattering, both with V Celli. In a similar vein, a theory of molecule-surface scattering was also derived and, more recently, a theory for direct scattering, trapping and desorption. Very interesting extensions to scattering with molten metal and liquid surfaces have also been carried out. Along with collaborators he has studied energy accommodation and sticking coefficients, providing a better understanding of their meaning. G Armand and Dick proposed the well-known corrugated Morse potential as an interaction potential model providing reliable results of diffraction patterns and selective adsorption resonances. This proposal was, in a certain sense, the result of many previous studies carried out by t
Sideband Rayleigh scattering from trapped atoms
Özgür E. Müstecapliouglu; L. You
2000-01-01
We present a detailed analysis of (inelastic) Rayleigh scattering from trapped low temperature atomic gas (S. Inouye et al.), Science 285, 571 (1999). with a new formulation for sideband generation. We found scattered light exhibit both oscillatory and exponential growth behaviors depending on density, temperature, and geometric shape of the gas sample. We also clarify the role of atomic quantum
Revised Primordial Helium Abundance Based on New Atomic Data
M. Peimbert; V. Luridiana; A. Peimbert
2007-06-04
We have derived a primordial helium abundance of Yp = 0.2477 +- 0.0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations and photoionization models of metal-poor extragalactic H II regions. The new atomic data increase our previous determination of Yp by 0.0086, a very significant amount. By combining our Yp result with the predictions made by the standard Big Bang nucleosynthesis model, we find a baryon-to-photon ratio, \\eta, in excellent agreement both with the \\eta value derived by the primordial deuterium abundance value observed in damped Lyman-\\alpha systems and with the one obtained from the WMAP observations.
Hydrogen and Helium atoms in strong magnetic fields
Anand Thirumalai; Jeremy S. Heyl
2012-02-07
The energy levels of hydrogen and helium atoms in strong magnetic fields are calculated in this study. The current work contains estimates of the binding energies of the first few low-lying states of these systems that are improvements upon previous estimates. The methodology involves computing the eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock partial differential equations for these one- and two-electron systems in a self-consistent manner. The method described herein is applicable to calculations of atomic structure in magnetic fields of arbitrary strength as it exploits the natural symmetries of the problem without assumptions of any basis functions for expressing the wave functions of the electrons or the commonly employed adiabatic approximation. The method is found to be readily extendable to systems with more than two electrons.
Coherently enhanced Raman scattering in atomic vapor
Yuan Chunhua; Chen, L. Q.; Jing, Jietai; Zhang, Weiping [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Ou, Z. Y. [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Department of Physics, Indiana University-Purdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202 (United States)
2010-07-15
We present a scheme to obtain the coherently enhanced Raman scattering in atomic vapor which is induced by a spin wave initially written by a weak write laser. The enhancement of Raman scattering is dependent on the number and the spatial distribution of the flipped atoms generated by the weak write laser. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy because of its simplicity.
Rayleigh Scattering at Atoms with Dynamical Nuclei
J. Fröhlich; M. Griesemer; B. Schlein
2007-01-01
Scattering of photons at an atom with a dynamical nucleus is studied on the subspace of states of the system with a total energy below the threshold for ionization of the\\u000a atom (Rayleigh scattering). The kinematics of the electron and the nucleus is chosen to be non-relativistic, and their spins are neglected. In a simplified\\u000a model of a hydrogen atom
NASA Astrophysics Data System (ADS)
Liu, Fusheng; Tian, Chunling; Cai, Lingcang; Jing, Fuqian
Based on ab initio self-consistent-field technique and atomic cluster method, the various many-body interactions among atoms in dense helium have been computed. By this way, the static high pressure measurements are perfectly explained. A new simple formula for calculation the total energy is proposed by directly combining the two-body potential with the atomic potential. Over a large volume and temperature range of 7.5~1.74 cm3/mol and 2000~21000K, the equation of state (EOS) of helium is given.
Li, Mubing; Manson, J. R.; Graham, Andrew P.
2001-04-15
The probabilities of multiple excitation (multiphonon transfer) of decoupled, oscillating adsorbates on a surface via impact by an atom or molecule are discussed using a dynamical scattering model, and comparisons are made with helium scattering results for carbon monoxide adsorbed on metal surfaces. The scattering model, which contains no free adjustable parameters, is shown to predict correctly the angular dependence of the distribution of the multiphonon excitations in addition to the variation with incident energy and adsorbate frequency. Furthermore, the model is used to calculate the excitation probability of other vibrational modes that have not yet been observed using helium-atom scattering.
Cross Sections for the DeExcitation of Helium Metastable Atoms by Collisions with Atoms
E. E. Benton; E. E. Ferguson; F. A. Matsen; W. W. Robertson
1962-01-01
The lifetimes of metastable helium atoms He(2 3S) and He(2 1S) were measured by a time-resolved optical absorption technique in the afterglow of a pulsed helium discharge at 10-mm pressure with small concentrations of various impurity gases added. The following de-excitation cross sections in units of 10-16 cm2 have been determined for He(2 3S): Ne-0.28, Ar-6.6, Kr-10.3, Xe-13.9, N2-6.4, and
Analysis of helium-ion scattering with a desktop computer
NASA Astrophysics Data System (ADS)
Butler, J. W.
1986-04-01
This paper describes a program written in an enhanced BASIC language for a desktop computer, for simulating the energy spectra of high-energy helium ions scattered into two concurrent detectors (backward and glancing). The program is designed for 512-channel spectra from samples containing up to 8 elements and 55 user-defined layers. The program is intended to meet the needs of analyses in materials sciences, such as metallurgy, where more than a few elements may be present, where several elements may be near each other in the periodic table, and where relatively deep structure may be important. These conditions preclude the use of completely automatic procedures for obtaining the sample composition directly from the scattered ion spectrum. Therefore, efficient methods are needed for entering and editing large amounts of composition data, with many iterations and with much feedback of information from the computer to the user. The internal video screen is used exclusively for verbal and numeric communications between user and computer. The composition matrix is edited on screen with a two-dimension forms-fill-in text editor and with many automatic procedures, such as doubling the number of layers with appropriate interpolations and extrapolations. The control center of the program is a bank of 10 keys that initiate on-event branching of program flow. The experimental and calculated spectra, including those of individual elements if desired, are displayed on an external color monitor, with an optional inset plot of the depth concentration profiles of the elements in the sample.
Attenuation of Scattered Thermal Energy Atomic Oxygen
NASA Technical Reports Server (NTRS)
Banks, Bruce A.; Seroka, Katelyn T.; McPhate, Jason B.; Miller, Sharon K.
2011-01-01
The attenuation of scattered thermal energy atomic oxygen is relevant to the potential damage that can occur within a spacecraft which sweeps through atomic oxygen in low Earth orbit (LEO). Although there can be significant oxidation and resulting degradation of polymers and some metals on the external surfaces of spacecraft, there are often openings on a spacecraft such as telescope apertures, vents, and microwave cavities that can allow atomic oxygen to enter and scatter internally to the spacecraft. Atomic oxygen that enters a spacecraft can thermally accommodate and scatter to ultimately react or recombine on surfaces. The atomic oxygen that does enter a spacecraft can be scavenged by use of high erosion yield polymers to reduce its reaction on critical surfaces and materials. Polyoxymethylene and polyethylene can be used as effective atomic oxygen scavenging polymers.
Electronic structure of helium atom in a quantum dot
Saha, Jayanta K; Mukherjee, T K
2015-01-01
Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) [n = 1-6] states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns [n = 2-5] and 2pnp [n = 2-5] configuration of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential representing the quantum dot. It has been explicitly demonstrated that electronic structure properties become a sensitive function of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the wi...
Study of Injection of Helium into Supersonic Air Flow Using Rayleigh Scattering
NASA Technical Reports Server (NTRS)
Seaholtz, Richard G.; Buggele, Alvin E.
1997-01-01
A study of the transverse injection of helium into a Mach 3 crossflow is presented. Filtered Rayleigh scattering is used to measure penetration and helium mole fraction in the mixing region. The method is based on planar molecular Rayleigh scattering using an injection-seeded, frequency-doubled ND:YAG pulsed laser and a cooled CCD camera. The scattered light is filtered with an iodine absorption cell to suppress stray laser light. Preliminary data are presented for helium mole fraction and penetration. Flow visualization images obtained with a shadowgraph and wall static pressure data in the vicinity of the injection are also presented.
Magee, Joseph W.
Publisher's Note: "Accurate Atomic Transition Probabilities for Hydrogen, Helium, and Lithium" J doi:10.1063/1.3254213 Key words: allowed and forbidden transitions; atomic transition probabilities; f values; helium; hydrogen; line strengths; lithium; oscillator strengths. This article was originally
Symmetric And Non-Symmetric Muonic Helium Atoms Studies
Mohammadi, S.
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
Dynamic polarizabilities of rare-earth-metal atoms and dispersion coefficients; published 29 March 2007 The dynamic scalar and tensor polarizabilities of the rare-earth-metal atoms coefficients for the interactions of the rare-earth-metal atoms with helium atoms. The static polarizabilities
Paris-Sud XI, Université de
INFLUENCE OF NITROGEN IMPURITIES ON AN ELECTRON-EXCITED HELIUM ATOM CONCENTRATION IN THE SELF at atmospheric pressure was studied. The concentrations of the low-excited helium atoms in states 21 s, 21 p, 23 of concentration of the low-excited helium atoms in cathode region even at nitrogen admixture of 0.5 % is occurred
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.
Microwave multiphoton ionization and excitation of helium Rydberg atoms
van de Water, W. (Physics Department, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (The Netherlands)); Yoakum, S. (Department of Physics, State University of New York at Stony Brook, Stony Brook, NY (USA)); van Leeuwen, T. (Physics Department, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (The Netherlands)); Sauer, B.E.; Moorman, L. (Department of Physics, State University of New York at Stony Brook, Stony Brook, NY (USA)); Galvez, E.J. (Department of Physics and Astronomy, Colgate University, Hamilton, NY (USA)); Mariani, D.R. (Schlumberger-Doll Research, Ridgefield, CT (USA)); Koch, P.M. (Department of Physics, State University of New York at Stony Brook, Stony Brook, NY (USA))
1990-07-01
We study experimentally and theoretically the detailed field-amplitude dependence of the multiphoton ionization and excitation probability of highly excited {ital n}{sub 0} {sup 3}{ital S} helium atoms in a 9.924-GHz linearly polarized microwave electric field. For ionization, with principal quantum numbers in the range {ital n}{sub 0}=25--32, we use a quasistatic analysis that employs integration of the time-dependent Schroedinger equation using basis states of the static field Hamiltonian. The calculated results are used to interpret the observed ionization threshold structure. For excitation, the results of {ital n}{sub 0} {sup 3}{ital S}{r arrow}{ital n}{sub 0} {sup 3}{ital L}, L{gt}2 excitation experiments are explained quantitatively and precisely using a theory of multiphoton resonances. We present maps of quasienergy levels that allow the study of the dynamics of the field-switching transients. These transient effects are analyzed along the lines of standard atomic collision theory and are shown to determine the shape of the observed resonances.
Topics in photon-atom scattering
Jonathan Paul Carney
1999-01-01
We make advances in predictions of both elastic (Rayleigh) and inelastic (Raman and Compton) scattering of x rays and gamma rays from atomic targets, including excited atoms, considering photon-polarization phenomena as well as the unpolarized cross sections. The availability of third-generation synchrotron sources permits precision measurements at the level of 1% or better. Current methods of calculation are insufficient, since
Positronium formation for positron scattering from helium ion
NASA Astrophysics Data System (ADS)
Zhi Zhang, Yong; Yu, Rong Mei; Xia Li, Shu; Song, Xiu Dan; Jiao, Li Guang
2015-09-01
Positronium (Ps) formation processes from helium ions by positron impact are studied using the two-channel two-center eikonal final state–continuum initial distorted wave method. The Ps(n = 1 and 2) and total Ps formation cross sections are calculated from the threshold to the high energy region, and the results are compared with other theoretical calculations available in the literature. It is found that the present results agree reasonably well with the close-coupling calculations, while other predictions, such as the Coulomb–Born approximation, the optical potential method, and the recent classical trajectory Monte Carlo method (Naginey 2014 Phys. Rev. A 89, 062704), are all much higher in the entire energy region. The maximum positions of the Ps(n) formation cross sections in our present work are in good agreement with the wave vector matching model of (Charlton 2014 J. Phys. B: At. Mol. Opt. Phys. 39, 4575). Finally, we discuss the scaling law of the Ps(n) formation cross sections with respect to the principal quantum number n of the Ps atom.
Method and means for helium/hydrogen ratio measurement by alpha scattering
NASA Technical Reports Server (NTRS)
Whitehead, A. B.; Tombrello, T. A. (inventors)
1980-01-01
An apparatus for determining helium to hydrogen ratios in a gaseous sample is presented. The sample is bombarded with alpha particles created by a self contained radioactive source and scattering products falling within a predetermined forward scattering angular range impact a detector assembly. Two detectors are mounted in tandem, the first completely blocking the second with respect to incident scattering products. Alpha particle/hydrogen or alpha particle/helium collisions are identified by whether scattering product impacts occur simultaneously in both detectors or only in the first detector. Relative magnitudes of the two pulses can be used to further discriminate against other effects such as noise and cosmic ray events.
Atomic analysis of the (n; t)-reaction of the helium-3 atoms with slow neutrons
NASA Astrophysics Data System (ADS)
Frolov, Alexei M.; Wardlaw, David M.
2011-05-01
Probabilities of formation of various hydrogenic species during the exothermic nuclear (n, 3He; t, p)-reaction of atomic helium-3 with slow neutrons are determined. In particular, we have found that the probability of forming the tritium atom 3H in its ground state is ?55.192 87 %, while the analogous probability of forming the protium atom 1H in its ground state is ?1.023 63%. Analogous probabilities of formation of the negatively charged hydrogen ions, i.e. the 3H- and 1H- ions, in the nuclear (n, 3He; t, p)-reaction with slow neutrons are ?7.8680% and ?0.065 83%, respectively. We also consider bremsstrahlung from fast fission-type reactions in atomic systems. The spectrum of emitted radiation is analysed.
Atomic analysis of the $(n;t)-$reaction of the helium-3 atoms with slow neutrons
Frolov, Alexei M
2011-01-01
Probabilities to form various hydrogen species during the exothermic nuclear $(n,{}^3$He$;t,p)-$reaction of atomic helium with slow neutrons are determined. In particular, we have found that the probability to form the tritium atom ${}^3$H in its ground state is $\\approx$ 55.19287 %, while analogous probability to form the protium atom ${}^1$H is $\\approx$ 1.02363 %. Analogous probabilities for the negatively charged hydrogen ions, i.e. for the ${}^3$H$^{-}$ and ${}^1$H$^{-}$ ions to be formed in the nuclear $(n,{}^3$He$; t,p)-$reaction with slow neutrons, are $\\approx$ 7.8680 % and $\\approx$ 0.06583 %, respectively. We also consider bremsstrahlung from fast fission-type reactions in atomic systems. The spectrum of emitted radiation is analyzed.
Importance of considering helium excited states in He+ scattering by an aluminum surface
NASA Astrophysics Data System (ADS)
Iglesias-García, A.; García, 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.
Rearrangement and annihilation in antihydrogen-atom scattering
Jonsell, Svante [Department of Physics, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom)
2008-08-08
I review some results for annihilation and rearrangement processes in low-energy antihydrogen-hydrogen and antihydrogen-helium scattering. For the strong nuclear force results using a {delta}-function potential are compared to a scattering length approach. It is found that the {delta}-function potential does not give correct annihilation cross sections in the case of antihydrogen-helium scattering. Problem associated with the use of the Born-Oppenheimer approximation for rearrangement calculations are reviewed.
Formation of long-lived gas-phase antiprotonic helium atoms and quenching by H2
T. Yamazaki; E. Widmann; R. S. Hayano; M. Iwasaki; S. N. Nakamura; K. Shigaki; F. J. Hartmann; H. Daniel; T. von Egidy; P. Hofmann; Y.-S. Kim; J. Eades
1993-01-01
IN 1964 Condo1 suggested that the decay characteristics of negative (pi- and K-) mesons in helium bubble chambers could be explained by the capture of these particles in large-angular-momentum meta-stable orbitals of exotic helium atoms. Russell2 predicted that similar \\
Classical limit states of the helium atom J. A. West,1,2
Stroud Jr., Carlos R.
Classical limit states of the helium atom J. A. West,1,2 Z. D. Gaeta,1,3 and C. R. Stroud, Jr.1,2 1 wave packets are used to explore the classical limit states of helium. A class of shape-preserving orbits is studied under the classical adiabatic approximation that separates the dynamics of the two
Inelastic scattering in atomic wires
NASA Astrophysics Data System (ADS)
Agrait, Nicolas; Untiedt, Carlos; Rubio-Bollinger, Gabino; Vieira, Sebastian
2001-03-01
Using a low-temperature STM, we fabricate stable freely suspended atomic wires up to 7 atoms in length[1], and show that the voltage dependence of their conductance reveals inelastic backscattering of electrons with phonons within the atomic wire. In the longer wires, backscattering takes place mostly with one phonon as expected for one-dimensional wires. Applying stress to the atomic wire we observe phonon softening and a strong increase in the backscattering rate, showing an enhancement of the electron-phonon interaction in the wire. [1] A.I. Yanson, G. Rubio Bollinger, H.E. van den Brom, N. Agrait and J.M. van Ruitenbeek, Nature 395, 783(1998).
Atomic-scale Mechanisms of Helium Bubble hardening in Iron
Osetskiy, Yury N.; Stoller, Roger E.
2015-06-03
Generation of helium due to (n, ) transmutation reactions changes the response of structural materials to neutron irradiation. The whole process of radiation damage evolution is affected by He accumulation and leads to significant changes in the material s properties. A population of nanometric He-filled bubbles affects mechanical properties and the impact can be quite significant because of their high density. Understanding how these basic mechanisms affect mechanical properties is necessary for predicting radiation effects. In this paper we present an extensive study of the interactions between a moving edge dislocation and bubbles using atomic-scale modeling. We focus on themore »effect of He bubble size and He concentration inside bubbles. We found that ability of bubbles to act as an obstacle to dislocation motion is close to that of voids when the He-to-vacancy ratio is in the range from 0 to 1. A few simulations made at higher He contents demonstrated that the interaction mechanism is changed for over-pressurized bubbles and they become weaker obstacles. The results are discussed in light of post-irradiation materials testing.« less
Atomic-scale Mechanisms of Helium Bubble hardening in Iron
Osetskiy, Yury N; Stoller, Roger E
2015-01-01
Generation of helium due to (n, ) transmutation reactions changes the response of structural materials to neutron irradiation. The whole process of radiation damage evolution is affected by He accumulation and leads to significant changes in the material s properties. A population of nanometric He-filled bubbles affects mechanical properties and the impact can be quite significant because of their high density. Understanding how these basic mechanisms affect mechanical properties is necessary for predicting radiation effects. In this paper we present an extensive study of the interactions between a moving edge dislocation and bubbles using atomic-scale modeling. We focus on the effect of He bubble size and He concentration inside bubbles. We found that ability of bubbles to act as an obstacle to dislocation motion is close to that of voids when the He-to-vacancy ratio is in the range from 0 to 1. A few simulations made at higher He contents demonstrated that the interaction mechanism is changed for over-pressurized bubbles and they become weaker obstacles. The results are discussed in light of post-irradiation materials testing.
Measurement of the Wigner function of an ensemble of helium atoms
Ch. Kurtsiefer; T. Pfau; J. Mlynek
1997-01-01
Beams of atoms can exhibit interference and diffraction phenomena just like waves of light. For a coherent beam of helium atoms in a double-slit experiment, measurements of the quantum-mechanical analogue of the classical phase-space distribution function show that the motion of atoms behaves in a strongly non-classical manner.
High harmonic generation in hydrogen and helium atoms subject to one{ and two{color laser pulses
Gross, E.K.U.
High harmonic generation in hydrogen and helium atoms subject to one{ and two{color laser pulses Surzburg Germany Abstract. We present simulations of harmonic generation in hydrogen and helium solving for the helium atom. #12; 2. Numerical procedure To study the process of high harmonic generation in hydrogen we
Scattering of twisted relativistic electrons by atoms
Serbo, V; Fritzsche, S; Seipt, D; Surzhykov, A
2015-01-01
The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 keV to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about, both the trans...
First Observation of the Ground-State Hyperfine-Structure Resonance of the Muonic Helium Atom
H. Orth; K.-P. Arnold; P. O. Egan; M. Gladisch; W. Jacobs; J. Vetter; W. Wahl; M. Wigand; V. W. Hughes; G. Zu Putlitz
1980-01-01
The first measurement of the hfs interval Deltanu for the muonic helium atom (4He++mu-e-)0 is reported. In terms of its electronic structure, it is a heavy isotope of hydrogen. Polarized atoms are formed by stopping polarized negative muons in a helium-gas target at 19.4 atm with a 1.5% admixture of Xe. The ground-state hfs splitting Deltanu was measured through observation
NASA Technical Reports Server (NTRS)
Huang, K.-N.
1977-01-01
A computational procedure for calculating correlated wave functions is proposed for three-particle systems interacting through Coulomb forces. Calculations are carried out for the muonic helium atom. Variational wave functions which explicitly contain interparticle coordinates are presented for the ground and excited states. General Hylleraas-type trial functions are used as the basis for the correlated wave functions. Excited-state energies of the muonic helium atom computed from 1- and 35-term wave functions are listed for four states.
First observation of laser-induced resonant annihilation in metastable antiprotonic helium atoms
N. Morita; M. Kumakura; T. Yamazaki; E. Widmann; H. Masuda; I. Sugai; R. S. Hayano; F. E. Maas; H. A. Torii; F. J. Hartmann; H. Daniel; T. von Egidy; B. Ketzer; W. Mueller; W. Schmid; D. Horváth; J. Eades
1994-01-01
We have observed the first laser-induced resonant transitions in antiprotonic helium atoms. These occur between metastable states and Auger dominated short lived states, and show that the anomalous longevity of antiprotons previously observed in helium media results from the formation of high-n high-l atomic states of p¯He+. The observed transition with vacuum wavelength 597.259+\\/-0.002 nm is tentatively assigned to (n,l)=(39,35)-->(38,34).
Semiempirical potentials for positron scattering by atoms
Assafrao, Denise; Walters, H. R. J.; Arretche, Felipe; Dutra, Adriano; Mohallem, J. R. [Departamento de Fisica, Universidade Federal do Espirito Santo, 29075-910, Vitoria, ES (Brazil); Department of Applied Mathematics and Theoretical Physics, Queen's University, Belfast, BT7 1NN (United Kingdom); Departamento de Fisica, Universidade do Estado de Santa Catarina, 89223-100, Joinville, SC (Brazil); Laboratorio de Atomos e Moleculas Especiais, Departamento de Fisica, ICEx, Universidade Federal de Minas Gerais, PO Box 702, 30123-970, Belo Horizonte, MG (Brazil)
2011-08-15
We report calculations of differential and integral cross sections for positron scattering by noble gas and alkaline-earth atoms within the same methodology. The scattering potentials are constructed by scaling adiabatic potentials so that their minima coincide with the covalent radii of the target atoms. Elastic differential and integral cross sections are calculated for Ne, Ar, Be, and Mg, and the results are very close to experimental and best theoretical data. Particularly, elastic differential cross sections for Be and Mg at low energies are reported.
Efficient atomization of cesium metal in solid helium by low energy (10 $?$J) femtosecond pulses
Mathieu Melich; Jacques Dupont-Roc; Philippe Jacquier
2009-08-27
Metal atoms in solid and liquid helium-4 have attracted some interest either as a way to keep the atoms in a weakly perturbing matrix, or using them as a probe for the helium host medium. Laser sputtering with nanosecond pulsed lasers is the most often used method for atom production, resulting however in a substantial perturbation of the matrix. We show that a much weaker perturbation can be obtained by using femtosecond laser pulses with energy as low as 10 $\\mu$J. As an unexpected benefit, the atomic density produced is much higher.
The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows
NASA Technical Reports Server (NTRS)
Hoppe, J. C.; Honaker, W. C.
1979-01-01
Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.
NASA Astrophysics Data System (ADS)
Ajana, I.; Makhoute, A.; Khalil, D.; Chaddou, S.
2015-04-01
The triple differential cross section for laser-assisted ionization of a helium target by slow electrons is analyzed within the framework of the second Born approximation. We evaluate the S -matrix elements using Volkov and Coulomb-Volkov wave functions for describing the continuum states of the scattered and the ejected electrons, respectively. The required scattering amplitudes are performed by expanding the atomic wave functions onto a complex-scaled Sturmian basis, which allows us to exactly take into account the contribution of the continuous spectrum to the dressing of the atomic states. Our results have been improved by taking into account exchange effects. Furthermore, the second-order Born correction is seen to be important and significantly affects the magnitudes of the binary and recoil peaks.
NASA Astrophysics Data System (ADS)
Henson, B. M.; Khakimov, R. I.; Dall, R. G.; Baldwin, K. G. H.; Tang, Li-Yan; Truscott, A. G.
2015-07-01
We present the first measurement for helium atoms of the tune-out wavelength at which the atomic polarizability vanishes. We utilize a novel, highly sensitive technique for precisely measuring the effect of variations in the trapping potential of confined metastable (2 3S1) helium atoms illuminated by a perturbing laser light field. The measured tune-out wavelength of 413.0938 (9stat)(2 0syst) nm compares well with the value predicted by a theoretical calculation [413.02(9) nm] which is sensitive to finite nuclear mass, relativistic, and quantum electrodynamic effects. This provides motivation for more detailed theoretical investigations to test quantum electrodynamics.
Henson, B M; Khakimov, R I; Dall, R G; Baldwin, K G H; Tang, Li-Yan; Truscott, A G
2015-07-24
We present the first measurement for helium atoms of the tune-out wavelength at which the atomic polarizability vanishes. We utilize a novel, highly sensitive technique for precisely measuring the effect of variations in the trapping potential of confined metastable (2^{3}S_{1}) helium atoms illuminated by a perturbing laser light field. The measured tune-out wavelength of 413.0938(9_{stat})(20_{syst})??nm compares well with the value predicted by a theoretical calculation [413.02(9) nm] which is sensitive to finite nuclear mass, relativistic, and quantum electrodynamic effects. This provides motivation for more detailed theoretical investigations to test quantum electrodynamics. PMID:26252681
Rayleigh Scattering at Atoms with Dynamical Nuclei
J. Froehlich; M. Griesemer; B. Schlein
2005-09-05
Scattering of photons at an atom with a dynamical nucleus is studied on the subspace of states of the system with a total energy below the threshold for ionization of the atom (Rayleigh scattering). The kinematics of the electron and the nucleus is chosen to be non-relativistic, and their spins are neglected. In a simplified model of a hydrogen atom or a one-electron ion interacting with the quantized radiation field in which the helicity of photons is neglected and the interactions between photons and the electron and nucleus are turned off at very high photon energies and at photon energies below an arbitrarily small, but fixed energy (infrared cutoff), asymptotic completeness of Rayleigh scattering is established rigorously. On the way towards proving this result, it is shown that, after coupling the electron and the nucleus to the photons, the atom still has a stable ground state, provided its center of mass velocity is smaller than the velocity of light; but its excited states are turned into resonances. The proof of asymptotic completeness then follows from extensions of a positive commutator method and of propagation estimates for the atom and the photons developed in previous papers. The methods developed in this paper can be extended to more realistic models. It is, however, not known, at present, how to remove the infrared cutoff.
Scattering of twisted relativistic electrons by atoms
V. Serbo; I. P. Ivanov; S. Fritzsche; D. Seipt; A. Surzhykov
2015-05-11
The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 keV to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about, both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams.
Scattering of twisted relativistic electrons by atoms
NASA Astrophysics Data System (ADS)
Serbo, V.; Ivanov, I. P.; Fritzsche, S.; Seipt, D.; Surzhykov, A.
2015-07-01
The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams.
Coupled-channel analysis of collisional effects on HFS transitions in antiprotonic helium atoms
G Ya Korenman; S. N. Yudin
2006-01-01
Collisions of metastable antiprotonic helium with atoms of a medium induce transitions between hyperfine structure sublevels as well as shifts and broadenings of the microwave M1 spectral lines. We consider these phenomena in the framework of a model with scalar and tensor interactions between and He atoms. S-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels (F =
The Computation of Wave Functions in Momentum Space - I: The Helium Atom
R. McWeeny; C. A. Coulson
1949-01-01
The possibilities of obtaining precise momentum wave functions for atoms by direct solution of the wave equation in momentum space are examined in some detail. An iterative method of approximating to the wave function is employed in computing the momentum distribution function for the helium atom. Although in this instance considerable accuracy is achieved, formidable difficulties arise in extending the
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.
Electrons above a Helium Surface and the One-Dimensional Rydberg Atom
Michael Martin Nieto
1999-11-17
Isolated electrons resting above a helium surface are predicted to have a bound spectrum corresponding to a one-dimensional hydrogen atom. But in fact, the observed spectrum is closer to that of a quantum-defect atom. Such a model is discussed and solved in analytic closed form.
A novel spacetime concept for describing electronic motion within a helium atom
Xu, Kunming
2006-01-01
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 orthogonal, symmetric and complementary quantities under the atomic spacetime. Electronic motion observed the rule of differential and integral operations that were implemented by dynamic trigonometric functions. It is demonstrated that the atomic spacetime is not a linear vector space with Newtonian time, and within which calculus has non-classical definition, and complex wave functions have fresh physical significances. This alternative approach is original, informative and refreshing but still compatible with quantum mechanics in the formulation. The description of electronic resonance in helium is also comparable with classical mechani...
Chy 475 Spring 2013 Estimating the energy of the Helium atom Dr. F. Amar Page 1 of 3
Amar, François G.
Chy 475 Spring 2013 Estimating the energy of the Helium atom Dr. F. Amar Page 1 of 3 Recall;Chy 475 Spring 2013 Estimating the energy of the Helium atom Dr. F. Amar Page 2 of 3 E(1) = (0)H(1 the energy of the Helium atom Dr. F. Amar Page 3 of 3 d) Finally where does Zeff come in? If we think about
Atom scattering from surface Einstein modes
Manson, J.R.
1988-04-15
We consider the scattering of thermal-energy atoms by a surface with a dilute coverage of adsorbates having a dispersionless Einstein vibrational mode. We show that the diffuse elastic scattered intensity has a Debye-Waller-type thermal attenuation only at low temperatures, and at large temperatures the attenuation saturates to a much weaker form. Similar thermal attenuation behavior occurs for the diffuse inelastic intensities. For an ordered adsorbate layer there is also a diffuse elastic intensity which increases with temperature at small temperatures.
a Theoretical Investigation of Doubly Excited States of the Helium Atom.
NASA Astrophysics Data System (ADS)
Cordes, Dietmar
The purpose of the present research is to develop a new method for applying hyperspherical coordinates, without the adiabatic hypothesis, in a variational basis consisting of Sturmian functions in the hyperradius R, Legendre polynomials in the angle separation Theta _{12}, and problem optimized functions in the pseudoangle alpha, in order to describe the characteristics of doubly excited states of the helium atom. In order to first gain insight into the suitability of our basis we have calculated energy values for the ground and three lowest excited singlet S states of helium. Plots of the deviation of our wave function from the true solution of the Schrodinger equation, (H - E)Phi(R,alpha,Theta _{12}), versus R and alpha are presented. We then applied a scattering variational principle to extract information on low lying doubly excited S states in helium converging to the n = 2 hydrogenic threshold of the residual ion. The resonances are described by our proposed basis of square integrable functions in hyperspherical coordinates. The continuum is treated by using positive-energy Coulomb functions on the energy shell. We present positions and widths of the lowest lying singlet and triplet S resonances along with their oscillator strengths to singlet and triplet P states ((1snp), n = 2,3,4). The background differential oscillator strength from the P states to the S continuum is also found and is very small. Computed branching ratios of nonradiative versus radiative transitions for these states indicate which state might be seen as a satellite line in an ion-atom collision experiment. Finally, we present a new theory for autoionizing states which are coupled to multiple continua via the concept of multi-channel configuration interaction in the continuum. The method is applied to the calculation of the partial cross sections for photoionization from the excited (1s 2p)^1P state in the vicinity of the (3,3a) ^1S and (3,3b) ^1S resonances, where the residual He^ {+} ion can be left in the 1s , 2s or 2p state. Results indicate a large probability of autoionization of the (3,3 a) ^1S state into the (1sks)^1S channel, whereas in the theoretical investigation of Ramaker and Schrader, which is the only existing reference, the (2 sks)^1S channel is preferred.
Discrete Self-Similarity Between RR Lyrae Stars And Singly-Excited Helium Atoms
R. L. Oldershaw
2008-03-29
Classical variable stars called RR Lyrae stars have pulsating outer envelopes comprised of excited atoms. Here we demonstrate that the qualitative and quantitative properties of RR Lyrae variables and one subclass of their atomic scale constituents: singly-excited helium atoms undergoing transitions between Rydberg states, share a remarkable degree of self-similarity. In terms of masses, radii, oscillation periods, morphologies and kinematics the stellar and atomic analogues obey a simple set of discrete self-similar scaling equations. The concept of stellar/atomic self-similarity may prove useful in the search for a deeper understanding of both stellar and atomic systems.
Collisional lasing on a self-terminating transition of a helium atom
Bel'skaya, E V; Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)
2011-01-24
Laser on a self-contained transition of a helium atom is studied under excitation of the helium mixture with molecular gases by single long-duration (up to 700ns) or double nanosecond pulses. In He - H{sub 2}O and He - NH{sub 3} mixtures, no limitations were found on the pulse repetition rate and the laser pulse duration obtained was equal to that of the pump pulse. (lasers and amplifiers)
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.
ERIC Educational Resources Information Center
Deeney, F. A.; O'Leary, J. P.
2012-01-01
For helium and helium-like ions, we have examined the differences between the values of the ionization energies as calculated from the Bohr theory and those measured in experiments. We find that these differences vary linearly with the atomic number of the system. Using this result, we show how the Bohr model for single-electron systems may be…
Allowed and forbidden transitions in artificial hydrogen and helium atoms
Toshimasa Fujisawa; David Guy Austing; Yasuhiro Tokura; Yoshiro Hirayama; Seigo Tarucha
2002-01-01
The strength of radiative transitions in atoms is governed by selection rules that depend on the occupation of atomic orbitals with electrons. Experiments have shown similar electron occupation of the quantized energy levels in semiconductor quantum dots-often described as artificial atoms. But unlike real atoms, the confinement potential of quantum dots is anisotropic, and the electrons can easily couple with
Benedek, G; Echenique, P M; Toennies, J P; Traeger, F
2010-08-01
Under special kinematic conditions helium atoms impinging upon a crystal surface can be inelastically trapped into a surface bound state and ride the created Rayleigh wave. This special case of phonon-assisted selective adsorption, leading to an atom-phonon bound state (atomic polaron), can explain previously unassigned resonant features observed in published helium atom scattering distributions. PMID:21399348
Excitation of metastable argon and helium atoms by electron impact
NASA Technical Reports Server (NTRS)
Borst, W. L.
1974-01-01
Using a time-of-flight method, the excitation of argon and helium metastables by electron impact is investigated in the energy range from threshold to about 50 eV. The secondary-electron yields of the metastable detector used are reviewed in detail. The effect of metastable recoil is also discussed. Comparisons with data from other investigators are presented.
MISSE Scattered Atomic Oxygen Characterization Experiment
NASA Technical Reports Server (NTRS)
Banks, Bruce A.; deGroh, Kim K.; Miller, Sharon K.
2006-01-01
An experiment designed to measure the atomic oxygen (AO) erosion profile of scattered AO was exposed to Low Earth Orbital (LEO) AO for almost four years as part of the Materials International Space Station Experiment 1 and 2 (MISSE 1 and 2). The experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), Tray 1, attached to the exterior of the International Space Station (ISS) Quest Airlock. The experiment consisted of an aperture disk lid of Kapton H (DuPont) polyimide coated on the space exposed surface with a thin AO durable silicon dioxide film. The aperture lid had a small hole in its center to allow AO to enter into a chamber and impact a base disk of aluminum. The AO that scattered from the aluminum base could react with the under side of the aperture lid which was coated sporadically with microscopic sodium chloride particles. Scattered AO erosion can occur to materials within a spacecraft that are protected from direct AO attack but because of apertures in the spacecraft the AO can attack the interior materials after scattering. The erosion of the underside of the Kapton lid was sufficient to be able to use profilometry to measure the height of the buttes that remained after washing off the salt particles. The erosion pattern indicated that peak flux of scattered AO occurred at and angle of approximately 45 from the incoming normal incidence on the aluminum base unlike the erosion pattern predicted for scattering based on Monte Carlo computational predictions for AO scattering from Kapton H polyimide. The effective erosion yield for the scattered AO was found to be a factor of 0.214 of that for direct impingement on Kapton H polyimide.
NASA Astrophysics Data System (ADS)
Li, Mubing; Manson, Joseph R.; Graham, Andrew P.
1999-11-01
Atom-surface scattering and He atom scattering in particular have proven to be useful tools in investigating the properties of surface adsorbates. Inelastic scattering of He atoms is uniquely sensitive to the low energy vibrational modes of surface adsorbates. In many cases one or more of the low energy adsorbate modes appears as a dispersionless Einstein mode which produces a very characteristic series of multiquantum overtone peaks in the inelastic scattering intensity for fixed incident beam and detector positions. The probabilities of multiple excitation (multiphonon excitation) of decoupled oscillating adsorbates on a surface due to impact by an atom or molecule are developed using a theory based on the generalized temperature-dependent Poisson distribution. Comparisons are made with helium scattering results for adsorbed carbon monoxide on metal substrates. Interestingly, the simplest form of the theory with no free parameters explains the number and relative intensities of the observed multiquantum overtone peaks. The inclusion of a scattering form factor based on the hard-core interaction potential between He and CO results in a relatively simple model which correctly predicts the angular dependence of the distribution of multiphonon excitations in addition to the variation with incident energy and adsorbate frequency. The model is used to calculate the excitation probabilities of other adsorbate vibrational modes which have not yet been observed using helium scattering. The model is also applied to the case of He atom scattering from monolayer coverages of metal substrates by heavier rare gases.
Three-body recombination in cold helium-helium-alkali-metal-atom collisions
Suno, Hiroya; Esry, B. D. [The Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001 (Japan); Department of Physics, Kansas State University, Manhattan, Kansas 66506 (United States)
2009-12-15
Three-body recombination in helium-helium-alkali-metal collisions at cold temperatures is studied using the adiabatic hyperspherical representation. The rates for the three-body recombination processes {sup 4}He+{sup 4}He+X->{sup 4}He+{sup 4}HeX and {sup 4}He+{sup 4}He+X->{sup 4}He{sub 2}+X, with X={sup 7}Li, {sup 23}Na, {sup 39}K, {sup 85}Rb, and {sup 133}Cs, are calculated at nonzero collision energies by including not only zero total angular momentum, J=0, states but also J>0 states. The three-body recombination rates show a relatively weak dependence on the alkali-metal species, differing from each other only by about one order of magnitude, except for the {sup 4}He-{sup 4}He-{sup 23}Na system.
Migration of helium atoms in copper at 25 K
Th. Wichert; M. Deicher; G. Grübel; E. Recknagel; W. Reiner
1985-01-01
Thy dynamics of He atoms, which were implanted into copper at 10 K, were observed via their trapping at 111In atoms, using the perturbed gammagamma angular correlation technique. During annealing in the temperature range 10 to 300 K, two types of In-He complexes were detected with the He atom occupying either a trapped single vacancy or an octahedral interstitial lattice
Interpretation of diffuse He-atom scattering from steps
Hinch, B.J.
1988-09-15
With the recent improvements in dynamic range of He-surface scattering experiments, the measurement of diffuse scattered intensity from surface defects: step edges or point defects: has become a frequently executable experiment. There remain, however, certain features in the experimental data that, to date, have not been fully explained. A calculational method applicable to the scattering from step edges is developed here, firstly to calculate the basic oscillatory form of the intensities, and then to look at the previously unexplained finer structure. In particular, the paper attempts to reproduce some experimental data; that is, helium-atom scattering from a randomly stepped Pt(111) crystal, in a fixed 90/sup 0/-angle geometry (see A. M. Lahee, J. R. Manson, J. P. Toennies, and Ch. Woell, Phys. Rev. Lett. 57, 471 (1986)). Even under a simple, hard-wall, eikonal approximation some of the previously unexplained features can be reproduced by the inclusion of a ''natural periodicity'' corrugation in the neighborhood of a step. This corrugation, with the periodicity of the lattice parameter, is allowed to decay away from the step. It is this decay length that is found to determine the characteristic width of the fine structure. The diffuse diffraction from a randomly stepped Pt(111), incidentally, now exhibits a certain degree of threefold symmetry. The enhanced corrugation amplitude in the neighborhood of a step is believed to be, of order at least, six times that observed on an unstepped Pt(111) surface. However, this enhancement factor is certainly very surface-orientation, and/or material, dependent.
Resonant two-photon ionization spectroscopy of Al atoms and dimers solvated in helium nanodroplets.
Krasnokutski, Serge A; Huisken, Friedrich
2015-02-28
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-He(n) 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 Al(n) photoion with n larger than two. PMID:25725735
NASA Technical Reports Server (NTRS)
Nickel, J. C.; Zetner, P. W.; Shen, G.; Trajmar, S.
1989-01-01
Procedures and calibration techniques for measuring the absolute elastic and inelastic differential cross sections (DCS) for electron impact on molecular (atomic) species are described and illustrated by examples. The elastic DCS for the molecule under study is first determined by calibration against helium using the relative flow technique. The second step involves the production of energy-loss spectra for the instrument response function, the unfolding of overlapping inelastic structures and the normalization of inelastic intensities to the elastic cross sections. It is concluded that this method of determining absolute differential electron-molecule (atom) scattering cross sections is generally applicable and provides reliable results.
Scattering of electrons from neon atoms
NASA Technical Reports Server (NTRS)
Dasgupta, A.; Bhatia, A. K.
1984-01-01
Scattering of electrons from neon atoms is investigated by the polarized-orbital method. The perturbed orbitals calculated with use of the Sternheimer approximation lead to the polarizability 2.803 a(0)-cube in fairly good agreement with the experimental value 2.66 a(0)-cube. Phase shifts for various partial waves are calculated in the exchange, exchange-adiabatic, and polarized-orbital approximations. They are compared with the previous results. The calculated elastic differential, total, and momentum-transfer cross sections are compared with the experimental results. The polarized-orbital approximation yields results which show general improvement over the exchange-adiabatic approximation.
Laser studies of the decay chain of metastable antiprotonic helium atoms
R. S. Hayano; F. E. Maas; H. A. Torii; N. Morita; M. Kumakura; T. Yamazaki; H. Masuda; I. Sugai; F. J. Hartmann; H. Daniel; T. von Egidy; B. Ketzer; W. Müller; W. Schmid; D. Horváth; John Eades; E. Widmann
1994-01-01
Laser studies of metastable antiprotonic helium atoms, which we recently initiated by observing a sharp increase of the antiproton annihilation rate induced by laser-stimulated resonant transitions, have been extended. With a single laser tuned to the resonance already found at 597.26 nm, we have now established the time dependence of the upper state population. With two lasers ignited at variable
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 ...
Helium AtomSCF-LCAO Calculation of the (1s)2 Ground State of the
NSDL National Science Digital Library
Using a double-zeta basis of Slater-type orbitals [STOs], this Java applet calculates the single determinant singlet ground state 1s2 wavefunction of the helium atom. The doubly occupied orbital is expanded in terms of two basis functions, 1s and 1s`.
Variational Calculation on the Helium Atom Using a Hydrogenic Trial Wave Function Frank Rioux
Rioux, Frank
Rioux Chemistry Department CSB|SJU Gaussian Trial Wave Function: r ,( ) 3 exp - rVariational Calculation on the Helium Atom Using a Hydrogenic Trial Wave Function Frank( ):= Demonstrate the wave function is normalized. 0 r r ,( )2 4 r 2 d assume 0>, simplify 1 The terms
Variational Calculation on the Helium Atom Using a Gaussian Trial Wave Function Frank Rioux
Chemistry Department CSB|SJU Gaussian Trial Wave Function: r ,( ) 2 3 4 exp - r 2Variational Calculation on the Helium Atom Using a Gaussian Trial Wave Function Frank Rioux ( ):= Demonstrate the wave function is normalized. 0 r r ,( )2 4 r 2 d assume 0>, simplify 1 The terms
Nobuhiro Yamanaka; Yasushi Kino; Hiroshi Kudo; Masayasu Kamimura
2001-01-01
We precisely calculate the fine and hyperfine structure splittings of the (v,J)=(1,35) state in the antiprotonic helium atom, where v is the vibrational quantum number and J is the total orbital angular momentum. The coupled rearrangement channel method is employed to efficiently describe correlation effects in the three-body system with atomic and molecular characters. An accuracy of better than alpha2~50
Density Measurement of Helium Metastable Atoms in a Plasma by the Laser-Induced Fluorescence Method
Kazuki Tsuchida
1984-01-01
Density profiles of helium metastable atoms in 23S and 21S levels have been measured in a plasma (ne˜ 1012 cm-3, Te˜ 7 eV, radius of the plasma column ˜ 1 cm) by the Laser-Induced Fluorescence Method (LIFM), where both quenching effects of fluorescence by plasma and characteristics of laser radiation are taken into account. The He(23S) metastable atoms are distributed
The hyperfine structure of the ground states in the helium muonic atoms
Alexei M. Frolov
2012-07-19
The hyperfine structures of the ground states in the ${}^{3}$He$^{2+} \\mu^{-} e^{-}$ and ${}^{4}$He$^{2+} \\mu^{-} e^{-}$ helium-muonic atoms are investigated with the use of highly accurate variational wave functions. The differences between corresponding levels of hyperfine structure (i.e. hyperfine splittings) are determined to very high numerical accuracy. In particular, we have found that the hyperfine structure splitting in the ground state of the ${}^{4}$He$^{2+} \\mu^{-} e^{-}$ atom is $\\Delta \
Elastic electron scattering by a Pb atom
NASA Astrophysics Data System (ADS)
Toši?, S. D.; Rabasovi?, M. S.; Ševi?, D.; Pej?ev, V.; Filipovi?, D. M.; Sharma, Lalita; Tripathi, A. N.; Srivastava, Rajesh; Marinkovi?, B. P.
2008-01-01
Differential (DCS), integral (QI) , momentum transfer (QM) , and viscosity (QV) cross sections are obtained both experimentally and theoretically for elastic electron scattering by lead atoms in the energy range from 10to100eV . The experiment is performed using an electron spectrometer with crossed electron and atom-beam arrangement. The relative DCS measurements are placed on an absolute scale using measured elastic-to-inelastic intensity ratios and the absolute DCS of the 6p7s P13 state [S. Milisavljevi?, M. S. Rabasovi?, D. Ševi?, V. Pej?ev, D. M. Filipovi?, L. Sharma, R. Srivastava, A. D. Stauffer, and B. P. Marinkovi?, Phys. Rev. A 76, 022714 (2007)] at a scattering angle of 10° for incident energies of 40, 60, 80, and 100eV and at 30° for 10 and 20eV . Corresponding theoretical results are obtained from a relativistic approach based on solving the Dirac equation using Hartree-Fock and Dirac-Fock wave functions to calculate cross sections at all the energies measured. Comparisons between the present experiment and theory, as well as comparisons with other available results, have been made.
de Aguiar, Marcus A. M.
1996-01-01
with the nucleus of the helium atom allows for the reduction to a one-dimensional Hamiltonian describing the frozen for classical motion of the helium atom. It is known that chaotic and regular motion coexist of the semiclassical limit of the quantum helium atom. In spite of the inherent difficulties the balance of electronic
Radial correlation limits of helium and heliumlike atoms
Toshikatsu Koga
1996-01-01
Radial correlation limits of two-electron atoms with atomic numbers Z=1-10 are calculated by using modified Kinoshita wave functions in which all the parameters are optimized. The optimal Kinoshita functions show a rapid energy convergence with the increasing number N of constituent terms, and the radial energies convergent to 10 significant figures are obtained. The results show that both the calculated
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 CERN’s antiproton decelerator facility. Its transition frequencies have recently been measured to nine digits of precision by laser spectroscopy. By comparing these experimental results with three-body QED calculations, the antiproton-to-electron massratio was determined as 1836.152674(5). This result contributed to the CODATA recommended values of the fundamental physical constants. PMID:20075605
Erge Edgu-Fry
2003-01-01
Single electron capture from atomic (and molecular) hydrogen by 0.32, 0.5 and 0.75 a.u. Ar8+ ions, and electron ejection from atomic hydrogen by 0.775, 1 and 1.415 a.u. protons and from helium by 0.895 to 2 a.u. protons were studied. Proton impact on helium experiments were done to close an existing energy gap studied in this system. Atomic hydrogen bombarded
NASA Astrophysics Data System (ADS)
T?kési, Károly; DuBois, Robert D.; Mukoyama, Takeshi
2014-09-01
The interaction between positronium and a helium atom is studied using the 5-body classical trajectory Monte Carlo method. We present the total cross sections for the dominant channels, namely for single ionization of the target, and ionization of the projectile, resulting from pure ionization and also from electron transfer (capture or loss) processes for 1-5.7 a.u. incident velocities of the positronium atom. Our results were compared with the calculated data using hydrogen projectiles having the same velocities as well as with the experimental data in collisions between H and He [R.D. DuBois, Á. Kövér, Phys. Rev. A 40, 3605 (1989)]. We analyze the similarities and deviations for ionization of helium atoms by positronium and hydrogen projectile impact. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.
Low-energy scattering of antihydrogen by helium and molecular hydrogen
Armour, E. A. G.; Todd, A. C.; Liu, Y.; Gregory, M. R. [School of Mathematical Sciences, Nottingham University, Nottingham NG7 2RD (United Kingdom); Jonsell, S. [Department of Physics, University of Wales Swansea, Swansea SA2 8PP (United Kingdom); Plummer, M. [CLRC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)
2008-08-08
In this paper, we describe in detail calculations that we have carried out of cross sections for rearrangement processes in very low-energy helium+antihydrogen (H-bar) scattering that result in He{sup +}p-bar+Ps or Hep-bar+e{sup +} or {alpha}p-bar+Ps{sup -}. The interaction between the leptons is taken into account very accurately. Results are presented for all three processes. A description is also given of a preliminary calculation of elastic and antiproton annihilation cross sections for very low-energy H{sub 2}+H-bar scattering.
Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel
NASA Astrophysics Data System (ADS)
Shirinzadeh, B.; Hillard, M. E.; Balla, R. J.; Waitz, I. A.; Anders, J. B.; Exton, R. J.
1992-10-01
Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters.
Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel.
Shirinzadeh, B; Hillard, M E; Balla, R J; Waitz, I A; Anders, J B; Exton, R J
1992-10-20
Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters. PMID:20733871
Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel
NASA Technical Reports Server (NTRS)
Shirinzadeh, B.; Hillard, M. E.; Balla, R. J.; Waitz, I. A.; Anders, J. B.; Exton, R. J.
1992-01-01
Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters.
Planar Rayleigh Scattering Results in Helium/Air Mixing Experiments in a Mach 6 Wind Tunnel
NASA Technical Reports Server (NTRS)
Shirinzadeh, B.; Balla, R. Jeffrey; Hillard, M. E.; Anders, J. B.; Exton, R. J.; Waitz, I. A.
1991-01-01
Planar Rayleigh scattering measurements using an ArF-excimer laser have been performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach 6facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross sectional area (5 cm by 10 cm) of the flow field in the absence of clusters.
An Instability in the Radiative Ionization of Atomic Hydrogen/Helium Gas
Ethan Bradford; Craig Hogan
1996-04-14
We show that the process of photoionizing a gas of atomic hydrogen and helium by line radiation whose energy is slightly above the helium single-ionization threshold is unstable if the helium fraction by number is less than approximately one half. However, in the two scenarios we consider here, based on the Decaying Dark Matter (DDM) model of cosmological reionization, there is no significant growth. In the first scenario we consider ionization and recombination to be approximately in equilibrium. This is relevant to high photon flux rates and early reionization, but in that case the heating is balanced by Compton cooling, which is very stabilizing. In the second scenario we ignore recombination. This is relevant to low photon flux rates or to the last stage of the reionization. In that case there is too little growth on a cosmological time scale to be significant.
A novel spacetime concept for describing electronic motion within a helium atom
Kunming Xu
2007-05-30
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 orthogonal, symmetric and complementary quantities under the atomic spacetime. Electronic motion observed the rule of differential and integral operations that were implemented by dynamic trigonometric functions. It is demonstrated that the atomic spacetime is not a linear vector space with Newtonian time, and within which calculus has non-classical definition, and complex wave functions have fresh physical significances. This alternative approach is original, informative and refreshing but still compatible with quantum mechanics in the formulation. The description of electronic resonance in helium is also comparable with classical mechanics such as an oscillating pendulum and with classical electromagnetism such as an LC oscillator. The study has effectively unified complex function, calculus, and trigonometry in mathematics, and provided a prospect for unifying particle physics with classical physics on the novel spacetime platform.
Rayleigh scattering from n =2 states of atomic hydrogen
Mihai Gavrila
1979-01-01
Exact analytic results are presented for the elastic scattering of photons from excited hydrogen atoms in then=2 states. The general form of the matrix elements required is inferred from previous work on the scattering by a completen=2 shell of a model atom, and is expressed in terms of one hypergeometric function of the Gauss type. The low-energy behavior of the
Rayleigh scattering from n=2 states of atomic hydrogen
Mihai Gavrila
1979-01-01
Exact analytic results are presented for the elastic scattering of photons from excited hydrogen atoms in the n=2 states. The general form of the matrix elements required is inferred from previous work on the scattering by a complete n=2 shell of a model atom, and is expressed in terms of one hypergeometric function of the Gauss type. The low-energy behavior
NASA Astrophysics Data System (ADS)
Nedanovska, E.; Nersisyan, G.; Morgan, T. J.; Hüwel, L.; Murakami, T.; Lewis, C. L. S.; Riley, D.; Graham, W. G.
2015-01-01
We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 ?s and 22.5 ?s after breakdown, the electron density decreases from 3.3 × 1017 cm-3 to 9 × 1013 cm-3, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 ?s reveal that during this time the laser induced plasma expands at a rate given by R ˜ t0.4 consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 ?s. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He2+ molecular ion play an important role.
Rydberg States of rb and cs Atoms on Helium Nanodroplets: a Rydberg-Ritz Analysis
NASA Astrophysics Data System (ADS)
Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.
2013-06-01
Rydberg series of Rb and Cs atoms on the surface of helium nanodroplets (He_{N}) have been studied by resonance enhanced multi-photon ionization spectroscopy and laser induced fluorescence spectroscopy. The recorded excitation spectra are analyzed by using a Rydberg-Ritz approach. The dependence of the quantum defects on the principal quantum number within a Rydberg series gives insight into the interaction between the alkali atom's valence electron and the superfluid helium droplet. For higher excited states a screening of the valence electron from the alkali atom core by the helium droplet is observed. For lower states the strength of the screening effect decreases and the quantum defects are found to lie closer to free atom values. In addition, the large spin-orbit (SO) constant of the Cs-He_{N} nP(^{2}?) states allows a detailed study of the influence of the helium droplet on the SO splitting as function of the principal quantum number. Within the pseudo-diatomic picture the alkali-He_{N} system represents a diatomic molecule. The coupling of the Cs valence electrons spin and the orbital angular momentum with the intermolecular axis, which is defined by the connection between the droplet center and the alkali nucleus, depends on the strength of the atomic SO interaction. While the splitting of the 6^{2}P_{1/2}(^{2}?_{1/2}) and 6^{2}P_{3/2}(^{2}?_{3/2}) components has an atom-like character (Hund's case (c) coupling), the SO splitting of higher n states is lower than the atomic value (Hund's case (a) coupling). C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) F. Lackner, G. Krois, M. Theisen, M. Koch, and W.E. Ernst, Phys. Chem. Chem. Phys., 13, 18781-18788 (2011) F. Lackner, G. Krois, and W.E. Ernst, J. Phys. Chem. Lett., 3, 1404-1408 (2012)
Johnson, Alexis M; Lancaster, Diane K; Faust, Jennifer A; Hahn, Christine; Reznickova, Anna; Nathanson, Gilbert M
2014-11-01
Atomic and molecular solutes evaporate and dissolve by traversing an atomically thin boundary separating liquid and gas. Most solutes spend only short times in this interfacial region, making them difficult to observe. Experiments that monitor the velocities of evaporating species, however, can capture their final interactions with surface solvent molecules. We find that polarizable gases such as N2 and Ar evaporate from protic and hydrocarbon liquids with Maxwell-Boltzmann speed distributions. Surprisingly, the weakly interacting helium atom emerges from these liquids at high kinetic energies, exceeding the expected energy of evaporation from salty water by 70%. This super-Maxwellian evaporation implies in reverse that He atoms preferentially dissolve when they strike the surface at high energies, as if ballistically penetrating into the solvent. The evaporation energies increase with solvent surface tension, suggesting that He atoms require extra kinetic energy to navigate increasingly tortuous paths between surface molecules. PMID:26278769
Exploiting Universality in Atoms with Large Scattering Lengths
Braaten, Eric
2012-05-31
The focus of this research project was atoms with scattering lengths that are large compared to the range of their interactions and which therefore exhibit universal behavior at sufficiently low energies. Recent dramatic advances in cooling atoms and in manipulating their scattering lengths have made this phenomenon of practical importance for controlling ultracold atoms and molecules. This research project was aimed at developing a systematically improvable method for calculating few-body observables for atoms with large scattering lengths starting from the universal results as a first approximation. Significant progress towards this goal was made during the five years of the project.
Atomic delay in helium, neon, argon and krypton
NASA Astrophysics Data System (ADS)
Palatchi, Caryn; Dahlström, 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. .
Threshold angular distributions of (e,2e) cross sections of helium atoms
J. Botero; J. H. Macek
1992-01-01
Cross sections for the electron-impact ionization of helium atoms in a coplanar symmetric geometry are computed by including in the Coulomb-Born approximation a normalization factor which approximately incorporates electron-electron interactions in the final-state wave function. This approximation yields excellent agreement with recent experimental observations at impact energies between 0.5 and 5 eV above the ionization threshold. It is shown that
Convergence properties of Fock's expansion for S-state eigenfunctions of the helium atom
John D. Morgan
1986-01-01
It is proved by functional analytic methods that for S-state solutions of Schrödinger's equation for the helium atom, Fock's expansion in powers of R1\\/2 and R ln R, where R is the hyperspherical radius r12+r22, converges pointwise for all R, thereby generalising a result of Macek that the expansion converges in the mean for all RE, Schrödinger's equation, considered as
Radiative Corrections to the Ground-State Energy of the Helium Atom
P. K. Kaibir; E. E. Salpeter
1957-01-01
The radiative corrections of relative order Z2alpha3 (absolute order Z4alpha3 ry), corresponding to the Lamb shift terms arising from the nuclear Coulomb potential, and some of the Zalpha3 corrections, arising from radiative interactions between the electrons, are calculated for the ground-state energy of the helium atom. The Z2alpha3 corrections are all calculated, but of the Zalpha3 corrections, which are expected
Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass
Masaki Hori; Anna Sótér; Vladimir I. Korobov
2014-04-30
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 these metastable states, to states with large ($\\sim 10^{11}$ s$^{-1}$) Auger rates. The $\\pi{\\rm He}^{2+}$ ion that remains after Auger emission of the $1s$ electron undergoes Stark mixing with the $s$, $p$, and $d$ states during collisions with the helium atoms in the experimental target. This leads to immediate nuclear absorption of the $\\pi^-$. The resonance condition between the laser beam and the atom is thus revealed as a sharp spike in the rates of neutrons, protons, deuterons, and tritons that emerge....(continued)
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.
Masili, Mauro; Starace, Anthony F. [Centro Universitario Central Paulista, UNICEP, Rua Miguel Petroni 5111, 13 563-470 Sa(tilde sign)o Carlos, Sa(tilde sign)o Paulo, (Brazil); Department of Physics and Astronomy, The University of Nebraska, 116 Brace Laboratory, Lincoln, Nebraska 68588-0111, USA (United States)
2003-07-01
We present a calculation of the static and dynamic dipole polarizability of the helium atom using a variationally stable treatment that incorporates the coupled-channel hyperspherical representation of the wave functions. Inclusion of logarithmic terms in intermediate functions as well as the effect of an optimization procedure for the variational parameter are analyzed. When available, our coupled-channel results are compared with other values in the literature.
Higher-Order Finite Difference Solutions of the Schro¨dinger Equation for the Helium Atom
C. G. Barraclough; J. R. Mooney
1971-01-01
Higher-order finite difference solutions of the Schro¨dinger equation for the helium atom have been obtained. For the S-limit equation the ground- and first-excited-state energy values were found. There was a substantial reduction in the difference error in comparison with the treatment of Winter, Diestler, and McKoy (1968). For the complete (nonrelativistic) Schro¨dinger equation for He finite difference expressions of error
Helium in chirped laser fields as a time-asymmetric atomic switch.
Kaprálová-Ž?ánská, Petra Ruth; Moiseyev, Nimrod
2014-07-01
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. PMID:25005289
NASA Astrophysics Data System (ADS)
M, Chabot; K, Béroff; T, Pino; G, Féraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier
2012-11-01
We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.
CASCADE CALCULATION OF EXOTIC HELIUM ATOMS -- s-orbit vs. p-orbit absorption rates
NASA Astrophysics Data System (ADS)
Koike, T.; Akaishi, Y.
2000-09-01
We construct a new model for the Stark-mixing process of exotic helium atoms using the impact-parameter method, and compared it with a phenomenological one used so far (sliding transition model). It turns out that the sliding transition model is justified only for low-n states and largely overestimates the Stark-mixing transition rate at high-n states. As a result of the atomic-cascade calculation, the s-(p-)orbit absorption rates in our new model are considerably smaller (larger) than those in the phenomenological one, although both our new model and old one well reproduce the experimental x-ray yields.
Dalkarov, O D
2015-01-01
A study of gravitational properties of matter presents a fundamental interest. The possibility of investigation of quantum gravitational states of matter by the example of helium atom is shown. The capability of the existence of helium quantum states in the gravitational field of a cold neutron star is examined. Observation of such states is done with the help of rotating neutron star's magnetic field. Periodically changing magnetic field induces transitions between gravitational states of helium atom and leads to the appearance of gravitational transitions' spectral lines in gigahertz frequency range.
Proposed method for laser spectroscopy of pionic helium atoms to determine the charged-pion mass
NASA Astrophysics Data System (ADS)
Hori, Masaki; Sótér, Anna; Korobov, Vladimir I.
2014-04-01
Metastable pionic helium (?He+) is a three-body atom composed of a helium nucleus, an electron occupying the 1s ground state, and a negatively charged pion ?- in a Rydberg state with principal and orbital angular momentum quantum numbers of n ˜?+1˜16. We calculate the spin-independent energies of the ?3He+ and ?4He+ isotopes in the region n =15-19. These include relativistic and quantum electrodynamics corrections of orders R??2 and R??3 in atomic units, where R? and ? denote the Rydberg and fine structure constants. The fine-structure splitting due to the coupling between the electron spin and the orbital angular momentum of the ?- and the radiative and Auger decay rates of the states are also calculated. Some states (n,?)=(16,15) and (17,16) retain nanosecond-scale lifetimes against ?- absorption into the helium nucleus. We propose the use of laser pulses to induce ?- transitions from these metastable states to states with large (˜1011 s-1) Auger rates. The ?He2+ ion that remains after Auger emission of the 1s electron undergoes Stark mixing with the s, p, and d states during collisions with the helium atoms in the experimental target. This leads to immediate nuclear absorption of the ? -. The resonance condition between the laser beam and the atom is thus revealed as a sharp spike in the rates of neutrons, protons, deuterons, and tritons that emerge. A resonance curve is obtained from which the ?He+ transition frequency can in principle be determined with a fractional precision of 10-8-10-6 provided the systematic uncertainties can be controlled. By comparing the measured ?He+ frequencies with the calculated values, the ?- mass may be determined with a similar precision. The ?He+ will be synthesized by allowing a high-intensity (>108 s-1) beam of ?-produced by a cyclotron to come to rest in a helium target. The precise time structure of the ?- beam is used to ensure a sufficient rate of coincidence between the resonant laser pulses and the ?He+ atoms.
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
Scattering of Cold-Atom Coherences by Hot Atoms: Frequency Shifts from Background-Gas Collisions
Gibble, Kurt
Scattering of Cold-Atom Coherences by Hot Atoms: Frequency Shifts from Background-Gas Collisions with room-temperature background gases that transfer momentum eject the cold atoms from the clock interactions produce the cold-atom background-gas shift. General considerations allow the loss of the Ramsey
Enhanced Raman scattering by spatially distributed atomic coherence
Chen, L. Q.; Zhang Guowan; Yuan Chunhua; Jing Jietai; Zhang Weiping [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Ou, Z. Y. [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Department of Physics, Indiana University-Purdue University Indianapolis, 402 N. Blackford Street, Indianapolis, Indiana 46202 (United States)
2009-07-27
We demonstrate experimentally an enhancement in Raman scattering in Rb atomic vapor due to the atomic coherence initially prepared by a weak write laser. We find that the enhanced Raman scattering depends on the spatial distribution of the atomic spin coherence and can be explained with a simple picture of three-wave mixing. This effect can in principle be used to have a light conversion efficiency near unity in Raman process. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy.
Multiple scattering of photons by atomic hyperfine multiplets
Mueller, Cord A. [Physikalisches Institut, Universitaet Bayreuth, D-95440 Bayreuth (Germany); Miniatura, Christian; Wilkowski, David; Kaiser, Robin [Institut Non Lineaire de Nice Sophia Antipolis, UMR 6618 du CNRS, 1361 route des Lucioles, F-06560 Valbonne (France); Delande, Dominique [Laboratoire Kastler Brossel, Universite Pierre et Marie Curie, 4 Place Jussieu, F-75005 Paris (France)
2005-11-15
Mesoscopic interference effects in multiple scattering of photons depend crucially on the internal structure of the scatterers. In the present paper, we develop the analytical theory of multiple photon scattering by cold atoms with arbitrary internal hyperfine multiplets. For a specific application, we calculate the enhancement factor of elastic coherent backscattering as a function of detuning from an entire hyperfine multiplet of neighboring resonances that cannot be considered isolated. Our theory permits one to understand why atoms behave differently from classical Rayleigh point-dipole scatterers, and how the classical description is recovered for larger but still microscopic objects like molecules or clusters.
Makoto Hamamoto; Mitsuo Maeda; Katsunori Muraoka; Masanori Akazaki
1981-01-01
The absolute density of metal atoms such as iron and aluminium atoms, the knowledge of which is urgently needed for study of the high temperature plasma-wall interaction, was measured by the laser resonance scattering method within an accuracy of 50%. The calibration of the optical system was performed by using the Rayleigh scattering from argon gas at sub-atmospheric pressure, and
Measurement, entanglement, and collapse, in atom-photon scattering
NASA Astrophysics Data System (ADS)
Ozeri, Roee; Glickman, Yinnon; Kotler, Shlomi; Akerman, Nitzan
2013-05-01
Photon scattering is a common tool in atomic physics experiments. We show how, entanglement, measurement and decoherence are intertwined in the process of photon scattering by a single trapped ion. We preform quantum process tomography on the spin of a single trapped 88Sr+ ion, undergoing resonant photon scattering. We observe that, following the scattering and detection of a single photon, a spin measurement basis emerges. The measurement basis is aligned with the scattered photon direction and its state are invariant under photon scattering. We also find that, while the measurement basis states themselves are classically correlated with the scattered photon polarization, superpositions of these basis state become entangled with the scattered photon. Quantum feedback, based on photon polarization measurement, can be used to reverse photon scattering decoherence.
Ionization and excitation of hydrogen and helium Rydberg atoms by microwaves
Moorman, L.; Sauer, B.E.; Yoakum, S.; Koch, P.M. (Physics Department, State University of New York, Stony Brook, NY (USA)); Galvez, E.J. (Department of Physics and Astronomy, Colgate University, Hamilton, NY (USA)); van de Water, W.; van Leeuwen, K.A.H. (Physics Department, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (The Netherlands))
1990-04-01
We have used the interaction of hydrogen Rydberg atoms with microwave fields to study multiphoton ionization. The minimum number of photons absorbed in the experiments ranges from about 300 to only 15. A brief overview is given of the extensive theoretical work that is under development to explain experimental data, including various observed structures. Similarly we report on ionization of helium Rydberg atoms, qualitatively explained in terms of a static picture. Finally we show selective excitation of He triplet {ital s}-state to higher angular momentum states, via absorption of several photons from the field. Using the Floquet method a close analogy between the microwave problem and slow atomic collisions can be made. Sharp resonant structures in the spectra can be linked to individual avoided crossings of calculated Floquet quasi-energy curves. Our theory that exploits a separation of timescales explains very well the positions, depths, and shapes of the observed structures, but a discrepancy still remains concerning their widths.
Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen
Safari, Laleh; Fritzsche, Stephan; Santos, José Paulo; Tashenov, Stanislav; Fratini, Filippo
2012-01-01
A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and expressed in terms of $B$ splines and $B$ polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 10 keV. Particular attention is p...
Atomic Physics of Raman Scattered He II?4332
NASA Astrophysics Data System (ADS)
Lee, Hee-Won
2013-02-01
Raman scattering of far UV photons with atomic hydrogen is important in studying the mass loss and accretion processes in many symbiotic stars. We present basic atomic physical properties for the inelastic scattering of He II 949 with a hydrogen atom, which results in Raman scattered He II 4332 blueward of H gamma. At line center of He II 949, the total scattering cross section is computed to be ? tot = 2.5 × 10-22 cm2 and the branching ratio into the level 2s is 0.12. It is proposed that comparisons of broad Balmer wings and Raman scattered He II features may provide an important diagnostic of far UV continuum around H I Lyman series.
Rayleigh scattering by atomic ions of low nuclear charge
G. Basavaraju; Lynn Kissel; John C. Parker; R. H. Pratt; S. C. Roy; S. K. Sen Gupta
1986-01-01
Rayleigh scattering amplitudes and elastic photon-atom scattering cross sections have been calculated for C0, C1+, C2+, C4+, Ne0, Ne1+, Ne2+, Ne4+, Ne6+, Ne8+, and Ne9+ atoms and ions in their ground state. Some data were also obtained for oxygen. X-ray energies considered are in the regions above and below the threshold energy for K-shell photoionization. Except in the immediate neighborhood
Scattering and absorption of ultracold atoms by nanotubes
B. Jetter; J. Märkle; P. Schneeweiss; M. Gierling; S. Scheel; A. Günther; J. Fortágh; T. E. Judd
2013-07-23
We investigate theoretically how cold atoms, including Bose-Einstein condensates, are scattered from, or absorbed by nanotubes with a view to analysing recent experiments. In particular we consider the role of potential strength, quantum reflection, atomic interactions and tube vibrations on atom loss rates. Lifshitz theory calculations deliver a significantly stronger scattering potential than that found in experiment and we discuss possible reasons for this. We find that the scattering potential for dielectric tubes can be calculated to a good approximation using a modified pairwise summation approach, which is efficient and easily extendable to arbitrary geometries. Quantum reflection of atoms from a nanotube may become a significant factor at low temperatures, especially for non-metallic tubes. Interatomic interactions are shown to increase the rate at which atoms are lost to the nanotube and lead to non-trivial dynamics. Thermal nanotube vibrations do not significantly increase loss rates or reduce condensate fractions, but lower frequency oscillations can dramatically heat the cloud.
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 - Nous avons mis au point une méthode de mesure des atomes métastables de l'hé--lium e t du néon par
Thumm, Uwe
Attosecond probing of instantaneous ac Stark shifts in helium atoms This article has been COMMUNICATION Attosecond probing of instantaneous ac Stark shifts in helium atoms Feng He1, Camilo Ruiz2 Contact us My IOPscience #12;IOP PUBLISHING JOURNAL OF PHYSICS B: ATOMIC, MOLECULAR AND OPTICAL PHYSICS J
Chu, Shih-I
Effect of electron correlation on high-order-harmonic generation of helium atoms in intense laser. The procedure is applied to the investigation of high-order-harmonic generation HHG of helium atoms initio nonperturbative treatment of multiphoton dynamics of atomic systems in intense laser fields
Four -body calculation of the 2p level shift in antikaonic helium K3 He atom
NASA Astrophysics Data System (ADS)
Tsiklauri, Shalva; Tenon, Joshua
2015-05-01
The strong interaction of charged antikaons (K -) with nucleons and nuclei in the low-energy is a intriguing subject matter. The antikaon plays an unusual role in nuclear physics due to the strong attraction antikaon-nucleon which is a key question for possible kaonic nuclear bound states. Low-lying energy levels of kaonic atoms are shifted from their pure electromagnetic values and widened due to the strong interaction between the antikaon and nucleon. The level shift and width of the kaonic atoms can be determined by x-ray spectroscopy. The X-ray measurements of K He atoms introduced inconsistency between theory and experiment both in the shift and width of the K He 2 p state. The average of the shift was large ~40 eV, while a majority of theoretical calculations suggested very small shift below 1 eV. This significant disagreement between the experimental results and the theoretical calculations is known as the ``kaonic helium puzzle.'' We suggest a new theoretical analysis of the four-body antikaonic 3He in the framework of the method of hyperspherical harmonics (HH) for solving four body Schrodinger equations. This is the first time when the HH microscopic method is applied to study kaonic helium.
Chu, Shih-I
A highly accurate study of a helium atom under pressure This article has been downloaded from.1088/1751-8113/42/26/265004 A highly accurate study of a helium atom under pressure Cecil Laughlin1,2 and Shih-I Chu2,3 1 School-relativistic ground-state energies and pressures of a helium atom confined at the centre of an impenetrable spherical
Some features of Rayleigh scattering from light atoms and ions
J. C. Parker; R. H. Pratt
1979-01-01
The Rayleigh scattering cross sections for atoms and ions of low nuclear charge, particularly for photon energies in the vicinity of the threshold for photoionization from the K-shell are discussed. A sequence of resonances in the elastic scattering amplitude which occur at an energy corresponding to the excitation of a K-shell electron to a higher unfilled shell is examined. An
Issues in numerical calculations of atomic Rayleigh scattering near edges
Kissel
1987-01-01
An overview of the relativistic S-matrix approach to the calculation of x-ray scattering is presented. Relativistic quantum electrodynamics, treated in lowest nonvanishing order in eÂ², provides the basic theoretical framework for this description of elastic photon-atom scattering. Rayleigh scattering is calculated as a second-order single-electron transition process from electrons bound in a relativistic self-consistent central potential. This method has previously
A new dispersion relation for electron-atom scattering
NASA Technical Reports Server (NTRS)
Temkin, A.; Bhatia, A. K.; Kim, Y. S.
1986-01-01
A new forward-angle dispersion relation (DR) for electron-atom scattering is proposed. It is based on a subtraction of the static-exchange amplitude from the exact elastic scattering amplitude. Arguments are advanced to explain why this should obviate the difficulties associated with the Gerjuoy-Krall DR, specifically with the exchange Born amplitude. The new DR is tested in the elastic energy range for e-H scattering and compared with the GKDR.
Relativistic theory of the double photoionization of helium-like atoms
Yerokhin, V A
2011-01-01
A fully relativistic calculation of the double photoionization of helium-like atoms is presented. The approach is based on the partial-wave representation of the Dirac continuum states and accounts for the retardation in the electron-electron interaction as well as the higher-order multipoles of the absorbed photon. The electron-electron interaction is taken into account to the leading order of perturbation theory. The relativistic effects are shown to become prominent already for the medium-Z ions, changing the shape and the asymptotic behaviour of the photon energy dependence of the ratio of the double-to-single photoionization cross section.
Precise Measurement of the Hyperfine-Structure Interval and Zeeman Effect in the Muonic Helium Atom
C. J. Gardner; A. Badertscher; W. Beer; P. R. Bolton; P. O. Egan; M. Gladisch; M. Greene; V. W. Hughes; D. C. Lu; F. G. Mariam; P. A. Souder; H. Orth; J. Vetter; G. Zu Putlitz
1982-01-01
Measurements of the hyperfine Zeeman transitions (DeltaMmu=+\\/-1, DeltaMJ=0) in the ground state of the muonic helium atom (4He++mu-e-) at magnetic fields of 11.5 and 13.6 kG have yielded values for the hfs interval, Deltanu=4465.004(29) MHz (6.5 ppm), and for the negative-muon magnetic moment, mumu-mup=3.183 28(15) (47 ppm). The theoretical value for Deltanu, including relativistic, radiative, and recoil contributions, agrees with
NASA Astrophysics Data System (ADS)
Hernando, A.; Masson, A.; Briant, M.; Mestdagh, J.-M.; Gaveau, M.-A.; Halberstadt, N.
2012-11-01
The stability of the ground or excited state calcium atom in an argon-doped helium droplet has been investigated using an extension of the helium density functional method to treat clusters. This work was motivated by the experimental study presented in a companion paper, hereafter called Paper I [A. Masson, M. Briant, J. M. Mestdagh, M. A. Gaveau, A. Hernando, and N. Halberstadt, J. Chem. Phys. 137, 184310 (2012), 10.1063/1.4762836], which investigated Ca2 photodissociation in an argon-doped helium droplet and the nature of the fluorescent species. It is found that one single argon atom is sufficient to bring the calcium atom inside the droplet, for droplets of over 200 helium atoms. The absorption and emission spectra of CaArM (M = 0-7) clusters have been simulated using the recently developed density sampling method to describe the influence of the helium environment. Absorption spectra exhibit broad, double bands that are significantly blueshifted with respect to the calcium atomic line. The emission spectra are less broad and redshifted with respect to the calcium resonance line. The shifts are found to be additive only for M ? 2, because only the first two argon atoms are located in equivalent positions around the calcium p orbital. This finding gives a justification for the fit presented in the companion paper, which uses the observed shifts in the emission spectra as a function of argon pressure to deduce the shifts as a function of the number of argon atoms present in the cluster. An analysis of this fit is presented here, based on the calculated shifts. It is concluded that the emitting species following Ca2 photodissociation in an argon-doped droplet in Paper I could be Ca*ArM in a partly evaporated droplet where less than 200 helium atoms remain.
Hernando, A; Masson, A; Briant, M; Mestdagh, J-M; Gaveau, M-A; Halberstadt, N
2012-11-14
The stability of the ground or excited state calcium atom in an argon-doped helium droplet has been investigated using an extension of the helium density functional method to treat clusters. This work was motivated by the experimental study presented in a companion paper, hereafter called Paper I [A. Masson, M. Briant, J. M. Mestdagh, M. A. Gaveau, A. Hernando, and N. Halberstadt, J. Chem. Phys. 137, 184310 (2012)], which investigated Ca(2) photodissociation in an argon-doped helium droplet and the nature of the fluorescent species. It is found that one single argon atom is sufficient to bring the calcium atom inside the droplet, for droplets of over 200 helium atoms. The absorption and emission spectra of CaAr(M) (M = 0-7) clusters have been simulated using the recently developed density sampling method to describe the influence of the helium environment. Absorption spectra exhibit broad, double bands that are significantly blueshifted with respect to the calcium atomic line. The emission spectra are less broad and redshifted with respect to the calcium resonance line. The shifts are found to be additive only for M ? 2, because only the first two argon atoms are located in equivalent positions around the calcium p orbital. This finding gives a justification for the fit presented in the companion paper, which uses the observed shifts in the emission spectra as a function of argon pressure to deduce the shifts as a function of the number of argon atoms present in the cluster. An analysis of this fit is presented here, based on the calculated shifts. It is concluded that the emitting species following Ca(2) photodissociation in an argon-doped droplet in Paper I could be Ca?Ar(M) in a partly evaporated droplet where less than 200 helium atoms remain. PMID:23163375
Numerical Aspects of Atomic Physics: Helium Basis Sets and Matrix Diagonalization
NASA Astrophysics Data System (ADS)
Jentschura, Ulrich; Noble, Jonathan
2014-03-01
We present a matrix diagonalization algorithm for complex symmetric matrices, which can be used in order to determine the resonance energies of auto-ionizing states of comparatively simple quantum many-body systems such as helium. The algorithm is based in multi-precision arithmetic and proceeds via a tridiagonalization of the complex symmetric (not necessarily Hermitian) input matrix using generalized Householder transformations. Example calculations involving so-called PT-symmetric quantum systems lead to reference values which pertain to the imaginary cubic perturbation (the imaginary cubic anharmonic oscillator). We then proceed to novel basis sets for the helium atom and present results for Bethe logarithms in hydrogen and helium, obtained using the enhanced numerical techniques. Some intricacies of ``canned'' algorithms such as those used in LAPACK will be discussed. Our algorithm, for complex symmetric matrices such as those describing cubic resonances after complex scaling, is faster than LAPACK's built-in routines, for specific classes of input matrices. It also offer flexibility in terms of the calculation of the so-called implicit shift, which is used in order to ``pivot'' the system toward the convergence to diagonal form. We conclude with a wider overview.
Ultra-precise single-ion atomic mass measurements on deuterium and helium-3
NASA Astrophysics Data System (ADS)
Zafonte, S. L.; Van Dyck, R. S., Jr.
2015-04-01
The former University of Washington Penning Trap Mass Spectrometer (UW-PTMS), now located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, was used in the decade before the move to determine new values for the deuteron atomic mass, M (2H+) = 2.013?553 212?745(40) u, and the deuterium atomic mass, M (2H) = 2.014?101 778?052(40) u, both of which are now more than an order-of-magnitude more accurate than the previous best 1994-MIT measurements of these quantities. The new value for the deuteron’s mass can then be used with the accepted 2010-CODATA proton mass and the most recent 1999-measurement of the 2.2 MeV gamma-ray binding energy of the deuteron to refine the neutron’s mass to mn = 1.008?664 916?018(435) u which has about half the uncertainty relative to the value computed using that previous 1994-MIT deuterium measurement. As a result, further improvements of mn must now come from a more accurate determination of the wavelength of this gamma ray. In this same period of time, this spectrometer has also been used to determine new values for the helion atomic mass, M (3He2+) = 3.014?932 246?668(43) u, and the neutral helium-3 atomic mass, M (3He) = 3.016?029 321?675(43) u, which are both about 60 times more accurate than the 2006-SMILETRAP measurements, but disagree with the 4.4-times less-accurate 2015-Florida-State measurements by 0.76 nu. It is expected that these helium-3 results will be used in the future 3H/3He mass ratio (to be determined by the Heidelberg, Germany version of the old UW-PTMS) in order to generate a more accurate value for the tritium atomic mass.
Rioux, Frank
Five Trial Wavefunctions for two-electron Atoms and Ions The purpose of this exercise is to examine five trial wavefunctions for the helium atom and several two-electron ions. The calculations begin with an uncorrelated wavefunction in which both electrons are placed in a hydrogenic orbital with scale factor
Barnat, E. V. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1423 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87185-1423 (United States); Kolobov, V. I. [CFD Research Corporation, Huntsville, Alabama 35805 (United States)] [CFD Research Corporation, Huntsville, Alabama 35805 (United States)
2013-01-21
Nonmonotonic radial distributions of excited helium atoms have been experimentally observed in a positive column of pulsed helium discharges using planar laser induced fluorescence. Computational analysis of the discharge dynamics with a fluid plasma model confirms the experimental observations over a range of pressures and currents. The observed effect is attributed to the peculiarities of electron population-depopulation of the excited states during the 'dynamic discharge' conditions with strong modulations of the electric field maintaining the plasma.
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.
Dynamics of entanglement between two atomic samples with spontaneous scattering
Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio
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.
Quantum Chaotic Scattering in Atomic Physics: Ericson Fluctuations in Photoionization
Stania, Gernot; Walther, Herbert
2005-11-04
We report the first experimental investigation of quantum chaotic scattering in an atomic system: {sup 85}Rb in strong crossed magnetic and electric fields in an energy regime beyond the ionization threshold, where the classical dynamics is an example of chaotic scattering. We find Ericson fluctuations in the spectra for photo excitation into this regime. This result constitutes the first observation of Ericson fluctuations in atomic and molecular physics. Furthermore, we confirm the prediction that chaotic scattering in the underlying classical dynamics implies Ericson fluctuations.
Dynamics of entanglement between two atomic samples with spontaneous scattering
Lisi, A D; Illuminati, F; Lisi, Antonio Di; Siena, Silvio De; Illuminati, Fabrizio
2003-01-01
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 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.
Rayleigh Scattering and the Electromagnetic Susceptibility of Atoms
W. R. Johnson; F. D. Feiock
1968-01-01
Rayleigh scattering of light by atoms is considered from the point of view of relativistic electron theory. The relationship between the coherent S-matrix element and the frequency-dependent electric and magnetic multipole susceptibilities of the atom is established. Single-particle radial equations are derived for the perturbed electron orbitals, assuming that the atom is described by a relativistic Hartree-Fock-Slater (RHFS) wave function.
Scattering properties of weakly bound dimers of fermionic atoms
Petrov, D.S. [ITAMP, Harvard-Smithsonian Center for Astrophysics, and Harvard-MIT Center for Ultracold Atoms, Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Salomon, C. [Laboratoire Kastler-Brossel, Ecole Normale Superieure, 24 rue Lhomond, 75005 Paris (France); Shlyapnikov, G.V. [Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030 (United States); Russian Research Center Kurchatov Institute, Kurchatov Square, 123182 Moscow (Russian Federation); Laboratoire Physique Theorique et Modeles Statistique, Universite Paris Sud, Batiment 100, 91405 Orsay (France); Van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65/67, 1018 XE Amsterdam (Netherlands)
2005-01-01
We consider weakly bound diatomic molecules (dimers) formed in a two-component atomic Fermi gas with a large positive scattering length for the interspecies interaction. We develop a theoretical approach for calculating atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic collisional relaxation of the molecules into deep bound states. This approach is based on the single-channel zero-range approximation, and we find that it is applicable in the vicinity of a wide two-body Feshbach resonance. Our results draw prospects for various interesting manipulations of weakly bound dimers of fermionic atoms.
Coherent scattering by a spherical medium of resonant atoms
Prasad, Sudhakar; Glauber, Roy J.
2011-06-15
We consider the problem of coherent resonant scattering of electromagnetic waves by a spherical medium of two-level atoms. The frequency dependence of the scattering amplitudes and cross sections reveals a complex structure of narrow peaks and dips. We relate these scattering resonances to the cooperative emission resonances characteristic of a sphere. We find the scattering to show considerable interference between the electric and magnetic multipole contributions, particularly in the lower multipole orders. This interference tends to enhance anisotropies in the differential scattering cross section even for small spheres. For such spheres, the peak values of the resonant contributions of the low-order multipoles to the total scattering cross section can increase with multipole order, in contrast to the usual decrease seen in nonresonant scattering.
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.
Quantum interference in attosecond transient absorption of laser-dressed helium atoms
Shaohao Chen; Mengxi Wu; Mette B. Gaarde; Kenneth J. Schafer
2013-01-04
We calculate the transient absorption of an isolated attosecond pulse by helium atoms subject to a delayed infrared (\\ir) laser pulse. With the central frequency of the broad attosecond spectrum near the ionization threshold, the absorption spectrum is strongly modulated at the sub-\\ir-cycle level. Given that the absorption spectrum results from a time-integrated measurement, we investigate the extent to which the delay-dependence of the absorption yields information about the attosecond dynamics of the atom-field energy exchange. We find two configurations in which this is possible. The first involves multi photon transitions between bound states that result in interference between different excitation pathways. The other involves the modification of the bound state absorption lines by the IR field, which we find can result in a sub-cycle time dependence only when ionization limits the duration of the strong field interaction.
NASA Astrophysics Data System (ADS)
Krems, R. V.; Buchachenko, A. A.
2005-09-01
Based on measurements of the Zeeman relaxation in a cold gas of He3 [C. I. Hancox, S. C. Doret, M. I. Hummon, L. Luo, and J. M. Doyle, Nature (London) 431, 281 (2004)], we show that the electronic interaction anisotropy between rare-earth atoms with nonzero electronic orbital angular momenta and helium is extremely small. The interaction of the rare-earth atoms with He gives rise to several adiabatic potentials with different electronic symmetries. It is demonstrated that the energy splitting between these potentials does not exceed 0.09cm-1 at interatomic distances larger than the turning point for collisions at 0.8K, including the region of the van der Waals interaction minima.
Krems, R V; Buchachenko, A A
2005-09-01
Based on measurements of the Zeeman relaxation in a cold gas of (3)He [C. I. Hancox, S. C. Doret, M. I. Hummon, L. Luo, and J. M. Doyle, Nature (London) 431, 281 (2004)], we show that the electronic interaction anisotropy between rare-earth atoms with nonzero electronic orbital angular momenta and helium is extremely small. The interaction of the rare-earth atoms with He gives rise to several adiabatic potentials with different electronic symmetries. It is demonstrated that the energy splitting between these potentials does not exceed 0.09 cm(-1) at interatomic distances larger than the turning point for collisions at 0.8 K, including the region of the van der Waals interaction minima. PMID:16178581
Wave functions and two-electron probability distributions of the Hooke's-law atom and helium
O'Neill, Darragh P.; Gill, Peter M. W.
2003-08-01
The Hooke's-law atom (hookium) provides an exactly soluble model for a two-electron atom in which the nuclear-electron Coulombic attraction has been replaced by a harmonic one. Starting from the known exact position-space wave function for the ground state of hookium, we present the momentum-space wave function. We also look at the intracules, two-electron probability distributions, for hookium in position, momentum, and phase space. These are compared with the Hartree-Fock results and the Coulomb holes (the difference between the exact and Hartree-Fock intracules) in position, momentum, and phase space are examined. We then compare these results with analogous results for the ground state of helium using a simple, explicitly correlated wave function.
A discrete variable representation for electron-hydrogen atom scattering
Gaucher, L.F.
1994-08-01
A discrete variable representation (DVR) suitable for treating the quantum scattering of a low energy electron from a hydrogen atom is presented. The benefits of DVR techniques (e.g. the removal of the requirement of calculating multidimensional potential energy matrix elements and the availability of iterative sparse matrix diagonalization/inversion algorithms) have for many years been applied successfully to studies of quantum molecular scattering. Unfortunately, the presence of a Coulomb singularity at the electrically unshielded center of a hydrogen atom requires high radial grid point densities in this region of the scattering coordinate, while the presence of finite kinetic energy in the asymptotic scattering electron also requires a sufficiently large radial grid point density at moderate distances from the nucleus. The constraints imposed by these two length scales have made application of current DVR methods to this scattering event difficult.
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
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){sub 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 NaHe{sub 200} 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.
Nakashima, Hiroyuki; Nakatsuji, Hiroshi [Quantum Chemistry Research Institute, JST, CREST, Kyodai Katsura Venture Plaza 106, Goryo Oohara 1-36, Nishikyo-ku, Kyoto 615-8245 (Japan)
2008-12-12
The local energy defined by H{psi}/{psi} must be equal to the exact energy E at any coordinate of an atom or molecule, as long as the {psi} under consideration is exact. The discrepancy from E of this quantity is a stringent test of the accuracy of the calculated wave function. The H-square error for a normalized {psi}, defined by {sigma}{sup 2}{identical_to}<{psi}|(H-E){sup 2}|{psi}>, is also a severe test of the accuracy. Using these quantities, we have examined the accuracy of our wave function of a helium atom calculated using the free complement method that was developed to solve the Schroedinger equation. Together with the variational upper bound, the lower bound of the exact energy calculated using a modified Temple's formula ensured the definitely correct value of the helium fixed-nucleus ground state energy to be -2.903 724 377 034 119 598 311 159 245 194 4 a.u., which is correct to 32 digits.
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\
Atomic Scattering Polarization. Observations, Modeling, Predictions
NASA Astrophysics Data System (ADS)
Bueno, J. Trujillo; Alemán, T. Del Pino; Belluzzi, L.
2015-10-01
This paper highlights very recent advances concerning the identification of new mechanisms that introduce polarization in spectral lines, which turn out to be key for understanding some of the most enigmatic scattering polarization signals of the solar visible spectrum. We also show a radiative transfer prediction on the scattering polarization pattern across the Mg ii h & k lines, whose radiation can only be observed from space.
Reversal of Photon-Scattering Errors in Atomic Qubits
NASA Astrophysics Data System (ADS)
Akerman, N.; Kotler, S.; Glickman, Y.; Ozeri, R.
2012-09-01
Spontaneous photon scattering by an atomic qubit is a notable example of environment-induced error and is a fundamental limit to the fidelity of quantum operations. In the scattering process, the qubit loses its distinctive and coherent character owing to its entanglement with the photon. Using a single trapped ion, we show that by utilizing the information carried by the photon, we are able to coherently reverse this process and correct for the scattering error. We further used quantum process tomography to characterize the photon-scattering error and its correction scheme and demonstrate a correction fidelity greater than 85% whenever a photon was measured.
Inelastic scattering of hydroxyl radicals with helium and argon by velocity-map imaging.
Sarma, Gautam; Marinakis, Sarantos; ter Meulen, J J; Parker, David H; McKendrick, Kenneth G
2012-12-01
The hydroxyl radical (OH) is one of the most interesting molecules in molecular dynamics. In particular, inelastic collisions of free radicals such as OH are profoundly important in environments ranging from combustion to astrochemistry. However, measuring the velocities of OH molecules in specific internal quantum states has proven to be very difficult. A method that can provide this important information is velocity-map imaging. Although this technique is very widely applicable in principle, it does require a sensitive and selective laser-ionization scheme. Here we show that, under the right conditions, velocity-map imaging can be applied to the study of the inelastic scattering of OH using crossed-molecular-beam methods. We measure fully quantum-state-specified product angular distributions for OH collisions with helium and argon. The agreement between exact close-coupling quantum scattering calculations on ab initio potential energy surfaces and experimental data is generally very satisfactory, except for scattering in the most forward directions. PMID:23174977
Ratschek, Martin; Pototschnig, Johann V; Hauser, Andreas W; Ernst, Wolfgang E
2014-08-21
The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y(7)P, a(5)S, and y(5)P excited states. The necessary Cr-He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (?He), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z(7)P ? a(7)S, y(7)P ? a(7)S, z(5)P ? a(5)S, and y(5)P ? a(5)S are compared to recent fluorescence and photoionization experiments. PMID:24906160
Calculation of electron-helium scattering at 40 eV
Bray, I.; Fursa, D.V.; McCarthy, I.E. (Electronic Structure of Materials Centre, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide 5001 (Australia))
1995-01-01
We apply the convergent close-coupling (CCC) method to calculation of 40-eV electrons scattering on the ground state of helium. We present the differential cross sections up to the [ital n][le]3 levels, as well as the electron-impact coherence parameters for the 3 [sup 1][ital D] state. We find our results to be in excellent agreement with the measurements. It is shown that at this energy treating the target continuum has a large effect on the presented results, and for this reason the CCC theory is the only one that is able to obtain agreement with experiment. Integrated, total ionization, and total cross sections are also presented, and are found to be in excellent agreement with experiment.
Testing quantum correlations in a confined atomic cloud by scattering fast atoms
A. B. Kuklov; B. V. Svistunov
1998-12-01
We suggest measuring one-particle density matrix of a trapped ultracold atomic cloud by scattering fast atoms in a pure momentum state off the cloud. The lowest-order probability of the inelastic process, resulting in a pair of outcoming fast atoms for each incoming one, turns out to be given by a Fourier transform of the density matrix. Accordingly, important information about quantum correlations can be deduced directly from the differential scattering cross-section. A possible design of the atomic detector is also discussed.
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.
Analytical evaluation of atomic form factors: application to Rayleigh scattering
Safari, L; Amaro, P; Jänkälä, K; Fratini, F
2014-01-01
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 wavefunctions. 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.
Analytical evaluation of atomic form factors: Application to Rayleigh scattering
NASA Astrophysics Data System (ADS)
Safari, L.; Santos, J. P.; Amaro, P.; Jänkälä, 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.
Atom-diatom scattering dynamics of spinning molecules
NASA Astrophysics Data System (ADS)
Eyles, C. J.; Floß, J.; Averbukh, I. Sh.; Leibscher, M.
2015-01-01
We present full quantum mechanical scattering calculations using spinning molecules as target states for nuclear spin selective atom-diatom scattering of reactive D+H2 and F+H2 collisions. Molecules can be forced to rotate uni-directionally by chiral trains of short, non-resonant laser pulses, with different nuclear spin isomers rotating in opposite directions. The calculations we present are based on rotational wavepackets that can be created in this manner. As our simulations show, target molecules with opposite sense of rotation are predominantly scattered in opposite directions, opening routes for spatially and quantum state selective scattering of close chemical species. Moreover, two-dimensional state resolved differential cross sections reveal detailed information about the scattering mechanisms, which can be explained to a large degree by a classical vector model for scattering with spinning molecules.
Ultra-low-temperature reactions of C(³P?) 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
Differential cross sections for muonic atom scattering from hydrogenic molecules
Adamczak, Andrzej
2006-10-15
The differential cross sections for low-energy muonic hydrogen atom scattering from hydrogenic molecules are directly expressed by the corresponding amplitudes for muonic atom scattering from hydrogen-isotope nuclei. The energy and angular dependence of these three-body amplitudes is thus taken naturally into account in scattering from molecules, without involving any pseudopotentials. Effects of the internal motion of nuclei inside the target molecules are included for every initial rotational-vibrational state. These effects are very significant as the considered three-body amplitudes often vary strongly within the energy interval < or approx. 0.1 eV. The differential cross sections, calculated using the presented method, have been successfully used for planning and interpreting many experiments in low-energy muon physics. Studies of {mu}{sup -} nuclear capture in p{mu} and the measurement of the Lamb shift in p{mu} atoms created in H{sub 2} gaseous targets are recent examples.
Bartl, Peter; Leidlmair, Christian; Denifl, Stephan; Scheier, Paul; Echt, Olof
2014-09-18
Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ? x ? 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ? 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions. PMID:24128371
Rayleigh scattering under light-atom coherent interaction
Takamizawa, Akifumi
2012-01-01
Semi-classical calculation of an oscillating dipole induced in a two-level atom indicates that spherical radiation from the dipole under coherent interaction, i.e., Rayleigh scattering, has a power level comparable to that of spontaneous emission resulting from an incoherent process. Whereas spontaneous emission is nearly isotropic and has random polarization generally, Rayleigh scattering is strongly anisotropic and polarized in association with incident light. In the case where Rabi frequency is much larger than frequency detuning and spontaneous emission rate, while the power of spontaneous emission varies with time at the Rabi frequency, the power of Rayleigh scattering oscillates at twice the Rabi frequency. Moreover, the radiation pressure force acting on an atom due to Rayleigh scattering exceeds that caused by spontaneous emission when frequency detuning is large.
Modified atomic decay rate near absorptive scatterers at finite temperature
NASA Astrophysics Data System (ADS)
Suttorp, L. G.; van Wonderen, A. J.
2015-07-01
The change in the decay rate of an excited atom that is brought about by extinction and thermal-radiation effects in a nearby dielectric medium is determined from a quantum-mechanical model. The medium is a collection of randomly distributed thermally excited spherical scatterers with absorptive properties. The modification of the decay rate is described by a set of correction functions for which analytical expressions are obtained as sums over contributions from the multipole moments of the scatterers. The results for the modified decay rate as a function of the distance between the excited atom and the dielectric medium show the influence of absorption, scattering and thermal-radiation processes. Some of these processes are found to be mutually counteractive. The changes in the decay rate are compared to those following from an effective-medium theory in which the discrete scatterers are replaced by a continuum.
Observation of cooperative Mie scattering from an ultracold atomic cloud
H. Bender; C. Stehle; S. Slama; R. Kaiser; N. Piovella; C. Zimmermann; Ph. W. Courteille
2010-04-28
Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead respectively to a suppression or an enhancement of the radiation pressure. We observe a maximum in the radiation pressure as a function of the induced phase shift, marking the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.
Observation of cooperative Mie scattering from an ultracold atomic cloud
Bender, H.; Stehle, C.; Slama, S.; Zimmermann, C. [Physikalisches Institut, Eberhardt-Karls-Universitaet Tuebingen, D-72076 Tuebingen (Germany); Kaiser, R. [Institut Non Lineaire de Nice, CNRS, Universite de Nice Sophia-Antipolis, F-06560 Valbonne (France); Piovella, N. [Dipartimento di Fisica, Universita Degli Studi di Milano, Via Celoria 16, I-20133 Milano (Italy); Courteille, Ph. W. [Physikalisches Institut, Eberhardt-Karls-Universitaet Tuebingen, D-72076 Tuebingen (Germany); Institut Non Lineaire de Nice, CNRS, Universite de Nice Sophia-Antipolis, F-06560 Valbonne (France); Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, 13560-970 Sao Carlos, SP (Brazil)
2010-07-15
Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure force exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead, respectively, to a suppression or an enhancement of the radiation pressure force. We observe a maximum in the radiation pressure force as a function of the phase shift induced in the incident laser beam by the cloud's refractive index. The maximum marks the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate relationship between Rayleigh scattering of light at a coarse-grained ensemble of individual scatterers and Mie scattering at the bulk density distribution.
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...
Probing Ultracold Atoms in Optical Lattices with Bragg Scattering
NASA Astrophysics Data System (ADS)
Miyake, Hirokazu; Siviloglou, Georgios; Puentes, Graciana; Jepsen, Niklas; Dimitrova, Ivana; Weld, David; Pritchard, David; Ketterle, Wolfgang
2011-05-01
A major thrust of the field of ultracold atoms in optical lattices has been to create novel phases of matter. Developing techniques to probe these systems is as important as the realization of such phases. We have applied the technique of Bragg scattering to study quantum degenerate bosonic 87Rb atoms from the superfluid phase to the Mott insulator phase in a 3D optical lattice. Bragg scattering can allow the direct detection of new phases such as antiferromagnetic ordering in 3D, both in the spin and occupation number sector. We acknowledge support from the DARPA OLE Program, NSF, and the Department of Defense.
Fluxes of energetic neutral helium atoms from the heliosheath and the IBEX Ribbon
NASA Astrophysics Data System (ADS)
Swaczyna, Pawel; Grzedzielski, Stan; Bzowski, Maciej
2014-05-01
Full sky maps of energetic neutral hydrogen atoms (H ENA) obtained with the Interstellar Boundary Explorer revealed a bright, arc-like Ribbon, which dominates over the heliosheath emission on large swaths of the sky. We simulate the emission of helium ENA from the heliosheath and the IBEX Ribbon. To estimate the heliosheath signal, we use a set of simple models of the heliosphere, where we take the newest results from the Voyagers spacecraft into account. We simulate the evolution of energy spectra of ?-particles and He+ ions using a number of binary interactions of He ions with plasma and neutral background in the heliosheath. The suprathermal ions from this distribution are a source of emerging He ENA flux, which we calculate. The fluxes in the observer frame are corrected for the Compton-Getting effect and the re-ionization losses on the path to detector. We conclude that the highest intensities should be expected from the heliospheric tail. For 1 keV He ENA, they are ~ 0.5 - 10 (cm2 ssrkeV )-1, depending on the employed model, whereas the expected intensities in the forward and flank sectors of the heliosphere in models with the heliosheath thickness ~ 25 AU do not exceed 0.02 (cm2 ssrkeV )-1 and 0.2 (cm2 ssrkeV )-1, respectively. For assessment of the IBEX Ribbon emission we compare the He ENA emissions from two models of the Ribbon origin previously developed to explain the hydrogen emission. In the first one, the Ribbon ENAs are produced outside the heliopause from the ionized neutral solar wind in the direction where the local interstellar magnetic field is perpendicular to the line-of-sight. The second model proposes the ENA production at the interface between the Local Interstellar Cloud (LIC) and the Local Bubble (LB). In the first model, the expected intensity is ~ 0.014 (cm2 ssrkeV )-1, i.e., of the order of the emission from the forward sector of the heliosphere, whereas in the second model, the intensity is ~ 2 - 7 (cm2 ssrkeV )-1. If the IBEX Ribbon requires a source population of ENAs leaving the heliosphere, then the Ribbon should not be visible in He ENA because of the insufficient supply of the He ENA from the neutralized ?-particles from the solar wind. Full-sky measurements of He ENA could create a possibility of distinction between proposed models of the Ribbon origin. We check that He ENA have a potential to probe distant sources of ENA production owing to the expected long mean free path against ionization and elastic scattering (up to 8000 AU for 1 keV/n He) in the interstellar medium.
Inelastic electron scattering from excited barium atoms
Srivastava, Rajesh; Stauffer, A.D. [Department of Physics, Indian Institute of Technology-Roorkee, Roorkee 247667 (India); Department of Physics and Astronomy, York University, Toronto, M3J 1P3 (Canada)
2005-05-15
We have carried out relativistic distorted-wave calculations for inelastic electron scattering from the 6s5d {sup 1,3}D{sub 2} and 6s6p {sup 1}P{sub 1} excited states of barium in the energy range from 20 to 40 eV. Results are presented for the differential cross sections and electron-impact coherence parameters and compared with experimental measurements and other theoretical calculations for these quantities.
Diffusion coefficient of krypton atoms in helium gas at low and moderate temperatures
NASA Astrophysics Data System (ADS)
Bouazza, M. T.; Bouledroua, M.
In the present work, using the Chapman-Enskog method for dilute gases, the diffusion coefficients of ground krypton atoms in a very weakly ionized helium buffer gas are revisited. The calculations are carried out quantum mechanically in the range of low and moderate temperatures. The 1 ?+ potential-energy curve via which Kr approaches He is constructed from the most recent ab initio energy points. The reliable data points used in the construction are smoothly connected to adequate long- and short-range forms. The calculations of the classical second virial coefficients and the Boyle temperature of the helium-krypton mixture are also discussed. These coefficients and their variations in terms of temperature are analysed by adopting the constructed HeKr potential and the Lennard-Jones form that fits it. The diffusion and elastic cross sections are also explored and the resonance features they exhibit are closely examined. The variation law of the diffusion coefficients with temperature is determined for typical values of density and pressure. The coefficients show excellent agreement with the available experimental data; the discrepancies do not exceed 5%.
Rayleigh scattering from excited states of atoms and ions
J. P. J. Carney; R. H. Pratt; Lynn Kissel; S. C. Roy; S. K. Sen Gupta
2000-01-01
Elastic photon scattering from the ground state and various excited states of carbon atoms and ions has been investigated, using the S-matrix formalism, for incident photon energies ranging from 100 eV to 10 keV, contrasting the results obtained for different configurations. The excited states considered include hollow-atom states, where one or more inner shells are completely vacated. Ionic cases are
Nonzero angular momentum states of the helium atom in a strong magnetic field
Wolfgang Becken; Peter Schmelcher
2000-06-07
The electronic structure of the helium atom in the magnetic field regime B=0-100a.u. is investigated, using a full configuration interaction approach which is based on a nonlinearly optimized anisotropic Gaussian basis set of one-particle functions. The corresponding generalized eigenvalue problem is solved for the magnetic quantum number M=-1 and for both even and odd z-parity as well as singlet and triplet spin symmetry. Accurate total electronic energies of the ground state and the first four excitations in each subspace as well as their one-electron ionization energies are presented as a function of the magnetic field. Additionally we present energies for electromagnetic transitions within the M=-1 subspace and between the M=-1 subspace and the M=0 subspace treated in a previous work. A complete table of wavelengths and field strengths for the detected stationary points is given.
Polarization Control in Two-Color Above-Threshold Ionization of Atomic Helium
Meyer, M.; Cubaynes, D.; Glijer, D.; Dardis, J.; Hayden, P.; Hough, P.; Richardson, V.; Kennedy, E. T.; Costello, J. T.; Radcliffe, P.; Duesterer, S.; Azima, A.; Li, W. B.; Redlin, H.; Feldhaus, J.; Taieeb, R.; Maquet, A.; Grum-Grzhimailo, A. N.; Gryzlova, E. V.; Strakhova, S. I.
2008-11-07
Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In the photoelectron spectrum, lines associated with direct ionization and above-threshold ionization show strong variations of their amplitudes as a function of both the intensity of the optical dressing field and the relative orientation of the linear polarization vectors of the two fields. The polarization dependence provides direct insight into the symmetry of the outgoing electrons in above-threshold ionization. In the high field regime, the monochromaticity of the XUV radiation enables the unperturbed observation of nonlinear processes in the optical field.
Learning Approach on the Ground State Energy Calculation of Helium Atom
Shah, Syed Naseem Hussain
2010-07-28
This research investigated the role of learning approach on the ground state energy calculation of Helium atom in improving the concepts of science teachers at university level. As the exact solution of several particles is not possible here we used approximation methods. Using this method one can understand easily the calculation of ground state energy of any given function. Variation Method is one of the most useful approximation methods in estimating the energy eigen values of the ground state and the first few excited states of a system, which we only have a qualitative idea about the wave function.The objective of this approach is to introduce and involve university teacher in new research, to improve their class room practices and to enable teachers to foster critical thinking in students.
Double-electron capture in collision of fast alpha particles with helium atoms
NASA Astrophysics Data System (ADS)
Ghanbari-Adivi, Ebrahim; Ghavaminia, Hoda
2014-11-01
A four-body boundary-corrected first-order Jackson-Schiff approximation (JS1-4B) is developed to calculate the differential and integral cross-sections (DCSs) for double-electron exchange in collision of fast alpha ions with helium atoms in their ground states. The influence of the static electron correlations on cross-sections is taken into account through choosing the different wave functions to describe the initial and final bound states of the electrons. The quantum-mechanical post and prior transition amplitudes for double charge exchange are derived in terms of two-dimensional real integrals which can be calculated numerically. The validity and utility of the applied approach is critically assessed in comparison with the available experimental data for differential and integral cross-sections. The present calculations are also compared with the results obtained from the other theories.
R. B. Doak; R. E. Grisenti; S. Rehbein; G. Schmahl; J. P. Toennies; Ch. Wöll
1999-01-01
A neutral, ground-state, 4He atom beam has been focused using Fresnel zone plates. At only moderate demagnification \\\\(0.40×\\\\), a focused spot diameter of <=2.0 mum is achieved at a signal intensity of 500 counts\\/s. This is an improvement over previous work by a factor of 10 in resolution, 103 in signal intensity, and 108 in focused beam density, and allows
NASA Astrophysics Data System (ADS)
Glukhov, I. L.; Nekipelov, E. A.; Ovsiannikov, V. D.
2010-06-01
New features of the blackbody-induced radiation processes on Rydberg atoms were discovered on the basis of numerical data for the blackbody-induced decay Pdnl(T), excitation Penl(T) and ionization Pionnl(T) rates of nS, nP and nD Rydberg states calculated together with the spontaneous decay rates Pspnl in neutral hydrogen, and singlet and triplet helium atoms for some values of the principal quantum number n from 10 to 500 at temperatures from T = 100 K to 2000 K. The fractional rates Rd(e, ion)nl(T) = Pnld(e, ion)(T)/Pspnl equal to the ratio of the induced decay (excitation, ionization) rates to the rate of spontaneous decay were determined as functions of T and n in every series of states with a given angular momentum l = 0, 1, 2. The calculated data reveal an essential difference between the asymptotic dependence of the ionization rate Pionnl(T) and the rates of decay and excitation Pd(e)nl(T)~T/n2. The departures appear in each Rydberg series for n > 100 and introduce appreciable corrections to the formula of Cooke and Gallagher. Two different approximation formulae are proposed on the basis of the numerical data, one for Rd(e)nl(T) and another one for Rionnl(T), which reproduce the calculated values in wide ranges of principal quantum number from n = 10 to 1000 and temperatures between T = 100 K and T = 2000 K with an accuracy of 2% or better. Modified Fues' model potential approach was used for calculating matrix elements of bound-bound and bound-free radiation transitions in helium.
Kar, Sabyasachi; Ho, Y. K. [Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan 106 (China)
2008-02-15
The asymptotic ratios of double-to-single photoionization cross sections of plasma-embedded helium atoms at very high but nonrelativistic photon energies are calculated for different shielding parameters that are based on the Debye model for weakly coupled plasmas. The ratio of double-to-single photoionization for free atom is determined as 1.644%, in good agreement with the synchrotron measurements. The asymptotic ratio of double-to-single photoionization cross sections for different screening parameters are reported.
Stimulated Raman scattering in atomic ensembles: Toward quantum state entanglement
NASA Astrophysics Data System (ADS)
Ji, Wenhai
Entanglement generation and verification are essential steps to achieve long-distance quantum communication with atomic ensembles according to some protocols. In this dissertation, new schemes for generating quantum state entanglement between two atomic ensembles by stimulated Raman scattering are proposed and analyzed under various practical factors such as linear dispersion, readout losses, and detector noise. In the photon-number-state entanglement scheme, new regimes of discrete-variable entanglement are found to be achievable at microscopic and mesoscopic excitation levels. In the field-quadrature-amplitude entanglement scheme, the inequality of quadrature variance satisfies the entanglement criteria for bipartite Gaussian state entanglement, even at low readout efficiency. Significant progress towards the experimental generation of such entanglement is reported. Population transfer between the atomic ground states is a prerequisite step to prepare the gain medium for stimulated Raman scattering. The high transfer efficiency is achieved through broadband optical pumping. The Stokes and time-delayed anti-Stokes scattering are observed, which is a primary step to verify the quantum memory effect in the atomic vapor. The photon statistics of the Stokes field is measured with a photon-number detection system operating at below the shot-noise level. The pulse energy dependence of Stokes fields on several practical factors is explored. Some new features and phenomena of stimulated Raman scattering in rubidium vapor are observed and analyzed. The simultaneous generation of Stokes and anti-Stokes scattering is observed in the cooperative Raman scattering process, in which only a single strong pump field is present. An enhanced Raman scattering process is also observed, in which the Stokes signal generated by the time-delayed second pump is enhanced by the presence of the first pump when the two pumps are in the Stokes pump frequency range. In addition, we observe very large pulse delay during propagation through 85Rb cell, and we explain it with a theoretical linear dispersion model.
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.
Generalized pseudopotential approach for electron-atom scattering.
NASA Technical Reports Server (NTRS)
Zarlingo, D. G.; Ishihara, T.; Poe, R. T.
1972-01-01
A generalized many-electron pseudopotential approach is presented for electron-neutral-atom scattering problems. A calculation based on this formulation is carried out for the singlet s-wave and p-wave electron-hydrogen phase shifts with excellent results. We compare the method with other approaches as well as discuss its applications for inelastic and rearrangement collision problems.
Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices
F.-R. Carminati; Laurent Sanchez-Palencia; Michele Schiavoni; Ferruccio Renzoni; Gilbert Grynberg
2003-01-01
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [S. Guibal et al., Phys. Rev. Lett. 78, 4709 (1997); C. Jurczak et al., Phys. Rev. Lett. 77, 1727 (1996)], we study whether the Rayleigh resonance originates from the diffraction on a density grating and is therefore a probe of transport of atoms in optical lattices. It
Resonant inelastic x-ray scattering from molecules and atoms
Arp, U.; Deslattes, R.D.; Miyano, K.E.; Southworth, S.H.
1995-12-31
X-ray fluorescence spectroscopy is one of the most powerful methods for the understanding of the electronic structure of matter. We report here on fluorescence experiments in the 2 to 6 keV photon energy range using tunable synchrotron radiation and the resulting experimental programs on resonant inelastic scattering in atoms and on polarization measurements in resonant molecular excitations.
Supercomputers and the future of computational atomic scattering physics
Younger, S.M.
1989-01-01
The advent of the supercomputer has opened new vistas for the computational atomic physicist. Problems of hitherto unparalleled complexity are now being examined using these new machines, and important connections with other fields of physics are being established. This talk briefly reviews some of the most important trends in computational scattering physics and suggests some exciting possibilities for the future. 7 refs., 2 figs.
Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen
Laleh Safari; Pedro Amaro; Stephan Fritzsche; José Paulo Santos; Stanislav Tashenov; Filippo Fratini
2012-08-15
A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and expressed in terms of $B$ splines and $B$ polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 10 keV. Particular attention is paid to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction.
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.
J-matrix calculation of electron-helium S-wave scattering
Konovalov, D. A.; Fursa, D. V.; Bray, I. [Discipline of Information Technology, School of Business, James Cook University, Townsville, Queensland 4811 (Australia); ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, Western Australia 6845 (Australia)
2011-09-15
The J-matrix approach to electron-atom scattering is revised by merging it with the Fano's multiconfiguration interaction matrix elements [U. Fano, Phys. Rev. 140, A67 (1965)]. The revised method is then applied to the S-wave model of the e-He scattering problem demonstrating remarkable computational efficiency and accuracy. In particular, the method is in complete agreement with the convergent-close-coupling elastic, 2{sup 1,3}S excitation and single ionization cross sections for impact energies in the range 0.1-1000 eV. The S-wave resonance structures in the elastic and 2{sup 1,3}S excitation cross sections are highlighted.
Speckle intensity correlations of photons scattered by cold atoms
Müller, Cord A; Miniatura, Christian
2015-01-01
The irradiation of a dilute cloud of cold atoms with a coherent light field produces a random intensity distribution known as laser speckle. Its statistical fluctuations contain information about the mesoscopic scattering processes at work inside the disordered medium. Following up on earlier work by Assaf and Akkermans [Phys.\\ Rev.\\ Lett.\\ \\textbf{98}, 083601 (2007)], we analyze how static speckle intensity correlations are affected by an internal Zeeman degeneracy of the scattering atoms. It is proven on general grounds that the speckle correlations cannot exceed the standard Rayleigh law. On the contrary, because which-path information is stored in the internal atomic states, the intensity correlations suffer from strong decoherence and become exponentially small in the diffusive regime applicable to an optically thick cloud.
Speckle-intensity correlations of photons scattered by cold atoms
NASA Astrophysics Data System (ADS)
Müller, Cord A.; Grémaud, BenoÃ®t.; Miniatura, Christian
2015-07-01
The irradiation of a dilute cloud of cold atoms with a coherent light field produces a random intensity distribution known as laser speckle. Its statistical fluctuations contain information about the mesoscopic scattering processes at work inside the disordered medium. Following up on earlier work by Assaf and Akkermans [Phys. Rev. Lett. 98, 083601 (2007), 10.1103/PhysRevLett.98.083601], we analyze how static speckle-intensity correlations are affected by an internal Zeeman degeneracy of the scattering atoms. It is proven on general grounds that the speckle correlations cannot exceed the standard Rayleigh law. On the contrary, because which-path information is stored in the internal atomic states, the intensity correlations suffer from strong decoherence and become exponentially small in the diffusive regime applicable to an optically thick cloud.
Neumark, Daniel M.
Photoionization of helium nanodroplets doped with rare gas atoms Jeong Hyun Kim, Darcy S. Peterka droplets doped with rare gas atoms Rg=Ne, Ar, Kr, and Xe was studied by time-of-flight mass spectrometry of the dopant rare gas atoms was observed, either by excitation or charge transfer from the surrounding He atoms
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)
Luppov, V.G.; Kaufman, W.A.; Hill, K.M.; Raymond, R.S.; Kirsch, A.D. )
1993-12-05
A 350 mK helium-4-coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an 8 T solenoid field. The four-coned mirror shape, which was designed specifically for operation in the gradient, increased the beam intensity focused by a sextupole magnet into a compression tube detector by a factor of about 7.5.
Spectroscopy of nS, nP, and nD Rydberg series of Cs atoms on helium nanodroplets.
Lackner, F; Krois, G; Theisen, M; Koch, M; Ernst, W E
2011-11-14
The preparation of an artificial superatom consisting of a positive charge inside a superfluid helium nanodroplet and an electron in an orbital surrounding the droplet is of fundamental interest and represents an experimental challenge. In this work, nanodroplets of several thousand helium atoms are doped with single caesium (Cs) atoms. While on the droplet, the Cs valence electron is excited in two steps through an intermediate state into nS, nP, and nD states. The excitation is monitored by laser induced fluorescence or, for high principal quantum numbers, by resonant three-photon-ionization. On-droplet Rydberg excitations are resolved up to about n = 20. The energies are compared with those of free Cs atom Rydberg states and quantum defects as well as the on-droplet ionization threshold are derived. PMID:21789302
Universal molecule injector in liquid helium: Pulsed cryogenic doped helium droplet source
Apkarian, V. Ara
as the ablation target: the droplet beam is imaged via Rayleigh scattering, while the beam past the plasma is imaged by the fluorescence of the entrained Cu atoms. The beam drags along copper ions and electrons for the injection of atomic impurities in bulk helium.1 The electrostatically driven injection of ions,12 injection
NASA Technical Reports Server (NTRS)
Kumar, Vijay; Subramanian, K. P.; Krishnakumar, E.
1987-01-01
Absolute electron-helium and electron-neon scattering cross sections have been measured at low electron energies using the powerful technique of photoelectron spectroscopy. The measurements have been carried out at 17 electron energies varying from 0.7 to 10 eV with an accuracy of + or - 2.7 percent. The results obtained in the present work have been compared with other recent measurement and calculations.
Thermal photoionization of Rydberg states in helium and alkali-metal atoms
NASA Astrophysics Data System (ADS)
Glukhov, I. L.; Ovsiannikov, V. D.
2009-04-01
Approximation formulae in the form of quadratic polynomials in combination with Planck's distribution are proposed for the thermal ionization rates of Rydberg states in helium and alkali atoms. The coefficients of the polynomials were determined by fitting the data for the rates calculated by integrating the photoionization cross sections obtained in the model potential approach for the S, P and D states with the principal quantum number ranging from n= 10 to n= 45, in product with Planck's frequency distribution for the flux of blackbody photons at temperatures from 100 K to 2000 K. Tables of the polynomial coefficients are presented for the atoms indicated. The deviations of the data given by the approximation formula from that of the straightforward integration of cross sections is less than 7% for states with n from 20 up to 55 in the temperature range from 70 K to about 1000 K, not exceeding 40-50% for states with n= 20-100 in the temperature range extending up to 10 000 K, thus providing rather simple and accurate estimates for experiments and for practical applications.
Two-photon double ionization of the helium atom by ultrashort pulses
Palacios, Alicia; Horner, Daniel A; Rescigno, Thomas N; McCurdy, C William
2010-05-14
Two-photon double ionization of the helium atom was the subject of early experiments at FLASH and will be the subject of future benchmark measurements of the associated electron angular and energy distributions. As the photon energy of a single femtosecond pulse is raised from the threshold for two-photon double ionization at 39.5 eV to beyond the sequential ionization threshold at 54.4 eV, the electron ejection dynamics change from the highly correlated motion associated with nonsequential absorption to the much less correlated sequential ionization process. The signatures of both processes have been predicted in accurate \\textit{ab initio} calculations of the joint angular and energy distributions of the electrons, and those predictions contain some surprises. The dominant terms that contribute to sequential ionization make their presence apparent several eV below that threshold. In two-color pump probe experiments with short pulses whose central frequencies require that the sequential ionization process necessarily dominates, a two-electron interference pattern emerges that depends on the pulse delay and the spin state of the atom.
Quantum entanglement of helium atom in high-lying Rydberg states
NASA Astrophysics Data System (ADS)
Jiao, Li-Guang; Ho, Y. K.
2015-05-01
Quantum entanglement for identical particles in atomic systems and quantum dots has attracted considerable interest in recent years. With the successes of our group in accurately calculating the quantum entanglement (measured by von Neumann or the linear entropy) for the helium atom in ground and lower-lying excited states, we move on to the higher-lying Rydberg states and concentrate on the asymptotic behavior of the entanglement in loosely bound states. By applying the Lowdin's canonical orthogonalization method to the Slater-type orbital configuration-interaction basis sets, we have obtained quite accurate wave functions for the 1 sn s1Se with n = 1 to 15 and 2 sn s3Se states, with n = 2 to 15, and from which entanglement entropies for such states are quantified by calculating the occupation numbers of the respective one-electron reduced density matrix < i |?1| j > through a generalized eigenvalue problem. At the meeting, we will present our results and show the correlation between energies, effective quantum numbers, and entanglement for states in these Rydberg series. Work supported by the Ministry of Science and Technology of Taiwan.
In-Situ Lattice Polarization Measurement by Atomic Wave Scattering
NASA Astrophysics Data System (ADS)
Schmidt, Felix; Bauer, Michael; Kindermann, Farina; Lausch, Tobias; Mayer, Daniel; Widera, Artur
2015-05-01
Optical dipole traps and lattices have become indispensable tools in atomic physics and atom optics. Especially the accurate alignment of the beam polarization is crucial, because a deviation from purely linear polarization will result in state dependent AC-stark vector light shifts, which are proportional to the atoms' magnetic mF substates. Such shifts can be either utilized as a tool for state dependent atomic transport and the creation of artificial gauge fields, or, in contrast, could cause unwanted dephasing in quantum information processing and spectroscopic experiments. Here, we present an in-situ measurement method of an optical lattice's polarization purity by employing the Kapitza-Dirac effect - the scattering of atoms by a standing light wave: We create a Rubidium-87 (Rb) BEC and shine in an optical lattice at 790 nm that is tuned in between the D1 and D2 lines of Rb. At this wavelength, the scalar dipole potentials of both lines counteract and ideally cancel out, yielding a high sensitivity to vector light shifts for different mF states. By analysing the scattering of Rb atoms in the residual potential for different mF states, we can extract the lattice polarization with high accuracy below 10-3.
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 ...
NASA Astrophysics Data System (ADS)
Agueny, Hicham
2015-07-01
We present results for single and double electron captures in intermediate energies H+ and 2H+ projectiles colliding with a helium target. The processes under investigations are treated using a nonperturbative semiclassical approach in combination with Eikonal approximation to calculate the scattering differential cross sections. The latter reveals pronounced minima and maxima in the scattering angles, in excellent agreement with the recent experimental data. It turns out that the present structure depends strongly on the projectile energy and shows only slight variations with different capture channels. The observed structure demonstrates the analogy of atomic de Broglie's matter-wave scattering with ?d B=1.3 -3.2 ×10-3 a.u. and Fraunhofer-type diffraction of light waves.
Four-body charge transfer processes in collisions of bare projectile ions with helium atoms
NASA Astrophysics Data System (ADS)
Jana, S.; Mandal, C. R.; Purkait, M.
2015-02-01
Single-electron capture by a bare ion from a helium atom at intermediate and high energies in the framework of four-body distorted wave (DW-4B) approximation in both prior and post form has been considered. In the entrance channel, the initial bound state wave function is distorted by the incoming projectile ion, and the corresponding distortion is related to the Coulomb continuum states of the active electron and the residual target ion in the field of the projectile ion respectively. Continuum states of the active electron and the projectile ion in the field of the residual target ion are also included in the exit channel. It may be mentioned that the effect of dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The total single-electron capture cross sections are obtained by summing over all contributions up to n = 3 shells and sub-shells respectively. In addition, the differential cross sections for alpha particle–helium collision are calculated at impact energies of 60, 150, 300, 450, and 630 keV amu?1, respectively. The cross sections exhibit a monotonically decreasing angular dependence, with clear peak structures around 0.1 to 0.2 mrad being found at low impact energies. The current theoretical results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collision, are compared with the available theoretical and experimental results. Current computed results have been found to be satisfactory in comparison with other theoretical and experimental findings.
Jackman, T.M.
1987-01-01
A theoretical investigation of the interaction potential between the helium atom and the antihydrogen atom was performed for the purpose of determining the feasibility of antihydrogen atom containment. The interaction potential showed an energy barrier to collapse of this system. A variational estimate of the height of this energy barrier and estimates of lifetime with respect to electron-positron annihilation were determined by the Variational Monte Carlo method. This calculation allowed for an improvement over an SCF result through the inclusion of explicit correlation factors in the trial wave function. An estimate of the correlation energy of this system was determined by the Green's Function Monte Carlo (GFMC) method.
Observation of cooperative Mie scattering from an ultracold atomic cloud
Bender, H; Slama, S; Kaiser, R; Piovella, N; Zimmermann, C; Courteille, Ph W
2010-01-01
Scattering of light at a distribution of scatterers is an intrinsically cooperative process, which means that the scattering rate and the angular distribution of the scattered light are essentially governed by bulk properties of the distribution, such as its size, shape, and density, although local disorder and density fluctuations may have an important impact on the cooperativity. Via measurements of the radiation pressure exerted by a far-detuned laser beam on a very small and dense cloud of ultracold atoms, we are able to identify the respective roles of superradiant acceleration of the scattering rate and of Mie scattering in the cooperative process. They lead respectively to a suppression or an enhancement of the radiation pressure. We observe a maximum in the radiation pressure as a function of the induced phase shift, marking the borderline of the validity of the Rayleigh-Debye-Gans approximation from a regime, where Mie scattering is more complex. Our observations thus help to clarify the intricate re...
Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices
Francois-Regis Carminati; Laurent Sanchez-Palencia; Michele Schiavoni; Ferruccio Renzoni; Gilbert Grynberg
2003-01-24
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals (S. Guibal {\\it et al}, Phys. Rev. Lett. {\\bf 78}, 4709 (1997); C. Jurczak {\\it et al}, Phys. Rev. Lett. {\\bf 77}, 1727 (1996)), we study whether the Rayleigh resonance originates from the diffraction on a density grating, and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance.
Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices
Carminati, F R; Schiavoni, M; Renzoni, F; Grynberg, G; Carminati, Francois-Regis; Sanchez-Palencia, Laurent; Schiavoni, Michele; Renzoni, Ferruccio; Grynberg, Gilbert
2003-01-01
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals (S. Guibal {\\it et al}, Phys. Rev. Lett. {\\bf 78}, 4709 (1997); C. Jurczak {\\it et al}, Phys. Rev. Lett. {\\bf 77}, 1727 (1996)), we study whether the Rayleigh resonance originates from the diffraction on a density grating, and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance.
Partial Wave Dispersion Relations: Application to Electron-Atom Scattering
NASA Technical Reports Server (NTRS)
Temkin, A.; Drachman, Richard J.
1999-01-01
In this Letter we propose the use of partial wave dispersion relations (DR's) as the way of solving the long-standing problem of correctly incorporating exchange in a valid DR for electron-atom scattering. In particular a method is given for effectively calculating the contribution of the discontinuity and/or poles of the partial wave amplitude which occur in the negative E plane. The method is successfully tested in three cases: (i) the analytically solvable exponential potential, (ii) the Hartree potential, and (iii) the S-wave exchange approximation for electron-hydrogen scattering.
Recent progress in electron scattering from atoms and molecules
NASA Astrophysics Data System (ADS)
Brunger, M. J.; Buckman, S. J.; Sullivan, J. P.; Palihawadana, P.; Jones, D. B.; Chiari, L.; Pettifer, Z.; da Silva, G. B.; Lopes, M. C. A.; Duque, H. V.; Masin, Z.; Gorfinkiel, J. D.; Garcia, G.; Hoshino, M.; Tanaka, H.; Limão-Vieira, P.
2014-03-01
We present and discuss recent results, both experimental and theoretical (where possible), for electron impact excitation of the 3s[3/2]1 and 3s'[1/2]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.
NASA Astrophysics Data System (ADS)
Hauser, Reas W.; Filatov, Michael; Ernst, Wolfgang E.
2013-06-01
We predict He-droplet-induced changes of the isotropic HFS constant a_{HFS} of the alkali-metal atoms M = Li, Na, K and Rb on the basis of a model description. Optically detected electron spin resonance spectroscopy has allowed high resolution measurements that show the influence of the helium droplet and its size on the unpaired electron spin density at the alkali nucleus. Our theoretical approach to describe this dependence is based on a combination of two well established techniques: Results of relativistic coupled-cluster calculations on the alkali-He dimers (energy and HFS constant as functions of the binding length) are mapped onto the doped-droplet-situation with the help of helium-density functional theory. We simulate doped droplets He_{N} with N ranging from 50 to 10000, using the diatomic alkali-He-potential energy curves as input. From the obtained density profiles we evaluate average distances between the dopant atom and its direct helium neighborhood. The distances are then set in relation to the variation of the HFS constant with binding length in the simplified alkali-He-dimer model picture. This method yields reliable relative shifts but involves a systematic absolute error. Hence, the absolute values of the shifts are tied to one experimentally determined HFS constant for ^{85}Rb-He_{N = 2000}. With this parameter choice we obtain results in good agreement with the available experimental data for Rb and K^{a,b} confirming the predicted 1/N trend of the functional dependence^{c}. M. Koch, G. Auböck, C. Callegari, and W. E. Ernst, Phys. Rev. Lett. 103, 035302-1-4 (2009) M. Koch, C. Callegari, and W. E. Ernst, Mol. Phys. 108 (7), 1005-1011 (2010) A. W. Hauser, T. Gruber, M. Filatov, and W. E. Ernst, ChemPhysChem (2013) online DOI: 10.1002/cphc.201200697
Multiple scattering of photons by atomic hyperfine multiplets Cord A. Mller,1
why atoms behave differently from classical Rayleigh point-dipole scatterers, and how the classicalMultiple scattering of photons by atomic hyperfine multiplets Cord A. Müller,1 Christian Miniatura involving multiple scattering of photons by atoms are well adapted to study general concepts of quantum
Decoherence of Superradiant Scattering from Atoms without Confinement
NASA Astrophysics Data System (ADS)
Wen, Ming-Xuan; Niu, Lin-Xiao; Wang, Zhong-Kai; Zhai, Yue-Yang; Chen, Xu-Zong; Zhou, Xiao-Ji
2013-06-01
We study the decoherence of superradiant Rayleigh scattering from condensed atoms without confinement, by using two same pumping pulses with an interval time. The first pulse is to establish a matter-wave grating, and the coherence between different momentum modes is measured by the second pulse after a variable interval time. Different from the case in the trap, the distruction of the grating owing to the phase perturbation is very fast, and the superradiant process is inhibited very soon afterwards for released atoms. A semi-classical model is applied to simulate this phase perturbation, and the calculation agrees with our experimental results.
Scattering approach to dispersive atom-surface interactions
Dalvit, Diego; Messina, Riccardo; Maia Neto, Paulo; Lambrecht, Astrid; Reynaud, Serge
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.
Cavity-modified collective Rayleigh scattering of two atoms.
Reimann, René; Alt, Wolfgang; Kampschulte, Tobias; Macha, Tobias; Ratschbacher, Lothar; Thau, Natalie; Yoon, Seokchan; Meschede, Dieter
2015-01-16
We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case (N=2) is almost equal to the single-emitter case (N=1), which is in contrast to free-space where one would expect an N^{2} scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic. PMID:25635545
Cavity-Modified Collective Rayleigh Scattering of Two Atoms
NASA Astrophysics Data System (ADS)
Reimann, René; Alt, Wolfgang; Kampschulte, Tobias; Macha, Tobias; Ratschbacher, Lothar; Thau, Natalie; Yoon, Seokchan; Meschede, Dieter
2015-01-01
We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case (N =2 ) is almost equal to the single-emitter case (N =1 ), which is in contrast to free-space where one would expect an N2 scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic.
Cavity-Modified Collective Rayleigh Scattering of Two Atoms
René Reimann; Wolfgang Alt; Tobias Kampschulte; Tobias Macha; Lothar Ratschbacher; Natalie Thau; Seokchan Yoon; Dieter Meschede
2015-01-15
We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity, which is close to the lossless-cavity limit. Monitoring the cavity output power, we observe constructive and destructive interference of collective Rayleigh scattering for certain relative distances between the two atoms. Because of cavity backaction onto the atoms, the cavity output power for the constructive two-atom case ($N=2$) is almost equal to the single-emitter case ($N=1$), which is in contrast to free-space where one would expect an $N^2$ scaling of the power. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between the constructive and destructive atom configurations. Thereby we improve the control over the system to a level where the implementation of two-atom entanglement schemes involving optical cavities becomes realistic.
Electronic isotope shifts, muonic atoms, and electron scattering
Shera, E.B.
1982-01-01
The roles of electronic isotope shift, muonic atom, and electron scattering experiments in studying the nuclear charge distribution are discussed in terms of the potentials of each probe. Barium isotope shift data are presented as an example of a combined muonic-optical analysis and the results are compared with droplet and IBA model predictions. A survey of muonic and (e,e) results is presented with emphasis on shell-structure related features.
Photoionization of atomic ions and related electron scattering processes
Manson, Steven T.; Turner, Clay S. [Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303 (United States); Altun, Zikri [Department of Physics, Marmara University, Istanbul (Turkey); Chakraborty, Himadri; Dias, Eric; Deshmukh, Pranawa C. [Department of Physics, Indian Institute of Technology-Madras, Madras, India 600 036 (India)
1998-09-28
A selection of recent theoretical results revealing new phenomenology in the photoionization and electron elastic scattering properties of multicharged atomic ions. Particularly striking is the non-smooth behavior of cross sections along isoelectronic and isonuclear sequences of ions, indicating that, although ionic phenomena become simpler eventually, this does not happen monotonically or quickly. This has importance concerning the possibility of transferring our vast knowledge of neutrals to ionic species.
Nephtali Garrido; Hector H. Hernandez
2012-01-19
We put to the test an effective three-dimensional electrostatic potential, obtained effectively by considering an electrostatic source inside a (5+$p$)-dimensional braneworld scenario with $p$ compact and one infinite spacial extra dimensions in the RS II-$p$ model, for $p=1$ and $p=2$. This potential is regular at the source and matches the standard Coulomb potential outside a neighborhood. We use variational and perturbative approximation methods to calculate corrections to the ground energy of the Helium atom modified by this potential, by making use of a 6 and 39-parameter trial wave function of Hylleraas type for the ground state. These corrections to the ground-state energy are compared with experimental data for Helium atom in order to set bounds for the extra dimensions length scale. We find that these bounds are less restrictive than the ones obtained by Morales et. al. through a calculation using the Lamb shift in Hydrogen.
Dynamic correlation in high-harmonic generation for helium atoms in intense visible lasers
G. A. McKenna; R. Nepstad; J. F. McCann; D. Dundas
2009-05-20
We investigate the effect of dynamic electron correlation on high-harmonic generation in helium atoms using intense visible light (\\lambda=390nm). Two complementary approaches are used which account for correlation in an approximate manner: time-dependent density-functional theory and a single-active-electron model. For intensities I~10^{14} W/cm^2, the theories are in remarkably good agreement for the dynamic polarization and harmonic spectrum. This is attributed to a low-frequency collective mode together with a high-frequency single-electron response due to the nuclear singularity, both of which dominate electron correlation effects. A time-frequency analysis is used to study the timing and emission spectrum of attosecond bursts of light. For short pulses, we find a secondary maximum below the classical cut-off. The imprint of the carrier-envelope-phase, for the time-integrated spectral density appears at frequencies above the high-frequency drop-off, consistent with previous studies in the infrared \\lambda~800nm.
A low energy helium atom diffraction study of decanethiol self-assembled on Au(111)
NASA Astrophysics Data System (ADS)
Camillone, N.; Leung, T. Y. B.; Scoles, G.
1997-03-01
We report the results of low energy helium atom diffraction studies of the surface of decanethiol self-assembled on the (111) face of single crystal gold. Our survey of 13 separate samples indicates that for decanethiol the standard self-assembly methodology results in monolayers of widely varying quality. We observe that surface order is generally enhanced by preparing monolayers in micromolar solution as compared to the usual millimolar preparation [M.D. Porter et al., J. Am. Chem. Soc. 109 (1987) 3559; C.D. Bain et al., J. Am. Chem. Soc. 111 (1989) 321]. This result is in agreement with a parallel study conducted using grazing-incidence X-ray diffraction (GIXD). Particular attention is focused on two exceptionally high-quality samples which show more clearly than ever before the c(4?3 × 2 ?3)R30° diffraction pattern first observed for octadecanethiol monolayers [N. Camillone III et al., J. Chem. Phys. 98 (1993) 3503]. The diffraction patterns observed for these samples and their structural implications are discussed in light of recent advances made in other laboratories. We also discuss the results of thermal annealing experiments.
Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.
Falcinelli, Stefano; Candori, Pietro; Bettoni, Marta; Pirani, Fernando; Vecchiocattivi, Franco
2014-08-21
The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X?(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B?(2)B2) excited states, respectively. The recorded energy shifts indicate that in the case of He* and Ne*-H2S the autoionization dynamics depends on the features of the collision complex and is mainly driven by an effective global attraction that comes from a balance among several non covalent intermolecular interaction components. This suggests that the Penning ionization should take place, in a specific range of intermolecular distances, as we have already observed in the case of Penning ionization of water molecules [Brunetti, B. G.; Candori, P.; Falcinelli, S.; Pirani, F.; Vecchiocattivi, F. J. Chem. Phys. 2013, 139, 164305-1-164305-8]. PMID:24796487
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
Scattering of Cold-Atom Coherences by Hot Atoms: Frequency Shifts from Background-Gas Collisions
NASA Astrophysics Data System (ADS)
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.
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.
S. Deguchi; W. D. Watson
1985-01-01
The profile of Lyman-alpha radiation in an expanding gas cloud is calculated in detail in order to determine the color temperature of the radiation scattered by an H I atom within the cloud. Scattering of Lyalpha is likely to dominate in the excitation of the 21 cm transition of H I in astronomical gas clouds with very low densities. The
Entanglement entropies in the ground states of helium-like atoms
Przemyslaw Koscik; Anna Okopinska
2014-06-01
We examine the entanglement in the ground states of helium and helium-like ions using an original Hylleraas expansion. The von Neumann and linear entropies of the reduced density matrix are accurately computed by performing the Schmidt decomposition of the S singlet spatial wavefunctions. The results presented are more accurate than currently available in published literature.
Double photoionization of helium with synchrotron x-rays: Proceedings
Not Available
1994-01-01
This report contains papers on the following topics: Overview and comparison of photoionization with charged particle impact; The ratio of double to single ionization of helium: the relationship of photon and bare charged particle impact ionization; Double photoionization of helium at high energies; Compton scattering of photons from electrons bound in light elements; Electron ionization and the Compton effect in double ionization of helium; Elimination of two atomic electrons by a single energy photon; Double photoionization of helium at intermediate energies; Double Photoionization: Gauge Dependence, Coulomb Explosion; Single and Double Ionization by high energy photon impact; The effect of Compton Scattering on the double to single ionization ratio in helium; and Double ionization of He by photoionization and Compton scattering. These papers have been cataloged separately for the database.
On highly accurate calculations of the excited $n^1S(L = 0)-$states in helium atoms
Alexei M. Frolov; David M. Wardlaw
2011-02-25
The total energies and various bound state properties of the excited $2^1S(L = 0)-$states in two-electron helium atoms, including the ${}^{\\infty}$He, ${}^4$He and ${}^3$He atoms, are determined to very high numerical accuracy. The convergence of the results obtained for some electron-nuclear and electron-electron expectation values and, in particular, for the electron-nuclear and electron-electron cusp values, is discussed. The field component of the isotope shift and lowest order QED correction are estimated for the $2^1S(L = 0)-$states in the ${}^4$He and ${}^3$He atoms. We also apply our highly accurate methods to numerical computations of the excited $n^1S-$states (for $n$ = 3 and 4) in two-electron atomic systems.
Scattering of an ultrashort electromagnetic radiation pulse by an atom in a broad spectral range
Astapenko, V. A.
2011-02-15
The scattering of an ultrashort electromagnetic pulse by atomic particles is described using a consistent quantum-mechanical approach taking into account excitation of a target and nondipole electromagnetic interaction, which is valid in a broad spectral range. This approach is applied to the scattering of single- and few-cycle pulses by a multielectron atom and a hydrogen atom. Scattering spectra are obtained for ultrashort pulses of different durations. The relative contribution of 'elastic' scattering of a single-cycle pulse by a hydrogen atom is studied in the high-frequency limit as a function of the carrier frequency and scattering angle.
Optical Manipulation of Light Scattering in Cold Atomic Rubidium
NASA Astrophysics Data System (ADS)
Olave, R. G.; Win, A. L.; Kemp, K.; Roof, S. J.; Balik, S.; Havey, M. D.; Sokolov, I. M.; Kupriyanov, D. V.
2015-06-01
A brief perspective on light scattering in dense and cold atomic rubidium is presented. We particularly focus on the influence of auxiliary applied fields on the system response to a weak and nearly resonant probe field. Auxiliary fields can strongly disturb light propagation; in addition to the steady state case, dynamically interesting effects appear clearly in both the time domain, and in the optical polarization dependence of the processes. Following a general introduction, two examples of features found in such studies are presented. These include nonlinear optical effects in (a) comparative studies of forward- and fluorescence-configuration scattering under combined excitation of a control and probe field, and (b) manipulation of the spatial structure of the optical response due to a light shifting strong applied field.
Optical Manipulation of Light Scattering in Cold Atomic Rubidium
Olave, R G; Kemp, Kasie; Roof, S J; Balik, S; Havey, M D; Sokolov, I M; Kupriyanov, D V
2014-01-01
A brief perspective on light scattering in dense and cold atomic rubidium is presented. We particularly focus on the influence of auxiliary applied fields on the system response to a weak and nearly resonant probe field. Auxiliary fields can strongly disturb light propagation; in addition to the steady state case, dynamically interesting effects appear clearly in both the time domain, and in the optical polarization dependence of the processes. Following a general introduction, two examples of features found in such studies are presented. These include nonlinear optical effects in (a) comparative studies of forward- and fluorescence-configuration scattering under combined excitation of a control and probe field, and (b) manipulation of the spatial structure of the optical response due to a light shifting strong applied field.
Observation of correlated X-ray scattering at atomic resolution
Mendez, Derek; Lane, Thomas J.; Sung, Jongmin; Sellberg, Jonas; Levard, Clément; Watkins, Herschel; Cohen, Aina E.; Soltis, Michael; Sutton, Shirley; Spudich, James; Pande, Vijay; Ratner, Daniel; Doniach, Sebastian
2014-01-01
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 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, Clément; 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
Rayleigh Scattering at Atoms with Dynamical J. Frohlich 1# , M. Griesemer 2+ and B. Schlein 3#
Rayleigh Scattering at Atoms with Dynamical Nuclei J. FrË?ohlich 1# , M. Griesemer 2+ and B. Schlein for ionization of the atom (Rayleigh scattering). The kinematics of the electron and the nucleus is chosen of Rayleigh scattering is established rigorously. On the way towards proving this result, it is shown that
Atomic form factors, incoherent scattering functions, and photon scattering cross sections
J. H. Hubbell; Wm. J. Veigele; E. A. Briggs; R. T. Brown; D. T. Cromer; R. J. Howerton
1975-01-01
Tabulations are presented of the atomic form factor, F (?,Z), and the incoherent scattering function, S (x,Z), for values of x (=sin &Vthgr;\\/2)\\/?) from 0.005 A??1 to 109 A??1, for all elements A=1 to 100. These tables are constructed from available state-of-the-art theoretical data, including the Pirenne formulas for Z=1, configuration-into action results by Brown using Brown-Fontana and Weiss correlated
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.
Ultracold neutron production and up-scattering in superfluid helium between 1.1 K and 2.4 K
Leung, K K H; Piegsa, F M; Simson, M; Zimmer, O
2015-01-01
Ultracold neutrons (UCNs) were produced in a 4 liter volume of superfluid helium using the PF1B cold neutron beam facility at the Institut Laue-Langevin and then extracted to a detector at room temperature. With a converter temperature of 1.08 K the number of accumulated UCNs was counted to be $91,\\!700 \\pm 300$. From this, we derive a volumetric UCN production rate of $(6.9 \\pm 1.7)\\,\\mathrm{cm^{-3}\\,s^{-1}}$, which includes a correction for losses in the converter during UCN extraction caused by a short storage time, but not accounting for UCN transport and detection efficiencies. The up-scattering rate of UCNs due to excitations in the superfluid was studied by scanning the temperature between 1.2-2.4 K. Using the temperature-dependent UCN production rate calculated from inelastic neutron scattering data in the analysis, the only UCN up-scattering process found to be present was from two-phonon scattering. Our analysis rules out contributions from the other scattering processes to $\\lesssim 10\\%$ of their ...
Ultracold neutron production and up-scattering in superfluid helium between 1.1 K and 2.4 K
K. K. H. Leung; S. Ivanov; F. M. Piegsa; M. Simson; O. Zimmer
2015-07-27
Ultracold neutrons (UCNs) were produced in a 4 liter volume of superfluid helium using the PF1B cold neutron beam facility at the Institut Laue-Langevin and then extracted to a detector at room temperature. With a converter temperature of 1.08 K the number of accumulated UCNs was counted to be $91,\\!700 \\pm 300$. From this, we derive a volumetric UCN production rate of $(6.9 \\pm 1.7)\\,\\mathrm{cm^{-3}\\,s^{-1}}$, which includes a correction for losses in the converter during UCN extraction caused by a short storage time, but not accounting for UCN transport and detection efficiencies. The up-scattering rate of UCNs due to excitations in the superfluid was studied by scanning the temperature between 1.2-2.4 K. Using the temperature-dependent UCN production rate calculated from inelastic neutron scattering data in the analysis, the only UCN up-scattering process found to be present was from two-phonon scattering. Our analysis rules out contributions from the other scattering processes to $\\lesssim 10\\%$ of their predicted levels.
Pifrader, Alexandra; Allard, Olivier; Auboeck, 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 ({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.
Many-electron scattering applied to atomic point contacts.
McDermott, Shane; Greer, J C
2012-03-28
Electron transport in a strong coupling regime is investigated by applying the many-electron correlated scattering (MECS) method to an atomic point contact model. Comparing the theoretical calculations to the quantum of conductance obtained experimentally for these systems allows for the error associated with the numerical implementation of the MECS method to be estimated and attributed to different components of the calculations. Errors associated with implementing the scattering boundary conditions and determination of the applied voltage in a finite explicit electrode model are assessed, and as well the impact on the basis set description on predicting the conductance is examined in this weakly correlated limit. The MECS calculation for the atomic point contact results in a conductance of 0.6G(0), in reasonable agreement with measurements for gold point contacts where approximately the conductance quantum G(0) is obtained. The analysis indicates the error attributable to numerical approximations and the explicit electrode model introduced in the calculations should not exceed 40% of the total conductance, whereas the effect of electron-electron correlations, even in this weakly correlated regime, can result in as much as a 30% change in the predicted conductance. PMID:22369783
He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth
NASA Astrophysics Data System (ADS)
Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.
He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth
Safron, S. A.; Skofronick, J. G.
1992-01-01
Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.
Luppov, V.G.; Kaufman, W.A.; Hill, K.M.
1993-04-01
A 350 mK helium-4 coated mirror was used to increase the intensity of an ultra-cold electron-spin-polarized atomic hydrogen beam. The mirror uses the observed specular reflection of atomic hydrogen from a superfluid-helium-covered surface. A quasi-parabolic polished copper mirror was installed with its focus at the 5 mm diameter exit aperture of an atomic hydrogen stabilization cell in the gradient of an 8 T solenoid. The four-coned mirror shape, which was designed specifically for operation in the gradient, increased the beam intensity focused by a sextupole magnet into a compression tube detector more than seven-fold.
Low-Energy Elastic Electron Scattering by Atomic Oxygen
NASA Technical Reports Server (NTRS)
Zatsarinny O.; Bartschat, K.; Tayal, S. S.
2006-01-01
The B-spline R-matrix method is employed to investigate the low-energy elastic electron scattering by atomic oxygen. Flexible non-orthogonal sets of radial functions are used to construct the target description and to represent the scattering functions. A detailed investigation regarding the dependence of the predicted partial and total cross sections on the scattering model and the accuracy of the target description is presented. The predicted angle-integrated elastic cross sections are in good agreement with experiment, whereas significant discrepancies are found in the angle-differential elastic cross sections near the forward direction. .The near-threshold results are found to strongly depend on the treatment of inner-core short-range correlation effects in the target description, as well as on a proper account of the target polarizability. A sharp increase in the elastic cross sections below 1 eV found in some earlier calculations is judged to be an artifact of an unbalanced description of correlation in the N-electron target structure and the (N+l)-electron-collision problems.
Physics of Polarized Scattering at Multi-level Atomic Systems
NASA Astrophysics Data System (ADS)
Stenflo, J. O.
2015-03-01
The symmetric peak observed in linear polarization in the core of the solar sodium D1 line at 5896 Å has remained enigmatic since its discovery nearly two decades ago. One reason is that the theory of polarized scattering has not been experimentally tested for multi-level atomic systems in the relevant parameter domains, although the theory is continually being used for the interpretation of astrophysical observations. A laboratory experiment that was set up a decade ago to find out whether the D1 enigma is a problem of solar physics or quantum physics revealed that the D1 system has a rich polarization structure in situations where standard scattering theory predicts zero polarization, even when optical pumping of the m state populations of the hyperfine-split ground state is accounted for. Here we show that the laboratory results can be modeled in great quantitative detail if the theory is extended to include the coherences in both the initial and final states of the scattering process. Radiative couplings between the allowed dipole transitions generate coherences in the initial state. Corresponding coherences in the final state are then demanded by a phase closure selection rule. The experimental results for the well understood D2 line are used to constrain the two free parameters of the experiment, collision rate and optical depth, to suppress the need for free parameters when fitting the D1 results.
Plasmon enhanced Raman scattering effect for an atom near a carbon nanotube.
Bondarev, I V
2015-02-23
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. PMID:25836436
Rayleigh scattering by neutral atoms, 100 eV to 10 MeV
Lynn Kissel; R. H. Pratt; S. C. Ray
1980-01-01
We calculate the contribution to elastic photon scattering from an atom due to scattering off the bound atomic electrons (Rayleigh scattering). We compare predictions resulting from our numerical evaluation of the relativistic second-order S matrix in a screened central potential with other theories, particularly the form-factor approximation. We give a prescription for accurate O(1%) evaluation of total-atom Rayleigh amplitudes (summed
Miyake, Hirokazu; Siviloglou, Georgios A; Puentes, Graciana; Pritchard, David E; Ketterle, Wolfgang; Weld, David M
2011-10-21
We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence. PMID:22107532
Plasmon enhanced Raman scattering effect for an atom near a carbon nanotube
Bondarev, I. V.
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.
Yixuan Wang; Conghao Deng; Dacheng Feng
1995-01-01
By introducing a simple spatially symmetric correlation function, we have modified a hyperspherical harmonic and generalized Laguerre function (HHGLF) into a correlation function HHGLF (CFHHGLF) expansion method and used it to solve directly the Schrödinger equations of ground-state lithium and excited helium (2 1S) atoms. In such a scheme, the wave function of the lithium atom is decomposed into the
Benoit Gremaud; Dominique Delande
1998-02-04
We calculate the photo-ionization cross-section from the ground state of the helium atom, using the complex rotation method and diagonalization of sparse matrices. This produces directly the positions and widths of the doubly excited 1Po resonances together with the photo-ionization cross-section. Our calculations up to the N=9 threshold are in perfect agreement with recent experimental data and show the transition from a regular structure at low energy to a chaotic one at high energy, where various resonances strongly overlap.
Equal energy sharing photo double ionization of the Helium atom at 20 and 40eV above threshold
Das, J N; Paul, S
2003-01-01
In this article we present TDCS for equal energy sharing kinematics for double photoionization of the helium atom at 20 and 40eV above threshold in the framework of the hyperspherical partial wave theory. This supplements our earlier work \\cite{DCP03} in which we were able to show gauge independence in our formalism. Also in this work we treat cases in which the Stokes parameter S$_1 < 1$ so that linear polarization of the photon source is also taken into account. Agreement in shape with the CCC \\cite{BK03,HB98} data and the experiments appears to be excellent.
The Influence of Atomic Model on Scattering Polarization Profile
NASA Astrophysics Data System (ADS)
Li, H.; Qu, Z. Q.
2014-09-01
The diagnostic of magnetic field is very important in solar physics. Stokes parameters I, Q, U, and V can give a complete description of the state of polarization of a beam of light. By inversion of Stokes parameters, the magnetic field in the sun can be obtained. In the recent decades, the diagnostic of magnetic field has been almost based on the Zeeman effect in presence of a strong magnetic field. But in the quiet sun region, the turbulent magnetic field strength is usually less than 100 Gs. Because the Hanle effect is sensitive to a weak magnetic field, it can provide a diagnostic tool for a weak magnetic field. However, it is not easy to obtain the weak field with this effect, and a complete understanding of the polarization mechanism is needed. This paper focuses on the influence of different atomic models on the scattering polarization and Hanle effect. We adopt the seven-, four-, and two-level atomic models to investigate the theoretical linear polarization profiles of MgI b triplet so that we can probe the magnetic field more precisely. In this calculation, we use a typical temperature of 5755 K, corresponding to the temperature of MgI b triplet formation region. It does find that the results for the seven- and four-level atomic models are almost the same. The polarization degrees are nearly unaffected by the populations of MgI atom's levels above the transition levels. There is a big difference between the results from the two- and multi-level atomic models. For the two-level atomic model, the b_4 line is not affected by the Hanle effect in the lower level. But for the multi-level atomic models, it does. And the lower level Hanle effect of b_2 line in the multi-level approximation is much more obvious than that in the two-level approximation. This study is thus useful to produce the theoretical profiles for diagnosing a weak magnetic field, and finally b_2 line is the most suitable candidate for the purpose.
NASA Astrophysics Data System (ADS)
Perez-Rios, Jesus; Ragole, Steve; Wang, Jia; Greene, Chris H.
2014-03-01
Classical trajectory and quantum calculations of helium three-body recombination are compared. The energies treated range from the ultracold up to the thermal regime. Quantum calculations are performed for the J? = 0+ symmetry of the three-body recombination rate in order to compare with the classical results for zero angular momentum, yielding a good agreement for E ~ 1 K. The classical calculations are treated as a scattering process in n = 6 -dimensions, and the results emerge from trajectory calculations. The classical threshold law is derived and numerically confirmed for the three-body recombination rate. Finally, a relationship is found between the quantum and classical three-body elastic cross section for a hard hypersphere that resembles the well-known shadow scattering in two-body collisions. Supported by the Department of Energy, Office of Science.
Characteristics of the Interstellar Helium by the He I 58.4-nm Optical Observation
NASA Astrophysics Data System (ADS)
Yamazaki, A.; Yoshikawa, I.; Shiomi, K.; Nakamura, M.; Miyake, W.
2001-05-01
There is a region with high-density helium gas in shape of a corn in the solar system, which is called the helium cone. The helium atoms originate from the local interstellar medium (LISM), and are injected into the heliosphere with the interstellar wind. The solar gravity force and radiation pressure decide the helium density distribution in the helium cone. Therefore the velocity, the density, and the temperature of the interstellar helium is estimated from the helium density distribution in the helium cone. An eXtreme Ultra-Violet (XUV) scanner has been built for Japanese first Mars Explorer, Planet-B. The scanner has detected the He I 58.4-nm emission resonantly scattered by the helium atoms in the helium cone on the Planet-B's cruise orbit to Mars. The He I emission rate is estimated from the helium cone formation model under the condition that the velocity vector of the interstellar wind and the loss rate (ionization rate) of helium atom in the interplanetary space are constant. The best agreement between the observation and the model gives the LISM parameters.
A. B. Kuklov; B. V. Svistunov
1999-05-29
We suggest measuring the one-particle density matrix of a trapped ultracold atomic cloud by scattering fast atoms in a pure momentum state off the cloud. The lowest-order probability for the process, resulting in a pair of outcoming fast atoms for each incoming one, as well as of its time reversed counterpart, turns out to be given by the Fourier transform of the density matrix. Accordingly, important information about quantum correlations can be deduced directly from the differential scattering cross-section of these processes. Several most interesting cases of scattering - from a single condensate containing a vortex, and from a split condensate characterized by some phase difference - are discussed.
Some moments of radial electron density in closed-shell atoms and their atomic scattering factors
NASA Astrophysics Data System (ADS)
Pucci, R.; March, N. H.
1982-04-01
The scattering factor f(K) for x rays from atomic ions with closed shells can be written in terms of the radial electron density D(r) = 4?r2?(r), with ?(r) the electron density. The small K expansion of f(K) focuses on the moments
Rayleigh Scattering in the Atmospheres of Hot Stars
NASA Astrophysics Data System (ADS)
Fišák, J.; Krti?ka, J.; Kubát, J.
2015-04-01
Rayleigh scattering is the process of interaction of photons with bound electrons. This process is often neglected in hot star model atmospheres. The reason is that a large fraction of hydrogen and helium atoms are singly ionized, and the scattering cross section of singly ionized helium is by two orders of magnitude lower than the neutral hydrogen scattering cross section. We studied the effect of Rayleigh scattering by neutral hydrogen and singly ionized helium in the stellar model atmospheres. We computed the models for the B-type stars with solar composition and helium overabundant atmospheres N(He)/N(H)=10. The results show that Rayleigh scattering by singly ionized helium can be a significant opacity source for the helium-rich stars, and this process can be included in hot star model atmospheres.
Superelastic electron scattering from laser-excited cesium atoms
Slaughter, D. S.; Karaganov, V.; Brunger, M. J.; Teubner, P. J. O. [School of Chemistry, Physics and Earth Sciences, Flinders University, GPO Box 2100, Adelaide, 5001 (Australia); Bray, I. [ARC Centre for Antimatter-Matter Studies, Curtin University, Perth, 6845 (Australia); Bartschat, K. [Department of Physics and Astronomy, Drake University, Des Moines, Iowa 50311 (United States)
2007-06-15
We present results from a joint experimental and theoretical investigation of superelastic electron scattering from laser-excited Cs atoms in the (6p){sup 2}P{sub 3/2} state. Comparison of the measured pseudo-Stokes parameters P{sub 1}, P{sub 2}, and P{sub 3} and the total degree of polarization P{sup +} for incident energies of 5.5 eV and 13.5 eV, respectively, with theoretical predictions based upon a nonrelativistic convergent close-coupling method and a 24-state semirelativistic Breit-Pauli R-matrix approach indicates that driving channel coupling to convergence for these observables is more important than accounting for relativistic effects.
Carroll, David L.
Gain and continuous-wave laser oscillation on the 1315 nm atomic iodine transition pumped by an air-helium on the 1315 nm transition of atomic iodine using the energy transferred to I 2 P1/2 from O2 a1 produced- ported by McDermott et al.1 operates on the electronic tran- sition of the iodine atom at 1315 nm, I 2 P1
NASA Astrophysics Data System (ADS)
Merabet, H.; Bruch, R.; Hanni, J.; Bailey, M.; Godunov, A. L.; McGuire, J. H.; Fursa, D. V.; Bray, I.; Bartschat, K.; Tseng, H. C.; Lin, C.-D.
2003-01-01
Experimental scattering-angle-integrated (total) cross-sections ?¯, (scattering) angle-integrated magnetic sublevel cross-sections ?¯ML, and degree of linear polarization data have been measured in the extreme ultraviolet (EUV) wavelength region following decay of HeI (1 snp) 1P 0 ( n=2-5) states induced by electron and proton impact on a neutral helium target. These measurements are compared with a first Born approach as well as more sophisticated theoretical calculations. Specifically, theoretical values for electron impact include convergent close-coupling (CCC) and R-matrix with pseudo states (RMPS) methods in addition to first Born (Born 1) approximation while proton induced excitation cross-sections are compared with atomic-orbital close-coupling (AOCC) and first Born predictions.
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.
Positron scattering from hydrogen atom embedded in dense quantum plasma
Bhattacharya, Arka [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India)] [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India); Kamali, M. Z. M. [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)] [Centre for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ghoshal, Arijit [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India) [Department of Mathematics, Burdwan University, Golapbag, Burdwan, West Bengal 713 104 (India); Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ratnavelu, K. [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)] [Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia)
2013-08-15
Scattering of positrons from the ground state of hydrogen atoms embedded in dense quantum plasma has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in dense quantum plasma have been represented by exponential cosine-screened Coulomb potentials. Variationally determined hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s?1s and 2s?2s elastic collisions, 1s?2s excitation, positronium formation, elastic proton-positronium collisions, have been reported in the energy range 13.6-350 eV. Furthermore, a comparison has been made on the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which the plasma screening effect has been represented by the Debye model. Our results for the unscreened case are in fair agreement with some of the most accurate results available in the literature.
Time-Dependent Approach to Electron--Atom Scattering.
NASA Astrophysics Data System (ADS)
Krilov, Goran
1997-04-01
The B-spline method [1] was used to represent the Hamiltonian describing the interaction of a projectile and a target on a discrete lattice. The time-dependent Schrödinger equation was then solved by explicit integration using different time propagation schemes, such as Taylor expansion and the ``leap-frog'' method [2]. In order to assess the accuracy and efficiency of the different approaches, the method was tested for several one-dimensional model problems, such as scattering of a Gaussian wavepacket from various arrangements of steps and barriers. The program is currently being applied to the two-dimensional Temkin-Poet model of electron scattering from atomic hydrogen [3]. The most recent results for excitation and ionization cross sections will be presented at the conference and compared with other theoretical work. 1. A.S. Umar, J. Wu, M.R. Strayer and C. Bottcher, J. Comp. Phys. 93, 1. 426 (1991) 2. W.H. Press, S.A. Teucholsky, V.T. Vetterling, and B.P. Flannery, 2. Numerical Recipes (Cambridge University Press, New York 1992) 3. A. Temkin, Phys. Rev. A 126, 130 (1962)
Electron-helium scattering in a 1.17 eV laser field: The effect of polarization direction
NASA Astrophysics Data System (ADS)
deHarak, B. A.; Nosarzewski, Benjamin; Siavashpouri, Mahsa; Martin, N. L. S.
2014-09-01
We report measurements of one-photon emission during the elastic scattering of electrons by He atoms through 90? in the presence of 1.17 eV photons from a Nd:YAG laser. The incident energy of the electrons was in the range 30-200 eV and the linear polarization direction of the laser was varied over 180? in the plane, perpendicular to the scattering plane, that contains the momentum transfer direction. Our results are perfectly consistent with the Kroll-Watson approximation. In particular, we see no evidence of free-free transitions when the polarization is perpendicular to the momentum transfer direction.
Relativistic effects on low-frequency Rayleigh scattering including spin flip for hydrogenic atoms
Viorica Florescu; M. Marinescu; R. H. Pratt
1990-01-01
An approximate analytic expression is presented for the LF ground-state relativistic Rayleigh scattering matrix elements for hydrogenic atoms, including the possibility of electron spin flip as a result of the elastic photon atom scattering. The expression is obtained by taking the long-wavelength approximation in the relativistic Coulomb matrix elements, without neglecting the photon frequency dependence in the Coulomb Green operator.
Manson, Joseph R.
Eikonal approximation in atom-surface scattering: Effects of a corrugated attractive well J. R for the scattering of atomic beams from surfaces, is extended to include a periodic corrugation of the leading edge for estimating small effects of corrugation of the attractive physisorption potential on the diffraction spectra
Paris-Sud XI, Université de
-25 RAYLEIGH AND BRILLOUIN SCATTERING FROM LIQUID HELIUM E. R. PIKE Royal Radar Establishment, St. Andrews Road of unshifted scattering in pure 4He below the 1point has been verified (Fig. 1). Above the 1point the Rayleigh of Rayleigh and Brillouin scattering has now been observed (Fig. 5). The intensity of scattering from
Exact quantum scattering calculations of transport properties: CH2(X?3B1, a?1A1)-helium.
Dagdigian, Paul J; Alexander, Millard H
2013-04-28
Transport properties for collisions of methylene, in both its ground X?(3)B1 and low-lying a?(1)A1 electronic states, with helium have been computed using recently computed high-quality ab initio potential energy surfaces (PESs). Because of the difference in the orbital occupancy of the two electronic states, the anisotropies of the PESs are quite different. The CH2(a?)-He PES is very anisotropic because of the strong interaction of the electrons on the helium atom with the unoccupied CH2 orbital perpendicular to the molecular plane, while the anisotropy of the CH2(X?)-He PES is significantly less since this orbital is singly occupied in this case. To investigate the importance of the anisotropy on the transport properties, calculations were performed with the full potential and with the spherical average of the potential for both electronic states. Significant differences (over 20% for the a? state at the highest temperatures considered) in the computed transport properties were found. PMID:23635136
ccsd-00000135:24Jan2003 Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices
Paris-Sud XI, Université de
ccsd-00000135:24Jan2003 Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices F: January 24, 2003) We investigate Rayleigh scattering in dissipative optical lattices. In particular-propagating material observables. In this work we investigate the mechanism behind the Rayleigh scatter- ing
State dependence of rayleigh scattering from a n =2 state of hydrogenlike atoms
Aurelia Cionga; Viorica Florescu
1986-01-01
We consider Rayleigh scattering from a hydrogenlike atom in an arbitrary excitedn=2 state, and we investigate theoretically the dependence of the scattered radiation intensity and Stokes parameters on the state multipoles for the case of unpolarized incident radiation. Because in then=2 case Rayleigh scattering can not be accompanied by the change of the electron angular momentum, only 10 out of
Scattering of Polarized Radiation by Atoms in Magnetic and Electric Fields
Yee Yee Oo; K. N. Nagendra; Sharath Ananthamurthy; G. Ramachandran
2005-09-26
The polarization of radiation by scattering on an atom embedded in combined external quadrupole electric and uniform magnetic fields is studied theoretically. Analytic formulae are derived for the scattering phase matrix. Limiting cases of scattering under Zeeman effect, and Hanle effect in weak magnetic fields are discussed.
Detection of individual atoms in helium buffer gas and observation of their real-time motion
NASA Technical Reports Server (NTRS)
Pan, C. L.; Prodan, J. V.; Fairbank, W. M., Jr.; She, C. Y.
1980-01-01
Single atoms are detected and their motion measured for the first time to our knowledge by the fluorescence photon-burst method in the presence of large quantities of buffer gas. A single-clipped digital correlator records the photon burst in real time and displays the atom's transit time across the laser beam. A comparison is made of the special requirements for single-atom detection in vacuum and in a buffer gas. Finally, the probability distribution of the bursts from many atoms is measured. It further proves that the bursts observed on resonance are due to single atoms and not simply to noise fluctuations.
Ruzic, D.N.; Cohen, S.A.
1985-04-01
Measurements of energy-dependent scattering cross sections for 30 to 1800 eV D incident on He, Ne, Ar, and Kr, and for 40 to 850 eV He incident on He, Ar, and Kr are presented. They are determined by using the charge-exchange efflux from the Princeton Large Torus tokamak as a source of D or He. These neutrals are passed through a gas-filled scattering cell and detected by a time-of-flight spectrometer. The cross section for scattering greater than the effective angle of the apparatus (approx. =20 mrad) is found by measuring the energy-dependent attenuation of D or He as a function of pressure in the scattering cell. The interatomic potential is extracted from the data.
Ha, Taekjip
The helium atom consists of a nucleus with charge +2e and no spin, and two electrons, each. The variation is to let the wave function of each of the two electrons be that of an atom of some other (not' that minimizes the helium ground state energy. NOTE: The ground state wave function of an electron
Elastic scattering of polarized protons on helium three at 800 MeV
Azizi, A.
1985-07-01
A set of spin dependent parameters and cross sections has been measured for polarized p-/sup 3/He elastic scattering over the range of q .7 to 4.2 fm/sup -1/. The experiment was done at the Los Alamos Meson Physics Facility (LAMPF) using the High Resolution Spectrometer (HRS) with a polarized proton beam at .8 GeV. The focal plane polarimeter of the HRS was used to determine the spin direction of the scattered proton. Since /sup 3/He is one of the simplest nuclei, polarized p-/sup 3/He scattering provides a very sensitive test of multiple scattering theories. The theoretical analysis was done by using two different wave functions for /sup 3/He as input to the multiple scattering theory. The theoretical calculations and experimental data together will give us useful information about nucleon-nucleon amplitudes and also help us to obtain a better understanding of the scattering process. 68 refs., 55 figs., 9 tabs.
Spectroscopy of li Atoms and li Dimers in the Triplet Manifold on the Surface of Helium Nanodroplets
NASA Astrophysics Data System (ADS)
Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.
2013-06-01
Helium nanodroplets (He_{N}) have attracted strong interest as superfluid nanocryostats and can serve as a tool for the efficient preparation of tailored molecules and clusters. Alkali-metal atoms and molecules are bound only weakly to the He_{N} surface. The fragility of these systems leads preferably to the formation of high-spin molecules on He_{N}. We use this property of helium nanodroplets for the preparation of Li dimers in their triplet ground state (1^{3}?_{u}^{+}). We present an excitation spectrum of the 2^{3}?_{g}(? ' = 0 - 10) ? 1^{3}?_{u}^{+}(? '' = 0) transition. The interaction between the molecule and the droplet manifests in a broadening of the transitions with a characteristic asymmetric form. The broadening extents to the blue side of each vibronic level, which is caused by the simultaneous excitation of the molecule and vibrations of the droplet (phonons). The two isotopes of Li form ^{6}Li_{2}, ^{7}Li_{2} as well as the isotope mixed ^{6}Li^{7}Li molecule on the droplet surface. By using resonance enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy isotope dependent effects could be studied. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) J. Higgins, C. Callegari, J. Reho, F. Stienkemeier, W.E. Ernst, M. Gutowski and G. Scoles, J. Phys. Chem. A, 102, 4952-4965 (1998) J. Higgins, C. Callegari, J. Reho, F. Stienkemeier, W.E. Ernst, K.K. Lehmann, M. Gutowski and G. Scoles, Science, 273, 629-631, (1996)
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)).
NASA Astrophysics Data System (ADS)
Blauth, D.; Winter, H.
2011-06-01
Negative ion fractions, projectile energy loss, and the emission of electrons is studied for grazing scattering of hydrogen and helium atoms/ions from a clean and oxidized NiAl(1 1 0) surface. Making use of translation energy spectroscopy and the coincident detection of the number of emitted electrons we have studied the electronic interaction mechanisms for the change from a clean metal target to an insulator surface via the preparation of a well defined ultrathin alumina film on top of the metal substrate. We find that already for a monolayer thick oxide film the characteristic different features of electronic processes for the surface of an insulator crystal are present.
Dynamics of scattering on a classical two-dimensional artificial atom.
Peelaers, H; Partoens, B; Tatyanenko, D V; Peeters, F M
2007-03-01
A classical two-dimensional (2D) model for an artificial atom is used to make a numerical "exact" study of elastic and nonelastic scattering. Interesting differences in the scattering angle distribution between this model and the well-known Rutherford scattering are found in the small energy and/or small impact parameter scattering regime. For scattering off a classical 2D hydrogen atom different phenomena such as ionization, exchange of particles, and inelastic scattering can occur. A scattering regime diagram is constructed as function of the impact parameter (b) and the initial velocity (v) of the incoming particle. In a small regime of the (b,v) space the system exhibits chaos, which is studied in more detail. Analytic expressions for the scattering angle are given in the high impact parameter asymptotic limit. PMID:17500808
Positive effect of scattering strength of a microtoroidal cavity on atomic entanglement evolution
Jin Jiasen; Yu Changshui; Pei Pei; Song Heshan [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)
2010-04-15
We show that the rough surface of a microtoroidal cavity (scattering strength) can play a constructive role by studying the entanglement of two atoms surrounding the cavity. Analytical results show that appropriate surface roughness can enhance the atomic entanglement. In particular, the rough surface can also compensate for the loss of maximal entanglement during the evolution caused by cavity leakage and atomic spontaneous emission.
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
NASA Astrophysics Data System (ADS)
Swaczyna, P.; Grzedzielski, S.; Bzowski, M.
2014-12-01
Expected fluxes of energetic neutral helium atoms (He ENA) emitted from the heliosheath and created by the Ribbon secondary ENA mechanism are relatively small for the directions of the nose and flanks of the heliosphere. The mean free path against ionization in the Local Interstellar Cloud (LIC) for the He ENA reaches ~8,000 AU for atoms of energy ~5 keV, i.e., about 10 times higher than the mean free path against ionization for hydrogen atoms for the same energy. Thus observation of potential sources in the Local Interstellar Medium by an ENA detector could be possible for distances over a dozen thousand AU. This includes a potential to observe processes at the LIC boundary, to which the closest distance is likely smaller than 10,000 AU. Measurements of He ENA could potentially be used to bridge the gap between direct in situ sampling of our Galactic environment, available from Ulysses and IBEX, and the parsec-scale telescopic observations of interstellar absorption lines. Estimates of the expected heliospheric emission of He ENA are taken from a simple model of the heliosphere, for which we have obtained results consistent with HSTOF observation of He ENA. We use analytical model of the secondary ENA emission with a simple heliolatitude dependence in the supersonic solar wind. For the extraheliospheric sources, we examine simple He ENA production models on distant (<~0.1 pc) boundary layer. One such model, proposed earlier as an extraheliospheric source for the IBEX Ribbon at the hypothetic interface between the LIC and the Local Bubble, is now extended to provide estimates of the fluxes at a wider energy range, from a few to a few tens of keV, taking various distances to the interface into account. Including an appropriate mass spectrometer in the IMAP energetic neutral atom detector will give opportunity to distinguish helium atoms from the general ENA flux. This added capability would provide IMAP with a potential to discover possible enhancements in the He ENA fluxes other than from the heliotail direction, which could enable studying kinetic non-equilibrium processes operating in the "dark gap" region currently inaccessible for observations by IBEX and by traditional astrophysical techniques. These processes are potentially ubiquitous in the interstellar medium.
High-sensitivity laser spectroscopy with atoms from a cooled helium jet
Lewis, D.A.; Evans, R.M.; Davids, C.N.; Finn, M.A.; Kaufman, S.L.; Greenlees, G.W.
1983-01-01
We have developed a cryogenic He-jet system which efficiently transports radioactive atoms produced on-line at the Argonne National Laboratory Tandem-Linac Accelertor away from the production region and forms them into a cool atomic beam. This atomic beam will be probed with high sensitivity laser spectroscopy using the photon burst method. The ultimate goal of this work is to determine the sizes, shapes, and magnetic moments of short-lived nuclei through their atomic hyperfine structure. Preliminary measurements with the He-jet system and the adaption of the photon burst method to this new geometry are described.
Krychowiak, M.; Koenig, R.; Klinger, T. [Max-Planck-Institut fuer Plasmaphysik, EURATOM-Association, Wendelsteinstrasse 1, D-17491 Greifswald (Germany); Mertens, Ph.; Schweer, B.; Brezinsek, S.; Schmitz, O.; Samm, U. [Institut fuer Energieforschung (IEF 4-Plasmaphysik), FZ Juelich, EURATOM-Association, TEC, Wilhelm-Johnen-Strasse D-52428 Juelich (Germany); Brix, M. [UKEA, JET- Experimental Department, EURATOM-Association, Culham Science Centre, ABINGDON, Oxfordshire, OX14 3DB (United Kingdom)
2008-03-19
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 model which is needed in order to obtain both plasma parameters from the measured relative intensities of atomic helium lines. Combination of a helium beam with a pulsed high-power laser provides a possibility of n{sub e} measurement which does not require a detailed knowledge of the collisional-radiative model. The method relies on resonant laser pumping of some levels and analyzing their fluorescence after the end of the laser pulse. Such measurements were already performed in low temperature plasmas with some content of atomic helium [1,2,3]. In this paper, we discuss the applicability of this method in the fusion edge plasma in the density range of {approx}10{sup 12}-10{sup 13} cm{sup -3} when exciting helium atoms with a laser at the wavelength of {lambda} = 388.9 nm tuned to the triplet transition 2{sup 3}S-vector3{sup 3}P deg. and observing the fluorescence light at the laser wavelength and at {lambda} = 587.6 nm(3{sup 3}D-vector2{sup 3}P deg.). A first test measurement at the TEXTOR tokamak in Juelich performed by use of an excimer-pumped dye laser in connection with a thermal helium beam is shown and discussed.
Haber, Louis H.; Doughty, Benjamin; Leone, Stephen R.
2011-07-15
Energy-dependent photoelectron angular distributions from two-color two-photon above threshold ionizations are investigated to determine the partial-wave characteristics of free-free electronic transitions in helium. Sideband photoelectron energies ranging from 0.18 to 13.0 eV are measured with different wavelengths of the perturbative infrared dressing field as well as different individually selected high-order harmonics. Using the experimentally measured cross-section ratios and anisotropy parameters together with analytical expressions derived from second-order perturbation theory, the partial-wave branching fractions going to the S and D waves in the positive and negative sidebands are determined as a function of photoelectron kinetic energy. The results provide a sensitive test for theoretical models of two-color two-photon above threshold ionization in atoms and molecules.
Das, J.N.; Paul, S.; Chakrabarti, K.
2004-04-01
Here we report a set of converged cross-section results for double photoionization of helium atoms obtained in the hyperspherical partial wave theory for equal energy sharing kinematics at 6 eV energy above threshold. The calculated cross section results are generally in excellent agreement with the absolute measured results of Doerner et al. [Phys. Rev. 57, 1074 (1998)].
Cohen-Tannoudj, Claude
lifetimes, and has led to accurate determinations of s-wave scattering lengths for alkali systems, which an original, ``calori- metric'' method for detecting the formation of these molecules. Instead of monitoring
Supersonic Beam Formation and Helium-Scattering from Gallium ARSENIDE(110)
NASA Astrophysics Data System (ADS)
Weaver, Bradley Duane
We describe (1) our contributions to the science of supersonic beam formation, (2) the results of a ^4He-scattering study from ion-damaged GaAs(110) surfaces, and (3) some preliminary results of ^4He-scattering from MBE-grown GaAs(100). In our study of supersonic beam formation, we measure the angular distribution of flux from electron microscope apertures used as supersonic nozzles. This allows (1) the ideal on-axis beam intensity to be calculated and a comparison to be made with effusive beams (a fourfold intensity enhancement occurs), and allows (2) accurate calculations of flow rates through the differential stages of a supersonic beam source. We also study (3) beam attenuation due to collisions with background gases, and show how skimmer-beam interference and condensation are avoided. The contributions (1)-(3) allow specification of the operating parameters leading to maximum beam signal. ^4He-beams are then used in comparing scattering intensities from clean and Ar^+ ion-damaged GaAs(110). We find that the average residual surface damage due to single ion impacts decreases from small groups of defects (vacancies and adatoms) at low sample temperature T during bombardment to isolated monovacancies at higher T. This decrease occurs even in the absence of thermal annealing, and is possibly due to the T-dependent accommodation of adatom energy by the crystal. We also show ^4He -scattering data from MBE-grown As-stabilized (2 x 4) reconstructed GaAs(100). The scattering intensity decays with a time constant of ~1 hour, about 100 times faster than a (110) surface under comparable vacuum conditions, but the cause of this instability is unknown.
Chaotic walking and fractal scattering of atoms in a tilted optical lattice
S. V. Prants; V. O. Vitkovsky
2012-05-20
Chaotic walking of cold atoms in a tilted optical lattice, created by two counter propagating running waves with an additional external field, is demonstrated theoretically and numerically in the semiclassical and Hamiltonian approximations. The effect consists in random-like changing the direction of atomic motion in a rigid lattice under the influence of a constant force due to a specific behavior of the atomic dipole-moment component that changes abruptly in a random-like manner while atoms cross standing-wave nodes. Chaotic walking generates a fractal-like scattering of atoms that manifests itself in a self-similar structure of the scattering function in the atom-field detuning, position and momentum spaces. The probability distribution function of the scattering time is shown to decay in a non-exponential way with a power-law tail.
Phase-operation for conduction electron by atomic-scale scattering via single point-defect
Nagaoka, Katsumi, E-mail: NAGAOKA.Katsumi@nims.go.jp; Yaginuma, Shin [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Nakayama, Tomonobu [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-0044 (Japan)
2014-03-17
In order to propose a phase-operation technique for conduction electrons in solid, we have investigated, using scanning tunneling microscopy, an atomic-scale electron-scattering phenomenon on a 2D subband state formed in Si. Particularly, we have noticed a single surface point-defect around which a standing-wave pattern created, and a dispersion of scattering phase-shifts by the defect-potential against electron-energy has been measured. The behavior is well-explained with appropriate scattering parameters: the potential height and radius. This result experimentally proves that the atomic-scale potential scattering via the point defect enables phase-operation for conduction electrons.
Scattering of a photon by an electron of the atom continuous spectrum
NASA Astrophysics Data System (ADS)
Khopersky, A. N.; Nadolinsky, A. M.; Koneev, R. V.; Yavna, V. A.
2015-08-01
The quantum effect of anomalous inelastic scattering of an X-ray photon by an ? p-electron of the 1 s ? ? p continuous spectrum of the state of atom photoionization is predicted theoretically. It is established that, in the region of elastic photon scattering by an electron of the continuous spectrum, together with the known contribution of the Thomson component ( l = 0), there appears a contribution of the infinite (and countable) number of scattering harmonics l ? [1;?]. As an object of the investigation, the Be atom is taken. The absolute values and shape of the triple differential cross section of the elastic, normal, and anomalous Compton scattering have been obtained.
Deep Inelastic Electron Scattering Off the Helium and Tritium Mirror Nuclei
Holt, Roy J. [Physics Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Petratos, Gerassimos G. [Department of Physics, Kent State University, Kent, OH 44242 (United States)
2011-09-21
We discuss a possible measurement of the ratio of nucleon structure functions, F{sub 2}{sup n}/F{sub 2}{sup p}, and the ratio of up to down quark distributions, u/d, at large Bjorken x, by performing deep inelastic electron scattering from the {sup 3}H and {sup 3}He mirror nuclei with the 11 GeV upgraded beam of Jefferson Lab. The measurement is expected to be almost free of nuclear effects, which introduce a significant uncertainty in the extraction of these two ratios from deep inelastic scattering off the proton and deuteron. The results are expected to test perturbative and non-perturbative mechanisms of spin-flavor symmetry breaking in the nucleon, and constrain the structure function parametrizations needed for the interpretation of high energy collider and neutrino oscillations data. The precision of the expected data can also test models of the nuclear EMC effect and provide valuable input for its full explanation.
Positron scattering by singly charged helium ions in the ground state
NASA Astrophysics Data System (ADS)
Bransden, B. H.; Noble, C. J.; Whitehead, R. J.
2001-06-01
A coupled channel approximation has been employed to calculate cross sections for positron collisions with He+(1s) in the energy ranges 0-40.8, 40.8-47 and 50-250 eV. In the lowest energy interval only elastic scattering is possible whereas in the intermediate energy interval both elastic and inelastic cross sections are calculated. Above the capture threshold total cross sections have been calculated for the excitation of He+, for the formation of positronium and for ionization. The target basis set includes the n = 1 and 2 eigenstates on the He+ and Ps centres together with up to 23 pseudostates centred on the He+. The coupled equations were solved using a new minimum-norm extension of the least-squares method. The new approach provides accurate solutions to even large coupled sets of scattering equations. Where possible the results of the present calculations have been compared with previous investigations.
Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics
Mekhov, Igor B.; Maschler, Christoph; Ritsch, Helmut
2007-11-15
We study off-resonant collective light scattering from ultracold atoms trapped in an optical lattice. Scattering from different atomic quantum states creates different quantum states of the scattered light, which can be distinguished by measurements of the spatial intensity distribution, quadrature variances, photon statistics, or spectral measurements. In particular, angle-resolved intensity measurements reflect global statistics of atoms (total number of radiating atoms) as well as local statistical quantities (single-site statistics even without optical access to a single site) and pair correlations between different sites. As a striking example we consider scattering from transversally illuminated atoms into an optical cavity mode. For the Mott-insulator state, similar to classical diffraction, the number of photons scattered into a cavity is zero due to destructive interference, while for the superfluid state it is nonzero and proportional to the number of atoms. Moreover, we demonstrate that light scattering into a standing-wave cavity has a nontrivial angle dependence, including the appearance of narrow features at angles, where classical diffraction predicts zero. The measurement procedure corresponds to the quantum nondemolition measurement of various atomic variables by observing light.
Electron loss to the Continuum in the Projectile ionization for Positronium - Helium atom collision
Roy, Susmita
2008-01-01
The dynamics of the electron loss to the continuum (ELC) from the light neutral projectile positronium (Ps) atom in collision with the He atom is studied in the framework of the post collisional Coulomb Distorted Eikonal Approximation (CDEA). Both the fully differential (TDCS) and the double differential (DDCS) cross sections are investigated in the intermediate and high incident energies. Results are compared with the existing experiment and other theories, where possible.
Complete Breakup of the Helium Atom by Proton and Antiproton Impact
Guan Xiaoxu; Bartschat, Klaus
2009-11-20
We present a fully ab initio, nonperturbative, time-dependent approach to describe single and double ionization of helium by proton and antiproton impact. The problem is discretized by a flexible finite-element discrete-variable representation on the radial grid. Good agreement with the most recent experimental data for absolute angle-integrated cross sections is obtained for projectile energies between 3 keV and 6 MeV. Also, angle-differential cross sections for two-electron ejection are predicted for a proton impact energy of 6 MeV. The time evaluation of the ionization process is portrayed by displaying the electron density as a function of the projectile location.
X-ray atomic scattering factors of low-Z ions with a core hole
Hau-Riege, Stefan P.
2007-10-15
Short and intense x-ray pulses may be used for atomic-resolution diffraction imaging of single biological molecules. One of the dominant damage mechanisms is atomic ionization, resulting in a large fraction of atoms with core holes. We calculated the atomic scattering factor of atoms with atomic charge numbers between 3 and 10 in different ionization states with and without a core hole. Our results show that orbital occupation and the change of the orbitals upon core ionization (core relaxation) have a significant impact on the diffraction pattern.
Coulomb correction effect in Delbrück scattering and atomic Rayleigh scattering of 1-4 MeV photons
B. Kasten; D. Schaupp; P. Rullhusen; F. Smend; M. Schumacher; Lynn Kissel
1986-01-01
Previous large-angle investigations of atomic Rayleigh and Delbrück scattering in the few MeV energy range have been extended to small scattering angles. Rayleigh predictions obtained by combining the second-order S matrix for inner shells with the modified form factor for outer shells are accurate to better than 3%. Tentative estimates of Coulomb correction terms for the Delbrück amplitudes are obtained
H. A. Torii; R. S. Hayano; M. Hori; T. Ishikawa; N. Morita; M. Kumakura; I. Sugai; T. Yamazaki; B. Ketzer; F. J. Hartmann; T. von Egidy; C. Maierl; D. Horváth; J. Eades; E. Widmann
1999-01-01
We have performed laser spectroscopy of metastable antiprotonic helium atoms (p¯He+) formed in helium media of 0.2-8.0 bars at 5.8-6.3 K and have observed a density dependence of the resonance vacuum wavelengths for the known transitions (n,l)=(39,35)-->(38,34) and (37,34)-->(36,33). They showed linear redshifts of 0.61+\\/-0.01 GHz and 0.22+\\/-0.02 GHz per 1 g\\/l, respectively. With the shift parameters above, the transition
Energy and momentum transfer of He atoms scattered from a lithium fluoride crystal surface
Manson, Joseph R.
Energy and momentum transfer of He atoms scattered from a lithium fluoride crystal surface H. Legge to be clean and very importantly, free of adsorbed water under the vacuum conditions of somewhat better than
Tracking Atomic Positions in Molecular Reactions by Picosecond X-ray Scattering at the ESRF
Ihee, Hyotcherl
Tracking Atomic Positions in Molecular Reactions by Picosecond X-ray Scattering at the ESRF LAURENT-resolved experiment, the evolution of a process is recorded by the detector just as a video camera records a football
Young`s interference experiment with light scattered from two atoms
Eichmann, U.; Bergquist, J.C.; Bollinger, J.J.; Gilligan, J.M.
1993-05-01
We report the first observation of interference in the light scattered from two trapped atoms ({sup 198}Hg{sup +} ions localized in a linear Paul trap). The visibility of the interference fringes can be explained in the frame-work of Bragg scattering by a harmonic crystal, but with important differences compared to the case of a large crystal. Comparison of the experimental data with theory shows that the interference pattern offers another method to determine ion temperatures and separations. Furthermore, by exploiting the atom`s internal structure we have found a way to obtain {open_quotes}which path{close_quotes} information without invoking the position-momentum uncertainty relation. If the light scattered by the atoms is detected in a polarization-sensitive way, then it is possible to selectively demonstrate either the particle-nature or the wave-nature of the scattered photons.
Effects of coupled atomic states on the resonance scattering of radiation
Srivastava, Rajendra P.; Fontana, Peter R.
1974-01-01
The excitation and decay probabilities for resonance scattering of radiation from an atom with two coupled excited states in an external static field are calculated as a function of time and frequency. Various oscillatory terms are found...
Chu, Shih-I; Dalgarno, A.
1975-08-01
The effective close-coupling method of Rabitz is tested and used to calculate the angular distributions of the elastic and inelastic scattering of molecular hydrogen in collision with atomic hydrogen when rotational transitions may occur...
Intershell correlations in nonresonant Compton scattering of an X-ray photon by an atom
Hopersky, A. N. Nadolinsky, A. M.; Ikoeva, K. Kh.; Khoroshavina, O. A.
2011-11-15
The role of intershell correlations in nonresonant Compton scattering of an X-ray photon by a free multielectron atom is studied theoretically for the Ar atom. The results of calculation are of a predictive nature. The developed mathematical formalism is general in nature and can be applied to a wide set of elements from the Periodic Table, for which the description of the wavefunctions of scattering states in the nonrelativistic Hartree-Fock approximation remains correct.
Atomic effects in heavy-ion elastic scattering
Casandjian, J.M.; Mittig, W.; Villari, A.C.C.; Auger, G.; Beunard, R.; Bianchi, L.; Ciffre, J.L.; Wieleczko, J.P. [GANIL, B.P. 5027, 14021 Caen Cedex (France)] [GANIL, B.P. 5027, 14021 Caen Cedex (France); Lepine-Szily, A. [Instituto de Fisica da Universidade de Sao Paulo, C.P. 66318, 05389-970, Sao Paulo, S.P. (Brazil)] [Instituto de Fisica da Universidade de Sao Paulo, C.P. 66318, 05389-970, Sao Paulo, S.P. (Brazil); Menchaca-Rocha, A. [Instituto de Fisica UNAM, A.P. 20-364, 01000 DF (Mexico)] [Instituto de Fisica UNAM, A.P. 20-364, 01000 DF (Mexico); Foti, A. [Dipartimento di Fisica and INFN -- Sez. CT, 95129 Catania (Italy)] Orr, N.A. [LPC-ISMRA, Bld du Marechal Juin, 14050 Caen (France)] Plagnol, E. [IPN Orsay, B.P. 1, 91406 Orsay (France)] Siemssen, R.H. [KVI, 9747 AA Groningen (The Netherlands)
1997-11-01
Angular distributions of a {sup 208}Pb beam on {sup 208}Pb thin targets at very small angles were measured. The shape of the experimental distribution is not Gaussian, indicating a plural scattering regime rather than multiple scattering. The distribution was well reproduced by a Monte Carlo simulation of the straggling process. For the first time we observed and quantified the influence of the production of electrons during the scattering. This effect was observed in the angular correlation of the scattered {sup 208}Pb nuclei detected in kinematic coincidence and also in the limiting angle of the {sup 208}Pb scattered in a {sup 107,109}Ag target. This effect introduces a spread in the scattered angle which is of the same order of magnitude as the angular straggling. {copyright} {ital 1997} {ital The American Physical Society}
Atomic Rayleigh scattering of phonons in the vicinity of K-absorption edges
S. K. Sen Gupta; N. C. Paul; J. Bose; G. C. Goswami; S. C. Das; N. Chaudhuri
1982-01-01
New measurements of coherent (Rayleigh) scattering of photons of energies in the vicinity of K-absorption edges of gold and lead atoms together with other recent measurements with a coverage in the momentum transfer region up to 1.0 mc are presented for a critical evaluation of (i) the latest relativistic calculation of coherent scattering factors, (ii) the anomalous dispersion correction to
NASA Astrophysics Data System (ADS)
Stein, T. S.; Jiang, J.; Kauppila, W. E.; Kwan, C. K.; Parikh, S. P.
2002-05-01
Although electron (e^-) and positron (e^+) scattering by alkali atoms and alkaline earth atoms provide an important testing ground for atomic scattering theories, direct absolute measurements of even such basic quantities as total scattering cross sections (Q_T's) for some of these target atoms, such as Li and Mg, are in extremely short supply for e^-'s and non-existent for e^+'s. In order to fill some of these gaps, we have used a beam- transmission technique^1 to measure direct absolute Q_T's for e^+'s and e^-'s (with energies from about 2 to 60 eV) scattered by Li and Mg atoms. Alkali atoms are of particular interest because positronium (Ps) can be formed by e^+'s of arbitrarily low energy (in contrast to the case for room-temperature gases which have Ps formation thresholds typically of several eV or more), so there are never less than two scattering channels (elastic and Ps formation) open. Mg also has a particularly low Ps formation threshold of 0.8 eV. There is additional interest in these atoms associated with recent theoretical predictions of their formation of bound states with e^+'s. For Li and for Mg there is reasonably good agreement between the present e^+ and e^- Q_ T measurements and the most elaborate recent corresponding calculations. ^1 C.K. Kwan et al., Phys. Rev. A 44, 1620 (1991).
NASA Astrophysics Data System (ADS)
Orazbayev, Azamat
Microscopic optical potentials taking into account the open shell structure of the halo nuclei 6He and 8He are derived and calculated for the first time for the elastic scattering of these nuclei from a polarized proton target. It is demonstrated that the inclusion of open shell effects leads to new terms in the optical potential. Terms associated with the scalar single particle density matrix in spin space are the same as the terms obtained for closed shell nuclei. It is shown that the single particle density matrices corresponding to vectors in spin space vanish in the case of closed shell nuclei. For the open shell nuclei 6He and 8He, the vector in spin space can couple to spin-dependent pieces of the nucleon-nucleon interaction. This leads to additional non-zero terms in the optical potential, which are derived for the first time. In the case of 6He and 8He, one additional central term and one additional spin-orbit term have been identified. The effect of the additional non-zero terms on the differential cross section and analyzing power is found to be small for the scattering energies between 71 and 300 MeV per nucleon. As the projectile kinetic energy increases, the differences between results calculated with the closed shell and modified optical potentials diminish. The nuclei 6He and 8He are described by harmonic oscillator wave functions, and the ground states are assumed to have 1s and 1p shells occupied. The higher levels of harmonic oscillator basis are excluded from consideration. Under this assumption, the harmonic oscillator wave functions do not describe the extended exponential distribution of matter specific to halo nuclei. In order to simulate exponential tails, the harmonic oscillator wave functions are replaced with exponential functions at distances greater than certain matching radii. It is found that exponential tails do not affect the observables at the considered energies. Because there are various estimations for the charge and matter radii of 6He and 8He, the effect of varying the radii is studied. It is established that the scattering observables are sensitive to both the charge and matter radii of the target nucleus. The effect in some cases is significant and can lead to distinctly different results.
Analysis of an atom laser based on the spatial control of the scattering length
Carpentier, Alicia V.; Michinel, Humberto; Rodas-Verde, Maria I.; Perez-Garcia, Victor M. [Area de Optica, Facultade de Ciencias de Ourense, Universidade de Vigo, As Lagoas s/n, Ourense, ES-32004 Spain (Spain); Departamento de Matematicas, ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain)
2006-07-15
In this paper we analyze atom lasers based on the spatial modulation of the scattering length of a Bose-Einstein condensate. We demonstrate, through numerical simulations and approximate analytical methods, the controllable emission of matter-wave bursts and study the dependence of the process on the spatial shape of the scattering length along the axis of emission. We also study the role of an additional modulation of the scattering length in time.
Influence of nearly resonant light on the scattering length in low-temperature atomic gases
P. O. Fedichev; Yu. Kagan; G. V. Shlyapnikov; J. T. M. Walraven
1996-01-01
We develop the idea of manipulating the scattering length $a$ in low-temperature atomic gases by using nearly resonant light. As found, if the incident light is close to resonance with one of the bound $p$ levels of electronically excited molecule, then virtual radiative transitions of a pair of interacting atoms to this level can significantly change the value and even
Influence of Nearly Resonant Light on the Scattering Length in Low-Temperature Atomic Gases
P. O. Fedichev; Yu. Kagan; G. V. Shlyapnikov; J. T. M. Walraven
1996-01-01
We develop the idea of manipulating optically the scattering length a in low-temperature atomic gases. If the incident light is close to resonance with one of the bound p levels of electronically excited molecules, virtual radiative transitions of a pair of interacting atoms to this level can significantly change the value and even reverse the sign of a. The decay
Manson, Joseph R.
in the accommodation of impact energy in atom- or molecule-surface interactions.1 These processes aid in the sticking of the adsorbate, or its interaction potential with the surface and the helium atom. Thus, the lack of significant that the details of the interaction potential are not important. The adsorption of CO on Cu 001 Refs. 6 and 8
Hiroyuki Nakashima; Hiroshi Nakatsuji
2008-01-01
The local energy defined by Hpsi\\/psi must be equal to the exact energy E at any coordinate of an atom or molecule, as long as the psi under consideration is exact. The discrepancy from E of this quantity is a stringent test of the accuracy of the calculated wave function. The H-square error for a normalized psi, defined by sigma2?
Superradiant Rayleigh Scattering and Collective Atomic Recoil Lasing in a Ring Cavity
S. Slama; S. Bux; G. Krenz; C. Zimmermann; Ph. W. Courteille
2007-01-01
Collective interaction of light with an atomic gas can give rise to superradiant instabilities. We experimentally study the sudden buildup of a reverse light field in a laser-driven high-finesse ring cavity filled with ultracold thermal or Bose-Einstein condensed atoms. While superradiant Rayleigh scattering from atomic clouds is normally observed only at very low temperatures (i.e., well below 1 Î¼K), the
Superradiant Rayleigh Scattering and Collective Atomic Recoil Lasing in a Ring Cavity
S. Slama; S. Bux; G. Krenz; C. Zimmermann; Ph. W. Courteille
2007-01-01
Collective interaction of light with an atomic gas can give rise to superradiant instabilities. We experimentally study the sudden buildup of a reverse light field in a laser-driven high-finesse ring cavity filled with ultracold thermal or Bose-Einstein condensed atoms. While superradiant Rayleigh scattering from atomic clouds is normally observed only at very low temperatures (i.e., well below 1muK), the presence
Momentum density of hcp and liquid helium-4 by inelastic neutron scattering
Hilleke, Russell Otto
1983-01-01
A measurement of the momentum density in hcp and liquid /sup 4/He by inelastic neutron scattering is reported. Using the Low Resolution Medium Energy Chopper Spectrometer at the Intense Pulsed Neutron Source at Argonne National Laboratory, momentum transfers in the range 12 to 22.5 A/sup -1/ were attained. At these momentum transfers, the momentum density of the sample is related to the dynamic structure factor by the impulse approximation. The measured momentum distribution is Gaussian and the kinetic energy is larger than proposed by existing theories. Data were taken on two solid samples, the first was a 19.45 cm/sup 3//mole hcp solid, the second was 18.20 cm/sup 3// mole; both solid samples were maintained at 1.70 K during data collection. Data were also taken on a liquid sample with a molar volume of 18.20 cm/sup 3//mole at 4.00 K. At 1.70 K the two solid samples are essentially in their ground states so that the measurement is of the ground state momentum density. The liquid sample was included to see if the difference between the liquid and solid momentum density at the same molar volume was observable.
NASA Astrophysics Data System (ADS)
Zayarnyi, D. A.; L'dov, A. Yu; Kholin, I. V.
2014-11-01
The processes of collision quenching of the resonance 5s[3/2]1o(3P1) state of the krypton atom are studied by the absorption probe method in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasmochemical reactions Kr* + Kr + He ? Kr*2 + He [(4.21 ± 0.42) × 10-33 cm6 s-1], Kr* + 2He ? HeKr* + He [(4.5 ± 1.2) × 10-36 cm6 s-1] and Kr* + He ? products + He [(2.21 ± 0.22) × 10-15 cm3 s-1] are measured for the first time. The rate constants of similar reactions are refined for krypton in the metastable 5s[3/2]2o (3P2) state.
Rayleigh x-ray scattering from many-electron atoms and ions
NASA Astrophysics Data System (ADS)
Surzhykov, A.; Yerokhin, V. A.; Stöhlker, 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.
Cavity-Enhanced Light Scattering in Optical Lattices to Probe Atomic Quantum Statistics
Mekhov, Igor B.; Maschler, Christoph; Ritsch, Helmut
2007-03-09
Different quantum states of atoms in optical lattices can be nondestructively monitored by off-resonant collective light scattering into a cavity. Angle resolved measurements of photon number and variance give information about atom-number fluctuations and pair correlations without single-site access. Observation at angles of diffraction minima provides information on quantum fluctuations insensitive to classical noise. For transverse probing, no photon is scattered into a cavity from a Mott insulator phase, while the photon number is proportional to the atom number for a superfluid.
Scattering properties of weakly-bound dimers of Fermi atoms
NASA Astrophysics Data System (ADS)
Petrov, Dmitry
2005-03-01
We discuss the behavior of weakly bound bosonic dimers formed in a two-component Fermi gas with a large positive scattering length for the interspecies interaction. We present a theoretical approach for solving a few-body scattering problem and describe the physics of dimer-dimer elastic and inelastic scattering. We explain why these diatomic molecules, while in the highest ro-vibrational level, are characterized by remarkable collisional stability. Co-authors are Christophe Salomon, LKB, Ecole Normale Superieure, Paris, France; Georgy Shlyapnikov, LPTMS, University of South Paris, Orsay, France.
Quasiparticles in Raman scattering of an electromagnetic wave by an atomic condensate
Il'ichev, L. V., E-mail: leonid@iae.nsk.su [Novosibirsk State University (Russian Federation)
2011-02-15
Raman scattering of an intense electromagnetic wave by a free atomic Bose condensate is considered. In a system of atoms and photons, a subsystem is separated whose dynamics can be naturally described in terms of quasiparticles: quasi-atoms and quasi-photons. The dispersion laws of quasiparticles are interrupted by the instability interval. The introduction of quasiparticles within this interval is impossible, while dispersion laws that are continued formally acquire imaginary components. The dynamic scattering model is generalized by including dissipative annihilation processes of scattered photons and uncondensed atoms. A stationary solution of the corresponding quantum control equation is found, allowing the calculation of momentum distributions of real particles and quasiparticles. The outlook for the experimental detection of quasiparticles is discussed.
The Scattering of Gas Atoms from Solid Surfaces
ERIC Educational Resources Information Center
Walton, Alan J.
1977-01-01
Traditional undergraduate courses in gas kinetic theory encourage the view that in all collisions between a gas atom and a surface, the angle of incidence of the gas atom equals its angle of reflection. This article illustrates and explains the incorrectness in assuming specular reflection and zero dwell time. (Author/MA)
NASA Technical Reports Server (NTRS)
Bledsoe, J. R.; Fisher, S. S.
1974-01-01
Nozzle-type atomic beams and time-of-flight detection methods are employed in studies of the scattering of thermal-energy He-4 atoms from LiF (001) and NaCl (001) surfaces under conditions where diffraction is observed and where substantial inelastic scattering occurs. Intensity and speed-distribution measurements are obtained for the portion of the scattering within the plane of incidence. For these measurements, incident-beam orientation with respect to target (polar angle and azimuth), incident-beam de Broglie wavelength (0.38-0.60 A), and crystal temperature (300-1000 K) are varied. For LiF, the measured intensity distributions exhibit sharp peaks comprised essentially of elastically scattered atoms and corresponding to up to third-order diffraction, inelastic scattering in the form of local dispersion about each of the elastic peaks, and a component of nominally diffuse scattering distributed below and between the peaks. For NaCl, the same general types of scattering are observed, with elastic scattering less prevalent, intensity peaks not as sharp, and dispersions of inelastic scattering harder to resolve.
Radiative transitions of the helium atom in highly magnetized neutron star atmospheres
Zach Medin; Dong Lai; Alexander Y. Potekhin
2008-01-18
Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree-Fock calculations of the polarization-dependent photoionization cross sections of the He atom in strong magnetic fields ranging from 10^12 G to 10^14 G. Convenient fitting formulae for the cross sections are given as well as related oscillator strengths for various bound-bound transitions. The effects of finite nucleus mass on the radiative absorption cross sections are examined using perturbation theory.
Precision Spectroscopy of Kaonic Helium-3 Atoms X-rays at J-PARC
NASA Astrophysics Data System (ADS)
Iio, M.; Bhang, H.; Cargnelli, M.; Choi, Seonho; Curceanu, C.; Doce, O. V.; Enomoto, S.; Fujioka, H.; Fujiwara, Y.; Guaraldo, C.; Hashimoto, T.; Hayano, R. S.; Hiraiwa, T.; Ishimoto, S.; Ishiwatari, T.; Itahashi, K.; Iwasaki, M.; Kou, H.; Kienle, P.; Marton, J.; Matsuda, Y.; Noumi, H.; Ohnishi, H.; Okada, S.; Outa, H.; Sakuma, F.; Sato, M.; Sekimoto, M.; Shi, H.; Sirghi, D.; Sirghi, F.; Suzuki, T.; Tanida, K.; Tatsuno, H.; Tokuda, M.; Tomono, D.; Toyoda, A.; Tsukada, K.; Vidal, A. R.; Widmann, E.; Wunschek, B.; Yamazaki, T.; Zmeskal, J.
2010-04-01
We will measure the Balmer-series x-rays of kaonic-3He atoms using large-area high-resolution silicon drift x-rays detectors in order to provide the crucial information of K--nucleus strong interaction at the low energy limit. The strong interaction 2p level shift will be determined with a precision of a few eV. At the present status, the construction of all detectors is in progress. In February, 2009, the first tuning of K1.8BR beamline was performed by the secondary beam generated in J-PARC hadron facility. The data taking will be started soon.
Vuletic, Vladan
]. Making use of Rayleigh or Raman scattering from a diffuse gas, conventional Doppler and polarization. If the atomic sample is spatially ordered, however, Rayleigh scattering by individual atoms does not correctlyObservation of Collective Friction Forces due to Spatial Self-Organization of Atoms: From Rayleigh
Wang, Xue Ping
Existence and Born-Oppenheimer Asymptotics of the Total Scattering Cross-Section in Ion-Atom-Ping.Wang@math.univ-nantes.fr Abstract We prove the #12;niteness of the total scattering cross-section for ion-atom collisions.e. the atom. Under more restrictive assumptions, we show that some e#11;ective interaction in Born
Rayleigh scattering and atomic dynamics in dissipative optical lattices.
Carminati, F R; Sanchez-Palencia, L; Schiavoni, M; Renzoni, F; Grynberg, G
2003-01-31
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [S. Guibal, Phys. Rev. Lett. 78, 4709 (1997)]; C. Jurczak, Phys. Rev. Lett. 77, 1727 (1996)
Kaonic hydrogen atom and kaon-proton scattering length
Y. Yan
2009-05-29
Kaonic hydrogen is studied with various realistic potentials in an accurate numerical approach based on Sturmian functions. The kaon-proton scattering length extracted from the 1s energy shift of the kaonic hydrogen by applying the Deser-Trueman formula is severely inconsistent with the one derived by directly solving the scattering Schoedinger equation. We pay special attention to the recent measurement of the energy shift and decay width of the 1s kaonic hydrogen state by the DEAR Collaboration. After taking into account the large discrepancy between the extracted and directly-evaluated scattering lengths, we found theoretical predictions of most chiral SU(3) based models for the kaonic hydrogen decay width are consistent with the DEAR data. We warn the SIDDHARTA collaboration that it may not be reasonable to extract kaon-nucleon scattering lengths, by using the Coulomb-interaction corrected Deser-Truemab formula, from the planned measurement of kaonic hydrogen.
NASA Technical Reports Server (NTRS)
Cooper, J.
1979-01-01
The scattering of radiation in the presence of collisions can be described quantum-mechanically in terms of essentially two processes. The first may be thought of as an absorption to the excited state followed subsequently (after propagating in the excited state) by emission. This gives rise to radiation redistributed about the transition frequency. The effects of m-degeneracy are particularly interesting for this first process. As an example a case is considered in which the incident frequency is in the quasi-static line wing, while the scattered frequency is close to the line center. It is found that under these circumstances the dominant contribution from this process in the scattered spectrum is obtained for an absorption of the incident frequency taking place during a strong (close) collision and reemission of the scattered frequency when the atom is essentially unperturbed
Hyperthermal Ar atom scattering from a C(0001) surface.
Gibson, K D; Sibener, S J; Upadhyaya, Hari P; Brunsvold, Amy L; Zhang, Jianming; Minton, Timothy K; Troya, Diego
2008-06-14
Experiments and simulations on the scattering of hyperthermal Ar from a C(0001) surface have been conducted. Measurements of the energy and angular distributions of the scattered Ar flux were made over a range of incident angles, incident energies (2.8-14.1 eV), and surface temperatures (150-700 K). In all cases, the scattering is concentrated in a narrow superspecular peak, with significant energy exchange with the surface. The simulations closely reproduce the experimental observations. Unlike recent experiments on hyperthermal Xe scattering from graphite [Watanabe et al., Eur. Phys. J. D 38, 103 (2006)], the angular dependence of the energy loss is not approximated by the hard cubes model. The simulations are used to investigate why parallel momentum conservation describes Xe scattering, but not Ar scattering, from the surface of graphite. These studies extend our knowledge of gas-surface collisional energy transfer in the hyperthermal regime, and also demonstrate the importance of performing realistic numerical simulations for modeling such encounters. PMID:18554044
Coherent forward scattering of starlight by a cloud of atomic hydrogen
Zagury, Frederic; 10.1016/j.optcom.2012.06.009
2012-01-01
Theory predicts that a plane wave scattered by a thin slab of gas yields, in the forward direction and under specific circumstances, a larger irradiance than would be observed in the absence of the gas. This enhanced Rayleigh scattering depends on the size of the Fresnel zones at the slab location, as seen from the observer's position, and results from the coherence of the scattering. On astronomical scales the exceptional size of Fresnel zones (~1500km) has particular relevance when considering forward-scattered starlight by an interstellar cloud of atomic hydrogen.
NASA Astrophysics Data System (ADS)
Alexander, Millard H.; Dagdigian, Paul J.; Lemoine, Didier
1991-10-01
The results of full close-coupled calculations of state-to-state cross sections for rotationally inelastic collisions of NH in its A 3? electronic state with helium, based on the recently calculated ab initio potential energy surfaces of Jonas and Staemmler [Z. Phys. D 14, 143 (1989)], are presented. The calculated ?-doublet resolved cross sections have been compared with predictions based on formal analyses of the scattering equations both in the Hund's case (a) and (b) limits. For transitions involving low J levels, a strong propensity toward conservation of the e/f label was found, as expected in the case (a) limit. For higher J, the cross sections connecting related pairs of ?-doublet levels were found to be unequal, reflecting a quantum mechanical interference between the two potential energy surfaces arising from the interaction of a molecule in a ?>0 state with a perturber. For transitions connected by even l terms in the expansion of the potentials, a simple analysis, based on the relative strengths of the l=2 coupling matrix elements of the electrostatic potential, was found capable of explaining the relative ordering of the cross sections in most cases. A similar success for predicting transitions coupled by odd l terms in the potential was not found; this reflects the fact that the l=3 terms are relatively small for the NH(A 3?)-He interaction. The calculated cross sections for large J also exhibit a propensity for conservation of the fine-structure label, as expected in the case (b) limit. As an indication of the reliability of the calculated interaction potential and our treatment of the collision dynamics, appropriately summed calculated cross sections reproduce well the experimental rates for transitions from selected f levels into all e levels, as measured by Stuhl and co-workers.
On Helium Anions in Helium Droplets: Interpreting Recent Experiments
NASA Astrophysics Data System (ADS)
Mauracher, Andreas; Huber, Stefan E.
2014-10-01
Helium droplets provide an ideal environment to study elementary processes in atomic systems at very low temperatures. Here, we discuss properties of charged and neutral, atomic and molecular helium species formed in helium droplets upon electron impact. By studying their interaction with atomic ground state helium we find that He, He2 and excited (metastable) He*- are well bound within the helium droplet. In comparison, He* , He2* and He2* are found to be squeezed out due to energetic reasons. We also present the formation pathways of atomic and molecular helium anions in helium droplets. Transition barriers in the energetic lowest He*- - He interaction potentials prevent molecule formation at the extremely low temperatures in helium droplets. In contrast, some excited states allow a barrier-free formation of molecular helium (anions). With these theoretical results at hand we can interpret recent experiments in which the resonant formation of atomic and molecular helium anions was observed. Furthermore, we give an outlook on the implications of the presence of these anionic species in doped helium droplets with regard to charge transfer reactions. Austrian Fund Agency (FWF, I 978-N20, DK+ project Computational Interdisciplinary Modelling W1227-N16)/Austrian Ministry of Science (BMWF, Konjunkturpaket II, UniInfrastrukturprogramm of the Focal Point Scientific Computing).
Inelastic and reactive scattering of hyperthermal atomic oxygen from amorphous carbon
NASA Technical Reports Server (NTRS)
Minton, Timothy K.; Nelson, Christine M.; Brinza, David E.; Liang, Ranty H.
1991-01-01
The reaction of hyperthermal oxygen atoms with an amorphous carbon-13 surface was studied using a modified universal crossed molecular beams apparatus. Time-of-flight distributions of inelastically scattered O-atoms and reactively scattered CO-13 and CO2-13 were measured with a rotatable mass spectrometer detector. Two inelastic scattering channels were observed, corresponding to a direct inelastic process in which the scattered O-atoms retain 20 to 30 percent of their initial kinetic energy and to a trapping desorption process whereby O-atoms emerge from the surface at thermal velocities. Reactive scattering data imply the formation of two kinds of CO products, slow products whose translational energies are determined by the surface temperature and hyperthermal (Approx. 3 eV) products with translational energies comprising roughly 30 percent of the total available energy (E sub avl), where E sub avl is the sum of the collision energy and the reaction exothermicity. Angular data show that the hyperthermal CO is scattered preferentially in the specular direction. CO2 product was also observed, but at much lower intensities than CO and with only thermal velocities.
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.
Non-reactive scattering of excited exotic hydrogen atoms
Korenman, G Y; Pomerantsev, V N
2005-01-01
The Coulomb deexcitation of light exotic atoms in collisions with hydrogen atoms has been studied in framework of quantum-mechanical treatment using the close-coupling method. The detailed calculations of the total cross sections have been performed for the principal quantum number $n=3 - 8$ and relative energies region $E=0.01 \\div 100$ eV. The obtained results leads to the new $n$ and $E$ dependences of the Coulomb deexcitation cross sections in comparison with semiclassical approach.
Liao, Chen-Ting; Sandhu, Arvinder; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B
2015-04-10
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. PMID:25910116
NASA Astrophysics Data System (ADS)
Liao, Chen-Ting; Sandhu, Arvinder; Camp, Seth; Schafer, Kenneth J.; Gaarde, Mette B.
2015-04-01
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.
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.
Liao, Chen-Ting; Camp, Seth; Schafer, Kenneth J; Gaarde, Mette B
2015-01-01
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.
Not Available
1992-11-01
Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.
Anisotropic diffusion at a melting surface studied with He-atom scattering
NASA Astrophysics Data System (ADS)
Frenken, J. W. M.; Hinch, B. J.; Toennies, J. P.; Wöll, Ch.
1990-01-01
Two-dimensional self-diffusion processes at surfaces can be studied on an atomic scale with quasielastic scattering of low-energy He atoms. The analytical strength of this new application of He-atom scattering is demonstrated for the Pb(110) surface at temperatures close to the bulk melting point, TPb=600.7m K. The width of the quasielastic-scattering energy distribution of diffusely scattered He atoms is a direct measure of the lateral atomic mobilities at the surface. The results show that at T>=(3/4TPbm the atoms of this surface have noticeable lateral diffusivities. Above ~535 K the surface mobilities exceed the bulk-liquid value. Measurements of the quasielastic energy broadening as a function of parallel momentum transfer provide direct information on the surface diffusion mechanisms. The results exhibit a strong directional anisotropy. The diffusion can be described in terms of jumps along the [11¯0] and [001] directions. Jump lengths along the close-packed [11¯0] direction seem to be continuously distributed around an average jump length of ~4.4 Å. Along [001] the diffusion proceeds in jumps over single lattice spacings.
Cavity-enhanced superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed atoms
Slama, Sebastian; Krenz, Gordon; Bux, Simone; Zimmermann, Claus; Courteille, Philippe W. [Physikalisches Institut, Eberhard-Karls-Universitaet Tuebingen, Auf der Morgenstelle 14, D-72076 Tuebingen (Germany)
2007-06-15
We report on the observation of collective atomic recoil lasing and superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed atoms in an optical ring cavity. Both phenomena are based on instabilities evoked by the collective interaction of light with cold atomic gases. This publication clarifies the link between the two effects. The observation of superradiant behavior with thermal clouds as hot as several tens of {mu}K proves that the phenomena are driven by the cooperative dynamics of the atoms, which is strongly enhanced by the presence of the ring cavity.
Cavity-enhanced superradiant Rayleigh scattering with ultra-cold and Bose-Einstein condensed atoms
Sebastian Slama; Gordon Krenz; Simone Bux; Claus Zimmermann; Philippe W. Courteille
2007-07-19
We report on the observation of collective atomic recoil lasing and superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed atoms in an optical ring cavity. Both phenomena are based on instabilities evoked by the collective interaction of light with cold atomic gases. This publication clarifies the link between the two effects. The observation of superradiant behavior with thermal clouds as hot as several tens of $\\mu\\textrm{K}$ proves that the phenomena are driven by the cooperative dynamics of the atoms, which is strongly enhanced by the presence of the ring cavity.
Cavity-enhanced superradiant Rayleigh scattering with ultra-cold and Bose-Einstein condensed atoms
Slama, S; Courteille, P W; Krenz, G; Zimmermann, C; Bux, Simone; Courteille, Ph. W.; Krenz, Gordon; Slama, Sebastian; Zimmermann, Claus
2007-01-01
We report on the observation of collective atomic recoil lasing and superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed atoms in an optical ring cavity. Both phenomena are based on instabilities evoked by the collective interaction of light with cold atomic gases. This publication clarifies the link between the two effects. The observation of superradiant behavior with thermal clouds as hot as several tens of $\\mu\\textrm{K}$ proves that the phenomena are driven by the cooperative dynamics of the atoms, which is strongly enhanced by the presence of the ring cavity.
Eigenmode description of Raman scattering in atomic vapors in the presence of decoherence
Jan Kolodynski; Jan Chwedenczuk; Wojciech Wasilewski
2012-07-06
A theoretical model describing the Raman scattering process in atomic vapors is constructed. The treatment investigates the low-excitation regime suitable for modern experimental applications. Despite the incorporated decoherence effects (possibly mode dependent) it allows for a direct separation of the time evolution from the spatial degrees of freedom. The impact of noise on the temporal properties of the process is examined. The model is applied in two experimentally relevant situations of ultra-cold and room-temperature atoms. The spatial eigenmodes of the Stokes photons and their coupling to atomic excitations are computed. Similarly, dynamics and the waveform of the collective atomic state are derived for quantum memory implementations.
Ground state properties of cold bosonic atoms at large scattering lengths.
Song, Jun Liang; Zhou, Fei
2009-07-10
In this Letter, we study bosonic atoms at large scattering lengths using a variational method where the condensate amplitude is a variational parameter. We further examine momentum distribution functions, chemical potentials, the speed of sound, and spatial density profiles of cold bosonic atoms in a trap in this limit. The latter two properties turn out to bear similarities to those of Fermi gases. The estimates obtained here are applicable near Feshbach resonances, particularly when the fraction of atoms forming three-body structures is small and can be tested in future cold atom experiments. PMID:19659218
Adiabatic asymmetric scattering of atoms in the field of a standing wave
Hakobyan, M V; Ishkhanyan, A M
2015-01-01
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.
Adiabatic asymmetric scattering of atoms in the field of a standing wave
NASA Astrophysics Data System (ADS)
Hakobyan, M. V.; Red’kov, 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.
NASA Astrophysics Data System (ADS)
Nagy, I.; Aldazabal, I.; Glasser, M. L.
2012-05-01
In the presence of an environment of mobile charges, the bound-state Schrödinger Hamiltonian for an embedded He atom differs from its vacuum form. The central problem of incorporating screening in the nucleus-bound-electron and bound-electron-bound-electron terms of this Hamiltonian is investigated here for the He ground state in a comparative manner by using two models, and the same product form of 1s-type parametric hydrogenic functions to perform exploratory variational calculations. Both models employ induced charge densities in the corresponding Poisson equations with a fixed point-like nucleus, but the underlying charge-density response of the host system is generated by differently chosen perturbations. These are the point-charge nucleus and the nucleus-bound-electron charge distribution as external perturbations. The repulsive bound-electron-bound-electron interaction in the Hamiltonian is modelled by a parametric Yukawa-type potential. Using the consistent variational results for the binding energies and wavefunctions, the charge-state-dependent stopping power of a metallic target for slowly moving He is briefly discussed.
Wang, Zhongkai; Niu, Linxiao; Zhang, Peng; Wen, Mingxuan; Fang, Zhen; Chen, Xuzong; Zhou, Xiaoji
2013-06-17
The superradiant Rayleigh scattering using a pump laser incident along the short axis of a Bose-Einstein condensate with a density distortion is studied, where the distortion is formed by shocking the condensate utilizing the residual magnetic force after the switching-off of the trapping potential. We find that very small variation of the atomic density distribution would induce remarkable asymmetrically populated scattering modes by the matter-wave superradiance with long time pulse. The optical field in the diluter region of the atomic cloud is more greatly amplified, which is not an ordinary mode amplification with the previous cognition. Our numerical simulations with the density envelop distortion are consistent with the experimental results. This supplies a useful method to reflect the geometric symmetries of the atomic density profile by the superradiance scattering. PMID:23787626
Bel'skaya, E V; Bokhan, P A; Zakrevskii, D E; Lavrukhin, M A [A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)
2012-02-28
Lasing on a self-terminating transition 2{sup 1}P{sup o}{sub 1} - 2{sup 1}S{sub 0} ({lambda} = 2.058 {mu}m) in helium atom is studied for a single- and double-pulse operation regimes under electron beam pumping in pure helium and its mixtures with H{sub 2}, N{sub 2}, O{sub 2}, CO{sub 2}, H{sub 2}O, NH{sub 3}, and N{sub 2}O. In pure helium, the maximal pulse duration is {approx}50 ns, which agrees with the calculated value. Recovery of lasing in the second pulse is observed at a time delay between the pulses of longer than 1.25 {mu}s. In adding CO{sub 2}, N{sub 2}O, NH{sub 3}, and H{sub 2}O, the relaxation rate for population of the metastable state He(2{sup 1}S{sub 0}) increases, which makes the delay, needed for recovering lasing, shorter up to pulse merging in the case of H{sub 2}O. At the exciting pulse base-level duration of 1.2 {mu}s, in mixtures of helium with NH{sub 3} and H{sub 2}O, laser pulses with a duration of {approx}0.8 {mu}s are observed, which testifies that collisional quasi-cw lasing occurs. Mechanisms of collisional lasing are discussed.
Design and construction of a sample preparation chamber for atomic beam scattering
Nielsen, C.
1992-05-18
A new type of atomic beam scattering spectrometer was built to advance the usefulness of the atomic beam scattering technique as a surface dynamics probe. The facility was not only built to investigate the typical alkali halide samples such as NaCl, NaF, and LiF, but also to investigate metallic surfaces. Metal samples are more complicated to study, due to their reactive surfaces and the sample preparation process. A surface analysis chamber was constructed as an attachment to the scattering facility to treat samples under ultra high vacuum (UHV) and then transfer these samples into the scattering facility. This surface analysis chamber is referred to as the sample preparation chamber and is the basis for this thesis.
Exciton-Polariton scattering for defect detection in cold atom Optical Lattices
Hashem Zoubi; Helmut Ritsch
2007-10-29
We study the effect of defects in the Mott insulator phase of ultracold atoms in an optical lattice on the dynamics of resonant excitations. Defects, which can either be empty sites in a Mott insulator state with one atom per site or a singly occupied site for a filling factor two, change the dynamics of Frenkel excitons and cavity polaritons. While the vacancies in first case behave like hard sphere scatters for excitons, singly occupied sites in the latter case can lead to attractive or repulsive scattering potentials. We suggest cavity polaritons as observation tool of such defects, and show how the scattering can be controlled in changing the exciton-photon detuning. In the case of asymmetric optical lattice sites we present how the scattering effective potential can be detuned by the cavity photon polarization direction, with the possibility of a crossover from a repulsive into an attractive potential.
Inelastic scattering of electrons by metastable hydrogen atoms in a laser field
Buica, Gabriela
2015-01-01
The inelastic scattering of fast electrons by metastable hydrogen atoms in the presence of a linearly polarized laser field is theoretically studied in the domain of moderate field intensities. The interaction of the hydrogen atom with the laser field is described by first-order time-dependent perturbation theory, while the projectile electrons interacting with the laser field are described by the Gordon-Volkov wave functions. An analytic expression is obtained for the differential scattering cross section in the first-order Born approximation for laser-assisted inelastic e-H(2s) scattering for the 2s-nl excitation. Detailed analytical and numerical results are presented for inelastic scattering accompanied by one-photon absorption, and the angular dependence and resonance structure of the differential cross sections is discussed for the 2s -4l excitation of metastable hydrogen.