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AbstractAbstract

[en] Level shifts and widths for hydrogenic states (nlm) interacting with a metal surface have been calculated perturbatively for large n(n=1...20) and different model perturbation potentials. The shifts approximately scale with the ion-surface distance in units of the classical orbital radius, r

_{n}, of the hydrogenic manifold. As special cases previous results were confirmed. Based on the perturbative results, self energy matrices including various n-manifolds were obtained which allowed for the calculation of diabatic and adiabatic non-perturbative level shifts and widths, and hybrid orbitals. A new close-coupling calculation is being developed around these matrix elements, that will be applied to the interaction of ions in various charge states with metal surfacesSource

27. annual meeting of the Division of Atomic, Molecular and Optical Physics (DAMOP) of the American Physical Society (APS); Ann Arbor, MI (United States); 15-18 May 1996; CONF-9605105--

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[en] Theory and experimental studies of slow multicharged ion (MCI, charge state q) impact on solid surfaces regard emission of slow and fast electrons and soft X-rays from transient open-quotes hollow atomsclose quotes above, at and below the surface. Faster MCI also cause kinetic electron emission which depends on q in a not yet well understood manner regarding, e.g., momentum transfer from variably screened MCI to free target electrons, and electron promotion in collisional quasimolecules. Measured electron number statistics delivered highly accurate (± 4%) total slow electron yields for impact of H

^{+}, He^{+}, He^{2+}, C^{q+}, N^{q+}, O^{q+}(q≤ 6; impact energy E from below KE threshold up to 40xq keV) on clean polycrystalline gold. Characteristic variations of the electron number statistics with E, and differences in electron yield for varying projectile species at given q and E provide important hints on the relevant KE contributionSource

27. annual meeting of the Division of Atomic, Molecular and Optical Physics (DAMOP) of the American Physical Society (APS); Ann Arbor, MI (United States); 15-18 May 1996; CONF-9605105--

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[en] RCI hfs constants have been obtained for all

^{133}CsII levels belonging to the 5p^{5}(6s + 5d + 6p) configurations using methodology presented elsewhere. Except for 2 levels, all A's agree with experiment to 10% or better. There are large many body effects present for the odd J=1,2 levels as a result of the interactions of nearby 5p^{5}6s and 5p^{5}5d, and the large discrepancy (60.77%) in A for 5d(3/2)[3/2]_{2}and 5d(3/2)[1/2]_{1}disappears once the residual errors in energy differences (300-600 cm^{-1}) are removed. Their values for the small quadruple hfs constants show large discrepancies with the few experimental values available. The authors think the fault lies mainly with experiment, and the B's should be remeasuredPrimary Subject

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27. annual meeting of the Division of Atomic, Molecular and Optical Physics (DAMOP) of the American Physical Society (APS); Ann Arbor, MI (United States); 15-18 May 1996; CONF-9605105--

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[en] In a model of interacting Rydberg manifolds, two sets of parallel energy levels, E

_{m}(t) = pt - mε and E_{m'}(t)=p't + m'ε' (m,m' = 0, ±1,...;p' ≠ p), are linearly shifted by an electric field F(t) = Ft. Atomic core coupling V occurs only at the point of each pair of levels intersection, with a Landau-Zener diabatic transition probability D = d^{2}= e^{-2}πV^{2}/|p-p'|. Adiabatic phases depend on the unit of action, var-phi = contour-integral dt E(t) = εε'/|p-p'|. The amplitudes for approaching the intersection of levels m and m' from an initial m = 0 at m' = 0 are found from recursion relations, similar to an earlier model but including paths' interference via operators ξ and η, where ηξ = ξηe^{ivar-phi}. Coefficients of ordered power ξ^{m}η^{m}^{'}in the generating functions 1 + η[1 + d(η-ξ) - ξη]^{-1}(ξ - d) and αξ[1 + d(η - ξ) - ηξ]^{-1}yield the amplitudes for m- and m'-levels. Another exact form for the amplitudes is obtained from integral representations. In the adiabatic limit (d → 0) the one for m-levels reduces to J_{m-m'}(2d sin [1/2m'var-phi]/sin[1/2 var-phi]); in the diabatic limit (d → 1) it reduces to a Whittaker function. These results help explain overall patterns in the population distributions during coherent evolution under field rampingPrimary Subject

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[en] The authors have used laser cooling and trapping techniques to investigate photoionization and cold collisions. With laser-trapped Rb, they have measured the photoionization cross section from the first excited (5P) level by observing the photoionization-induced loss rate of neutral atoms from the trap. This technique has the advantage that it directly measures the photoionization rate per atom. Knowing the ionizing laser intensity and the excited-state fraction, the measured loss rate gives the absolute cross section. Using this technique, the Rb 5P photoionization cross section at ∼400 nm has been determined with an uncertainty of 9%. The authors are currently attempting to extend this method to the 5D level. Using time-ordered pulses of diode-laser light (similar to the STIRAP technique), they have performed very efficient two-photon excitation of trapped Rb atoms to 5D. Finally, they will present results from a recent collaboration which combines measurements form conventional molecular spectroscopy (single photon and double resonance) with photoassociation collisions of ultracold Na atoms to yield a precise (≤1 ppm) value for the dissociation energy of the X Σ

_{g+}ground state of the Na_{2}moleculePrimary Subject

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[en] Early angular distribution measurements on the Cd 4d

^{9}5s^{2}5p^{3}P_{1}autoionizing level did not correspond with those expected from a single level of mixed^{3}P+^{1}P character. An analysis indicated that the results were consistent with the combined angular distributions of the^{3}P_{1}level and a previously unknown^{1}D_{2}even parity autoionizing level at a slightly displaced ejected-electron energy. Recent (e,2e) energy spectra measurements that spanned the 4d^{9}5s^{2}5p energy region were interpreted with the help of ab-initio structure and plane wave Born amplitude calculations. It was found that the experimental data could be modeled satisfactorily without including a^{1}D_{2}level close to the^{3}P_{1}level. The authors will present new calculations which reconcile these apparent contradictions between the angular distributions and energy spectraPrimary Subject

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[en] The authors present results of calculations of rates for ionization of H

_{2}^{+}by up to 6 photons within the framework of perturbation theory. The internuclear separation is fixed at 2 a.u. There are numerous intermediate state resonances, which can be identified by united-atom-limit quantum numbers. Some of these resonances rise gradually above the background, i.e. they are prominent for rather large detunings, while others are extremely narrow. The relative prominence of the resonances can be understood by making the closure approximation to estimate the strength of the coupling of the intermediate state to the ground state. The calculations are done using complex basis functions in prolate spheroidal coordinates; the advantages and disadvantages of this basis will be discussedPrimary Subject

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[en] In linear polarization (LP), earlier work showed clearly the onset of QSTI at 9.908 GHz (flat-top pulse 250 field osc. long, with rise/fall of 22 field osc). For the principal quantum number n

_{o}≤ 28, measured data were reproduced by 3d quantal calculations using semiclassical methods (QM:SC) for static field rates integrated through the field pulse, whereas 3d classical Monte Carlo calculations (3dCL) gave 10-thresholds F_{o}(0.1) about 10% higher. Here the authors study for n_{o}≥ 28 the polarization dependence at 9.904 GHz (but half-sine pulse with 154 field osc). In LP, QM:SC and 3dCL are near experimental F_{o}(0.1) values for n_{o}below about 35. The pulse shape explains the differences from the 1992 results. In CP, however, for n_{o}below about 40, the experimental F_{o}(0.1) values are reproduced reasonably well only by QM:SC; 3dCL values rise higher as n_{o}decreases in this range. In the co-rotating frame the field is static for CP, which explains why tunneling ionization occurs more readily for CP than for LP, for which the field is not staticPrimary Subject

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[en] The authors present an eigenchannel R-matrix calculation for photodetachment of Al

^{-}(3s^{2}3p^{23}P) below the 3s^{2}4s (^{2}S) threshold for Al. They make the approximation that, for the energies of interest, Al^{-}may be treated as a quasi-two electron system. A strong doubly-excited state resonance is found below the 3s^{2}4s (^{2}S) threshold, with primarily 4s4p character. Their results agree well with the resonance structure observed in a recent experimentPrimary Subject

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[en] 10-15 eV electron impact on H

_{2}is observed to give many resonances associated with simultaneous excitation of electronic and nuclear motions. The complexity of the observations has lead to much confusion over their interpretation. Previous calculations have been performed with the nuclei fixed at the equilibrium geometry. In order to carry out any calculations involving motion of the nuclei, it is necessary to know how resonances change with geometry. A series of fixed-nuclei scattering calculations has been performed over a range of internuclear separations. Results are presented for eight symmetries of the (H_{2}+e) system, and show the variation of resonance width and position with bond-length. Eigenphase sums and cross sections are also produced. These calculations are the first stage in the production of a full-CI, non-adiabatic model of inelastic electron-hydrogen molecule collisionsPrimary Subject

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