Perturbation theory for plasmonic eigenvalues

We develop a perturbative approach for calculating, within the quasistatic approximation, the shift of surface resonances in response to a deformation of a dielectric volume. Our strategy is based on the conversion of the homogeneous system for the potential which determines the plasmonic eigenvalues into an inhomogeneous system for the potential's derivative with respect to the deformation strength, and on the exploitation of the corresponding compatibility condition. The resulting general expression for the first-order shift is verified for two explicitly solvable cases, and for a realistic example of a deformed nanosphere. It can be used for scanning the huge parameter space of possible shape fluctuations with only quite small computational effort

Dissociative recombination measurements of HCl+ using an ion storage ring

We have measured dissociative recombination of HCl+ with electrons using a merged beams configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present the measured absolute merged beams recombination rate coefficient for collision energies from 0 to 4.5 eV. We have also developed a new method for deriving the cross section from the measurements. Our approach does not suffer from approximations made by previously used methods. The cross section was transformed to a plasma rate coefficient for the electron temperature range from T=10 to 5000 K. We show that the previously used HCl+ DR data underestimate the plasma rate coefficient by a factor of 1.5 at T=10 K and overestimate it by a factor of 3.0 at T=300 K. We also find that the new data may partly explain existing discrepancies between observed abundances of chlorine-bearing molecules and their astrochemical models.Comment: Accepted for publication in ApJ (July 7, 2013

Storage-ring measurement of the hyperfine induced 47Ti18+(2s 2p 3P0 -> 2s2 1S0) transition rate

The hyperfine induced 2s 2p 3P0 > 2s2 1S0 transition rate AHFI in berylliumlike 47Ti18+ was measured. Resonant electron-ion recombination in a heavy-ion storage ring was employed to monitor the time dependent population of the 3P0 state. The experimental value AHFI=0.56(3)/s is almost 60% larger than theoretically predicted.Comment: 4 pages. 3 figures, 1 table, accepted for publication in Physical Review Letter

Modern Michelson-Morley experiment using cryogenic optical resonators

We report on a new test of Lorentz invariance performed by comparing the resonance frequencies of two orthogonal cryogenic optical resonators subject to Earth's rotation over 1 year. For a possible anisotropy of the speed of light c, we obtain 2.6 +/- 1.7 parts in 10^15. Within the Robertson-Mansouri-Sexl test theory, this implies an isotropy violation parameter beta - delta - 1/2 of -2.2 +/- 1.5 parts in 10^9, about three times lower than the best previous result. Within the general extension of the standard model of particle physics, we extract limits on 7 parameters at accuracies down to a part in 10^15, improving the best previous result by about two orders of magnitude

Spectroscopy and dissociative recombination of the lowest rotational states of H3+

The dissociative recombination of the lowest rotational states of H3+ has been investigated at the storage ring TSR using a cryogenic 22-pole radiofrequency ion trap as injector. The H3+ was cooled with buffer gas at ~15 K to the lowest rotational levels, (J,G)=(1,0) and (1,1), which belong to the ortho and para proton-spin symmetry, respectively. The rate coefficients and dissociation dynamics of H3+(J,G) populations produced with normal- and para-H2 were measured and compared to the rate and dynamics of a hot H3+ beam from a Penning source. The production of cold H3+ rotational populations was separately studied by rovibrational laser spectroscopy using chemical probing with argon around 55 K. First results indicate a ~20% relative increase of the para contribution when using para-H2 as parent gas. The H3+ rate coefficient observed for the para-H2 source gas, however, is quite similar to the H3+ rate for the normal-H2 source gas. The recombination dynamics confirm that for both source gases, only small populations of rotationally excited levels are present. The distribution of 3-body fragmentation geometries displays a broad part of various triangular shapes with an enhancement of ~12% for events with symmetric near-linear configurations. No large dependences on internal state or collision energy are found.Comment: 10 pages, 9 figures, to be published in Journal of Physics: Conference Proceeding

Ion-lithium collision dynamics studied with an in-ring MOTReMi

We present a novel experimental tool allowing for kinematically complete studies of break-up processes of laser-cooled atoms. This apparatus, the 'MOTReMi', is a combination of a magneto-optical trap (MOT) and a Reaction Microscope (ReMi). Operated in an ion-storage ring, the new setup enables to study the dynamics in swift ion-atom collisions on an unprecedented level of precision and detail. In first experiments on collisions with 1.5 MeV/amu O$^{8+}$-Li the pure ionization of the valence electron as well as ionization-excitation of the lithium target has been investigated

Dielectronic Recombination in Photoionized Gas. II. Laboratory Measurements for Fe XVIII and Fe XIX

In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj --> nl'j' core excitations (Dn=0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII Dn=0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX Dn=0 DR DR rate coefficients. Significant discrepancies exist between our inferred rates and those of published calculations. These calculations overestimate the DR rates by factors of ~2 or underestimate it by factors of ~2 to orders of magnitude, but none are in good agreement with our results. Almost all published DR rates for modeling cosmic plasmas are computed using the same theoretical techniques as the above-mentioned calculations. Hence, our measurements call into question all theoretical Dn=0 DR rates used for ionization balance calculations of cosmic plasmas. At temperatures where the Fe XVIII and Fe XIX fractional abundances are predicted to peak in photoionized gases of cosmic abundances, the theoretical rates underestimate the Fe XVIII DR rate by a factor of ~2 and overestimate the Fe XIX DR rate by a factor of ~1.6. We have carried out new multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli calculations which agree with our measured resonance strengths and rate coefficients to within typically better than <~30%. We provide a fit to our inferred rate coefficients for use in plasma modeling. Using our DR measurements, we infer a factor of ~2 error in the Fe XX through Fe XXIV Dn=0 DR rates. We investigate the effects of this estimated error for the well-known thermal instability of photoionized gas. We find that errors in these rates cannot remove the instability, but they do dramatically affect the range in parameter space over which it forms.Comment: To appear in ApJS, 44 pages with 13 figures, AASTeX with postsript figure