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

Effective Schroedinger dynamics on ϵ \epsilon -thin Dirichlet waveguides via Quantum Graphs I: star-shaped graphs

We describe the boundary conditions at the vertex that one must choose to obtain a dynamical system that best describes the low-energy part of the evolution of a quantum system confined to a very small neighbourhood of a star-shaped metric graph.Comment: in memory of Pierre Duclo

Anisotropic fragmentation in low-energy dissociative recombination

On a dense energy grid reaching up to 75 meV electron collision energy the fragmentation angle and the kinetic energy release of neutral dissociative recombination fragments have been studied in a twin merged beam experiment. The anisotropy described by Legendre polynomials and the extracted rotational state contributions were found to vary on a likewise narrow energy scale as the rotationally averaged rate coefficient. For the first time angular dependences higher than 2$^{nd}$ order could be deduced. Moreover, a slight anisotropy at zero collision energy was observed which is caused by the flattened velocity distribution of the electron beam.Comment: 8 pages, 4 figures; The Article will be published in the proceedings of DR 2007, a symposium on Dissociative Recombination held in Ameland, The Netherlands (18.-23. July 2008); Reference 19 has been published meanwhile in S. Novotny, PRL 100, 193201 (2008

Radiative rotational lifetimes and state-resolved relative detachment cross sections from photodetachment thermometry of molecular anions in a cryogenic storage ring

Photodetachment thermometry on a beam of OH$^-$ in a cryogenic storage ring cooled to below 10 K is carried out using two-dimensional, frequency and time dependent photodetachment spectroscopy over 20 minutes of ion storage. In equilibrium with the low-level blackbody field, we find an effective radiative temperature near 15 K with about 90% of all ions in the rotational ground state. We measure the J = 1 natural lifetime (about 193 s) and determine the OH$^-$ rotational transition dipole moment with 1.5% uncertainty. We also measure rotationally dependent relative near-threshold photodetachment cross sections for photodetachment thermometry.Comment: Manuscript LaTeX with 5 pages, 3 figures, and 1 table plus LaTeX supplement with 12 pages, 3 figures and 3 tables. This article has been accepted by Physical Review Letter

Electron-ion recombination measurements motivated by AGN X-ray absorption features: Fe XIV forming Fe XIII

Recent spectroscopic models of active galactic nuclei (AGN) have indicated that the recommended electron-ion recombination rate coefficients for iron ions with partially filled M-shells are incorrect in the temperature range where these ions form in photoionized plasmas. We have investigated this experimentally for Fe XIV forming Fe XIII. The recombination rate coefficient was measured employing the electron-ion merged beams method at the Heidelberg heavy-ion storage-ring TSR. The measured energy range of 0-260 eV encompassed all dielectronic recombination (DR) 1s2 2s2 2p6 3l 3l' 3l'' nl''' resonances associated with the 3p1/2 -> 3p3/2, 3s -> 3p, 3p -> 3d and 3s -> 3d core excitations within the M-shell of the Fe XIV 1s2 2s2 2p6 3s2 3p parent ion. This range also includes the 1s2 2s2 2p6 3l 3l' 4l'' nl''' resonances associated with 3s -> 4l'' and 3p -> 4l'' core excitations. We find that in the temperature range 2--14 eV, where Fe XIV is expected to form in a photoionized plasma, the Fe XIV recombination rate coefficient is orders of magnitude larger than previously calculated values.Comment: 4 pages, 4 figures, 1 table submitted to Ap