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We have measured total absolute cross sections for the Mutual Neutralization (MN) of O- with O+/N+. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems with a multi-channel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N+ + O- collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements., Comment: 5 pages, 4 figures

We have measured the spontaneous neutral particle emission from copper cluster anions (Cu$_n^-$, $n=3-6$) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the DESIREE (Double ElectroStatic Ion Ring ExpEriment) facility at Stockholm University. The measured rate of emission from the stored Cu$_3^-$ ions follows a single power law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu$_3$ as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu$_4^-$, Cu$_5^-$ and Cu$_6^-$ are well-described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu$_6^-$ ions that were excited by 1.13 eV or 1.45 eV photons after 46 milliseconds of storage.

The intrinsic lifetime of the upper level in the bound-bound 3d$^9$4s$^2$ $^2$D$_{3/2}$ $\rightarrow$ 3d$^9$4s$^2$ $^2$D$_{5/2}$ radiative transition in Ni$^-$ was measured to be 15.1 $\pm$ 0.4 s. The experiment was performed at cryogenic temperatures in one of the ion-beam storage rings of the DESIREE (Double ElectroStatic Ion Ring Experiment) facility at Stockholm University. The storage lifetime of the Ni$^-$ ion-beam was measured to be close to five minutes at a ring temperature of 13 K., Comment: 12 pages, 5 figures

We report the direct detection of two metastable H(2S) atoms coming from the dissociation of a single cold H_2 molecule, in coincidence measurements. The molecular dissociation was induced by electron impact in order to avoid limitations by the selection rules governing radiative transitions. Two detectors, placed close from the collision center, measure the neutral metastable H(2S) through a localized quenching process, which mixes the H(2S) state with the H(2P), leading to a Lyman-\alpha detection. Our data show the accomplishment of a coincidence measurement which proves for the first time the existence of the H(2S)-H(2S) dissociation channel., Comment: 5 pages, 5 figures

Made available in DSpace on 2022-04-29T08:48:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-01 Energy transfer excited multiwavelength visible upconversion emission and white light generation is described in a single sample ofPbGeO 3-PbF2-CdF2 glass-ceramic triply doped with Ho/Tm/Yb under single infrared laser excitation. Blue (475 nm), green (540 nm), and red (650 nm), upconversion luminescence signals are generated, and the emissions are assigned, respectively, to thulium (1G4- 3H6), and holmium (5S2) →5F4)→5I8, 5F5→5I8 ions transitions, both excited via successive energy transfers from ytterbium ions. It is experimentally shown that with a proper combination of the rare earth ions contents, white light may be produced, with the simultaneous generation of fluorescence with controllable intensities at the wavelengths of the three primary colours in a single sample and using a single near-infrared excitation source. Departamento de Física Universidade Federal Rural de Pernambuco, Recife, PE- 52171/900 Instituto de Química UNESP, Araraquara, SP - 14800/900 Instituto de Química UNESP, Araraquara, SP - 14800/900

Made available in DSpace on 2022-04-29T08:48:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-01 Cooperative energy transfer upconversion luminescence is investigated in Tb3+/Yb3+-codoped PbGeO3-PbF 2-CdF2 glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the 5D3(5G 6)→7Fj (J=6,5,4) and 5D 4→7Fj (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined. Departamento de Física Universidade Federal Rural de Pernambuco, Recife, PE-52171/900 Institute de Química UNESP, Araraquara, SP-14800/900 Institute de Química UNESP, Araraquara, SP-14800/900