279 research outputs found
Hyperfine Structure and Nuclear Moment of Rhenium
The Re I spectrum has been photographed in the range 3000A to 6800A with spectrographs of high resolving power at the Mount Wilson Observatory, and the majority of lines are found to be complex, having 2 to 6 components
Doppler-free Yb Spectroscopy with Fluorescence Spot Technique
We demonstrate a simple technique to measure the resonant frequency of the
398.9 nm 1S0 - 1P1 transition for the different Yb isotopes. The technique,
that works by observing and aligning fluorescence spots, has enabled us to
measure transition frequencies and isotope shifts with an accuracy of 60 MHz.
We provide wavelength measurements for the transition that differ from
previously published work. Our technique also allows for the determination of
Doppler shifted transition frequencies for photoionisation experiments when the
atomic beam and laser beam are not perpendicular and furthermore allows us to
determine the average velocity of the atoms along the direction of atomic beam
Re II and Other Exotic Spectra in HD 65949
Powerful astronomical spectra reveal an urgent need for additional work on
atomic lines, levels, and oscillator strengths. The star HD 65949 provides some
excellent examples of species rarely identified in stellar spectra. For
example, the Re II spectrum is well developed, with 17 lines between 3731 and
4904 [A], attributed wholly or partially to Re II. Classifications and
oscillator strengths are lacking for a number of these lines. The spectrum of
Os II is well identified. Of 14 lines attributed wholly or partially to Os II,
only one has an entry in the VALD database. We find strong evidence that Te II
is present. There are NO Te II lines in the VALD database. Ru II is clearly
present, but oscillator strengths for lines in the visual are lacking. There is
excellent to marginal evidence for a number of less commonly identified
species, including Kr II, Nb II, Sb II, Xe II, Pr III, Ho III, Au II, and Pt II
(probably Pt-198), to be present in the spectrum of HD 65949. The line Hg II at
3984 [A] is of outstanding strength, and all three lines of Multiplet 1 of Hg I
are present, even though the surface temperature of HD 65949 is relatively
high. Finally, we present the case of an unidentified, 24 [mA], line at 3859.63
[A], which could be the same feature seen in magnetic CP stars. It is typically
blended with a putative U II line used in cosmochronology.Comment: ASOS9 Poster (Lund, Sweden, August 2007), to be published in Journal
of Physics: Conference Series (JPCS), 6 pages 1 figur
Experimental and theoretical lifetimes and transition probabilities in Sb I
We present experimental atomic lifetimes for 12 levels in Sb I, out of which
seven are reported for the first time. The levels belong to the 5p(P)6s
P, P and 5p(P)5d P, F and F terms. The
lifetimes were measured using time-resolved laser-induced fluorescence. In
addition, we report new calculations of transition probabilities in Sb I using
a Multiconfigurational Dirac-Hartree-Fock method. The physical model being
tested through comparisons between theoretical and experimental lifetimes for
5d and 6s levels. The lifetimes of the 5d F levels (19.5,
7.8 and 54 ns, respectively) depend strongly on the -value. This is
explained by different degrees of level mixing for the different levels in the
F term.Comment: 10 page
Optical emission spectroscopy of metal-halide lamps: Radially resolved atomic state distribution functions of Dy and Hg
Absolute line intensity measurements are performed on a metal-halide lamp. Several transitions of atomic and ionic Dy and atomic Hg are measured at different radial positions from which we obtain absolute atomic and ionic Dy intensity profiles. From these profiles we construct the radially resolved atomic state distribution function (ASDF) of the atomic and ionic Dy and the atomic Hg. From these ASDFs several quantities are determined as functions of radial position, such as the (excitation) temperature, the ion ratio Hg^+/Dy^+, the electron density, the ground state, and the totaldensity of Dy atoms and ions. Moreover, these ASDFs give us insight about the departure from equilibrium. The measurements show a hollow density profile for the atoms and the ionization of atoms in the center. In the outer parts of the lamp molecules dominate
Ab-initio study of model guanine assemblies: The role of pi-pi coupling and band transport
Several assemblies of guanine molecules are investigated by means of
first-principle calculations. Such structures include stacked and
hydrogen-bonded dimers, as well as vertical columns and planar ribbons,
respectively, obtained by periodically replicating the dimers. Our results are
in good agreement with experimental data for isolated molecules, isolated
dimers, and periodic ribbons. For stacked dimers and columns, the stability is
affected by the relative charge distribution of the pi orbitals in adjacent
guanine molecules. pi-pi coupling in some stacked columns induces dispersive
energy bands, while no dispersion is identified in the planar ribbons along the
connections of hydrogen bonds. The implications for different materials
comprised of guanine aggregates are discussed. The bandstructure of dispersive
configurations may justify a contribution of band transport (Bloch type) in the
conduction mechanism of deoxyguanosine fibres, while in DNA-like configurations
band transport should be negligible.Comment: 21 pages, 6 figures, 3 tables, to be published in Phys. Rev.
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