181 research outputs found
Precision measurement of the rotational energy-level structure of the three-electron molecule He
The term values of all rotational levels of the
He{_2}^+\,X^+\,^2\Sigma_u^+\,(\nu^+=0) ground vibronic state with
rotational quantum number have been determined with an accuracy of
8 x 10 cm ( MHz) by MQDT-assisted Rydberg spectroscopy
of metastable He. Comparison of these term values with term values
recently calculated ab initio by Tung et al. [J. Chem. Phys. 136, 104309
(2012)] reveal discrepancies that rapidly increase with increasing rotational
quantum number and reach values of 0.07 cm ( GHz) at
.Comment: 11 pages, 6 figure
Spatially Resolved Raman Spectroscopy of Single- and Few-Layer Graphene
We present Raman spectroscopy measurements on single- and few-layer graphene
flakes. Using a scanning confocal approach we collect spectral data with
spatial resolution, which allows us to directly compare Raman images with
scanning force micrographs. Single-layer graphene can be distinguished from
double- and few-layer by the width of the D' line: the single peak for
single-layer graphene splits into different peaks for the double-layer. These
findings are explained using the double-resonant Raman model based on ab-initio
calculations of the electronic structure and of the phonon dispersion. We
investigate the D line intensity and find no defects within the flake. A finite
D line response originating from the edges can be attributed either to defects
or to the breakdown of translational symmetry
Raman imaging of doping domains in graphene on SiO2
We present spatially resolved Raman images of the G and 2D lines of
single-layer graphene flakes. The spatial fluctuations of G and 2D lines are
correlated and are thus shown to be affiliated with local doping domains. We
investigate the position of the 2D line -- the most significant Raman peak to
identify single-layer graphene -- as a function of charging up to |n|~4 10^12
cm^-2. Contrary to the G line which exhibits a strong and symmetric stiffening
with respect to electron and hole-doping, the 2D line shows a weak and slightly
asymmetric stiffening for low doping. Additionally, the line width of the 2D
line is, in contrast to the G line, doping-independent making this quantity a
reliable measure for identifying single-layer graphene
Raman mapping of a single-layer to double-layer graphene transition
Abstract.: We report on confocal Raman spectroscopy on a few-layer graphene flake. Adjacent single- and double-layer graphene sections allow mapping the transition in vibrational and electronic properties to a second stacked graphene sheet and with it a weak interlayer coupling. Most prominently the width of the D' peak doubles upon going from a single to a double layer, which can be explained within the double-resonant Raman model. The intensities of the G and G' lines decrease at the crossover to a single layer. Contrary to the G' line the G peak position shifts to higher wave numbers, however, not uniformly over the entire section: its frequency fluctuates spatially. The Raman map of the D line intensity shows a non-zero contribution at the boundaries of the flake and the individual sections, which can be attributed either to defects and disorder or to the breakdown of translational symmetry, whereas within the flake no D line signal is detecte
Collision photography: polarization imaging of atom-molecule collisions
We report differential scattering experiments on the laser excitation of Na+Mcollision pairs with M=Nâ‚‚, CO, Câ‚‚Hâ‚‚, and COâ‚‚. The collision event is probed by the laser polarization revealing geometric and electronic properties of the collision pair. The experimental data are compared to the results of a Monte Carlo trajectory simulation using ab initio quantum chemical data.Financial support from the Deutsche Forschungsgemeinschaft
and the Schweizerischer Nationalfond (Project No. 20-
065290.01) is gratefully acknowledged
Optimization of Generalized Multichannel Quantum Defect reference functions for Feshbach resonance characterization
This work stresses the importance of the choice of the set of reference
functions in the Generalized Multichannel Quantum Defect Theory to analyze the
location and the width of Feshbach resonance occurring in collisional
cross-sections. This is illustrated on the photoassociation of cold rubidium
atom pairs, which is also modeled using the Mapped Fourier Grid Hamiltonian
method combined with an optical potential. The specificity of the present
example lies in a high density of quasi-bound states (closed channel)
interacting with a dissociation continuum (open channel). We demonstrate that
the optimization of the reference functions leads to quantum defects with a
weak energy dependence across the relevant energy threshold. The main result of
our paper is that the agreement between the both theoretical approaches is
achieved only if optimized reference functions are used.Comment: submitte to Journal of Physics
Dissociation energy of the hydrogen molecule at 10 accuracy
The ionization energy of ortho-H has been determined to be
cm
from measurements of the GK(1,1)--X(0,1) interval by Doppler-free two-photon
spectroscopy using a narrow band 179-nm laser source and the ionization energy
of the GK(1,1) state by continuous-wave near-infrared laser spectroscopy.
(H) was used to derive the dissociation energy of
H, (H), at cm with a
precision that is more than one order of magnitude better than all previous
results. The new result challenges calculations of this quantity and represents
a benchmark value for future relativistic and QED calculations of molecular
energies.Comment: 6 pages, 5 figure
Determination of the Interval between the Ground States of Para- and Ortho- H2
ISSN:0031-9007ISSN:1079-711
IRIS: Efficient Visualization, Data Analysis and Experiment Management for Wireless Sensor Networks
The design of ubiquitous computing environments is challenging, mainly due to the unforeseeable impact of real-world environments on the system performance. A crucial step to validate the behavior of these systems is to perform in-field experiments under various conditions. We introduce IRIS, an experiment management and data processing tool allowing the definition of arbitrary complex data analysis applications. While focusing on Wireless Sensor Networks, IRIS supports the seamless integration of heterogeneous data gathering technologies. The resulting flexibility and extensibility enable the definition of various services, from experiment management and performance evaluation to user-specific applications and visualization. IRIS demonstrated its effectiveness in three real-life use cases, offering a valuable support for in-field experimentation and development of customized applications for interfacing the end user with the system
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