1,039 research outputs found
The periodic table and the physics that drives it
As the International Year of the Periodic Table came to an end in 2019, the authors reflect on the chemistry and physics that drive the periodic table of the elements. This includes aspects of periodic trends, relativistic electronic-structure theory, nuclear-structure theory and the astrophysical origin of the elements. Mendeleev's introduction of the periodic table of elements is one of the most important milestones in the history of chemistry, as it brought order into the known chemical and physical behaviour of the elements. The periodic table can be seen as parallel to the Standard Model in particle physics, in which the elementary particles known today can be ordered according to their intrinsic properties. The underlying fundamental theory to describe the interactions between particles comes from quantum theory or, more specifically, from quantum field theory and its inherent symmetries. In the periodic table, the elements are placed into a certain period and group based on electronic configurations that originate from the Pauli and Aufbau principles for the electrons surrounding a positively charged nucleus. This order enables us to approximately predict the chemical and physical properties of elements. Apparent anomalies can arise from relativistic effects, partial-screening phenomena (of type lanthanide contraction) and the compact size of the first shell of everyl-value. Further, ambiguities in electron configurations and the breakdown of assigning a dominant configuration, owing to configuration mixing and dense spectra for the heaviest elements in the periodic table. For the short-lived transactinides, the nuclear stability becomes an important factor in chemical studies. Nuclear stability, decay rates, spectra and reaction cross sections are also important for predicting the astrophysical origin of the elements, including the production of the heavy elements beyond iron in supernova explosions or neutron-star mergers. In this Perspective, we critically analyse the periodic table of elements and the current status of theoretical predictions and origins for the heaviest elements, which combine both quantum chemistry and physics.Peer reviewe
Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne
In the catalytic addition of water to propyne the Au(III) catalyst is not
stable under non-relativistic conditions and dissociates into a Au(I) compound
and Cl2. This implies that one link in the chain of events in the catalytic
cycle is broken and relativity may well be seen as the reason why Au(III)
compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl
The tensor hypercontracted parametric reduced density matrix algorithm: coupled-cluster accuracy with O(r^4) scaling
Tensor hypercontraction is a method that allows the representation of a
high-rank tensor as a product of lower-rank tensors. In this paper, we show how
tensor hypercontraction can be applied to both the electron repulsion integral
(ERI) tensor and the two-particle excitation amplitudes used in the parametric
reduced density matrix (pRDM) algorithm. Because only O(r) auxiliary functions
are needed in both of these approximations, our overall algorithm can be shown
to scale as O(r4), where r is the number of single-particle basis functions. We
apply our algorithm to several small molecules, hydrogen chains, and alkanes to
demonstrate its low formal scaling and practical utility. Provided we use
enough auxiliary functions, we obtain accuracy similar to that of the
traditional pRDM algorithm, somewhere between that of CCSD and CCSD(T).Comment: 11 pages, 1 figur
The convergence of the ab-initio many-body expansion for the cohesive energy of solid mercury
A many-body expansion for mercury clusters of the form E = \sum_{i<j}\Delta
\epsilon_{ij} + \sum_{i<j<k}\Delta \epsilon_{ijk} + ... \quad, does not
converge smoothly with increasing cluster size towards the solid state. Even
for smaller cluster sizes (up to n=6), where van der Waals forces still
dominate, one observes bad convergence behaviour. For solid mercury the
convergence of the many-body expansion can dramatically be improved by an
incremental procedure within an embedded cluster approach. Here one adds the
coupled cluster many-body electron correlation contributions of the embedded
cluster to the bulk HF energy. In this way we obtain a cohesive energy (not
corrected for zero-point vibration) of 0.79 eV in perfect agreement with the
experimental value.Comment: 10 pages, 3 figures, accepted PR
Identification of the slow E3 transition 136mCs -> 136Cs with conversion electrons
We performed at ISOLDE the spectroscopy of the decay of the 8- isomer in
136Cs by and conversion-electron detection. For the first time the excitation
energy of the isomer and the multipolarity of its decay have been measured. The
half-life of the isomeric state was remeasured to T1/2 = 17.5(2) s. This isomer
decays via a very slow 518 keV E3 transition to the ground state. In addition
to this, a much weaker decay branch via a 413 keV M4 and a subsequent 105 keV
E2 transition has been found. Thus we have found a new level at 105 keV with
spin 4+ between the isomeric and the ground state. The results are discussed in
comparison to shell model calculations.Comment: Phys. Rev. C accepted for publicatio
Verification of a Central Pacemaker in Brain Stem by Phase-Coupling Analysis Between HR Interval- and BOLD-Oscillations in the 0.10–0.15 Hz Frequency Band
The origin of slow intrinsic oscillations in resting states of functional magnetic resonance
imaging (fMRI) signals is still a matter of debate. The present study aims to test
the hypothesis that slow blood oxygenation level-dependent (BOLD) oscillations with
frequency components greater than 0.10 Hz result from a central neural pacemaker
located in the brain stem. We predict that a central oscillator modulates cardiac beatto-
beat interval (RRI) fluctuations rapidly, with only a short neural lag around 0.3 s.
Spontaneous BOLD fluctuations in the brain stem, however, are considerably delayed
due to the hemodynamic response time of about 2–3 s. In order to test these
predictions, we analyzed the time delay between slow RRI oscillations from thorax and
BOLD oscillations in the brain stem by calculating the phase locking value (PLV). Our
findings show a significant time delay of 2.2 0.2 s between RRI and BOLD signals in
12 out of 23 (50%) participants in axial slices of the pons/brain stem. Adding the neural
lag of 0.3 s to the observed lag of 2.2 s we obtain 2.5 s, which is the time between
neural activity increase and BOLD increase, termed neuro-BOLD coupling. Note, this
time window for neuro-BOLD coupling in awake humans is surprisingly of similar size as
in awake head-fixed adult mice (Mateo et al., 2017)
First identification of large electric monopole strength in well-deformed rare earth nuclei
Excited states in the well-deformed rare earth isotopes Sm and
Er were populated via ``safe'' Coulomb excitation at the Munich MLL
Tandem accelerator. Conversion electrons were registered in a cooled Si(Li)
detector in conjunction with a magnetic transport and filter system, the
Mini-Orange spectrometer. For the first excited state in Sm at
1099 keV a large value of the monopole strength for the transition to the
ground state of could be extracted. This confirms the interpretation of the lowest
excited state in Sm as the collective -vibrational
excitation of the ground state. In Er the measured large electric
monopole strength of clearly identifies the state at 1934 keV to be the
-vibrational excitation of the ground state.Comment: submitted to Physics Letters
High resolution spectroscopy of methyltrioxorhenium: towards the observation of parity violation in chiral molecules
Originating from the weak interaction, parity violation in chiral molecules
has been considered as a possible origin of the biohomochirality. It was
predicted in 1974 but has never been observed so far. Parity violation should
lead to a very tiny frequency difference in the rovibrational spectra of the
enantiomers of a chiral molecule. We have proposed to observe this predicted
frequency difference using the two photon Ramsey fringes technique on a
supersonic beam. Promising candidates for this experiment are chiral oxorhenium
complexes, which present a large effect, can be synthesized in large quantity
and enantiopure form, and can be seeded in a molecular beam. As a first step
towards our objective, a detailed spectroscopic study of methyltrioxorhenium
(MTO) has been undertaken. It is an ideal test molecule as the achiral parent
molecule of chiral candidates for the parity violation experiment. For the
187Re MTO isotopologue, a combined analysis of Fourier transform microwave and
infrared spectra as well as ultra-high resolution CO2 laser absorption spectra
enabled the assignment of 28 rotational lines and 71 rovibrational lines, some
of them with a resolved hyperfine structure. A set of spectroscopic parameters
in the ground and first excited state, including hyperfine structure constants,
was obtained for the antisymmetric Re=O stretching mode of this molecule. This
result validates the experimental approach to be followed once a chiral
derivative of MTO will be synthesized, and shows the benefit of the combination
of several spectroscopic techniques in different spectral regions, with
different set-ups and resolutions. First high resolution spectra of jet-cooled
MTO, obtained on the set-up being developed for the observation of molecular
parity violation, are shown, which constitutes a major step towards the
targeted objective.Comment: 20 pages, 6 figure
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