18,269 research outputs found
Nuclear effects in atomic transitions
Atomic electrons are sensitive to the properties of the nucleus they are
bound to, such as nuclear mass, charge distribution, spin, magnetization
distribution, or even excited level scheme. These nuclear parameters are
reflected in the atomic transition energies. A very precise determination of
atomic spectra may thus reveal information about the nucleus, otherwise hardly
accessible via nuclear physics experiments. This work reviews theoretical and
experimental aspects of the nuclear effects that can be identified in atomic
structure data. An introduction to the theory of isotope shifts and hyperfine
splitting of atomic spectra is given, together with an overview of the typical
experimental techniques used in high-precision atomic spectroscopy. More exotic
effects at the borderline between atomic and nuclear physics, such as parity
violation in atomic transitions due to the weak interaction, or nuclear
polarization and nuclear excitation by electron capture, are also addressed.Comment: review article, 53 pages, 14 figure
Entrance Channel X-HF (X=Cl, Br, and I) Complexes studied by High-Resolution Infrared Laser Spectroscopy in Helium Nanodroplets
Rotationally resolved infrared spectra are reported for halogen atom - HF
free radical complexes formed in helium nanodroplets. An effusive pyrolysis
source is used to dope helium droplets with Cl, Br and I atoms, formed by
thermal dissociation of Cl, Br and I. A single hydrogen fluoride
molecule is then added to the droplets, resulting in the formation of the X-HF
complexes of interest. Analysis of the resulting spectra confirms that the
observed species have ground electronic states, consistent with
the linear hydrogen bound structures predicted from theory. Stark spectra are
also reported for these species, from which the permanent electric dipole
moments are determined.Comment: 41 pages, 16 figures, 5 table
Semiclassical evaluation of kinetic isotope effects in 13-atomic system
The semiclassical instanton approach discussed by Kryvohuz [J. Chem. Phys. 134, 114103 (2011)10.1063/1.3565425] is applied to calculate kinetic H/D isotope effect (KIE) of intramolecular hydrogen transfer in cis-1,3-pentadiene. All 33 vibrational degrees of freedom are treated quantum mechanically with semiclassical approximation. Nuclear quantum effects such as tunneling under the barrier and zero-point energy are automatically incorporated in the theory, and are shown to be responsible for the observed appreciable kinetic isotope effect in cis-1,3-pentadiene. Over the barrier passage is also automatically included. Numerical calculations are performed on an empirical valence bond potential energy surface and compared with the previous experimental and theoretical studies. An estimation of heavy-atom ^(12)C/^(13)C KIE in the same system is also provided and the factors contributing to it are discussed
Isotope shifts of 6s5d D-states in neutral Barium
Laser spectroscopy of the low lying P and D states in atomic barium
has been performed. This work contributes substantially to the development of
an effective laser cooling and trapping for heavy alkaline earth elements and
aims in particular for a better understanding of the atomic wave function of
these systems. Isotope shifts and hyperfine structures are ideal probes for the
wave functions at the position of the nucleus. This is essential input for a
theoretical evaluation of the sensitivity to fundamental symmetry breaking
properties like permanent electric dipole moments. We report the first isotope
shift measurements of the D-P transitions. A deviation of
the King plot from its expected behavior has been observed. Further we have
optically resolved the hyperfine structure of the D states.Comment: 7 pages, 7 figure
Influence of Dielectric Environment upon Isotope Effects onGlycoside Heterolysis: Computational Evaluation and AtomicHessian Analysis
Isotope effects depend upon the polarity of the bulk medium in which a chemical process occurs. Implicit solvent calculations with molecule-shaped cavities show that the equilibrium isotope effect (EIE) for heterolysis of the glycosidic bonds in 5′-methylthioadenosine and in 2-(p-nitrophenoxy)tetrahydropyran, both in water, are very sensitive in the range 2 ≤ ε ≤ 10 to the relative permittivity of the continuum surrounding the oxacarbenium ion. However, different implementations of nominally the same PCM method can lead to opposite trends being predicted for the same molecule. Computational modeling of the influence of the inhomogeneous effective dielectric surrounding a substrate within the protein environment of an enzymic reaction requires an explicit treatment. The EIE (KH/KD) for transfer of cyclopentyl, cyclohexyl, tetrahydrofuranyl and tetrahydropyranyl cations from water to cyclohexane is predicted by B3LYP/6-31+G(d) calculations with implicit solvation and confirmed by B3LYP/6-31+G(d)/OPLS-AA calculations with averaging over many explicit solvation configurations. Atomic Hessian analysis, whereby the full Hessian is reduced to the elements belonging to a single atom at the site of isotopic substitution, reveals a remarkable result for both implicit and explicit solvation: the influence of the solvent environment on these EIEs is essentially captured completely by only a 3 × 3 block of the Hessian, although these values must correctly reflect the influence of the whole environment. QM/MM simulation with ensemble averaging has an important role to play in assisting the meaningful interpretation of observed isotope effects for chemical reactions both in solution and catalyzed by enzymes
Correlation between muonic levels and nuclear structure in muonic atoms
A method that deals with the nucleons and the muon unitedly is employed to
investigate the muonic lead, with which the correlation between the muon and
nucleus can be studied distinctly. A "kink" appears in the muonic isotope shift
at a neutron magic number where the nuclear shell structure plays a key role.
This behavior may have very important implications for the experimentally
probing the shell structure of the nuclei far away from the -stable
line. We investigate the variations of the nuclear structure due to the
interaction with the muon in the muonic atom and find that the nuclear
structure remains basically unaltered. Therefore, the muon is a clean and
reliable probe for studying the nuclear structure. In addition, a correction
that the muon-induced slight change in the proton density distribution in turn
shifts the muonic levels is investigated. This correction to muonic level is as
important as the Lamb shift and high order vacuum polarization correction, but
is larger than anomalous magnetic moment and electron shielding correction.Comment: 2 figure
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