76,512 research outputs found
Excitation energies, polarizabilities, multipole transition rates, and lifetimes of ions along the francium isoelectronic sequence
Relativistic many-body perturbation theory is applied to study properties of
ions of the francium isoelectronic sequence. Specifically, energies of the 7s,
7p, 6d, and 5f states of Fr-like ions with nuclear charges Z = 87 - 100 are
calculated through third order; reduced matrix elements, oscillator strengths,
transition rates, and lifetimes are determined for 7s - 7p, 7p - 6d, and 6d -
5f electric-dipole transitions; and 7s - 6d, 7s - 5f, and 5f_5/2 - 5f_7/2
multipole matrix elements are evaluated to obtain the lifetimes of low-lying
excited states. Moreover, for the ions Z = 87 - 92 calculations are also
carried out using the relativistic all-order single-double method, in which
single and double excitations of Dirac-Fock wave functions are included to all
orders in perturbation theory. With the aid of the SD wave functions, we obtain
accurate values of energies, transition rates, oscillator strengths, and the
lifetimes of these six ions. Ground state scalar polarizabilities in Fr I, Ra
II, Ac III, and Th IV are calculated using relativistic third-order and
all-order methods. Ground state scalar polarizabilities for other Fr-like ions
are calculated using a relativistic second-order method. These calculations
provide a theoretical benchmark for comparison with experiment and theory.Comment: 13 figures, 11 table
Excitation energies, polarizabilities, multipole transition rates, and lifetimes in Th IV
Excitation energies of the ns_{1/2} (n=7-10), np_j (n=7-9), nd_j (n=6-8),
nf_{j} (n=5-7), and ng_{j} (n=5-6) states in Th IV are evaluated. First-,
second-, third-, and all-order Coulomb energies and first- and second-order
Coulomb-Breit energies are calculated. Reduced matrix elements, oscillator
strengths, transition rates, and lifetimes are determined for the 96 possible
nl_j-n'l'_j' electric-dipole transitions. Multipole matrix elements
(7s_{1/2}-6d_j, 7s_{1/2}-5f_j, and 5f_{5/2}-5f_{7/2}) are evaluated to obtain
the lifetimes of the and 7s_{1/2}$ states. Matrix elements are
calculated using both relativistic many-body perturbation theory, complete
through third order, and a relativistic all-order method restricted to single
and double (SD) excitations. Scalar and tensor polarizabilities for the
5f_{5/2} ground state in Th3+ are calculated using relativistic third-order and
all-order methods. These calculations provide a theoretical benchmark for
comparison with experiment and theory.Comment: 9 pages, 9 figure
Relativistic many-body calculation of energies, lifetimes, polarizabilities, blackbody radiative shift and hyperfine constants in Lu2+
Energy levels of 30 low-lying states of Lu2+ and allowed electric-dipole
matrix elements between these states are evaluated using a relativistic
all-order method in which all single, double and partial triple excitations of
Dirac-Fock wave functions are included to all orders of perturbation theory.
Matrix elements are critically evaluated for their accuracy and recommended
values of the matrix elements are given together with uncertainty estimates.
Line strengths, transition rates and lifetimes of the metastable 5d(3/2) and
5d(5/2) states are calculated. Recommended values are given for static
polarizabilities of the 6s, 5d and 6p states and tensor polarizabilities of the
5d and 6p(3/2) states. Uncertainties of the polarizability values are estimated
in all cases. The blackbody radiation shift of the 6s(1/2)-5d(5/2) transition
frequency of the Lu2+ ion is calculated with the aid of the recommended scalar
polarizabilities of the 6s(1/2) and 5d(5/2) states. Finally, A and B hyperfine
constants are determined for states of 175Lu2+ with n <= 9. This work provides
recommended values of transition matrix elements, polarizabilities and
hyperfine constants of Lu2+, critically evaluated for accuracy, for benchmark
tests of high-precision theoretical methodology and planning of future
experiments.Comment: 9 pages, 10 table
Forbidden M1 and E2 transitions in monovalent atoms and ions
We carried out a systematic high-precision relativistic study of the
forbidden magnetic-dipole and electric-quadrupole transitions in Ca+, Rb, Sr+,
Cs, Ba+, Fr, Ra+, Ac2+, and Th3+. This work is motivated by the importance of
these transitions for tests of fundamental physics and precision measurements.
The relative importance of the relativistic, correlation, Breit correction, and
contributions of negative-energy states is investigated. Recommended values of
reduced matrix elements are presented together with their uncertainties. The
matrix elements and resulting lifetimes are compared with other theoretical
values and with experiment where available.Comment: 9 pages, 6 table
Coupled-cluster calculations of properties of Boron atom as a monovalent system
We present relativistic coupled-cluster (CC) calculations of energies,
magnetic-dipole hyperfine constants, and electric-dipole transition amplitudes
for low-lying states of atomic boron. The trivalent boron atom is
computationally treated as a monovalent system. We explore performance of the
CC method at various approximations. Our most complete treatment involves
singles, doubles and the leading valence triples. The calculations are done
using several approximations in the coupled-cluster (CC) method. The results
are within 0.2-0.4% of the energy benchmarks. The hyperfine constants are
reproduced with 1-2% accuracy
Two-photon E1M1 decay of 2 3P0 states in heavy heliumlike ions
Two-photon E1M1 transition rates are evaluated for heliumlike ions with
nuclear charges in the range Z = 50-94. The two-photon rates modify previously
published lifetimes/transition rates of 2 3P0 states. For isotopes with nuclear
spin I not equal 0, where hyperfine quenching dominates the 2 3P0 decay,
two-photon contributions are significant; for example, in heliumlike 187 Os the
two-photon correction is 3% of the total rate. For isotopes with I= 0, where
the 2 3P0 decay is unquenched, the E1M1 corrections are even more important
reaching 60% for Z=94. Therefore, to aid in the interpretation of experiments
on hyperfine quenching in heliumlike ions and to provide a more complete
database for unquenched transitions, a knowledge of E1M1 rates is important.Comment: 6 pages, 3 figures, 3 table
Film thickness measurements on five fluid formulations by the mercury squeeze film capacitance technique
The thinning characteristics of five fluids were studied by measuring film thickness as a function of time. The mercury squeeze film capacitance technique was used. All tests were performed at room temperature. The synthetic hydrocarbon plus a nematic liquid crystal, N-(p-methoxybenzylidene)-p-butylaniline, thinned according to a Newtonian model and retained its bulk viscosity. The synthetic hydrocarbon plus a phosphonate antiwear additive and the synthetic hydrocarbon plus n-hexadecanol produced residual thick films. The synthetic hydrocarbon base fluids and the synthetic hydrocarbon plus a paraffinic resin displayed viscosity increases during thinning, but no residual films were formed
Properties from relativistic coupled-cluster without truncation: hyperfine constants of , , and
We demonstrate an iterative scheme for coupled-cluster properties
calculations without truncating the dressed properties operator. For
validation, magnetic dipole hyperfine constants of alkaline Earth ions are
calculated with relativistic coupled-cluster and role of electron correlation
examined. Then, a detailed analysis of the higher order terms is carried out.
Based on the results, we arrive at an optimal form of the dressed operator.
Which we recommend for properties calculations with relativistic
coupled-cluster theory.Comment: 13 pages, 4 figures, 5 table
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