6,489 research outputs found
Semiclassical model for calculating fully differential ionization cross sections of the H molecule
Fully differential cross sections are calculated for the ionization of H
by fast charged projectiles using a semiclassical model developed previously
for the ionization of atoms. The method is tested in case of 4 keV electron and
6 MeV proton projectiles. The obtained results show good agreement with the
available experimental data. Interference effects due to the two-center
character of the target are also observed and analyzed.Comment: 11 pages, 4 figure
A novel method for unambiguous ion identification in mixed ion beams extracted from an EBIT
A novel technique to identify small fluxes of mixed highly charged ion beams
extracted from an Electron Beam Ion Trap (EBIT) is presented and practically
demonstrated. The method exploits projectile charge state dependent potential
emission of electrons as induced by ion impact on a metal surface to separate
ions with identical or very similar mass-to-charge ratio.Comment: 8 pages, 5 figure
Excitations and benchmark ensemble density functional theory for two electrons
A new method for extracting ensemble Kohn-Sham potentials from accurate
excited state densities is applied to a variety of two electron systems,
exploring the behavior of exact ensemble density functional theory. The issue
of separating the Hartree energy and the choice of degenerate eigenstates is
explored. A new approximation, spin eigenstate Hartree-exchange (SEHX), is
derived. Exact conditions that are proven include the signs of the correlation
energy components, the virial theorem for both exchange and correlation, and
the asymptotic behavior of the potential for small weights of the excited
states. Many energy components are given as a function of the weights for two
electrons in a one-dimensional flat box, in a box with a large barrier to
create charge transfer excitations, in a three-dimensional harmonic well
(Hooke's atom), and for the He atom singlet-triplet ensemble,
singlet-triplet-singlet ensemble, and triplet bi-ensemble.Comment: 15 pages, supplemental material pd
Spin gaps and spin-flip energies in density-functional theory
Energy gaps are crucial aspects of the electronic structure of finite and
extended systems. Whereas much is known about how to define and calculate
charge gaps in density-functional theory (DFT), and about the relation between
these gaps and derivative discontinuities of the exchange-correlation
functional, much less is know about spin gaps. In this paper we give
density-functional definitions of spin-conserving gaps, spin-flip gaps and the
spin stiffness in terms of many-body energies and in terms of single-particle
(Kohn-Sham) energies. Our definitions are as analogous as possible to those
commonly made in the charge case, but important differences between spin and
charge gaps emerge already on the single-particle level because unlike the
fundamental charge gap spin gaps involve excited-state energies. Kohn-Sham and
many-body spin gaps are predicted to differ, and the difference is related to
derivative discontinuities that are similar to, but distinct from, those
usually considered in the case of charge gaps. Both ensemble DFT and
time-dependent DFT (TDDFT) can be used to calculate these spin discontinuities
from a suitable functional. We illustrate our findings by evaluating our
definitions for the Lithium atom, for which we calculate spin gaps and spin
discontinuities by making use of near-exact Kohn-Sham eigenvalues and,
independently, from the single-pole approximation to TDDFT. The many-body
corrections to the Kohn-Sham spin gaps are found to be negative, i.e., single
particle calculations tend to overestimate spin gaps while they underestimate
charge gaps.Comment: 11 pages, 1 figure, 3 table
Magnetic-dipole transition probabilities in B-like and Be-like ions
The magnetic-dipole transition probabilities between the fine-structure
levels (1s^2 2s^2 2p) ^2P_1/2 - ^2P_3/2 for B-like ions and (1s^2 2s 2p) ^3P_1
- ^3P_2 for Be-like ions are calculated. The configuration-interaction method
in the Dirac-Fock-Sturm basis is employed for the evaluation of the
interelectronic-interaction correction with negative-continuum spectrum being
taken into account. The 1/Z interelectronic-interaction contribution is derived
within a rigorous QED approach employing the two-time Green function method.
The one-electron QED correction is evaluated within framework of the anomalous
magnetic-moment approximation. A comparison with the theoretical results of
other authors and with available experimental data is presented
Reply to No evidence for individual blood-brain barrier phenylalanine transport to influence clinical outcome in typical phenylketonuria patients
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Three-body Interactions In Proton-helium Angular Scattering
H++He scattering at 0.5 MeV has been investigated using a coincidence technique that completely determines the three-body transverse momentum exchange in single ionization collisions. Three scattering regions could be distinctly recognized that are dominated by proton helium-nucleus, proton-electron, or electron helium-nucleus interactions. Calculations and the experimental data show that the coupling between the electronic and nuclear degrees of freedom is required to understand the dynamics for more than 97% of the ionizing collisions. © 1989 The American Physical Society
Decay rate measurement of the first vibrationally excited state of MgH in a cryogenic Paul trap
We present a method to measure the decay rate of the first excited
vibrational state of simple polar molecular ions being part of a Coulomb
crystal in a cryogenic linear Paul trap. Specifically, we have monitored the
decay of the == towards the ==
level in MgH by saturated laser excitation of the ==-== transition followed by state selective
resonance enhanced two-photon dissociation out of the == level. The technique enables the determination of decay rates, and
thus absorption strengths, with an accuracy at the few percent level.Comment: 5 pages, 4 figure
Fully Differential Cross Sections for the Single Ionization of Helium by Ion Impact
We present experimental and theoretical fully differential cross sections for the single ionization of He by heavy-ion impact for electrons emitted into the scattering plane. Data were obtained for 2 MeV amu-1 C6+ and 3.6 MeV amu-1 AuQ+ (Q = 24, 53) projectiles, corresponding to perturbations (projectile charge to velocity ratio) ranging from 0.7 to 4.4, a regime which is inaccessible for electron-impact ionization. We observe a decreasing recoil peak intensity (relative to the binary peak) and at the same time an increasing peak in the forward direction with increasing perturbations. Large discrepancies between the experimental data and theoretical predictions are found, which can at least be partly attributed to the use of hydrogenic wavefunction
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