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Register a new userNon-dipole effects in time delay of photoelectrons from atoms, negative ions, and endohedrals
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In this Letter, we investigate the non-dipole effects in time delay of photoelectrons emitted by multi-electron atoms, negative ions, and respective endohedrals. We present the necessary general formulas in the frame of the random phase approximation with exchange (RPAE) applied to atoms, negative ions, and properly adjusted to endohedrals. We concentrate on low photon energy region, where non-dipole effects are very small in the cross-sections but become observable in angular distributions. We not only derive the formulas for non-dipole effects in time delay, but perform corresponding numeric calculations. We demonstrate how the non-dipole corrections can be isolated in experiment. Concrete calculations are performed for noble gas atoms Ar and Xe, isoelectronic to them negative ions Cl- and I- and endohedrals Ar(Cl-)C60 and Xe(I-)@C60. We found that the forward-backward photoelectron time delay differences give direct information on non-dipole effects. They proved to be quite measurable and prominently affected by the presence of the fullerenes shell.
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In this Letter, we investigate the time delay of photoelectrons by fullerenes shell in endohedrals. We present general formulas in the frame of the random phase approximation with exchange (RPAE) applied to endohedrals A@CN that consist of an atom A located inside of a fullerenes shell constructed of N carbon atoms C. We calculate the time delay of electrons that leave the inner atom A in course of A@CN photoionization. Our aim is to clarify the role that is played by CN shell. As concrete examples of A we have considered Ne, Fr, Kr and Xe, and as fullerene we consider C60. The presence of the C60 shell manifests itself in powerful oscillations of the time delay of an electron that is ionized from a given subshell nl by a photon with energy. Calculations are performed for outer, subvalent and d-subshells.
We present electric dipole polarizabilities ($alpha_d$) of the alkali-metal negative ions, from H$^-$ to Fr$^-$, by employing four-component relativistic many-body methods. Differences in the results are shown by considering Dirac-Coulomb (DC) Hamiltonian, DC Hamiltonian with the Breit interaction, and DC Hamiltonian with the lower-order quantum electrodynamics interactions. At first, these interactions are included self-consistently in the Dirac-Hartree-Fock (DHF) method, and then electron correlation effects are incorporated over the DHF wave functions in the second-order many-body perturbation theory, random phase approximation and coupled-cluster (CC) theory. Roles of electron correlation effects and relativistic corrections are analyzed using the above many-body methods with size of the ions. We finally quote precise values of $alpha_d$ of the above negative ions by estimating uncertainties to the CC results, and compare them with other calculations wherever available.
Apropos to the growing interest in the study of long-range interactions which for their applications in cold atom physics, we have performed theoretical calculation for the two-dipole $C_6$ and three-dipole $C_9$ dispersion coefficients involving alkaline-earth atoms with alkaline-earth atoms and alkaline-earth ions. The $C_6$ and $C_9$ coefficients are expressed in terms of the dynamic dipole polarizabilities, which are calculated using relativistic methods. Thereafter, the calculated $C_6$ coefficients for the considered alkaline-earth atoms among themselves are compared with the previously reported values. Due to unavailability of any other earlier theoretical or experimental results, for the $C_6$ coefficients for alkaline-earth atoms with alkaline-earth ions and the $C_9$ coefficients, we have performed separate fitting calculations and compared. Our calculations match in an excellent manner with the fitting calculations. We have also reported the oscillator strengths for the leading transitions and static dipole polarizabilities for the ground states of the alkaline-earth ions, i.e., Mg$^+$, Ca$^+$, Sr$^+$, and Ba$^+$ as well as the alkaline-earth atoms, i.e., Mg, Ca, Sr, and Ba. These, when compared with the available experimental results, show good agreement.
Investigations of low-energy electron-scattering of the lanthanide atoms Eu, Nd, Tb, Tm demonstrate that electron-correlation effects and core polarization are the dominant fundamental many-body effects responsible for the formation of metastable states of negative ions. Ramsauer Townsend minima, shape resonances and binding energies of the resultant anions are identified and extracted from the elastic total cross sections calculated using the complex angular momentum method. The large discrepancy between the recently measured electron affinity of 0.116 and the previously measured value of 1.053 eV for Eu is resolved. Also, the previously measured electron affinities for Nd, Tb and Tm are reconciled and new values are extracted from the calculated total cross sections. The large electron affinities found here for these atoms, should be useful in negative ion nanocatalysis, including methane conversion to methanol without CO2 emission, with significant environmental impact.. The powerful complex angular momentum method which requires only a few poles, yields reliable binding energies for the metastable states of negative ions with no a priori knowledge of experimental or other theoretical data and should be applicable to other complex systems for the fundamental understanding of their interactions.
The photon-ion merged-beams technique for the photoionization of mass/charge selected ionized atoms, molecules and clusters by x-rays from synchrotron radiation sources is introduced. Examples for photoionization of atomic ions are discussed by going from outer-shell ionization of simple few-electron systems to inner-shell ionization of complex many-electron ions. Fundamental ionization mechanisms are elucidated and the importance of the results for applications in astrophysics and plasma physics is pointed out. Finally, the unique capabilities of the photon-ion merged-beams technique for the study of photoabsorption by nanoparticles are demonstrated by the example of endohedral fullerene ions.
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