Photoionization of atomic krypton confined in the fullerene C60
TL;DR: In this article, the combined effects of interchannel coupling, relativistic interactions and endohedral confinement on the photoionization of atomic Kr are studied, and the confinement of the Kr atom placed at the centre of the C60 cage is modelled by placing the atom inside an annular spherical potential.
Abstract: The combined effects of interchannel coupling, relativistic interactions and endohedral confinement on the photoionization of atomic Kr are studied. The confinement of the Kr atom placed at the centre of the C60 cage is modelled by placing the atom inside an annular spherical potential. Cross sections for the photoionization and angular distribution of photoelectrons from the 4p, 4s, 3d and 3p subshells are reported within the framework of the relativistic-random-phase approximation.
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TL;DR: Electron density analysis shows that the He-He interaction in He2@B16N16 is of closed-shell type whereas for the same in He 2@B12N12 there may have some degree of covalent character, and confinement causes some type of orbital interaction between two He atoms, which akins to some degree.
Abstract: The stability of Ngn@B12N12 and Ngn@B16N16 systems is assessed through a density functional study and ab initio simulation. Although they are found to be thermodynamically unstable with respect to the dissociation of individual Ng atoms and parent cages, ab initio simulation reveals that except Ne2@B12N12 they are kinetically stable to retain their structures intact throughout the simulation time (500 fs) at 298 K. The Ne2@B12N12 cage dissociates and the Ne atoms get separated as the simulation proceeds at this temperature but at a lower temperature (77 K) it is also found to be kinetically stable. He-He unit undergoes translation, rotation and vibration inside the cavity of B12N12 and B16N16 cages. Electron density analysis shows that the He-He interaction in He2@B16N16 is of closed-shell type whereas for the same in He2@B12N12 there may have some degree of covalent character. In few cases, especially for the heavier Ng atoms, the Ng-N/B bonds are also found to have some degree of covalent character. But the Wiberg bond indices show zero bond order in He-He bond and very low bond order in cases of Ng-N/B bonds. The energy decomposition analysis further shows that the ΔEorb term contributes 40.9% and 37.3% towards the total attraction in the He2 dimers having the same distances as in He2@B12N12 and He2@B16N16, respectively. Therefore, confinement causes some type of orbital interaction between two He atoms, which akins to some degree of covalent character.
55 citations
Journal Article•
TL;DR: In this paper, the dynamical and static dipole polarizabilities of the C 60 molecule have been calculated on the basis of the experimental data on the cross section of the fullerene photoabsorption.
Abstract: Abstract The dynamical and static dipole polarizabilities of the C 60 molecule have been calculated on the basis of the experimental data on the cross section of the fullerene photoabsorption. It has been shown that the fullerene shell in the static electric field behaves most likely as a set of separate carbon atoms rather than as a conducting sphere.
38 citations
TL;DR: In this paper, a review of investigations of the electronic structure and dynamics of atoms encaged in a single molecule is presented, where the major effects of confinement on the dynamical properties, e.g., confinement resonances, hybridization, Wigner time delay, are delineated.
Abstract: Confined atomic systems are of great importance owing a multitude of possible applications in various areas of science and technology. Of particular interest are atoms encaged in the $$\hbox {C}_{{60}}$$
molecule, $$\hbox {A}@\hbox {C}_{{60}}$$
, since the near-spherical symmetry of $$\hbox {C}_{{60}}$$
simplifies theoretical studies, and the stability of $$\hbox {C}_{{60}}$$
renders it amenable to experimental examination. A review of investigations of the electronic structure and dynamics of $$\hbox {A}@\hbox {C}_{{60}}$$
is presented in this manuscript focusing on developments in the last decade. Addressed mainly are how the confinement affects electronic structure properties such as ionization potentials, localization of atomic electrons, Shannon entropy, correlation effects, relativistic interactions, and others. In the area of dynamics, photoionization and e-
$$\hbox {A}@\hbox {C}_{{60}}$$
scattering are reviewed and summarized, and the major effects of confinement on the dynamical properties, e.g., confinement resonances, hybridization, Wigner time delay, are delineated.
15 citations
TL;DR: In this article, the static exchange method is applied to investigate photoionization of a confined system, Ar@C60, which explicitly includes the position of each carbon atom in the C60, a considerable improvement over methods to address the structure and photo dynamics of a constrained system where the carbon shell is modelled by a spherically symmetric model potential.
Abstract: The static-exchange method is applied to investigate photoionization of a confined system, Ar@C60. The realistic confinement potential employed in the present work explicitly includes the position of each carbon atom in the C60, which is a considerable improvement over methods to address the structure and photo dynamics of a confined system where the carbon shell is modelled by a spherically symmetric model potential. In the present study, photoionization from the deepest of the valence shells of C60 and Ar with ag symmetry is considered. There is a one-to-one correspondence between resonances that appear in the Ar@C60 system when the hole is in the 3s of the Ar, when the hole is in the C60 shell, or when the hole is in a free C60 system. Encapsulation of the Ar atom leads to some differences in the shapes and shifts in the energies of the resonant features in the cross-sections. However the qualitative features of the resonant state wave functions are very similar in the corresponding resonances of Ar@C60 and C60.
12 citations
TL;DR: In this article, two transient phase methods have been used to directly compute the photoionization phase shift and Wigner time delay of confined atoms (A@C60) in the single-active electron (SAE) approximation.
Abstract: In contrast to the conventional finite difference methods, two transient phase methods have been effectively used in the present work to directly compute the photoionization phase shift and Wigner time delay of confined atoms (A@C60) in the single-active electron (SAE) approximation. The different phase methods: (A) employing logarithmic derivatives at shell boundaries, and (B) Born approximation are verified with the help of well-established finite difference methods in SAE approximation and sophisticated many-electron techniques. In this work, confinement oscillations on the dipole phase and photoelectron group delay following ionization from 1s subshell of H@C60, 3p subshell of Ar@C60 and 5p subshell of Xe@C60 are analyzed. The comparison with many-body calculation shows that the features in the time delay of a confined system are governed mainly by the effects of screening apart from that due to the external potential. A systematic study and comparison of the results from phase methods and many-electron techniques indicate that these techniques can be effectively used in the analysis of photoionization phase shift and time delay in confined atoms.
9 citations
References
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TL;DR: In this paper, the relativistic random-phase approximation (RRPA) is applied to study radiative transitions from $n=2$ states along the He isoelectronic sequence.
Abstract: The relativistic random-phase approximation (RRPA) is applied to study radiative transitions from $n=2$ states along the He isoelectronic sequence. The strengths of various decay modes and the energy splittings of the $n=2$ multiplets are investigated. At low $Z$ the present results agree with earlier nonrelativistic studies, whereas, at high $Z$ our results provide new information about oscillator strengths, branching ratios, and multiplet structure for the $n=2$ states.
199 citations
TL;DR: In this paper, a relativistic random-phase approximation (RRPA) for photoionization of atoms is presented, which generalizes the nonrelativistic time-dependent Hartree-Fock equations using the Dirac-Breit Hamiltonian to describe the atomic electrons.
Abstract: A multichannel relativistic random-phase approximation (RRPA) for the photoionization of atoms is presented. The RRPA equations are obtained by generalizing the nonrelativistic time-dependent Hartree-Fock equations using the Dirac-Breit Hamiltonian to describe the atomic electrons. The angular decomposition of the RRPA equations to a set of coupled equations for the radial wave functions is given, and the radiative-transition operators are developed for arbitrary electric and magnetic multipoles. Formulas are obtained for the total photoionization cross sections and angular distributions, including all multipoles. The method of constructing multichannel solutions from the RRPA radial wave functions is described and various ways of choosing approximate potentials for the photoelectron are given.
161 citations
TL;DR: In this article, an overview of the theory of photoelectron angular distributions for atoms is presented, which are embodied in a single asymmetry parameter in the electric dipole approximation, and examined within the framework of the angular momentum transfer formulation.
Abstract: An overview of the theory of photoelectron angular distributions for atoms is presented. Its features, which are embodied in a single asymmetry parameter $\ensuremath{\beta}$ in the electric dipole approximation, are examined within the framework of the angular momentum transfer formulation. The $\ensuremath{\beta}$ parameter is in principle always energy dependent. Within the $\mathrm{LS}$ coupling approximation, however, there are instances, each representing a multitude of particular photoionization processes, in which $\ensuremath{\beta}$ is an analytically determined constant. The energy dependence of the $\ensuremath{\beta}$ parameters in such instances is due entirely to spin-orbit and other relativistic interactions. The study of the energy dependence of the $\ensuremath{\beta}$ parameter in these cases is thus of interest because it spotlights weak-interaction effects which are usually overwhelmed by stronger interactions. We illustrate the general predictions by a detailed consideration of the energy dependence of the $\ensuremath{\beta}$ parameter for $s$-subshell photoionization processes. It is shown that the asymmetry parameters for atomic $s$ subshells are particularly suitable for distinguishing between purely geometrical effects on the photoelectron angular distribution, resulting from physical conservation laws, and dynamical effects arising from relativistic interactions and electron exchange and correlation. In general, the $\ensuremath{\beta}$ parameters for $s$ subshells vary with energy; such variation is largest near minima in the cross sections for the corresponding photoelectron channels and in the vicinity of resonances. However, a number of atomic photoionization transitions are identified for which $\ensuremath{\beta}$ would be a constant (equal to one of the three values 2, $\frac{1}{5}$, or - 1) were it not for relativistic interactions and (in some cases) final-state interchannel coupling and/or initial-state electron correlations. Measurement or calculation of the $\ensuremath{\beta}$ parameters for such transitions thus provides a sensitive measure of the strength of relativistic interactions as well as of electron correlations.
141 citations
TL;DR: In this article, the relativistic random-phase approximation for the outer shells in the rare gases, neon, argon, krypton, and xenon, were determined and compared with experiment and with alternative calculations at low energies.
Abstract: Multichannel photoionization calculations using the relativistic random-phase approximation for the outer shells in the rare gases, neon, argon, krypton, and xenon, are presented Total cross sections and partial cross sections for $\mathrm{ns}$ subshells are determined and compared with experiment and with alternative calculations at low energies Branching ratios of $^{2}P_{\frac{3}{2}}:^{2}P_{\frac{1}{2}}$ cross sections which are sensitive to relativistic and correlation effects are presented and compared with experiment Angular distribution asymmetry parameters $\ensuremath{\beta}$ determined for each subshell are found and compared with experiment; the differences between $\ensuremath{\beta}$ values for $^{2}P_{\frac{1}{2}}$ and $^{2}P_{\frac{3}{2}}$ subshells in krypton and xenon emphasize the importance of relativistic effects in outer subshells of heavy elements Values of $\ensuremath{\beta}$ are given for outermost $s$ electrons which show large relativistic effects near the "Cooper minima" of the corresponding partial cross sections Eigenphases from the multichannel analysis are presented for argon to illustrate mathematical features of the present calculation
138 citations
TL;DR: In this article, the modern semiclassical method developed over the past few decades and used for describing the properties of the electronic subsystems of matter is reviewed, and its application to quantum physics problems is illustrated.
Abstract: The modern semiclassical method developed over the past few decades and used for describing the properties of the electronic subsystems of matter is reviewed, and its application to quantum physics problems is illustrated. The method involves the Thomas–Fermi statistical model and allows an extension by including additive corrections that take the shell structure of the electronic spectrum and other physical effects into account. Applying the method to the study of matter and finite systems allowed the following, inter alia: (1) an analysis of the total electron energy oscillations as a function of the number of particles in a 1D quantum dot; (2) a description of spatial oscillations of the electron density in atoms and atomic clusters; (3) a description of the stepwise temperature dependence of the ionicity and ionization energy in a Boltzmann plasma; (4) an evaluation of free ion ionization potentials; (5) an interpretation and evaluation of the difference in the patterns of oscillations in the mass spectra of metal clusters.
135 citations