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Journal ArticleDOI

Photoionization of atomic krypton confined in the fullerene C60

28 Sep 2012-Journal of Physics B (IOP Publishing)-Vol. 45, Iss: 18, pp 185001
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.
Topics: Photoionization mode (66%), Photoionization (63%), Atom (52%), Krypton (52%)
Citations
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Journal ArticleDOI
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.

45 citations


Journal Article
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


Journal ArticleDOI
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.

11 citations



Journal ArticleDOI
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.

7 citations


References
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Journal ArticleDOI
TL;DR: The goal is to combine kinetic and kinematic data to examine translational motions during microgravity adaptations to encourage fine-control motions as these reduce the risk of injury and increase controllability.
Abstract: Introduction: Astronauts soaring through space modules with the grace of birds seems counterintuitive. How do they adapt to the weightless environment? Previous spaceflights have shown that astronauts in orbit adapt their motor strategies to each change in their gravitational environment. During adaptation, performance is degraded and can lead to mission-threatening injuries. If adaptation can occur before a mission, productivity during the mission might improve, minimizing risk. The goal is to combine kinetic and kinematic data to examine translational motions during microgravity adaptations. Methods: Experiments were performed during parabolic flights aboard NASA's C-9. Five subjects used their legs to push off from a sensor, landing on a target 3.96 m (13 ft) away. The sensor quantified the kinetics during contact, while four cameras recorded kinematics during push-off. Joint torques were calculated for a subset of traverses (N = 50) using the forces, moments, and joint angles. Results: During the 149 traverses, the average peak force exerted onto the sensor was 224.6 ± 74.6 N, with peak values ranging between 65.8―461.9 N. Two types of force profiles were observed, some having single, strong peaks (N = 64) and others having multiple, weaker peaks (N = 86). Conclusions: The force data were consistent with values recorded previously in sustained microgravity aboard Mir and the Space Shuttle. A training program for astronauts might be designed to encourage fine-control motions (i.e., multiple, weaker peaks) as these reduce the risk of injury and increase controllability. Additionally, a kinematic and kinetic sensor suite was successfully demonstrated in the weightless environment onboard the C-9 aircraft.

5,638 citations


Journal ArticleDOI
01 Mar 2009-Nature Materials
TL;DR: This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset.
Abstract: A limiting factor of the power conversion efficiencies of organic photovoltaic devices is low voltage output Methano derivatives of the trimetallic endohedral fullerene Lu3N@C80 have now been synthesized and used as the acceptor in organic photovoltaics The open circuit voltage of the devices is significantly above those made using alternative fullerenes So far, one of the fundamental limitations of organic photovoltaic (OPV) device power conversion efficiencies (PCEs) has been the low voltage output caused by a molecular orbital mismatch between the donor polymer and acceptor molecules Here, we present a means of addressing the low voltage output by introducing novel trimetallic nitride endohedral fullerenes (TNEFs) as acceptor materials for use in photovoltaic devices TNEFs were discovered in 1999 by Stevenson et al 1; for the first time derivatives of the TNEF acceptor, Lu3N@C80, are synthesized and integrated into OPV devices The reduced energy offset of the molecular orbitals of Lu3N@C80 to the donor, poly(3-hexyl)thiophene (P3HT), reduces energy losses in the charge transfer process and increases the open circuit voltage (Voc) to 260 mV above reference devices made with [6,6]-phenyl-C61-butyric methyl ester (C60-PCBM) acceptor PCEs >4% have been observed using P3HT as the donor material This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset

540 citations


Journal ArticleDOI
01 Jun 1996-Physics Reports
Abstract: The problem of the influence of spatial confinement on the physical and chemical properties of many quantum mechanical systems is discussed. It covers low-dimensional electron gas or impurity atoms in artificial mesoscopic scale semiconductor structures as well as atoms and molecules trapped in microscopic cavities like molecular zeolite sieves. Particular emphasis is put on the methods for calculating the influence of a confinement on the electronic structure of the confined objects. More attention is paid to the surface Green function matching (SGFM) formalism and to the concept of a Green function satisfying periodic boundary conditions. Applications to an electron gas confined in different types of quantum wells are briefly discussed. Other methods, in particular those used for description of 1D and 0D systems, are also presented. Exactly solvable models of spatially confined atoms are reviewed. Approximate methods for describing the energy structure of impurity atoms and excitons in low-dimensional systems are also presented. For the case of atoms and molecules trapped in zeolite-like cavities the methods, which reduce to simple modifications of the commonly used basis set quantum chemical calculations are discussed with more details.

329 citations


Journal ArticleDOI
27 Feb 2002-Physical Review A
Abstract: We propose an alternative concept for a scalable spin quantum computer that combines aspects of other proposals with the advantageous features of endohedral fullerenes. The key advantages are that electron spins instead of nuclear spins are used and that the manipulation of fullerene molecules is fairly easy. Qubits are set and read out via pulsed electron-spin resonance. Addressing is provided by local magnetic fields or field gradients $(A$ gate). The qubit-qubit interaction is mediated by magnetic dipolar coupling and can be controlled via the direction of the magnetic field with respect to the distance vector of the qubits $(J$ gate). Molecular as well as solid-state architectures are discussed.

272 citations


Journal ArticleDOI
01 Jan 1977-Physical Review A
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.

196 citations


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