Search results for "atomic physics"
showing 10 items of 5530 documents
Circular dichroism of magnetically induced transitions for D 2 lines of alkali atoms
2018
In this letter we study magnetic circular dichroism in alkali atoms exhibiting asymmetric behaviour of magnetically induced transitions. The magnetic field induces transitions between hyperfine levels of alkali atoms and in the range of magnetic field, the intensities of these transitions experience significant enhancement. We have inferred a general rule applicable for the D 2 lines of all alkali atoms, that is the transition intensity enhancement is around four times larger for the case of than for excitation for , whereas it is several hundreds of thousand times larger in the case of than that for polarization for . This asymmetric behaviour results in circular dichroism. For experimenta…
The dependence of circular dichroism in photoemission on the optical properties of Cs monolayers on Pt(111)
1997
We report on the dependence of dichroic photoemission excited by circularly polarised light on the angle of photon incidence. We measured the difference in the angle-resolved photoemission intensities from Cs 5p semi-core levels excited by photons of opposite helicity, which is known as CDAD. We found that the dependence of the measured differences on the angle of light incidence deviates strongly from the model of CDAD for free atoms, as expected. Using the Fresnel equations and a complex index of refraction, one finds that not only the third component but also the second component of the Stokes vector is responsible for the excitation process. Both Stokes components change sign if the ini…
Influence of the symmetry on the circular dichroism in angular resolved core-level photoemission
2002
The model for angular resolved photoemission from adsorbed atoms is extended to account for the non-axial symmetry of atoms in a crystal field. In particular, circular dichroism in the angular distribution (CDAD) is theoretically investigated. A special emphasis is put on the case when incident photons are propagating along the principal axis of an atom in Cnv symmetry. The model, although mainly developed for adsorbates, may also be used as a base for emission from solid surfaces. An extension to simple bulk symmetries, like D for hexagonal or O for cubic crystals, is included. The CDAD 6 hh for normal incidence does not vanish in the extended model and reflects the symmetry of the adsorpt…
Circular dichroism in angular resolved photoemission from pure and Rb-doped C60 and C22H14 layers on platinum and tungsten
1997
Abstract Polycrystalline C60 and Pentacene films grown on W(110) and Pt(111) have been studied in valence band photoemission using circularly polarised synchrotron radiation from BESSY with special emphasis on circular dichroism in photoemission. For thin films of C60, dichroic asymmetries of about 10% occur independent of the temperature and the substrate hinting that the rotation of the topmost layer is hindered even at room temperature. For Pentacene we found asymmetries up to 50% in the region of the σ-electrons. Moreover, we found for this molecule a dichroic asymmetry in normal emission, that is a forbidden geometry. This hints on adsorption with the molecules perpendicularly oriented…
Black hole-neutron star coalescence: effects of the neutron star spin on jet launching and dynamical ejecta mass
2020
Black hole-neutron star (BHNS) mergers are thought to be sources of gravitational waves (GWs) with coincident electromagnetic (EM) counterparts. To further probe whether these systems are viable progenitors of short gamma-ray bursts (sGRBs) and kilonovae, and how one may use (the lack of) EM counterparts associated with LIGO/Virgo candidate BHNS GW events to sharpen parameter estimation, we study the impact of neutron star spin in BHNS mergers. Using dynamical spacetime magnetohydrodynamic simulations of BHNSs initially on a quasicircular orbit, we survey configurations that differ in the BH spin ($a_{\rm BH}/M_{\rm BH}=0$ and $0.75$), the NS spin ($a_{\rm NS}/M_{\rm NS}=-0.17,\,0,\,0.23$ a…
Ultrafast dynamics of halogens in rare gas solids
2007
We perform time resolved pump-probe spectroscopy on small halogen molecules ClF, Cl2, Br2, and I2 embedded in rare gas solids (RGS). We find that dissociation, angular depolarization, and the decoherence of the molecule is strongly influenced by the cage structure. The well ordered crystalline environment facilitates the modelling of the experimental angular distribution of the molecular axis after the collision with the rare gas cage. The observation of many subsequent vibrational wave packet oscillations allows the construction of anharmonic potentials and indicate a long vibrational coherence time. We control the vibrational wave packet revivals, thereby gaining information about the vib…
Mass-asymmetric fission in the 40ca+142Nd reaction
2016
Shell effects play a major role in fission. Mass-asymmetric fission observed in the spontaneous and low energy fission of actinide nuclei was explained by incorporating the fragment shell properties in liquid drop model. Asymmetric fission has also been observed in the low energy fission of neutron-deficient 180 Hg nuclei in recent β -delayed fission experiments. This low-energy β -delayed fission has been explained in terms of strong shell effects in pre-scission configurations associated with the system after capture. Calculations predicted asymmetric fission for heavier Hg isotopes as well, at compound nuclear excitation energy as high as 40 MeV. To explore the evolution of fission fragm…
Multicollision-induced dissociation of multiply charged gold clusters, Aun2+, n = 7–35, and Aun3+, n = 19–35
2000
Abstract Multicollision-induced dissociation (MCID) has been applied to gold clusters, Au n 2+ (n = 7–35) and Au n 3+ (n = 19–35) stored in a Penning trap. By application of ion cyclotron resonance excitation and pulses of argon collision gas, fragmentation yields have been measured as a function of the clusters’ kinetic energy. The corresponding dissociation energies have been determined by use of the impulsive collision theory and the quantum Rice–Ramsperger–Kassel (RRK) model for the energy transfer to internal cluster modes and for delayed dissociation, respectively. As compared to earlier measurements of singly charged gold clusters the variation of the stability as a function of clust…
A Theoretical Determination of the Low-lying Electronic States of the p-Benzosemiquinone Radical Anion
2000
The low-lying electronic states of the p-benzosemiquinone radical anion are studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) ba...