Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session K2: Multi-Particle Fragmentation of Atoms and Negative Ions |
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Chair: Klaus Bartschat, Drake University Room: Knoxville Convention Center Ballroom EFG |
Thursday, May 18, 2006 8:00AM - 8:36AM |
K2.00001: Probing Dynamics from Within in Negative Ions, Neutral Molecules and van der Waals Clusters Invited Speaker: Nora Berrah We have investigated with unprecedented levels of detail, processes and phenomena involving photodetachment of negative ions and photoionization of molecules and van der Waals clusters using the brightness, spectral resolution, tunability and polarization of the Advanced Light Source at Lawrence Berkeley National Laboratory. Photodetachment of negative ions exhibit structure and processes differing substantially from corresponding processes in neutral and positive ions, owing to the dominance of correlation in both the initial and final states. We will report on investigations carried out in inner-valence CN$^{-}$ molecules giving rise to absolute double photodetachment cross sections as well as on fragmentation of negative ions clusters. We will also present absolute inner-shell photodetachment of atoms leading to multi-Auger decay [1] and discuss threshold laws [2] and PCI effects [3]. The measurements were conducted using collinear photon-ion spectroscopy. The evolution of inner-shell photoionization of clusters, as a function of photon energy, will be presented and compared to analogous measurements in atoms. The measurements were conducted using angle resolved two-dimensional photoelectron spectroscopy. Molecular fragmentation results using an ion imaging detector will briefly be presented. \newline \newline [1] R. C. Bilodeau, J. D. Bozek, G. D. Ackerman, N. D. Gibson, C. W.Walter, A. Aguilar, G. Turri, I. Dumitriu and N. Berrah, PRA \textbf{72}, 050701(R), 2005. \newline [2] R. C. Bilodeau, J. D. Bozek, N. D. Gibson, C. W. Walter, G. D. Ackerman, I. Dumitriu, and N. Berrah, Phys. Rev. Lett. \textbf{95}, 083001 (2005). \newline [3] R. C. Bilodeau, J. D. Bozek, A. Agular, G. D. Ackerman, and N. Berrah, (in press PRA brief report). [Preview Abstract] |
Thursday, May 18, 2006 8:36AM - 9:12AM |
K2.00002: Multiple Photoionization of C60 Invited Speaker: Ralf Wehlitz Relative C$_{60}^{2+}$/ C$_{60}^{+}$, C$_{60}^{3+}$/ C$_{60}^{+}$, and C$_{60}^{4+}$/ C$_{60}^{+}$ photoionization cross-section curves have been obtained using monochromatized light of the Synchrotron Radiation Center in the energy range between the double-ionization threshold (19 eV) and $K$-shell excitations (284 eV). In addition, we have measured the photoionization-induced fragmentation of C$_{60}$ for different charge states. Our measurements are a great improvement to existing data \footnote{T.\ Drewello {\it et al.}, Int. Journal of Mass Spectrom. and Ion Processes {\bf 124}, R1 (1993).} \footnote{A.\ Reink\"oster {\it et al.}, J.\ Phys.\ B {\bf 37}, 2135 (2004).} regarding energy range and accuracy. Of particular interest is the C$_{60}^{2+}$/ C$_{60}^{+}$ ratio curve that surprisingly exhibits a modulation with local enhancements of the ratio at certain excess energies (= photon energy minus double-ionization threshold). Our data analysis reveals that one of the two photoelectrons created in the double photoionization process has a de Broglie wavelength, calculated for each of the ratio-enhanced excess energies, that matches a certain distance in the C$_{60}$ cluster. These distances can be associated with the C$_{60}$ cluster's diameter, the diameter of a hexagon, and the distance between two neighboring carbon atoms \footnote{P.N.\ Juranic {\it et al.}, Phys.\ Rev.\ Lett.\ {\bf 96}, 023001 (2006).}. [Preview Abstract] |
Thursday, May 18, 2006 9:12AM - 9:48AM |
K2.00003: Momentum Imaging Study of the H$_{2}$ Coulomb Explosion Invited Speaker: Photodouble ionisation (PDI) of molecular hydrogen results in a ``Coulomb explosion,'' as the two protons rapidly separate in opposite directions. Energy and angle-resolved detection of all four particles -- with a well-defined light polarisation state - allows one to study correlated electron pair dynamics within the \textit{molecular} frame. These fully differential cross sections (FDCS) measurements provide the most stringent tests for theory and the greatest possible physical insight into this 4-body process. We report on such measurements recently performed at the Elettra 3$^{rd}$ generation synchrotron source operated in the four bunch mode using the CIEL momentum imaging apparatus. Absolute FDCS of high statistical quality were obtained for h$\nu $ = 76 eV. Equal electron-energy sharing results will be presented which illustrate the effects of molecular orientation within the Feagin's helium-like model. In the coplanar kinematics the relevant parameters of the FDCS are completely determined, while in the orthogonal kinematics departures from this first-order model are clearly observed. The results will be compared with that of earlier experiments and ongoing theoretical work using the Exterior Complex Scaling (ECS) method. Data for asymmetric electron energy sharing conditions will also be presented. [Preview Abstract] |
Thursday, May 18, 2006 9:48AM - 10:24AM |
K2.00004: Double Potoionization of Molecular Hydrogen Invited Speaker: We report a complete numerical solution of the Schr\"odinger equation for the double photoionization of H2, a process where a single photon emits two electrons. The results suggest that the distribution of photoelectrons emitted from aligned molecules reflects electron correlation effects that are purely molecular in origin. It confirms recent experimental results in experiments on oriented hydrogen molecules. These experiments observed that the ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as well as the orientation with respect to the polarization of the photon. We give an overview of the numerical methods we used to solve the exact Schrodinger equation for this problem. We also discuss the different molecular effect we observe in our calculations and compare with experimental observations [Preview Abstract] |
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