Photo double ionization of fixed in Space Hydrogen

1. , Photo double ionization of fixed in Space Hydrogen Th. Weber (a), R. Doerner (a), A. Czasch (a), A. Landers (b), T. Osipov (c), L. Cocke (c), O. Jagutzki (a), M. Prior (d), H. Schmidt-Boecking (a) a) Institut fuer Kernphysik Frankfurt, Frankfurt am Main, Germany b) Department of Physics, Western Michigan University, Kalamazoo, USA c) Department of Physics, Kansas State University, Manhattan, USA d) Lawrence Berkeley National Laboratory, Berkeley, USA weber@hsb.uni-frankfurt.de / hsb.uni-frankfurt.de excess ion energy photon energy binding energy Technical features of the experimental setup: 4 psolid angle pulsed extraction for the recoil-ions: 60 V/cm recoil-ion double hit electron double hit 3 V/cm recoil-ion detector electron-detector • Magnetic field to guide the electrons • electrons up to 100 eV (for 10 Gauss) • Time of Flight and 2dim position • 3dim momentum vector • High resolution for 0 eV • < 10 meV electronic energy electric field magnetic field HITEC powered by AOC & ROENTDEK Using a magnetic field in order to prevent electrons leaving the spectrometer, the electrons were spiraled up. These wiggles are a good tool to determine the magnitude of the magnetic field. At the same time they help calibrating the time of flight direction (see figure above). Measuring the outgoing momentum vectors of the two running out cores in the final state of the reaction one can conclude directly to the spatial orientation of the two centers of the molecule at the time of the photoabsorption. The momentum vectors of the two electrons represent the square of the wave function in the final state. See figure to the left: New kind of delay line anodes for the position readout of Multi Channel Plate (MCP) detectors have been developed in order to reduce multihit deadtime problems (Hexanode). Using three layers instead of two, the spatial distance of two hits on the detector as a function of time difference could be reduced to a circle with 10 mm in diameter. For the common two layer anodes like the DL80 the blind zone has a cross like shape dividing the detector by two perpendicular lines with 10 mm strength (see upper row). One of the central questions of today's atomic physics concerns the dynamic-electron-electron-correlation of many electron systems. Stationary many body systems are already examined in atomic physics successfully with high precision and are theoretically very well described. However dynamical multi-particle processes are not understood very well today. Electron and Recoil Ion Momen-tum Spectroscopy was used in order to image the photo double ionization of hydrogen (see figure above). The electrons and the ions were guided on position sensitive detectors applying an electrostatic and magnetic field. In order to gain resolution for the electrons the electric extraction field for the ions was pulsed. From Time of Flight (TOF) and the position on the detectors the momentum vector of all four outgoing particles could be determined. DL80anode: Dt < 100ns Dt < 8ns !!! Dt < 5ns Dt < 10ns Hexanode: equal energy sharing e1 See figure to the right: While discerning the different molecular orientations one can see that the alignment of the polarization vector and the internuclear axis in parallel results in much more contribution along the nodal axis (blue and red dashed lines on the right) in proportion to the interval of polar angles allowed in the case of helium. Helium H2 all orientations H2 e Hydrogen molecule Forcing the second electron to be emitted in the molecular plane, defined by the inter-nuclear axis and the polarization vector, one can probe the molecule. It was the aim to determine Triple Differential Cross Sections (TDCS) for a fixed in space electron relative to the molecular axis. The intensity and the angular correlation can give explanation about the influence of rotation statuses and about possible interference effects of the molecule. The nodes in the distributions, which can be expected, can give a hint of the importance of symmetries (b-parameter) in the molecule in contrast to the observed helium atom: See figure above: Even when integrating over all molecular orientations, below an emission angle of 45 degree versus the polarization vector of electron 1, the polar angular distribution of electron 2 show distinct differences in comparison to helium. For the case of 25 degree one can see contributions along the blue and red lines (lower row on the right) representing the nodes in case of helium. Increasing the angle of electron 1 versus the polarization vector these contributions vanish (not shown here). In order to survey the influence of the molecular orientation, for 25 degree the distribution is split into three scenarios showing the results for hydrogen aligned parallel and perpendicular to the polarization vector. kin. energy of the nuclei Electron-electron “correlation” has been switched off by orientating the first electron rectangular to the molecular plane. While varying the energy sharing of the electrons the distribution changes due to angular momentum transfer and the influence of the polarization. In the energy spectrum the re-pulsive curve of the H++H+state maps directly the initial state into the continuum. Going vice versa is shown to the left: ...which orientation is relevant ? See left side: The photo double ioni-zation of hydrogen re-sults in four free par-ticles in the final state. Which coordi-nates are relevant to discover the interac-tion between the el-ectrons and the pro-tons ? The distribu-tions are sensitive to angular momentum transfer (see figure to the left - the lower row is generated by using Jacobi coordi-nates). e1 equal energy sharing Scanning the sum energy of the ions (e.g. the coulomb explosion; see the inset in the figures to the right), one even can probe vibrational states of the hydrogen mo-lecule at the time of photo-ionization: H2 e1 No angular momentum transfer In terms of Legendre Polynoms, for the case aligning the molecule perpendicular to the polarization vector, one can see the angular distribution of electron 2 changing from d- to f like shape. This scenario shows a different evolution for unequal energy sharing (not shown here). e1+2 e2 H2