Photoelectron-Photoion Coincidence Experiments with Synchrotron Radiation

Experimentally determined molecular-frame photoelectron angular distributions (MFPADs) of the 1(s) photoelectrons 1sg (top) and 1su (bottom) from molecular nitrogen recorded at 419 eV photon energy (~10 eV photoelectron kinetic energy) via momentum-resolved photoelectron-photoion coincidences at the synchrotron radiation source DORIS [Rolles2005].

The study of molecular photoionization processes was revolutionized by the development of angle-resolved photoelectron-photoion coincidence techniques in the 1990s [Cherepkov1992, Shigemasa1995, Heiser1997], which enabled the determination of molecular-frame photoelectron angular distributions (MFPADs) and gave access to an unprecedented level of detailed information [Gessner2002, Motoki2002, Rolles2005, Akoury2007, Schoeffler2008, Zimmermann2008]. We have developed a double-sided Velocity Map Imaging (VMI) electron-ion coincidence spectrometer (equipped with two delay-line anodes) which allows measuring full MFPADs for all molecular orientations simultaneously such that these experiments are now feasible for a wide range of electron kinetic energies within a very reasonable amount of beamtime. This allows a much more systematic comparison to theoretical predictions (e.g. from multiple scattering calculations) than it was previously possible with rather sparse data sets. Our experiments are performed at PETRA III and the ALS.

Own References:

R. Boll et al., Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules, Faraday Discussions 171 (in press).

D. Rolles et al., Isotope-induced Partial Localization of Core Electrons in the Homonuclear Molecule N2, Nature 437, 711-715 (2005).

B. Zimmermann, D. Rolles, B. Langer, R. Hentges, M. Braune, S. Cvejanović, O. Geßner, F. Heiser, S. Korica, T. Lischke, A. Reinköster, J. Viefhaus, R. Dörner, V. McKoy, and U. Becker, Coherence and Coherence Transfer in Molecular Photoelectron Double-slit Experiments, Nature Phys. 4, 649-655 (2008).


Other relevant publications in the research field:

N.A.Cherepkov, A.V.Golovin, and V.V.Kuznetsov, Photoionization of oriented molecules in a gas phase, Z. Phys. D, 24, 371 (1992).

E. Shigemasa et al., Angular Distributions of 1ss Photoelectrons from Fixed-in-Space N2 Molecules, Phys. Rev. Lett. 74, 359 (1995).

F. Heiser et al., Demonstration of Strong Forward-Backward Asymmetry in the C1s Photoelectron Angular Distribution from Oriented CO Molecules , Phys. Rev. Lett. 79, 2435 (1997).

O. Geßner et al., 4s-1 Inner Valence Photoionization Dynamics of NO Derived from Photoelectron-Photoion Angular Correlations, Phys. Rev. Lett. 88, 193002 (2002).

S. Motoki et al., Direct Probe of the Shape Resonance Mechanism in 2sg-Shell Photoionization of the N2 Molecule, Phys. Rev. Lett. 88, 063003 (2002).

D. Akoury et al., The Simplest Double Slit: Interference and Entanglement in Double Photoionization of H2, Science 318, 949 (2007).

M. Schöffler et al., Ultrafast Probing of Core Hole Localization in N2, Science 320, 929 (2008).