Quasifree Photoionization under the Reaction Microscope

Abstract

We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H2 at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by Miron Amusia more than four decades ago. We found the distinct four-fold symmetry in the angular emission pattern of QFM electrons from H2 double ionization that has previously only been observed for He. Furthermore, we provide experimental evidence that the photon momentum is not imparted onto the center of mass in quasifree photoionization, which is in contrast to the situation in single ionization and in double ionization mediated by the shake-off and knock-out mechanisms. This finding is substantiated by numerical results obtained by solving the system’s full-dimensional time-dependent Schrödinger equation beyond the dipole approximation.

“Atoms” Special Issue (Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

“…The novel quasi-free mechanism (QFM) of single-photon double ionization of the helium atom was predicted theoretically by Amusia and co-authors [21], to be confirmed experimentally nearly 50 years later in the group of Experimental Atomic Physics at the Goethe University Frankfurt [22,23]. The work by Grundmann et al [20] provides new insights into the elusive QFM photoionization. They found a distinct four-fold symmetry in the angular emission pattern of QFM electrons from the He atom and H 2 molecule.…”

“…Grundmann et al [20] put the process of quasi-free photoionization under the reaction microscope. The novel quasi-free mechanism (QFM) of single-photon double ionization of the helium atom was predicted theoretically by Amusia and co-authors [21], to be confirmed experimentally nearly 50 years later in the group of Experimental Atomic Physics at the Goethe University Frankfurt [22,23].…”