Circular dichroism in molecular-frame photoelectron angular distributions in the dissociative photoionization ofH2andD2molecules

Abstract

The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules has been put in evidence recently through the measurement of molecular-frame photoelectron angular distributions in dissociative photoionization of H 2 [Dowek et al., Phys. Rev. Lett. 104, 233003 (2010)]. In this work we present a detailed study of circular dichroism in the photoelectron angular distributions of H 2 and D 2 molecules, oriented perpendicularly to the propagation vector of the circularly polarized light, at different photon energies (20, 27, and 32.5 eV). Circular dichroism in the angular distributions at 20 and to a large extent 27 eV exhibits the usual pattern in which inversion symmetry is preserved. In contrast, at 32.5 eV, the inversion symmetry breaks down, which eventually leads to total circular dichroism after integration over the polar emission angle. Time-dependent ab initio calculations support and explain the observed results for H 2 in terms of quantum interferences between direct photoionization and delayed autoionization from the Q 1 and Q 2 doubly excited states into ionic states (1sσ g and 2pσ u ) of different inversion symmetry. Nevertheless, for D 2 at 32.5 eV, there is a particular case where theory and experiment disagree in the magnitude of the symmetry breaking: when D + ions are produced with an energy of around 5 eV. This reflects the subleties associated to such simple molecules when exposed to this fine scrutiny.

Electron Localization in DissociatingH2+by Retroaction of a Photoelectron onto Its Source

“…We demonstrate experimentally that the transient field of the photoelectron which is ejected when an H 2 + ion is created by photoionization is sufficient to preferentially localize the bound electron at one side of the molecule. This retroaction of the photoelectron onto its parent molecule has recently been suggested in pioneering theoretical work by Serov and Kheifets [10] but has never been recognized in an experiment [9,[11][12][13].…”

“…Thus for a KER smaller than 2 eV according to the two step model the photoelectron is described by a wave function of pure ungerade parity and the ion by a wave function of pure gerade parity. It has therefore been implicitly assumed or even concluded in several experimental [9,[11][12][13] and theoretical [19,20] studies that the electron angular distribution in the molecular frame should be symmetric with respect to the p and H side of the fragmentation. This consensus has only recently been challenged theoretically by Serov and Kheifets [10].…”

A Review on Ab Initio Approaches for Multielectron Dynamics

“…By construction, this method does not account for double ionization. Bachau, Martín et al have developed their method initially for linear polarization along the z direction, i.e., parallel to the molecular axis, but recently extended it to circular polarization whose electric field is in the yz plane [104]. They have intensively studied various aspects of dissociative photoionization of H 2 and D 2 molecules by attosecond and femtosecond XUV pulses, e.g., autoionization [101], control by pulse duration [102], electron localization [105], and circular dichroism in molecularframe photoelectron angular distributions [104].…”

“…Bachau, Martín et al have developed their method initially for linear polarization along the z direction, i.e., parallel to the molecular axis, but recently extended it to circular polarization whose electric field is in the yz plane [104]. They have intensively studied various aspects of dissociative photoionization of H 2 and D 2 molecules by attosecond and femtosecond XUV pulses, e.g., autoionization [101], control by pulse duration [102], electron localization [105], and circular dichroism in molecularframe photoelectron angular distributions [104].…”

Discrimination of Excited States of Acetylacetone through Theoretical Molecular-Frame Photoelectron Angular Distributions

“…The coincidence method has been used mostly in the last decade in studies of one-photon ionization, taking advantage of the performance of third-generation synchrotron radiation facilities. Experiments on the MFPADs can be performed not only by using linearly polarized light but also with circularly or elliptically polarized light [ 29 , 30 , 31 ]. This permits the investigation of circular dichroism effects in the MF angular distributions and determining complete sets of matrix elements and phases.…”