Abstract
We show that the combination of two achiral components - atomic or molecular target plus a circularly polarized photon - can yield chirally structured photoelectron angular distributions. For photoionization of CO, the angular distribution of carbon K-shell photoelectrons is chiral when the molecular axis is neither perpendicular nor (anti-)parallel to the light propagation axis. In photo-double-ionization of He, the distribution of one electron is chiral, if the other electron is oriented like the molecular axis in the former case and if the electrons are distinguishable by their energy. In both scenarios, the circularly polarized photon defines a plane with a sense of rotation and an additional axis is defined by the CO molecule or one electron. This is sufficient to establish an unambiguous coordinate frame of well-defined handedness. To produce a chirally structured electron angular distribution, such a coordinate frame is necessary, but not sufficient. We show that additional electron-electron interaction or scattering processes are needed to create the chiral angular distribution.
Highlights
An object is chiral if it cannot be brought to superposition with its mirror image by rotation or translation
We discuss the chirality of photoelectron angular distributions (PADs), which are produced from the three-dimensional momentum vectors of photoelectrons
Photoelectron circular dichroism (PECD), as the term is used in most works today, refers to a forward/backward asymmetry of electron emission with respect to the light propagation direction that inverts upon inversion of the light helicity
Summary
An object is chiral if it cannot be brought to superposition with its mirror image by rotation or translation. The emission pattern consists of individual photoionization events for each of which the direction of the photoelectron momentum vector is measured It may not come as a surprise that PADs arising from chiral molecules have a chiral structure in the molecular frame of reference, which can be obtained from multicoincidence experiments (see, e.g., [1,2]). We show that chiral electron emission patterns can be produced by one-photon double ionization (PDI) of a helium atom, i.e., a perfectly spherical symmetric initial state: hνcirc + He → He2+ + 2e− This process has been much studied in the past for linearly and circularly polarized photons (see [14,15] for reviews). As the coordinate frame has no well-defined handedness in this case, the resulting PADs cannot be chirally structured
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