A Case for Chiral Contributions to Nondipole Effects in Photoionization Using Linearly Polarized Soft X-rays

Modelling angular distributions of photoelectrons requires making accurate approximations of both the incoming light and the behavior of bound electrons. The experimental determination of photoelectron angular distributions is crucial to the development of accurate theoretical models governing the light-matter interaction. To date, many models have relied upon the dipole approximation, which assumes a constant electric field as the source of ionization. Despite knowing that the dipole approximation would break down as photon energy increased, the precise limit was unclear. Over the past two decades, a strong case has been made that corrections to the dipole approximation are necessary for accurately describing photoionization using soft x-rays (100 – 1000 eV). This energy region is widely studied, as it has become more readily accessible thanks to third-generation synchrotron radiation facilities. This work provides experimental evidence for first-order corrections to the dipole approximation, known as nondipole effects, for atoms and molecules, focusing on Xe 3d photoionization, which showcases the role of interchannel coupling in nondipole angular distributions, N 1s photoionization from molecular nitrogen in an attempt to settle a dispute over molecular nondipole effects, and C 1s photoionization from the chiral molecule camphor, which provides the first-ever experimental determination of a theoretically predicted chiral-specific nondipole effect. All of the experiments were performed using electron time-of-flight spectroscopy at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL)