Evidence of orbital mixing upon ionization via Cooper minimum photoelectron dynamics in epichlorohydrin. Experiment and theory

A peculiar electron correlation effect, leading to orbital rotation upon ionization, theoretically predicted long ago, was never experimentally characterized. The effect is expected to appear prominently in the photoionization of chiral molecules, due to the lack of symmetry constraints on wave-function mixing. This is observed to have a profound effect on the photoelectron dynamics, as here demonstrated by investigating the β asymmetry parameter and partial cross-section observables in the Cl 3p Cooper minimum region of epichlorohydrin, a chiral prototype system. Angle-resolved photoelectron spectroscopy with tunable synchrotron radiation allowed measuring Cooper minimum β oscillations, which were observed for solely two valence photoionization channels. The nature and number of channels exhibiting such dynamical behavior, along with the extent of the observed oscillation amplitudes, could not be accounted for by predictions based on Hartree-Fock and density functional theory. These features could only be explained by incorporating correlation effects, which mix single-hole configurations of identical symmetry, in the characterization of the four lowest-lying molecular cation states via equation-of-motion coupled-cluster-singles-and-doubles Dyson orbitals.