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

TL;DR

This study experimentally and theoretically investigates orbital mixing effects during ionization in chiral molecules, revealing correlation-driven dynamics in photoelectron behavior near the Cooper minimum, which are not explained by standard models.

Contribution

It demonstrates the first experimental observation of orbital rotation effects caused by electron correlation in chiral molecules, supported by advanced theoretical modeling.

Findings

Observed Cooper minimum $eta$ oscillations in photoelectron spectra.

Correlation effects are essential to explain the observed photoionization dynamics.

Standard HF and DFT predictions fail to account for the experimental results.

Abstract

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 to wave-functions mixing. This is observed to have a profound effect on the photoelectron dynamics, as here demonstrated by investigating \b{eta} asymmetry parameters 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 $\beta$ 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 (HF) and Density Functional Theory (DFT). 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.