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

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 $β$ 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 (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.

Figures (6)

• Figure 1: Experimental outer valence PE spectra of epichlorohydrin recorded at the magic angle $\theta = 54.7^\circ$(red) and $\theta = 0^\circ$ (black), and at different photon energies (panels a-f).
• Figure 2: Asymmetry parameters $\beta_i$ as a function of the photon energy for orbitals (channels) 24a, 23a, 22a and 21a. Experiment versus computational results obtained using a DFT representation of the continuum together with Hartree-Fock (label HF-DFT), Density Function Theory (label DFT-DFT) and EOM-CCSD Dyson (label DYS-DFT) orbitals.
• Figure 3: Asymmetry parameters $\beta_i$ as a function of the photon energy for orbitals (channels) 24a, 23a, 22a and 21a. Experiment versus computational results obtained using a TDDFT representation of the continuum together with Hartree-Fock (HF-TDDFT), Density Function Theory (DFT-TDDFT) and EOM-CCSD Dyson (DYS-TDDFT) orbitals.
• Figure 4: Cross section $\sigma$ (Mb, logarithmic scale) as a function of the photon energy for orbitals 24, 23, 22 and 21. Experiment versus computational results obtained using a DFT representation of the continuum together with Hartree-Fock (HF-DFT), Density Function Theory (DFT-DFT) and EOM-CCSD Dyson (DYS-DFT) orbitals.
• Figure 5: Cross section $\sigma$ (Mb) as a function of the photon energy for orbitals 24a, 23a, 22a and 21a. Experiment versus computational results obtained using a TDDFT representation of the continuum together with Hartree-Fock (HF-TDDFT), Density Function Theory (DFT-TDDFT) and EOM-CCSD Dyson (DYS-TDDFT) orbitals.