Photoelectron Wave Function in Photoionization: Plane Wave or Coulomb Wave?

Abstract

The calculation of absolute total cross sections requires accurate wave functions of the photoelectron and of the initial and final states of the system. The essential information contained in the latter two can be condensed into a Dyson orbital. We employ correlated Dyson orbitals and test approximate treatments of the photoelectron wave function, that is, plane and Coulomb waves, by comparing computed and experimental photoionization and photodetachment spectra. We find that in anions, a plane wave treatment of the photoelectron provides a good description of photodetachment spectra. For photoionization of neutral atoms or molecules with one heavy atom, the photoelectron wave function must be treated as a Coulomb wave to account for the interaction of the photoelectron with the +1 charge of the ionized core. For larger molecules, the best agreement with experiment is often achieved by using a Coulomb wave with a partial (effective) charge smaller than unity. This likely derives from the fact that the effective charge at the centroid of the Dyson orbital, which serves as the origin of the spherical wave expansion, is smaller than the total charge of a polyatomic cation. The results suggest that accurate molecular photoionization cross sections can be computed with a modified central potential model that accounts for the nonspherical charge distribution of the core by adjusting the charge in the center of the expansion.

A study of interstellar aldehydes and enols as tracers of a cosmic ray-driven nonequilibrium synthesis of complex organic molecules

“…Photoionization cross-sections of acetaldehyde, vinyl alcohol, propanal, and (E)/(Z)-1-propenol were computed using the protocol reported by Gozem et al (43) (SI Appendix, Theoretical Approach and Table S2). First, structures are optimized using density functional theory with the ωB97X-D functional and the augmented correlation-consistent triple-zeta (aug-cc-pVTZ) basis set (44).…”

“…Dyson orbitals and ionization energies are computed in Q-Chem (45) using the equation-of-motion coupled-cluster (EOM-CC) approach (46)(47)(48). The photoionization cross-sections are computed by ezDyson Version 3.0 (43,46,49). In addition to the Dyson orbitals, which contain all of the necessary information about the molecular system (46-48), cross-section calculations also need the photoelectron wave function which can be described by using Coulomb waves with a partial (effective) charge Z that is between 0 and 1 (43).…”

“…The photoionization cross-sections are computed by ezDyson Version 3.0 (43,46,49). In addition to the Dyson orbitals, which contain all of the necessary information about the molecular system (46-48), cross-section calculations also need the photoelectron wave function which can be described by using Coulomb waves with a partial (effective) charge Z that is between 0 and 1 (43). Zero-point energy corrections to the ionization energies are computed at the ωB97X-D/aug-cc-pVTZ level of theory.…”

Size-Resolved Photoelectron Anisotropy of Gas Phase Water Clusters and Predictions for Liquid Water

“…Since the spatial extent of clusters with n ≲ 20 is very small (~7-10 Å) the long-range scattering potential is essentially an unshielded Coulombpotential. Even semi-quantitative descriptions of the cluster PADs would require very highlevel quantum chemical calculations [17,[42][43][44] -still a big challenge for such complex systems.…”

Effects of probe energy and competing pathways on time-resolved photoelectron spectroscopy: the ring-opening of 1,3-cyclohexadiene

“…Time-dependent photoionisation cross-sections are calculated using the Dyson orbital approach. 61 The resulting model allow us to predict the time-resolved photoelectron spectra for the ring-opening reaction and test the effectiveness of a variety of probe energies and the importance of including a sufficient number of ionisation channels in the theoretical description.…”