Photoionization dynamics of cis-dichloroethene from investigation of vibrationally resolved photoelectron spectra and angular distributions

Abstract

The influence of vibronic coupling on the outer valence ionic states of -dichloroethene has been investigated by recording photoelectron spectra over the excitation range 19-90 eV using plane polarized synchrotron radiation, for two polarization orientations. The photoelectron anisotropy parameters and electronic state branching ratios derived from these spectra have been compared to theoretical predictions obtained with the continuum multiple scattering approach. This comparison shows that the photoionization dynamics of theB, A, A, and B states, all of which are formed through the ejection of an electron from a nominally chlorine lone-pair orbital, exhibit distinct evidence of the Cooper minimum associated with the halogen atom. While retaining a high degree of atomic character, these orbital ionizations nevertheless display clear distinctions. Simulations, assuming the validity of the Born-Oppenheimer and the Franck-Condon approximations, of the B, B, and B state photoelectron bands have allowed some of the vibrational structure observed in the experimental spectra to be assigned. The simulations provide a very satisfactory interpretation for the B state band but appear less successful for the B and B states, with irregularities appearing in both. The A and A state photoelectron bands exhibit very diffuse and erratic profiles that cannot be reproduced at this level. Photoelectron anisotropy parameters, β, have been evaluated as a function of binding energy across the studied photon energy range. There is a clear step change in the β values of the B band at the onset of the perturbed peak intensities, with β evidently adopting the value of the A band β. The B band β values also display an unexpected vibrational level dependence, contradicting Franck-Condon expectations. These various behaviors are inferred to be a consequence of vibronic coupling in this system.

Decoupling vibration and electron energy dependencies in the photoelectron circular dichroism of a terpene, 3-carene

“…This study is performed as previously described. 21,22,41,42 Briefly, the ground and excited states are the nuclear coordinates and k is the photoelectron momentum. Assuming separability of the electronic and vibrational motion,  and  represent, respectively, the purely electronic and vibrational wavefunctions.…”

An experimental and theoretical study of the photoelectron spectra of cis-dichloroethene: Valence shell vertical ionization and vibronic coupling in the low-lying cationic states

“…We have measured photoelectron spectra, and derived the corresponding -parameters, in the photon energy range 19-90 eV. 68 These measurements show that the value of the photoelectron anisotropy parameter for the peak occurring around 11.8 eV is always similar to those corresponding to the two main components of theB 2 A 1 state band, rather than the value characterizing the low energy portion of theà 2 B 2 state band. This behavior is particularly evident in the excitation range around 40 eV, due to the influence of the Cl 3p Cooper minimum.…”

“…65 The electron spectra were corrected for the transmission efficiency of the analyzer as a function of kinetic energy. 67 The electron binding energy scale was calibrated by comparing a simulation, which included hot-band excitations, of theX 2 B 1 state photoelectron band 68 with the adiabatic ionization energy determined in the MATI experiment.…”

“…4). The influence of hot-bands on the vibrational structure has been considered in detail by Powis et al 68…”

“…This behavior is particularly evident in the excitation range around 40 eV, due to the influence of the Cl 3p Cooper minimum. 73 The effect of vibronic interactions on the electronic state photoelectron angular distributions and branching ratios of dichloroethene is considered in detail by Powis et al 68…”