Valence shell photoelectron angular distributions and vibrationally resolved spectra of imidazole: A combined experimental–theoretical study

Patanen, M.; Abid, A. R.; Pratt, S. T.; Kivimäki, A.; Trofimov, A. B.; Skitnevskaya, A. D.; Grigoricheva, E. K.; Gromov, E. V.; Powis, I.; Holland, D. M. P.

Abstract

Linearly polarized synchrotron radiation has been used to record polarization dependent valence shell photoelectron spectra of imidazole in the photon energy range 21-100eV. These have allowed the photoelectron angular distributions, as characterized by the anisotropy parameter β, and the electronic state intensity branching ratios to be determined. Complementing these experimental data, theoretical photoionization partial cross sections and β-parameters have been calculated for the outer valence shell orbitals. The assignment of the structure appearing in the experimental photoelectron spectra has been guided by vertical ionization energies and spectral intensities calculated by various theoretical methods that incorporate electron correlation and orbital relaxation. Strong orbital relaxation effects have been found for the 15a′, nitrogen lone-pair orbital. The calculations also predict that configuration mixing leads to the formation of several low-lying satellite states. The vibrational structure associated with ionization out of a particular orbital has been simulated within the Franck-Condon model using harmonic vibrational modes. The adiabatic approximation appears to be valid for the X 2A″ state, with the β-parameter for this state being independent of the level of vibrational excitation. However, for all the other outer valence ionic states, a disparity occurs between the observed and the simulated vibrational structure, and the measured β-parameters are at variance with the behavior expected at the level of the Franck-Condon approximation. These inconsistencies suggest that the excited electronic states may be interacting vibronically such that the nuclear dynamics occur over coupled potential energy surfaces.

Citation

Patanen, M., Abid, A. R., Pratt, S. T., Kivimäki, A., Trofimov, A. B., Skitnevskaya, A. D., …Holland, D. M. P. (2021). Valence shell photoelectron angular distributions and vibrationally resolved spectra of imidazole: A combined experimental–theoretical study. Journal of Chemical Physics, 155(5), Article 054304. https://doi.org/10.1063/5.0058983

• Journal Article Type: Article
• Acceptance Date: Jul 9, 2021
• Online Publication Date: Aug 4, 2021
• Publication Date: Aug 7, 2021
• Deposit Date: Aug 6, 2021
• Publicly Available Date: Aug 13, 2021
• Journal: Journal of Chemical Physics
• Print ISSN: 0021-9606
• Electronic ISSN: 1089-7690
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 155
• Issue: 5
• Article Number: 054304
• DOI: https://doi.org/10.1063/5.0058983
• Keywords: Physical and Theoretical Chemistry; General Physics and Astronomy
• Public URL: https://nottingham-repository.worktribe.com/output/5957448
• Publisher URL: https://aip.scitation.org/doi/10.1063/5.0058983
• Additional Information: The following article has been accepted by The Journal of Chemical Physics . After it is published, it will be found at https://aip.scitation.org/doi/10.1063/5.0058983.