Valence shell electronically excited states of imidazole and 1-methylimidazole

D. M. P. Holland*, D. A. Shaw, D. Townsend, I. Powis

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)
29 Downloads (Pure)


The absolute photoabsorption cross section of imidazole, and that of 1-methylimidazole, have been measured from threshold up to 10.8 eV using synchrotron radiation. For each molecule, the absorption spectrum exhibits several broad bands due to transitions into excited valence states and some sharp structure associated with Rydberg states. Assignments have been proposed for some of the observed absorption bands using calculated transition energies and oscillator strengths. Quantum defect analyses have also helped guide these assignments. Natural transition orbital plots indicate that many of the electronically excited states have a mixed Rydberg/valence character. This mixing leads to irregularities in both the transition energies and the relative intensities of the absorption bands ascribed to Rydberg states. The vibrational progressions belonging to some of the Rydberg states have been interpreted using simulations of the corresponding cation’s vibrational structure obtained within the Franck-Condon model employing harmonic frequencies and normal modes.

Original languageEnglish
Article numbere2122614
JournalMolecular Physics
Issue number7-8
Early online date22 Sept 2022
Publication statusPublished - 18 Apr 2023


  • excited valence and Rydberg states
  • Imidazole photoabsorption spectrum
  • natural transition orbitals
  • quantum defects

ASJC Scopus subject areas

  • Biophysics
  • Molecular Biology
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry


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