Bending Vibrational Levels in the Electronic Spectra of Small Radicals

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The role played by bending vibrations in the spectroscopy of small carbon-containing radicals is illustrated by the patterns and effects shown by C3, CCH, and C3Ar. Because of the large change in the bending frequency between the (Formula presented.) 1Σ+ g and à 1Πu states of C3, the à 1Πu state provides one of the best known examples of the coupling of electronic and vibrational motion in linear molecules (the Renner–Teller effect). The (Formula presented.) 2Σ+ and à 2Π states of CCH provide a classic instance of vibronic coupling between two close-lying electronic states, which leads very rapidly to a chaotic pattern of mixed-state vibrational energy levels, which can only be understood by extensive high-quality ab initio calculations. C3Ar is an approximately T-shaped molecule with no less than four large-amplitude vibrations. Its à state provides a beautiful example of what happens to the angular momentum of a Π state of C3 when the symmetry is lowered by complex formation.

Original languageEnglish
Pages (from-to)395-404
Number of pages10
JournalJournal of the Chinese Chemical Society
Issue number4
StatePublished - Apr 2018


  • Physical chemistry
  • Spectroscopy


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