Renner-teller, spin-orbit and fermi-resonance interactions in x2Π ncs investigated by lif spectroscopy

Frederick J Northrup, Trevor J. Sears

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56 Scopus citations


The electronic spectrum of the NCS radical is obtained following UV excimer-laser photolysis of C2H5NCS in a large excess of inert gas in a supersonic free jet expansion. The spectrum is complicated by the presence of Renner-Teller and spin-orbit coupling and a Fermi resonance between the doubly excited bending vibration and v3, the CS stretching vibration. Bending vibronic level structure in the X2π ground state of the radical is determined from a variety of laser-induced-fluorescence techniques, including stimulated-emission pumping. These energy levels are used to determine vibronic-coupling parameters for the radical. Coupling between close-lying bending levels with different v2 and K (= ∆ + I) is found to be important because some of these levels are close together in NCS owing to the very large spin-orbit coupling. A parameter representing this effect is related to the dipolar contribution ε1 to the Renner-Teller coupling parameter ε by applying perturbation theory to a simple model involving the X2π and B2Σ+ electronic states of NCS. This procedure results in an estimate for ε1 that agrees approximately with that determined from the vibronic-coupling parameter gK, assuming the same model for the interacting electronic states.

Original languageEnglish (US)
Pages (from-to)45-64
Number of pages20
JournalMolecular Physics
Issue number1
StatePublished - Sep 1990

ASJC Scopus subject areas

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

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