Microwave spectroscopy of the HCCS and DCCS radicals (X̃2Πi) in excited vibronic states: A study of the Renner-Teller effect

Jian Tang, Shuji Saito

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44 Citations (Scopus)


The microwave spectra of the HCCS and DCCS radicals are studied in the frequency range of 160-400 GHz and the rotational transition series are assigned to several low-lying vibronic states in the CCS or H(D)CC bending vibration. Analysis is carried out to obtain effective constants for respective vibronic states. The γeff constants for the vibronic μ/κ2Σ states are found to be anomalous, in that the variation of the γeff constants in the same bending mode is large up to 3 GHz and the γeff value can reach to nearly twice the rotational constants Bv. This behavior cannot be understood by the current Renner-Teller theory. We have developed a theory to include cross vibronic interaction between two vibronic 2Σ(vt = 1) states in different bending modes. Since the difference of the vibrational quantum numbers for these states is Δ(v4 + v5) = 0, the interaction has a much larger effect than the one considered by Petelin and Kiselev [Int. J. Quantum Chem. 6, 701 (1972)] for the vibronic states with Δ(v4 + u5) = ± 2. Calculation with the newly derived expressions for γeff reproduces the anomaly in HCCS when the Renner parameters are fixed at ε4=-0.37 and ε5=+0.10 from the ab initio calculation, and the parameter |ε45| for the cross vibronic interaction is varied to be 0.4, a value which is obtained for the first time. The relative sign of the above ε4 and ε5 values is explicitly judged to be correct. In addition, the Beff and the P-doubling constants in the 2Πi and 2Δi states are found to be effected by a higher-order perturbation of the cross vibronic interaction.

Original languageEnglish
Pages (from-to)8020-8033
Number of pages14
JournalJournal of Chemical Physics
Issue number18
Publication statusPublished - Jan 1 1996
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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