### Abstract

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 γ_{eff} constants for the vibronic μ/κ^{2}Σ states are found to be anomalous, in that the variation of the γ_{eff} constants in the same bending mode is large up to 3 GHz and the γ_{eff} value can reach to nearly twice the rotational constants B_{v}. This behavior cannot be understood by the current Renner-Teller theory. We have developed a theory to include cross vibronic interaction between two vibronic ^{2}Σ(v_{t} = 1) states in different bending modes. Since the difference of the vibrational quantum numbers for these states is Δ(v_{4} + v_{5}) = 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(v_{4} + u_{5}) = ± 2. Calculation with the newly derived expressions for γ_{eff} reproduces the anomaly in HCCS when the Renner parameters are fixed at ε_{4}=-0.37 and ε_{5}=+0.10 from the ab initio calculation, and the parameter |ε_{45}| 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 ε_{4} and ε_{5} values is explicitly judged to be correct. In addition, the B_{eff} and the P-doubling constants in the 2Π_{i} and ^{2}Δ_{i} states are found to be effected by a higher-order perturbation of the cross vibronic interaction.

Original language | English |
---|---|

Pages (from-to) | 8020-8033 |

Number of pages | 14 |

Journal | The Journal of Chemical Physics |

Volume | 105 |

Issue number | 18 |

Publication status | Published - 1996 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

^{2}Π

_{i}) in excited vibronic states: A study of the Renner-Teller effect.

*The Journal of Chemical Physics*,

*105*(18), 8020-8033.

**Microwave spectroscopy of the HCCS and DCCS radicals (X̃ ^{2}Π_{i}) in excited vibronic states : A study of the Renner-Teller effect.** / Tang, Jian; Saito, Shuji.

Research output: Contribution to journal › Article

^{2}Π

_{i}) in excited vibronic states: A study of the Renner-Teller effect',

*The Journal of Chemical Physics*, vol. 105, no. 18, pp. 8020-8033.

}

TY - JOUR

T1 - Microwave spectroscopy of the HCCS and DCCS radicals (X̃2Πi) in excited vibronic states

T2 - A study of the Renner-Teller effect

AU - Tang, Jian

AU - Saito, Shuji

PY - 1996

Y1 - 1996

N2 - 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.

AB - 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.

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M3 - Article

VL - 105

SP - 8020

EP - 8033

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 18

ER -