He Sheng-Gui, Clouthier Dennis J
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
J Chem Phys. 2005 Jul 1;123(1):014317. doi: 10.1063/1.1938948.
We have studied the tetra-atomic Renner-Teller effect in the ground state of the jet-cooled HCCS and DCCS free radicals. The reactive intermediates were produced in a pulsed discharge jet using thiophene or deuterated thiophene precursors and the ground-state vibronic energies were measured using the single vibronic level emission spectroscopy technique. In HCCS, emission and fluorescence depletion experiments proved that some previously unassigned laser-induced fluorescence (LIF) features were anomalous 2Delta32-2Pi32 transitions, which gave information on several ground-state 2Delta32 levels. In DCCS, rotational mixing of the excited state v'=0(2Pi32) level with the 4(1)(1 2Sigma12) level allowed several ground-state 2Sigma levels to be observed in emission. In addition, we have shown that some previously unassigned weak LIF bands of DCCS are anomalous 2Pi12-2Pi32 transitions which have allowed us to accurately measure the ground-state spin-orbit splitting (259.0 cm(-1)) for the first time. All of the expected ground-state 2Pi32 levels and the majority of the 2Pi12 levels up to 1700 cm(-1) have been observed for both isotopomers. The data have been fitted by an effective Hamiltonian matrix treatment that included Renner-Teller, spin-orbit coupling, anharmonicity, and Fermi resonance effects for the two bending vibrations and the CS stretching mode. This has allowed an unusually complete description of the orbital angular momentum coupling effects, including the determination of the epsilon4, epsilon5, and epsilon45 terms for the first time. Subtle effects in both the LIF and emission spectra signal the presence of Sears resonances in both the ground and excited states of these radicals.
我们研究了喷射冷却的HCCS和DCCS自由基基态中的四原子Renner-Teller效应。使用噻吩或氘代噻吩前体通过脉冲放电喷射产生反应中间体，并使用单振动能级发射光谱技术测量基态振转能量。在HCCS中，发射和荧光耗尽实验证明，一些先前未归属的激光诱导荧光（LIF）特征是异常的2Δ3/2 - 2Π3/2跃迁，这给出了几个基态2Δ3/2能级的信息。在DCCS中，激发态v' = 0(2Π3/2)能级与4(1)(1 2Σ1/2)能级的转动混合使得在发射中可以观察到几个基态2Σ能级。此外，我们已经表明，DCCS的一些先前未归属的弱LIF带是异常的2Π1/2 - 2Π3/2跃迁，这使我们首次能够准确测量基态自旋轨道分裂（259.0 cm⁻¹）。对于两种同位素异构体，都观察到了所有预期的基态2Π3/2能级以及高达1700 cm⁻¹的大部分2Π1/2能级。通过有效的哈密顿矩阵处理对数据进行了拟合，该处理包括Renner-Teller、自旋轨道耦合、非谐性以及两个弯曲振动和CS伸缩模式的费米共振效应。这使得能够对轨道角动量耦合效应进行异常完整的描述，包括首次确定ε4、ε5和ε45项。LIF和发射光谱中的细微效应表明这些自由基的基态和激发态中都存在Sears共振。
