Departement für Chemie und Biochemie, Universität Bern, Bern, Switzerland.
J Phys Chem A. 2011 Nov 10;115(44):12380-9. doi: 10.1021/jp207290g. Epub 2011 Oct 14.
We combine the technique of femtosecond degenerate four-wave mixing (fs-DFWM) with a high repetition-rate pulsed supersonic jet source to obtain the rotational coherence spectrum (RCS) of cold cyclohexane (C(6)H(12)) with high signal/noise ratio. In the jet expansion, the near-parallel flow pattern combined with rapid translational cooling effectively eliminate dephasing collisions, giving near-constant RCS signal intensities over time delays up to 5 ns. The vibrational cooling in the jet eliminates the thermally populated vibrations that complicate the RCS coherences of cyclohexane at room temperature [Brügger, G.; et al. J. Phys. Chem. A 2011, 115, 9567]. The rotational cooling reduces the high-J rotational-state population, yielding the most accurate ground-state rotational constant to date, B(0) = 4305.859(9) MHz. Based on this B(0), a reanalysis of previous room-temperature gas-cell RCS measurements of cyclohexane gives improved vibration-rotation interaction constants for the ν(32), ν(6), ν(16), and ν(24) vibrational states. Combining the experimental B(0)(C(6)H(12)) with CCSD(T) calculations yields a very accurate semiexperimental equilibrium structure of the chair isomer of cyclohexane.
我们将飞秒简并四波混频（fs-DFWM）技术与高重复率脉冲超声速射流源相结合，以获得具有高信噪比的冷环己烷（C(6)H(12)）的转动相干光谱（RCS）。在射流膨胀中，近平行流模式与快速平移冷却相结合，有效地消除了退相碰撞，从而在长达 5 ns 的延迟时间内获得近乎恒定的 RCS 信号强度。射流中的振动冷却消除了室温下使环己烷的 RCS 相干复杂化的热占据振动[Brügger, G.; 等人。J. Phys. Chem. A 2011, 115, 9567]。转动冷却降低了高-J 转动态的种群，得到了迄今为止最准确的基态转动常数，B(0) = 4305.859(9) MHz。基于此 B(0)，对先前环己烷室温气室 RCS 测量的重新分析给出了 ν(32)、ν(6)、ν(16)和 ν(24)振动态的改进振动-转动相互作用常数。将实验 B(0)(C(6)H(12))与 CCSD(T)计算相结合，得到了环己烷椅式异构体非常准确的半实验平衡结构。
