Femtosecond Rotational Raman Coherence Spectroscopy of Cyclohexane in a Pulsed Supersonic Jet

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• 作者：Georges Br眉gger ; Hans-Martin Frey ; Patrick Steinegger ; Philipp Kowalewski ; Samuel Leutwyler
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：November 10, 2011
• 年：2011
• 卷：115
• 期：44
• 页码：12380-12389
• 全文大小：1187K
• 年卷期：v.115,no.44(November 10, 2011)
• ISSN：1520-5215

文摘

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 (C₆H₁₂) 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 [Br眉gger, 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, B₀ = 4305.859(9) MHz. Based on this B₀, a reanalysis of previous room-temperature gas-cell RCS measurements of cyclohexane gives improved vibration鈥搑otation interaction constants for the 谓₃₂, 谓₆, 谓₁₆, and 谓₂₄ vibrational states. Combining the experimental B₀(C₆H₁₂) with CCSD(T) calculations yields a very accurate semiexperimental equilibrium structure of the chair isomer of cyclohexane.