Accurate Determination of the Structure of Cyclohexane by Femtosecond Rotational Coherence Spectroscopy and Ab Initio Calculations

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• 作者：Georges Bru虉gger ; Hans-Martin Frey ; Patrick Steinegger ; Franziska Balmer ; Samuel Leutwyler
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：September 1, 2011
• 年：2011
• 卷：115
• 期：34
• 页码：9567-9578
• 全文大小：1100K
• 年卷期：v.115,no.34(September 1, 2011)
• ISSN：1520-5215

文摘

We combine femtosecond time-resolved rotational coherence spectroscopy with high-level ab initio theory to obtain accurate structural information for the nonpolar molecules cyclohexane (C₆H₁₂) and cyclohexane-d₁₂ (C₆D₁₂). We measured the rotational B₀ and centrifugal distortion constants D_J, D_JK of the v = 0 states of C₆H₁₂ and C₆D₁₂ to high accuracy, for example, B₀(C₆H₁₂) = 4306.08(5) MHz, as well as B_v for the vibrationally excited states 谓₃₂, 谓₆, 谓₁₆ and 谓₂₄ of C₆H₁₂ and additionally 谓₁₅ for C₆D₁₂. To successfully reproduce the experimental RCS transient, the overtone and combination levels 2谓₃₂, 3谓₃₂, 谓₃₂ + 谓₆, and 谓₃₂ + 谓₁₆ had to be included in the RCS model calculations. The experimental rotational constants are compared to those obtained at the second-order M酶ller鈥揚lesset (MP2) level. Combining the experimental and calculated rotational constants with the calculated equilibrium bond lengths and angles allows determination of accurate semiexperimental equilibrium structure parameters, for example, r_e(C鈥揅) = 1.526 卤 0.001 脜, r_e(C鈥揌_axial) = 1.098 卤 0.001 脜, and r_e(C鈥揌_equatorial) = 1.093 卤 0.001 脜. The equilibrium C鈥揅 bond length of C₆H₁₂ is only 0.004 脜 longer than that of ethane. The effect of ring strain due to the unfavorable gauche interactions is mainly manifested as small deviations from the C鈥揅鈥揅, C鈥揅鈥揌_axial, and C鈥揅鈥揌_equatorial angles from the tetrahedral value.