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

作者：Bruegger Georges; Frey Hans Martin; Steinegger Patrick; Balmer Franziska; Leutwyler Samuel^*

来源：Journal of Physical Chemistry A, 2011, 115(34): 9567-9578.

DOI：10.1021/jp2001546

We combine femtosecond time-resolved rotational coherence spectroscopy with high-level ab initio theory to obtain accurate structural information for the nonpolar molecules cyclohexane (C(6)H(12)) and cyclohexane-d(12) (C(6)D(12)). We measured the rotational B(0) and centrifugal distortion constants D(J), D(JK) of the v = 0 states of C(6)H(12) and C(6)D(12) to high accuracy, for example, B(0)(C(6)H(12)) = 4306.08(5) MHz, as well as B(v) for the vibrationally excited states v(32), v(6), v(16) and v(24) of C(6)H(12) and additionally v(15) for C(6)D(12). To successfully reproduce the experimental RCS transient, the overtone and combination levels 2v(32), 3v(32), v(32) + v(6), and v(32) + v(16) had to be included in the RCS model calculations. The experimental rotational constants are compared to those obtained at the second-order Moller-Plesset (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-C) = 1.526 +/- 0.001 angstrom, r(e)(C-H(axial)) = 1.098 +/- 0.001 angstrom, and r(e)(C-H(equatorial)) = 1.093 +/- 0.001 angstrom. The equilibrium C-C bond length of C(6)H(12) is only 0.004 angstrom 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-C-C, C-C-H(axial), and C-C-H(equatorial) angles from the tetrahedral value.

• 出版日期2011-9-1