Microwave Spectrum, r0 Structure, Dipole Moment, Barrier to Internal Rotation, and Ab Initio Calculations for Fluoromethylsilane

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• 作者：James R. Durig ; Savitha S. Panikar ; Peter Groner ; Hossein Nanaie ; Hans Brger ; Peter Moritz
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：April 1, 2010
• 年：2010
• 卷：114
• 期：12
• 页码：4131-4137
• 全文大小：121K
• 年卷期：v.114,no.12(April 1, 2010)
• ISSN：1520-5215

文摘

The microwave spectra of seven isotopomers of fluoromethylsilane, CH₂FSiH₃, in the ground vibrational state were measured and analyzed in the frequency range 18−40 GHz. The rotational and centrifugal distortion constants were evaluated by the least-squares treatment of the observed frequencies of a- and b-type R- and b-type Q-transitions. The values for the components of the dipole moment were obtained from the measurements of Stark effects from both a- and b-type transitions and the determined values are: |μ_a| = 1.041(5), |μ_b| = 1.311(6), and |μ_t| = 1.674(4) D. Structural parameters have been determined and the heavy atom distances (r₀) in Angstroms are: Si−C = 1.8942(57) and C−F = 1.4035(55) and the angle in degree, SiCF = 109.58(14). A semi-experimental r_e structure was also determined from experimental ground state rotational constants and vibration−rotation constants derived from ab initio force fields. The internal torsional fundamental, SiH₃, was observed at 149.2 cm⁻¹ with two accompanying hot bands at 138.8 and 127.5 cm⁻¹. The barrier to internal rotation was obtained as 717.3(16) cm⁻¹ (2.051(46) kcal mol⁻¹) by combining the analysis of the microwave A and E splittings and the torsional fundamental and hot band frequencies. Ab initio calculations have been carried out with full electron correlation by the second-order perturbation method with several different basis sets up to MP2/6-311+G(d,p) to obtain geometrical parameters, barriers to internal rotation, and centrifugal distortion constants. Adjusted r₀ structural parameters have been obtained by combining the ab initio MP2/6-311+G(d,p) predicted values with the determined rotational constants for the fluoride as well as with the previously reported microwave data for the chloro- and bromo- compounds. These experimental results are compared to the corresponding parameters for the carbon analogues.