Microwave Spectrum, Dipole Moment, Structure, and Internal Motion of 1-Silabicyclo[2.2.1]heptane

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Abstract
The rotational constants of 1-silabicyclo[2.2.1]heptane in the ground vibrational state were determined to be A0=2744.775 (2) MHz, B0=2662.017 (2) MHz, and C0=2145.994 (2) MHz, with the standard deviations in parentheses. Because the spectrum was very rich, the Stark effects of two transitions were analyzed by a simulation technique. The dipole moments thus obtained are μb=0.5±0.1 D, μc=0.05±0.01 D, and μt=0.5±0.1 D. The observed spectra did not exhibit any anomalies which were due to deviations of the molecular symmetry from Cs. Three structural parameters, Si–C(7), ∠C(2)–Si–C(6), and ∠Si–C(2)–C(3), were adjusted so as to reproduce the rotational constants observed for the ground state. The Si–C(7) bond was found to be longer than Si–C(2) by 0.07 Å. Two vibrational satellites were detected and were assigned to the v=1 and the v=2 states of a torsional mode of the skeleton. A relative-intensity measurement resulted in the excitation energies of 70±25 cm−1 and 160±60 cm−1 for v=1 and v=2, respectively. The molecular structure and the internal motions were discussed in terms of intramolecular forces.
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