MICROWAVE SPECTROSCOPY OF TRANSIENT PYROLYSIS PRODUCTS: 1,1-DIMETHYLSILAETHYLENE***
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Date
1989
Journal Title
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Publisher
Ohio State University
Abstract
Reactive species produced by gas phase pyrolysis have often been studied by microwave spectroscopy. However, the conventional methods are limited to species having lifetimes of the order of seconds or longer. We have extended this range by outfitting a Flygare/Balle, Fourier transform spectrometer with a heated pulsed nozzle. The nozzle heats the sample as high as 1400 K for less than 0.1 msec before cooling the products to a few K by supersonic expansion. The quick quenching of the pyrolysis and the inherent sensitivity of the spectrometer enable us to detect quite readily the rotational transitions of reactive species like chloroketene, difluorocarbene, and 1,1-dimethylsilaethylene (DMSE). Chloroketene and difluorocarbene have been observed by conventional methods but not DMSE. We have found a number of low-J, b-dipole transitions for DMSE, resolving the fine structure from internal rotation of the methyl groups. The DMSE was produced by pyrolysis of 1,1-dimethylsilacyclobutane at -1300 K. Preliminary analysis of the data collected thus far gives rigid rotor, rotational constants of 6037.7, 5896,9, and 3093.6 MHz for A, B, and C respectively, and a barrier to internal rotation of 1.0 kcal/mole. The rotational constants agree with the Si-C double-bond length of 1,692 A predicted theoretically rather than with the electron diffraction result of 1.815 A. A more detailed analysis will be presented.
Description
$^{\ast}$ Work supported by NSF and PRF. $^{1}$ H. F. Schaefer, Acc. Chem. Res. 15, 283 (1982).
Author Institution: Noyes Chemical Laboratory, University of Illinois
Author Institution: Noyes Chemical Laboratory, University of Illinois