MICROWAVE-SPECTRA OF TRIMETHYLSILYLETHYNE, ME3SICCH, 1-CYANO-2-TRIMETHYLSILYLETHYNE, ME3SICCCN, AND 1-CYANO-4-TRIMETHYLSILYLBUTADIYNE, ME3SI(CC)2CN

The microwave spectra of the title compounds, recorded in the 26.5-40.0 GHz region, are characteristic of symmetric top molecules, complicated by internal rotation and accompanied by vibrational satellites attributed to low-frequency skeletal bending modes. For Me3SiC = CH, B(o) = 1962.163 MHz and relative intensity measurements on the vibrational satellites give a value of 110 +/- 15 cm-1 for the degenerate Si-C = C bending mode. Measurements on Me3SiC = CD have been made, and the Si-C = bond length has been determined as 1.83 +/- 0.01 angstrom. For Me3SiC = CC = N, B(o) = 711.8646 MHz, whilst for Me3Si(C = C)2C = N, twenty broad-band symmetric-top transitions, from J = 41 to 60, have been observed and a B value of 331 +/- 2 MHz has been estimated.