The equilibrium structure of silene H2C=SiH2 from millimeter wave spectra and from ab initio calculations

Silene, H2CSiH2, has been efficiently produced by pyrolysis of 5,6-bis(trifluoromethyl)-2-silabicyclo[2.2.2]octa-5,7-diene (SBO). Seven isotopomers have been observed by millimeter- and submillimeter-wave spectroscopy. From the different sets of experimental molecular parameters and from ab initio calculations of the rovibrational interaction parameters, the equilibrium structure has been obtained by a least squares analysis of the rotational constants. The results are: r(e)(Si=C) = 1.7039(18) Angstrom, r(e)(C-H) = 1.0819(12) Angstrom, r(e)(Si-H) = 1.4671(9) Angstrom, angle HCSi = 122.00(4)degrees, and angle HSiC = 122.39(3)degrees. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with a cc-pV(Q,T)Z basis set. This is the first experimental determination without any constraint of the Si=C double bond length in the parent compound of the silaalkene family. A lifetime of 30 ms has been observed for this molecule in the gas phase at low pressure. (C) 1997 American Institute of Physics.