NONCLASSICAL STRUCTURES IN SILICON-CONTAINING MOLECULES - THE MONOBRIDGED ISOMER OF SI2H2

A monobridged isomer of the disilyne Si2H2, the planar bridged-2 form Si(H)SiH, has been detected through its millimeter- and submillimeter-wave rotational spectrum. The molecules are produced in a low pressure, low power plasma in a mixture of SiH4 and Ar cooled at liquid nitrogen temperature. From the analysis of a total of 148 lines, a set of accurate rotational constants have been derived. Using the geometry predicted by ab initio calculations (see the preceding paper), the spectrum of Si(D)SiD has been predicted, observed, and analyzed. From the two sets of rotational constants, a preliminary molecular structure has been derived by fixing the Si1-Si2-bridged H angle to the ab initio value of 52.5-degrees: Si1-S2=2.119 angstrom; Si2-bridged H=1.629 angstrom; Si2-terminal H=1.474 angstrom; Si1-Si2-terminal H=157.5-degrees.