, By varying their stoichiometry these compounds can be used as single source feedstock gases for layers with tailor-made composition. In a new approach to the epitaxial deposition of silicon carbide, halogencontaining feedstock gases are expected to show improved properties owing to a greater reversi bility of the deposition process. W hereas polysilylalkanes halogenated at carbon are well rep resented in the literature [1 0 , 1 1 ], only limited information is available on the corresponding alkenes. The low thermal stability of polysilylated haloalkanes makes these compounds unsuitable for practical processes. The ethene analogues are expected to exhibit greater thermal stability and to be more amenable regarding storage and con * Reprint requests to Prof. Dr. H. Schmidbaur. tinuous handling. Although several sterically crowded polysilyl ethenes have been the subject of investigations of their molecular structure, dy namics and energy characteristics [12][13][14][15][16], the num ber of structurally characterized compounds is still small. Following work on silylalkanes, our more recent studies have therefore focused on silyl olefines. In the course of these investigations we have undertaken the X-ray structure determ i nations of bis(trichlorosilyl)acetylene and of the two most crowded trichlorosilylethenes, tris(trichlorosilyl)ethene and tetrakis(trichlorosilyl)-ethene.