The volatile products from the thermal reaction (414°C) of silane in excess acetylene are hydrogen, ethylene, vinylsilane, ethynylsilane, vinylethynylsilane (possibly divinylsilane) and ethynyl-divinylsilane (1,2). We have reexamined this reaction using a 3 C2 H2/1 SiH4 reaction mixture and have obtained product yield curves for these products versus percent silane loss. We have also found that product curves are unaffected when propylene at pressures equal to that of acetylene is also present. Since only trace quantities of propylsilane are produced in the presence of propylene, we can rule out reactions involving silyl radicals. Thus the SiH4−C2H2 reaction involves silylene and silene intermediates. The products can be explained by a mechanism similar to one proposed by Barton and Burns (3).