The UV, preresonance Raman, and IR spectra of the stable silene t-BuMe2Si(Me3Si)Si=2-Ad (1) have been measured as well as its J(Si=C) NMR coupling constant. The normal modes involving the v(Si=C) stretching coordinate were identified for the first time for a stable silene. The experimental data and computations of potential energy distribution and mode eigenvectors show that there is no single vibrational normal mode which can be assigned as v(Si=C). Raman intensity enhancement on approaching resonance strongly supports the conclusion that there are five lines in the region 1000-1370 cm(-1) which include significant contribution from the v(Si=C) stretching coordinate. Both the Si=C force constant and the J(Si=C) NMR coupling constant (as well as the Si=C bond length) indicate that the Si=C bond order is smaller in I than that in simpler silenes of the type R2Si=CH2, (R = H, Me).