Far-infrared, combination band, and Raman spectra of the ring-puckering vibration of 1,4-disilacyclohexa-2,5-diene

The far-infrared spectrum of 1,4-disilacyclohexa-2,5-diene shows a series o f four closely spaced bands originating at 70.5 cm(-1) resulting from the r ing-puckering vibration. Four mid-infrared bands near 2214 cm(-1) result fr om combinations of the puckering with the Raman active B-2g SiH2 antisymmet ric stretch at 2143.2 cm(-1), and seven difference bands near 2083 cm(-1) r esult from combinations with the Raman active A(g) SiH2 symmetric stretch a t 2154.0 cm(-1). The ring-puckering transitions result from a single-minimu m potential energy function, V(cm(-1)) = 1.23 x 10(4)x(2) + 2.40 x 10(4)x,( 4) where x is the puckering coordinate. The molecule is planar and less rig id than 1,4-cyclohexadiene, thus apparently showing no unusual interactions between the silicon atoms and the C=C pi systems.