Vibrational spectra of disilenes. Normal coordinate analysis and identification of the v(Si=Si) stretching vibration

• Published in: Journal of organometallic chemistry 1997-05, Vol.536-537, p.425-432
• Main Authors: Leites, L.A., Bukalov, S.S., Garbuzova, I.A., West, R., Mangette, J., Spitzner, H.
• Format: Article
• Language: English
• Subjects: Disilene; Normal coordinate analysis; Raman and IR spectra; Si=Si stretching vibration; Silicon
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/S0022-328X(96)06872-6

Experimental vibrational spectra are reported for three carbon-substituted disilenes along with data on normal coordinate analysis of several simplified disilene models. Calculations show that there is no normal mode in the disilene spectrum which is well-localized in the Si=Si bond. The Si=Si and Si-C stretching coordinates are heavily mixed. Their in-phase combination results in a normal mode with frequency in the region 450–550 cm−1 which manifests itself as a Raman line of variable intensity (the so-called v(Si=Si)). Their out-of-phase combination gives a mode in the region of about 700 cm−1 which shows itself as an intense Raman line (the so-called vS(Si-C)). Vibrations of an aromatic ring, if present in a disilene molecule, can also couple with the v(Si-Si). Particular eigenvector elements of the two modes in question and thus their potential energy distributions strongly depend on the structure and symmetry of a given disilene molecule. However, the contribution of the Si=Si stretching coordinate to the normal coordinate with frequency in the region 450–550cm−1 is always significant, justifying the designation of this mode as the v(Si=Si).