Normal coordinate analysis of disilenes and diphosphenes. The ν(SiSi) and ν(PP) stretching vibrations

Abstract

Normal coordinate analysis (NCA) of some disilene and diphosphene molecules has been performed and compared with NCA of corresponding alkenes. For various models of disilenes containing the C 2SiSiC 2 moiety, NCA shows that SiSi and SiC stretching coordinates are heavily mixed, their in-phase combination resulting in a normal mode in the region 450–550 cm −1, while their out-of-phase combination is in the region 600–750 cm −1. In contrast, the results of NCA for diphosphenes show that the vibration at ≈ 600 cm −1 is well localized, being predominantly νPP stretch (≈ 90% in PED).