Infrared and Raman Spectroscopy of Diphenylsilane. Vibrational Assignment by Hartree-Fock and Density-functional Theory Calculations

Abstract

Infrared and Raman spectra were measured to elucidate both the conformation and the vibrational modes of diphenylsilane in the fundamental state. The vibrational fundamentals were assigned with the aid of density-functional theory (DFT) and Hartree-Fock (HF) calculations. The most intense IR line at 843 cm 1 is attributed to the out-of-plane C-H fundamental. However, the Raman line at 999 nm has the highest intensity, in which ring puckering and SiH2 bending vibrations are involved. Interestingly, we observe an intense IR fundamental and a Raman line associated with the Si H2 vibration. The strong IR absorption is due to the Si-H bond polarity associated with the sizable electronegativity dierence between Si and H. The intense Raman scattering involving the Si H2 vibration is attributed to the displacement of the relatively large electron cloud of Si. A ring torsional fundamental vibration is observed at 91 cm 1 , the lowest energy vibrations in the Raman spectrum. Also, the displacement of the electron cloud is reflected in the intense Raman lines.