The infra-red absorption spectra of crystals which were enriched with 16O or 18O were investigated. In addition to known lines which were related to the vibrations of interstitial bond-centered Oi, a weak infra-red absorption line at 1819.5/cm (1764/cm in 18O samples) was found to arise from Oi. The band was attributed to a combination mode of 3 fundamentals of the Oi symmetrical stretching plus asymmetrical stretching plus a 2-dimensional low-frequency mode. In electron-irradiated 16O samples, 2 new vibrational bands were observed at about 1370 and 1430/cm. A good correlation was found between intensity changes in these lines, and those in bands at 836 and 885/cm, respectively. The latter bands were known to originate from the asymmetrical stretching vibrations of an O atom in the neutral and negative vacancy-O complex. All 4 lines were found to exhibit similar isotopic and temperature shifts.

New Infrared Vibrational Bands Related to Interstitial and Substitutional Oxygen in Silicon L.I.Murin, V.P.Markevich, T.Hallberg, J.L.Lindström: Solid State Phenomena, 1999, 69-70, 309-14