The oscillator strength of the SI II 3s2 3p (P-2)-3s3p2 D-2 multiplet and the interstellar abundance of silicon

Spontaneous radiative rates, calculated using sophisticated configuration interaction wavefunctions, are presented for Si II resonance transitions in the 3s23p 2Pj-3s3p2 2Dj multiplet. For the J = 1/2 to J' = 3/2 transition, an oscillator strength of 0.0020 (with an estimated uncertainty of 25%) is deduced. This value is significantly lower than those found in some previous studies; the reasons for this and in particular the crucial role of the energy splitting of the 3s3P2 2D and 3s23d 2D levels are investigated. The implication of these new atomic data for gas phase silicon abundances in the interstellar medium is briefly discussed.