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

Abstract

Spontaneous radiative rates, calculated using sophisticated configuration interaction wavefunctions, are presented for Si II resonance transitions in the 3s<SUP>2</SUP>3p <SUP>2</SUP>P<SUB>j</SUB>-3s3p<SUP>2</SUP> <SUP>2</SUP>D<SUB>j</SUB> 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 3s<SUP>3</SUP>P<SUP>2</SUP> <SUP>2</SUP>D and 3s<SUP>2</SUP>3d <SUP>2</SUP>D levels are investigated. The implication of these new atomic data for gas phase silicon abundances in the interstellar medium is briefly discussed.