THE OSCILLATOR STRENGTH OF THE SI-II 3S23P 2P-3S3P2 2D 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 3s(2)3p 2P(J)-3s3p2 2D(J') 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 3s(2)3d 2D levels are investigated. The implication of these new atomic data for gas phase silicon abundances in the interstellar medium is briefly discussed.