Keywords

atomic data

Abstract

Intensity ratios of lines of the spin-changing "intersystem" multiplet of Si II (⁴P → ²P^o) at 234 nm have been used to determine electron densities and temperatures in a variety of astrophysical environments. However, the accuracy of these diagnostic calculations have been limited by uncertainties associated with the available atomic data. We report the first laboratory measurement, using an ion-trapping technique, of the radiative lifetimes of the three metastable levels of the 3s3p^{2 4}P term of Si II. Our results are 104 ± 16, 406 ± 33, and 811 ± 77 µs for lifetimes of the J = 1/2, 5/2, and 3/2 levels, respectively. A-values were derived from our lifetimes by use of measured branching fractions. Our A-values, which differ from calculated values by 30% or more, should give better agreement between modeled and observed Si II line ratios.

Original Publication Citation

Anthony G. Calamai, Peter L. Smith, and S. D. Bergeson. Transition probabilities for the 3s2 3p(2P0)-3s3p2(4P) intersystem lines of Si II. Astrophys. J. 415 (1), L59-L62 (1993).