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Transition probabilities for the 3s2 3p(2P0)-3s3p2(4P) intersystem lines of Si IIIntensity ratios of lines of the spin-changing 'intersystem' multiplet of S II (4P yields 2P0) 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 3s3p2 4P term of Si II. Our results are 104 +/- 16, 406 +/- 33, and 811 +/- 77 micro-s 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 percent or more, should give better agreement between modeled and observed Si II line ratios.
Document ID
19930072503
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Calamai, Anthony G. (Philadelphia College of Pharmacy and Science, PA; Harvard-Smithsonian Center for Astrophysics, Cambridge MA, United States)
Smith, Peter L. (Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Bergeson, S. D. (Wisconsin Univ. Madison, United States)
Date Acquired
August 16, 2013
Publication Date
September 20, 1993
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 415
Issue: 1
ISSN: 0004-637X
Subject Category
ATOMIC AND MOLECULAR PHYSICS
Funding Number(s)
CONTRACT_GRANT: NAGW-1596
CONTRACT_GRANT: NAGW-2908
CONTRACT_GRANT: NAGW-1687
Distribution Limits
Public
Copyright
Other