S. Muller, A. Beelen, M. Guélin, S. Aalto, J. H. Black, F. Combes,
S. J. Curran, P. Theule, and S. N. Longmore
used the Australia Telescope Compact Array (ATCA) to study the molecular content of a foreground galaxy at z = 0.89 (FG0.89 consisting of two subsources, FG0.89SW and FG0.89NO) in absorption toward the quasar PKS 1830-211:
Molecules at z = 0.89: A 4-mm-Rest-Frame Absorption-Line Survey toward PKS 1830-211
Astron. Astrophys. 535, (2011) Art. No. A103.
SO+ was identified by its J = 3/2 1/2 transition of the lower energy fine structure component 2Π1/2 with rest frequencies of 69.4 and 69.8 GHz because of the Λ-doubling. The lower frequency e component was blended with the F = 5/2 3/2 hyperfine component of the 2Π1/2, J = 3/2 1/2, f transition of NS. The different contributions could be disentangled because of the well-resolved hyperfine structure of NS.