B. Parise, P. Bergman, and F. Du,
used the IRAM 30 m and the APEX 12 m radio telescopes for the
Detection of the Hydroperoxyl Radical HO₂ toward //ρ// Ophiuchi A: Additional Constraints on the Water Chemical Network
Astron. Astrophys. 541, Art. No. L11 (2012).
The J_{K_a,K_c} = 2_0,2 – 1_0,1 and 4_0,4 – 3_0,3 around 130.35 and 260.67 GHz, respectively, were detected. Both transitions displayed fine structure splitting of about 200 MHz. In addition, H-hyperfine splitting was resolved for the lower quantum number transition.
The source is the same in which H₂O₂ was detected and the tentative detection of O₂ was confirmed very recently. The column density of HO₂ is very similar to that of H₂O₂, in reasonable agreement with model calculations.

Contributor(s): H. S. P. Müller; 05, 2012