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 JKa,Kc = 20,2 10,1 and 40,4 30,3 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.