2011A&A...531L...8B

The molecular species hydrogen peroxide, HOOH, is likely to be a key ingredient in the oxygen and water chemistry in the interstellar medium. Our aim with this investigation is to determine how abundant HOOH is in the cloud core ρ Oph A. By observing several transitions of HOOH in the (sub)millimeter regime we seek to identify the molecule and also to determine the excitation conditions through a multilevel excitation analysis. We have detected three spectral lines toward the SM1 position of ρ Oph A at velocity-corrected frequencies that coincide very closely with those measured from laboratory spectroscopy of HOOH. A fourth line was detected at the 4σ level. We also found through mapping observations that the HOOH emission extends (about 0.05pc) over the densest part of the ρ Oph A cloud core. We derive an abundance of HOOH relative to that of H₂ in the SM1 core of about 1x10^–10. To our knowledge, this is the first reported detection of HOOH in the interstellar medium.