===== On the Detection of Hydrogen Peroxide, H2O2, in the ISM =====

Six rotational transitions of hydrogen peroxide, H<sub>2</sub>O<sub>2</sub>, were searched for with the APEX 12 m radio telescope toward //ρ// Oph A by\\
P. Bergman, B. Parise, R. Liseau, B. Larsson, H. Olofsson, K. M. Menten, and R. Güsten,\\
**[[https://doi.org/10.1051/0004-6361/201117170|Detection of Interstellar Hydrogen Peroxide]]**\\
//Astron. Astrophys.// **531**, Art. No. L8 (2011).\\
The //J<sub>K<sub>a</sub>,K<sub>c</sub></sub>// = 3<sub>0,3</sub> – 2<sub>1,1</sub> and 5<sub>0,5</sub> – 4<sub>1,3</sub> of the //τ// = 4 – 2 ladder near 219.2 and 318.2 GHz, respectively, as well as the 6<sub>1,5</sub> – 5<sub>0,5</sub> and 4<sub>0,4</sub> – 3<sub>1,2</sub> of the //τ// = 2 – 4 ladder near 251.9 and 269.0 GHz, respectively, were detected in emission; albeit the latter one only barely with significance.\\
The non-observation of the 1<sub>1,0</sub> – 0<sub>0,0</sub>, //τ// = 3 – 1 transition near 670.6 GHz was attributed to subthermal excitation.\\
A column density of 8 (3) × 10<sup>12</sup>cm<sup>–2</sup> and a rotational temperature of 22 ± 3 K were derived. Since the column density of H<sub>2</sub> is rather uncertain, the fractional abundances of H<sub>2</sub>O<sub>2</sub> with respect to H<sub>2</sub> should be viewed with great caution.\\
The number of observed transitions may seem a bit small, but the low rotational temperature and the corresponding small number of lines detected in that source suggest the observation to be rather secure. Moreover, the strongest evidence for molecular oxygen in the ISM stem from observations of this source.


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Contributor(s): H. S. P. Müller; 06, 2011

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