2012A&A...538A..91D

The formation of water on the dust grains in the interstellar medium may proceed with hydrogen peroxide (H₂O₂) as an intermediate. Recently gas-phase H₂O₂ has been detected in ρ Oph A with an abundance of ∼10^–10 relative to H₂. We aim to reproduce the observed abundance of H₂O₂ and other species detected in ρ Oph A quantitatively. We make use of a chemical network that includes gas phase reactions, as well as processes on the grains. Desorption from the grain surface through chemical reaction is also included. We ran the model for a range of physical parameters. The abundance of H₂O₂ can be best reproduced at ∼6x10⁵yr, which is close to the dynamical age of ρ Oph A. The abundances of other species such as H₂CO, CH₃OH, and O₂ can also be reasonably reproduced at this time. In the early time, the gas-phase abundance of H₂O₂ can be much higher than the currently detected value. We predict a gas phase abundance of O₂H at the same order of magnitude as H₂O₂, and an abundance on the order of 10^–8 for gas phase water in ρ Oph A. A few other species of interest are also discussed. We demonstrate that H₂O₂ can be produced on the dust grains and released into the gas phase through nonthermal desorption via surface exothermic reactions. The H₂O₂ molecule on the grain is an important intermediate in the formation of water. That H₂O₂ is overproduced in the gas phase for a range of physical conditions suggests that its destruction channel in the current gas phase network may be incomplete.