Production of interstellar hydrogen peroxide (H2O2) on the surface of dust grains

Artikel i vetenskaplig tidskrift, 2012

Context. 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. Aims. We aim to reproduce the observed abundance of H2O2 and other species detected in ρ Oph A quantitatively. Methods. 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. Results. The abundance of H2O2 can be best reproduced at ~6 × 105 yr, 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. Conclusions. 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.