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

TL;DR

This study models the formation and abundance of hydrogen peroxide (H2O2) on interstellar dust grains, successfully reproducing observed levels in { ho} Oph A and highlighting its role as an intermediate in water formation.

Contribution

The paper introduces a comprehensive chemical network model including grain-surface processes and desorption, providing new insights into H2O2 production in interstellar environments.

Findings

H2O2 abundance peaks at ~6E5 years, matching the age of { ho} Oph A.

Gas-phase H2O2 can be over-produced, indicating incomplete destruction pathways.

Predicted O2H abundance is comparable to H2O2, around 1E-10.

Abstract

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 {\rho} Oph A with an abundance of ~1E-10 relative to H2. Aims. We aim to reproduce the observed abundance of H2O2 and other species detected in {\rho} Oph A quantitatively. Methods. We make use of a chemical network which includes gas phase reactions as well as processes on the grains; desorption from the grain surface through chemical reaction is also included. We run the model for a range of physical parameters. Results. The abundance of H2O2 can be best reproduced at ~6E5 yr, which is close to the dynamical age of {\rho} Oph A. The abundances of other species such as H2CO, CH3OH, and O2 can be reasonably reproduced also at this time. In the early time the gas-phase abundance of H2O2 can be much higher than the current detected value. We predict a gas phase abundance of O2H at the same order of magnitude as H2O2, and an abundance of the order 1E-8 for gas phase water in {\rho} 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 non-thermal desorption via surface exothermic reactions. The H2O2 molecule on the grain is an important intermediate in the formation of water. The fact that H2O2 is over-produced in the gas phase for a range of physical conditions suggests that its destruction channel in the current gas phase network may be incomplete.