2011ApJ...743..131S

Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H₂O₂), for the production of water (H₂O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H₂O₂ ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H₂O₂ should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H₂O₂/H₂ O ice films between 2.5 and 200 µm, from 10 to 180 K, containing 3%, 30%, and 97% H₂O₂ice. Integrated absorbances for all the absorption features in low-temperature H₂O₂ice have been derived from these spectra. For identifying H₂O₂ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 µm. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H₂ O ice absorption bands, no absorption features are found that can definitely be identified with H₂O₂ ice. In the absence of definite H₂O₂features, the H₂O₂abundance is constrained by its possible contribution to the weak absorption feature near 3.47 µm found on the long-wavelength wing of the 3 µm H₂ O ice band. This gives an average upper limit for H₂O₂, as a percentage of H₂O, of 9%±4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.