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On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular CloudsRecent 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/H2O ice films between 2.5 and 200 micron, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 micron. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 micron found on the long-wavelength wing of the 3 micron H2O 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.
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Document Type
Reprint (Version printed in journal)
Smith, R. G. (New South Wales Univ. Canberra, Australia)
Charnely, S. B. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Pendleton, Y. J. (NASA Ames Research Center Moffett Field, CA, United States)
Wright, C. M. (New South Wales Univ. Canberra, Australia)
Maldoni, M. M. (Geoscience Australia Canberra, Australia)
Robinson, G. (New South Wales Univ. Canberra, Australia)
Date Acquired
August 26, 2013
Publication Date
November 29, 2011
Publication Information
Publication: Astrophysical Journal
Volume: 743
Issue: 2
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