Astrophys. J., 743, 131 (2011/December-3)
On the formation of interstellar water ice: constraints from a search for hydrogen peroxide ice in molecular clouds.
SMITH R.G., CHARNLEY S.B., PENDLETON Y.J., WRIGHT C.M., MALDONI M.M. and ROBINSON G.
Abstract (from CDS):
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.
infrared: ISM - ISM: abundances - ISM: clouds - ISM: lines and bands - ISM: molecules - molecular processes
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<Available at CDS (J/ApJ/743/131): table2.dat table3.dat table4.dat table5.dat table6.dat table7.dat table10.dat>
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