Binding Energies Of N2, CH4, And H2O-ice Systems

Details Binding Energies Of N2, CH4, And H2O-ice Systems Binding Energies Of N2, CH4, And H2O-ice Systems

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.3806m&link_type=abstract

American Astronomical Society, DPS meeting #39, #38.06; Bulletin of the American Astronomical Society, Vol. 39, p.490

Astronomy and Astrophysics

Astrophysics

Scientific paper

We will present measurements of binding energies of the following systems: CH4-CH4, CH4-H2O, N2-N2, and N2-H2O determined from measurements made in a cryo-vacuum system following the methods of Sandford and Allamandola (1, 2). Briefly, for the N2-N2 and CH4-CH4 measurements, we monitored the area of relevant infrared features with time at three different temperatures (<50 K) and use the results to estimate sublimation rates. For the mixtures H2O/CH4 = 20 and H2O/N2= 20, we carried out a series of experiments in which we deposited the mixtures at increasingly higher temperatures (starting at 15 K) until the infrared features of the more volatile component are no longer seen (usually at > 50 K). We then use the deposition rate of H2O to estimate the residence time of the more volatile species (N2 or CH4). In previous measurements (3), binding energies of several volatile molecules (CO, CO2, H2) to H2O-ice were found to be considerably higher than the binding energies of these molecules to themselves. For example, the binding energy of CO on CO is ΔHs/k = 960 K, while that of CO on H2O is ΔHs/k = 1740 K. These results have implications for the condensation, residence time, and sublimation of volatile species on icy surfaces inside and outside of the Solar System. 1. S. A. Sandford, L. Allamandola, Icarus 87 (1990). 2. S. A. Sandford, L. Allamandola, Icarus 76, 201 (1998). 3. S. A. Sandford, L. J. Allamandola, Astrophysical Journal 417, 815 (1993).

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