Desorption rates and sticking coefficients for CO and N2 interstellar ices

By S. Bisschop, Helen J. Fraser, K. Oberg, E. Dishoeck, Stephan Schlemmer. 2006

177 citations recorded by the source corpus.

We present Temperature Programmed Desorption (TPD) experiments of CO and N2 ices in pure, layered and mixed morphologies at various ice "thicknesses" and abundance ratios as well as simultaneously taken Reflection Absorption Infrared Spectra (RAIRS) of CO. A kinetic model has been developed to constrain the binding energies of CO and N2 in both pure and mixed environments and to derive the kinetics for desorption, mixing and segregation. For mixed ices N2 desorption occurs in a single step whereas for layered ices it proceeds in two steps, one corresponding to N2 desorption from a pure N2 ice environment and one corresponding to desorption from a mixed ice environment. The latter is dominant for astrophysically relevant ice "thicknesses". The ratio of the binding energies, R_BE, for pure N2 and CO is found to be 0.936 ± 0.03, and to be close to 1 for mixed ice fractions. The model is applied to astrophysically relevant conditions for cold pre-stellar cores and for protostars which start to heat their surroundings. The importance of treating CO desorption with zeroth rather than first order kinetics is shown. The experiments also provide lower limits of 0.87 ± 0.05 for the sticking probabilities of CO-CO, N2-CO and N2-N2 ices at 14 K. The combined results from the desorption experiments, the kinetic model, and the sticking probability data lead to the conclusion that these solid-state processes of CO and N2 are very similar under astrophysically relevant conditions. This conclusion affects the explanations for the observed anti-correlations of gaseous CO and N2H+ in pre-stellar and protostellar cores.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/ae27f01aa7389dfe83386163768fcefd1d7b6454

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In Astronomy and Astrophysics

1. Simon Bruderer
2. P. Caselli
3. E. Dishoeck
4. E. Bergin
5. M. Tafalla
6. P. Myers
7. D. Wilner
8. S. Andrews

In Atmospheric Science

1. P. Caselli
2. E. Dishoeck
3. E. Bergin
4. Simon Bruderer
5. M. Tafalla
6. K. Oberg
7. V. Wakelam
8. R. Garrod

Citations in the corpus

• The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, methodology): “As in Visser et al. (2009b), we use the same pre-exponential factor for all species except for H2O (Fraser et al. 2001) and CO (Bisschop et al. 2006).”
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions (2010, background): “The diffusion and desorption energies of a limited set of molecular species have been derived (e.g., Katz et al., 1999; Bisschop et al., 2006;̈Oberg et al., 2007).”
• Astrochemistry and compositions of planetary systems (2020, background): “CO depletes from the gas-phase through freeze-out onto grains in cloud cores when grain temperatures are <18 K (Bisschop et al. 2006) if CO mainly binds to other CO molecules, and at somewhat higher grain temperatures if CO freezes out on top of water ice (Collings et al.”
• The chemical history of molecules in circumstellar disks - I. Ices (2009, background): “The pre-exponential factor,ν(X), and the binding energy,Eb(X)/k, are set to 7× 1026 cm−2 s−1 and 855 K for CO and to 1× 1030 cm−2 s−1 and 5773 K for H2O (Bisschop et al. 2006; Fraser et al. 2001).”
• ALMA OBSERVATIONS OF CIRCUMSTELLAR DISKS IN THE UPPER SCORPIUS OB ASSOCIATION (2016, background): “The gas temperature in the disk where the CO is present is expected to be > 20 K, as CO will freeze out onto dust grains at lower temperatures (Collings et al. 2003; Bisschop et al. 2006).”
• THE RELATION BETWEEN GAS AND DUST IN THE TAURUS MOLECULAR CLOUD (2010, background): “Here we assumed a sticking coefficient 4 of unity (Bisschop et al. 2006) and that at the H2 volume densities of interest adsorption mechanisms dominate over those of desorption (we therefore assume that the desorption rate is zero).”
• Cold Dark Clouds: The Initial Conditions for Star Formation (2007, methodology): “Current work has greatly benefited from laboratory work on low temperature gas phase reactions, grain binding energies, and on surface catalysis (Florescu-Mitchell & Mitchell 2006; Collings & McCoustra 2005; Nagaoka et al. 2005; Bisschop et al. 2006; Hornekær et al. 2003; Katz et al. 1999).”
• Direct mapping of the temperature and velocity gradients in discs Imaging the vertical CO snow line around IM Lupi (2017, background): “The constant 21 K of the lower surface is consistent with the expected CO condensation temperature for binding onto pure CO ice (e.g. Sandford & Allamandola 1988; Bisschop et al. 2006; Martín-Doménech et al. 2014; Fayolle et al. 2016).”
• On the internal structure of starless cores II. A molecular survey of L1498 and L1517B (2006, background): “Recent laboratory measurements by Öberg et al. (2005) and Bisschop et al. (2006), however, show that the two binding energies differ by less than 10%, and this may seem insufficient to account for the different depletion behavior of CO and N2H+ (note however that Aikawa et al. 2001 find…”
• Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio (2008, unknown): “With an N2 binding energy similar to the CO binding energy (Öberg et al. 2005, Bisschop et al. 2006), these two molecules are expected to behave similarly.”
• A COLD COMPLEX CHEMISTRY TOWARD THE LOW-MASS PROTOSTAR B1-b: EVIDENCE FOR COMPLEX MOLECULE PRODUCTION IN ICES (2010, background): “CO evaporates at 17–25 K on astrophysical time scales (Bisschop et al. 2006), and thus HCO-X ices will mainly form in cold, UV-exposed ices.”
• Photodesorption of ices I: CO, N₂, and CO₂ (2008, background): “(7) the gas temperature T is set to 10 K, mCO2 is the CO2 mass in atomic mass units, and S is the sticking coefficient, which is assumed to be 1 (Bisschop et al. 2006).”