Photodesorption of CO Ice

By K. Oberg, G. W. Fuchs, Z. Awad, Helen J. Fraser, Stephan Schlemmer, E. V. van Dishoeck, Harold Linnartz. 2007

166 citations recorded by the source corpus.

At the high densities and low temperatures found in star-forming regions, all molecules other than H2 should stick on dust grains on timescales shorter than the cloud lifetimes. Yet these clouds are detected in the millimeter lines of gaseous CO. At these temperatures, thermal desorption is negligible, and hence a nonthermal desorption mechanism is necessary to maintain molecules in the gas phase. Here the first laboratory study of the photodesorption of pure CO ice under ultra-high vacuum conditions is presented, which gives a desorption rate of 3 × 10-3 CO molecules per UV (7-10.5 eV) photon at 15 K. This rate is factors of 102-105 larger than previously estimated and is comparable to estimates of other nonthermal desorption rates. The experiments constrain the mechanism to a single photon desorption process of ice surface molecules. The measured efficiency of this process shows that the role of CO photodesorption in preventing total removal of molecules in the gas has been underestimated.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/5e06a1690d438ce47f7cd54cf77dd51ce782e1be

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Citations in the corpus

Formation rates of complex organics in UV irradiated CH3OH-rich ices I: Experiments (2009, background): “These yields agree with previous photodesorption studies of other molecules (Westley et al. 1995;Öberg et al. 2007, 2009a,b) and confirms the assumption in several observational and model papers that most ice molecules have similar photodesorption yields, around 10−3 per incident UV photon.”
WATER, O2, AND ICE IN MOLECULAR CLOUDS (2008, unknown): “Recent laboratory measurements of CO photodesorption imply a yield similar to that for H2O (Öberg et al. 2007).”
Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges (2010, background): “One of the major outcomes of these stuides is that photodesorption, a non-thermal desorption mechanism, is quite efficient and thus important in the cold interstellar medium (see Öberg et al. 2007, 2009b,c, for CO, N2, CO2 and H2O ice photodesorption efficiencies, respectively).”
Grain Surface Models and Data for Astrochemistry (2017, methodology): “Photodesorption was revisited much later by (Öberg et al. 2007, 2009a,b) who investigated the photodesorption yields of pure CO, N2, CO2, and H2O ices under ultra-high vacuum conditions (base pressure better than 10−9 mbar) at low temperatures using a broadband hydrogen microwave discharge lamp…”
CHEMICAL PROCESSES IN PROTOPLANETARY DISKS (2010, unknown): “In contrast, the photodesorption rates are indiscriminate, based on the experimental results of Westley et al. (1995) and Öberg et al. (2007).”
The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, methodology): “We assume the same yields used by Visser et al. (2009b), following Öberg et al. (2007, 2009b).”
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).”
Gas and grain chemical composition in cold cores as predicted by the Nautilus three-phase model (2016, methodology): “Over the last years, quantitative photo-desorption yields have been measured experimentally for pure ices sample using hydrogen discharge lamps: CO (Öberg et al. 2007; Muñoz Caro et al. 2010), H2O (Öberg et al. 2009c), N2, CO2 (Öberg et al. 2009a; Yuan & Yates 2013) and CH3OH (Öberg et al.…”
Photodesorption of ices I: CO, N₂, and CO₂ (2008, methodology): “In the case of CO, there is no measurable photodissociation in this wavelength range and the measured photon-induced loss yield is the photodesorption yield (Gerakines et al. 1996; Cottin et al. 2003; Öberg et al. 2007).”
Laboratory Evidence for Efficient Water Formation in Interstellar Ices (2008, background): “Since literature values of transmission band strengths cannot be used in reflection measurements, an apparent absorption strength is obtained froma calibration experiment in which a pure water ice layer desorbs at constant temperature until the submonolayer regime (Öberg et al. 2007).”
PHOTODESORPTION OF ICES. II. H2O AND D2O (2008, methodology): “Experiments The experimental set-up (CRYOPAD) is described in detail by Fuchs et al. (2006) and Öberg et al. (2007b).”
Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim (2009, background): “Rdes,cri = f (70K) R des,th i (70K) ζCR 5× 10−17s−1 (63) a: Aikawa et al. (1996);b: Sandford & Allamandola (1990);c: Öberg et al. (2007);d: Westley et al. (1995);e: assumed values. whereζCR is the cosmic ray ionization rate of H2, f (70K) = 3.16×10−19 the ’duty-cycle’ of the grain at 70 K…”
The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. I. H2O and the 5-8 μm Bands (2007, methodology): “It should be kept in mind, however, that some features may still be the result of interactions of species with H2O in solid state matrices, such as the narrow peak induced in H2O:CO2 mixtures (§6.3; Knez et al. 2005; Öberg et al. 2007).”
The chemical history of molecules in circumstellar disks - I. Ices (2009, background): “The gas-phase abundances can also be enhanced by allowing for photodesorption of the ices in addition to the thermal desorption considered here (Shen et al. 2004; Öberg et al. 2007, 2009).”