UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption

Bertin, M.; Fayolle, Edith C.; Romanzin, C.; Öberg, Karin I.; Michaut, X.; Moudens, Audrey; Philippe, L.; Jeseck, Pascal; Linnartz, H.; Fillion, J.-H.

doi:10.1039/c2cp41177f

Cited by 86 publications

(116 citation statements)

References 41 publications

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“…This leads one to conclude that massive ice damage is occurring in this experiment. A similar energy relaxation upon the electronic excitation process has been studied by Bertin et al (2012). The radiation-induced lattice damage process is accompanied by lattice healing due to annealing at 75 K, and radiation damage may therefore be reversed to some degree by annealing in the dark at 75 K, as seen in Figures 5 and 6, as well as in Figure 4.…”

Section: Deep Defect Formation In Co 2 (Ice) By Lyα Radiation-the Promentioning

confidence: 67%

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO₂(ICE)

Yuan

Yates

2013

ApJ

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Photodesorption from a crystalline film of CO 2 (ice) at 75 K has been studied using Lyα (10.2 eV) radiation. We combine quantitative mass spectrometric studies of gases evolved and transmission IR studies of species trapped in the ice. Direct CO desorption is observed from the primary CO 2 photodissociation process, which occurs promptly for CO 2 molecules located on the outermost surface of the ice (Process I). As the fluence of Lyα radiation increases to ∼5.5 × 10 17 photons cm −2 , extensive damage to the crystalline ice occurs and photo-produced CO molecules from deeper regions (Process II) are found to desorb at a rapidly increasing rate, which becomes two orders of magnitude greater than Process I. It is postulated that deep radiation damage to produce an extensive amorphous phase of CO 2 occurs in the 50 nm ice film and that CO (and CO 2 ) diffusive transport is strongly enhanced in the amorphous phase. Photodesorption in Process II is a combination of electronic and thermally activated processes. Radiation damage in crystalline CO 2 ice has been monitored by its effects on the vibrational line shapes of CO 2 (ice).Here the crystalline-to-amorphous phase transition has been correlated with the occurrence of efficient molecular transport over long distances through the amorphous phase of CO 2 (ice). Future studies of the composition of the interstellar region, generated by photodesorption from ice layers on grains, will have to consider the significant effects of radiation damage on photodesorption rates.

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Section: Deep Defect Formation In Co 2 (Ice) By Lyα Radiation-the Promentioning

confidence: 67%

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO₂(ICE)

Yuan

Yates

2013

ApJ

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“…For the photodesorption rates, we use the most recent experimental values for the photodesorption yields (Öberg et al 2009a,b). In this model, we include a "coverage" factor, θ s , accounting for recent experimental results which suggest that photodesorption occurs from the top few monolayers only (Bertin et al 2012). For molecules which do not have constrained photodesorption yields, Y i , we use the early experimental value determined for water ice by Westley et al (1995) of 3 × 10 −3 molecules photon −1 (see Table 1 and Eq.…”

Section: Chemical Modelmentioning

confidence: 99%

Complex organic molecules in protoplanetary disks

Walsh

Millar

Nomura

et al. 2014

A&A

220

356

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Context. Protoplanetary disks are vital objects in star and planet formation, possessing all the material, gas and dust, which may form a planetary system orbiting the new star. Small, simple molecules have traditionally been detected in protoplanetary disks; however, in the ALMA era, we expect the molecular inventory of protoplanetary disks to significantly increase. Aims. We investigate the synthesis of complex organic molecules (COMs) in protoplanetary disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA. Methods. We have coupled a 2D steady-state physical model of a protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs. We compare the resulting column densities with those derived from observations and perform ray-tracing calculations to predict line spectra. We compare the synthesised line intensities with current observations and determine those COMs which may be observable in nearby objects. We also compare the predicted grain-surface abundances with those derived from cometary comae observations. Results. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ∼10 −6 -10 −4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, ∼10 −12 -10 −7 . Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H 2 CO observed towards T Tauri star-disk systems. There is poor agreement with HC 3 N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH 3 OH are consistent with upper limits determined towards all sources. Our models suggest CH 3 OH should be readily observable in nearby protoplanetary disks with ALMA; however, detection of more complex species may prove challenging, even with ALMA "Full Science" capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun's natal disk.

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“…Following recent lab results (Öberg et al 2009;Bertin et al 2012), FUV photodesorption is treated as a zeroth-order process (i.e., molecules can only desorb from the top few layers). Öberg et al (2009) give a photodesorption yield of where Y pd,0 = 10 −3 is the photodesorption yield for thick ice, and θ M is the monolayer coverage factor…”

Section: Simplified Water Network (Swan)mentioning

confidence: 99%

Water in low-mass star-forming regions withHerschel

Schmalzl

Visser

Walsh

et al. 2014

A&A

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Aims. Our aim is to determine the critical parameters in water chemistry and the contribution of water to the oxygen budget by observing and modelling water gas and ice for a sample of eleven low-mass protostars, for which both forms of water have been observed. Methods. A simplified chemistry network, which is benchmarked against more sophisticated chemical networks, is developed that includes the necessary ingredients to determine the water vapour and ice abundance profiles in the cold, outer envelope in which the temperature increases towards the protostar. Comparing the results from this chemical network to observations of water emission lines and previously published water ice column densities, allows us to probe the influence of various agents (e.g., far-ultraviolet (FUV) field, initial abundances, timescales, and kinematics). Results. The observed water ice abundances with respect to hydrogen nuclei in our sample are 30−80 ppm, and therefore contain only 10-30% of the volatile oxygen budget of 320 ppm. The keys to reproduce this result are a low initial water ice abundance after the pre-collapse phase together with the fact that atomic oxygen cannot freeze-out and form water ice in regions with T dust > ∼ 15 K. This requires short prestellar core lifetimes < ∼ 0.1 Myr. The water vapour profile is shaped through the interplay of FUV photodesorption, photodissociation, and freeze-out. The water vapour line profiles are an invaluable tracer for the FUV photon flux and envelope kinematics. Conclusions. The finding that only a fraction of the oxygen budget is locked in water ice can be explained either by a short precollapse time of < ∼ 0.1 Myr at densities of n H ∼ 10 4 cm −3 , or by some other process that resets the initial water ice abundance for the post-collapse phase. A key for the understanding of the water ice abundance is the binding energy of atomic oxygen on ice.

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UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption

Cited by 86 publications

References 41 publications

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO₂(ICE)

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO₂(ICE)

Complex organic molecules in protoplanetary disks

Water in low-mass star-forming regions withHerschel

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UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption

Cited by 86 publications

References 41 publications

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO2(ICE)

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO2(ICE)

Complex organic molecules in protoplanetary disks

Water in low-mass star-forming regions withHerschel

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Product

Resources

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RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO₂(ICE)

RADIATION DAMAGE AND ASSOCIATED PHASE CHANGE EFFECT ON PHOTODESORPTION RATES FROM ICES—LYα STUDIES OF THE SURFACE BEHAVIOR OF CO₂(ICE)