Cosmic ray sputtering yield of interstellar H2O ice mantles : Ice mantle thickness dependence

Abstract

Interstellar grain mantles present in dense interstellar clouds are in constant exchange with the gas phase via accretion and desorption mechanisms such as UV, X-ray photodesorption, cosmic ray induced sputtering, grain thermal fluctuations, and chemical reaction energy release. The relative importance of the various desorption mechanisms is of uttermost importance for astrophysical models to constrain the chemical evolution in such high density dense cloud regions. In this experimental work we investigated the sputtering yield as a function of ice mantle thickness, exposed to Xe ions at 95MeV. The ion induced ice phase transformation and the sputtering yield were simultaneously monitored by IR spectroscopy and mass spec- trometry, respectively. The sputtering yield is constant above a characteristic ice layer thickness and starts to decrease below this thickness. An estimate of the sputtering depth corresponding to this length can be evaluated. In these experiments the measured desorption depth corresponds to 30 ice layers. Assuming an effective cylindrical shape for the volume of sputtered molecules, the aspect ratio is close to unity; in the semi-infinite ice film case this ratio is the diameter to height of the cylinder. This result shows that most ejected molecules arise from a rather compact volume. The measured infinite thickness sputtering yield for water ice mantles scales as the square of the ion electronic stopping power (Se). We expect that the desorption depth dependence varies with Se^a , where a=0.5. Astrophysical models should take into account the thickness dependence constraints of these ice mantles in the interface regions when ices are close to their extinction threshold. In the very dense cloud regions, most of the water ice mantles are above this limit for the bulk of the cosmic rays.

arXiv comment6 pages, 5 figures

References in corpus (16)

• The Spitzer ice legacy: Ice evolution from cores to protostars
• The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects: I. H2O and the 5-8 um Bands
• Gas and grain chemical composition in cold cores as predicted by the Nautilus 3-phase model
• Photodesorption of Ices II: H2O and D2O
• CO ice photodesorption: A wavelength-dependent study
• UV photodesorption of methanol in pure and CO-rich ices: desorption rates of the intact molecule and of the photofragments
• New Three Micron Spectra of Young Stellar Objects with H_2O Ice Bands
• On Cosmic Ray-Driven Grain Chemistry in Cold Core Models
• A Study of Absorption Features in the Three Micron Spectra of Molecular Cloud Sources with H${}_2$O Ice Bands
• The negligible photodesorption of methanol ice and the active photon-induced desorption of its irradiation products
• Surface chemistry in the Interstellar Medium II. ${\mathrm{H}}_2$ formation on dust with random temperature fluctuations
• Wavelength-dependent UV photodesorption of pure N2 and O2 ices
• X-ray photodesorption from water ice in protoplanetary disks and X-ray dominated regions
• Chemical and physical characterization of collapsing low-mass prestellar dense cores
• Spectrally-resolved UV photodesorption of CH4 in pure and layered ices
• New measurements on water ice photodesorption and product formation under ultraviolet irradiation

Cited by in corpus (19)

• Formation of complex organic molecules in hot molecular cores through nondiffusive grain-surface and ice-mantle chemistry
• Efficiency of non-thermal desorptions in cold-core conditions. Testing the sputtering of grain mantles induced by cosmic rays
• Laboratory and Computational Studies of Interstellar Ices
• Modeling C-Shock Chemistry in Isolated Molecular Outflows
• Non-thermal desorption of complex organic molecules: Cosmic-ray sputtering of CH3OH embedded in CO2 ice
• Cosmic ray sputtering yield of interstellar ice mantles: CO and CO2 ice thickness dependence
• Complex organic molecules in protoplanetary disks : X-ray photodesorption from methanol-containing ices. Part I -- Pure methanol ices
• Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices. Part II -- Mixed methanol-CO and methanol-H2O ices
• Ice mantles on dust grains: dramatic variation of thickness with grain size
• Vacuum ultraviolet photodesorption and photofragmentation of formaldehyde-containing ices
• Electron-stimulated desorption from molecular ices in the sub-keV regime
• On Modelling Sputtering of Interstellar Grain Ices
• Bombardment of CO ice by cosmic rays: I. Experimental insights into the microphysics of molecule destruction and sputtering
• Simulation of CH${}_3$OH ice UV photolysis under laboratory conditions
• H2S ice sublimation dynamics: experimentally constrained binding energies, entrapment efficiencies, and snowlines
• Constraints on the non-thermal desorption of methanol in the cold core LDN 429-C
• The Cosmic-Ray Induced Sputtering Process On Icy Grains
• Chemical constraints on the dynamical evolution of the cold core L694
• Simulation of proton radiolysis of H2O and O2 ices with the Nautilus code