Cosmic ray sputtering yield of interstellar ice mantles. CO and CO2 ice thickness dependence

Aims. Methanol ice is embedded in interstellar ice mantles present in dense molecular clouds. We aim to measure the sputtering efficiencies starting from different ice mantles of varying compositions experimentally, in order to evaluate their potential impact on astrochemical models. The sputtering yields of complex organic molecules is of particular interest, since few mechanisms are efficient enough to induce a significant feedback to the gas phase. Methods. We irradiated ice film mixtures made of methanol and carbon dioxide of varying ratios with swift heavy ions in the electronic sputtering regime. We monitored the evolution of the infrared spectra as well as the species released to the gas phase with a mass spectrometer. Methanol (12C) and isotopically labelled 13C-methanol were used to remove any ambiguity on the measured irradiation products. Results. The sputtering of methanol embedded in carbon dioxide ice is an efficient process leading to the ejection of intact methanol in the gas phase. We establish that when methanol is embedded in a carbon-dioxide-rich mantle exposed to cosmic rays, a significant fraction (0.2–0.3 in this work) is sputtered as intact molecules. The sputtered fraction follows the time-dependent bulk composition of the ice mantle, the latter evolving with time due to the radiolysis-induced evolution of the bulk. If methanol is embedded in a carbon dioxide ice matrix, as the analyses of the spectral shape of the CO2 bending mode observations in some lines of sight suggest, the overall methanol sputtering yield is higher than if embedded in a water ice mantle. The sputtering is increased by a factor close to the dominant ice matrix sputtering yield, which is about six times higher for pure carbon dioxide ice when compared to water ice. These experiments are further constraining the cosmic-ray-induced ice mantle sputtering mechanisms important role in the gas-phase release of complex organic molecules from the interstellar solid phase.

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Solid State Pathways towards Molecular Complexity in Space

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311025142 ◽

2011 ◽

Vol 7 (S280) ◽

pp. 390-404 ◽

Cited By ~ 7

Author(s):

Harold Linnartz ◽

Jean-Baptiste Bossa ◽

Jordy Bouwman ◽

Herma M. Cuppen ◽

Steven H. Cuylle ◽

...

Keyword(s):

Solid State ◽

Interstellar Medium ◽

Vacuum Ultraviolet ◽

Cosmic Ray ◽

Solid State Reactions ◽

Thermal Heating ◽

Interstellar Ice ◽

Molecular Complexity ◽

Physical And Chemical ◽

Complex Organic

AbstractIt has been a long standing problem in astrochemistry to explain how molecules can form in a highly dilute environment such as the interstellar medium. In the last decennium more and more evidence has been found that the observed mix of small and complex, stable and highly transient species in space is the cumulative result of gas phase and solid state reactions as well as gas-grain interactions. Solid state reactions on icy dust grains are specifically found to play an important role in the formation of the more complex “organic” compounds. In order to investigate the underlying physical and chemical processes detailed laboratory based experiments are needed that simulate surface reactions triggered by processes as different as thermal heating, photon (UV) irradiation and particle (atom, cosmic ray, electron) bombardment of interstellar ice analogues. Here, some of the latest research performed in the Sackler Laboratory for Astrophysics in Leiden, the Netherlands is reviewed. The focus is on hydrogenation, i.e., H-atom addition reactions and vacuum ultraviolet irradiation of interstellar ice analogues at astronomically relevant temperatures. It is shown that solid state processes are crucial in the chemical evolution of the interstellar medium, providing pathways towards molecular complexity in space.

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Cosmic ray sputtering yield of interstellar H2O ice mantles

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833277 ◽

2018 ◽

Vol 618 ◽

pp. A173 ◽

Cited By ~ 9

Author(s):

E. Dartois ◽

M. Chabot ◽

T. Id Barkach ◽

H. Rothard ◽

B. Augé ◽

...

Keyword(s):

Cosmic Rays ◽

Cosmic Ray ◽

Thermal Fluctuations ◽

Cylindrical Shape ◽

Interstellar Clouds ◽

Water Ice ◽

Dense Cloud ◽

Measured Characteristic ◽

Deposited Energy ◽

Sputtering Yield

Aims. 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. Methods. The sputtering yields for swift ions simulating the effects of cosmic rays are most often measured in the semi-infinite limit using thick ice targets with the determination of the effective yield per incident ion. In this experimental work we investigated the sputtering yield as a function of ice mantle thickness, exposed to Xe ions at 95 MeV. The ion induced ice phase transformation and the sputtering yield were simultaneously monitored by infrared spectroscopy and mass spectrometry. Results. The sputtering yield is constant above a characteristic ice layer thickness and then starts to decrease below this thickness. An estimate of the typical sputtering depth corresponding to this length can be evaluated by comparing the infinite thickness yield to the column density where the onset of the sputtering yield decrease occurs. In these experiments the measured characteristic 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, deposited energy per unit path length). Considering the experiments on insulators, we expect that the desorption depth dependence varies with Seα, where α ~ 1. 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.

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Thickness dependence of the sputtering yield from solid deuterium by light keV ions

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms ◽

10.1016/0168-583x(90)90176-u ◽

1990 ◽

Vol 48 (1-4) ◽

pp. 530-533 ◽

Cited By ~ 15

Author(s):

B. Stenum ◽

O. Ellegaard ◽

J. Schou ◽

H. Sørensen

Keyword(s):

Thickness Dependence ◽

Solid Deuterium ◽

Sputtering Yield

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Cosmic ray processing of N2-containing interstellar ice analogues at dark cloud conditions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx3302 ◽

2017 ◽

Vol 475 (2) ◽

pp. 1819-1828 ◽

Cited By ~ 4

Author(s):

G Fedoseev ◽

C Scirè ◽

G A Baratta ◽

M E Palumbo

Keyword(s):

Cosmic Ray ◽

Dark Cloud ◽

Interstellar Ice

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Infrared Observations of Interstellar Ices

Symposium - International Astronomical Union ◽

10.1017/s0074180900164745 ◽

2000 ◽

Vol 197 ◽

pp. 135-146 ◽

Cited By ~ 8

Author(s):

P. Ehrenfreund ◽

W. A. Schutte

Keyword(s):

Molecular Clouds ◽

Cosmic Ray ◽

Dust Particles ◽

Early Solar System ◽

Infrared Space Observatory ◽

Infrared Observations ◽

Interstellar Ice ◽

Low Mass ◽

Interstellar Ices ◽

Ice Chemistry

In the recent years revolutionary results concerning the nature of icy dust particles have been obtained with the help of the Infrared Space Observatory (ISO) and ground based observations. To date interstellar ice features of H2O, CO, CO2, CH3OH, CH4, H2CO, OCS and HCOOH as well as other minor species are observed. Interstellar grains act as important catalysts in the interstellar medium. Processes such as UV irradiation, cosmic ray processing and temperature variations determine the grain mantle growth and chemical evolution. ISO has revealed that ice segregation is an important and ubiquitous process in the vicinity of massive protostars and reflects the extensive thermal processing of grains in such environments.In this paper a recent view on the inventory of interstellar ices is presented. Constraints on the reservoirs of oxygen in dense clouds are discussed, taking into account recent measurements of oxygen-bearing species. Large abundances of CO2 and CH3OH in dense molecular clouds provide challenging perspectives to investigate the differences of ice chemistry in the vicinity of high and low-mass protostars. Accurate abundances of ice species and knowledge on the ice distribution in the protostellar regions are an important tool to define the environmental conditions in molecular clouds. A global understanding of interstellar ice chemistry also allows monitoring the incorporation and evolution of volatiles in planetesimals and comets and to reveal processes predominant in the early Solar System.

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Photochemical Evolution of Interstellar/Precometary Organic Material

International Astronomical Union Colloquium ◽

10.1017/s0252921100014585 ◽

1997 ◽

Vol 161 ◽

pp. 23-47 ◽

Cited By ~ 11

Author(s):

Louis J. Allamandola ◽

Max P. Bernstein ◽

Scott A. Sandford

Keyword(s):

Origin Of Life ◽

Building Blocks ◽

Complex Species ◽

Infrared Observations ◽

Interstellar Ice ◽

Polycyclic Aromatic ◽

Ultraviolet Photolysis ◽

The Origin Of Life ◽

Simple Molecules ◽

Complex Organic

AbstractInfrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Since comets are thought to be a major source of the volatiles on the primative earth, their organic inventory is of central importance to questions concerning the origin of life. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, CH4, H2, and probably some NH3and H2CO, as well as more complex species including nitriles, ketones, and esters. The evidence for these, as well as carbonrich materials such as polycyclic aromatic hydrocarbons (PAHs), microdiamonds, and amorphous carbon is briefly reviewed. This is followed by a detailed summary of interstellar/precometary ice photochemical evolution based on laboratory studies of realistic polar ice analogs. Ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(= O)NH2(formamide), CH3C(= O)NH2(acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including polyoxymethylene and related species (POMs), amides, and ketones. The ready formation of these organic species from simple starting mixtures, the ice chemistry that ensues when these ices are mildly warmed, plus the observation that the more complex refractory photoproducts show lipid-like behavior and readily self organize into droplets upon exposure to liquid water suggest that comets may have played an important role in the origin of life.

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Analytical Electron Microscopy of Extraterrestrial Ice Analogs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181737 ◽

1990 ◽

Vol 48 (1) ◽

pp. 594-595

Author(s):

D.F. Blake ◽

LJ. Allamandola ◽

G. Palmer ◽

A. Pohorille

Keyword(s):

Solar System ◽

Analytical Electron Microscopy ◽

Biogenic Elements ◽

Widespread Occurrence ◽

Interstellar Ice ◽

Analytical Electron ◽

History Of ◽

Interstellar Material ◽

Astrophysical Ices ◽

Interstellar Molecular Clouds

The natural history of the biogenic elements H, C, N, O, P and S in the cosmos is of great interest because it is these elements which comprise all life. Material ejected from stars (or pre-existing in the interstellar medium) is thought to condense into diffuse bodies of gravitationally bound gas and dust called cold interstellar molecular clouds. Current theories predict that within these clouds, at temperatures of 10-100° K, gases (primarily H2O, but including CO, CO2, CH3OH, NH3, and others) condense onto submicron silicate grains to form icy grain mantles. This interstellar ice represents the earliest and most primitive association of the biogenic elements. Within these multicomponent icy mantles, pre-biotic organic compounds are formed during exposure to UV radiation. It is thought that icy planetesimals (such as comets) within our solar system contain some pristine interstellar material, including ices, and may have (during the early bombardment of the solar system, ∼4 Ga) carried this material to Earth.Despite the widespread occurrence of astrophysical ices and their importance to pre-biotic organic evolution, few experimental data exist which address the relevant phase equilibria and possible structural states. A knowledge of the petrology of astrophysical ice analogs will allow scientists to more confidently interpret astronomical IR observations. Furthermore, the development and refinement of procedures for analyzing ices and other materials at cryogenic temperatures is critical to the study of materials returned from the proposed Rosetta comet nucleus and Mars sample return missions.

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