scholarly journals Efficient diffusive mechanisms of O atoms at very low temperatures on surfaces of astrophysical interest

2014 ◽  
Vol 168 ◽  
pp. 151-166 ◽  
Author(s):  
Emanuele Congiu ◽  
Marco Minissale ◽  
Saoud Baouche ◽  
Henda Chaabouni ◽  
Audrey Moudens ◽  
...  
Keyword(s):  
Low Temperatures ◽  
Interstellar Dust ◽  
Oxidation Reactions ◽  
Weakly Bound ◽  
Water Ice ◽  
Atom Diffusion ◽  
Interstellar Dust Grains ◽  
Diffusion Rates ◽  
Experimental Values ◽  
Simple Reduction

At the low temperatures of interstellar dust grains, it is well established that surface chemistry proceeds via diffusive mechanisms of H atoms weakly bound (physisorbed) to the surface. Until recently, however, it was unknown whether atoms heavier than hydrogen could diffuse rapidly enough on interstellar grains to react with other accreted species. In addition, models still require simple reduction as well as oxidation reactions to occur on grains to explain the abundances of various molecules. In this paper we investigate O-atom diffusion and reactivity on a variety of astrophysically relevant surfaces (water ice of three different morphologies, silicate, and graphite) in the 6.5–25 K temperature range. Experimental values were used to derive a diffusion law that emphasizes that O atoms diffuse by quantum mechanical tunnelling at temperatures as low as 6.5 K. The rates of diffusion on each surface, based on modelling results, were calculated and an empirical law is given as a function of the surface temperature. The relative diffusion rates are kH2Oice > ksil > kgraph ≫ kexpected. The implications of efficient O-atom diffusion over astrophysically relevant time-scales are discussed. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O or OH) at a faster rate than that of accretion. Also, as dense clouds mature, H2 becomes far more abundant than H and the O : H ratio grows, and the reactivity of O atoms on grains is such that O becomes one of the dominant reactive partners together with H.

scholarly journals Theoretical Simulations of Grain-Surface Processes

2000 ◽  
Vol 197 ◽  
pp. 293-302
Author(s):  
Junko Takahashi
Keyword(s):  
Interstellar Dust ◽  
Realistic Model ◽  
Surface Processes ◽  
Dust Grains ◽  
Water Ice ◽  
Whole Process ◽  
Interstellar Dust Grains ◽  
Desorption Mechanism ◽  
Grain Surface ◽  
Theoretical Simulations

Recent advances in theoretical simulations of grain-surface processes are reviewed. Classical molecular dynamics (MD) computer simulations were performed to investigate the whole process of H2 formation on icy mantles of interstellar dust grains within a single model. Amorphous water ice slabs were generated at 10 K and 70 K as a realistic model surface of dust grains, and then two incident H atoms were successively thrown onto the surface to reproduce the H2 formation process via H + H → H2 on the dust surface. The following fundamental processes were studied in detail; 1) the sticking of H atom onto the grain surface, 2) the diffusion of H atom on the surface, 3) the reaction of two H atoms on the surface, 4) the ejection of H2 from the surface. Then, the formation pumping mechanism of H2 and the chemical desorption mechanism of frozen CO molecules in the vicinity of H2 forming sites on dust grains were also studied.

Behaviour of radicals on interstellar dust analogues

2019 ◽  
Vol 15 (S350) ◽  
pp. 116-122
Author(s):  
Naoki Watanabe
Keyword(s):  
Interstellar Dust ◽  
Surface Reactions ◽  
Multiphoton Ionization ◽  
Complex Molecules ◽  
Water Ice ◽  
Chemical Models ◽  
Interstellar Dust Grains ◽  
Ionization Methods ◽  
And Diffusion ◽  
Dust Surface

AbstractSurface reactions of radicals play important roles in the formation of complex molecules on interstellar dust grains. Under interstellar conditions, because the coverage of adsorbates on dust is significantly low, surface reactions are often limited by precedent processes, namely, the adsorption and diffusion of reactants. Therefore, to appropriately incorporate dust surface reactions into chemical models, information on the adsorption and diffusion of radicals is crucial. However, it is not easy to follow the behaviour of radicals on surfaces by conventional experimental methods. To monitor radicals on interstellar dust analogues, we have recently succeeded in applying a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods. In this paper, we briefly review our recent experiments for clarifying radical behaviour on water ice, pure solid CO and diamond-like carbon.

Temperature fluctuations in interstellar dust grains

1979 ◽  
Vol 65 (1) ◽  
pp. 155-166 ◽  
Author(s):  
Per A. Aannestad ◽  
Scott J. Kenyon
Keyword(s):  
Interstellar Dust ◽  
Temperature Fluctuations ◽  
Dust Grains ◽  
Interstellar Dust Grains

PREPARATION OF ANTIMONY-PLATINUM SURFACE ALLOY ELECTRODE BY ATOM DIFFUSION IN THE SOLID PHASE

2006 ◽  
Vol 20 (25n27) ◽  
pp. 3999-4004
Author(s):  
HIROSHI MATSUI ◽  
KAZUFUMI WATANABE
Keyword(s):  
Diffraction Pattern ◽  
Low Temperatures ◽  
Solid Phase ◽  
Electrochemical Measurement ◽  
X Ray Diffraction ◽  
Platinum Surface ◽  
X Ray ◽  
Atom Diffusion ◽  
Heat Treated ◽  
Titanium Substrates

Antimony-platinum bilayers were prepared on titanium substrates by the two-step electrodeposition in the usual baths, and then surface alloys were formed by the atom diffusion in the solid phase. The simple antimony layer was little influenced by the substrate in both the measurements of X-ray diffraction and the i - E characteristic in a sulfuric acid solution. Regarding the bilayers, the catalytic activity in hydrogen evolution reaction was very sensitive to the presence of platinum, while the hydrogen adsorbability was quite insensitive. An interaction between antimony and platinum was confirmed by the appearance of a new dissolution wave in the electrochemical measurement and the occurrence of a new diffraction in the X-ray diffraction pattern after the heat-treatment of about 400°C. Although the new diffraction disagreed with any of the reported alloys, clear diffraction pattern of PtSb 2 alloy was observed, when the bilayers were heat-treated at about 600°C for one hour. Considering the penetration depth of X-ray, the alloying of antimony and platinum seems to occur also at low temperatures at least at the top surface.

scholarly journals CO2formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel

2013 ◽  
Vol 559 ◽  
pp. A49 ◽  
Author(s):  
M. Minissale ◽  
E. Congiu ◽  
G. Manicò ◽  
V. Pirronello ◽  
F. Dulieu
Keyword(s):  
Interstellar Dust ◽  
Dust Grains ◽  
Interstellar Dust Grains

scholarly journals The formation of the building blocks of peptides on interstellar dust grains

2019 ◽  
Vol 15 (S350) ◽  
pp. 216-219
Author(s):  
N. F. W. Ligterink ◽  
J. Terwisscha van Scheltinga ◽  
V. Kofman ◽  
V. Taquet ◽  
S. Cazaux ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Reaction Network ◽  
Building Blocks ◽  
Dust Grains ◽  
Reaction Products ◽  
Experimental Conditions ◽  
Interstellar Dust Grains ◽  
Temperature Programmed ◽  
Life On Earth ◽  
Emergence Of Life

AbstractThe emergence of life on Earth may have its origin in organic molecules formed in the interstellar medium. Molecules with amide and isocyanate groups resemble structures found in peptides and nucleobases and are necessary for their formation. Their formation is expected to take place in the solid state, on icy dust grains, and is studied here by far-UV irradiating a CH4:HNCO mixture at 20 K in the laboratory. Reaction products are detected by means of infrared spectroscopy and temperature programmed desorption - mass spectrometry. Various simple amides and isocyanates are formed, showing the importance of ice chemistry for their interstellar formation. Constrained by experimental conditions, a reaction network is derived, showing possible formation pathways of these species under interstellar conditions.

scholarly journals Conversion of HI Molecule to H2 Molecule

2015 ◽  
Vol 5 ◽  
pp. 82-86
Author(s):  
Arjun Kumar Gautam
Keyword(s):  
Historical Development ◽  
Molecular Hydrogen ◽  
Interstellar Dust ◽  
Formation Rate ◽  
Theoretical Models ◽  
Molecular Gas ◽  
Astronomical Data ◽  
Interstellar Dust Grains ◽  
H2 Formation ◽  
H2 Molecule

In this article I review the historical development and conversion of atomic to molecular hydrogen in astronomy. I discuss how the discoveries of HI and H2 in the interstellar medium were followed by studies of the relative abundance of atomic and molecular gas. Understanding this led to increasingly sophisticated theoretical models for H2 formation on the surface of interstellar dust grains. In certain situations, astronomical data can be used to constrain the formation rate of H2 molecules. Finally, I use the reasonably well-determined chemistry of HI and H2 to determine the overall timescale of star formation. The Himalayan Physics Vol. 5, No. 5, Nov. 2014 Page: 82-86

scholarly journals LIFECYCLE OF THE INTERSTELLAR DUST GRAINS IN OUR GALAXY VIEWED WITH AKARI/MIR ALL-SKY SURVEY

2012 ◽  
Vol 27 (4) ◽  
pp. 117-122
Author(s):  
D. Ishihara ◽  
H. Kaneda ◽  
A. Mouri ◽  
T. Kondo ◽  
S. Suzuki ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Dust Grains ◽  
Interstellar Dust Grains ◽  
Sky Survey
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