Quantum tunneling diffusion of Oxygen atoms on cold surface
Transcript of Quantum tunneling diffusion of Oxygen atoms on cold surface
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Quantum tunneling diffusion of Oxygen atoms on cold surface
Marco Minissale
Université de Cergy-Pontoise
and Observatoire de Paris
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Diffuse Cloud
Dense Cloud
Accretion Disk
Solar System
Diffuse Cloud
Mass Loss - SN
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Grains as catalysts
hν
CR
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SET UP: FORMOLISM
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SET UP: FORMOLISM
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O atoms (and O2 molecules) irradiate the cold sample (300 K)
We have varied the following parameters:
1) Substrate morphology (ASW, porous and compact, crystalline ice, (SiO)
x, graphite)
2) Coverage, from 0.1 to 1 ML
3)Substrate temperature, from 6.5 to 25 K
4)Dissociation rate (from 35% to 80 %)
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Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
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Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
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Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
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Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
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Temperature programmed desorpition (TPD)
Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
(cps
)
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Our Results
Ozone is formed very efficiently
Ozone signal is constant with Temperature (IR spectra)
At high coverage, O2 reaches a steady state, O3 signal increases (experiments as function of
coverage)
O3/O2 ratio increases with Temperature (experiments as function of Temperature)
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How can we explain our results?
O+O → O2
O+O2 → O
3
When?At T
S
(IR spectrum)
How?Eley-Rideal and
Langmuir- Hinsherlwood
(diffusion)
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Diffusion or not diffusion,
what is the difference?
With Without
or
O2 < O
3 O
2 > O
3
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Rate equations model
ER
LH
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k=0
We are here
O3
O2
O
O3
O2
O
k=100
Diffusion
No diffusionDiffusion is important at low coverage
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k ∝ exp(-U0 /T) k ∝ exp(-U
0 /T)/T
Messiah, 1961Cazaux&Tielens, 2004
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Diffusion coefficient of O atoms
Minissale et al, 2012 submitted,
E
Ea
a
Width
Height
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Conclusion
Ediff_Oxygen
≈300K400K in Tielens & Hagen (1982), 900K in Cazaux et al. (2010).
Not far from that of O diffusion in matrix, 240±80 K Benderskii & Wight (1996)
O+O and O2+O barrier < 190 K
Minissale et al. (2012 submitted)
O chemistry competitive with H chemistryin some interstellar environments (dense clouds)
The solid-state astrochemistry of cold regions should be reconsidered
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My Co-workers
Université de Cergy-Pontoise
Francois Dulieu, Emanuele Congiu,
Saoud Baouche, Henda Chaabouni
Audrey Moudens
Università di Catania
Valerio Pirronello
Giulio Manico, Mario Accolla
Kapteyn Astronomical Institute
Stephanie Cazaux
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Thanks
''The Astronomer'', J. Veermer, Paris, Louvre Museem
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k=15 O3
O
O2
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Surface reaction mechanisms
Langmuir Hinshelwood (Diffusion)
Eley Rideal
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Some results : IR spectrum …
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Some results : IR spectrum …
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...and TPD spectrum as function of coverage
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