quantum tunneling diffusion of oxygen atoms on cold surface
TRANSCRIPT
Quantum tunneling diffusion of Oxygen atoms on cold surface
Marco Minissale
Université de Cergy-Pontoise
and Observatoire de Paris
Diffuse Cloud
Dense Cloud
Accretion Disk
Solar System
Diffuse Cloud
Mass Loss - SN
Grains as catalysts
hν
CR
SET UP: FORMOLISM
SET UP: FORMOLISM
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 %)
Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
Temperature programmed desorpition (TPD)
Experimental methods
1) Infrared spectroscopy
2) Mass spectroscopy
(cps
)
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)
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)
Diffusion or not diffusion,
what is the difference?
With Without
or
O2 < O
3 O
2 > O
3
Rate equations model
ER
LH
k=0
We are here
O3
O2
O
O3
O2
O
k=100
Diffusion
No diffusionDiffusion is important at low coverage
k ∝ exp(-U0 /T) k ∝ exp(-U
0 /T)/T
Messiah, 1961Cazaux&Tielens, 2004
Diffusion coefficient of O atoms
Minissale et al, 2012 submitted,
E
Ea
a
Width
Height
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
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
Thanks
''The Astronomer'', J. Veermer, Paris, Louvre Museem
k=15 O3
O
O2
Surface reaction mechanisms
Langmuir Hinshelwood (Diffusion)
Eley Rideal
Some results : IR spectrum …
Some results : IR spectrum …
...and TPD spectrum as function of coverage
