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Oxygen diffusion and reactivity at low temperature on bare amorphous olivine-type silicate
M Minissale1, E Congiu1, F Dulieu1
1LERMA-LAMAp, Université de Cergy-Pontoise, Observatoire de Paris, ENS, UPMC, UMR 8112 du CNRS, 5 Mail Gay Lussac, 95000 Cergy Pontoise Cedex, France.
The Journal of Chemical Physics
|February 25, 2014
Summary
Oxygen atom mobility on silicate surfaces at low temperatures is crucial for space molecule formation. This study reveals efficient ozone production via enhanced diffusion and quantum tunneling, impacting interstellar chemistry.
Area of Science:
- Astrochemistry
- Surface Science
- Quantum Mechanics
Background:
- The role of oxygen atom mobility at low temperatures in interstellar chemistry is often overlooked.
- Understanding surface reactions on interstellar dust grains is key to explaining molecular complexity in space.
Purpose of the Study:
- To investigate the mobility and reactivity of oxygen atoms on amorphous silicate surfaces at low temperatures (6.5–30 K).
- To determine the mechanisms and efficiency of ozone (O3) formation through O + O and O2 + O reactions.
Main Methods:
- Experimental study using reflection absorption infrared spectroscopy and temperature-programmed desorption.
- Investigation of O2 and O3 formation in a submonolayer regime on silicate surfaces.
- Modeling using rate equations to analyze reaction mechanisms and diffusion rates.
Main Results:
- Efficient ozone formation was observed on silicate surfaces at temperatures as low as 6.5 K.
- The activation barriers for O + O and O2 + O reactions were found to be low (∼150 K/kb).
- Oxygen atom diffusion rates are significantly higher than expected, driven by quantum tunneling and the Langmuir-Hinshelwood mechanism.
Conclusions:
- Fast oxygen atom diffusion, enhanced by quantum tunneling, is critical for low-temperature ozone formation on interstellar dust.
- Neither Eley-Rideal nor hot atom mechanisms alone explain the observed reaction rates; the Langmuir-Hinshelwood mechanism is favored.
- Efficient interstellar O3 formation suggests large reservoirs of oxygen atoms and provides a pathway to explain observed CO2 and H2O abundances.
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