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Reactive adsorption of molecules and radicals on surfaces under plasma exposure

Abstract : Atomic sources, thermal protection for atmospheric re-entry and plasma-catalyst systems for air pollution control are just few examples of applications where interaction between N2/O2 containing plasmas and the surface plays a central role. Mechanisms of heterogeneous processes in plasmas are still barely understood. Unknown conditions on the surface limit the accuracy and predictive capability of the kinetic models. In the first part of this work we investigate adsorption and chemical reactions of O and N atoms on oxide surfaces (silica, Pyrex, TiO2) under plasma exposure. We use tuneable laser absorption spectroscopy, broad-band UV absorption spectroscopy, two-photon absorption laser-induced fluorescence (TALIF) and mass spectrometry to monitor interaction between gas phase species and the surface. Surface analysis is performed using x-ray photoelectron spectroscopy (XPS). It has been shown that stable Oads and Nads atoms are grafted to oxide surfaces under exposure to low pressure (~1 mbar) plasmas in O2 and N2. The coverage and reactivity of adsorbed atoms has been probed by exposing the pretreated surface to stable molecules (NO, C2H2) and radicals (O, N). Using isotopic exchange 15N↔14Nads and 18O↔16Oads under plasma exposure the role of chemisorbed species in surface catalysed recombination of atoms has been investigated. In the second part of this thesis, relaxation of vibrationally excited N2 molecules on catalytic surfaces is studied using infrared (IR) titration technique. Mixtures containing 0.05 - 1% of CO2 (CO, N2O) in N2 at p=1.3 mbar are excited by a single dc discharge pulse. The kinetics of vibrational relaxation of IR tracers during the post-discharge is followed using quantum cascade laser absorption spectroscopy. Due to a very efficient vibrational energy transfer between N2 and CO2 (CO, N2O), excitation of IR tracers is an image of the vibrational excitation of N2. Relaxation measurements have been interpreted in terms of a numerical model of non-equilibrium vibrational kinetics. Probability of N2 vibrational quantum loss has been determined from the best agreement between the experiment and the model.
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Contributor : Daniil Marinov Connect in order to contact the contributor
Submitted on : Friday, November 16, 2012 - 5:42:41 PM
Last modification on : Sunday, June 26, 2022 - 11:57:25 AM
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  • HAL Id : pastel-00752987, version 1


Daniil Marinov. Reactive adsorption of molecules and radicals on surfaces under plasma exposure. Plasma Physics [physics.plasm-ph]. Ecole Polytechnique X, 2012. English. ⟨pastel-00752987⟩



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