Initial Polymerization Reactions in Particle-Forming Ar/He/C2H2 Plasmas Studied via Quantitative Mass Spectrometry

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• 作者：A. Consoli ; J. Benedikt ; A. von Keudell
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：November 13, 2008
• 年：2008
• 卷：112
• 期：45
• 页码：11319-11329
• 全文大小：363K
• 年卷期：v.112,no.45(November 13, 2008)
• ISSN：1520-5215

文摘

The initial polymerization reactions in particle forming Ar/He/C₂H₂ plasmas are studied using molecular beam mass spectrometry (MBMS). The measured mass spectra are disentangled and quantified with the help of Bayesian probability theory. This approach uses the measured mass spectra and the cracking patterns (CPs) of the species that are formed in the plasma as the main input parameter. The CPs are either taken from calibration measurements or the NIST database or estimated based on a comparison to CPs of similar molecules. These estimated CPs are then modified by Bayesian analysis to fit the measured data. The CPs of C₆H₂, C₆H₄, and C₈H₂, which are not available in the NIST database, are determined in this way and can serve as good estimation until precise data is published. The temporal evolution after plasma ignition of the densities of in total 22 species (hydrocarbons, noble gases, and impurities) are quantified and expressed as partial pressures. The most abundant products in our plasma are C₄H₂ and C₆H₂ molecules with maximum partial pressures of 0.1 and 0.013 Pa, respectively. Our quantitative data can be used to validate plasma chemistry models. First comparison is made to a plasma chemistry model of similar C₂H₂ plasma already available in the literature. The comparison indicates that dissociative electron attachment to C_2nH₂ (n > 1) molecules is a dominant source of negative ions in C₂H₂ plasmas. Additionally, the C₂H₄ has been identified as a precursor for C_nH₄ molecules.