Time-resolved molecular beam mass spectrometry of the initial stage of particle formation in an Ar/He/C2H2 plasma
Time-resolved molecular beam mass spectrometry of the initial stage of particle formation in an Ar/He/C2H2 plasma
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DOI：
10.1021/jp072892w
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发表时间：
2007-10-25
影响因子：
2.9
通讯作者：
von Keudell, A.
中科院分区：
文献类型：
--
作者：
Benedikt, J.;Consoli, A.;von Keudell, A.
中性等离子体化学产物的时间演变的电容耦合等离子体从氩/氦/乙炔是通过分子束质谱与时间分辨率为100毫秒。几个化学途径得到解决。(i)C_2nH_2（n = 2-5）分子的形成是通过以下顺序进行的：在C_2H_2的电子碰撞解离中产生高活性CH自由基，然后C_2H诱导C_2nH_2（n = 1-4）的链聚合。(ii)CnH 4（n = 4，5，6）化合物已经在放电的早期阶段检测到，排除了与CH自由基的聚合反应是其形成的原因。相反，亚乙烯基与乙炔的反应或离子物种的相互中和反应被提出作为它们形成的来源。(iii)表面反应被确定为C8 H6的来源。测得的碳氢化合物分子代表可能的前体负离子形成通过解离电子附着反应，因此可以在粒子成核中发挥至关重要的作用。在将我们的数据与文献中乙炔等离子体的实验和模拟结果进行比较的基础上，我们提出C2 nH 2（n > 1）分子是负离子形成的重要前体。
The temporal evolution of the neutral plasma chemistry products in a capacitively coupled plasma from argon/helium/acetylene is followed via molecular beam mass spectrometry with a time resolution of 100 ms. Several chemistry pathways are resolved. (i) The formation of C2nH2 (n = 2-5) molecules proceeds via the following sequence: the production of highly reactive CH radicals in electron impact dissociation of C2H2 is followed by C2H induced chain polymerization of C2nH2 (n = 1-4). (ii) CnH4 (n = 4, 5, 6) compounds are detected already at an early stage of the discharge excluding polymerization reactions with CH radical being responsible for their formation. Instead, vinylidene reactions with acetylene or mutual neutralization reactions of ionic species are proposed as sources of their formation. (iii) Surface reactions are identified as the source of C8H6. The measured hydrocarbon molecules represents possible precursors for negative ion formation via dissociative electron attachment reactions and can hence play a crucial role in particle nucleation. On the basis of the comparison of our data with available experimental and modeling results for acetylene plasmas in the literature, we propose C2nH2 (n > 1) molecules as important precursors for negative ion formation.