Reactions of fluorine atoms with self-assembled monolayers of alkanethiolates
Reactions of fluorine atoms with self-assembled monolayers of alkanethiolates
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氟原子与链烷硫醇盐自组装单层的反应
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
R. Graham
中科院分区：
文献类型：
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作者：
G. N. Robinson;A. Freedman;R. Graham
在305K下，在超高真空环境中，金表面自组装单分子膜(SAM)被暴露在原子束中。单分子膜的原位X射线光电子能谱表明，进入的氟原子穿透紧密堆积的链，反应形成单氟亚甲基和二氟亚甲基，而不会对金衬底进行氟化，碳原子很少或没有损失。与分子氟无反应。在每个碳链累积剂量为∼680个氟原子后，20个链碳原子中大约有7个已经氟化。氟化很可能是通过一种机制发生的，在这种机制中，进入的氟原子提取链亚甲基氢原子，为随后的氟原子加成创造一个自由基位。氟原子吸收的动力学模拟表明，抽氢和加成的截面比气相的相应截面略小，这表明空间位阻限制了总的氟原子吸收。两种终止方式不同的导弹的反应性没有明显差异。结果表明，C20-烷硫醇自组装膜是一种有效的防止气相反应物氧化金属表面的涂层。
Self-assembled monolayers (SAMs) of methyl- and vinyl-terminated n-alkanethiolates on gold have been exposed at 305 K to beams of atomic fluorine in an ultrahigh-vacuum environment. In situ X-ray photoelectron spectroscopy of the resulting monolayers indicates that the incoming fluorine atoms penetrate the close-packed chains and react to form mono- and difluorinated methylene groups without fluorination of the gold substrate and with little or no loss of carbon atoms. No reaction was observed with molecular fluorine. After a cumulative dose of ∼680 fluorine atoms per carbon chain, approximately seven of the 20 chain carbon atoms have been fluorinated. The fluorination most likely occurs by a mechanism in which an incoming fluorine atom abstracts a chain methylene hydrogen atom, creating a radical site for subsequent addition of fluorine atom. Kinetic modeling of the fluorine atom uptake indicates that the cross sections for hydrogen abstraction and fluorine addition are somewhat smaller than their gas phase counterparts, suggesting that steric crowding limits the overall fluorine atom uptake. No significant differences between the reactivities of the two differently terminated SAMs could be discerned. Our results indicate that C 20 -alkanethiolate SAMs are effective coatings for preventing oxidation of metallic surfaces by gas phase reactants.