Dynamics of the reaction of O(3P) atoms with alkylthiol self-assembled monolayers.
Dynamics of the reaction of O(3P) atoms with alkylthiol self-assembled monolayers.
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O(3P) 原子与烷基硫醇自组装单层反应的动力学。
DOI：
10.1021/jp8109868
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
K. McKendrick
中科院分区：
文献类型：
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作者：
C. Waring;P. Bagot;Minna T. Räisänen;M. Costen;K. McKendrick
研究了O（（3）P）原子与烷基硫醇自组装膜（SAMs）的反应动力学。超高温O（（3）P）原子，具有相当宽的实验室坐标系动能分布（平均值= 16 kJ mol（-1），fwhm = 26 kJ mol（-1）），是由在SAM表面上方低压下引入的NO（2）在355 nm处光解产生的。通过激光诱导荧光检测新生OH v' = 0产物。研究了两种不同烷基链长C（6）和C（18）的自组装膜。SAM层的存在，并在我们的实验条件下，在相关的测量期间，其鲁棒性，证实了扫描隧道显微镜（STM）。使用全氘代C（6）D（13）-SAM样品验证SAM表面的反应为羟基自由基的真实来源。OH的外观轮廓作为光解探针延迟的函数，并在其峰值处的旋转状态分布，与液体角鲨烷（C（30）H（62），2，6，10，15，19，23-六甲基二十四烷）的那些进行了比较。发现自组装膜和角鲨烷的反应性相当。我们的结论是，O（（3）P）原子必须能够访问更活跃的仲氢原子沿着的烷基链的自组装膜。我们发现两个SAM链长之间的反应性或产物能量处置没有明显的差异。两者都以相对较高的速度产生相当大部分的OH，这一定是由直接的脉冲反应引起的。还有一个较慢的组件，与热，捕获解吸机制的速度一致。该组分的比例对于自组装膜似乎低于角鲨烷。这将与SAM表面在分子尺度上的预期更大光滑度相容。我们发现很少的证据显着的旋转激发的OH产品，虽然任何平移和旋转能量释放之间的相关性的细节需要进一步调查。我们比较了我们的结果与有限的可用的先验理论模型的O（（3）P）+ SAM系统。
We have studied the dynamics of the reactions of O((3)P) atoms with alkylthiol self-assembled monolayers (SAMs). Superthermal O((3)P) atoms, with a fairly broad distribution of laboratory-frame kinetic energies (mean = 16 kJ mol(-1), fwhm = 26 kJ mol(-1)), were generated by 355 nm photolysis of NO(2) introduced at a low pressure above the SAM surface. Nascent OH v' = 0 products were detected by laser-induced fluorescence. SAMs of two different alkyl chain lengths, C(6) and C(18), were studied. The existence of SAM layers, and their robustness under our experimental conditions during the relevant measurement period, were confirmed by scanning-tunneling microscopy (STM). Reaction at the SAM surface was verified as the authentic source of the hydroxyl radicals using a perdeuterated C(6)D(13)-SAM sample. The OH appearance profiles as a function of photolysis-probe delay, and the rotational-state distributions at their peaks, were compared with those of liquid squalane (C(30)H(62), 2,6,10,15,19,23-hexamethyltetracosane). The reactivity of the SAMs and of squalane was found to be comparable. We conclude that the O((3)P) atoms must be able to access the more reactive secondary hydrogen atoms along the alkyl chains of the SAMs. We find no perceptible differences in reactivity or product energy disposal between the two SAM chain lengths. Both produce a substantial fraction of the OH with relatively high velocities, which must result from direct, impulsive reaction. There is also a slower component, with velocities consistent with a thermal, trapping-desorption mechanism. The proportion of this component appears to be lower for SAMs than for squalane. This would be compatible with the expected greater smoothness of the SAM surface at the molecular scale. We find little evidence for significant rotational excitation of the OH products, although the details of any correlation between translational and rotational energy release require further investigation. We compare our results with the limited available prior theoretical modeling of O((3)P) + SAM systems.