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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Surface Residence and Uptake of Methyl Chloride and Methyl Alcohol at the Air/Water Interface Studied by Vibrational Sum Frequency Spectroscopy and Molecular Dynamics
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Surface Residence and Uptake of Methyl Chloride and Methyl Alcohol at the Air/Water Interface Studied by Vibrational Sum Frequency Spectroscopy and Molecular Dynamics

机译：振动和谱和分子动力学研究空气和水界面中甲基氯和甲醇的表面停留和吸收

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摘要

Vibrational sum frequency generation (VSFG) spectroscopy and molecular dynamics (MD) simulations are used to study the surface residence and organization of gas-phase methyl halide and methyl alcohol molecules adsorbed to the air/water interface, while Raman spectroscopy is used to detect the uptake of the gas-phase species into the bulk aqueous phase. Spectroscopy results reveal the presence of methyl alcohol in the bulk and at the surface. Methyl chloride is detected in the bulk, but not at the surface. This indicates that methyl alcohol adsorbs to the aqueous surface in a layer that is ordered, in agreement with previous studies, and is also readily taken up into the bulk aqueous phase, whereas methyl chloride adsorbs, but, while being taken up into the bulk liquid, has lower surface number density and/or forms a more disordered surface layer than methyl alcohol. MD simulations show that methyl halide molecules transition readily between the gas phase and interface, resulting in significantly shorter residence times at the surface for the methyl halides relative to methyl alcohol. Both the geometries that the methyl species adopt at the interface and the interactions between the methyl species and the interfacial water molecules differ for the halides and the alcohol. Complementary studies of butyl species show similar results: butyl alcohol adsorbs to the aqueous surface in a layer that exhibits a certain degree of order corresponding to the chains aligned along the surface normal, while a markedly more disordered surface layer and shorter residence times are observed in MD simulations for the butyl halides as compared to the alcohol. Desorption from the interface was found to be less frequent for the butyl halides than for the methyl halides by MD simulations. Although Raman studies show uptake of the butyl alcohol into the bulk phase, neither Raman studies nor MD simulations provide any evidence for uptake of the butyl halides into the bulk phase. The profound difference in preferred orientations between alkyl halides and alcohols at the aqueous surface, with the halogen atom of the alkyl halides being to a large degree exposed to the vapor phase, is likely to have consequences for chemistry of alkyl halides adsorbed on the surface of atmospheric aerosol particles.
机译：振动总和频率生成（VSFG）光谱和分子动力学（MD）模拟用于研究吸附到空气/水界面的气相卤代甲烷和甲醇分子的表面驻留和组织，而拉曼光谱则用于检测将气相物质吸收到本体水相中。光谱结果表明，在本体中和表面存在甲醇。在大部分中检测到了甲基氯，但在表面未检测到。这表明与先前的研究一致，甲醇以有序的方式吸附到水表面，并且也很容易被吸收到本体水相中，而氯甲烷则被吸收，但是被吸收到本体液体中。具有比甲醇低的表面数密度和/或形成更无序的表面层。 MD模拟表明，卤代甲烷分子在气相和界面之间容易过渡，导致卤代甲烷相对于甲醇在表面的停留时间明显缩短。对于卤化物和醇，甲基物质在界面处采用的几何形状以及甲基物质与界面水分子之间的相互作用都不同。对丁基物质的补充研究显示了相似的结果：丁醇吸附到水表面的层中，该层表现出一定程度的有序性，对应于沿着表面法线排列的链，而在表面上观察到明显更无序的表面层和较短的停留时间。与醇相比的丁基卤化物的MD模拟。通过MD模拟发现丁基卤化物比甲基卤化物从界面上的解吸频率更低。尽管拉曼研究显示丁醇被吸收到本体相中，但拉曼研究或MD模拟都没有提供丁基卤化物被吸收到本体相中的任何证据。烷基卤化物和醇在水表面的优选取向存在巨大差异，而烷基卤化物的卤原子在很大程度上暴露于气相，这可能会对吸附在卤化物表面的烷基卤化物的化学反应产生影响。大气气溶胶颗粒。

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