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首页> 外文期刊>The Journal of Chemical Physics >The origin of soft vibrational modes of alkanes adsorbed on Cu: An experimental and theoretical investigation
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The origin of soft vibrational modes of alkanes adsorbed on Cu: An experimental and theoretical investigation

机译：铜吸附烷烃的软振动模式的起源：实验和理论研究

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摘要

A detailed experimental and theoretical analysis of the metal-induced softening of C-H vibrational modes has been carried out for highly symmetric cyclic saturated hydrocarbons and short chain linear saturated hydrocarbons. The softening of the C-H stretching modes of cyclopropane, cyclohexane, as well as propane and its deuterated analogs adsorbed on Cu(111) was examined experimentally using reflection adsorption infrared spectroscopy and theoretically using ab initio Hartree-Fock and correlated calculations. The investigation showed that molecules are present in two bound orientations for both cyclopropane and propane. The data further reveal taht significant mode softening is associated with only some (not all) of the bound states of these molecules. Soft modes with significant intensity were found to be present for cyclohexane and propane bound on Cu(111) in a planar orientation. A theoretical analysis of the various adsorbed forms of these three types of molecules confirms the surprising experimental observation that cyclopropane has no soft mode that attends its binding on Cu(111). The calculations show that the occurrence of soft modes in the vibrational spectra of cyclohexane (where a broad, intense soft C-H mode exists) and propane (where a weaker, more narrow linewidth soft mode is found) correlates with a small, but still significant degree of charge transfer that governs the alkane-metal interaction. No evidence is found to support a previously proposed theory of a weak hydrogen-bonding interaction that mediates the metal/H-C interaction.
机译：对于高度对称的环状饱和烃和短链线性饱和烃，已经对金属引起的C-H振动模态的软化进行了详细的实验和理论分析。使用反射吸收红外光谱实验性地检测了环丙烷，环己烷以及丙烷及其吸附在Cu（111）上的氘代类似物的C-H拉伸模式的软化，并从头开始使用Hartree-Fock和相关计算从理论上进行了研究。研究表明，对于环丙烷和丙烷，分子以两种结合方向存在。数据进一步表明，显着的模式软化仅与这些分子的某些（不是全部）结合态有关。发现以显着强度的软模式存在于平面取向的环己烷和丙烷结合在Cu（111）上。对这三种类型分子的各种吸附形式的理论分析证实了令人惊讶的实验观察，即环丙烷没有参与其与Cu（111）结合的软模式。计算表明，在环己烷（存在宽而强的软CH模式）和丙烷（存在较弱，更窄的线宽软模式）的振动谱中，软模式的发生与较小但仍显着的程度相关控制烷烃-金属相互作用的电荷转移。没有证据支持先前提出的介导金属/ H-C相互作用的弱氢键相互作用理论。

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