State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
J Chem Phys. 2011 Oct 7;135(13):134707. doi: 10.1063/1.3643766.
The chemical enhancement effects in surface-enhanced Raman scattering of p-aminothiophenol (PATP, it is also called p-mercaptoaniline or p-aminobenzenthiol) adsorbed on coinage metal surfaces with single thiol end or trapped into metal-molecule-metal junctions with both thiol and amino groups have been studied by density functional theory (DFT). We focus on the influence of photon-driven charge transfer (PDCT) and chemical bonding interaction (ground-state charge transfer) on the intensity enhancement and frequency shift in the surface Raman spectra of PATP. For comparison, the electronic structures and transitions of free PATP are studied first. The simulated pre-resonance UV Raman spectra illustrate that b(2) modes can be selectively enhanced via vibronic coupling. The fundamentals of all the b(2) modes in the frequency range of 1000 to 1650 cm(-1) are assigned in detail. For PATP adsorbed on coinage metals, the time-dependent-DFT calculations indicate that the low-lying CT excited state arises from the π bonding orbital of molecule to the antibonding s orbital of metallic clusters. Our results further show that the PDCT resonance-like Raman scattering mechanism enhances the totally symmetric vibrational modes and the NH(2) wagging vibration. Finally, the effect of chemical bonding interaction is also investigated. The amino group binding to metals gives a characteristic band of the NH(2) wagging mode with the large blueshift frequency and an intense Raman signal.
通过密度泛函理论（DFT）研究了单端巯基吸附在贵金属表面或同时含有巯基和氨基的金属-分子-金属结中的对氨基苯硫酚（PATP，也称为对巯基苯胺或对氨基苯硫醇）在表面增强拉曼散射中的化学增强效应。我们关注的是光子驱动电荷转移（PDCT）和化学键相互作用（基态电荷转移）对 PATP 表面拉曼光谱中强度增强和频率位移的影响。为了进行比较，首先研究了游离 PATP 的电子结构和跃迁。模拟的预共振紫外拉曼光谱表明，通过振子耦合可以选择性地增强 b(2)模式。详细分配了频率范围在 1000 到 1650 cm(-1) 之间的所有 b(2)模式的基频。对于吸附在贵金属上的 PATP，含时密度泛函理论计算表明，低能 CT 激发态来源于分子的π键轨道与金属团簇的反键 s 轨道之间的相互作用。我们的结果还表明，PDCT 共振拉曼散射机制增强了完全对称的振动模式和 NH(2)摇摆振动。最后，还研究了化学键相互作用的影响。氨基与金属结合会产生 NH(2)摇摆模式的特征带，具有较大的蓝移频率和强烈的拉曼信号。
