Hulteen John C, Young Matthew A, Van Duyne Richard P
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
Langmuir. 2006 Dec 5;22(25):10354-64. doi: 10.1021/la0612264.
Electrochemical surface-enhanced hyper-Raman scattering (SEHRS) and surface-enhanced Raman scattering (SERS) of centrosymmetric molecules on Ag film over nanosphere (AgFON) electrodes are presented. The SEHR spectra of trans-1,2-bis(4-pyridyl)ethylene (BPE) at different potentials (vs Ag/AgCl) are presented for the first time, and a reversible potential tuning of the SEHR spectra of BPE is demonstrated. The SEHRS and SERS techniques were used to determine to what extent either site symmetry reduction or field gradient effects dictate the origin of the observed vibrational spectra. It is found that the SEHR and SER spectra for the molecules studied were distinctly different at all frequency regions at a fixed voltage, suggesting that centrosymmetry is largely retained upon adsorption to the AgFON surface and that field gradient effects are negligible. This work also shows that the SEHR spectra clearly depend on potential, whereas the SER spectra are essentially independent of potenial. It is determined that the combination of changes in deltaGads and the presence of coadsorbed counterions are responsible for altering the local symmetry of the adsorbate and only SEHRS has the sensitivity to detect these changes in the surface environment. Thus, SEHRS is a uniquely useful spectroscopic tool that is much more sensitive to the local adsorption environment than is SERS.
本文介绍了在纳米球上的银膜（AgFON）电极上对中心对称分子进行的电化学表面增强超拉曼散射（SEHRS）和表面增强拉曼散射（SERS）。首次展示了反式-1,2-双（4-吡啶基）乙烯（BPE）在不同电位（相对于Ag/AgCl）下的SEHR光谱，并证明了BPE的SEHR光谱的可逆电位调谐。利用SEHRS和SERS技术来确定位点对称性降低或场梯度效应在多大程度上决定了所观察到的振动光谱的起源。发现在固定电压下，所研究分子的SEHR和SER光谱在所有频率区域都明显不同，这表明在吸附到AgFON表面时中心对称性在很大程度上得以保留，且场梯度效应可忽略不计。这项工作还表明，SEHR光谱明显依赖于电位，而SER光谱基本上与电位无关。已确定ΔGads的变化与共吸附抗衡离子的存在共同作用导致吸附质局部对称性的改变，并且只有SEHRS具有检测表面环境中这些变化的灵敏度。因此，SEHRS是一种独特有用的光谱工具，它对局部吸附环境的敏感度远高于SERS。
