Janesko Benjamin G, Scuseria Gustavo E
Department of Chemistry, Rice University, Houston, TX 77005-1892, USA.
J Chem Phys. 2006 Sep 28;125(12):124704. doi: 10.1063/1.2345368.
We present a model for electromagnetic enhancements in surface enhanced Raman optical activity (SEROA) spectroscopy. The model extends previous treatments of SEROA to substrates, such as metal nanoparticles in solution, that are orientationally averaged with respect to the laboratory frame. Our theoretical treatment combines analytical expressions for unenhanced Raman optical activity with molecular polarizability tensors that are dressed by the substrate's electromagnetic enhancements. We evaluate enhancements from model substrates to determine preliminary scaling laws and selection rules for SEROA. We find that dipolar substrates enhance Raman optical activity (ROA) scattering less than Raman scattering. Evanescent gradient contributions to orientationally averaged ROA scale to first or higher orders in the gradient of the incident plane-wave field. These evanescent gradient contributions may be large for substrates with quadrupolar responses to the plane-wave field gradient. Some substrates may also show a ROA contribution that depends only on the molecular electric dipole-electric dipole polarizability. These conclusions are illustrated via numerical calculations of surface enhanced Raman and ROA spectra from (R)-(-)-bromochlorofluoromethane on various model substrates.
我们提出了一种用于表面增强拉曼光学活性（SEROA）光谱中电磁增强的模型。该模型将先前对SEROA的处理扩展到了诸如溶液中的金属纳米颗粒等底物，这些底物相对于实验室坐标系是取向平均的。我们的理论处理将未增强的拉曼光学活性的解析表达式与由底物的电磁增强修饰的分子极化率张量相结合。我们评估了来自模型底物的增强，以确定SEROA的初步缩放定律和选择规则。我们发现偶极底物对拉曼光学活性（ROA）散射的增强小于对拉曼散射的增强。倏逝梯度对取向平均ROA的贡献在入射平面波场的梯度中按一阶或更高阶缩放。对于对平面波场梯度具有四极响应的底物，这些倏逝梯度贡献可能很大。一些底物还可能表现出仅取决于分子电偶极 - 电偶极极化率的ROA贡献。通过对（R）-（-）-溴氯氟甲烷在各种模型底物上的表面增强拉曼光谱和ROA光谱进行数值计算来说明这些结论。
