Jensen Lasse, Schatz George C
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA. l.
J Phys Chem A. 2006 May 11;110(18):5973-7. doi: 10.1021/jp0610867.
In this work, we present the first calculation of the resonance Raman scattering (RRS) spectrum of rhodamine 6G (R6G) which is a prototype molecule in surface-enhanced Raman scattering (SERS). The calculation is done using a recently developed time-dependent density functional theory (TDDFT) method, which uses a short-time approximation to evaluate the Raman scattering cross section. The normal Raman spectrum calculated with this method is in good agreement with experimental results. The calculated RRS spectrum shows qualitative agreement with SERS results at a wavelength that corresponds to excitation of the S(1) state, but there are significant differences with the measured RRS spectrum at wavelengths that correspond to excitation of the vibronic sideband of S(1). Although the agreement with the experiments is not perfect, the results provide insight into the RRS spectrum of R6G at wavelengths close to the absorption maximum where experiments are hindered due to strong fluorescence. The calculated resonance enhancements are found to be on the order of 10(5). This indicates that a surface enhancement factor of about 10(10) would be required in SERS in order to achieve single-molecule detection of R6G.
在这项工作中，我们首次计算了罗丹明6G（R6G）的共振拉曼散射（RRS）光谱，R6G是表面增强拉曼散射（SERS）中的一个原型分子。计算使用了最近开发的含时密度泛函理论（TDDFT）方法，该方法采用短时近似来评估拉曼散射截面。用此方法计算的常规拉曼光谱与实验结果吻合良好。计算得到的RRS光谱在对应于S(1)态激发的波长处与SERS结果有定性的一致性，但在对应于S(1)振转边带激发的波长处与测量的RRS光谱存在显著差异。尽管与实验的一致性并不完美，但这些结果为接近吸收最大值波长处R6G的RRS光谱提供了见解，在该波长处由于强烈荧光实验受到阻碍。计算得到的共振增强因子约为10(5)。这表明在SERS中要实现R6G的单分子检测，表面增强因子约需10(10)。
