Kerker M, Wang D S, Chew H
Appl Opt. 1980 Dec 15;19(24):4159-74. doi: 10.1364/AO.19.004159.
A model for Raman scattering by a molecule adsorbed at the surface of a spherical particle is articulated by treating the molecule as a classical electric dipole. This follows Moskovits's suggestion [J. Chem. Phys. 69, 4159 (1978)] and the experiments by Creighton et al. [J. Chem. Soc. Faraday Trans. II, 75, 790 (1979)] that such a system may exhibit SERS similar to that at roughened electrode surfaces. The molecule is stimulated by a primary field comprised of the incident and near-scattered fields. Emission consists of the dipole field plus a scattered field, each at the shifted frequency. Addition of feedback terms between the dipole and the particle makes only a negligible contribution to the fields. For pyridine adsorbed at the surface of a silver sphere, the 1010-cm(-1) band is enhanced by ~10(6) if the radius is much less than the wavelengths and the excitation wavelength is ~382 nm, a wavelength for which the relative refractive index of silver is close to m = radical2i. Detailed results are given for the effect upon the angular distribution and the polarization of the Raman emission of particle size, distance from the surface, excitation wavelength, and location of the molecule upon the surface. These results simulate those observed at roughened silver electrodes and suggest that the mechanism of SERS at those electrodes may resemble the electromagnetic mechanism elucidated here. We predict that comparable effects should be observed for fluorescent scattering.
通过将分子视为经典电偶极子，构建了一个关于吸附在球形颗粒表面的分子的拉曼散射模型。这遵循了莫斯科维茨的建议[《化学物理杂志》69, 4159 (1978)]以及克里顿等人的实验[《化学学会法拉第会刊II》75, 790 (1979)]，即这样的系统可能表现出与粗糙电极表面类似的表面增强拉曼散射（SERS）。分子受到由入射场和近散射场组成的初级场的激发。发射由偶极场加上散射场组成，每个场都处于频移后的频率。在偶极子和颗粒之间添加反馈项对场的贡献可忽略不计。对于吸附在银球表面的吡啶，如果半径远小于波长且激发波长约为382 nm（银的相对折射率接近(m = \sqrt{2}i)的波长），则1010 (cm^{-1}) 波段增强约(10^{6}) 倍。给出了颗粒尺寸、距表面距离、激发波长以及分子在表面的位置对拉曼发射的角分布和偏振影响的详细结果。这些结果模拟了在粗糙银电极上观察到的结果，并表明那些电极上的SERS机制可能类似于此处阐明的电磁机制。我们预测荧光散射也应观察到类似的效应。
