基于键极化加和模型及其实验修正方法的超拉曼微观极化率张量元微分的简化方案-C_(2v)对称性

A Simplified Method of Microscopic Polarizability Tensor Differential of Hyper-Raman Spectroscopy Based on Experimental Correction Bond Additivity Model-C_(2v) Symmetry

相干反斯托克斯拉曼光谱(CARS)和相干反斯托克斯超拉曼光谱(CAHRS)等高阶非线性光谱技术已经应用在动力学过程、基因表达谱筛选、高分辨率光谱分析等诸多领域。但因其涉及到的高阶微观极化率张量元数量众多,对其光谱信号进行定量分析非常困难。文献通过理论分析将CARS和CAHRS的微观极化率张量元分解为拉曼微观极化率张量元微分α′i′j′和超拉曼微观极化率张量元微分β′i′j′k′的乘积,将高阶光谱定量分析的困难简化为对低阶光谱的分析。该研究处理了具有C_(2v)对称性分子基团,提出一种利用键极化加和模型及其实验修正的方法简化超拉曼微观极化率张量元微分β′i′j′k′比值的方案。首先利用键极化加和模型方法,在对C_(2v)分子基团局域模式假设的基础上,进行单键的局域模式假设,通过对单键伸缩振动进行简正振动模式的分析,并与单键的偶极矩表达式进行比较,得到单键的超拉曼微观极化率张量元微分β′i′j′k′。在单键β′i′j′k′结果的基础上利用键极化加和模型,对C_(2v)分子基团进行对称性分析,将基团中两个单键伸缩振动的β′i′j′k′耦合,得到C_(2v)分子基团对称振动和反对称振动两种简正振动模式的超拉曼微观极化率张量元微分β′i′j′k′的表达式。在此基础上对C_(2v)分子基团对称振动和反对称振动的β′i′j′k′表达式进行理论推导,结合对应振动模式下不同偏振组合的超拉曼退偏率ρHR-SS和ρHR-AS及HV偏振组合时实验测量的超拉曼光谱强度比,得到超拉曼实验修正的C_(2v)分子基团β′i′j′k′之间的比值。再结合文献中拉曼实验修正的拉曼微观极化率张量元微分α′i′j′之间的比值,即可得到C_(2v)分子基团CARS和CAHRS的微观极化率张量元之间的比例关系,为定量分析高阶非线性光谱信息提供理论基础。

Coherent Anti-Stokes Raman Spectroscopy(CARS)and Coherent Anti-Stokes Hyper-Raman Spectroscopy(CAHRS),as the high-order nonlinear spectroscopy techniques,have been used in many research studies fields such as dynamic process,gene expression spectrum screening,and high-resolution spectroscopy.However,it is difficult to make a quantitative analysis of the spectral signals that involved many high-order micro-polarizability tensors.It has reported that the CARS and CAHRS microscopic hyperpolarizability tensor elements can be decomposed into the product of the differentiation of Raman microscopic polarizability tensorα′i′j′and Hyper-Raman microscopic polarizability tensorβ′i′j′k′which simplifies the difficulty of quantitative analysis of higher-order spectra to the analysis of lower-order spectra.In this paper,we use the bond additivity model(BAM)combined with the experimental correction to address the C_(2v) symmetry molecular and present the simplified scheme for differentiation of Hyper-Raman microscopic polarizability tensor elementsβ′i′j′k′.The differentiation of Hyper-Raman microscopic polarizability tensor elementsβ′i′j′k′of the C_(2v) molecular group is obtained and the expressions ofβ′i′j′k′for symmetric and antisymmetric vibrations of the C_(2v) molecular group also are deduced.According to the experimental measurement of the Hyper-Raman spectral intensity ratio of different polarization combinations of theρHR-SS andρHR-AS,along with HV polarization combinations of the corresponding vibration modes,the ratio betweenβ′i′j′k′of C_(2v) molecular group modified by Hyper-Raman experiment is obtained.Finally,substituting the experimentally corrected differentiation of Raman microscopic polarizability tensor elementsα′i′j′in the literature into the ratio above can obtain the proportional relationship between CARS the microscopic polarizability tensor elements and CAHRS of the C_(2v) molecular group.This method can provide the basis for the quantitative analysis of high-order nonlinear spectral.