密度泛函理论研究银上吸附对巯基吡啶的SERS化学增强效应

发布时间：2018-07-23 08:29

【摘要】：基于密度泛函理论计算和拉曼光谱理论分析,我们研究了对巯基吡啶(4MPY)分子的拉曼光谱和其在银上的表面增强拉曼光谱(SERS),并进一步探讨了SERS与界面吸附结构、异构化、质子化和氢键作用以及低能激发态的关系。首先,我们对两种分子异构体的相对稳定性和拉曼光谱进行了理论分析。在此基础上,进而研究了该分子与不同银簇作用时的拉曼光谱,结果表明,4MPY以巯基硫与银簇作用形成强的Ag S键,导致拉曼光谱的线型不依赖于所选银簇的大小。接着我们考虑了吡啶氮端作用的两种情况。(1)当4MPY-银簇复合物同时以吡啶氮与水簇或水合质子簇形成氢键时,结果表明吡啶环的部分振动频率随氢键和质子化发生蓝移。(2)当考虑吡啶氮与银簇作用时,吡啶环三角畸变振动发生蓝移。上述情况不仅解释了实验观测的振动频率变化,而且表明了化学环境改变对相对拉曼强度的影响。最后,我们计算了当对巯基吡啶分子以单端或双端与银簇作用,在考虑激发光与低能激发态的能量匹配时,拉曼光谱强度与低能激发态的关系。计算结果表明,在双端吸附构型下,与吡啶氮成键的银簇受激发产生电荷转移态,不仅导致吡啶环v_(12)、v_1和v_(8a)振动的拉曼信号增强,而且选择性地增强吡啶环C H面内对称弯曲振动v9a的拉曼信号。
[Abstract]:Based on density functional theory (DFT) calculation and Raman spectrum analysis, we studied the Raman spectra of 4-mercaptopyridine (4MPY) molecules and their surface-enhanced Raman spectra (SERS) on silver, and further discussed the adsorption structure and isomerization of SERS with the interface. The relationship between protonation and hydrogen bonding and low energy excited states. Firstly, the relative stability and Raman spectra of the two isomers are theoretically analyzed. On this basis, the Raman spectra of the molecule interacting with different silver clusters have been studied. The results show that 4MPY formed a strong Ag / S bond by mercaptosulfur and silver clusters, leading to the linear type of Raman spectra independent of the size of the selected silver clusters. Then we consider two cases of nitrogen terminal interaction of pyridine. (1) when 4MPY- silver cluster complex forms hydrogen bond with water cluster or hydrated proton cluster with pyridine nitrogen at the same time, The results show that the partial vibration frequency of pyridine ring is blue shifted with hydrogen bond and protonation. (2) when the interaction of pyridine nitrogen with silver cluster is considered, the triangular distortion vibration of pyridine ring is blue shifted. The above results not only explain the vibration frequency change observed in the experiment, but also indicate the influence of the chemical environment change on the relative Raman intensity. Finally, we calculate the relationship between Raman spectrum intensity and low energy excited states when we consider the energy matching between excited light and low energy excited states when the mercaptopyridine molecules interact with silver clusters at one or two ends. The calculated results show that the charge transfer states of the silver clusters bonded to pyridine nitrogen are generated under the two-terminal adsorption configuration, which not only leads to the enhancement of Raman signals of the virion vibration of the pyridine ring v _ (12) / v _ (1) and v _ (8a). Moreover, the Raman signal of symmetric bending vibration v9a in the plane of pyridine ring C ~ (2 +) H is selectively enhanced.
【作者单位】：厦门大学化学化工学院化学系固体表面国家重点实验室能源材料化学协同创新中心;
【基金】：国家自然科学基金(21273182,21533006,21373172)资助项目~~
【分类号】：O641.1

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