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Resonance Raman Spectroscopic and Theoretical Study of Geometry Distortion of Thiourea in 21A State
Hai-bo Zhang,Yan-ying Zhao,Xu-ming Zheng*
Author NameAffiliationE-mail
Hai-bo Zhang Department of Chemistry, State Key Laboratory of advanced Textiles Materials and Manufacture Tech-nology, MOE, Zhejiang Sci-Tech University, Hangzhou 310018, China  
Yan-ying Zhao Department of Chemistry, State Key Laboratory of advanced Textiles Materials and Manufacture Tech-nology, MOE, Zhejiang Sci-Tech University, Hangzhou 310018, China  
Xu-ming Zheng* Department of Chemistry, State Key Laboratory of advanced Textiles Materials and Manufacture Tech-nology, MOE, Zhejiang Sci-Tech University, Hangzhou 310018, China zxm@zstu.edu.cn 
Abstract:
The A-band resonance Raman spectra of thiourea were obtained in water and acetonitrile so-lution. B3LYP/6-311++G(3df,3pd) and RCIS/6-311++G(3df,3pd) calculations were done to elucidate the ultraviolet electronic transitions, the distorted geometry structure and the saddle point of thiourea in 21A excited state, respectively. The resonance Raman spectra were assigned. The absorption spectrum and resonance Raman intensities were modeled using Heller's time-dependent wavepacket approach to resonance Raman scattering. The re-sults indicate that largest change in the displacement takes place with the C=S stretch mode ν6 (|△|=0.95) and noticeable changes appear in the H5N3H6+H8N4H7 wag ν5 (|△|=0.19), NCN symmetric stretch+C=S stretch+N3H6+H8N4 wag ν4 (|△|=0.18), while the moderate intensities of 2ν15 and 4ν15 are mostly due to the large excited state frequency changes of ν15, but not due to its significant change in the normal mode displacement. The mechanism of the appearance of even overtones of the S=CN2 out of plane deformation is explored. The results indicate that a Franck-Condon region saddle point is the driving force for the quadric phonon mechanism within the standard A-term of resonance Raman scattering, which leads to the pyramidalization of the carbon center and the geometry distortion of thiourea molecule in 21A excited state.
Key words:  Thiourea, Excited state structural dynamics, Resonance Raman, Time-dependent wavepacket approach, Density functional theory
FundProject:
硫脲21A激发态扭曲几何结构的共振拉曼光谱和理论研究
张海波,赵彦英,郑旭明*
摘要:
获得了硫脲在水和乙腈溶液中A吸收带的共振拉曼光谱,通过B3LYP/6-311++G(3df,3pd)和RCIS/6-311++G(3df,3pd)分别对硫脲的电子跃迁和21A 激发态鞍点结构进行了研究.对共振拉曼光谱进行了归属,并通过含时波包理论对吸收光谱和共振拉曼光谱进行拟合,结果表明硫脲动态结构特征主要沿着:C=S伸缩振动ν6(|△|=0.95)、H5N3H6+H8N4H7弯曲振动ν5(|△|=0.19)、NCN对称伸缩振动+C=S伸缩振动+N3H6+H8N4弯曲振动ν4(|△|=0.18).ν15倍频2ν15和4ν15强度主要归因于ν15激发态频率的改变而不是简正模位移量的变化.对S=CN2面外变形振动ν15倍频出现的机理进行了探究,结果表明Franck-Condon区域势能面鞍点是标准A项共振拉曼散射里的二次声子机制的驱动力,导致碳原子中心的锥形化,并使硫脲在21A激发态发生几何结构扭曲.
关键词:  硫脲,激发态结构动力学,共振拉曼光谱,含时波包理论,密度泛泛理论
DOI:10.1088/1674-0068/25/01/1-10
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