采用紫外激光诱导碎片光谱结合DFT/TDDFT计算研究气相中的二价金属离子配合物

This project is focusing on metal dication complexes in the gas phase. Modified experimental techniques for recording spectra in the gas phase are combined with the theoretical methods required to interpret the spectra of metal dication complexes, which reviews how metal ion-molecule might promote chemical reactions. For experimental section, it attempts to identify two aspects of barriers. First, difficulties that might exist to measuring the optical spectra of metal dication complexes using current ion beam technology. Secondly, estimates of photofragment yields based on typical absorption cross sections and the kinetics of fragmentation highlight the difficulties involved in measuring such spectra. A typical experiment will involve measuring either photofragment yield or ion beam depletion as function of laser wavelength. Of the theoretical part, method for calculating spectral transitions in metal complexes is time-dependent density functional theory (TDDFT). It is shown that although TDDFT is for the most part satisfactory, extreme caution should be exercised when investigating the electronic states of open-shell complexes. A theoretical method that predicts the correct ground state geometry of an open-shell complex does not necessarily yield the correct electronically excited states due to multi-electron character and/or spin contamination in the excited state manifold. This project is attempt to develop experimental techniques for recording more accurate “electronic state resolved” or/and "conformation resolved"spectra, which will provide new and more demanding benchmarks for refinement of theoretical methods.

本项目通过高分辨紫外激光诱导碎片光谱，结合计算化学，探索二价金属离子-分子配合物体系的微观结构、激发态性质、离子-分子相互作用规律。实验方面，采用激光电离和超声冷流分子束技术制备二价金属配合物离子。采用四极杆-离子阱串联质谱和波长可调激光器记录光致解离碎片高分辨光谱。计算方面，采用密度泛函(DFT)方法计算二价金属配合物离子的电子基态、微观结构、结合能等。采用时间依赖密度泛函（TDDFT）方法计算电子垂直激发能量和相应振子强度。针对高分辨光谱、TDDFT计算方法、二价金属离子配合物微观结构、化学性质、金属离子与配体分子相互作用规律、自旋污染和非物理激发对TDDFT计算的影响等关键科学问题进行研究。发展了DFT/TDDFT计算理论，将其有效应用于二价金属离子配合物体系微观结构与化学性质的计算和科学分析。

随着实验技术的飞速发展，激光广泛地与质谱仪配合使用研究分子离子的气相结构与理化性质。本项目采用激光诱导碎片光谱方法，结合计算化学，研究了一系列金属离子-分子配合物和分子离子体系的结构、激发态性质、离子-分子反应规律。实验方面，采用激光电离和电喷雾离子源在气相中制备了一系列生物、材料领域热门分子离子，并基于傅里叶变换离子回旋共振质谱仪(FT-ICR-MS)搭建了“超宽波段光解离/激发系统”。该系统可将光解离实验光子拓展到210-3700 nm范围，并一站式获得丰富的光解离质谱、光谱信息。基于该实验平台，采用红外多光子解离(IRMPD)质谱-光谱方法结合理论计算，揭示了氨基酸二聚体气相结构，发现其结构与氨基酸的质子亲和势(PA)和侧链类型的相关性，为全面理解氨基酸分子之间相互作用总结了一般规律。阐明了氨基酸-金属离子配合物的不同构型在能量上的统计规律以及随温度变化的分布规律，为解释复杂的红外多光子解离光谱提供了方便。采用紫外光解离(UVPD)质谱-光谱方法发现了一系列色胺类化合物和硝基苯并咪唑同分异构体分子紫外光解离的波长依赖效应，并通过计算解释了各解离通道的反应机理。首次提出通过改变激光波长控制光解离反应通道的设想，为解释色胺类重要生物分子的生物功能提供了新思路。采用高分辨质谱仪在气相中模拟“伯奇还原反应(birch reduction)”过程，并采用化学计算方法解释了新型无氨催化体系催化伯奇还原反应的机理，推动了计算化学在有机合成中的应用。

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