Si_2Br_6的分子振动光谱的理论研究

Studies on Vibrational Spectra and Normal Coordinate Analysis of Hexabrominedisilane

用量化从头算方法（ＨＦ／６－３１Ｇ＊）和密度泛函方法（Ｂ３ＬＹＰ／６－３１Ｇ＊）以６－３１Ｇ标准基组加一个极化函数，对Ｓｉ２Ｂｒ６分子的平衡几何构型和振动频率分别进行优化和计算，优化的结果与实验结果吻合得较好．按照Ｐｕｌａｙ的建议对ＨＦ／６－３１Ｇ＊水平上所计算的谐性力场进行标度（标度因子取０．９）．用ＨＦ／６－３１Ｇ＊ＳＱＭ力场所计算的基频预测值和实验值的平均误差为９．４ｃｍ－１，最大误差为２３．６ｃｍ－１；用Ｂ３ＬＹＰ／６－３１Ｇ＊未标度力场所计算的基频预测值和实验值的平均误差为８．６ｃｍ－１，最大误差为１６．６ｃｍ－１；用该密度泛函方法所计算的基频预测值比用ＨＦ／６－３１Ｇ＊的标度后的ＳＱＭ力场所计算的基频预测值和实验值（除Ｓｉ—Ｓｉ键扭转振动基频之外的１１条振动基频）吻合得更好．ＨＦ／６－３１Ｇ＊和Ｂ３ＬＹＰ／６－３１Ｇ＊计算给出Ｓｉ—Ｓｉ键扭转振动基频的预测值分别为１４ｃｍ－１和９ｃｍ－１．

The optimized geometries, infrared intensities, Raman activities and fundamental vibrational frequencies and PEDs are reported for D3d symmetry of Si2Br6 utilizing HF/631G* and B3LYP/631G* method. The predicted value of SiSi torsional vibrational frequency is given. A normal coordinate analysis has been carried out and HF force field is scaled with scale factor of 0.9 pertinent to all vibrational modes. The average error between the predicted frequencies obtained from HF/631G* SQM force field and the observed fundamental vibrational frequencies is 94 cm-1; the average error between the predicted value from unrefined DFT force field and the observed result is 86 cm-1. The fundamental vibrational frequencies obtained from DFT calculation with B3LYP/631G* are in good agreement with the experimental results.