Si_2Cl_6分子的内旋转能垒和振动基频的理论研究

Computational Studies of the Structure and Vibrational Spectra of Hexachlorodisilane

用从头算方法HF/6-31G^(**)和密度泛函方法B3LYP/6-31G^(**),对Si_2Cl_6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si_2Cl_6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.184kJ/mol吻合得较好.对Si_2Cl_6分子的振动基频进行计算.用HF/6-31G^(**)SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^(-1),用B3LYP/6-31G^(**)未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^(-1).该密度泛函方法(B3LYP/6-31G^(**))的理论计算值比用HF/6-31G^(**)标度后的SQM力场计算的频率与实验值(除Si-Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si—Si键扭转振动基频的预测值.

Ab initio restricted Hartree-Fock (RHF) calculations and density functional theory calculations using B3' exchange and Lee-Yang-Parr's correlation functionals (B3LYP) with 6-31G* * basis set were carried out to study and optimize equilibrium structure and to obtain energies of two rotational conformers and fundamental vibrational frequencies in the equilibrium structure for Si2Cl6. The optimized structural parameters are in good agreement with experimental results. The calculated potential barriers to internal rotation are 8.786 and 6.694kJ/mol determined from the calculations using HF/6 -31G* * and B3LYP/6 - 31G* * methods, respectively. The B3LYP/6 - 31G* * value is in good agreement with the observed value of 4.1868kJ/mol. Infrared intensities, Raman activities and vibrational frequencies are reported for Si2Cl6 under D3d symmetry. A normal coordinate analysis employing scaled ah initio ( HF/6 - 31G * * ) force field has been carried out. The average error between the predicted fundamentals utilizing scaled HF/6 - 31G* * force field with a scale factor of 0. 9 pertinent to all vibrational modes and observed fundamental vibrational frequencies is 7.3cm-1. Moreover, a mean absolute deviation between fundamentals obtained from B3LYP/6-31G** calculations using unrefined SQM force field and the observed frequencies is 6.0cm-1.