采用密度泛函(DFT)B3P86方法优化得到了氨分子的基态稳定构型、红外光谱和拉曼光谱，利用对称匹配耦合簇组态相互作用(SAC/SAC-CI)方法在D95++基组水平上，研究了氨分子基态的激发特征。结果表明，氨分子基态的红外光谱频率和拉曼光谱频率移位是完全相符的，振动的红外光谱和拉曼光谱都是活性的，这与理论分析一致。二维垂直振动ν3,5的红外强度为0.206 km/mol，接近于零，这与氨分子的激发特征有关。基态氨分子是C3V群，激发态则变为D3h群，基态转变成激发态引起对称性增加和能量升高，这种变化不是Jahn-Teller效应，而是电子态与振动态相互作用的结果。从理论上分析了这种电子态与振动态相互作用，理论分析与计算结果一致。

The ground state, infrared spectrum and Raman spectrum of the NH3 molecule are optimized using the density functional theory (DFT) B3P86. The excitation characteristics of NH3 molecule are studied by symmetry-adapted cluster/symmetry-adapted cluster-configuration interaction (SAC/SAC-CI) method with basis set D95++. It is shown that the infrared spectral frequency and Raman spectral frequency of NH3 molecule for the ground displacement are completely consistent; vibratory infrared and Raman spectra are active, which are consistent with the theoretical data. A two-dimensional vertical vibration (ν3,5) of infrared intensity is 0.206 km/mol, almost zero, which is related to the excitation characteristics of NH3 molecules. The C3V group becomes D3h group when NH3 molecules are excited from the ground state. This change causes the increases of symmetry and energy. This kind of change doesn′t result in Jahn-Teller effect, but results in the electronic state and dynamic interaction. The electronic state and dynamic interaction are analysed theoretically. It is found that the theoretical analysis is in agreement with the calculated results.