范德华复合物Kr-C2H2的势能面和振转光谱的理论研究

采用[CCSD（T）]-F12方法和aug-cc-pVTZ基组，同时引入中心键函数（3s3p2d1f1g）构建了Kr-C₂H₂体系的高精度四维势能面.在构建势能面时考虑了分子间的振动方式及C₂H₂单体内的ν₁对称伸缩和ν₃反对称伸缩振动.将计算得到的四维势能面在Q₁方向和Q₃方向分别做积分得到C₂H₂单体分别处于振动基态和（ν₁，ν₃）=（1，1）激发态的平均势能面.计算结果表明，这2个平均势能面均存在2个等价的T型全局极小值和2个等价线性极小值.全局极小值的几何构型位于R=0.41 nm，θ=65.6°/114.4°，势阱深度为151.88 cm^-1.对径向部分采用离散变量表象法（DVR），角度部分采用有限基组表象法（FBR），并结合Lanczos循环算法计算了Kr-C₂H₂的振转能级和束缚态.计算结果表明，复合物在（ν₁，ν₃）=（1，1）区域的带心位移为-1.48 cm^-1，表现为红移，与实验值-1.38 cm^-1很接近；计算得到的红外跃迁频率也与实验值相吻合，说明得到的从头算势能面具有高精度.

Theoretical Studies of the Potential Energy Surface and Rovibrational Spectra for Kr-C2H2

A new four-dimensional(4D) potential energy surface(PES) for the Kr-C₂H₂ complex including the Q₁ and Q₃ normal modes for the ν₁ symmetric stretching vibration and ν₃ antisymmetric stretching vibration of C₂H₂ was studied. The PES was calculated at the coupled-cluster singles and doubles with noniterative inclusion of connected triples[CCSD(T)] -F12 level with augmented correlation-consistent polarized-valence quadruplet-zeta(aug-cc-pVTZ) basis set plus the midpoint bond function(3s3p2d1f1g). Two averaged vibrational potential energy surfaces of C₂H₂ at both the vibrational ground and (ν₁,ν₃)=(1,1) excited states were generated from the integration of the four-dimensional potential over the Q₁ and Q₃ coordinates. The averaged potential energy surfaces have two equivalent T-shaped global minima, two equivalent local linear minima as well as three saddle points between the minima. The global minima are located at R=0.41 nm and θ=65.6°/114.4° with a well depth of 151.88 cm^-1. The radial discrete variable representation(DVR)/angular finite basis representation(FBR) method and Lanczos algorithm were employed to calculate the rovibrational energy levels and bound states. The calculated vibrational band origin for the Kr-C₂H₂ complex is red shifted by -1.48 cm^-1, which is closed to the observed value of -1.38 cm^-1. The infrared spectra agree well with the experiment data. The good agreement with the experiment values verifies the high quality of ab initio PESs.