Zhou Yanzi, Xie Daiqian, Zhang Dong Hui
Laboratory of Mesoscopic Chemistry, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093, China.
J Chem Phys. 2006 Apr 14;124(14):144317. doi: 10.1063/1.2189227.
We report a three-dimensional ab initio potential energy surface for He-N(2)O using a supermolecular method at the coupled-cluster singles and doubles with noniterative inclusion of connected triple level. Besides the intermolecular stretching and bending modes, we included the Q(3) normal mode for the nu(3) antisymmetric stretching vibration of N(2)O molecule in order to simulate the observed infrared spectra in the nu(3) region of N(2)O, especially to explain the frequency shift of the band origin in the infrared spectra. The harmonic oscillator approximation is used for the potential curve of the Q(3) mode of the isolate N(2)O molecule. The intermolecular potential energy surfaces are calculated for five potential-optimized discrete variable representation grid points of the Q(3) mode. The three-dimensional discrete variable representation method was employed to calculate the rovibrational states without separating the inter- and intramolecular nuclear motions. The calculated transition frequencies and line intensities of the rotational transitions in the nu(3) region of N(2)O for the van der Waals ground vibrational state are in good agreement with the observed infrared spectra. The calculated band shifts are found to be 0.1704 and 0.1551 cm(-1) for (4)He-N(2)O and (3)He-N(2)O, respectively, which agree well with the observed values of 0.2532 and 0.2170 cm(-1).
我们使用超分子方法，在耦合簇单双激发并非迭代包含连接三重激发水平的情况下，报道了He-N₂O的三维从头算势能面。除了分子间的伸缩和弯曲模式外，我们还纳入了N₂O分子ν₃反对称伸缩振动的Q₃简正模式，以模拟在N₂O的ν₃区域观察到的红外光谱，特别是解释红外光谱中谱带起源的频率位移。对于孤立N₂O分子的Q₃模式的势能曲线，采用了简谐振子近似。针对Q₃模式的五个势能优化离散变量表示网格点计算了分子间势能面。采用三维离散变量表示方法计算振转态，而不分离分子间和分子内的核运动。对于范德华基振动态，计算得到的N₂O的ν₃区域转动跃迁的跃迁频率和谱线强度与观察到的红外光谱吻合良好。对于⁴He-N₂O和³He-N₂O，计算得到的谱带位移分别为0.1704和0.1551 cm⁻¹，与观察值0.2532和0.2170 cm⁻¹吻合良好。
