【作者】 陈军宪；

【导师】 谢代前；

【作者基本信息】 四川大学 ， 物理化学， 2004， 硕士

【摘要】 许多重要的物理、化学和生命现象中都包含有大量的 vdW 体系,并且分子间作用力起着决定性作用。对这类体系的从头算研究对于解释和预测分子间振动态的实验结果,提供分子的动力学信息,揭示分子间作用力,有着重要指导意义。Rg-N2O 是典型的具有大角度各向异性的 vdW 体系,其分子间弱相互作用是近年来一直备受关注的研究课题。本文采用高精度的量子化学超分子CCSD(T) 对 Rgn-N2O(Rg=Kr,Xe;n=1,2)型体系弱相互作用进行了较系统的理论研究,所取得的主要研究结果如下: 1. 采用 CCSD(T)方法研究了范德华分子体系 Kr-N2O 复合物的势能面和振转光谱性质. 研究表明, 该势能面有三个极小点,分别对应 T 构型、线性Kr-ONN 和 Kr-NNO 构型。采用离散变量表象和 Lanczos 算法计算了体系的振转能级. 计算结果表明, CCSD(T)势能面支持 62 个振动束缚态。计算得到的Xe-N2O 转动跃迁频率与实验值吻合得较好。 2.采用 CCSD(T)方法研究了范德华分子体系 Xe-N2O 复合物的势能面和振转光谱性质. 研究表明, 该势能面有两个极小点,分别对应 T 构型和线性Xe-ONN 构型。采用离散变量表象和 Lanczos算法计算了体系的振转能级. 计算结果表明, CCSD(T)势能面支持 97 个振动束缚态。计算得到的 Xe-N2O 转动跃迁频率与实验值吻合得较好。 3 . 优化得到三聚体 Kr2N2O 和 Xe2N2O 的两种稳定构型:变形四面体和平面构型。定量获得非加和性三体相互作用的大小。两个体系的两种构型得出相同的结论:体系的三体作用贡献都很小;并且 Xe2N2O 的三体作用比 Kr2N2O的强。这为更大体系比如四聚体的研究奠定了坚实的理论基础。更多还原

【Abstract】 Theoretical studies on the vdW molecular ro-vibrational spectrum from abinitio potential energy surfaces (PESs) could predict and assign the energy levels,calculate the transition intensities, test the ab initio PESs, and provide usefulinformation about vdW molecular dynamics. A detailed understanding of theeffects of many-body nonadditive contributions in intermolecular interactions is ofconsiderable importance for the understanding of macroscopic systems. As Rg-N2Ois one of the most representative vdW systems, which shows a large angularanisotropy, it thus has become a challenging research field in recent years. In this work, we study the PESs and ro-vibrational spectrum of dimersKr-N2O and Xe-N2O, and the three-body nonadditive effects of trimers Kr2-N2Oand Xe2-N2O. For dimers Kr-N2O and Xe-N2O, ab initio PESs are generated usingsupermolecular approach at coupled-cluster (CCSD (T)) level, with an ECP basisset (Xe and Kr) and cc-pVQZ basis sets (N and O). including bond function. Twodimers have a T-shaped global minimum, where Rg atom is close to the O atom.With the ab initio PESs, we calculate the ro-vibrational energy levels usingSinc-DVR method. The CCSD (T) PES supports 62 and 97 vibrational bound statesfor Kr-N2O and Xe-N2O complexes respectively. We also calculated therovibrational levels of two dimers with N2O in its ground and ?3 excited states, andthe calculated rotational transition frequencies are in good agreement withexperimentally observed data. For trimers Kr2-N2O and Xe2-N2O, optimal molecular structures aredetermined by means of second-order M?ller-Plesset (MP2) method. Both trimersare found that the distorted tetrahedral structure (T-trimer) is the global minimum,and the planar structure (L-trimer) is the local minimum. Three-body nonadditiveeffects are performed using CCSD (T) method for both structures. Our calculationsshow that the nonadditivity is quite small percentage, and the nonadditive effects<WP=5>lead to the destabilization for both trimers.更多还原