三氧化硫分子杂化轨道的探讨

Investigation on the Hybrid Orbitals of SO3 Molecule

分别选用量子化学从头算MP2、QCISD、CCSD法和密度泛函B3LYP方法,在6-311++G(3df,3pd)基组水平下对SO.分子的结构进行了优化比较,结果显示QCISD/6-311++G(3df,3pd)条件下的计算结果最优.在此条件下,用自然键轨道理论(NBO)对SO3分子的杂化轨道、杂化方式、离域π键进行了研究.结果表明S原子采取sp2等性杂化,杂化后形成含3对电子的sp2轨道和1个空的3pz轨道,O原子采取sp3不等性杂化.S与O原子之间的σ键为S→O配位键,3个O原子各1对2pz孤对电子与S原子的3pz空轨道形成π64离域π键.Mayer键级显示S=O键级为1.77,呈现明显的双键特性.

The structure of SO3 was optimized and compared by the ab initio methods of MP2, QCISD, CCSD and density function theory（DFT） method of B3 LYP under the basis set of6-311 + +G（3df,3pd）,and the results showed the optimization geometry parameters were optimal through QCISD/6-311 + +G（3df,3pd） method. Based on this method, the hybrid orbitals,hybrid modes and delocalization π bonds of S03 were analyzed through the natural bond orbital（NBO） theory. The results reveal that S adopts sp2 equivalent hybridization and each sp2 orbital is resided by one pair electrons and remaining an unfilled 3pz orbital. O atoms adopt sp3 nonequivalent hybridization. In fact, the σ bonds between S and O atoms are S→O coordination bonds.’The coupling of three 2pz lone pair electrons in O atoms with empty 3pz orbital of S atom forms the π46 delocalization π bond in SO3 molecule. The Mayer bond order is 1. 77 between S and O atoms, which further verifies the obvious double bond property of S=O bonds.