自由基CH2CO~+的平衡构型和超精细耦合常数的从头计算

ab initio CALCULATIONS OF EQUILIBRIUM GEOMETRY AND HYPERFINE COUPLING CONSTANTS OF CATION CH2CO+

本文用UHF从头计算法处理π自由基CHCO~+,确定基态并研究其平衡构型,电子结构和自旋性质。在自旋性质的计算中,本文使用了由Amos和Snyder提出的方法。通过从UHF波函数中投影去掉最主要的污染自旋成分,得到近似的自旋纯态波函数。由这种波函数得到的关于自旋性质的计算结果比UHF结果大为改善,计算的hfc常数与ESR实验结果符合得相当好。

The equilibrium geometry and hyperfine coupling constants of cation CHCOhave been calculated by the UHF method, within the ab initio MO LCAO SCF approximation. The minimal basis set STO-3G was used. The ground state of this cation is ~2Band it is a π-radical. Compared with its neutral parent molecule, the cation has a markedly long C=C bond (1.4138A) and a slightly short C=O bond (1.1738A), which have been explained by raeans of the analysis of their electronic structures. Based on the theory of Amos and Snyder, annihilation of the quartet contamination in the UHF wavefunetion results in an approximate pure doublet wavefunction. The isotropic hyperfine coupling constants aof cation CHCOwere evaluated from both the spin densities without and with quartet annihilation, which are 49.9G and 16.3G, respectively. The latter one is close to the experimental value (≈20G).