The ground-state equilibrium geometries of the linear carbon chain cations NC2n N+ (n = 1-5) have been investigated by the RCCSD(T) calculations. The studies indicate that these species are found to have single-triple bond alternate structures. The vertical excitation energies of the dipole-allowed 12Πu/g← x2Πg/u transitions, obtained by the CASPT2 approach, are 2.26 eV, 2.09 eV, 1.91 eV, 1.72 eV, and 1.56 eV, respectively, in reasonable agreement with the available experimental values of 2.15 eV, 2.08 eV, 1.89 eV, 1.67 eV, and 1.49 eV.%运用RCCSD(T)的研究了线性阳离子NC2nN+(n=1-5)的基态平衡几何构型.结果表明,这些物种都具有单-叁键交替的结构.采用CASPT2方法,得到了体系的偶极允许跃迁的垂直激发能分别是2.26 eV,2.09 eV,1.91 eV,1.72 eV和1.56 eV,与可利用的实验值(2.15 eV,2.08 eV,1.89 eV,1.67 eV和1.49 eV)符合得很好.
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