CASPT2 studies on the electronic spectra of linear heteroatom-containing carbon chain anions C₄O⁻, C₄S⁻ and C₄Se⁻

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• 作者：Wenpeng Wu ; Jinglai Zhang and Zexing Cao
• 刊名：Journal of Molecular Structure: THEOCHEM
• 出版年：2006
• 出版时间：15 June 2006
• 年：2006
• 卷：765
• 期：1-3
• 页码：137-141
• 全文大小：117 K

文摘

Structures of linear valence isoelectronic carbon chain anions C₄O⁻, C₄S⁻ and C₄Se⁻ in their ground states have been investigated by density functional theory (DFT-B3LYP) and coupled cluster with single–double substitution (CCSD) approach. Complete-active-space-self-consistent-field (CASSCF) method has been used for geometry optimization of selected low-lying states. The vertical excitation energies from the ground state to selected low-lying excited states have been carried out with complete-active-space-second-order-perturbation-theory (CASPT2). All of them have a similar set of excited states. In comparison with available experimental observations, the predicted excitation energies for the allowed transitions have an accuracy of no more than 0.12 eV. Moreover, the calculations here confirm that the previous assignments of the observed electronic absorption bands of C₄O⁻ and C₄S⁻ are reliable. The excitation energies of 2²Π←X²Π and 1²Σ⁻←X²Π transitions in C₄Se⁻ are predicted to be 2.09 and 3.90 eV, with oscillator strengths 0.1941 and 0.0105, respectively, which may be observed in future experiment. CASPT2 also evaluated the vertical electron detachment energies for C₄O⁻, C₄S⁻ and C₄Se⁻ to be 3.55, 3.40 and 3.40 eV, respectively.