七氟异丁腈负离子结构与反应活性的理论研究

新型环保绝缘气体七氟异丁腈(C4)在高压输电应用中备受关注. 本文采用多种高精度量子化学理论方法研究了C4吸附电子后形成C4^-负离子的结构、 光谱、 寿命以及与CO₂的反应机理和动力学. 结果表明， 电子进入C≡N的π^*反键轨道, 通过弯曲C—C=N形成C4^-负离子, 绝热电子亲合能的最佳预测值为0.30 eV. 在 0~2 eV范围内C4^-具有显著的光电子吸收峰, 亚稳态C4^-负离子经约9 kJ/mol能垒断裂C—F键生成稳定的长寿命F...(CF₃)₂CCN]^-中间体. C4^-+CO₂反应存在进攻F或CN上的C和N 3种复合-解离机理, 在电气应用条件下, 以CO₂进攻氰基CN途径为主, 诱发负电荷从CN向CO₂转移.

Theoretical Investigations on the Electronic Structures and Reactivity of Heptafluoro-iso-butyronitrile Anion

Heptafluoro-iso-butyronitrile（C4） has attracted considerable interest for its use as a novel eco-friendly dielectric gas in various high-voltage applications. Electronic structures， photoelectron spectra， lifetime， reaction mechanisms， and kinetics for the C4^- anion formed by electron attachment to C4， together with the C4^-+CO₂ reaction， were calculated using various high-level ab initio methods. The electron in the π^* anti-bond orbital of C≡N leads to the bent C—C=N geometry of C4^- anion， and best theoretical adiabatic electron affinity is 0.30 eV. Photodetachment spectrum of C4^- anion exhibits significant absorption in the range 0—2 eV peaked at 1.63 eV. C4^- anion prefers to decompose via C—F bond fission， surmounting a barrier of ca. 9 kJ/mol， to form the long-lived ［F...（CF₃）₂CCN］^- intermediate， in which the C...F distance is as long as around 0.2 nm. The C4^-+CO₂ reaction takes place via three stepwise association/elimination mechanisms， namely， F， C or N of CN site-specified attacking by CO₂， resulting in energetically feasible electron-transfer from CN to CO₂. The present theoretical results shed new light on the high dielectric strength of C4 and the synergistic effect of the C4/CO₂ gas mixture.