七氟异丁腈负离子结构与反应活性的理论研究

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

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CO_(2)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...(CF_(3))_(2)CCN]−中间体.C4−+CO_(2)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CO_(2)进攻氰基CN途径为主,诱发负电荷从CN向CO_(2)转移.

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−+CO_(2) reac⁃tion,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.Photode⁃tachment 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...(CF_(3))_(2) CCN]−intermediate,in which the C...F distance is as long as around 0.2 nm.The C4−+CO_(2) reaction takes place via three stepwise association/elimination mechanisms,namely,F,C or N of CN site-specified attacking by CO_(2),resulting in energetically feasible electron-transfer from CN to CO_(2).The present theoretical results shed new light on the high dielectric strength of C4 and the synergistic effect of the C4/CO_(2) gas mixture.