椅式(5,5)单壁碳纳米管内硝基甲烷热解反应的理论研究

采用完全活性空间自洽场方法（CASSCF）以及组合的量子化学ONIOM方法，研究了硝基甲烷受限于椅式（5，5）单壁碳纳米管内的结构及热解过程。分子结构分析表明，椅式（5，5）碳纳米管内的硝基甲烷其构型发生扭转，Cs对称性消失，C—N键长略微缩短。热解势能面分析发现，硝基甲烷单体沿C—N键的热解是一个无过渡态的解离过程，而硝基甲烷在椅式（5，5）碳纳米管内的热解需经历一个过渡态，所需克服的能垒约为198kJ·mol^-1，比硝基甲烷单体的解离能降低了21kJ·mol^-1左右。此外，计算结果还表明，椅式（5，5）碳纳米管内的硝基甲烷热解过程中的分子结构、NO2和CH3基团电荷变化与单体解离过程亦有所不同。

Theoretical Study on Thermal Decomposition of Nitromethane Confined Inside a Armchair (5,5) Single-wall Carbon Nanotube

The molecular structures and thermal decomposition of nitromethane confined inside a armchair (5,5) single-wall carbon nanotube were studied by using the complete active space self-consistent field (CASSCF) and ONIOM level of theory. Results show that nitromethane confined inside a CNT (5,5) has no Cs symmetry and the C-N bond becomes short slightly. Analysis of the potential energy curves along the C-N bond length shows that a transition state exists for the thermal decomposition of nitromethane/ CNT(5 ,5 ) , which is different from that of nitromethane monomer (no transition state for the C-N bond dissociation). For nitromethane/CNT (5,5) ,the energy barrier of the transition state is calculated to be about 198 kJ · mol~(-1), which is about 21 kJ · mol~(-1) lower than that of the C-N bond dissociation energy of nitromethane monomer. In addition, calculated results show that the (5,5) single-wall carbon nanotube has effect on the changing in the molecular structure and electronic charge of NO_2 and CH_3 groups during the thermal decomposition process of nitromethane.