甲烷燃烧过程中由于高活性小分子自由基反应使实验室测定困难,影响了其燃烧机理的研究.本文采用量子化学从头算和密度泛函理论(DFT)对CH₃自由基和H₂反应机理进行了探索.在B3LYP/6-31G^*、6-311G^**、6-311++G^**和cc-pvtz基组水平上优化了CH₃+H₂→CH₄＋H反应过程中各驻点(反应物、中间体、过渡态和产物)的几何构型,并计算出它们的振动频率和零点振动能.各物种的总能量由B3LYP/6-31G^*和B3LYP/6-311++G^**给出,并对能量进行了零点能校正,同时应用内禀反应坐标(IRC)理论分析了该反应沿极小能量途径(MEP)相互作用分子间化学键的变化、原子自旋密度变化以及沿IRC的分子振动模式变化.研究结果表明,基组选择方式对各驻点几何构型无明显影响;在6-31G^*水平上计算出来的位垒为39.61kJ/mol,与实验值39.41kJ/mol相吻合;反应途径上存在一个引导反应进行的j振动模式,该振动区间为-0.57—0.60amu1/2Bohr.

Density functional theory is used to study the CH₃+H₂ reaction mechanism, based on the group level of the B3LYP/6-31G^*, 6-311G^**, 6-311++G^**, and cc-pvtz, the CH₃+H₂→CH₄+H reaction, including reaction intermediates, transition states, and product geometries, are optimized in order to calculate the energy, at the same time the vibration analysis is carried out. The results show that the selection of the basis set does not affect stationary points geometries; the barrier 39.61kJ/mol calculated at the 6-31G^* level is consistent with the 39.41kJ/mol of experimental value; there is a j vibration mode guiding reaction process on the reaction pathway, the vibration interval is in the range of -0.57 to 0.60 amu1/2Bohr.