Effect of'O_2(a~1△_g) on the low-temperature mechanism of CH_4 oxidation

摘要

The effect of electronically excited oxygen O_2(a~1△_g) on the combustion of methane in air at low temperatures is investigated. Sensitivity and rate of production analysis indicated that reactions CH_3 + O_2(a~1△_g) ←→CH_3O_2(A'); CH_2O + OH; CH_3O + O are important for low-temperature methane oxidation. The potential energy surface of the reactions was investigated at the multi-reference configuration interaction level of theory. It was found that the association reaction corresponding to the channel of excited CH_3O_2(A') formation has a threshold with an energy of 8.5 kcal/mole. The rate parameter of the reaction CH_3 + O_2(a~1△_g)→CH_3O_2(A') was refined and makes k = 2.76 × 10~(-7) × T~(-2.71) x exp (-8.51 kcal/mole/RT). The influence of O_2(a~1△_g) on the rate of low-temperature methane oxidation in the refined model was analyzed. The study indicates significant suppression of the contribution of the channel CH_3 + O_2(a~1△_g)→CH_3O_2 due to peculiar properties of the potential energy surface of the reaction with participation of O_2(a~1△_g). At the same time, high contribution of the reaction channels leading to CH_2O and CH_3O results in effective use of the energy of electronic excitation for acceleration of the methane oxidation in presence of the O_2(a~1△_g) at low temperatures.