OH+C_2H_2与OH+C_2H_4加成反应的热力学和动力学

THERMODYNAMIC AND KINETIC STUDY ON REACTIONS OH+C_2H_2 AND OH+C_2H_4

OH基与乙炔(乙烯)的反应是控制大气中OH基浓度的重要化学反应。对反应OH+C_2H_2,1975年Davis等用FP-RF技术测定了反应的速率常数。1977年,Perry又用同样方法对该反应作出了研究;结果表明,此反应的速率常数强烈地依赖于压力,与Davis等人的实验结果不符。对反应OH+C_2H_4,Atkinson等人的实验研究表明,压力在30.0kPa以下,反应的速率常数随压力而改变;而在30.0—88.4 kPa之间,与压力无关.这与前人的结果不同。两个反应的产物也因温度不同而异.此外,上述反应一般是在近101kPa下发生的,而实验结果大多是在低压下获得的。且目前尚无直接的理论计算结果。为此,我们在从头算水平上用统计热力学方法。

The reactions of OH radical with C_2H_2 and C_2H_4 have been studied with ther- modynamic and kinetic methods based on ab initio level. The changes of the ther-modynamic function of the reactions were calculated at a range of 200-1600K oftemperature. The results indicate that both of the reactions are exothermic, which is135. 60±2. 76 and 100. 58±7. 32 kJ·mol^(-1) respectively at the cited temperature in-tervals. The reaction of OH radical with C_2H_2 can proceed easier than with C_2H_4.Also, the A factor and the rate constant of the reactions were calculated with transi-tion state theory. Pressure dependence of the rate constants was found. At 298K,80. 0 kPa, the rate constant k_1 equals 5. 09×10~5m^3·mol^(-1)·s^(-1), the experimental datais (4.49±1.63)×10~5m^3·mol^(-1)·s^(-1); at 299.2 K, 88.31kPa, k_2 is equal to 6.64×10~6m^3·mol^(-1)·s^(-1), and the experimental data is (4. 73±4. 76)×10~6m^3·mol^(-1)·s^(-1),which are in good agreement.