Abstract: 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 200-1600 K of temperature. The results indicate that both of the reactions are exothermic, which is 135.60±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 transition state theory. Pressure dependence of the rate constants was found. At 298 K, 80.0 kPa, the rate constant k_1 equals 5.09×10~5 m~3·mol~(-1)·s~(-1), the experimental data is (4.49±1.63)×10~5 m~3·mol~(-1)·s~(-1); at 299.2 K, 88.31 kPa, k_2 is equal to 6.64×10~6 m~3·mol~(-1)·s~(-1), and the experimental data is (4.73±4.76)×10~6 m~3·mol~(-1)·s~(-1), which are in good agreement.

Key words: Addition on ethylene, Addition on acetylene, Thermodynamic, Kinetic