Experimental and theoretical studies on the reaction of H atom with C3H6

Abstract

AbstractA comprehensive study on the reaction of H + C3H6 has been conducted in order to clarify the temperature and pressure dependence of product branching. Site‐specific rate of addition of a hydrogen atom to the center carbon is measured by a comparative method for the evolutions of H atoms behind reflected shock waves. The rate constant for the addition to the center carbon can be given by ln(k1‐2/cm3molecule–1s–1) = – (1.67 ± 0.65) × 103 T–1 – (24.18 ± 0.55) for H + C3H6 → n‐C3H7* → products (T = 1065‐1306 K) without pressure dependence for P = 1‐2 bar. Theoretical calculation was conducted to evaluate the pressure dependence of the product branching for the H + C3H6 reaction by using transition‐state theory and RRKM theory based on quantum‐chemical calculations of potential‐energy surfaces. The result indicates that transition of the main reaction channel from addition to the terminal carbon in the low temperature range to the central carbon at moderate pressures (0.001‐10 bar) and elevated temperatures causes S‐shaped non‐Arrhenius temperature dependence of the total reaction rate against T–1; at the transition temperature, a strong pressure dependence was predicted. Our experimental result of k1‐2 agrees very well with the predicted value and available experimental data. The predicted rate constant ratio for the terminal versus nonterminal additions at the high‐pressure limits agrees well with the temperature dependence reported by Manion and Awan for the analogous H + C4H8 reaction. Furthermore, the importance of H‐abstraction reactions at elevated temperatures from three different sites of C3H6 was predicted in this calculation. For kinetic modeling of combustion and pyrolysis of hydrocarbons, we have recommended the rate constants for the 3 abstraction reactions as well as for the production of i‐ and n‐C3H7 radicals by addition reactions at the high‐ and low‐pressure limits over the temperature range of 300‐2000 K.