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

Abstract

A comprehensive study on the reaction of H + C 3 H 6 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(k 1-2 /cm 3 molecule-1 s-1) =-(1.67 ± 0.65) × 10 3 T-1-(24.18 ± 0.55) for H + C 3 H 6 → n-C 3 H 7 * → 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 + C 3 H 6 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 k 1-2 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 + C 4 H 8 reaction. Furthermore, the importance of H-abstraction reactions at elevated temperatures from three different sites of C 3 H 6 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-C 3 H 7 radicals by addition reactions at the high-and low-pressure limits over the temperature range of 300-2000 K.

Hierarchical Study of the Reactions of Hydrogen Atoms with Alkenes: A Theoretical Study of the Reactions of Hydrogen Atoms with C2–C4 Alkenes

“…The rate constant for terminal addition (black) is approximately a factor of 2 faster than that calculated here. However, as mentioned by Chen et al, 20 the higher values reported by Miller and Klippenstein may be attributed to input data errors. An error in symmetry number affects the energy barriers and pressure-dependent rate constant expressions.…”

“… High-pressure limiting rate constant comparisons for the reactions of Ḣ atom addition to propene. Solid lines represent the current work (ROCCSD(T)/aug-cc-pVXZ); dotted lines, Curran; 59 dashed lines, Miller and Klippenstein; 18 dashed-dotted lines, Chen; 20 ■, Seakins et al; 23 △, Watanabe et al; 27 ○, Kurylo et al. ; 26 ◀, Harris et al; 31 and □, Kerr et al 24 …”

“…The difference observed at higher temperatures can be attributed to the difference in entropy of activation. For the rate constant recommendation for 1-alkenes, an average of the rates calculated in this work and previous studies as well as that by Chen et al 20 is taken.…”

“…The predicted high-pressure limiting rate constant ratio for terminal versus nonterminal addition agrees well with that reported by Manion et al 19 for the analogous reaction of Ḣ atoms with butene. Both Chen et al 20 and Manion et al 19 state that their predicted branching ratio for terminal versus nonterminal addition differ from that calculated by Miller and Klippenstein who studied the dissociation of propyl radicals and other reactions on the Ċ 3 H 7 PES. 18 With minor adjustments to several of the barrier heights, Miller and Klippenstein showed excellent agreement between their theoretical values and experimental results available in the literature over a wide range of conditions.…”

“…Fewer studies exist for the reactions of Ḣ atoms with propene and the butene isomers. Experimental studies of Ḣ atoms with propene include refs ( 18 − 19 , 23 − 32 ), with the most recent one by Chen et al 20 studying the temperature and pressure dependence of the product branching ratio of the Ḣ + propene reaction. This was done behind reflected shock waves in a diaphragm-less shock tube using the Ḣ-ARAS technique in the temperature range 1065–1306 K at 1 and 2 bar.…”