Kinetics and Mechanisms of the Allyl + Allyl and Allyl + Propargyl Recombination Reactions

Abstract

The kinetics and mechanisms of the self-reaction of allyl radicals and the cross-reaction between allyl and propargyl radicals were studied both experimentally and theoretically. The experiments were carried out over the temperature range 295-800 K and the pressure range 20-200 Torr (maintained by He or N(2)). The allyl and propargyl radicals were generated by the pulsed laser photolysis of respective precursors, 1,5-hexadiene and propargyl chloride, and were probed by using a cavity ring-down spectroscopy technique. The temperature-dependent absorption cross sections of the radicals were measured relative to that of the HCO radical. The rate constants have been determined to be k(C(3)H(5) + C(3)H(5)) = 1.40 × 10(-8)T(-0.933) exp(-225/T) cm(3) molecule(-1) s(-1) (Δ log(10)k = ± 0.088) and k(C(3)H(5) + C(3)H(3)) = 1.71 × 10(-7)T(-1.182) exp(-255/T) cm(3) molecule(-1) s(-1) (Δ log(10)k = ± 0.069) with 2σ uncertainty limits. The potential energy surfaces for both reactions were calculated with the CBS-QB3 and CASPT2 quantum chemical methods, and the product channels have been investigated by the steady-state master equation analyses based on the Rice-Ramsperger-Kassel-Marcus theory. The results indicated that the reaction between allyl and propargyl radicals produces five-membered ring compounds in combustion conditions, while the formations of the cyclic species are unlikely in the self-reaction of allyl radicals. The temperature- and pressure-dependent rate constant expressions for the important reaction pathways are presented for kinetic modeling.

Computational study on the recombination reaction between benzyl and propargyl radicals

“…As in the case of the allyl + propargyl reaction 10,11, the ring‐formation steps in reaction (R3) involve the potential energy surfaces with strong open‐singlet characters. The properties and energies of the diradicals were calculated by using the same procedure, as in the previous study 10, utilizing the singlet–triplet (S–T) energy gaps. Briefly, the geometries and vibrational properties of the both singlet and corresponding triplet diradicals were calculated at the UB3LYP/6‐311G(d,p) level.…”

“…As one of the most important ring‐formation reactions, the self‐recombination of the propargyl (C 3 H 3 ) radicals has been extensively studied, and its kinetics and mechanisms are well established 7–9. Recently, the reaction between allyl (C 3 H 5 ) and propargyl radicals has also been investigated experimentally 10 and theoretically 9–11, and its role on the ring‐formation process in the hydrocarbon flames was illustrated 12,13. Reaction (R2) proceeds by the cyclization of the initially formed chain‐structure adducts via diradical intermediates to five‐membered ring compounds and radicals, which are rapidly converted to benzene in the subsequent reactions 14.…”

Photochemistry of C3Hphydrocarbons in Titan’s stratosphere revisited

“…Photoabsorption cross sections for c−C 3 H 2 (top), l−C 3 H 2 (middle) and t−C 3 H 2 (bottom) along with the dissociation limits for the various channels considered. (Atkinson & Hudgens 1999;Eisfeld 2006;Matsugi et al 2011), attributed to predissociation in the excited state. This leads to an upper limit of 360.1 kcal mol −1 for the bond dissociation energy, which corresponds to 346 nm and yields c−C 3 H 2 + H. The second (strongest) absorption near 240 nm has been confirmed by Deyerl et al (1999) by H-atom photofragment yield spectra.…”

“…• CH 2 will be dominated by absorption near 403 nm (Tonokura & Koshi 2000;Matsugi et al 2011) and by the strongest absorption in the 220−240 nm range (Selby et al 2008;Nakashima & Yoshihara 1987). The absorption cross section of C 3 H 5 is given in Fig.…”

Quantum chemical and master equation study of OH + CH2O → H2O + CHO reaction rates in supercritical CO2 environment

“…SSUMES program suite was used to solve the steady‐state unimolecular master equations based on the Rice–Ramsperger–Kassel–Marcus (RRKM) theory . The energy grain size used was set to default value of 100 cm −1 , which typically gives converged results for combustion reactions . Collisional energy transfer probability was estimated using exponential‐down model .…”