On the Combination Reactions of Propargyl Radical with Hydroxyl Radical and the Isomerization and Dissociation of trans-Propenal.

Ab initio investigation for the ground-electronic potential energy surface (PES) of the CH2CCH + OH combination and the trans-CH2CHCHO isomerization and decomposition has been performed at the UCCSD(T)/CBS(TQ5)//M06-2X/aug-cc-pVTZ level of theory. Thermal and microcanonical rate constants, as well as branching ratios in the 300-2000 K temperature range have been predicted based on optimized structures and vibrational frequencies of species involved using statistical theoretical VRC-TST and RRKM master equation computations. The calculated results are in good agreement with the prior reported data; particularly as an accurate scaling of the energy barriers was carried out. Based on the view of PES and kinetic-predicted values, the reaction paths leading to C2H2 + CO + H2, CH3CH + CO, C2H4 + CO, C2H3 + HCO, and C3H3O + H are the prevailing product channels for the C3H3 + OH bimolecular reaction under the considered 300-2000 K temperature range. Among those products, CH3CH + CO is the most dominant one in low-temperature condition; however, C2H2 + CO + H2 becomes the most favorable product in high-temperature region. Alternatively, the C3H4O dissociation processes leading to C2H2 + CO + H2, C2H3 + HCO, C2H4 + CO, and CH2C + CH2O constitute the major paths; in which, C2H2 + CO + H2 is the most critical one with the ~62% and ~59% branching ratios at E = 148 and 182 kcal/mol, respectively. The overall second-order rate constants of the bimolecular reaction C3H3 + OH → products obtained at the pressure 760 Torr (Ar) can be illustrated by the modified Arrhenius expression of k(T) = 1.36 × 10-13 T1.26 exp[(-1.12  0.43 kcal.mol-1)/RT] and/or k(T) = 3.77 × 1017 T-7.58 exp[(-18.82  0.20 kcal.mol-1)/RT] cm3 molecule-1 s-1, covering the temperature range of 300-1300 K and/or 1300-2000 K, respectively. The total high-pressure limit rate constant for the C3H3 + OH  CH2CCHOH barrierless processes is in good agreement with the k(T) = 8.30  10-10 T-0.1 cm3 molecule-1 s-1 literature data. Moreover, microcanonical rate constants for the C3H4O isomerization and dissociation are in excellent accordance with the previously predicted values given by Chin and Lee. The present study supplies a thorough insight into the mechanisms and kinetics of the C3H3 + OH combination as well as the C3H4O multistep isomerization/dissociation pathways.