Theoretical and kinetic study of reaction C2H + C3H6 on the C5H7 potential energy surface

The reaction mechanisms for reaction C 2 H + C 3 H 6 (propene) on the C 5 H 7 potential energy surface (PES) have been investigated by using quantum chemical calculations combined with canonical transition state theory and Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) theory. The optimization of the geometries and the calculation of the vibrational frequencies of reactants, transition states, and products are performed at the B3LYP/CBSB7 level of theory. The composite CBS-QB3 method is applied for energy calculations. The rate constants for reactions with tight transition states are obtained by canonical transition state theory, while the rate constants for barrierless reactions at the high-pressure limit are determined by the variational transition state theory. The rate constants for pressure-dependent reactions are obtained by RRKM/ME theory. The reaction of C 2 H + C 3 H 6 is initiated by the internal and terminal additions of C 2 H to C 3 H 6 without an entrance barrier, and the adduct of the internal and terminal additions is 2-methyl-1-butyl-3-yne (C 5 H 7 ) and 4-pentyl-1-yne (C 5 H 7 ), respectively. Products vinylacetylene (C 4 H 4 ) + CH 3 and 2-methyl-1-buten-3-yne (C 5 H 6 ) + H are favored by the internal C 2 H addition to C 3 H 6 , whereas products 3-penten-1-yne (C 5 H 6 ) + H and 4-penten-1-yne (C 5 H 6 ) + H are preferred for the terminal C 2 H addition. The calculated rate constants are in good agreement with those available from the literature, and they are also given in modified Arrhenius equation form, which are useful in combustion modeling of hydrocarbons.