An ab initio/Rice-Ramsperger-Kassel-Marcus prediction of rate constant and product branching ratios for unimolecular decomposition of propen-2-ol and related H + CH_2COHCH_2 reaction

摘要

Enols have been found to be important intermediates in the combustion flames of hydrocarbon [C. A. Taatjes , Science 308, 1887 (2005)]. The removal mechanism of enols in combustion flame has not been established yet. In this work, the potential energy surface for the unimolecular decomposition of syn-propen-2-ol and H+CH2COHCH2 recombination reactions have been first investigated by CCSD(T) method. The barrier heights, reaction energies, and geometrical parameters of the reactants, products, intermediates, and transition states have been investigated theoretically. The results show that the formation of CH3CO+CH3 via the CH3COCH3 intermediate is dominant for the unimolecular decomposition of syn-propen-2-ol and its branching ratio is over 99% in the whole temperature range from 700 to 3000 K, and its rate constant can be expressed as an analytical form in the range of T=700-3000 K at atmospheric pressure. This can be attributed to the lower energy barrier of this channel compared to the other channels. The association reaction of H with CH2COHCH2 is shown to be a little more complicated than the unimolecular decomposition of syn-propen-2-ol. The channel leading to CH3CO+CH3 takes a key role in the whole temperature range at atmospheric pressure. However at the higher pressure of 100 atm, the recombination by direct formation of syn-propen-2-ol through H addition is important at T < 1000 K. In the range of T>1400 K, the recombination channel leading to CH3CO+CH3 turns out to be significant.