Adventures on the C3H5O potential energy surface: OHÂ +Â propyne, OHÂ +Â allene and related reactions

We mapped out the stationary points and the corresponding conformational space on the C3H5O potential energy surface relevant for the OH + allene and OH + propyne reactions systematically and automatically using the KinBot software at the UCCSD(T)-F12b/cc-pVQZ-F12//M06-2X/6-311++G(d,p) level of theory. We used RRKM-based 1-D master equations to calculate pressure- and temperature-dependent, channel-specific phenomenological rate coefficients for the bimolecular reactions propyne + OH and allene + OH, and for the unimolecular decomposition of the CH3CCHOH, CH3C(OH)CH, CH2CCH2OH, CH2C(OH)CH2 primary adducts, and also for the related acetonyl, propionyl, 2-methylvinoxy, and 3-oxo-1-propyl radicals. The major channel of the bimolecular reactions at high temperatures is the formation propargyl + H2O, which makes the title reactions important players in soot formation at high temperatures. However, below ∼1000 K the chemistry is more complex, involving the competition of stabilization, isomerization and dissociation processes. We found that the OH addition to the central carbon of allene has a particularly interesting and complex pressure dependence, caused by the low-lying exit channel to form ketene + CH3 bimolecular products. We compared our results to a wide range of experimental data and assessed possible uncertainties arising from certain aspects of the theoretical framework.