Theoretical Chemical Kinetic Study of the H-atom Abstraction from Ethanol by Hydroperoxyl Radical

Reactions of ethanol + hydroperoxyl radical (H?2) are well known a crucial reaction class in oxidation mechanism of ethanol. However, the kinetic parameters of the reactions are basically extrapolated by analogy with n-butanol + H?2 system calculated by Zhou et al. [1]. The reliability of such the analogy remains to be seen, as no directly theoretical or experimental evidence is available in literature to date. In this study, thermal rate coefficients of H-atom abstraction reactions for ethanol + H?2 system were calculated at both CCSD(T)/cc-pVTZ//M06-2x/def-TZVP and CCSD(T)/CBS//M06-2x/def-TZVP levels of theory, with an uncertainty of a factor of 3, by means of using both conventional transition-state theory and canonical variational transition-state theory. Similar to n-butanol + H?2 system, the title reactions are dominated by alpha site H-abstraction, whereas the rate coefficients of all channels of ethanol are slightly slower than that of n-butanol + H?2 system. Generally, the new calculations show only limited effect on ethanol reactivity at low pressures and high temperatures (over 1300 K) but it prevents the kinetic mechanisms to over-predict ignition delay times under engine relevant conditions.