Rate constants for the H abstraction from alkanes (R-H) by R'Oj radicals: A systematic study on the impact of R and R

摘要

A possible source of chain-branching in low temperature combustion is thermal decomposition of alkyl hydropeioxid.es (R'OOH) One way these species can be produced is via H atom abstraction reactions from alkanes (RH) by alkylperoxy radicals R'Ol,. An earlier study focussing on the abstraction from ethane by HO;,, CH3O2 and C2H5O2 revealed that these reactions have a noticeable impact on calculated ignition times of ethane/O2 mixtures Another outcome was that the abstraction rate constants for CH3OJ and C2H5O;, are virtually identical but smaller than that for HOj, The associated activation energies followed an Evans-Polanyi relationship while a common A-factor could be used to describe the kinetics of all three reactions within a factor of about 2-3. In this current study, we extend the investigation by (1) considering a set of alkanes (RH = CH4, C2H6, C3H8, C4H10) and (2) by including additional peroxy species (R'O^ with R' = H, CH3, C2H5, C3H7, C4H9, HC=O, and CH3C=O). We present rate constants for a total of 32 reactions and analyze the data with respect to systematic trends in the reactivity. The results reveal that the rate constants decrease in the order acylperoxy > HOj > alkylperoxy. The reactivity of different C-H bonds follows the bond strengths. Overall the heat of reaction is found to be the dominant but not the only late constant controlling parameter. The accuracy of the calculations and implications of the results are discussed.