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Theoretical Investigation on the Reaction between OH Radical and 4,4-Dimethyl-1-pentene in the Presence of O2.

The atmospheric oxidation mechanism of 4,4-dimethyl-1-pentene (DMP441) initiated by OH radical has been theoretically investigated at the BH&HLYP/6-311++G(d,p) and CCSD(T)/6-31+G(d,p) levels of theory. HC(O)H and 3,3-dimethylbutanal [(CH3)3CCH2C(O)H] are identified in our calculations as major products in the OH-radical-initiated degradation of DMP441 in the presence of O2. However, the epoxide conformers and enols are expected to be minor products because of the high isomerization barriers involved. The calculated results are in qualitative accordance with experimental evidence. Conventional transition state theory has been used to calculate the rate constants of the initial addition channels of the OH + DMP441 reaction over the temperature range 220-500 K. The computed total rate constant at 298 K is 2.20 × 10(-11) cm(3) molecule(-1) s(-1), which is in very good agreement with the experimental value. Furthermore, it has been found that the calculated rate constant exhibits a weak non-Arrhenius behavior over the temperature range 220-500 K. The computed expression for the rate constant is k(OH+DMP441) = 1.22 × 10(-12) exp[(880 K)/T] cm(3) molecule(-1) s(-1).