دانلود رایگان مقاله واکنش تغییر هیدروژن در رادیکال پراکسی چهار متیل بوتانول (MBO)

Abstract

We investigate the hydrogen shift (H-shift) reactions in the peroxy radicals derived from four different methyl-buten-ol (MBO) molecules; 2-methyl-3-buten-2-ol (MBO232), 2-methyl-3-buten-1-ol (MBO231), 3-Methyl-3-buten-2-ol (MBO332) and 3-methyl-3-buten-1-ol (MBO331), with quantum mechanical calculations. The rate constants of the 1,5 H-shift reactions in all four MBO peroxy radicals are greater than the rate constants of the 1,4 or 1,6 H-shift reactions. The rate constants for the 1,5 H-shift reaction from either a CH group or an OH group are approximately 1 s−1 and 10−3 s−1, respectively. The atmospheric impact of the MBO232 oxidation is investigated with the global chemical transport model (GEOS-Chem). The 1,4-CH and 1,5-OH H-shift reactions in the MBO232 peroxy radical play a minor role with a total yield of about 2%. The major atmospheric reactions of the MBO232 peroxy radical are the reactions with NO and HO2, with reaction yield of 85% and 13%, respectively.

4. Conclusion

We have investigated the H-shift reactions in four MBO peroxy radicals by calculating transition state theory rate constants with the M06-2X/aug-cc-pVTZ method. We observed that the 1,5-CH and 1,5-OH H-shift reactions are 10-104 times faster than the 1,4- CH and 1,6-OH H-shift reactions. The rate constants for the forward 1,5-CH H-shift reactions are about 1 s1 , whereas the rate constants for the reverse reaction are about 105 s 1 . For the 1,5-OH H-shift reactions, the rate constants for the forward 1,5-OH H-shift are between 104 -103 s 1 , whereas the reverse H-shift reactions are very fast with rate constants around 1010-1011 s 1 . We have further investigated the possible atmospheric impact of the H-shift reactions in MBO232. The GEOS-Chem simulation, showed that the H-shift reactions in the MBO232 peroxy radical are a minor atmospheric reaction with a total H-shift yield of about 2%, whereas the MBO232 peroxy radical reaction with NO was found to be 85% and 13% for the reaction with HO2. Our results are in good agreement with earlier experimental findings and kinetically-inferred conclusions that the products from the MBO232 peroxy radicals predominantly comes from their reaction with NO or HO2. We i