Theoretical study on mechanism for O 3-initiated atmospheric oxidation reaction of β-caryophyllene

Abstract

β-caryophyllene is a kind of sesquiterpene and has an important biogenic emission from natural resources. In the troposphere, the reaction of β-caryophyllene with O 3 is regarded as its major loss process. In this paper, the mechanism for the O 3-initiated atmospheric oxidation reaction of β-caryophyllene was studied by using high-accuracy molecular orbital theory. The geometrical parameters of reactants, intermediates, transition states, and products were optimized at the MPWB1K level with a standard 6-31G(d) basis set. The single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level. The profile of the potential energy surface was constructed, and the possible channels involved in the reaction were discussed. Several experimentally uncertain products were determined. The theoretical study shows that the main products of O 3-initiated β-caryophyllene oxidation are β-caryophyllonic acid, β-caryophyllene aldehyde and formaldehyde, which are low vapor pressure compounds and are inclined to form secondary organic aerosols. An energetically favorable formation pathway for β-caryophyllonic acid is revealed for the first time. The formation of the lactone (7,11,11-trimethyl-2-oxabicyclo[8.2.0]dodec-6-en-3-one) is energetically unfavorable under the general atmospheric conditions.