Theoretical study on the ozonolysis of α-humulene in the atmosphere

Abstract

α-Humulene is a major sesquiterpene which is produced by plants and can easily react with ozone in the atmosphere. The ozonolysis mechanism of α-humulene in the atmosphere was investigated by density functional theory and calculated rate constants using transition-state theory in this paper. In the ozonolysis of α-humulene, primary ozonides (POZ) are first formed after an addition reaction. Then, with the broken O-O bond, Criegee intermediates (CIs) are formed. The results discussed the subsequent reaction of CIs in detail, including the formation of secondary ozonide (SOZ) and the reaction of CIs with H2O. For the formation of SOZ, the path of SOZ6 is the best path in all six paths, with a low energy barrier (3.80 kcal mol−1) and high total rate constants (3.34 × 108 s−1) at 298 K and 1 atm. For the reaction of CIs with H2O, the production of P6 is the best path in all six paths, with a low energy barrier (9.87 kcal mol−1) and high total rate constants (9.58 × 10−11 cm3 molecule−1 s−1) at normal temperature and pressure. This work provides reaction mechanisms of the ozonolysis of α-humulene and finds the reliable paths in the subsequent reactions.