Kinetics and degradation of camphene with OH radicals and its subsequent fate under the atmospheric O2 and NO radicals - A theoretical study

• Published in: Chemosphere (Oxford) 2021-03, Vol.267, p.129250, Article 129250
• Main Authors: Subramani, Mohanapriya, Saravanan, Vinnarasi, Theerthagiri, Jayaraman, Subramaniam, Vijayakumar, Pazhanivel, Thangavelu, Ramasamy, Shankar, Manickam, Sivakumar
• Format: Article
• Language: English
• Subjects: Branching ratio; Camphene; Lifetime; OH radical; Rate constant
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2020.129250

Camphene (C10H16) is an abundant bicyclic monoterpene in the atmosphere which can be easily oxidized by the atmospheric OH radicals. In this study, the oxidation of camphene with OH radicals and its subsequent reactions are studied using quantum chemical method. Thermochemical parameters show that the addition of OH radicals to the terminal C10 atom of camphene is thermodynamically more stable than the addition of OH radicals to the internal C7 atom of camphene. The reaction force profile demonstrates that the formation of two hydroxyalkoxy radical intermediates (I1a and I2a) are mainly dominated by the structural rearrangement with 94.28% and 99.43% of the total energy, respectively. The overall reaction rate coefficient for camphene + OH radical is 2.1⨯10−12 cm3 molecule−1 sec−1 at 298 K and 1 atm which agree well with the experimental reaction rate coefficient (5.58⨯10−11 cm3 molecule−1 sec−1) for the reaction of camphene with OH radical. The branching ratio for the addition of OH radical to the C10 position of camphene is 68.32%, and the C7 position of camphene is 31.68% at 298 K. The calculated lifetime reveals that camphene degrades quickly in the atmosphere owing to its short lifetime of 5.3 h. The obtained mechanistic and kinetic results reveal that the addition of OH radical to the C10 position is more dominant than the C7 position, and it is more stable and spontaneous in the atmosphere. [Display omitted] •OH radical reaction at C10 position of camphene is more dominant and spontaneous.•Overall rate coefficient is 5.2⨯10−12 cm3 molecule−1 sec−1.•Theoretical rate coefficient was well agreeing with experimental values.•Branching ratio for the C10 position of camphene is calculated to be 68.32%.•Camphene degrades quickly in the atmosphere due to its short lifetime of 5.3 h.