Computational Study on the Atmospheric Oxidation Mechanism of 6-Chlorobenzo[a]pyrene Initiated by OH Radicals
Density functional theory (DFT) calculations at the MPWB1K/ 6-311+G(3df,2p) level were performed to study OH-initiated atmospheric oxidation reactions of 6-chlorobenzo[a]pyrene (6-ClBaP). The rate constants for key elementary reactions were estimated by means of transition state theory. The computed results demonstrate that only four of the twelve possible intermediates (INT1, INT3, INT4, and INT12) can be generated kinetically. The principal atmospheric oxidation products of 6-ClBaP, benzo[a]pyrenols, can be produced by subsequent reactions of INT1, INT3, INT4, and INT12, although their hydrogen abstraction mechanism is not exactly the same. For peroxy radical intermediates formed by O2 addition toward INT4 intramolecular hydrogen transfer from −OH to −OO was found to be a highly non-spontaneous process and hence difficult to proceed. The rate-controlling steps for subsequent reactions of INT1, INT3, INT4, and INT12 involving NO2 or NO were found to be very slow kinetically.
Keywords:atmospheric oxidation reaction 6-chlorobenzo[a]pyrene (6-ClBaP) OH radicals oxidation products
This work was funded by the National Natural Science Foundation of China (no. 21876143), Key Scientific Research Projects of Universities in Henan Province (no. 19B610003), Nanhu Scholars Program for Young Scholars of XYNU, and High Performance Computing Lab of Xinyang Normal University.
- 25.M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, et al., Gaussian 09 (Gaussian Inc., Wallingford CT, 2009).Google Scholar
- 26.M. J. Pilling and P. W. Seakins, Reaction Kinetics (Oxford Univ. Press, New York, 1999).Google Scholar