Experimental\nand Theoretical Study of the OH-Initiated\nDegradation of Ethylenediamine (NH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>) under Simulated Atmospheric Conditions. Part\n1: Kineti

The ethylenediamine (NH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>) reaction with OH radicals was studied under\nnatural\nsunlight conditions in a large outdoor atmospheric simulation chamber\nand in theoretical calculations based on CCSD(T*)-F12a/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ\nquantum chemistry results. The OH rate coefficient was determined\nin relative rate experiments employing online PTR-ToF-MS detection\nto be <i>k</i><sub>OH</sub> = (2.8 ± 0.8) × 10<sup>–10</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup> at 308 ± 3 K and 1013 ± 3 hPa. The theoretical\nstudy includes a conformational mapping of ethylenediamine showing\nnine conformers to be considered in reaction kinetics modeling, CCSD(T*)-F12a/aug-cc-pVTZ\noptimized geometries, and results from vibrational anharmonicity calculations\nfor all conformers. The rate coefficients for the OH radical reaction\nwith each of the nine ethylenediamine conformers were obtained in\nmaster equation calculations showing the kinetics being governed by\nboth the formation of prereaction adducts and by tight transition\nstates giving a Boltzmann conformer weighted rate coefficient <i>k</i><sub>OH</sub> = 2.9 × 10<sup>–10</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup>, and a\n1:1 branching between H-abstraction from the NH<sub>2</sub> and CH<sub>2</sub> groups at 298 K and 1013 hPa. The calculated rate coefficient\nshows a negative temperature dependence and a negligible variation\nwith pressure under atmospheric conditions. The theoretical kinetics\ndata were aligned to the experimental result, and the rate coefficient\nin the 200–400 K region can be approximated by a modified Arrhenius\nexpression <i>k</i>(T) = 1.23 × 10<sup>–10</sup> × (T/298)<sup>0.6</sup> × exp(249 K/T) cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup>.