Experimental and Theoretical Study of the OH-Initiated Degradation of Ethylenediamine (NH2CH2CH2NH2) under Simulated Atmospheric Conditions. Part 1: Kinetics of the Ethylenediamine + OH Gas Phase Reaction
Year: 2024
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide The ethylenediamine (NH 2 CH 2 CH 2 NH 2 ) reaction with OH radicals was studied under natural sunlight conditions in a large outdoor atmospheric simulation chamber and in theoretical calculations based on CCSD(T*)-F12a/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ quantum chemistry results. The OH rate coefficient was determined in relative rate experiments employing online PTR-ToF-MS detection to be k OH = (2.8 ± 0.8) × 10 –10 cm 3 molecule –1 s –1 at 308 ± 3 K and 1013 ± 3 hPa. The theoretical study includes a conformational mapping of ethylenediamine showing nine conformers to be considered in reaction kinetics modeling, CCSD(T*)-F12a/aug-cc-pVTZ optimized geometries, and results from vibrational anharmonicity calculations for all conformers. The rate coefficients for the OH radical reaction with each of the nine ethylenediamine conformers were obtained in master equation calculations showing the kinetics being governed by both the formation of prereaction adducts and by tight transition states giving a Boltzmann conformer weighted rate coefficient k OH = 2.9 × 10 –10 cm 3 molecule –1 s –1, and a 1:1 branching between H-abstraction from the NH 2 and CH 2 groups at 298 K and 1013 hPa. The calculated rate coefficient shows a negative temperature dependence and a negligible variation with pressure under atmospheric conditions. The theoretical kinetics data were aligned to the experimental result, and the rate coefficient in the 200–400 K region can be approximated by a modified Arrhenius expression k (T) = 1.23 × 10 –10 × (T/298) 0.6 × exp(249 K/T) cm 3 molecule –1 s –1 .
Source: ACS Earth and Space Chemistry
Institution: University of Oslo
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
Funder: Norges Forskningsråd
Award: G595720807
OpenAlex ID: W4404518276