Details

Autor(en) / Beteiligte

• Chhantyal-Pun, Rabi
• Shannon, Robin J
• Tew, David P
• Caravan, Rebecca L
• Duchi, Marta
• Wong, Callum
• Ingham, Aidan
• Feldman, Charlotte
• McGillen, Max R
• Khan, M. Anwar H
• Antonov, Ivan O
• Rotavera, Brandon
• Ramasesha, Krupa
• Osborn, David L
• Taatjes, Craig A
• Percival, Carl J
• Shallcross, Dudley E
• Orr-Ewing, Andrew J

Titel

Experimental and computational studies of Criegee intermediate reactions with NH and CHNH

Ist Teil von

• Physical chemistry chemical physics : PCCP, 2019-07, Vol.21 (26), p.1442-1452

Erscheinungsjahr

2019

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Ammonia and amines are emitted into the troposphere by various natural and anthropogenic sources, where they have a significant role in aerosol formation. Here, we explore the significance of their removal by reaction with Criegee intermediates, which are produced in the troposphere by ozonolysis of alkenes. Rate coefficients for the reactions of two representative Criegee intermediates, formaldehyde oxide (CH 2 OO) and acetone oxide ((CH 3 ) 2 COO) with NH 3 and CH 3 NH 2 were measured using cavity ring-down spectroscopy. Temperature-dependent rate coefficients, k (CH 2 OO + NH 3 ) = (3.1 ± 0.5) × 10 −20 T 2  exp(1011 ± 48/ T ) cm 3 s −1 and k (CH 2 OO + CH 3 NH 2 ) = (5 ± 2) × 10 −19 T 2  exp(1384 ± 96/ T ) cm 3 s −1 were obtained in the 240 to 320 K range. Both the reactions of CH 2 OO were found to be independent of pressure in the 10 to 100 Torr (N 2 ) range, and average rate coefficients k (CH 2 OO + NH 3 ) = (8.4 ± 1.2) × 10 −14 cm 3 s −1 and k (CH 2 OO + CH 3 NH 2 ) = (5.6 ± 0.4) × 10 −12 cm 3 s −1 were deduced at 293 K. An upper limit of ≤2.7 × 10 −15 cm 3 s −1 was estimated for the rate coefficient of the (CH 3 ) 2 COO + NH 3 reaction. Complementary measurements were performed with mass spectrometry using synchrotron radiation photoionization giving k (CH 2 OO + CH 3 NH 2 ) = (4.3 ± 0.5) × 10 −12 cm 3 s −1 at 298 K and 4 Torr (He). Photoionization mass spectra indicated production of NH 2 CH 2 OOH and CH 3 N(H)CH 2 OOH functionalized organic hydroperoxide adducts from CH 2 OO + NH 3 and CH 2 OO + CH 3 NH 2 reactions, respectively. Ab initio calculations performed at the CCSD(T)(F12*)/cc-pVQZ-F12//CCSD(T)(F12*)/cc-pVDZ-F12 level of theory predicted pre-reactive complex formation, consistent with previous studies. Master equation simulations of the experimental data using the ab initio computed structures identified submerged barrier heights of −2.1 ± 0.1 kJ mol −1 and −22.4 ± 0.2 kJ mol −1 for the CH 2 OO + NH 3 and CH 2 OO + CH 3 NH 2 reactions, respectively. The reactions of NH 3 and CH 3 NH 2 with CH 2 OO are not expected to compete with its removal by reaction with (H 2 O) 2 in the troposphere. Similarly, losses of NH 3 and CH 3 NH 2 by reaction with Criegee intermediates will be insignificant compared with reactions with OH radicals. The significance of removal of atmospheric ammonia and amines by reaction with Criegee intermediates is assessed by kinetic studies.