Effects of water vapor on the reaction of CH2OO with NH3. Issue 40 (7th October 2019)

• Record Type: Journal Article
• Authors: Chao, Wen; Yin, Cangtao; Takahashi, Kaito; Lin, Jim Jr-Min
• Is Part Of: Physical chemistry chemical physics. Volume 21:Issue 40(2019)
• Page Start: 22589
• Page End: 22597
• Publication Date: 2019-10-07
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp04682h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : A strong synergic effect of water and ammonia molecules may enhance the formation of H2 NCH2 OOH. Abstract : The reaction of the simplest Criegee intermediate, CH2 OO, with ammonia and water vapor has been investigated at 278–308 K and under 100–760 Torr by monitoring the strong UV absorption of CH2 OO. We found that the observed decay rate of CH2 OO becomes much larger when ammonia and water vapor are both present; the combinational effect of ammonia and water vapor is significantly greater than the sum of their individual contributions, revealing a strong synergic effect. The kinetic data are consistent with a termolecular process of CH2 OO + NH3 + H2 O reaction, of which the reaction rate coefficient was determined to be k NH3 +H2 O = (8.2 ± 1.2) × 10 −31 cm 6 s −1 at 298 K with a negative activation energy, E a = −8.0 ± 0.8 kcal mol −1 [ k NH3 +H2 O ( T ) = 1.04 × 10 −36 exp(4047/ T )]. Quantum chemistry calculation (at the QCISD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2d, 2p) level) found a low-energy reaction pathway, on which water accepts a hydrogen atom (or proton) from ammonia and releases another hydrogen atom to the terminal oxygen of CH2 OO. The predicted products are H2 NCH2 OOH and a new H2 O molecule, indicating water catalysis. This reaction is very fast and probably barrierless, which poses a theoretical challenge to modeling the related kinetics.