Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 21, Issue 25, Pages 13633-13640Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c9cp02534k
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Funding
- Academia Sinica [CDA-106-M05]
- Ministry of Science and Technology, Taiwan [MOST 107-2113-M-001-002, MOST 106-2113-M-001-026-MY3]
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Carbonyl oxides, also known as Criegee intermediates, are generated from ozonolysis of unsaturated hydrocarbons in the atmosphere. Alcohols are often used as a scavenger of the Criegee intermediates in laboratory studies. In this work, the reaction kinetics of CH3CHOO with methanol vapor was investigated at various temperatures, pressures, and isotopic substitutions using time-resolved UV absorption spectroscopy. The observed rate coefficients of the reaction of anti-CH3CHOO with methanol show a linear dependence on [CH3OH]. The bimolecular rate coefficient was determined to be k(1Ha) = (4.8 +/- 0.5) x 10(-12) cm(3) s(-1) at 298 K and 250 Torr with a negative activation energy E-a = -2.8 +/- 0.3 kcal mol(-1) for T = 288-315 K [k(T) = A exp(-E-a/RT)]. For the reaction of syn-CH3CHOO with methanol vapor, the observed rate coefficients show a quadratic dependence on [CH3OH], indicating that two methanol molecules participate in the reaction. The termolecular rate coefficient was determined to be k(2Hs) = (8.0 +/- 1.0) x 10(-32) cm(6) s(-1) at 298 K and 250 Torr with a strong negative temperature dependence (E-a = -13.2 +/- 0.3 kcal mol(-1)) at 273-323 K. No significant pressure effect was observed at 250-760 Torr. A kinetic isotope effect, k(2Hs)/k(2Ds) = 2.5, was observed by changing CH3OH to CH3OD. Quantum chemistry and transition state theory calculations suggest that the observed isotope effect is mainly attributed to the changes of the vibrational zero-point energies and partition functions while tunneling plays a very minor role. The reaction of syn-CH3CHOO with one CH3OH molecule was not observed in the studied concentration range.
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