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Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO 2 Radicals
Author(s) -
Morajkar Pranay,
Schoemaecker Coralie,
Okumura Mitchio,
Fittschen Christa
Publication year - 2014
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20817
Subject(s) - chemistry , radical , reaction rate constant , acetaldehyde , formaldehyde , equilibrium constant , photodissociation , torr , analytical chemistry (journal) , molecule , atmospheric temperature range , photochemistry , thermodynamics , kinetics , organic chemistry , physics , quantum mechanics , ethanol
Rate and equilibrium constants for the reaction of HO 2 with formaldehyde R1CH 2 O + HO 2 ↔ HOCH 2 O 2( R 1 )and acetaldehyde R2CH 3 CHO + HO 2 ↔ CH 3 CH ( OH ) O 2( R 2 )have been directly measured. The concentration of HO 2 radicals was followed in a time‐resolved method by coupling cw‐CRDS (cavity ringdown spectroscopy) to laser photolysis. The reaction of HO 2 with CH 2 O (R1) was measured at 50 Torr helium over the temperature range 292–306 K, whereas the reaction of CH 3 CHO with HO 2 (R2) was measured in 50 Torr He but at only 294 K. The observed HO 2 decay profiles were modeled to take into account secondary chemistry, especially that of the reaction products, hydroxyl‐peroxy radical adducts. The rate constants for forward and back reactions of (R1) at 297 K were found to be k 1 = (3.3 ± 0.6) × 10 −14 cm 3 molecule −1 s −1 and k −1 = (55 ± 5) s −1 , respectively, both roughly a factor of two slower than earlier measurements (possibly due to falloff effects), while the equilibrium constant was found to be K 1 = (6.0 ± 1.8) × 10 −16 molecule −1 cm 3 at 297 K, in good agreement with earlier, more indirect determinations. The equilibrium constant of the reaction with CH 3 CHO was found to be K 2 = (1.7 ± 0.5) × 10 −17 molecule −1 cm 3 at 294 K, with the forward rate constant k 2 = (1.5 ± 0.75) × 10 −14 cm 3 molecule −1 s −1 and the rate constant for the back reaction k − 2 = (900 ± 450) s −1 .