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Kinetics and Mechanism of the C 6 H 5 + CH 3 CHO Reaction: Experimental Measurement and Theoretical Prediction of the Reactivity toward Four Molecular Sites
Author(s) -
Choi Y. M.,
Park J.,
Lin M. C.
Publication year - 2004
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200301201
Subject(s) - chemistry , reaction rate constant , hydrogen atom abstraction , reaction mechanism , transition state theory , chemical kinetics , hydrogen , ab initio , reactivity (psychology) , density functional theory , kinetics , atmospheric temperature range , reaction rate , computational chemistry , chemical reaction , thermodynamics , catalysis , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics
The kinetics and mechanism of the reaction of C 6 H 5 with CH 3 CHO have been investigated experimentally and theoretically. The total rate constant for the reaction has been measured by means of the cavity ring‐down spectrometry (CRDS) in the temperature range 299–501 K at pressures covering 20–75 Torr. The overall bimolecular rate constant can be represented by the expression k =(2.8±0.2)×10 11 exp[−(700±30)/ T ] cm 3 mol −1 s −1 , which is slightly faster than for the analogous C 6 H 5 +CH 2 O reaction determined with the same method in the same temperature range. The reaction mechanism for the C 6 H 5 +CH 3 CHO reaction was also explored with quantum‐chemical calculations at various hybrid density functional theories (DFTs) and using ab initio high‐level composite methods. The theories predict that the reaction may occur by two hydrogen‐abstraction and two addition channels with the aldehydic hydrogen‐abstraction reaction being dominant. The rate constant calculated by the transition state theory for the aldehydic hydrogen‐abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier (+0.3 kcal mol −1 ). Contributions from other product channels are negligible under our experimental conditions. For combustion applications, we have calculated the rate constants for key product channels in the temperature range of 298–2500 K under atmospheric‐pressure conditions; they can be represented by the following expressions in units of cm 3 mol −1 s −1 : k 1,cho =8.8×10 3 T 2.6 exp(−90/ T ), k 2,ch3 =6.0×10 1 T 3.3 exp(−950/ T ), k 3a (C 6 H 5 COCH 3 +H)=4.2×10 5 T 0.6 exp(−410/ T ) and k 3b (C 6 H 5 CHO+CH 3 )=6.6×10 9 T −0.5 exp(−310/ T ).