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The formaldehyde decomposition chain mechanism
Author(s) -
Irdam Erwin A.,
Kiefer John H.,
Harding Lawrence B.,
Wagner Albert F.
Publication year - 1993
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.550250408
Subject(s) - chemistry , reaction rate constant , arrhenius equation , extrapolation , dissociation (chemistry) , kinetic energy , atmospheric temperature range , potential energy surface , branching fraction , reaction mechanism , thermodynamics , computational chemistry , activation energy , atomic physics , kinetics , molecule , organic chemistry , mathematical analysis , physics , mathematics , quantum mechanics , catalysis
A kinetic mechanism for the chain decomposition of formaldehyde consistent with recent theoretical and experimental results is presented. This includes new calculations and measurements of the rate constant for the abstraction reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 2} {\rm O + H} \to {\rm HCO + H}_{\rm 2} $$\end{document}The calculation uses a multi‐reference configuration interaction wavefunction to construct the potential energy surface which is used in a tunneling‐corrected TST calculation of the rate constant. The rate constant for the bond fission\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 2} {\rm O + M} \to {\rm HCO + H + M} $$\end{document}at high temperatures was determined by an RRKM extrapolation of direct low temperature measurements. This mechanism has been successfully tested against laser‐schlieren measurements covering the temperature range 2200–3200 K. These measurements are insensitive to all but the above two reactions and they confirm the large, non‐Arrhenius rate for the abstraction reaction derived here from theory. Modeling of previous experiments using IR emission, ARAS, and CO laser absorption with this mechanism is quite satisfactory. The branching ratio of the rate of the faster molecular dissociation (CH 2 O + (M) → CO + H 2 + (M)), to that of the bond fission reaction, was estimated to be no more than 2 or 3 over 2000 to 3000 K. Such a ratio is consistent with one recent theoretical estimate and most of the experimental observations. © 1993 John Wiley & Sons, Inc.