Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociations

Document Type

Article

Publication Date

1-1-2003

Abstract

Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH2=C=0) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H2CHO) and the acetyl radicals (CH3C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (ΔHf°298) were determined using isodesmic reaction analysis at the CBS-QCI/APNO and the CBSQ levels. Entropies (S°298) and heat capacities (Cp°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6-311G(d, p) level of theory. Internal rotor contributions were included in the S and Cp(T) values. A hydrogen atom can add to the CH 2-group of the ketene to form the acetyl radical, CH 3C·O (Ea = 2.49 in CBS-QCI/APNO, units: kcal/mol). The acetyl radical can undergo β-scission back to reactants, CH 2=C=0 + H (Ea = 45.97), isomerize via hydrogen shift (Ea = 46.35) to form the slight higher energy, formyl methyl radical, C·H2CHO, or decompose to CH3 +CO (Ea = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H2CHO (Ea = 6.72). This formyl methyl radical can undergo β scission back to reactants, CH2=C=0 + H (E a = 43.85), or isomerize via hydrogen shift (Ea = 40.00) to form the acetyl radical isomer, CH3·O, which can decompose to CH3 + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice-Ramsperger-Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH3 +CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH2=C=0 by H to form, ketenyl radical plus H2 is identified with a barrier of 12.27, at the CBS-QCI/APNO level. ΔHf°298 values are estimated for the following compounds at the CBS-QCI/APNO level: CH3C·O (-3.27), C·H2CHO (3.08), CH2=C=0 (-11.89), HC-CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc.

Identifier

0036461052 (Scopus)

Publication Title

International Journal of Chemical Kinetics

External Full Text Location

https://doi.org/10.1002/kin.10103

e-ISSN

10974601

ISSN

05388066

First Page

20

Last Page

44

Issue

1

Volume

35

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