Irdam, E.A., Kiefer, J.H., Harding, L.B., and Wagner, A.F. (1993)
The Formaldehyde Decomposition Chain Mechanism
Int. J. Chem. Kinet. 1993, 25, 285.
Abstract
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
(58). 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 (-54) 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 (-83), 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.
REACTION RATE COEFFICIENTS SUGGESTED IN THIS WORK:
GRI-Mech
Number
('-' sign
means
reverse) |
Reaction |
Rate Coefficient
A T^n exp(-E/RT) |
Temperature
Range
(K) |
A
(mol,cm3,s) |
n
(T in K) |
E
(cal/mol) |
| -54 |
CH2O + M -> H + HCO + M |
1.62E+36 |
-5.54 |
96700 |
2200-3200 |
| 55 |
H + HCO -> H2 + CO |
1.48E+14 |
|
2100 |
1300-3200 |
| 58 |
H + CH2O -> HCO + H2 |
7.24E+14 |
|
11400 |
250-3200 |
| 167 |
HCO + M -> H + CO + M |
1.86E+17 |
-1.0 |
17000 |
2200-3200 |