Forst, W. (1983)
Tunneling in Thermal Unimolecular Reactions. Formaldehyde
J. Phys. Chem. 1983, 87, 4489.
Abstract
Using available data, mostly photochemical, at discrete energies near threshold
for reaction, as well as thermochemical data and results of ab initio
calculations, I have computed specific-energy rate constants for the
decomposition of formaldehyde into H2 + CO, which involves tunneling, and into H
+ HCO, which does not. The corresponding thermal rate constants and activation
energies are then obtained and it is shown that tunneling causes the thermal rate
and activation energy to fall off "forever" with pressure. Despite the
uncertainties regarding some of the experimental data and theoretical parameters,
it is concluded that the photochemical and thermal experimental data are
reasonably consistent with one another, in particular with the notion that the
decomposition into H2 + CO proceeds by tunneling.
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 |
3.4E+16 |
|
81400 |
2000 |
| -83* |
CH2O + M -> H2 + CO + M |
7.8E+15 |
|
71200 |
2000 |
* at total concentration 1E-5 mol/cm3