Theoretical Prediction of CH₃O and CH₂OH Gas-Phase Decomposition Rate Coefficients

Abstract

Theoretical predictions are made for the pressure and temperature dependences of two reactions involved in methanol combustion: (A) CH₃O → CH₂O + H and (B) CH₂OH → CH₂O + H. The calculations are carried out by using RRKM theory with a Gorin model for the activated complexes, with fall-off effects being taken into account by using the master equation. Results for the high-pressure rate coefficients (s^-1) are (A) 3×10¹⁴ exp(-108 kJ mol^-1 /RT), (B) 7×10¹⁴ exp(-124 kJ mol^-1 /RT) at 1000 K. For the low-pressure limiting rate coefficient (cm³ s^-1) over the range 600- 1000 K (A) 8×10^-9 exp(-90 kJ mol^-1 /RT); (B) 2×10^-8 exp(-108 kJ mol^-1 /RT). At 1000 K, the pressure at which the fall-off rate coefficients are one-half of their limiting high-pressure values are 3x10⁸ Pa for both reactions. Formulae for inclusion of these reactions (including fall- off effects) over the range 300-2000 K and 10^-2-10⁶ Pa in modelling complex kinetic schemes are presented.