Studies on the Kinetics of the CH + H₂ Reaction and Implications for the Reverse Reaction, ³CH₂ + H

Abstract

The reaction of CH radicals with H2 has been studied by the use of laser flash photolysis, probing CH decays under pseudo-first-order conditions using laser-induced fluorescence (LIF) over the temperature range 298–748 K at pressures of ∼5–100 Torr. Careful data analysis was required to separate the CH LIF signal at ∼428 nm from broad background fluorescence, and this interference increased with temperature. We believe that this interference may have been the source of anomalous pressure behavior reported previously in the literature (BrownswordR. A. Brownsword, R. A. J. Chem. Phys.199710676627677). The rate coefficient k 1 shows complex behavior: at low pressures, the main route for the CH3* formed from the insertion of CH into H2 is the formation of 3CH2 + H, and as the pressure is increased, CH3* is increasingly stabilized to CH3. The kinetic data on CH + H2 have been combined with experimental shock tube data on methyl decomposition and literature thermochemistry within a master equation program to precisely determine the rate coefficient of the reverse reaction, 3CH2 + H → CH + H2. The resulting parametrization is k CH2+H(T) = (1.69 ± 0.11) × 10–10 × (T/298 K)(0.05±0.010) cm3 molecule–1 s–1, where the errors are 1σ.

Combustion in a Sustainable World: From Molecules to Processes

“…Discrepancies between state-of-the-art theory and experiments have also been noted in the temperature dependence of the self-reaction of HO 2 + HO 2 leading to H 2 O 2 + O 2 ; these could be resolved using a multiscale informatics approach that takes into account experimental raw data and, compared to previous work, includes the formation of a HOOOOH intermediate . Experimental investigations with laser and synchrotron-based techniques have led to an improved understanding of several reaction systems of combustion and astrophysical interest, including the CH + H 2 ⇌ 3 CH 2 + H reaction, and the photodissociation dynamics of propyl derivatives . Such techniques also support the identification of transient reaction intermediates, such as phenoxy radical, which is a key intermediate in benzene oxidation and biomass conversion .…”

“…The decomposition of H 2 O 2 into two OH radicals, an important chain-branching reaction at intermediate temperatures, has been found to behave unusually as a function of pressure, indicating that nonstatistical effects may play a role. 2 Discrepancies between state-of-the-art theory and experiments have also been noted in the temperature dependence of the self-reaction of HO 4 and the photodissociation dynamics of propyl derivatives. 5 Such techniques also support the identification of transient reaction intermediates, such as phenoxy radical, which is a key intermediate in benzene oxidation and biomass conversion.…”