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.