Temperature dependence of CH radical reactions with H₂O and CH₂O

The temperature dependence of the reactions CH+H₂O and CH+CH₂O were studied from 297 to 670 K in 100 torr of argon using the two-laser photolysis/LIF probe technique. The CH radicals were produced by the multiphoton dissociation of CHBr₃ at 266 nm and monitored by LIF at 429.8 nm. The reaction CH+H₂O is independent of total pressures between 20 and 300 torr at room temperature and can be fit to the Arrhenius expression, k=(9.49±0.05)×10^-12exp[(380±20)/T] cm³s^-1 for the temperature range 298 to 669 K. The reaction CH+CH₂O is also independent of total pressure between 20 and 300 torr at room temperature and can be fit to the Arrhenius expression, k=(1.57±0.14)×10^-10 exp[(260±30)T] cm³s^-1 for the temperature range 297 to 670 K. The negative activation energies, energetics, and known CH behavior point to CH insertion into both H₂O and CH₂O as the primary reaction paths. The insertion products undergo rapid decomposition and collisional stabilization is unable to compete under these conditions.