Temperature dependence of CH radical reactions with O₂, NO, CO and CO₂

The temperature dependence of the reactions of CH radicals with NO, O₂, CO₂ and CO was studied in the range from 297 to 676K in 100 torr of Ar buffer gas using a two-laser, photolysis/probe technique. The CH radicals were generated by the multiphoton dissociation of CHBr₃ at 266 nm and detected by LIF at 429.8 nm. The reactions of CH with No and O₂ show very little temperature dependence with k=(1.9±0.3)×10^-10 and k=(5.4 ±1.0)×10^-11 cm³ molecule^-1 s^-1, respectively. The rate of reaction of CH with CO₂ increases with increasing temperature and can be described in the temperature range studied by k =(5.7±0.9)×10^-12exp[(-345±53)/T] cm³ molecule^-1s^-1. The reaction of CH with CO has a negative temperature coefficient and was also found to be pressure-dependent. The rate constant for the reaction in 100 torr of Ar buffer gas is k=(4.6±1.0) ×10^-13 exp [(861±101)/T] cm³ molecule^-1 s^-1 in the temperature range studied. The rate constant at room temperature increases by a factor of 3 over the range of buffer gas pressure from 50 to 640 torr. These observations are explained in terms of a long-lived complex, the HC₂O adduct.