Quenching of CH(A²Δ, B²Σ -and C²Σ+)radicals by chloromethanes

The quenching rate constants of CH （A, B, C） by CH₃Cl and CH （C） by CH₂Cl₂, CHCl₃ and CCl₄ were measured at room temperature by means of laser photodissoctation-fluorescence quenching technique. It is found that for chloromethane molecules CH（C） quenching rate constants are similar to those for CH（B） quenching and both are larger than those for CH （A） quenching, but they all are of the order of the gas kinetic collision rate. This implies that the quenching may be latgely by chemical reaction rather than by Physical quenching. In addition, the quenching rate constants for CH（A, B,C） increase with the increasing number of C-Cl bonds contained in chloromethsne molecules. The formation cross sections of complexes between CH（A, B） and chloromethane molecules are calculated using collision complex model. The results would suggest that the quenching processes of electronically exited CH are entrance-channel controlled.