The Measurements of Quenching Rate Constants of CH（A²Δ） Free Radicals By Chloromethane Molecules

The measurements of quenching rate constants of CH（A²Δ） by CH₂Cl₂, CHCl₃, and CCl₄ molecules at 298K are presented. CH（A²Δ） radicals were produced by laser photolysis of CHBr₃ molecules. The time-resolved spectroscopy of emission CH（A²Δ-X² Π） was observed. The measured quenching rate constants are as follows:
k（CH₂Cl₂）=（0.98±0.22）×10^-10cm³·molec^-1·s^-1
k（CHCl₃）=（1.95±0.28）×10^-10cm³·molec^-1s^-1
k（CCl₄）=（1.28±0.28）×10^-10cm³·molec^-1s^-1
In addition, we calculated the collision quenching rate cross sections of CH（A²Δ） by CH₄, CH₂Cl₂, CHCl₃ and CCl₄ by using collision complex model and evaluated the dependence of the quenching cross section on the number of chlorine atoms contained in quenching molecules. It is found that the calculated values are quanlitatively consistent with experimental results. It means that attractive forces are important in these quenching processes.