Reactive scattering of methyl radicals: velocity analysis of CH3+ I2, ICl

Angular and velocity distribution measurements of CH3I reactive scattering from crossed beams of CH3 radicals and halogen molecules I2, ICl are reported. The CH3 beam is generated by pyrolysis of azomethane flowing through a heated tantalum tube at ∼1800 K; the halogen molecule beam issues from a nozzle beam source at ∼380 K. The product time-of-flight distribution was recorded at each laboratory scattering angle by a minicomputer. Differential reaction cross sections are obtained as polar contour maps in centre-of-mass angle-velocity coordinates. The differential reaction cross section for CH3 + I2 is similar to that for D + I2 and the discrepancies may be largely due to the mass difference between CH3 and D. Thus, the potential energy surfaces for CH3 + I2 and D + I2 may be even more quantitatively similar than was suggested by a previous qualitative molecular orbital theory. The differential reaction cross sections for CH3 + ICl and D + ICl again exhibit the same similarity but precise comparison is inhibited in this case by the large contribution of initial energy to the total available energy.