Methyl-radical absorption cross-section at 216.4 nm and rate constant for methyl-radical recombination

Molecular modulation spectrometry has been used to measure the absorption cross-section at 216.4 nm of the CH3 radical and the rate constant for CH3 recombination, at 302 K and 4–575 Torr. The values obtained are σ=(3.51 ± 0.39)× 10–17 cm2 molecule–1 and k=(3.97 ± 0.49)× 10–11 cm3 molecule–1 s–1, in good agreement with those previously obtained by this method, but lower than those recently measured by flash photolysis.